TRADING QUALITY FOR QUANTITY: AN ASSESSMENT OF

TRADING QUALITY FOR QUANTITY: AN ASSESSMENT OF
TRADING QUALITY FOR QUANTITY: AN ASSESSMENT OF
SALINITY CONTAMINATION GENERATED BY GROUNDWATER
CONSERVATION POLICY IN THE TUCSON BASIN
by
James Craig Tinney
A Dissertation Submitted to the Faculty of the
SCHOOL OF RENEWABLE NATURAL RESOURCES
In Partial Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
WITH A MAJOR IN WATERSHED MANAGEMENT
In the Graduate College
THE UNIVERSITY OF ARIZONA
1987
THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
As members of the Final Examination Committee, we certify that we have read
the dissertation prepared by
entitled
James Craig
Trading Quality for Quantity:
Tinney
An Assessment of Salinity
Contamination Generated by Groundwater Conservation Policy
in the Tucson Basin
and recommend that it be accepted as fulfilling the dissertation requirement
for the Degree of
Doctor of Philosophy
Dateit
Date
Date
Date
9
/ffiitai
/PM?
• /7/
t7r7
Final approval and acceptance of this dissertation is contingent upon the
candidate's submission of the final copy of the dissertation to the Graduate
College.
I hereby certify that I have read this dissertation prepared under my
direction and recommend that it be accepted as fulfilling the dissertation
requirement.
Date
Dissertation Co -Direct
511fil
/A7
5Date
STATEMENT BY AUTHOR
This dissertation has been submitted in partial
fulfillment of requirements for an advanced degree at The
University of Arizona and is deposited in the University
Library to be made available to borrowers under rules of the
Library.
Brief quotations from this dissertation are
allowable without special_ permission, provided that accurate
acknowledgment of source is made. Requests for permission
for extended quotation from or reproduction of this
manuscript in whole or in part may be granted by the head of
the major department or the Dean of the Graduate College
when in his or her judgment the proposed use of the material
is in the interests of scholarship. In all other instances,
however, permission must be obtained fripm7the a thor%
SIGNED:
\"...,)
ACKNOWLEDGMENTS
I would like to express my deepest gratitude to Dr.
Susan C. Nunn for enduring countless discussions and reviews
of dissertation drafts. Without her gentle guidance this
project would not have been possible.
I give special thanks to Dr. David A. King for his
patience and moral support support for five long years.
I am grateful to my friends I worked with at the
Arizona Department of Water Resources/Tucson Active
Management Area for sharing their experiences in the
regulatory arena.
I am grateful for my experiences working with the
staff of the University of Arizona Water Resource Research
Center. Special thanks to Dr. William Lord for his support
and suggestions.
Special thanks to Richard Fife who patiently typed
this dissertation and to Erika Louie for her many
suggestions.
Lastly, I want to dedicate this work to my wife,
Jacquie, and daughter, Ariel. Jacquie's love helped me
through each day and the thought of my playful princess,
Ariel, made me look forward to the next.
111
TABLE OF CONTENTS
Page
1.
LIST OF TABLES vii
LIST OF ILLUSTRATIONS xi
ABSTRACT xii
INTRODUCTION
Statement of the Problem
Research Objectives
Overview
2.
WATER RESOURCES AND SUPPLY
IN THE TUCSON BASIN
Hydrogeologic Characteristics
of the Tucson Basin
Aquifer Storage Tucson's Water Resources Groundwater Wastewater Central Arizona Project Tucson Water Department Municipal Well Fields The Pattern of Water Use
in the City of Tucson Summary 3.
GROUNDWATER CONSERVATION PROGRAMS 1980 Arizona Groundwater
Management Act Summary of Rights and Permits AGMA Groundwater Conservation
Programs Summary of Rights and Permits Wastewater Reuse for Irrigation Groundwater Conservation Achieved
by CAP iv
1
3
4
5
8
9
11
13
13
15
24
36
39
43
49
52
53
56
62
65
66
69
TABLE OF CONTENTS--Continued
Page
72
72
75
75
Water Use: Projected and Actual Groundwater Water Conservation Actual Water Use Summary 4.
A FRAMEWORK TO EVALUATE THE TRADEOFFS
BETWEEN QUALITY AND QUANTITY Efficiency and Regulation Marginal Social Cost of Salinity An Economic Model of Policy-Induced
Social Costs Over Time Ordering Policies by External
Social Costs
Present Value and the Discount Rate Beyond the Planning Horizon Changes in Consumer Benefits Summary 5.
ESTIMATION OF SALINITY DAMAGE COSTS Defining a Damage Function Defining a Damage Function Damage Annual Costs Literature on Economic Damages of
Salinity Salinity Damage Function for Tucson Estimators of Appliance Lifetime Annualized Costs Cost Per Household Summary 6.
THE MUNICIPAL WATER-SALINITY CYCLE Institutional Constraints Affecting
the Salinity Cycle Previous Estimates of Salinity
Degradation in the Tucson Basin Projecting the Rate of
Salinity Degradation Time of Recharge Arrival
in the Aquifer Summary 79
80
86
90
93
98
100
101
102
104
104
104
104
106
107
117
117
120
125
128
132
135
139
140
158
164
vi
TABLE OF CONTENTS--Continued
Page
7.
COSTS OF GROUNDWATER CONSERVATION Projecting the Economic Costs
of Salinity Damage Calculation of Total Annual Costs Policy Scenarios Description of Data Rate of Aquifer Degradation Costs of Salinity Damage Present Value of Costs Generated
by Salinity Discussion of the Scenario Results Amounts of Groundwater Conserved Salinity Damage Costs per Acre-foot
of Decreased Groundwater Conserved . Costs of Conservation Programs Water Supply Cost Estimates Total Expenditures for Conservation Expenditures per Acre-foot
of Groundwater Conserved The Value of Groundwater Conservation
to the Consumer Changes in Consumer Surplus Discussion of Consumer Surplus Summary 8.
WEIGHING THE COST OF GROUNDWATER CONSERVATION
PROGRAMS: CONCLUSIONS The Municipal Water-Salinity Cycle The Responsibility for Salinity
Degradation Summary of the Costs of
Groundwater Conservation Salinity Damage Costs Investments in Groundwater
Conservation Terminal Value and Conservation Recommendation for Further Research REFERENCES 166
168
169
169
172
174
177
179
186
192
. 194
197
197
200
200
203
203
204
207
209
210
211
212
213
215
216
221
223
LIST OF TABLES
Page
Table
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Nondiscretionary Groundwater Inflow
and Outflow 14
Effluent Quality for the Wastewater Treat
ment Plants Servicing the City of
Tucson and
Limits for Long-Term Irrigation 22
Average Increases in Concentrations
from Tap Water to Secondary Effluent 23
Flow-weighted Annual Average Salinity
of theColorado River at Parker Dam,
1972-1980
27
Water Quality of the Colorado River
at Parker Dam 29
Estimated Salinity at Parker Dam Under
Various Salinity Control Scenarios,
Hydrologic Conditions, and Depletion
Rates for the Years 1990 and 1991 30
Tucson Water Department Water Pumpage by
Wellfield, 1979-1980
42
Salinity of the City Well Fields
and the CAP 44
Results from the City of Tucson Water Quality
Sampling Program, 1951 - 1980 45
Total Water Useage by Class. City of
Tucson, 1978-1984
Percentage Change in Water Use from Previous
Year for Various Water Use Categories . .
Projected Percentage Change in Water Use
from Previous Year for Various Water Use
Categories vii
46
47
48
viii
LIST OF TABLES--Continued
Page
Table
13.
14.
15.
Projected Wastewater Reuse Potential for
Municipal Landscape Irrigation 67
Projected Turf Acreage in the Tucson
Metropolitan Area, 1990-2030
68
Blend Ratio of CAP Water to Groundwater
to Meet City of Tucson Municipal
Water Requirements 71
16.
First Management Plan Baseline Projects .
.
73
17.
Projected Future Conditions Assuming First
Management Plan Conservation Requirements
Tucson Active Management Area,
1980-2025
74
18.
19.
Tucson Active Management Area Reported Water
Withdrawals and Use 76
Test for Significantly Different Expected
Lifetimes of Appliances for Two Areas
with Differing TDS Concentrations 110
Annual Cost per Household per mg/1 TDS and
Total Cost per mg/1 TDS - Central
Arizona Project Service Area,
1975 dollars 112
Regression estimates for length of average
lifetime and salinity 118
Replacement Costs for Various Water-Using
Appliances 124
Cumulative Annual Capital Recovery Costs for
TDS Concentrations Beyond 300 mg/1 126
Average Number of Water-Using Appliances in
Households in the Tucson Area 129
25. Degradation Cycle Time for Groundwater with
an Initial TDS of 300 mg/1 to Reach
Final TDS or Given Annual Salinity
Pick-up Rates 136
20.
21.
22.
23.
24.
ix
LIST OF TABLES--Continued
Page
Table
26.
27.
28.
29.
30.
31.
32.
33.
Comparison of Salt Concentrations of Various
Water Supplies in Tucson, Arizona 143
Hydrologic Characteristics of Proposed
Reclaimed Wastewater Irrigation Sites
in the City of Tucson, Arizona 147
Estimated Salinity Concentration One Mile
Down-gradient of Proposed Wastewater Reuse
Sites 148
Estimated Incidental Recharge Amounts for
Selected Sources in the Tucson Area Estimated First Year TDS Concentration of
Groundwater for Various Recharge Amounts
and Salinity Given Available Aquifer
Mixing Volumes 153
155
Tucson Active Management Area Water-Use
Targets for Water Providing Agencies,
First Management Plan Targets 173
Projected Average Annual Salinity Pick-Up
Rate for Various Policy Scenarios 176
Estimated Mean TDS Concentrations in the
Tucson Basin Aquifer for the Year 2025
Given Various Policy Scenarios 178
34.
Present Value of Damage Costs to SingleFamily Residences Generated Directly
by CAP Salinity under Various Scenarios . . . 180
35.
Present Value of Costs Associated with
Salinity Damages Resulting from
Groundwater Degradation for Single
Family Residences for Various
Scenarios, Given Various
Discount Rates 36. Present Value of Total Damage Costs
Generated by Salinity under Various Scenarios
182
184
X
LIST OF TABLES--Continued
Table
Page
37. CAP Water Use, Groundwater Use, and Total
Water Use Summed over the Study Period.
38.
39.
40.
41.
Average Present Value of Salinity Damage per
Acre-foot of Decreased Groundwater
Withdrawals, 1986 Dollars Discounted at
Four Percent, Aquifer Dilution Volume
Assumed as 5 Million Acre-feet .....
. 193
. 195
Estimated Present Value of Total
Expenditures for Water Acquisition and
Net for Groundwater Conservation Under
Various Scenarios 201
Present Value of Expenditures for Groundwater Conservation Programs per Acrefoot of Groundwater Conserved 202
Estimated Present Value of Total Costs of
Salinity Damage and Total Expenditures
for Groundwater Conservation Under
Various Scenarios 217
LIST OF ILLUSTRATIONS
Page
Figure
1.
Projected Colordo River Salinity 32
2.
Active Management Areas 54
3.
Marginal Analysis of External Costs and
Regulatory Costs 82
Relationship of Water Heater Lifetime
to Salinity 121
Relationship of Galvanized Water Pipe
Lifetime to Salinity 122
Relationship of Dishwater Lifetime
to Salinity 123
Estimated Annual Salinity Damage Costs
Per Single-Family Residence 130
8.
Municipal Water-Salinity Cycle 133
9.
Aquifer Degradation over Time for Various
Zero Year Lag. . . . 160
Salinity Pick-up Rates,
10.
Aquifer Degradation over Time for Various
Ten Year Lag . . . . 161
Salinity Pick-Up Rates,
11.
Aquifer Degradation over Time for Various
20 Year Lag. .
Salinity Pick-Up Rates,
4.
5.
6.
7.
12.
Loss In Consumers Surplus for a Reductionin-Use 13. Distribution of Total Costs per Acre-Foot
by Percentage Groundwater Conserved . .
xi
. . 162
205
. . 220
ABSTRACT
The State of Arizona adopted strict groundwater
conservation policies under the Arizona Groundwater Act of
1980. The Act mandates direct controls on groundwater use
and provides incentives to seek alternative water supplies
to offset the groundwater overdraft and restrict the
expansion of municipal well fields.
The City of Tucson, to reduce its groundwater dependency, is contracting for Central Arizona Project (CAP)
water. CAP water comes from the Colorado River and carries
with it nearly a ton of salts per acre-foot. Conservation
programs being investigated by the city include reclaimed
wastewater reuse for municipal use and artificial recharge.
Salinity, a conservative contaminant, will rise as
the water carrying it evaporates away during use. Some
saline incidental recharge from wastewater irrigated acreage
in the municipal well field is picked-up by groundwater
pumpage in what is described as the municipal water-salinity
cycle. The rate of salinity pick-up is compounded in the
cycle.
Those responsible for achieving groundwater conservation under the mandates of the Act do not include the
costs generated by salinity damages and suffered by
xii
xiii
municipal water-consumers into their conservation plans.
Salinity damages costs are generated by the direct use of
CAP water and the use of degraded groundwater supplies.
The study results show that under assumptions of
limited groundwater dilution volumes the annual rate of
salinity pick-up can range from about 1.4 percent to nearly
2.0 percent. An annual average pick-up rate of 2.0 percent
could degrade Tucson's groundwater supplies from the present
average salinity of 300 mg/1 to 1000 mg/1 in 61 years.
Thirteen scenarios were evaluated and the present
value of incremental costs of both salinity damage and
expenditures associated with conservation were calculated.
While estimates of salinity damage costs are many times
lower than the conservation program expenditures, increased
salinity in groundwater will lower the future capital value
of the resource in the future if ignored.
CHAPTER 1
INTRODUCTION
Groundwater conservation policy now occupies the
center arena in water resources management in the Southwest
and, especially in the Tucson basin. Arizona's commitment
to employ alternative water sources is evidenced in its
eagerness to accept Central Arizona Project (CAP) water.
To assure the delivery of CAP water, Arizona adopted strict
language in the 1980 Arizona Groundwater Management Act
(AGMA). The city of Tucson Water Department has established
water-use awareness programs, seasonal rates, increasing
block pricing schedules, and has acquired farmlands for
their water rights because of concerns about groundwater
shortage. The Pima Association of Governments (PAG) has
implemented education programs aimed at water conservation.
In the private sector, the Southern Arizona Water Resources
Association (SAWARA), created by public and business
interests to lobby for the local water-using community,
embraces, as one of its missions, water-conservation
education. The broad base of public and private interests
which seek to preserve groundwater supplies demonstrates
that the public perceives that a groundwater shortage, which
1
2
may limit prosperity in the region. is imminent. Groundwater is to be conserved by Colorado River water importation
via the Central Arizona Project (CAP), wastewater reuse for
municipal irrigation, and reduction-in-use programs. In
Arizona, groundwater conservation is to accomplished by two
policy instruments; demand management and supply augmentation.
Water quality also has received state-wide attention. Recent legislation contains strict monitoring
requirements for hazardous waste discharges and imposes
severe penalties on those who contaminate. The public's
strong interest in preserving groundwater as a drinking
water resource is also exemplified by Governor Babbit's 1986
"State of the State" address in which new water-quality
legislation was identified as a first-order priority. The
Tucson basin, too, has been involved in regional water
quality management; the Tucson basin has been designated a
sole source aquifer under the Safe Drinking Water Act and is
undergoing a massive cleanup of groundwater contaminated by
organic solvents (TCE). However, salinity is not recognized
as a primary water pollutant in the Federal Safe Drinking
Water Act. The Safe Drinking Water Act does not protect
against contamination by salts. Because salinity contamination is not identified explicitly it is not included in
water resources decision-making under this statute.
3
The value of water is determined by many factors,
two of which are the joint characteristics of quantity and
quality. Salinity degradation of groundwater may defeat one
of the goals of groundwater conservation, which is to
preserve groundwater resources for the use of future
generations, if increased salinity reduces the utility of
that water for prevailing uses. Progressive concentration
of salts can decrease the value of groundwater in storage.
This is important since Tucson will also suffer
direct damages from the main groundwater conservation
instrument, the CAP. Here a conflict exists between
policies of quantity and quality. Do the benefits of
conservation exceed the costs of higher salinity in water
supplies?
Statement of the Problem
Importation of CAP water, the main groundwater
conservation instrument, into the Tucson basin also imports
salinity. Each acre-foot of CAP water contains nearly 2,000
pounds of salts as compared with about 820 pounds of salt
per acre-foot of Tucson well water. The salinity of the CAP
water generates two streams of economic costs. Salinity is
introduced in municipal water by the direct use of CAP water
as a primary water supply and indirectly through groundwater
degradation when the salts recharge into the native waters.
4
Trends and present policies indicate that wastewater
will be used increasingly in the future to meet irrigation
requirements; its desirability depends upon its quality.
The quality of wastewater will be impaired if groundwater
conservation programs deteriorate the quality of municipal
water. Municipal irrigation with low-quality, highly saline
wastewater recharges and degrades the aquifer. A municipal
water-salinity cycle can be created which compounds the
salinity of groundwater with water of ever increasing
salinity being recharged into the aquifer. This situation
is especially important because of the unique aquifer
characteristics of the Tucson basin and the regional
hydrologic cycle. No previous research has focused on water
quality problems associated with a municipal water-salinity
cycle.
Research Objectives
The objective of this dissertation is to evaluate
the economic costs of selected groundwater conservation
policies. The external costs generated by increasing salt
concentrations in municipal water supplies are quantified in
terms of damages to a class of residential water-using
appliances. Conservation policies are evaluated on the
basis of the salinity damage costs and the expenditures for
groundwater conservation programs.
5
The specific objectives of this study are to:
1.
Describe the physical characteristics of the Tucson
basin which affect the water-salinity cycle and
identify the quantity and quality of Tucson's water
resources.
2.
Determine which groundwater conservation policies
will generate nonmarket or external user-costs.
3.
Specify the economic costs of increased salinity
concentrations in municipal water supplies.
4.
Evaluate user-costs generated by groundwater
conservation policies.
5. Compare and contrast the costs associated with
salinity degradation to the implementation costs of
groundwater conservation programs.
Overview
Chapter 2 is a description of water resources and
supplies in the Tucson basin. The hydrologic regime of the
Tucson basin is characterized for water occurrence and
flow. Service area and population data describing the major
municipal water provider in the basin, Tucson Water, is
presented to identify the population which will be affected
by salinity damages.
The determination of how groundwater conservation
policies will affect the water-salinity cycle is the subject
of Chapter 3. Policies intended to preserve groundwater
6
supplies are examined for their potential for generating
increased salinity in water supplies. Imported water,
wastewater reuse, and reduction-in-use programs are among
the policy instruments aimed at achieving groundwater
conservation.
An economic model is presented in Chapter 4 which
describes the external diseconomies generated by groundwater
conservation policy. Groundwater conservation policy can
increase the salt concentration in municipal water supplies;
salinity generates costs which may not be accounted for in
groundwater conservation policy decisions.
Salinity damage costs are developed for the city of
Tucson in Chapter 5. Past efforts to evaluate salinity
damages are reviewed. An evaluation framework which can be
applied to Tucson is developed and a damage function is
estimated.
Chapter 6 defines the municipal water-salinity
cycle. Municipal sewage is to be treated and relied on as a
water resource. Wastewater reuse creates recharge water
whose quality depends of the quality of the wastewater.
Salinity concentrates in the cycle in any case, but its
effects are greater when recharge water is captured in wells
before complete mixing in the aquifer with native groundwater, used and then reused, further degrading the quality
of wastewater recharge. Salinity compounds in the cycle and
generates increasing costs due to salinity damages.
7
In Chapter 7, a model is developed to evaluate the
costs of salinity damages when selected groundwater policy
instruments are employed. The costs associated with direct
use of CAP water and those associated with groundwater
degradation are estimated. Also estimated are the costs of
implementing groundwater conservation programs. Incremental
total capital costs associated with groundwater conservation
programs are presented.
Chapter 8 presents the conclusions and recommendations for further research.
CHAPTER 2
WATER RESOURCES AND SUPPLY IN THE TUCSON BASIN
In this chapter the sources of water supply for the
Tucson basin as they affect salinity management are
surveyed. These sources include groundwater, wastewater
reuse, and CAP water. Since the city of Tucson is the major
water provider in the basin and plans large-scale wastewater
reuse and CAP water use, the Tucson Water Department is the
focus of the study.
The impacts of salinity degradation on the aquifer
must be analyzed in the context of the hydrologic cycle.
Recharge of the aquifer is constantly taking place both
naturally and incidentally to the use of the land over the
aquifer. Land-use activities such as irrigation, mining,
and waste disposal affect the quality of incidental
recharge. Of these activities, municipal irrigation with
wastewater has the greatest potential for degrading
groundwater because it recharges low-quality water in the
municipal service area.
8
9
Hydrozeologic Characteristics
of the Tucson Basin
The city of Tucson presently pumps groundwater from
the Tucson basin to meet all water demand. Tucson is
located in the northern part of the Santa Cruz basin which
is an alluvial valley bounded by mountain ranges. In this
study, the Tucson basin is defined as the northern section
of the Santa Cruz basin and that area south of Cortaro where
the city of Tucson pumps its water. Groundwater is the only
dependable source of water supply in the Tucson basin
because streamflows in the area are ephemeral, with no
storage facilities.
The basin is located in the Sonoran desert. The
climate is semi-arid with high precipitation losses (90%)
attributed to evapotranspiration. Average annual precipitation is a function of altitude, typically 11 inches at the
lower elevations (2,000 feet) and 25 inches or more in the
mountainous regions (Davidson, 1973). Precipitation tends
to come in two seasons with 50 percent of the total falling
in July and August. The characteristics of rainfall for the
basin include both the cyclonic, winter storms and the
convective, summer storms of wide spatial variation (Sellers
and Green, 1968).
The Tucson basin is a north-south oriented basin
separated from other troughs and basins by chains of
mountain ranges (Strahler, 1963). The topography of the
10
area is described by the U.S. Geological Survey (Atlas
HA-55, no date) as comprised of three principal zones which
are:
1.
the mountain chains;
2.
the intermountain basin;
3. the belts of foothills and of shallow bedrock which
form zones between the main parts of the mountains
and basins.
Within these zones, four groundwater areas are
differentiated by the water-bearing characteristics of their
principal rock types. These areas are composed of:
1.
essentially non-water-bearing materials largely
comprised of crystalline rocks but also including
some indurated sedimentary and volcanic rocks;
2.
locally water-bearing Paleozoic limestone;
3.
locally water-bearing volcanic rocks;
4.
generally water-bearing alluvial deposits.
The first three groundwater areas include mountains and
belts of foothills and shallow bedrock; the fourth
groundwater area is entirely within the basins. The
groundwater zones and their boundaries are highly
generalized; because of local variations in rock type and
structure, conditions at any particular place within any
groundwater area may differ considerably from those
considered to be typical.
11
Aquifer Storage
The sedimentary basin-fill is several thousands of
feet thick and has the highest degree of porosity and
permeability; wells developed in this fill will yield large
quantities of water. The younger sedimentary deposits store
and transmit the largest quantities of groundwater per unit
volume. Although their hydrologic characteristics are
different, sedimentary deposits in the basin form single
aquifers. Typical basin sedimentations include clay, silt,
sand, gravel, and silty sandstone. Water storage takes
place in the saturated sediments which are several thousand
feet thick; however, there is economic water yield only in
about the upper 1200 feet.
Davidson (1973) delineated four alluvial levels,
three of which are water-bearing units forming a single
aquifer in the basin-fill sediments of the Tucson basin.
The units in descending order are recent alluvium, the Fort
Lowell Formation, the Tinaja Beds, and the Pantano
Formation. The recent alluvium consists mainly of sands,
silts, and gravels deposited by current stream channels,
alluvial fans, and sheet flows. The Fort Lowell Formation
(Pleistocene age) of the upper sedimentary deposit consists
of gravel, sand, and silt. It ranges from a few feet to 400
feet in total thickness. The Fort Lowell Formation has been
the main water supply level of the aquifer, but is now
dewatered in some areas of the basin. Below the Fort Lowell
12
are the Tinaja Beds. The Tinaja Beds (Miocene to
Pleistocene age) are composed of gravels, sands, and
mudstone. The gravels and sands are usually unconsolidated
to weakly cemented. These sediments range from hundreds of
feet to over 2,000 feet thick. The lower unit is the
Pantano Formation (Oligocene age) which ranges from several
hundred to a thousand feet thick. It is composed
predominately of conglomerates, gravels, sandstones, and
muds tones.
The majority of the groundwater is pumped from the
upper two sedimentary units, the Fort Lowell Formation and
the Tinaja Beds. Pumpage is preferred from the upper units,
not only for the lower lift costs, but because the lower
units are usually of lower permeability and thus yield less
water. In addition, the lower units yield water of lower
quality.
Groundwater flow in the basin is generally to the
northwest. It is comprised of the northerly flow from the
southern, higher portions of the basin and the westerly flow
from the mountains in the east. The flow exits the basin at
the Rillito Narrows.
The groundwater aquifer is a storage basin or
reservoir. An analogy to the aquifer is a bowl slightly
tipped to one side with an incoming flow on the high edge,
sides which act as a catchment, and an outflow on the low
edge. The inflow is from contiguous basins of higher
13
altitudes. Rain water moves down the impermeable slopes of
the mountain chains and foothills where it soaks into the
basins; this is the mountain front or perimeter recharge of
the aquifer. Recharge from precipitation also takes place
in the stream beds; this is termed streamflow infiltration.
Other significant sources of recharge to the aquifer include
sewage-effluent return, industrial return, and irrigation
return. Not all streamflow infiltrates; some leaves the
basin in the form of surface flow as the water seeks lower
elevations.
Table 1 shows the relative amounts of groundwater
entering and leaving the aquifer in the natural system. The
net natural recharge is nearly 75,000 acre-feet.
Tucson's Water Resources
Groundwater
The volume of the aquifer beneath the Tucson basin
is broken into two parts: total storage and recoverable
water. The Bureau of Reclamation (1984) estimates the total
storage volume of the Tucson basin aquifer as 47 million
acre-feet to a depth of 1,200 feet below the land surface;
however, the boundaries of this estimate extend well beyond
the city of Tucson. Griffin (1980) reports that because the
productivity of the Tucson basin aquifer drops off below 600
to 800 feet, recoverable water is in the upper 700 feet of
the aquifer. At this depth in the Tucson basin, Griffin
14
Table 1. Nondiscretionary Groundwater Inflow and Outflow.
-- Tucson Basin Aquifer, 1975.
Sub-total
Total
Thousands of Acre-Feet
Inflow
i) Groundwater underflow
ii) Mountain front recharge
iii) Surface water infiltration
17.8
31.0
47.8
96.6
Outflow
i) Groundwater underflow
ii) Evapotranspiration
10.0
12.0
(-22.0)
Natural Recharge
(Modified from Davidson, 1973 p. E73)
74.6
15
(1980) estimates there to be about 10 million acre-feet of
recoverable water. Even with net depletion reaching 250
thousand acre-feet per year (TAMA, 1984), the groundwater
resources of the basin can last into the second half of the
next century. There is some urgency to assure that the
groundwater resources are not completely depleted. But,
time exists to make decisions concerning the tradeoffs
between conserving groundwater and importing saline water.
Wastewater
Wastewater increasingly will be looked to as a
source of water in the Tucson basin. Wastewater is a
product of municipal water use whose value as a source of
municipal water is just now being realized. Wastewater
quality is a function of its source waters, low-quality
municipal water generates low-quality wastewater for reuse.
Historically, wastewater in the Tucson area was used only in
non-food crop irrigation, but with modern reclamation
technology wastewater has applications in municipal
landscape irrigation. Wastewater can be reclaimed for
potable uses, too. Barriers which hold back wastewater
treatment for potable uses are economic and attitudinal.
The first applications of wastewater to irrigation
created groundwater contamination problems. The wastewater
was nearly raw effluent and contained biological pathogens
and high nitrate concentrations. While wastewater treatment
16
technologies have been developed that can economically
control the biological pathogens, these technologies do not
control the conservative, inorganic contaminants such as
salts, copper, and sulfates. Conservative contaminants are
not reduced in conventional wastewater treatment. Water
treatment processes to remove conservative, inorganic
contaminants include chemical precipitation processes,
distillation, and reverse osmosis. However, blending is the
strategy of choice for reducing the impact of these
contaminants at the present. But, as is discussed later,
blending sources are limited.
Historical Wastewater Use. Agricultural wastewater
use in the Tucson basin dates to 1900 when grain crops were
irrigated with raw sewage (Yu, 1977). The first primary
treatment plant was constructed in 1928. Originally called
the Sweetwater Road Wastewater Treatment Plant, it was later
renamed the Roger Road Wastewater Treatment Plant. Early
records from the city of Tucson Wastewater Division
(1953-1955) show sales of wastewater to the City Sewer
Farm. The contracts ranged from a minimum of 2,310
acre-feet to a maximum of 3,200 acre-feet of wastewater per
year for irrigating a 640-acre farm. The water was priced
at $4.00 per acre-foot, delivered to the highest site of the
farm. Another large purchaser was the Oshrin Farms who in
1955 contracted for all excess wastewater to irrigate a
2,100-acre farm (City of Tucson, 1955). The contracted
17
price was $1.00 per acre-foot and the conveyance expenses
were borne by the Farms. A regulating pond was constructed
as temporary storage.
Pima County Sanitary District One purchased the
storage and conveyance systems in 1963. They maintained
preexisting contracts and acquired the right to purchase and
resell any effluent in excess of 13 million gallons per
day. When the conveyance system failed in 1970 and a rise
in nitrate levels in the groundwater was detected, the
wastewater was diverted into the Santa Cruz River bed
(Martin, 1980). The conveyance system was never repaired.
The Cortaro-Marana Irrigation District, in 1977, contracted
for up to 6,000 acre-feet of wastewater from the County for
$2.65 per acre-foot (Bookman-Edmonston, 1978). It continues
to use wastewater which is released from the treatment
plants into the Santa Cruz River and pumped by the district
from the channel. The conveyance system is the channel.
The irrigation district reported using approximately 3,400
acre-feet for each of the years 1982, 1983, and 1984
(Condit, 1985). This represents about 10 percent of their
total usage. The Randolph Park Golf Course has irrigated
with wastewater which has received secondary treatment and
disinfection since 1975. In 1977, the Arthur Pack and
Silverbell Golf Courses began receiving wastewater for
irrigation from the Ina Road Treatment Plant.
18
Wastewater Quality Regulation. The Federal Water
Pollution Control Act of 1972 (FWPCA), which requires
secondary treatment of most municipal wastewater, supplied
the impetus for the expansion of Tucson's wastewater
treatment facilities. Subsequently, the 1977 amendments to
the FWPCA, also known as the Clean Water Act (CWA),
implemented a federal assistance program and directed the
planning effort under sections 201 and 208, which provide
for uniform wastewater treatment standards. One result of
the CWA is wastewater that is more valuable because it is of
better quality. The final determination of reuse standards
is under state jurisdiction.
The Arizona Department of Health Services (ADHS)
adopted reuse standards in 1972 which stated maximum
parameter limits for various organisms and constituents.
The Regulations for the Reuse of Wastewater (Title 9,
Chapter 20, Article 4) were enacted in 1985 with the
purposes of expanding the number of quality parameters which
are monitored, increasing monitoring frequencies, and
establishing a permitting program.
The 1985 State of Arizona regulations for wastewater
reuse require that treatment facilities or other owners of
reclaimed wastewater obtain a permit from ADHS prior to
releasing effluent. The permit is a legally enforceable
contract in which conditions and responsibilities for reuse
of reclaimed wastewater are specified. The owner of
19
reclaimed wastewater is liable for meeting the conditions of
the permit and the reuser is liable for damages arising from
misapplication of the wastewater. Contracts also accompany
transfers of ownership. Users must provide additional
treatment to meet the standards of reuse as set forth in the
regulations. Blending can be used to meet the limits. The
reuse regulations specifically provide for control of
pathogens whereas salinity is not subject to the standards.
Wastewater for irrigation is to be applied at a rate
that does not exceed the consumptive requirements of the
crops, although leaching water can be used to alleviate salt
buildup. The minimum quality of reclaimed wastewater for
irrigation is established in the ADHS reuse regulations
under the Allowable Limits for Specific Reuse (Title 9,
Chapter 20). The regulations specify access for areas where
low-quality wastewater is used and the disposition of
harvests or cuttings.
Wastewater Quantity Regulation. Wastewater reuse is
not regulated by the Arizona Department of Water Resources
(DWR) under the AGMA, thus for the Tucson area it is the
only unregulated source of water which can be used for
irrigation. Further, the restrictions of the AGMA with
respect to the development of recreational lakes do not
apply to wastewater as they do for groundwater. Because it
is not regulated, as alternative sources are, wastewater is
attractive to use. Groundwater conservation policy (AGMA)
20
has created a demand for wastewater because of it can be
used without restrictions, other than those pertaining to
water quality.
The city of Tucson and Pima County adopted an
intergovernmental agreement in 1979 establishing ownership
of wastewater produced from the Ina Road and Roger Road
Treatment Facilities. The County is entitled to ten percent
of the wastewater production after the terms of the Southern
Arizona Water Settlement Act (SAWSA) entitlement to exchange
waters are met. The County is responsible for the
maintenance, operation and construction of the sewer system
and treatment facilities and sewer billing is done in
conjunction with the City water billing. The City has use of
the remaining wastewater and has pledged to utilize the
effluent in place of groundwater whenever possible, in the
hope of offsetting dependence upon groundwater.
The Mayor and City Council of Tucson adopted an
effluent reuse policy in July, 1982 (Resolution 11955). The
policy has 18 sections which provide for priorities of
allocation, pricing, and areas of use. An assessment of
wastewater reuse for the city was conducted by CH2M
Hill/Rubel & Hager (1983). The assessment examined the
quantity, quality, and feasibility of wastewater reuse. The
authors recommended the use of wastewater for irrigation and
groundwater recharge. They identified 4,241 acres of turf
and landscape areas which could use an estimated 23,230
21
acre-feet of wastewater. The effects of wastewater reuse on
water quality is examined further in Chapter 6.
Present Quality of Wastewater. Presently, the
quality of the wastewater in the Tucson basin is quite good
for irrigation. Table 2 shows the concentration of
contaminants in effluent from each of the local treatment
plants in relation to recommended limits for irrigation.
Included in the irrigation limits are heavy metals which may
affect health if used over a long time period.
Water treatment improves the quality of water with
respect to biological pathogens, but degrades water quality
by concentrating the conservative constituents in
wastewater. Most reclamation and treatment facilities do
not attempt to remove these contaminants.
Table 3 shows the average quality degradation to be
expected from wastewater treatment. The additional salt
concentration estimates of Table 3 compares well to the city
of Tucson wastewater reuse report (CH2M Hill/Rubel and
Hager, 1983) which estimates the increase in salt
concentration (TDS) from tap water with a TDS concentration
of 300 mg/1 to secondary effluent with a salt concentration
of 542 mg/l. The city of Tucson estimate is about 25
percent less than the estimate in Table 3.
22
Table 2. Effluent Quality for the Wastewater Treatment
Plants Servicing the City of Tucson and Limits for
Long-Term Irrigation.
Constituent
Average Effluent Concentration Recommended
Roger Road Ina Road Randolph Pk.
Limits
mg/1 Heavy Metals
Arsenic
Boron
Cadmium
Chromium
Cobalt
Copper
Fluoride
Iron
Lead
Manganese
Nickel
Selenium
Zinc
Other
pH
TDS
Chloride
SAR
0.005
0.34
<0.01
<0.02
0.008
0.03
0.68
0.11
<0.05
0.02
0.04
<0.01
0.05
<0.005
0.36
<0.01
<0.02
0.007
0.04
0.32
0.20
<0.05
0.02
0.03
<0.01
0.04
<0.01
0.03
7.4
535
78
3.3
6.5
471
84
3.5
7.6
465
52
3.0
(CH2M Hill/Rubel and Hager, 1983)
0.005
0.33
<0.01
<0.02
<0.02
0.44
0.07
<0.05
0.01
0.1
0.75
0.01
0.1
0.05
0.2
1.0
5.0
5.0
0.2
0.2
>.02
2.0
4.5-9.0
<1500
< 350
<
6
23
Table 3. Average Increases in Concentrations from Tap Water
to Secondary Effluent.
Item
Increase
Organics
BOD
Sodium
Potassium
Ammonium-N
Calcium
Magnesium
Chloride
Nitrate-N
Nitrite-N
Bicarbonate (HCO3)
Carbonate (CO3)
Sulfate (SO4)
Silica (SiO3)
Phosphate (P O4)
Hardness (as CaCO3)
Alkalinity (as CaCO3)
Total dissolved solids (TDS)
(Weinberger et al., 1966)
Average
(mg/1)
52
25
70
10
16
15
7
75
2
0.3
100
0
30
15
8
70
85
320
24
Central Arizona Project
Legislation related to the quality of Colorado River
water within the U.S. was initiated with the Water Quality
Act of 1965 (P.L. 89-234) which required states to adopt
water quality criteria applicable to interstate waters or
portions thereof within their boundaries. Explicit
reference to the increasing problem in the Colorado River is
found in the Federal Water Pollution Control Act Amendments
of 1972 (P.L. 92-500), where it is recommended that a
salinity policy be adopted for the Colorado River system
that would have as its objective the maintenance of salinity
concentrations at or below levels presently (June 1972)
found in the lower main stem.
It stated, "...the salinity
problem must be treated as a basinwide problem that needs to
be solved to maintain Lower Basin water salinity at or below
present levels while the Upper Basin continues to develop
its compact-apportioned waters."
The 1972 amendments were interpreted by the
Environmental Protection Agency to require assignment of
numeric quality standards. Representatives of the seven
basin states recommended flow-weighted average annual
numeric salinity criteria for three locations in the lower
main stem of the Colorado River System: Hoover Dam 723 mg/1;
Parker Dam 747 mg/1; and Imperial Dam 879 mg/l.
The passage of the Colorado River Basin Salinity
Control Act (P.L. 93-320) on June 24, 1974 was a step in the
25
implementation of the EPA standards. The principal
components of the plan to implement the standards are:
1.
Prompt construction and operation of the initial
four salinity control units authorized by Title II
of P.L. 93-320.
2.
Construction of the 12 other units listed in Title
II of P.L. 93-320 or their equivalent after receipt
of favorable planning reports.
3.
The placing of effluent limitations on industrial
discharges.
4.
The reformulation of previously authorized, but
unconstructed, federal water projects to reduce the
salt loading effect.
5. Use of saline water for industrial purposes whenever
practical, programs by water users to cope with the
river's high salinity, studies of means to minimize
salinity in municipal discharges, and studies of
future possible salinity control programs.
Implementation of the legislation has been impeded
by the complexity of managing a multi-state river system.
The construction of the salinity control units has been
delayed; only two units had been completed as of 1984,
nearly ten years after they were scheduled for operation.
Among the impediments are state water right statutes and
environmental concerns. Under Colorado and Wyoming water
26
law, the impoundment of water in evaporation ponds to
control natural saline water seeps does not qualify as a
beneficial use, yet the water right needed for such
impoundments can be obtained only for a beneficial use.
Moreover, large evaporation ponds may have fish and wildlife
impacts, a concern that was ignored in the 1972
legislation. The Department of Agriculture has had some
success in realizing its goal of on-farm salinity controls.
However, the Department of Agriculture and the Bureau of
Reclamation differ in the economic evaluation of the
programs, in estimates of salt tonnage contributions, and in
the scheduling of program implementation (Colorado River
Water Quality Control Office, 1984). The Bureau of Land
Management has opted for a program of continued studies.
Annual average salinity in the 1972-1980 period at
Parker Dam was low, as seen in Table 4. This is due to the
abstraction of the large amount of upper basin river water
required to fill Lake Powell and high flow years in 1979 and
1980. Projections of the effects of future increases in
upper basin depletions show the salinity increasing by as
much as 300 mg/1 in the 1985 to 2020 period. A persistent
dry or wet period of three years has an estimated effect of
increasing or decreasing salinity concentrations as much as
250 mg/1, respectively (Colorado River Basin Salinity Forum,
1981).
27
Table 4. Flow-weighted Annual Average Salinity of the
Colorado River at Parker Dam, 1972-1980.
Year
1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982
TDS mg/1
747 726 700 703 689 681 681 703 684 721 717
(Colorado River Basin Salinity Forum, 1981; ADHS, 1984)
28
The present water quality of the Colorado River at
Parker Dam is shown in Table 5. It is low in heavy metal
concentrations and is slightly alkaline. The TDS
concentration is lower than the future expected levels.
Projections of the future salinity of the river
indicate deteriorating quality (Colorado River Water Quality
Office, 1984; Colorado River Basin Salinity Forum, 1981).
Most estimates used in the planning of water treatment
assume salinity control programs are in place. Table 6
shows the near-term estimates of salinity at Parker Dam
(Colorado River Basin Salinity Control Forum, 1981). The
interplay of salinity control programs such as salt-seep
diversions, hydrologic conditions of flow, and depletion
rates in the upper basin states, will greatly affect the
salinity of the river. The main decision variable that
Arizona can influence is the salinity control projects. The
table shows that the depletion rates and the flow conditions
of the river can negate the effects of the control
projects. The forecast reveals a trend of steady salinity
degradation.
The economic impact of increased salinity in the
Colorado River is very large because its water affects a
large population and many uses. Cities and agricultural
regions in Colorado, Nevada, California, and Arizona suffer
damages caused by salinity. Anderson and Kleinman (1979)
summarize the magnitude of the costs of salinity damage for
29
Table 5. Water Quality of the Colorado River at Parker Dam.
Water Quality Constituent
Alkalinity as CaCO3
Arsenic, Dissolved
Arsenic, Total
Barium, Total
Boron
Cadmium, Dissolved
Cadmium, Total
Calcium
Organic Carbon, Total
Carbonate
Chloride
Chromium, Total
Copper, Total
Cyanide, :Total
Oxygen, Dissolved
Fecal Coliforms (per 100 ml)
Fluoride, Dissolved
Hardness, Total as CaCO3
Hardness, Noncarbonate
Iron, Total
Lead, Dissolved
Lead, Total
Magnesium
Manganese, Total
Mercury, Total
Nitrate, Total as N
pH (pH Units)
Phosphorus, Total as P
Potassium
Selenium, Dissolved
Selenium, Total
Specific Cond. (uU/cm)
Silver, Total
Sodium
Sodium Adsorption Ratio (no units)
Sulfate
Total Dissolved
Solids (TDS at 180oC)
Zinc, Dissolved
Zinc, Total
Units
129.
0.00414
0.0033309
O .134
O .195
0.000351
0.00455
84.8
4.54
4.54
93.1
0.00366
0.00807
O .00108
8.54
5.54
0.377
336.
207.
0.204
O .00145
O .0399
30.7
O .223
O .0000445
0.258
7.96
O .0288
5.13
0.00295
0.00275
1110.
0.00344
105.
2.51
304.
713.
0.00896
0.0241
(Bureau of Reclamation, April 1983, Table IV-24.)
30
Table 6. Estimated Salinity at Parker Dam Under Various
Salinity Control Scenarios, Hydrologic Conditions,
and Depletion Rates for the Years 1990 and 1991.
Year
1995
1990
Average
Virgin
Flow (MAF)
13
14
15
13
14
15
Depletions
Low
Medium
High
Without Salinity Control Projects
(mg/1) 781
789
809
752
762
781
756
763
782
Low
Medium
High
813
831
872
783
800
835
748
767
804
With Three Salinity Control Projects
(mg/1) Low
Medium
High
720
730
750
749
757
775
728
738
756
697
707
727
767
784
821
742
758
791
710
728
763
With All Salinity Control Projects
(mg/1) 722
732
750
691
701
721
739
755
788
(Colorado River Water Quality Office, 1984)
718
734
764
687
705
740
31
various affected populations who rely on Colorado River
water. The annual damages to agriculture in the Imperial
Valley of California can be as high as $66.4 thousand per
mg/1 of salinity. Municipal damages to single-family
residences alone are estimated by Anderson and Kleinman
(1979) to be about $11.3 thousand per mg/1 in the Los
Angeles basin and $11.0 thousand per mg/1 in the CAP
supplied regions of Arizona (1974 dollars).
Long-term salinity forecasts are shown in Figure 1.
This figure uses the forecast results of the Bureau of
Reclamation efforts to model the salt load in the Colorado
River through the year 2040. The results of the CAPSIM
model are a function of underlying assumptions about Upper
Basin States water use and the effectiveness of salinity
control projects.
The CAPSIM estimates assume that many of the
salinity control projects initially recommended in the
Colorado River Salinity Control Act (PL 93-320) are
realized. The ongoing federal assistance needed to realize
the conditions in the Bureau of Reclamation studies and the
future level of Upper Basin Colorado River depletions can
alter these estimates greatly. Presently, they are the most
reliable projection for the range of future salinity values.
Uncertainties abound in the estimated effects of salinity
management on the Colorado River. The uncertainties listed
by the Bureau of Reclamation are: (1) poorly defined target
32
I
I
0 0
co
III
I
a
0
0
0
<a to -4 rl
0
III
0
.
N. N N. N. N.
0
0
II
a
0
III
a
ci$ co r. co
rn ca W<D. cc
,
0
a
0
"4- tr)
QS CD CD
crs
cr$
33
load reductions; (2) a broad range of alternative solutions;
(3) incomplete data on control options and effects, limiting
the scope of the projections, and (4) the lack of complete
understanding of the interactive salt load/hydrologic system
and of the reservoir impacts (Colorado River Water Quality
Office, 1984).
The Bureau of Reclamation CAPSIM model predictions
were published in the report of Tucson Water Treatment Plant
Project Phase 1 Preliminary Investigations
(Montgomery-Johnson-Brittain, 1983). This report assessed
the median salinity of the CAP water arriving in Tucson as
690 mg/1 for purposes of their analysis. The use of the
median as an expected value introduces two biases since it
misrepresents the effects of very high and low values, and
it assumes there are no interactions between time periods.
Consideration of extreme values and interactions between
time periods is necessary if there is any residual effect,
as is the case for salinity returns to the groundwater
supplies.
The Montgomery-Johnson-Brittain report (1983) listed
the inflows of the Bill Williams and the Agua Fria Rivers as
having substantial dilution effects on CAP water. However
there is less than a 10 percent probability that both rivers
combined would contribute more than 100,000 acre-feet in any
given year; the mean contribution of both rivers to the CAP
would be slightly greater than one percent.
34
The CAPSIM model is based on 15 historical flow
sequences which are presented as scenarios. The first four
scenarios use 60-year series of actual Colorado River data
starting in 1906, subsequent scenarios are based on shorter
data time series up to 1982. Flow routing and operation
processes for the river are based on other Colorado River
models used by the Bureau, principally the Colorado River
Simulation System (CRSS) and the Colorado River Storage
Project (CRSP).
Two assumptions underlie the CAPSIM results. First,
the four salinity control units at Grand Valley and Paradox
Valley in Colorado, Crystal Geyser in Utah, and the Las
Vegas Wash in Nevada are assumed to be in operation.
However, plans for the salinity control projects have
changed since this model was run. Paradox Valley and the
Las Vegas Wash units are scheduled for completion in 1997
and 1991, respectively (Colorado River Basin Salinity
Control Forum, 1981; Colorado River Water Quality Office,
1984). Grand Valley stage 1, Meeker Dome petroleum field
closures, and two USDA irrigation return controls have
reduced the salinity in the Lower Colorado River as much as
28 mg/l. The Crystal Geyser Unit has been deferred
indefinitely. While other salinity control units were
recommended, the future for federal assistance is not
optimistic.
35
The second assumption in the CAPSIM results is that
future water use for irrigation and energy development will
reach a maximum by the year 2000. Recently, demand
projections were reevaluated and projected depletions in the
upper and lower basins of the Colorado River were estimated
to increase through 2040 (Colorado River Water Quality
Office, 1984). Higher depletion rates in the upper basin
states probably bias the CAPSIM results downward since, as
was seen in the section on the Colorado River, diversions
exacerbate the salinity of the river. The CAPSIM results as
published in city of Tucson Water Treatment Plant Project
Report (Montgomery-Johnson-Brittain, 1983) were used as the
basis of this analysis
The projected annual salt
concentration of CAP water arriving in Tucson is the average
of the five series of CAPSIM results for the projections
based on 1956, 1961, 1966, 1971, and 1976 starting years,
see Figure 1. This decreases the variability of the data
series but does include the effects of the most recent dams
and operating procedures. The projected TDS concentration
data range for the study period 1991 to 2025 is between 633
and 790; the mean is 720. The projected salinity used in
this study is less than the 760 mg/1 TDS mean published by
the Bureau of Reclamation (1983) in its Environmental Impact
Statement for the Tucson Aqueduct.
Summary. The struggles over interstate allocation
of Colorado River waters have gone on for many years.
36
Quality is a much more recent concern. Now, however,
quality receives nearly as much attention as quantity
because of international obligations and perceptions of
large costs associated with municipal and agricultural
damages caused by salinity.
The salinity of the CAP water is a function of its
primary source, the Colorado River, and of any additional
water sources which may be used. From the evidence provided
by the Colorado River Study Commission (1981), it is highly
probable that the salt load in the river will increase.
Tucson Water Department
The city of Tucson Water Department (TWD) is
operated and maintained as a self-supporting, municipally
owned utility. In 1983 there were approximately 129,300
service connection customers including residential,
commercial, industrial, and other accounts, located both
within and outside of the corporate limits of the city. The
service population is approximately 435,000 people. The
city presently obtains its municipal water supply from four
well fields containing over 230 wells. Wells reach down 50
to 700 feet into the aquifer. Groundwater supplies are of
good quality and do not require treatment. Water is pumped
directly into the distribution system; about 3,000 miles of
pipe, from the Santa Cruz, Southside, and Avra Valley well
fields and from interior or central system wells. Other
37
water providers in the Tucson basin account for less than 3
percent of the total water provided in the Tucson (TAMA,
1984).
The TWD is obligated to provide water and to collect
revenues to recover its operation and maintenance costs.
Implicit in its obligation as a municipal facility is a
commitment to best serve the long-term interests of the
city. The stated objectives of the TWD planning programs
are to eliminate existing water system deficiencies, to
accommodate future urban growth in the Tucson metropolitan
area, and to prepare for the future delivery of a major
imported source of water (TWD, 1982).
Plans for capital improvements, water system
financing strategy, and water user charges and fees are
prepared and evaluated by the TWD staff, the Citizen's Water
Advisory Committee, and consultants. Annual reports and
interim requests concerning the financial and physical state
of the municipal utility are made available to the Mayor and
City Council for deliberation and legislation. In 1977 the
Citizen's Water Advisory Committee made an extensive
examination of the city's water policies. The Mayor and
Council adopted the Committee's recommendations for basic
water policies to ensure the self-sufficiency of the water
systems. The basic policy states that all costs associated
with the operation and improvement of the utility should be
covered by revenues derived from water rates and other
38
water-related income sources (Black and Veatch, 1982). The
principal policies adopted were (Citizen's Water Advisory
Committee, 1977):
1.
Charges for water utility service, insofar as
feasible, shall be made in direct proportion to the
cost of securing, developing and delivering water to
the various classifications of customers of the
Tucson Water Utility.
2.
The City shall maintain a water rate structure which
incorporates summer and winter rate differentials,
increasing block rates for residential usage, a
summer surcharge for large multi-family and
commercial customers; separate charges for new
connections and reconnection to the system; a
minimum charge called a service charge to cover the
costs of meter-reading, billing and the fixed
expense of individual water services, and an
isolated area surcharge for water service in areas
not contiguous to the main urban water system.
3.
Changes to this basic structure shall be based for
the most part on the concept of cost of service and
be implemented incrementally so as to avoid sudden
and large scale shifts in the economic impact of the
rate structure.
4.
Water rates and charges shall be reviewed annually.
39
Municipal Well Fields
TWD obtains its groundwater from three well fields
in the service area supplemented by groundwater from the
Avra Valley. The interior or Central well field is
comprised of approximately 200 wells located within the
incorporated portions of the city. Most of the wells were
acquired in the last 30 years through the purchase of
private water companies. In recent years, TWD has upgraded
the well facilities to realize greater efficiencies,
reducing operation and maintenance costs. The wells are
local service wells pumping directly into distribution lines
within the city. The prospects for increasing the number of
wells in this field are limited since there are fewer
private wells to acquire and very few new, high-capacity
well sites (Johnson, 1978). The groundwater table declined
in the well field from 40 feet to over 100 feet between
1947-1977 (Wright and Johnson, 1976).
The Southside well field, south of the central well
field along the channel of the Santa Cruz River, has 13
wells and pumps the least volume of all the fields. This
well field is topologically and hydrologically up-gradient
from the central city of Tucson. Thus, the flow into the
distribution system is assisted by gravity and transmission
is inexpensive. The pumpage is largely from underflow in
the Santa Cruz River channel. The groundwater table is
greatly affected by flows in the channel bed during
40
persistent rainstorm seasons and can rise significantly.
The number of wells in this field fully exploits the present
hydraulic capacity of the aquifer and no new well
construction is being planned.
The Santa Cruz well field is directly south of
Tucson and provides approximately 20 percent of the water
pumped by TWD. The Santa Cruz field is adjacent to Indian
and non-Indian agricultural lands. As was previously
discussed in the geologic summary, the groundwater table is
more or less a continuous formation of water-bearing sands
and fragmented rock, so high pumpage in one area lowers the
groundwater table in the nearby areas. Because of
voluminous agricultural pumpage nearby, the Santa Cruz well
field yield has declined; the decline in yield for the
1968-1977 period was almost 9,000 gallons per minute, a 40
percent decrease. Further development of the Santa Cruz
well field is not planned because of the declining capacity
and on-going litigation disputing the TWD pumpage effects on
the groundwater supply for irrigation of the neighboring
Tohono O'odam Indian Reservation farmlands.
The Avra Valley west of Tucson supplied about 20
percent of the city's water in 1979. The percentage of
water supplied from Avra Valley well fields has decreased
significantly over time; 1984 pumpage accounted for about 15
percent of Tucson's groundwater pumpage. Most of the water
pumped from the Avra Valley for the city of Tucson is from
41
agricultural land which is purchased and retired to obtain
the water rights as a source of municipal service water.
From its almost 20,000 acres of retired irrigation lands,
the city of Tucson is entitled to about 50,000 acre-feet per
year. This is equal to over 50 percent of Tucson's 1984
pumpage; however, TWD restricts its pumpage in the Avra
Valley area. The transportation costs from Avra Valley are
very high, which makes Avra Valley water less attractive
than pumped water from the other city fields, a burden that
CAP water shares.
Most of Tucson's present water supply is from the
Central wellfield (Table 7). For salinity management,
anything that affects the water quality of the Central
wellfield will have major effects upon city water users.
Because there is no central distribution system for
municipal water, only limited adjustments can made by
blending the water from the various well fields. With the
CAP, a central transmission and distribution system will be
necessary to enlarge the city-wide distribution capacity.
The main area to receive CAP water in the city will be the
central section (McLean and Davis, 1981). The city has not
disclosed plans to blend CAP and groundwater to reduce the
salinity of delivered water. City planning documents state
that there is no reason to blend for salinity reduction
(Montgomery-Johnson-Brittain, 1983). Thus some areas may
receive unblended CAP water while others get higher-quality
42
Tucson Water Department Water Pumpage by
Wellfield, 1979-1980.
Table 7.
Wellfield
Number of
Active Wells
Pumpage
(mgd)
Percent
135
35.5
54
Avra Valley
16
13.4
20
Santa Cruz
25
12.6
19
Southside
11
1.5
2
Isolated
30
3.1
5
217
66.1
100
Interior
TOTAL
(Davis,
1981)
43
groundwater. Table 8 compares the water quality of various
sources of city water. It is evident that there is a large
difference between the median salinity concentration in
groundwater and CAP water.
The City of Tucson Water Department has an on-going
water quality testing program. A thirty-year compendium of
the results of the water quality sampling program is given
in Table 9. The main constituents which have exceeded the
water quality standards are TDS and sulfates, these are
secondary standards and are not enforced. The water samples
which exceed water quality standards are mainly within the
City's boundary whereas Avra Valley has higher quality
water.
The Pattern of Water Use
in the City of Tucson
The main class of water user in the city of Tucson
is single-family residences (Table 10) accounting for nearly
60 percent of all water usage. The reported total groundwater pumpage for the city of Tucson in 1984 is 82,539
acre-feet (Wellford, 1985). About 9 percent of the pumped
groundwater is unaccounted for, the main class of
unaccounted-for-water is system leaks.
The water use for each user class, and past and
projected rates of change, are shown in Table 10, 11,
and 12. Multi-family residential water uses are the fastest
44
Table 8. Salinity of the City Well Fields and the CAP.
Range
Median
Interior Santa Cruz Avra Valley
CAP (Colorado
River water)
(mg/1)
276 461
282
720
65-1034
179-2275
178-489
401-1039
(Montgomery-Johnson-Brittain, 1983; Bureau of Reclamation,
1983)
45
Table 9. Results from the City of Tucson Water Quality
Sampling Program 1951 - 1980.
Tucson Well Fields
Constituent
Interior
Santa Cruz
Avra Valley
(Total Number of Samples/Number Exceeding Standards)
Chloride
Copper
Iron
Manganese
pH
Sulfate
Total Dissolved
Solids
Zinc
980/0
227/0
360/34
235/1
708/3
977/11
251/1
50/0
31/3
31/2
177/2
250/24
131/0
17/0
17/3
17/1
121/0
131/0
996/74
182/0
249/111
31/0
131/0
17/0
These estimates are based on laboratory values, not
field values.
(Montgomery-Johnson-Brittain, 1983).
Note:
N0
46
r-
r-4
CO
Ul
4
CO
r-N.
CV
1/40
1-4
r-1Q
r-1
CV
4
e-4
CV
I/1
m
r-
4
co
1/4c)
t-4
o
h
CV
r-1O
CO CO (N h
r-4
ON
CV
1- 4r-1
ON
CV
CV
CV
to
co
(7)
en
%.13
Lfl
0
Cr)
N-
4
1-4
Cs1
ON
-4
en
en
o
('4
I-1
0
c).
co
N.0
Lrt
,-1
ON
CV
NO
CsJ
o
co
e-4
co
co
4en
r-4
v-4
ON
CV
4
CV
en
co
en
cr.
en 4
O t.o
4
4 CV Cs1
o 4 r-
0
r-1
00
CO
r-4
CO
ON
r-4
in
Cs'
incs4
4
CV
rel
Cs1
CV
1-1
en
OcnN.
oO
%.0
r-.4
c‘.1
r-1
Cee
4in
en
en
4
CV
en
r-1
r-4
N.
CV
1-1
CV
en
r 4
N.0
1/40
ON
ON
ON
N.
4
00
4
co
en
ce)
4
0
t.0in
ON
CV
ON
r-4
en
CV 0
cne--1
bD
cri
e-4
4
In
47
r4 CM Ul -4
1/1000Mg-IN.-4
• •
•
•
•
•
•
00 UI Ul 1-4
4
M
CNJ 01
r-4
CD Ul
un
01
U1 kg).
%.0
Ul
• •
•
•
•
•
•
01 Ul 00 C) Ul r-4 CD
r-4 r-1
01
ON I's cr)
U1
401, CT .41. 0 un
CN 0s1 01 r, g.0 CD 04
• •
•
•
•
•
•
U1 0 CO C•.) g-I ON g•-•4
VD
r-4
0SI
1/40 01 0.1 VO VD
CV
4
CD4'n 44U11/400*.
4
•••••••
1-1 ul CD 0g r, 0 r,r-f
r r
n4œ4
un .4 CD CD VD
-
•
•
co
-
•
•
01 01
•
•
•
r-4 r4
1-1 •r-4
00
•
V)
• r-4
CN CM Ul
CN CV Ch Cs) VD
CN
•
•
•
•
• •
•
r- CD CM Ch rn v-4 CD
r-4 1
1
01
CM 4 1-4
Ul
4 00 4 CV ON 4 CD
• •
•
•
•
•
•
01 CM 04 01 en
01 1-1
rCs4
00
4
40
Ul
r-4
rA
E E CC) CG
•,1
CG
og-I
>-1
-.A
a)PArzAuc.)
O.
•
4A
O
ww
HZ0C)0. -4
IZZOUP
4.)
X
,
b0,-4,1W,--4WZ
O ca.0WOPT)
. -IEWEW0
mqw.-Im)-1)-4
,
H
0
H
▪
•
48
ul 00 CN r,ul r,VD
cv
vD CD ND rl rs 00 rl ,4
•
•
• •
•
•
,4 ul ul rl cel ,4 cV C4
CO
v-4
r
Csi
rl cy a> CV ,A
V) C) Ul
r, CT .7 -4
• •
•
•
• - •
•
,4 Ul ul rl rl ,A CV C)
CV
Ch Ch Ps VD
:7
. . .
.
cl cl rl ,A CV CV
C4
,
r, 9-4 Ps CV r, oo ,A ul
ON
.
.
v4
.
CV
Ul
Ch Ul CV CV 4 - r4
00 rl VD -7 Ch CD 441 Ul
Cs4
Ul el rl ,4 CV C)
C4
el Ch Ul rl rl r, r, CO
cs CD No nT 00 ND CV :7
Cg
v4 U1
•
•
•
ul
•
•
•
•
•
..4t
•
WI el rl ,4 CV C)
W
co
ul r, cv r, ND CD ,4 ,4
CV
CO C•1 1".•
Cs!
r-- o
•
•
•
•
r-4 441 ul rl
•
•
•
•
rl ,4 rl Ul
Cs;
CV Ps 00 st Ch CD C) rl
./
00 r4 r, ,T oo
,A
• •
•
in
•
•
•
•
cy
•
.-4 Cs4 ri
cl cm ND r, ND ND
Ch CV .7 ul
00 CV 00
•
•
•
• -
• • •
,4 ul Ul rl rl ri CV CV
co
r, on r, Ch CD st CV ND
CD Ul CO VD ,4 CV Ul Ch
•
•
• • • • - -
,4 CV CV
CV Ul Ul rl
00
,4•
CV
Ps
CV
CV
CV .47 :t VD CD
.7 1-4 Ch CV
co
CV ul V) rl CV CV ,4
CV
vt ul
en co cY cm
Ps
PN
,4 ,A
,4
eaSC)
co
oo
.
ul
CV
•
X g
0.1
r44
.7-44
e
• (11
14
(To E1-1
E
.;4 ";4 0 0
7'0
w x. Z Z C.) C.)
•
61) 1-4 (1)
O
co
co a
cn
E (I3
fp
co
co 3.4
(43
In 0
o
..0
cn
1-1
o
F.
49
growing use categories. Overall, water use increased by
about four percent per year over the 1978 to 1984 period.
The largest projected increases in use are for the
duplex-triplex and small multi-family residence categories
(Table 12). Commercial uses are expected to level off. The
increase in total water use is expected to be about 2.2
percent a year.
From both historical and projected growth rates in
water use (Tables 11 and 12), it is seen that residential
water uses will remain the largest category. This suggests
that the damages due to salinity degradation will be borne
largely by residential users. Because of the magnitude of
residential water use, it will probably also bear a large
part of the groundwater conservation effort in the city's
reduction-in-use program.
Summary
The Tucson basin is in an arid region with low
precipitation, deep groundwater, and little drainage.
Natural recharge of the aquifer is smaller than withdrawals,
so that aquifer overdraft occurs. All recharge events,
natural and incidental, will affect the quality of the
groundwater. Also the limited drainage means that water
recharging from land-use activities will remain in the area
and affect the groundwater.
50
Aquifer materials are connected but they are
stratified into discernable layers each possessing unique
characteristics. Upper layers are drained easier than the
lower layers; recharged water is picked up readily in the
upper layers. Since the depth of wells is determined by
economic objectives such as minimum cost for a given
capacity, pumpage will occur in the highest possible level.
Wastewater reuse is a major groundwater conservation
policy in the Tucson basin. Wastewater quality presently is
good and reuse under present quality conditions poses little
concern for groundwater quality. However, with increasing
wastewater reuse and decreasing quality the potential for
salinity loading in local groundwater supplies is high.
Water brought in by the CAP is more saline than the
groundwater of the Tucson basin. Salinity management
programs in the Colorado River are being implemented but
because of the many factors which contribute to the salinity
load, they are not assured of success. Development in the
Upper Colorado River Basin states, continued farming, and
funding for salinity control all are uncertain. All
estimates project ever increasing salinity in the Colorado
River.
Water resources available to the Tucson basin lie in
many jurisdictions. Colorado River policies are made by an
inter-state commission but influenced by several federal
agencies, states, and water-users along the river.
51
Groundwater use is limited by the provisions of the 1980
Arizona Groundwater Management Act (see Chapter 3) but the
Tucson Water Department determines well placement and supply
policy. Policy directed at wastewater reuse is set by the
federal and state governments for quality concerns and by
county and city governments for quantity concerns. Fragmented institutional responsibilities for water resources
have made unified water management difficult.
CHAPTER 3
GROUNDWATER CONSERVATION PROGRAMS
Groundwater conservation programs in the Tucson
Basin have been implemented by state, county, and city
governments. Conservation activities include both demand
management and supply augmentation. State activities are
directed by the 1980 Arizona Groundwater Management Act
(AGMA) with the goal of reducing groundwater withdrawals.
Pima County and the City of Tucson are developing wastewater
reuse programs to offset reliance on groundwater. The most
significant groundwater conservation program for the Tucson
area is the CAP which will import about 5 million acre-feet
of Colorado River water into the Tucson basin by 2035.
Some public-education programs have been heralded as
conservation programs, particularly the city's "Beat the
Peak" program. "Beat the Peak" is not actually a major
water conservation program; its goal is management of peak
water load.
The objective of this chapter is to identify which
groundwater conservation policies will be important in the
Tucson basin and to describe how the groundwater conservation policies will affect the municipal water-salinity
52
53
cycle. Focus will be on major groundwater conservation
policies which include: the 1980 Arizona Groundwater
Management Act, the CAP, and wastewater reuse. All are
long-term programs which deserve scrutiny since they
directly affect the salt load of recharge water in the
water-salinity cycle.
1980 Arizona Groundwater Management Act
The AGMA was enacted on June 12, 1980 and embodied a
comprehensive legislative framework for the management of
groundwater resources in Arizona. It established Active
Management Areas (AMA's) in those parts of the State where,
due to the magnitude of groundwater overdraft and the
importance of groundwater supplies for economic activities,
active groundwater management is perceived as necessary to
ensure long-term supplies. The AMA's included the areas in
and around Tucson, Phoenix, Prescott, and Pinal County
(Figure 2). Most provisions of the AGMA apply only in these
areas.
For the Tucson, Phoenix, and Prescott AMA's the law
prescribes a management goal of safe yield by the year
2025. Safe yield under the AGMA means the attainment and
maintenance of a long-term balance between groundwater
withdrawal and recharge, both natural and artificial.
The AGMA created the Arizona Department of Water
Resources (DWR) and charged it with the responsibility to
54
lAPACH E
COCON INO
MOHAVE
AJO1
Flagstaff
I
1
L- 0
i YA va PA I L- PRESCOTT
Ç)ç M
TH
6
JOS
3
CIT
I NA
H
INA
LA PAZ
i MA R ICOPA
YUMA j
I•\I
r-- — — PIMA
C OCHISE
DOUGLAS
INA
Figure 2. Active Management Areas.
55
administer the law. The Governor was instructed to appoint
a director for the agency, who in turn was empowered to
appoint AMA directors. In addition, the AGMA directed the
Governor to appoint for each AMA a five member Groundwater
User's Advisory Council (GUAC) to represent the interests of
area groundwater users. The GUAC provides public input into
the conservation programs in the AMAs and influences the
programs greatly.
The major provisions of the AGMA are: (1) a system
of property rights for groundwater which both protects
existing rights and establishes procedures to acquire new
rights; (2) groundwater reduction-in-use programs for the
agricultural, municipal, and industrial water use sectors;
and 3) engineering standards and monitoring requirements.
Also, there are incentives to seek alternative water
supplies to substitute for groundwater resources.
Alternative water supplies and reduction-in-use
programs have the greatest potential to effect changes in
the water-salinity cycle. There is no recognition of
quality effects arising from the management and conservation
programs in the AGMA.
Provisions in the AGMA which affect allocations and
water use include: restrictions on new agricultural irrigation acreage, grandfathered water rights, groundwater
permits for non-municipal users, registration and regulation
of small domestic wells and groundwater withdrawal by
56
cities, towns, and private water companies, and reductionin-use programs for agricultural, domestic, and certain
classes of industrial water users.
A developer must obtain
a Certificate of Assured Water Supply from DWR before
applying for required land development permits. Assured
water supply is defined by the AGMA as sufficient water of
adequate quality to meet the area's projected needs for 100
years and must be consistent with the water use reduction
goals of the groundwater management plan.
Summary of Rights and Permits
Irrigation Grandfathered Rights. Irrigation
Grandfathered Rights (ARS 45-465) apply to areas of 2 acres
or more, irrigated between 1975 and 1980 for the purpose of
growing plants for sale or human consumption or to use as
animal feed (TAMA, 1984). An irrigation grandfathered right
defines the land base, "water duty acres", which can receive
irrigation. The amount of water that is allocated to the
acreage is defined in the management plan. The basis for
allocations of water to those who have irrigation grandfathered rights are historical irrigation water use and
irrigation application efficiencies which define the water
duty. No new acreage can be brought into production once
the final rights are verified and the AMA application
process is finished. However, there are provisions for
moving water duty acreage to other land in order to utilize
57
CAP water or to replace flood damaged land. There are 504
certificates of irrigation rights, encompassing about 53,000
acres, in the Tucson AMA.
The use of historical crop acreage as the basis of
the allocation is intended to allow the continuation of
historical crop production and thus protect the income
potential of the right holder. The water reduction aspect
of the program is intended to increase the application
efficiency of irrigation waters by decreasing the water
duty. Irrigation water duties are computed on the basis of
feasible reductions in water use through the employment of
high efficiency irrigation technology. However, the
adoption of specific devices is not mandatory. Thus if the
allotment is cut back and irrigators do not choose to
improve their irrigation technology, they can continue
production by decreasing the cropped acreage or by switching
to a low water use crop. The policy is enforced by fines
and the threat of extinguishing the right.
The main effect on water quality arising from the
agricultural reduction-in-use program is that it limits
farmer's ability to leach contaminants into the aquifer by
reducing over-irrigation. For agrochemicals, such as
pesticides and nitrates, the low leaching factor will force
agriculturalists to employ advanced management practices
(Gordon et al., 1985).
However, the load of water-carried,
conservative contaminants such as salinity will decrease
58
only if the concentration of the contaminants do not
increase. If salinity increases, the positive effects
generated by reduction-in-use may be negated by the
increased salt load carried by the reduced leaching water.
CAP water has a salt load which is greater than the well
water in many areas of the state. The salt load passing to
the aquifer can increase, even under reduced wastewater
application, if CAP water is substantially saltier than the
groundwater in the irrigated area.
An irrigation allocation must be used on water duty
acres; no part of the allotment can be transferred to other
sites except as indicated above. This prohibition limits
the management potential of water transfer for water quality
reasons. Agriculturalists cannot lease their water to be
used for other purposes such as the provision of high
quality water for domestic or residential uses.
Type 1 Non-Irrigation Rights. Type
1 Rights (ARS
45-463) apply to retired farmland. The retirement must have
occurred after January 1, 1965 and must have been for the
purpose of transferring irrigation waters to non-irrigation
purposes. The amount of pumpage allowed is limited to the
lesser of historical irrigation water use on the land or
three acre-feet per acre. The right is appurtenant to the
retired acreage and may not be transferred to another
location, though the water itself may be transported
elsewhere. Retirement of acreage for purposes of
59
transferring water rights from Grandfathered Irrigation
Rights to Type 1 Rights must be made by the original
Irrigation Rights holder. As of December 1984, there were
35 Type 1 certificates representing 20,158 retired
irrigation acres and 60,474 acre-feet of water in the Tucson
AMA. The largest holders of Type 1 rights are copper mines
and the City of Tucson.
Only original owners of the irrigated acreage, as of
the date of AMA designation, may receive Type 1
grandfathered rights. Opportunities to purchase Type 1
rights to obtain good quality water will diminish as
irrigated acreage changes hands.
Type 1 rights are important since they offer an
opportunity for domestic water providers to expand their
well field areas. If water quality management is a concern,
this is a method open to water providers to obtain higher
quality supplies outside of their service area.
Type 2 Non-Irrigation Rights. Type 2 Rights (ARS
45-464) apply to non-irrigation withdrawals of groundwater
in existence as of June 12, 1980 (TAMA, 1984). The right is
based on the maximum amount of water withdrawn and used for
non-irrigation purposes in any one year of the five years
preceding the establishment of the AMA. The right allows
the withdrawal of water from any location and is
transferable but not divisible. The Tucson AMA received
2,700 Type 2 applications, however only 380 certificates
60
were verified and issued (McNulty, 1984). The total
allocation in the Tucson basin is about 111,000 acre-feet.
Most of the rights are held by industrial users. Type 2
non-irrigation rights are assigned for purposes of
electrical power generation, mineral extraction, sand and
gravel, turf industries, and general industrial uses.
Because Type 2 rights are not appurtenant to
specific acreage they offer an opportunity for domestic
water providers to pump water in regions outside of their
service areas for water quality reasons. Since there are
few Type 2 rights and the average amounts of each permit are
large in the Tucson area their price can be expected to be
bid up in the future.
Service Area Rights.Service area rights (ARS
45-491 to 45-498) empower cities, towns, private water
companies, and irrigation districts to withdraw water from
within a service area to fulfill the requirements of their
customers. A service area is defined as the land area
actually served by the entity and any additional areas that
contain an operating distribution system owned by the entity
and used primarily for the delivery of non-irrigation water
to water utilities and to irrigation districts (TAMA,
1984). The service area entities are called water
providers. There are two designations of providers: large
providers are those that serve 500 people or more and small
providers who serve less than 500.
61
In 1980, there were 29 large providers in the TAMA
who served 99 percent of the municipal water use and 96
percent of the total AMA population with a total withdrawal
of 104,715 acre-feet. In the same year, there were 129 small
providers who served about 2 percent of the AMA population
and one percent of the municipal population. The total
withdrawal of small providers in 1984, the first year with
reliable records, was 6,066 acre-feet (Wellford, 1985).
There is no explicit standard in the AGMA for the
quantity of groundwater to be allocated to service areas.
The allocation is defined by the municipal conservation
program in the AMA management plans. The AGMA restricts the
expansion of service areas for the purposes of: encompassing
a non-service entity well field, furnishing disproportionately large amounts of water to a large water-user
unless the use is consistent with the management plan, and
the encompassment of irrigation acres to extinguish the
potential conversion of an irrigation right which may be
conveyed to a Type 1 non-irrigation right.
The service area restrictions are meant to limit the
encroachment of water providers upon other water users.
This has far-reaching consequences in terms of water quality
management, since the expansion of service area well fields
may be necessary for management of quality.
Groundwater Withdrawal Permits. Permits (ARS 45-511
to 45-528) are available to those who do not have
62
groundwater withdrawal rights and can demonstrate a nonirrigation beneficial purpose for groundwater withdrawals.
The permit defines limits on the amount and duration of the
withdrawal. There are seven types of permit activities:
1.
Dewatering
2.
Mineral extraction and processing
3.
General industrial use
4.
Poor quality withdrawal
5.
Temporary electric power generation
6.
Temporary dewatering
7. Drainage
In 1985, there were 14 general industrial use permits for
about 2,874 acre-feet, 2 mineral extraction permits for 130
acre-feet, and 2 dewatering permits for 1,620 acre-feet
(Rossi, 1985). The poor quality withdrawal permit is for
dewatering a contaminated area, and not for the provision of
high-quality water.
Future new uses of groundwater will be assigned by
permit when rights are not obtainable. Permits are not
always transferable and they are subject to renewal.
AGMA Groundwater Conservation Programs
Reduction-in-Use Programs. Each of the four AMAs
has evolved a unique approach to its "reduction-in use
programs" in its First Management Plan. Reduction-in-use is
a term used to differentiate these programs from other
63
groundwater conservation activities such as supply augmentation. The GUAC oversees the tailoring of the requirements
to user conditions in each of the regions.
The exact amount of the reduction target is a
policy decision. While the GUAC creates the reduction
target it provides little direction as to the amount of
water reduction in each sector. The water use reduction
requirements are a product of compromises made in public
participation processes. The main public participation
forums are the GUAC and public hearings which are required
before the promulgation of the management plans. The
importance of these forums in policy formation is shown in a
statement by Lester Snow (1983) to the GUAC:
The Groundwater Management Act emphasizes the
development of "reasonable" conservation requirements. In determining what is reasonable, consideration of the technical aspects of conservation
is complemented by an understanding of the public
perception of conservation. The public should be
informed of proposed conservation requirements and
(sic) provided with an opportunity to express
general attitudes about conservation and specific
attitudes about the requirements.
Reduction-in-use programs are prepared by the AMA
staffs and presented in the Management Plans. Municipal,
industrial, and agricultural requirements aimed at reducing
groundwater use are contained in the plans. Because the
focus of this research is at the municipal level the
municipal reduction-in-use program is examined closely
herein.
64
Municipal Conservation Policy. Municipal use means
"all non-irrigation uses of water supplied by a city, town,
private water company or irrigation district" (ARS
45-561.5). There are several types of water providers
involved, this includes: municipally owned utilities,
privately owned firms, cooperatives, and other distribution
system arrangements. The First Management Plan specifies
guidelines for the municipal water use reduction program as:
A conservation program for all non-irrigation uses
of groundwater. For municipal uses, the program
shall require reasonable reductions in per capita
use and such other conservation measures as may be
appropriate for individual users. For industrial
uses including industrial uses within the exterior
boundaries of the service area of a city,town,
private water company or irrigation district, the
program shall require use of the latest commercially
available conservation technology consistent with
reasonable economic return. (ARS 45-564.A.2.)
The mandated reductions are in per capita use, not
total use, and are thus not directly related to the goal of
achieving safe-yield. Wastewater reuse is especially
attractive since it does not count against the per capita
requirements.
Water quality effects may result from wastewater
reuse if the wastewater is high in conservative contaminants
such as salinity.
First Management Plan Municipal Programs Which May
Affect Groundwater Quality. Specific requirements apply to
open bodies of water, landscape provisions, and turf
65
irrigation. The filling or refilling with groundwater of
all or a portion of any body of water, including a lake,
pond, lagoon, or swimming pool having a surface area greater
than 12,320 square feet used for landscaping, scenic, or
recreational purposes, is prohibited. Thus, expansion of
recreational lakes and so on must rely on reclaimed wastewater. Large quantities of wastewater could recharge the
groundwater and could present a potential for contamination.
Also, there is a provision for turf-management
industries and turf-related facilities. Turf is to be
managed in the same manner as agriculture with per acre use
requirements and allotments. Turf managers expected to
employ up-to-date irrigation techniques and to monitor the
application depth. Again, wastewater is uncounted in the
turf irrigation requirements and has potential for overuse.
Summary
The AGMA establishes groundwater rights, allocation
programs, monitoring requirements, and engineering standards. Although quality is not managed directly, the AGMA
does affect the management of groundwater quality. Rights
for distinct uses and service area restrictions limit
wellfield management alternatives. But engineering standards have a positive impact since they will prevent direct
groundwater contamination due to land-use activities by
66
insuring that well heads are sealed and are not a conduit of
pollution.
Wastewater Reuse for Irrigation
The city of Tucson is active in a number of programs
to conserve groundwater resources. They have funded
education programs, retired agricultural acreage, contracted
for CAP water, and began construction on wastewater reuse
systems. Wastewater plans are ambitious and include use on
most large public turf facilities including: schools, golf
courses, and parks. Further, the City would like to serve
reclaimed wastewater to private turf facilities.
Wastewater reuse plans for the City of Tucson
(CH2MHi11/Rubel and Hager, 1983) are shown in Table 13. The
city plans to use about 30 percent of the projected effluent
flow for municipal landscape irrigation from 1990 to 2030.
In 1983, there were 452 acres of municipal landscape irrigated with wastewater. The 1983 acreage represents about 13
percent of the estimated turf acreage (see Table 14). Plans
call for a 17-fold increase in irrigation acreage by 2030.
The amount of wastewater used for irrigation and the
recharge from irrigated acreage will increase
proportionately. The estimates of wastewater reuse will be
employed in a presentation of the municipal water-salinity
cycle in Chapter 6.
67
Table 13. Projected Wastewater Reuse Potential for
Municipal Landscape Irrigation. -- City of
Tucson.
1990-2030.
Year
Total
Landscape
Acreage
ac.
1990
2000
2010
2020
2030
4,200
5,040
5,960
6,880
7,750
Total Annual
Irrigation
Requirements
ac-ft/yr 23,000
28,000
33,000
38,000
43,000
(CH2M Hill/Rubel and Hager, 1983)
Projected
Effluent
Flow
ac-ft/yr
61,000
79,000
101,000
122,000
144,000
68
Table 14. Projected Turf Acreage in the Tucson Metropolitan
Area.
1990-2030.
User Category
1990
2000
2010
2020
2030
acres
Parks
Golf Courses
School Grounds
Cemeteries
Medians
820
2,020
1,100
190
70
870
2,600
1,300
200
70
930
3,200
1,550
210
70
990
3,800
1,800
220
70
1,050
4,400
2,000
230
70
Total
4,200
5,040
5,960
6,880
7,750
(CH2M Hill/Rubel and Hager, 1983)
69
The cost of expanding the Roger Road Wastewater
Treatment Plant to accommodate the increased reuse of
wastewater for municipal irrigation is about 16.7 million
dollars in capital costs and 690 thousand dollars per year
for operation and maintenance (CH2MHi11/Rubel and Hager,
1983).
Conservation achieved by wastewater reuse for
municipal irrigation could be significant. Assuming that
per capita water use is 140 gallons per day and the 2030
Tucson area population is about 1.6 million, planned
irrigation wastewater reuse would offset about 17 percent of
the total water requirements for the City of Tucson.
The Tucson AMA, in its water budget projections,
assumes 100 percent reuse of wastewater. Wastewater reuse
is a city/county responsibility and the DWR has no direct
control over wastewater reuse programs. Wastewater is not
included in the reporting requirements of the AGMA and does
not count as water use against the requirements of the
municipal reduction-in-use program. Thus the AGMA creates
benefits in the use of wastewater.
Groundwater Conservation Achieved by CAP
CAP water is due to arrive in the Tucson basin by
1991. The maximum contracted annual amount is about 151
thousand acre-feet for Tucson Water. Metropolitan Water,
another water provider in the basin, has contracted for
70
about 8 thousand acre-feet per year. The final delivery
schedule has not been determined but consultants for the
city have made projections (CH2MHi11/Rubel and Hager, 1983;
Montgomery-Johnson-Brittian, 1983) (see Table 15).
Projected water requirements are given in Table 15.
The proportion of CAP water to annual requirements shows
that CAP water will make up from about 30 to 60 percent of
total annual water requirements.
Although use of CAP water is not mandated in the
AGMA it is the key to the achievement of the safe-yield goal
for the Tucson area. Incentives to use CAP water found in
the AGMA focus on the requirements for an assured water
supply and the restrictions on expanding the municipal water
service area. Presently, a signed contract for CAP water is
considered an assured water supply; this is an incentive to
contract for CAP water.
The total estimated inflow of CAP water for the
period 1991-2035 is 5 million acre-feet (Bureau of
Reclamation, 1983). CAP water delivered to the city is
intended for direct consumption after treatment
(Montgomery-Johnson-Brittian, 1983). The treatment
processes will remove particulate matter and chlorinate for
disinfection; salt concentration will not be reduced. The
CAP brings with it a large salt load, nearly 1 ton per acre
foot.
71
Table 15. Blend Ratio of CAP Water to
Groundwater to Meet City of
Tucson Municipal Water
Requirements. -- For various
Periods, Tucson.
Period
Blend Ratio
CAP to Groundwater
1990
31:69
1995
27:73
2000
28:72
2005
43:57
2010
48:52
2015
54:46
2020
59:41
2025
64:36
(CH2M Hill/Rubel and Hager, 1983)
72
Water Use: Projected and Actual
Groundwater Water Conservation
Projections
Tables 16 and 17 show the TAMA's estimates of
groundwater use without and with the first management plan
conservation efforts, respectively. By the year 2025, CAP
water comprises 36 percent of total water supplies, return
flow is 32 percent of the total, and mined groundwater is 12
percent of the total. Under the TAMA conservation
programs, projected in Table 17, mined groundwater's share
falls to 9 percent, an absolute savings of about 23
thousand acre-feet annually. The conservation programs of
the first management period are projected to conserve about
23 thousand acre-feet annually by 2025.
CAP water is one of two main tools to offset the
use of mined groundwater. The 1990 agricultural and
municipal demands are estimated to decrease 10 thousand
acre-feet due to the effects of the reduction-in-use
programs. The reduction-in-use programs have only a minor
role in comparison to CAP as a means to decrease reliance on
groundwater.
An assumption made in the Tucson AMA projections is
that all wastewater will be reused. Daily per capita water
use is assumed to be 140 gallons and the amount of
wastewater estimated in the budget is 90 gallons per capita
per day. Under this assumption, about 64 percent of all
73
Table 16. First Management Plan Baseline Projections. Tucson Active Management Area. 1980-2025.
Bas e a1990
2025
Population (1000's)
Irrigated Acres (1000's)
491
46
WATER DEMANDS AND SUPPLIES
(1000's of Acre-Feet)
720
47
1590
30
Water Demands b
Agricultural
Municipal and Industrial
Lossesc
Total Demands
230
179
62
471
237
243
62
542
148
454
62
664
Depletions
Agricultural
Municipal and Industrial
Losses c
Total Depletions
184
133
62
379
190
150
62
402
118
270
62
450
46
47
30
37
9
92
27
66
140
38
146
214
130
92
130
140
130
214
O
249
471
Od
272
542
239
81
664
Return Flows
Agricultural Recharge
Municipal and
Industrial Recharge
Effluent Use
Total Return Flows
Water Supplies
Total Inflow
Return Flow
Central Arizona Project
(CAP)
Mined Groundwater
Total Supplies
a.
The "Base" year represents the average annual demand
conditions for the period 1975 to 1980.
b.
Includes all conveyance losses.
c.
Includes water lost due to phreatophytes and basin
outflows.
d.
Full deliveries of CAP to Tucson.
74
Table 17. Projected Future Conditions Assuming First
Management Plan Conservation Requirements.
Tucson Active Management Area. 1980-2025.
Bas e a
4
91
(1000's)
Population
46
Irrigated Acres (1000's)
WATER DEMANDS AND SUPPLIES
Water Demands b
Agricultural
Municipal and Industrial
Losses'
Total Demands
Depletions
Agricultural
Municipal and Industrial
Losses'
Total Depletions
Return Flows
Agricultural Recharge
Municipal and Industrial
Recharge
Effluent Use
Total Return Flows
Water Supplies
Total Inflow
Return Flow
Central Arizona Project
(CAP)
Mined Groundwater
Total Supplies
(1000'S
1990
2025
720
47
1590
30
of Acre-Feet)
230
179
62
471
227
233
62
522
141
435
62
638
184
133
62
379
182
141
62
385
113
252
62
427
46
45
28
37
9
92
26
66
137
37
146
211
30
92
130
137
130
211
Od
255
522
239
58
638
0
249
471
a. The "Base" Year represents the average annual demand
conditions for the period 1975 to 1980.
b. Includes all conveyance losses.
c. Includes water lost due to phreatophytes and basin
outflows.
d. Full deliveries of CAP to Tucson are not expected to
begin until 1991.
(TAMA, 1984)
75
municipal water will be reused. It is evident that the role
of wastewater is considered to be very important. However,
the assumption of complete reuse does not match the city of
Tucson wastewater reuse plans.
Actual Water Use
Reported water use in the Tucson AMA for 1984 is
shown in Table 18. If all allotted rights were used, water
use would be over 525 thousand acre-feet; reported water use
is 52 percent of that figure. Water use for grandfathered
rights was less than 50 percent of allocations. Municipal
water use was nearly equal to the estimated allotment
because municipal allotments are not claims to real property
but rather the product of a per capita allocation formula
allocation. Because the allotments are calculated on a per
capita actual basis, the allotments are expected to be equal
to actual water use.
Summary
The AGMA established programs to manage groundwater
resources in critical regions in the state. Critical
groundwater regions include Tucson and Phoenix, which must
be able to supply water to their large populations. Three
ways to deal with water shortage are augmentation of
supplies, reuse, and reduction in use. The AGMA provides
incentives for augmenting supplies, for reuse, and for
reducing use but does not provide incentives which would
76
Table 18. Tucson Active Management Area Reported Water
Withdrawals and Use.
Type of Use
Category
1984 Ground- Total Allotments Percent of
Water With-
First Management Allotment
drawals aPlan
Used
(ac.ft.)
Municipal service
areas
109,416.3
Irrigation
Districts
93.2
Total
111,247.0b
98.4
0.0
0.0
238,157.3
61,008.7
50.3
4.6
41,937.2
10,079.0
61,068.0
27.4
27.3
46.0
2,715.7
4,638.7
58.5
276,802.9
528,135.9
52.4
Grandfathered Rights
Irrigation
119,728.4
Type 1
2,480.4
Type 2
Non-Irr.
11,495.4
2,748.4
Elec. Power
Mineral Extr.
28,125.1
Permits
(ac.ft.)
a.
89% of total certificates reported as of Sept. 27, 1985.
b.
Calculated as average municipal gpcd target (156) times
total population.
(TAMA, 1985)
77
take water out of low-valued uses. Cities and industries do
not have strong incentives to buy irrigation rights, even
though such a policy shifts rights to higher-valued uses.
The main instruments to be employed in groundwater
conservation policy are importing Colorado River water via
the CAP, wastewater reuse, and reduction-in-use programs.
About 50 percent of Tucson's municipal water supplies will
come from CAP water by early in the next century. The CAP
is relied on by the Tucson AMA as necessary to meeting the
conservation goals of the AGMA. Inasmuch as Colorado River
water is high in salinity, increased salinity is to be
expected in Tucson's municipal water supplies.
Wastewater reuse will be important in Tucson's
future since it can offset groundwater withdrawals for
municipal landscape irrigation. The quality of wastewater
will effect changes in parts of the aquifer that are
recharged by wastewater irrigation. In the municipal
water-salinity cycle, wastewater reuse and subsequent
recharge are the link between land-use activities and
groundwater quality.
The efficacy of reduction-in-use programs in terms
of actually conserving groundwater seems insignificant in
the Tucson area, where the per capita use rate is already
near the target. However, public awareness about
groundwater conservation has increased, this may play a
major role in reducing water consumption, in addition to
78
developing support for the policies of the DWR. The effect
of reduction-in-use programs on salinity degradation of
groundwater is not clear. If lower water use would preclude
the delivery of large amounts of Colorado River water, then
the effects would be positive. If on the other hand, a
greater share of municipal water is supplied by CAP due to
decreased municipal water requirements, then
reduction-in-use will result in more salinity in municipal
supplies.
Whereas wellfield service area restrictions are not
a conservation policy, they have the potential to affect
water salinity. By decreasing the choice of well sites,
site selection for wells may be mandated in areas where the
salinity of recharge water is inefficiently diluted with
native groundwater.
CHAPTER 4
A FRAMEWORK TO EVALUATE THE TRADEOFFS
BETWEEN QUALITY AND QUANTITY
The goal of water quality policy is to protect water
supplies from contamination and the goal of water quantity
policy is to resolve conflicts over the allocation of scarce
water. Both types of policies should ensure that the net
benefits of policy outcomes are maximized. Ingram and
Ullery (1980) note that the important variables of policy
are the costs and benefits (a community's perceptions of
policy impacts) imposed by governmental action. Poor, or
suboptimal, policies can result when, for any reason, some
costs or benefits are not considered as policies are
formulated.
When policies are developed in a fragmented manner
the instruments used to meet one goal may conflict with the
attainment of another goal. Decision-makers responsible for
groundwater conservation policy calculate the costs and
benefits of groundwater conservation only in terms of
quantity goals. Tucson faces this situation, groundwater
conservation policies frequently ignore the water quality
costs associated with increasing salt concentrations in
municipal water supplies. A more appropriate approach is
79
80
integrated management of quantity and quality that strives
to provide the quantities and qualities of water demanded at
particular times and locations.
In this analysis the author develops an economic
framework to rank the impact of policy instruments used in
groundwater conservation policy in terms of their effects on
water quality. The focus is on the tradeoffs between
conservation and the social costs of salinity damages which
can reduce the economic value of water.
Efficiency and Regulation
In a social welfare context, pollution damage occurs
when the value to society of a polluting activity is less
than its deleterious effects. Beyond some point, an
increase in polluting activity generates environmental costs
greater than the additional benefits experienced by the
polluter. If polluters had to pay for the environmental
costs, they would be motivated to reduce pollution to an
efficient level. Since polluters rarely are required to
compensate for the costs of environmental degradation
generated by their disposal activities, environmental costs
will not be included in the costs of production of the
polluter. Overproduction of pollution is the result.
Because few markets exist which assign prices to the
use of the environment for disposal, the price of pollution
is very low or zero for pollutants, such as salinity, that
81
are not regulated. Given there is no market price for such
pollutants, Allen Kneese (1970) observed it is no surprise
that a heavy toll is placed on the quality of the
environment by development and its residues.
An economic model of the allocation of environmental
resources, based on the marginal net benefits of alternative
water supplies, i.e. net of water acquisition costs, and the
marginal costs of increased salinity, is represented in
Figure 3a. Shown on the horizontal axis, are increasing
quantities of alternative water supplies and increasing
quantities of salinity given achievement of safe-yield for
the water provider. Cost per unit is on the vertical axis.
For simplicity, assume in Figure 3a that increasing salinity
is directly proportional to increases in water supply. When
a water provider, such as TWD, must acquire increasing salt
to acquire increasing amounts of water to meet safe-yield,
water degradation is an external cost of water acquistion.
When a resource use has unpriced external effects,
the case considered here, we do not expect the water
provider's choices to be efficient for society as a whole,
because the provider does not bear the external costs
arising from its actions. If the external cost borne by the
water provider seeking alternative water supplies is zero,
the provider, who realizes the marginal net benefits (MNB),
will pollute to the level OQ', the amount which maximizes
his net benefits and meets the safe-yield goal. Total net
82
1
Marginal
Net Benefits
of Alternative Water Supplies
$/Unit
Marginal
Cost of
Salinity Damage
a
1
1
1
1
1
1
1
0
$/Unit
rt-....°
Marginal
Regulatory
Cost
1
t
t
1
1
1
1
1
1
1
1
1
1
1
1
Marginal
Decrease in
Net Benefits
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
t
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
b
Q'
( - )
Figure 3. Marginal Analysis of External Costs and
Regulatory Costs.--(a) Net Benefits of
Alternative Water Supplies; and
(h) Regulatory Cost.
83
benefits to the water provider are shown as the sum of the
areas A, B and C. The external marginal salinity costs (MC)
are borne by the public. As more alternative water supplies
available to TWD are exploited, the last ones chosen are
more expensive and have more salinity. With the addition of
each unit of alternative water supply, marginal net benefits
are decreasing and marginal costs of salinity are
increasing. For the amount of water OQ', society suffers
total costs of salinity damage represented by the area under
the marginal cost function, or areas B, C and D. The gains
from pollution are areas A+B+C and the losses caused by
pollution are areas B+C+D. Net gains to society are
represented by the difference between the areas A and D.
Inequality of marginal costs and marginal benefits
indicates a socially inefficient allocation of environmental
services. The socially efficient level occurs at OQ * . At
this point, the water provider gains benefits equal to the
areas A and B and the social losses caused by salinity are
area B. Net benefits are at a maximum when the salinity
level is OQ * , and are represented by area A. Maximum net
benefits are attained when marginal benefits equal marginal
costs, a condition of economic efficiency. This condition
implies that society is as well-off as can possibly be,
given its resource base, its production technology, and the
tastes and preferences of its members.
84
If salinity damages are greater than 0Q * , an
improvement which moves toward the efficient level can be
achieved when the costs of salinity damage are included in
the water provider's decisions. The improvement can occur
by assigning the right to low saline water supplies to the
public and making the provider pay for the damages imposed
by salinity. Alternatively, if the provider has the right
to supply highly saline water those who would be affected
adversely by the salinity could pay the provider to reduce
salinity to acceptable levels. With zero transactions
costs, the marginal cost should represent the public's
willingness-to-pay for salinity abatement; in Figure 3a this
would be areas C and D. The efficiency of the allocation
that results from such negotiations is discussed in Coase
(1960), Turvey (1963), and Buchanan (1969).
However, institutional constraints, in the form of
the AGMA, impede the achievement of the efficient allocation
of alternative water supplies and salinity damage. The AGMA
with its single goal of safe-yield does not recognize
salinity damage. The requirement of the AGMA to achieve
safe-yield serves as an incentive to find substitutes for
groundwater, incurring increasing external salinity costs,
or through regulation that absolutely reduces use. These
policies give rise to regulatory costs through monitoring of
withdrawals, enforcement, and legal procedings.
85
In Figure 3b, the marginal external costs of
salinity which are created by the introduction of substitute saline water supplies are subtracted from the
marginal benefits of the supplies, giving a Marginal
Decrease in Net Benefits, or excess marginal costs,
function. At OQ * , in Figure 3b, the interception of the
Marginal Decrease in Net Benefits function with the axis
meams there are no marginal costs in excess of marginal
benefits and efficiency is satified. The excess of marginal
costs over benefits, as shown in this hypothetical example,
are high at OQ', because these costs are external to the
policy decision for safe-yield.
From OQ', the regulatory costs required to achieve a
marginal unit of reduction-in-use in in place of substitute
supplies would be small. As more and more reduction-in-use
restrictions replace substitute water supplies, higher and
higher costs must be incurred to maintain safe-yield. Thus,
the schedule of regulatory costs, the Marginal Regulatory
Cost Function, is downward sloping. The marginal regulatory
cost function is discussed in Anderson and Lee (1986).
Given that regulation to reduce the external costs
of salinity is costly, the "efficient level of pollution",
OQ * , costs more to achieve than the benefits it generates.
Once regulatory costs are included in the analysis, the
point at which net social benefits are maximized is OQ",
where the marginal decrease in net benefits is just equal to
86
marginal regualtory costs. However, so long as the agency
charged with implementing the goals of the AGMA is not
accountable for the salinity costs of substitute water
supplies, the agency's objectives are still maximized at
OQ', so that an avoidable externality remains.
Thus, we see the problem at hand is one of external
costs induced by public policy. There are non-market goals
in public policy and policy administrators who seek to
minimize regulatory costs. Because of the nature of public
commodities and pollution an economic welfare model used for
public commodities is examined. In this model the condition
of an assumed constant relationship between water quantities
and salinity is relaxed.
Marginal Social Cost of Salinity
McGuckin and Young (1981), hereafter referred to as
M-Y, examined a case where the household production function
includes both quantity of water and salinity. While
households can choose quantity, they have limited control
over salinity. Water for community use and the delivered
salinity levels of this water are multiple products of the
water utility. The utility can adjust both the costs of
water supply and the salinity level and these adjustments
are made through a specific production relationship. These
authors employed a partial equilibrium model with an
externality modified from the work of Baumol and Oates
87
(1975), where salinity is treated as a damage to be abated.
In the model, it is assumed that the community is in
competitive equilibrium except for the provision of water at
the preferred level of salinity. The water provider is
represented as one of the firms in a competitive i-person,
k-good economy producing water, which is sold as a private
good. The level of TDS in this water is determined by the
production decisions of the water supplier, production
conditions are such that more water can be provided if
higher levels of TDS are accepted, i.e. 6S t /611 t > 0, where
other production factors are held constant. Since all water
provided has the same salinity, salinity is a nonrival,
nonexcludable characteristic, thus it is a public good,
produced by the water firm. Because salinity is a public
good, the costs of the marginal increase in TDS, denoted
MSC, are the sum of salinity costs experienced by all water
users.
M-Y derive from the Kuhn-Tucker conditions in their
general model three conditions for optimal water
quantity/quality management, which are shown in Equations
(1), (2), and (3). M-Y redefine their equations as:
P w = MV(i) = MP w (k) = MC w ,
MSC = MC s ,
P w = 6S/SW * (MSC)
for all i,k
(1)
(2)
(3)
88
where:
P w=
Price of water;
MV(i) = Marginal value to the (i)th individual of
a unit of water;
MP w (k) = Marginal product to the (k)th firm of
water;
MC w=
Marginal cost of producing a unit of
water;
MG s=
MSC
Marginal cost of salinity reduction;
= Marginal social cost of salinity;
6S/SW = Marginal rate of technical substitution
between salinity and quantity of water.
Second-order conditions for the maximization of net
benefits require that the set of constraints must define a
feasible region which is everywhere convex. For a local
maximum, the original objective function must be concave in
the neighborhood of the maximum point; a global maximum is
achieved if the concavity conditions hold throughout
(Baumol, 1977).
The first set of conditions in Equation (1) are the
usual equimarginal conditions for private goods in the
partial equilibrium model: In a competitive market, the
price of water should equal its marginal cost as well as its
marginal values in production and consumption. The
second-order conditions for an optimum are met if a change
89
in resource use decreases net marginal benefits. Equation
(2) is the condition on the public good, salinity abatement,
suggests that the marginal social cost of TDS (that is, the
sum of all costs experienced by producers and consumers as a
result of the marginal increments of TDS) should be equal,
at the optimum, to the costs of abating salinity at the
margin. Equation (3) relates salinity abatement and water
supply in the utility's management decision. The term,
6S/6W t , is a technical substitution term describing the
increment in TDS that must be accepted to get an increment
in water supply, all other factors held constant. This
equation suggests the social cost of the TDS accepted for
the marginal increment in water supply should equal the
price of water at the optimum. Therefore, (5S/614 t must be
positive if the price of water is non-negative and if MSC is
positive, as it will be if salinity produces damages.
Interpretation of the technical substitution term infers
that water of highest quality is used first to meet the
conditions of optimization for equilibrium.
The efficient economic allocation of water as
developed by M-Y directly yields an expression for optimal
salinity abatement and quantity of water produced. The
adoption of an efficient water quantity/quality policy would
increase net social benefits by allowing resources to be
used for the highest-valued purposes. A water utility which
is not responsible for costs incurred by consumers as a
90
result of salinity, may not include the MSC of salinity in
its decision criterion, and probably will not meet the
conditions in Equations (1) and (3). McGuckin and Young's
model shows that if the social cost of salinity
contamination is significant, there may be potential gains
to management of salinity level in water supplies.
In their analysis, M-Y identify the tradeoffs
between quality and quantity in a single time period. Water
policy affects water use over long periods of time. A
framework for intertemporal analysis is necessary to achieve
the objective of this research, which is to evaluate the
groundwater conservation policy instruments for their
effects on salinity.
An Economic Model of Policy-Induced
Social Costs Over Time
The costs associated with salinity in municipal
water supplies may be broken into two parts: direct costs
generated by the initial use of saline water supplies (such
as CAP water) and indirect costs, which occur due to use of
groundwater which has been degraded by recharge of saline
water into the aquifer. These costs may offset partially
the benefits of groundwater conservation policies, such as
the substitution of wastewater and CAP water for
groundwater. Both direct and indirect salinity create costs
through corrosion in household water-using appliances,
thereby effecting a decrease in the appliance's service
91
lifetime. The two sets of salinity costs differ in that the
costs of direct CAP use are a function of a single policy
variable, CAP water deliveries, and the level of salinity
must be accepted on delivery whereas the costs of
groundwater degradation are affected by a range of
groundwater conservation policies.
Total costs, as the sum of the direct and indirect
costs of using saline water, are represented as:
cq — cd + ci
(4)
where:
Cg — Total costs of salinity damage;
Cd
—
Direct costs associated with initial use of
imported saline-water;
Ci — Indirect costs associated with groundwater
degradation which result from policy actions.
Incremental costs are generated by additional
salinity in the municipal water supplies. The additional
salinity can come from either imported water or from
groundwater degradation. The contract for imported water is
for the amount of water delivery, there is no contract
condition under which water can be refused because of
excessive salinity. The user cost associated with
groundwater degradation is the result of current period
groundwater conservation policies. These policies include
92
the wastewater reuse and artificial recharge which can
recharge the aquifer with highly saline water. Additional
salinity in groundwater supplies over time is represented by
the differential between Equation 5a and 5b:
t-1
C (A) =
t
t
C
C
(A)*Q
t-1
(A) + C
Q
t-1
t-1
(N)*Q
(A) + Q
t-1
t-1
(N) + C
(N) + Q
t-1
t-1
(P)*Q
(P)
t-1
(5a)
(P)
C(A)*Q (A) + C(N)*Q(N) + C (P)Q (P)
t
t
tt
t
(A) =
t+1Q (A) + Q (N) + Q (P)
t
t
t
(5b)
Subject to:
0 < C t < Saturation
where:
C t (A) = Salt concentration of groundwater in
aquifer in time t;
Qt(A) = Quantity of groundwater in the aquifer
which mixes with natural, non-policy
affected, and policy affected recharge
waters in time t;
C t (N) = Salt concentration of natural and nonpolicy affected recharge waters in time t;
Qt(N) — Quantity of natural and non-policy
affected recharge waters in time t;
93
C t (P) — Salt concentration of policy affected
recharge in time t;
Q t (P) = Quantity of policy affected recharge in
time t.
The difference between Equations (5a) and (5b),
hereafter refered to as P t , is the policy influenced
increase in salinity concentration, or the salinity
pick-up . It is argued that salinity pick-up is affected by
water supply policies enacted in the name of groundwater
conservation. These policies degrade groundwater by
increasing the salt concentration of policy influenced
recharge such as the incidental recharge resulting from
municipal irrigation.
Ordering Policies by External Social Costs
An optimal resource allocation is defined as that
allocation which maximizes the present value of the
difference between benefits and costs. The benefits in this
section are generated by alternative water supply and demand
management policies, and the costs result from salinity in
municipal water supplies; the water supply and demand
management policy decisions result in different streams of
salinity damage costs.
Considering the effects of those policy instruments
which change the salt concentration of groundwater pumped
for municipal supplies in period t, we define P t as the
94
change in salt inflow to municipal groundwater supplies in
time period t as the result of a conservation policy.
Conservation policy instruments include: use of Colorado
River water imported via the CAP, reuse of wastewater,
artificial recharge of CAP water and/or effluent, and
service area and recharge siting policies which affect the
degree of mixing and dilution, or the effective values of
Q t (A). The importance of dilution volume can be seen in
Chapter 7. These policies affect the external costs
associated with concentrations of salts in pumped
groundwater.
Salt concentration in municipal water supplies at
time t, s t , is determined by the TDS concentration of local
groundwater at the beginning of the current period, s t _i,
and the amount of salinity pick-up, P t , in the current
period. A simple representation of this transitional
relation is:
St = s t _i + P t .
(6)
This representation oversimplifies the physical system.
Hydrologic conditions which govern the dilution potential in
the Tucson basin are examined in Chapter 6.
Because water supply and conservation policies
affect the salinity pick-up, we can define an ordering of
these policies with respect to salinity pick-up, P t , by
fixing an upper limit to P, say 1 mg/l. Let cb be the set
95
of conservation policies which do not exceed the limit.
Define B t (P t ), water supply benefits as a function of P t , as
the maximum level of water supply benefits, from any element
of 4), that can be achieved without exceeding P t , so that
B t (1) is the maximum benefit generated by any policy with
salinity pick-up which is less than or equal to 1, all else
equal. As we relax the constraint on pick-up amounts, a
wider range of water-supply policies becomes available, and
more groundwater conservation benefits can be realized.
As P t is allowed to increase, additional
conservation policies are brought into the set (1), B t (P t ),
therefore rises (or at least cannot decline) with P. This
relationship is shown in Equation (7).
d(B t )/dP t0
(7)
The costs associated with salinity damage in singlefamily residences, during period t, are a function of
salinity, C(s t ). These costs have been determined
empirically to increase in (s t ) (d'Arge and Eubanks, 1978).
The positive relation which exists between damage costs and
salt concentration can be written as:
dC/ds t0
Substituting into the general maximization problem above:
(8)
96
T
MAX Z(P t ,s t ) — E [B t (P t ) - C(s t )]
t
subject to:
where:
fi t
(9)
s t = s t _i_ + P t
s t ?.-.. 0
so = 300 mg/1 at time t=0.
TDS concentration in pumped water, s t , a state
variable, is shown in transition equation (6) as being
influenced by conservation policy through the salinity
pick-up, P t .- P t is the control variable, in this
representation, as it is implicitly chosen when a water
supply/conservation policy is determined.
The Lagrangian expression associated with this
system can be written:
T
X = E [B t (P t ) - C(s t )]fi t
t=0
T
+ E A .t[st - st-1 - Pt]
(10)
t=0
The Kuhn-Tucker conditions for this constrained
maximization problem are:
dC
t
—
A < 0 and 6X s = 0 (11)
-A
1s
+
t
t
ds 13t
6s 6
t
t
6.t
t
6.t
—
dBt(P t )
6P tdP t
.5.t
fi t - A t 0 and 6P P t
t
— 0
(12)
97
SX
SX
-- s - s
- P 0 and
SA (
t
t5A
1
t
t
A
t
t
(13)
— 0
If there is positive salinity in pumped water at time, t, an
optimum requires:
St
Ss
— 0 or A
t
r—T
= E
t
r=t
LLL— fi r + TV(s )
ds
T
(14)
r
The multiplier, A t , of the transition equation is
the imputed present value of the costs generated by an
increment in P t due to its impact on the salinity of pumped
water s t , in all future time periods, plus the impact on
salvage value of the resource at time T, the end of the
planning horizon, TV(s T ).
If the increment to pick-up amount is positive
during time t, an optimum requires:
SX
SP
dBt(Pt)
=
t
dP
t
tdBt(Pt)
/3 - At
= 0 or A
t
=
dP
t
fi
(15)
t
At the optimum, the present value of marginal
benefits of the conservation policy associated with P t
should equal the imputed present value of marginal costs
created by P t as reflected in changes in the salinity
associated with demand management and alternative water
supplies.
The decision rule, for an optimum at every time t,
can be written as:
98
dB
t
(P
dP
t
t)
fi
r=T dC(s t )
fir
dsr
r=t
+
TV(s)
(16)
The right-side of the decision rule is the
discounted sum of all future salinity costs which result
from P t plus a terminal value, TV. The terminal value is
whatever cost is associated with the incremental change in
s t as a result of P t at the terminal time, T, and may be
thought of as the impact of P t on the salvage value of the
aquifer stock. The left-side of the decision rule is the
change in benefits associated with specific demand
management and water supply policies discounted to time t.
Present Value and the Discount Rate
There are two schools of thought that attempt to
define the appropriate social discount rate: the private
opportunity rate approach and the social time preference
approach. Both speak to the existence of a rate of time
preference where goods and services today may be more
valuable than goods and services in the future. The private
opportunity rate approach argues that the source of funds
for any public project ultimately the private sector, so
that net returns from any public project ought to discounted
by the rate of return in the private sector. The social
rate of time preference approach notes the dependence of
some individual's utility on future consumption by others.
The distinction between social and individual preferences is
99
reflected in how one perceives the fairness of intertemporal
allocations: Should private capital markets compete with
future generations or is there a responsibility to provide
endowments for future generations?
Factors which comprise the discount rate include:
return on investment, risk, and inflation. Arrow and Lind
(1970), in their investigaion on uncertainity and public
investment, conclude that if the net returns (and also the
risk) from a single investment are sufficiently spread among
individuals, such as for a public investment, the cost of
risk-bearing approaches zero. Arrow and Fisher (1974) go on
to state that in a situation where uncertainity about the
occurence of an irreversable adverse environmental
externality resulting from a public investment exists,
social policy should err on the side of refraining from the
adverse activity. Opportunity losses generated by a too
conservative policy can be cut at a later date, but the
reverse is not possible. Randall (1981) takes a more
pessimistic view and claims that public investments are not
risk-free. Randall sees public investment to be about as
risky as the large loans made by banks to favored
corporations and claims the risk premium in the banks' prime
rate is appropriate for public investment.
The policies in this study can cause long-term
environmental damage by contaminating the aquifer. The
opportunity losses suffered by a conservative discount rate
100
are primarily in the form of having fewer alternative water
supplies. To reflect the situation of groundwater being a
high-valued future resource, a low discount rate is favored,
in the region of about 4 percent.
Beyond the Planning Horizon
The planning horizon of this study is 1991-2025. In
the decision rule developed in Equation (16), a terminal
value is identified. The terminal value is affected by how
the groundwater supplies are used in previous time periods,
and by aquifer management policies for the period beyond
2025.
It can be inferred that the future value of the
aquifer is quite high because the policies that strive
toward safe-yield are far-reaching and costly. The aquifer
is a water management tool which will insure Tucson against
drought and serve as a reservior for water supplies imported
in excess of immediate needs. If groundwater quality is
impaired, then its utility as a management tool is lessened.
If, in the future, imported water supplies are
curtailed and groundwater becomes a primary supply,
groundwater quality will be very important. New environmental quality legislation in Arizona initially classifies
all aquifers as drinking water sources. Such a classification highlights the fact that groundwater pollution is
no longer perceived as a costless waste collector.
101
Changes in Consumer Benefits
The benefits to water consumers of alternative
groundwater conservation policies are unchanging if the
prevailing water requirements of the city of Tucson are met.
Consumers may suffer increased costs generated by salinity
from policy actions but it is assumed that benefits are
merely a function of supplied amounts of water. Most
groundwater conservation policies are aimed at augmenting
water supplies with but one exception, reduction-in-use
requirements. To meet the safe-yield goals of the AGMA,
reduction-in-use is employed as a conservation instrument;
this instrument does not generate benefits by increasing
water supply alternatives, Equation (16).
The effect of reduction-in-use policies is a
reduction in consumer surplus. Consumer surplus is the gain
to consumers who would be willing to pay more for their
water but need only pay the market price.
The imposition of the reduction-in-use restrictions
cuts back supplies. Previous to the imposition of the new
policy, consumers enjoyed all the excess benefits generated
by not paying more than the market price for water. When
more restrictive allotments are made by a reduction-in-use
policy, there is a decrement in water benefits under the
new, more restrictive reduction-in-use policy. Estimation of
the change in benefits requires information about the demand
relationship so that the responsiveness of price to quantity
102
can be determined (such information is in the price factor
of demand which is equal to the inverse of the price
elasticity of demand). The value of the loss in benefits is
the area beneath the demand curve and above price between
the old supply amount and the new supply amount.
Summary
User costs generated by increasing salinity in
groundwater are not considered in the determination of
groundwater conservation policy. The result of neglecting
these costs is that the social benefits of conservation
policy have been overvalued by the amount of the discounted
sum of user costs. The chosen policy will generate social
improvement if the marginal user cost generated by P t is
less than the marginal benefits of a conservation policy
that causes an increment in
P.
If marginal user costs
exceed associated marginal benefits, the chosen conservation
policy has a negative impact on social welfare. User costs
should be compared to the conservation or water-supply
benefits of the policy, as determined by the agency or by
the public, to judge whether a given policy results in a net
improvement. Estimates of user costs are developed in the
following chapters. These cost estimates are the periodic
costs generated by salinity in delivered water under various
policy scenarios. Calculating the discounted sum of the
103
costs for each policy allows the evaluation of policies in
terms of costs of degradation of quality.
Those responsible for achieving long-term
groundwater balance are employing water supply policies that
will result in the introduction of large quantities of salts
into the Tucson basin. Since these public officials are not
liable for damages caused by water salinity, they perceive
the damages to be low compared to conservation benefits. At
the optimum, the marginal benefits, in terms of which water
supply policies are implemented, should be balanced against
the marginal costs that include the introduction of salts.
The decision-rule for choosing water conservation
policies with respect to their effect on salinity damage
costs is to equate the marginal benefits associated with
alternative water supplies to the marginal damages generated
by groundwater degradation.
CHAPTER 5
ESTIMATION OF SALINITY DAMAGE COSTS
Groundwater conservation policies in the Tucson
basin can adversely affect the salt concentration of
municipal water supplies causing damages to municipal
water-users. One example of the damages caused to residences is decreased service lifetimes for water-using
appliances. Other potentially adverse impacts include
increased costs of industrial production and toxicity
effects.
In this chapter, a damage function is developed
which links salt concentrations in municipal water to
damages in order to estimate the water quality costs of
groundwater conservation. The function is employed in
Chapter 7 to evaluate various groundwater conservation
policy scenarios.
Defining a Damage Function
Damage
Damage is a loss in welfare and is defined for this
study as a loss to municipal water-users' income generated
by increases in the salinity of water. Salinity in delivered water deposits scale on surfaces which it contacts.
104
105
Scale shortens the usable lifetime of appliances, pipes, and
industrial machinery. Another cost is generated by hardness, one of the constitutents of salinity, which decreases
the cleansing action of soaps and other cleansing agents.
The damage function in this chapter is for singlefamily residences only. This is for two reasons:
(1) the
largest class of water users in the Tucson basin is singlefamily residences (see Table 10), and (2) literature about
municipal salinity damages has focused on water-using
appliances in single-family residences. Estimates of the
relationships between expected service lifetime of household
water-using appliances and TDS concentrations, which are
available in recent literature, the annual incremental cost
per unit of TDS for TDS concentrations above the present
concentration is calculated for the appliances employed in a
representative Tucson household. The resulting function
relates annual increments in household costs to mg/1 of TDS.
For this study, appliances are defined as devices
which render a service when used with water, a definition
which includes washing machines and dishwashers as well as
pipes and soap. The costs to machines and pipes are best
described as accelerated depreciation of capital. Costs
such as increased soap useage are increased operating costs.
Both types of costs are considered in this chapter, for
simplicity, their representations are as annual costs.
106
Annual Costs
In general, the damage (D) to the water using
appliances generated by salinity is calculated by finding
the annual replacement cost without the increment, the
annual replacement cost with the increase in salinity, and
attributing the difference to the increased salinity. This
is a three step process:
1.
Appliance lifetime is a function of TDS
concentration; Li — 1(s)
2.
Annualized cost of salinity damage for a given
concentration of TDS at time t for a water-using
appliance is then;
Ai(s t ) = (r * (1 + r) L / (1 + r)L - 1) * K
3. Incremental cost of damage;
Di(s t ) — [Ai(s t ) - Ai(s0)]
where:
Li
= service lifetime of the (i) the appliance;
t
— time in years;
s
— salinity or TDS concentration;
s t—
so
estimated TDS concentration at time t;
— present TDS concentration, 300 mg/1;
Ai(s t ) — annual capital replacement value or
depreciation value of the (i) the
water-using appliance at for a given s at
time t;
r
= discount rate;
107
K
= replacement cost;
Di
= annual increment in replacement costs for
the (i)th appliance generated by TDS
concentration which differ from the present
concentration s(to).
Literature on Economic Damages of Salinity
Eubanks and d'Arge (1976; 1978) estimated the
economic losses to household water conveyance systems
and
household appliances for different levels of TDS in the
water supplied to households grouped into two study
areas: (1) the Los Angeles basin, and (2) areas in Arizona
and Nevada. For the Los Angeles area, they estimated
regression models which correlate the lifetime of a specific
water-using appliance to TDS concentration and selected
socio-economic variables. In the Arizona and Nevada areas,
which they call the CAP study areas (since the areas receive
Colorado River water), differences in the expected lifetimes
of water-using appliances between areas of differing salinity concentration were tested for statistical significance.
The statistical tests of d'Arge and Eubanks
proceeded in two parts: first, differences in the expected
lifetimes of water-using appliances between areas of
differing salinity concentration were tested for significance; second, regression analysis was used to estimate the
relationship between appliance lifetime, TDS concentration,
108
and socio-economic explanatory variables. In general, TDS
tended to be the most significant predictor of lifetimes.
Of the socio-economic variables, only number of persons per
household was significant. This result may have been due to
difficulties in identifying substantial variation in household characteristics or to an incorrect specification of the
relevant economic variables.
The Los Angeles damage data were based on interview
responses of plumbers and appliance servicemen in areas of
the city which water supplies differ in concentrations of
salts. The survey questions were aimed primarily at obtaining estimated typical lifetimes for various water-using
appliances.
D'Arge and Eubanks found that total damages per
household increased with increasing TDS concentration. The
estimated present value of the losses resulting from and
increase of 500 mg/1 salinity concentration in the water
supply ranged, in 1975 dollars, from $620 to $1,010 per
household under the assumptions of a 60-year planning
horizon and 8 percent discount rate.
In the CAP study area, D'Arge and Eubanks used data,
obtained with the same questionnaires, from 173 plumbing
contractors and 60 appliance dealers to identify appliances
for which the differences in lifetimes related to different
TDS concentrations are significantly different from zero.
Water quality differences were apparent between two groups
109
of urban areas:
(1) Phoenix (SMSA), Boulder City, and
Henderson, Nevada; and (2) Tucson and Las Vegas, Nevada.
The first had an average water quality of 735 mg/1 and the
second 500 mg/1, respectively. Table 19 lists the appliances which demonstrated differences in estimated mean
lifetime between the two areas. Only galvanized water
pipes, water heaters, toilet flushing mechanisms, dishwashers, and garbage disposals displayed significant
differences in lifetimes between the two groups.
Estimated annual damage costs were calculated in a
two step procedure; (1) interview responses of the useful
appliance service life was coorelated to the level of TDS
present in the interview respondent's areas; and (2) appliance replacement costs, given the service lifetimes, were
discounted and summed over the 60-year study period. For
example, water heaters in two areas of differing water
quality are exposed to water with an average salinity of 735
mg/1 and 500 mg/1, respectively, and the water heater
lifetimes associated with these salinity levels are 7.79
years and 9.66 years. There are 7.7 water heater replacements associated with 750 mg/1 salinity and 6.2 water heater
replacements with 500 mg/1 salinity over a 60-year period.
If each replacement cost is $135.00, the present value of
the sum of replacements for the 60-year period, discounted
at 8 percent, is $351.18 and $301.90 for 750 mg/1 and 500
mg/1 salinity, respectively.
110
Table 19. Test for Significantly Different Expected
Lifetimes of Appliances for Two Areas with
Differing TDS Concentrations.
Item
Estimated Mean Lifetime
(Years)
PhoenixBoulder City-
Las VegasHenderson
Tucson
(735 mg/1)
(500 mg/1)
Statistical
Significance
Galvanized
Wastewater Pipes
42.23
40.15
No Difference
Galvanized Water
Pipes
16.39
19.85
Different at 0.05
Water Heater
7.79
9.66
Different at 0.02
Toilet Flushing
Mechanisms
6.18
8.02
Different at 0.10
Brass Faucets
9.48
10.28
No Difference
Clothes Washers
8.69
8.63
No Difference
Dishwashers
7.28
9.01
Different at 0.02
Evaporative Coolers
8.96
7.23
No Difference
Garbage Disposals
6.03
7.58
Different at 0.05
(d'Arge and Eubanks,
1978)
111
Incremental costs of salinity damage per unit of TDS
are calculated as the difference in the present value
between the two areas divided by the difference in their
average salinity concentration. In this example, there is a
$49.28 difference in present value of water heater replacement costs which, when divided by the difference in salinity, 235 mg/1, yields an estimate of $0.21 per mg/1 of TDS.
The $0.21 per mg/1 is the estimated present value of the
costs of salinity damage per mg/1 to one household's water
heater. Representative average single-family residences'
complement of appliances were reported in the 1970 Census of
Housing.
Only a few of the water-using appliances previously
considered important by other research efforts such as Black
and Veatch (1967) and Tihansky (1974) are represented. The
costs of increased bottled water and soap usage were considered significant in the Black and Veatch (1967) and
Tihansky (1974) studies. There are only five appliances
listed as showing service lifetimes significantly affected
by increased salinity in the d'Arge and Eubanks (1978) study
(see Table 20). Since d'Arge and Eubanks (1978) did not
consider increased costs generated by salinity to products
such as bottled water and soap their estimates of total
annual costs are a lower-bound estimate of municipal damage
caused by salinity for the Arizona CAP area.
112
Table 20. Annual Cost per Household per mg/1 TDS and Total
Cost per mg/1 TDS, Central Arizona Project
Service Area (1975 dollars).
Item
Household
Annual
Cost/mg/1
Total
Households
Total
Annual
Cost/mg/1
Thousand
Dollars
Dollars
Galvanized Water
Pipe System
0.0118
245,000
2,891
Toilet Flushing
Mechanisms
0.0064
245,000
1,568
Water Heaters
0.0167
245,000
4,092
Dishwashing
Machines
0.0051
245,000
1,250
Garbage Disposals
0.0058
245,000
1,421
(d'Arge and Eubanks, 1978)
113
The study method used by d'Arge and Eubanks (1978)
is similar to that employed by Tihansky (1974).
Tihansky
(1974) integrated previous research on salinity damages
prepared by Black and Veatch (1967), Metcalf and Eddy
(1972), and the Orange County Water District (1972). He
used the data sets of the previous studies but noted each
had statistical problems due to improperly identified
functions and functional forms. Much of the previous
research directly identified dollar costs as opposed to
appliance lifetimes. The functional forms were often
assumed linear over large ranges of TDS concentrations.
The methods differ in how the cost streams of
appliance damages were calculated over time; Tihansky (1974)
calculated annual damages by employing a capital recovery
factor and presented annual damages, while d'Arge and
Eubanks summed the discounted replacement costs for each
appliance replacement for a 60-year period. D'Arge and
Eubanks (1978) were not concerned with changes in the annual
salt concentration and elected to discount the stream of
costs generated by an unchanging salt concentration in
municipal water supplies. In comparison, if TDS does not
change the methods are equivalent; but if TDS does change,
Tihansky's method, which calculates annual costs, can evaluate easily the fluctuations whereas d'Arge and Eubanks'
method is cumbersome for such changes.
114
The city of Tucson contracted a study of treatment
alternatives for CAP water (Montgomery-Johnson-Brittain,
1983). The study report discussed the nature of the costs
incurred for: bottled water, household softeners, soaps and
cleaning agents, water heaters, pipe failure, swimming pool
operation, landscape, waste disposal, and under-the-sink
purification.
Few salinity damage estimates were calculated. The
cost computation of salinity damage in the city of Tucson
report used results provided by Patterson and Banker
(1968).
The method and data for annualizing the costs were
not explicit in the Montgomery-Johnson-Brittain (1983)
report; the reported annual increment to water heater
replacement cost generated by salinity damage was one
dollar. The overall Montgomery-Johnson-Brittain (1983)
report suffered from lack of consistency in computation, no
reporting of the data or assumptions underlying the results,
and inadequate background research in the area of salinity
damages to municipal water users.
The costs estimates by Montgomery-Johnson-Brittain
(1983), included only the costs of water heater replacement
and soap and cleaning products as significant. Bottled
water and water softeners were considered to be voluntary
costs and were excluded from consideration. The reported
decrease in water heater lifetime for an increase in TDS
concentration of approximately 200 mg/1 was one year.
115
However, using the Patterson and Banker (1968) method and
recalculating the lifetime, the estimated decrease in water
heater lifetime is approximately 1.65 years.
In comparison,
the d'Arge and Eubanks' (1978) regression estimate yields a
2.25 year decrease in water heater lifetime for a 200 mg/1
increase in TDS concentration. The Patterson and Banker
(1968) data were used for the Montgomery-Johnson-Brittain
(1983) estimate.
In their report, Patterson and Banker
(1968) warned, "the results...should be looked upon as an
initial investigation, certainly subject to more complete
survey investigation and analysis."
The basic research from which Montgomery-Johnson
Brittain (1983) developed the costs of expenditures on soap
and cleaning products as a function of salinity is from
DeBoer and Larson (1961) and was well calculated and
presented. Although the study by DeBoer and Larson (1961)
is dated, there has been little thorough effort to estimate
the costs of degradation of products with short lifetimes
such as soap.
In summary, the literature on damages to the
municipal water consumer generated by salinity shows that
methods to measure the damages have evolved, as have the
approaches to data gathering and to experimental design.
For instance, Tihansky (1974) and d'Arge and Eubanks (1978)
agree that statistically reliable data, can gathered from
plumbing contractors and appliance dealers rather than from
116
water users. The former have a wider field of experience
with lifetimes and frequency of repair for many household
water appliances than do consumers.
D'Arge and Eubanks (1978) note that the earlier
efforts neglected to quantify the relationships of other
explanatory variables such as: income levels, number of
persons per unit, age of housing and so on. Given the weak
regression relationships in Table 19, other variables may
play a large role in developing willingness-to-pay relationships to estimate the demand for high quality, low TDS
water.
Lastly, variations in water quality over time are
not adequately dealt with. D'Arge and Eubanks (1978) note
that time is excluded in earlier research but fail to calculate directly the impacts of future changes in salinity
concentrations in the CAP service area. The water quality
of the CAP is expected to vary over time and the impacts
will vary with it. The damages are a function of unidentified stochastic processes; however, they can be estimated
for various projections and scenarios. Also, the population
served will increase over time, increasing the total
impacts. Further, salinity introduced into the hydrologic
system through CAP water will eventually be recycled to the
groundwater resource, inflicting additional rounds of damage
as it is repumped.
117
Salinity Damaze Function for Tucson
Estimates of costs of salinity damage to household
water-using appliances generated by groundwater conservation
policies are developed in two stages. First, estimators of
appliance lifetime were chosen from existing research, and
second, a damage function relating annual costs of appliance
depreciation to various levels of TDS concentration is
developed.
Estimators of Appliance Lifetime
The research by d'Arge and Eubanks (1978) is considered to best represent the Tucson situation. The reasons
for this choice are: Tucson will use Colorado River water
for municipal water supplies and the estimators of appliance
lifetime are the most recent. The presentation of d'Arge
and Eubanks' (1978) regression equations is clear and complete, allowing their estimators to be evaluated systematically. The regression equations for appliance lifetimes
are given in Table 21.
The appliances chosen for use in this study were
galvanized wastewater pipe, galvanized water pipe, water
heaters, toilet flushing mechanisms, dishwashers, and
garbage disposals. These appliances were chosen because of
their statistical significance (see Tables 19 and 20).
Soap consumption was also chosen as important, based on the
results of DeBoer and Larson (1961).
118
Table 21. Regression estimates for length of average
lifetime and salinity.
Water Heaters:
ln L=5.43771-0.42435(ln TDS)-0.99322(ln #PERS/UNIT)
(4.967) a,b(3.925)b
+ 0.36828 (DUMMY)
(2.406) b
F = 13.34 b
R 2 - 0.60
Galvanized Wastewater Pipes:
ln L-7.42425-0.79571(ln TDS)+1.05941 (DUMMY)
(4.227) b(3.248)b
F = 11.23 b
R 2 - 0.51
Galvanized Water Pipes:
L
16.56015 - 0.00666 (TDS) - 3.78336 (DUMMY)
(1.584)
(1.883)
F
R 2 - 0.23
Brass Faucets:
ln L - 6.35863 - 0.69277 (ln TDS) + 1.28617 (DUMMY)
(1.351)
(1.420)
F - 1.4
R 2 - 0.15
Dishwashers:
ln L - 4.05324 - 0.34538 (ln TDS) + 0.42955 (DUMMY)
(3.175) b(1.870)
F
5.18c
R 2 = 0.30
Washers:
L - 9.62161 - 0.00360 (TDS) + 1.45762 (DUMMY)
(1.933)
(1.305)
F - 2.07
R 2 - 0.15
118
Table 21. Regression estimates for length of average
lifetime and salinity.
Water Heaters:
ln L-5.43771-0.42435(ln TDS)-0.99322(ln #PERS/UNIT)
(4.967) a,b(3.925)b
+ 0.36828 (DUMMY)
(2.406) b
F - 13.34 b
R 2 - 0.60
Galvanized Wastewater Pipes:
ln L=7.42425-0.79571(ln TDS)+1.05941 (DUMMY)
(4.227) b(3.248)b
F = 11.23 b
R 2 = 0.51
Galvanized Water Pipes:
L - 16.56015 - 0.00666 (TDS) - 3.78336 (DUMMY)
(1.883)
(1.584)
F = 3.94 c
R 2 - 0.23
Brass Faucets:
ln L - 6.35863 - 0.69277 (ln TDS) + 1.28617 (DUMMY)
(1.420)
(1.351)
F - 1.4
R 2 - 0.15
Dishwashers:
ln L - 4.05324 - 0.34538 (ln TDS) + 0.42955 (DUMMY)
(3•175) b(1.870)
F - 5.18 c
R 2 = 0.30
Washers:
L - 9.62161 - 0.00360 (TDS) + 1.45762 (DUMMY)
(1.305)
(1.933)
F - 2.07
R 2 = 0.15
119
Table 21--Continued
Garbage Disposals:
ln L — 2.82352 - 0.13076 (ln TDS) + 0.03794 (ln DUMMY)
(0.145)
(1.013)
F — 0.55
R 2 — 0.05
a.
The values in parentheses are T-Statistics.
b.
Denotes statistically different from zero at the 99%
level of a 1-tailed test.
c. Denotes statistically different from zero at the 95%
level of a 1-tailed test.
(d'Arge and Eubanks, 1978)
120
Appliances which are not evaluated here but which
may experience increased replacement and operating costs are
faucets, evaporative coolers, clothes washers, bottled
water, water softeners, and swimming pools.
The calculated lifetimes of the appliances with
respect to various TDS concentrations are shown in Figures
4, 5, and 6.
Annualized Costs
The annual capital recovery cost of a water-using
appliance is based on its replacement cost, service lifetime, and assumed discount rate. The replacement costs for
water-using appliances are listed in Table 22. The replacement costs were developed by inflating the d'Arge and
Eubanks (1978) estimates of appliance replacement costs to
1986 dollars and reviewing them with local area plumbing
contractors. The contractors emphasized that these are
replacement costs and not new installation costs; new
installation is less expensive. The replacement costs are
multiplied by the capital recovery factor to calculate the
annualized capital recovery cost. The capital recovery
factor amortizes a fixed investment with a known service
lifetime into annual payments for a given interest rate.
The annualized replacement cost is calculated as follows:
Rf — Ri *
(
r * (1 + r) L / (1 + r)L - 1)
121
122
••n
nn••
Iwo
—
o
CTS
a
re)
srea
123
CO
CO
In
124
Table 22. Replacement Costs for Various Water-Using
Appliances
Item
Cost
Dollars
Water Heater
200
Galvanized Water Pipe
1600
Galvanized Wastewater Pipe
1200
Dishwasher
500
Garbage Disposal
125
Toilet Flushing Mechanism
50
125
where:
Rf
— annual capital recovery cost;
Ri
= replacement cost;
r
= discount rate;
L
= is the estimated lifetime of the appliance.
To calculate the increment to annual costs of
increased salinity concentrations, the annualized capital
replacement costs of TDS concentrations above 300 mg/1 and
the costs of the present TDS concentration are subtracted.
Table 23 is a schedule of the cumulative additions to annual
costs of salinity damage for increases in TDS above 300
mg/l.
Cost Per Household
The annualized capital recovery costs, Table 23,
were weighted by the average complement of appliances
expected to be found in a Tucson household. The weighting
factors, presented in Table 24, are from the 1970 Census of
Housing. Because plumbing contractors interviewed informally for this study claimed that current construction uses
more poly-vinyl-chloride and copper pipe than galvanized
pipe, the census figures for pipe were adjusted downward by
approximately 30 percent. The remaining appliances are as
listed in the census.
Total household costs for a single-family residence
are calculated by multiplying the appliance costs found in
126
Table 23. Cumulative Annual Capital Recovery Costs for TDS
Concentrations Beyond 300 mg/l.
Salinity
Water
Heater
Galvanized Water
Wastewater
Pipe
Pipe
mg/1
Dollars
Dishwasher
300
0.00
0.00
0.00
0.00
400
4.12
3.71
13.17
4.60
500
7.70
7.86
28.03
8.50
600
10.87
12.46
39.02
11.95
700
13.78
17.63
51.57
15.05
800
16.45
23.43
63.89
17.85
900
18.93
30.06
75.94
20.45
1000
21.27
37.60
87.80
22.90
1100
23.48
46.29
99.46
25.15
1200
25.57
56.37
110.94
27.30
127
Table 23.--Continued.
Salinity
Garbage Disposal
mg/1
Toilet
Soap and
Flushing
Cleansing Agents
Mechanism (Operating Costs)
Dollars
300
0.00
0.00
0.00
400
0.44
0.78
1.24
500
0.79
1.57
2.48
600
1.08
2.35
3.72
700
1.33
3.13
4.96
800
1.56
3.91
6.20
900
1.75
4.70
7.44
1000
1.95
5.48
8.68
1100
2.11
6.26
9.92
1200
2.26
7.05
11.16
128
Table 23 by the representative complement of appliances in
Table 24. The results are graphically shown in Figure 7.
The function which represents the cost to TDS relationship
for annual damage beyond 300 mg/1, i.e. represents the costs
in excess of the present Tucson well water, is of the form:
Annual Cost per Household — 0.12424*(TDS) - 35.9021
This relationship that can be used to estimate the
annualized damage cost per single-family household at
various levels of TDS concentration.
Summary
Estimates of the costs of salinity damage were
developed from estimates of the effects of salinity on the
service lifetime of water-using appliances available in the
literature. Annualized costs were calculated as the annualized difference in capital replacement cost associated with
the difference in specified service lifetimes of water-using
appliances. Damage costs for each appliance were aggregated
into household complements of water-using appliances representative of the number of water-using appliances expected
to be found in Tucson single-family residences.
The method employed to determine salinity damages
was similar to the research of d'Arge and Eubanks (1978)
except for the calculation of annualized costs. Annualized
129
Table 24. Average Number of Water-Using Appliances in
Households in the Tucson Area.
Average Number of
Items Per Household
Water Heater
0.99
Galvanized Water Pipe
0.35
Galvanized Wastewater Pipe
0.35
Dishwashers
0.20
Garbage Disposals
0.61
Toilet Flushing Mechanisms
1.60
130
I
a)
61)
N-4
C/)
CL)
0..
co
co
o
L)
a)
to
.0
ca
E
,—i
-.,
to
IA
p-,
4..)
-,-1
›
.1
•IJ
1.
.
CO
cn
co
al
0
.H
TI
4
aj
O
•r-I
,--1
V)
.
r-I W
fli C-1
0 0
O a)
O "0
.4
•r-4
(f)
"Cl (1)
a) r4
4.)
al
E ,.-1
•ri .1-1
CO RS
rx.1 rx-t
0
0
1
1
1
1
1
1
1
1
1I
1
1
1
101
O a 0 0 0 0 0 0 0 0 0 0 0 0 0
4. tn. Cs1 ..— 0 OS CO l's (.0 WI •4- r) Csi ...
1
d
In
—
-
siuTT0CE
131
costs in this study were estimated as capital recovery
costs.
CHAPTER 6
THE MUNICIPAL WATER-SALINITY CYCLE
Concentrations of conservative contaminants such as
salinity will increase in groundwater as water cycles
through successive uses. Water evaporates during municipal
use, wastewater treatment processes, and irrigation, leaving
less water to carry the same salt load. Dilution with
groundwater and drainage out of the aquifer would serve to
mitigate the effects of the additional load. However,
current groundwater conservation policies which substitute
large volumes of saline Colorado River water and recycled
wastewater for high quality groundwater may overload the
drainage capacity of the natural system. A municipal
water-salinity cycle for the Tucson basin is described in
this chapter. Focus is on the components of the hydrologic
system which may increase the salinity of water in the
aquifer.
The following discussion identifies the hydraulic
manipulations of the municipal water cycle that affect
salinity concentration (see Figure 8). The cycle begins
with source development such as groundwater pumpage. The
water is put to use, causing salt concentrations to increase
132
133
r
EVAPORATION
1P\\ SALT "'
NATURAL
RECHARGE
AND CAP
INCIDENTIAL
RECHARGE
Figure 8. liunicipal Water-Salinity Cycle.
EVAPORATION
134
or remain the same (SALT' ^ SALT). In use, water that is
not evaporated infiltrates and is called incidental
recharge. While water is lost to evaporation in use, the
salts are not, in this way salt concentrates. In a single
cycle, water salinity increases because of evaporation, i.e.
SALT' SALT" SALT'" SALT '"'.
Groundwater degradation occurs as some of the
infiltrated water passes through the soil as deep
percolation and eventually becomes aquifer recharge. The
below-ground cycle includes aquifer recharge, dilution, and
recapture or outflow. The result is a recycling of the
salts leading to higher concentrations in the aquifer. The
only mitigating agent is aquifer outflow.
Groundwater conservation as seen by DWR mitigates
water quality degradation by stabilizing the level of the
groundwater table, since deep groundwater has a higher
concentration of salts (TAMA, 1984). But the importation of
highly saline Colorado River water via the CAP, the reuse of
wastewater, and artificial recharge all have a potential to
increase the concentration of salts in the aquifer. There
is a compounding effect in this cycle of concentration which
has not been studied to date. Thus, progressive degradation
may at least partially offset the benefits of reaching the
perpetual-yield goal for groundwater.
135
The compounding effect of the salinity cycle is
illustrated in Table 25. In this example, the initial
salinity of the aquifer is assumed to be uniform at 300
mg/l. A one percent annual pick-up rate results in the
salinity concentration increasing to 303.00 mg/1 in the
first year, to 306.03 mg/1 in the second year, to 309.09
mg/1 in the third year, and so on.
This example illustrates how rapidly degradation can
occur. Under the existing hydrological regime, the Tucson
basin has not experienced much salinity degradation; the
annual salinity pick-up rate is speculated to be less than
one-half of one percent. No estimates of groundwater
salinity over time are available. The present low salinity
pick-up rate is due to the high quality of the groundwater
and the fact that past use/recharge activities in the basin
were small relative to the use/recharge being planned. With
the advent of imported Colorado River water, and the salt it
carries, into the basin the slow pace of the present
salinity cycle will be accelerated.
Institutional Constraints Affecting
the Salinity Cycle
The Tucson basin has experienced serious overdraft
and there are mistaken perceptions of imminent groundwater
shortages. The 1980 Arizona Groundwater Management Act
(AGMA) mandates controls on groundwater used in each of the
three major water-use sectors: agriculture, municipal, and
136
Table 25. Degradation Cycle Time for Groundwater with an
Initial TDS of 300 mg/1 to Reach Final TDS for
Given Annual Salinity Pick-up Rates.
Annual Salinity Pick-up
Rate in the Aquifer
Final
TDS
.50%
mg/1
500
600
700
800
900
1000
1.00%
2.00%
Number of Years
102
139
170
197
220
241
51
70
85
99
110
121
26
35
43
50
55
61
3.00%
4.00%
17
23
29
33
37
41
13
18
22
25
28
31
Note: Percolation time for recharge is not included in these
estimates.
137
industry. These are reduction-in-use programs. As a
political concession, the AGMA also provides controls on the
expansion of the well fields of water providers to placate
agricultural concerns that the water table would be lowered
by expanding municipalities. Other provisions of the AGMA
encourage supply augmentation by providing incentives to
import CAP water and reuse wastewater.
Reductions. Reduction-in-use requirements directly
reduce water use by consumers. The requirements affect
water quality if the water saved through reduction is
replaced by imported water or wastewater reuse of lower
quality. However, CAP contracts and wastewater reuse plans
do not reflect the potential for tradeoffs between
groundwater conservation achieved by reduction-in-use
programs and that achieved by supply augmentation.
Institutional sanctions which prevent this tradeoff may also
prevent high-quality water from being used before
low-quality water.
Service Area Restrictions. As municipal use rises
absolutely, a geographical redistribution of pumpage and
recharge will occur due to restrictions on location of
municipal wells. The expansion of municipal well fields is
constrained by the service area requirements of the AGMA
which limit the area from which a municipal provider may
pump. As the water table in specific locales falls,
municipal wells are lowered into deeper saturated zones
138
which yield water of poorer quality. In addition, the
restrictions on well field locations in the service area
forces wells to locate close to recharge sites, reducing the
potential for dilution. More salinity will be picked up if
the salinity of recharge is greater than the salinity of
native groundwater. Expansion of wellfields would decrease
the salinity of recharge water by decreasing the mean
salinity of initial water use.
Incentives to Reuse Wastewater. The First
Management Plan of the ADWR/Tucson AMA assumes all
wastewater produced after 1990 will be reused (TAMA, 1984).
As discussed in Chapter 2, wastewater has become an
especially valuable water source since a recent court ruling
released it from the restrictions of the AGMA. However,
with large-scale use of saline effluent the amount of salts
going into recharge is greater and results in accelerated
aquifer degradation.
Imported Water. The CAP is contracted to bring an
average of 100 thousand acre-feet of Colorado River water
per year into the Tucson basin and each acre-foot contains
almost a ton of salts. Criticisms of the CAP, such as its
enormous expense (over 2 billion dollars) and the shift from
an agriculturally based project to a municipally based
project, have not impeded its construction. Contracting for
CAP water can satisfy the requirements for an "assured water
supply" which are required for many types of new urban
139
development under the AGMA, thus it is very attractive. CAP
salinity problems are discounted for political reasons but
are main the disturbance to the salinity balance.
Previous Estimates of Salinity Degradation
in the Tucson Basin
The Bureau of Reclamation (1984) estimated the
expected increase in TDS concentration in the Tucson basin
due to the CAP at 51 mg/1 over the first 50 years of
operation. Their estimate is based on several assumptions:
(1) there will be complete three-dimensional mixing of the
recharge waters with all waters in the aquifer; (2) the
overall recharge, natural and incidental, of withdrawn water
is constant and equal to 32 percent of the basin water
budget; (3) the amount of groundwater drainage leaving the
basin is constant; and (4) the initial quality of
groundwater and recharge throughout the aquifer is uniform.
These assumptions lead to an underestimation of the
salinity increases that can be expected in the aquifer.
Complete mixing of the aquifer is not taking place; indeed,
water quality in the aquifer is known to be stratified.
Because there are differentiated alluvia in the aquifer,
generalizing the characteristics of storativity, vertical
and horizontal transmissivity, recharge, and discharge
misrepresents the way in which the aquifer system operates.
The movement of groundwater is slow. Further, the effects
of decreased aquifer drainage, which occur as the water
140
table is drawn down, were not included in the estimate nor
were the effects of wastewater reuse and salinity pick-up.
CH2M Hill/Rubel and Hager (1983) estimated that
reuse combined with the salinity imported in the CAP water
will increase the salinity in the Tucson basin aquifer by
about 60 mg/1 per decade, substantially higher than the
Bureau of Reclamation's estimate (1984). They recognized
the effect of highly saline wastewater recharge but did not
project the compounding property of continual reuse of the
same groundwater.
In summary, both the Bureau of Reclamation and the
CH2M Hill/Rubel and Hager studies failed to fully recognize
the adverse water quality effects of groundwater conservation policies. The Bureau did not recognize the potential
for degradation due to wastewater reuse and both studies
ignored well known characteristics of the Tucson aquifer
system. Compounding of the salinity was not included in
either study.
Projecting the Rate of Salinity Degradation
The first step in the recharge of water used on the
surface is percolation through the soils of the vadose
zone. Salinity can be attenuated in soil through the
processes of dispersion, ion exchange, and precipitation
into solids. However, these attenuation processes are
rapidly exhausted in areas where frequent, heavy irrigation
141
is practiced, such as in municipal landscape and turf
industries. At best, the degree of attenuation is small
since not all salinity compounds are affected; in fact, the
process of ion exchange does not effect change in the mass
of salts at all--it only alters the chemical make-up. With
continual saturation, the attenuation would last only a
short while, perhaps a year or two. It is assumed in this
analysis that the salinity carried into the semi-saturated
vadose zone will pass through to the aquifer with no
significant attenuation. The mass balance approach is
appropriate for large area analyses such as this one. To
project impacts for a specific locale, however, a more
in-depth analytical method would be necessary.
Because salinity is a conservative contaminant, the
dominant mitigating process with respect to the salinity
concentration of the aquifer is dilution--the blending of
incidental recharge with natural recharge and native groundwater. Todd and McNulty (1976) specified that groundwater
dilution is determined by:
1.
The concentration and mass emission of pollutants in
the water table.
2.
Quality of native groundwater in a three dimensional
sense.
3. Aquifer hydraulic properties, including
transmissivity, vertical hydraulic head gradients,
and vertical hydraulic conductivity.
142
4.
Quantity and quality of recharge from other sources.
5.
Well construction and local pumping patterns.
Projections of the potential for degradation are
based on Todd and McNulty's (1976) dilution principles. The
dilution effects listed by Todd and McNulty are examined
below.
Concentration and Mass Emission of Salinity. While
salinity is usually expressed as mg/1 of total dissolved
solids (TDS), for large volumes it can be expressed in
pounds of salts per acre-foot. A one mg/1 concentration
means there are about 2.72 pounds of salt per acre-foot of
water. Table 26 gives the concentrations and the weight per
acre-foot of various water supplies for the city of Tucson.
The striking differences between the salt content of various
water sources are evident in this table. The accumulated
total of CAP water from the first delivery to the year 2035
(estimated to be about 5 million acre-feet) will bring
slightly less than 5 million tons of salts into the Tucson
basin (Bureau of Reclamation, 1984). While some of the salt
will leave the Tucson basin via underflow in the Santa Cruz
River, much of it will recharge the aquifer and subsequently
will be recaptured by wells.
Quality of Native Groundwater. The groundwater of
the Tucson basin is quite good in the upper regions of the
aquifer, it has less than 500 mg/1 of TDS and is of moderate
143
Table 26. Comparison of Salt Concentrations of Various
Water Supplies in Tucson, Arizona.
Water Supply
Salt Supply Concentration
mg/1
Pounds Per
acre-foot
Tucson Municipal
Water
298
811
Present
Wastewater
540
1,469
Central Arizona
Project
760
2,067
Projected Wastewater
with CAP and GroundWater Blend
870
2,366
(Bureau of Reclamation, 1984; CH2M Hill/ Rubel and Hager,
1983)
144
hardness (Laney,1972). The water served to TWD customers is
around 300 mg/1 of TDS (Montgomery-Johnson-Brittain, 1983).
At depths beyond 1000 feet the groundwater is more highly
mineralized, although not as hard as in the upper levels;
potability is limited because fluoride concentrations exceed
the drinking water standard of 1 mg/1 with a range of 1 to
11 mg/1 (Laney, 1972). As the groundwater table falls,
Tucson can expect to pump lower quality water in the future.
Aquifer Hydraulic Properties. Withdrawing water
changes the physical operating properties of the aquifer.
As water levels decline due to continued pumping, some
effects of partial hydraulic boundaries such as increased
vertical flow become more pronounced. A partial hydraulic
boundary occurs when there exists a strata of less permeable
aquifer materials below the pumping region, creating an
increase in vertical flow from above. Recharged water is
drawn into the well in greater amounts and the dilution with
aquifer storage water is lessened.
A pumping well significantly increases the gradient
of the piezometric surface of the aquifer at the point of
extraction (the phenomenon of drawdown); the gradient
gradually decreases as distance from the point of extraction
increases. The effect of many wells in a well field greatly
alters the groundwater gradient over a large area. Before
intensive pumping began, water levels conformed to the land
surface. Now, after more than 40 years of pumping, water
145
levels exhibit large-scale depressions. The depth to water
varies from less than 50 feet below stream channels to over
500 feet at the margins of the basins (Babcock and Hix,
1982). The depth to water below the Tucson area is between
150 feet and 300 feet.
Areas in the aquifer that have gradients steeper
than the static water level can recapture recharge water
arriving from the surface before it has effectively mixed
with the other waters in the aquifer. Recapture before
adequate mixing was noticed by the Pima Association of
Governments in their study of the Green Valley area where
the water within 200 feet of the surface and two miles down
gradient of the incidental recharge site of the wastewater
treatment plant was found to be high in salinity (FAG,
1985).
The Tucson Water Department's demonstration recharge
project in the Tucson basin is designed to recapture
recharge. The department is counting on the limited mixing
between hydrogeologic levels and the phenomenon of gradient
changes due to drawdown from pumpage described above to
achieve the recapture of a high percentage of recharge water
(Randall and Johnson, 1985). Here the effects of dilution
with groundwater are kept to a minimum by taking advantage
of hydraulic properties which limit mixing. This is
precisely the phenomenon that takes place unintentionally
when pumping and recharge are confined to a service area.
146
When the objective is to recapture water with potential
contaminants, low mixing potential is a positive attribute;
if the objective is to dilute the contaminants with
better-quality native water, low mixing potential is a
negative attribute.
Hydrologic variations in the aquifer are apparent in
the CH2M Hill/Rubel and Hager (1983) Wastewater Reuse Report
for the city of Tucson which identified 10 subareas around
the city which are prime candidates for wastewater
irrigation. The aquifer's hydrologic characteristics for
specific areas are given in Table 27.
The transmissivity of the aquifer varies from 10,000
to 180,000 gallons per day per foot; it is a function of
both the hydraulic conductivity and the local thickness of
the aquifer. The hydraulic gradient of the aquifer is very
low in subareas 5E and 6E, which lowers the total potential
underflow to just slightly over 1000 acre-feet per year
across more than four miles of aquifer flow.
CH2M Hill/Rubel and Hager's analysis of the salinity
loading impacts on areas of the aquifer one mile directly
down gradient of the proposed wastewater reuse sites is
presented in Table 28. The assumptions underlying the estimates shown in this table are that the recharge irrigation
water percolates straight down 500 feet into the aquifer and
mixes with the aquifer evenly for one horizontal mile.
These assumptions are unrealistic because mixing is actually
147
Table 27. Hydrologic Characteristics of Proposed Reclaimed
Wastewater Irrigation Sites in the City of
Tucson. Arizona.
Irrigated Applied TransmisSubareas a Waterb
sivityc
lE
2E
3E
4E
5E
6E
1S
2S
3S
2N
Total
Average
Potential
Total
Hydraulic Site
f
Width
e
Underflow
Gradient d
ft/mile
ac-ft
gpd/ft
1,165
395
2,096
1,585
1,230
2,167
2,068
290
1,135
3,807
75,000
100,000
10,000
10,000
50,000
50,000
50,000
180,000
140,000
50,000
0.0041
0.0026
0.0190
0.0190
0.0009
0.0009
0.0027
0.0018
0.0095
0.0110
60,664
0.0090
15,938
ft
ac-ft/yr
13,000
10,000
26,000
13,000
6,000
16,000
6,000
8,000
10,000
5,000
4,478
2,912
5,533
2,767
289
771
907
2,903
14,898
3,080
113,000
38,539
a.
Adapted from CH2M Hill/Rubel and Hager, 1983.
b.
Irrigation requirements are 5.5 ac-ft/ac (Rubel and
Hager, 1983).
c.
Anderson, 1972.
d.
Tucson Water, 1982.
e.
Width of site across direction of groundwater movement.
f.
Underflow calculated as a function of transmissivity,
gradient, and width. It is only the calculated
potential as it does not account for local disruptions
to the system such as pumpage.
148
Table 28. Estimated Salinity Concentration One Mile
Down-gradient of Proposed Wastewater Reuse
Sites . a
Total
Irrigated
Subareas bUnderflow
ac-ft/yr
lE
2E
3E
4E
5E
6E
1S
2S
3S
2N
Total:
Average:
a.
Recharge from
Irrigation
Water c
ac-ft/yr
4,478
2,912
5,533
2,767
289
771
907
2,903
14,898
3,080
233
79
419
317
246
433
414
58
227
761
38,539
3,188
Aquifer
Volumed
Average
Salinity
ac-ft
mg/1
157,565
121,204
315,130
157,565
72,722
193,926
72,722
96,963
121,204
60,602
306
303
305
308
314
309
323
302
307
348
1,369,604
310
Initial TDS concentration of the aquifer is assumed to
be 300 mg/l.
b. CH2M Hill/Rubel and Hager, 1983.
c. Irrigation application efficiency is assumed to be 80%
and the TDS of the reclaimed wastewater is 871 CH2M
Hill/Rubel and Hager, 1983.
d. Assumed mixing region is the upper 500 feet of the
aquifer and the average aquifer porosity is 20%.
149
uneven vertically and horizontally, but they serve to
illustrate the effects of hydrological characteristics and
the potential for very high salinity areas such as 1S and
2N. If well fields are placed in these areas they will
contribute greatly to the salinity pick-up of the cycle.
Quantity and Quality of Recharge from Other Sources.
Estimates of natural and incidental recharge in the Tucson
basin abound. The estimated total annual inflow and return
flow for the Tucson Active Management Area are 130,000 and
92,000 acre-feet, respectively (TAMA, 1984).
The mean
annual recharge in the Tucson basin, which is a portion of
the Tucson Active Management Area, is estimated to be
100,000 acre-feet per year with a range of 70,000 to 150,000
(Anderson, 1972; Davidson, 1973).
Davidson (1973) identified the major sources of
natural recharge as mountain fronts and streamflow, which
occur in a limited area of the basin. Streamflow
infiltration for the Tucson basin has been estimated to
range from 2.5 to 11.0 feet/day in the channel beds.
Streamflow infiltration is highly variable due to temporal
and spatial variability of flow and channel characteristics
(Wilson, DeCook, and Neuman, 1980). Because the recharge
within the Tucson basin is not spatially homogeneous,
dilution of incidental recharge with natural recharge cannot
be expected if their locations are not in proximity.
150
Incidental recharge occurs from irrigation water
applied in excess of the consumptive use of the vegetation
being irrigated and from releases of wastewater into the
stream channels. The major irrigation activities in the
Tucson basin can be divided into two categories: (1) crop
production for food and fiber, and (2) turf and landscape.
Under the AGMA, crop-irrigation can only take place on
certified water-duty acres; there were 3,403 water-duty
acres verified by the DWR as being in production in
agricultural planning region 4, Eastern Pima County (Tinney,
1985). The amount of recharge from local agricultural
irrigation is presently about 4,000 acre-feet, assuming an
irrigation efficiency of 75 percent. This amount will
decrease as future groundwater management restrictions
require higher irrigation efficiencies. The estimated
concentration of TDS in irrigation recharge is about 1,200
mg/1 presently (assuming the salt concentration of the water
is 300 mg/1 and the irrigation efficiency is 75 percent) and
will increase as irrigation efficiencies increase. However,
no new land can be brought into crop-irrigation, the
incidental recharge from this activity will decrease over
time.
Recharge from municipal landscape irrigation
activities can be broken into two subcategories by
source: potable water and wastewater. The amount of potable
water presently used for landscape irrigation is about
151
18,500 acre-feet per year (CH2M Hill/Rubel and Hager, 1983)
and the return flow which recharges the aquifer is about
3,700 acre-feet per year. The present TDS concentration of
the return flow is about 1,500 mg/1, assuming the salinity
of the applied water is 300 mg/1 and the irrigation
efficiency is 80 percent. The CH2M Hill/Rubel and Hager
report (1983) recommends the irrigation of all projected
increases in municipal landscape with reclaimed wastewater;
the projected landscape area in the year 2000 is 5,040 acres
and the irrigation water use is 28,000 acre-feet. The same
report projects the TDS concentration of the wastewater to
be 871 mg/l. The amount of recharge from municipal
irrigation can be estimated to be 4,500 acre-feet in that
year with a TDS concentration of 4,355 mg/l. The increase
in salts in municipal irrigation recharge caused by changing
irrigation sources from well water to CAP water is 8,582
pounds per acre-foot and the total annual mass of salt in
the recharge for all irrigated acreage projected in the year
2000 is 21,626 tons. This estimate is based on an assumed
80 percent irrigation efficiency with an annual consumptive
use of bermuda grass of 3.5 acre-feet per acre per year and
an Active Management Area allocation of 4.4 acre-feet per
acre per year (TAMA, 1984).
Waste disposal activities are another source of
recharge. Almost 50,000 acre-feet of wastewater are
discharged into the Santa Cruz River from the local
152
treatment plants; estimates of the percentage of this
discharge which enters the aquifer range from 80 percent
(Wilson, 1983) to 40 percent (Travers and Mock, 1984). The
TDS concentration of the recharge water is not readily
available because the effects of evaporation on the water
have not been quantified. However, the expected TDS of
wastewater in Tucson, projected to be 871 mg/1 (CH2M
Hill/Rubel and Hager, 1984), would be a lower-bound estimate
of the concentration.
The amounts of incidental recharge from various
sources are listed in Table 29. The estimated TDS
concentration of the recharge for each source varies over
time with quantity and quality of CAP water (see Figure 1).
The salinity of irrigation recharge is a function of the
source water and the irrigation efficiency. For example, if
the wastewater to be reused for municipal irrigation has a
TDS concentration of 871 mg/1, the recharge would carry a
concentration of 4,355 mg/1; whereas irrigation recharge
from well water with an initial TDS concentration of 300
mg/1 would carry a concentration of 1,200 mg/1 into the
aquifer, assuming both are applied at 80 percent irrigation
efficiency. The relationship between irrigation efficiency
and amount of recharge is shown as:
QR — QI ' (1 - E I )
153
Table 29. Estimated Incidental Recharge Amounts for
Selected Sources in the Tucson Area.
Year
Local
Municipal
Irrigationa
River
Releases
Agricultural of Treated
Irrigation bWastewater'
ac ft
Total
Incidental
Recharge
1991
3,856
4,033
8,069
15,957
1995
4,158
4,033
11,071
19,262
2000
4,536
3,226
15,086
22,848
2005
4,950
3,226
19,346
27,522
2010
5,364
3,226
24,250
32,840
2015
5,778
3,226
28,617
37,621
2020
6,192
3,226
32,985
42,403
2025
6,584
3,226
37,398
47,208
a Only municipal irrigation using reclaimed wastewater
(CH2M Hill/Rubel and Hager, 1983). The assumed
irrigation efficiency is 80%.
b There are 3403 acres of Irrigation Grandfathered Rights
in the Tucson area. The average water duty is 4.74
acre-feet per acre. The assumed irrigation efficiency
is 70% until the year 2000 and 80% thereafter.
c River releases of treated wastewater are assumed to
recharge at 50% of the amount discharged from the
treatment plant. Estimates of the amount of treated
water are from CH2M Hill/Rubel and Hager, 1983.
Estimates of wastewater recharge vary from 80% (Wilson,
1983) to 40% (Travers and Mock, 1984).
154
where:
QR - Amount of Recharge
QI - Amount of Irrigation Water
EI = Irrigation Efficiency
The relationship between irrigation efficiency and salinity
of recharge is shown as:
S R = S I • (1 - EI)
where:
SR - Salinity of recharge
SI - Salinity of Irrigation Water
EI
Irrigation Efficiency
Flow-weighted estimates of the TDS concentration of
the first year incidental recharge from municipal landscape
irrigation, local agricultural irrigation, and releases of
wastewater into the Santa Cruz River are presented in Table
30 with estimated final TDS concentrations resulting from
dilution with various volumes of groundwater. The formula
for a flow-weighted average is:
(s1*Q1) +
+ (s n *Q n )
0
(Q1
Qn)
where:
0
the final TDS concentration of the blend of
all source water;
155
Table 30. Estimated First Year TDS Concentration of
Groundwater for Various Recharge Amounts and
Salinity Given Available Aquifer Mixing Volumes.
Year
Incidental
Recharge
Amount
Recharge
Concentration
Available Mixing Volume
(thousand ac-ft)
2,000
ac-ft
5,000
10,000
mg/1
----Salinity, mg/1 1991
15,957
1,467
309
304
302
1995
19,262
1,338
310
304
302
2000
22,848
1,355
312
305
302
2005
27,522
1,294
313
305
303
2010
32,840
1,283
316
306
303
2015
37,621
1,313
319
308
304
2020
42,403
1,353
322
309
304
2025
47,208
1,403
325
310
305
156
Qi ... Q n — the quantity of each water source - CAP,
groundwater, and various recharge sources;
sl ....s n
—
the TDS concentration of each water source.
First year compounding effects occur when the
recharge has had sufficient time to percolate through the
vadose zone. Percolation times are discussed in a later
section. The mixing volumes shown in Table 30 are chosen
arbitrarily with the purpose of demonstrating the influence
of changes in mixing volumes. Mixing volumes in the aquifer
are influenced by the proximity of well to recharge sites;
the closer the hydrological connection in the aquifer the
lower the mixing volume.
In Table 30, the TDS concentration of the recharge
falls until 2010 because most of the wastewater generated in
the basin is still being discharged into the Santa Cruz
River; after 2010, wastewater reuse is large relative to
river discharges (CH2M Hill/Rubel and Hager, 1983). The
final TDS of the groundwater increases steadily as incidental recharge increases.
Other sources of incidental recharge are from
industry. The copper mines south of Tucson have large
discharges, though the exact amounts are not known. Other
industries discharge wastewater which may or may not reach
the groundwater aquifer. However, in all cases it can be
157
assumed that the quality of industrial effluent is impaired
or else it would be reused.
What can be said with certainty about the quantity
and quality of recharge in the Tucson basin is that the
natural recharge sources will not increase and the
incidental recharge of salt contaminants will not decrease.
The amounts of natural recharge and aquifer volume are not
enough, in themselves, to guarantee enough dilution to
completely negate significant salinity degradation of the
aquifer in the future. Therefore, groundwater salinity will
increase. We can take greater advantage of high-quality
natural recharge, however, by properly locating incidental
recharge with respect to well placement.
Well Construction and Local Pumping Patterns. The
last of Todd and McNulty's criteria for dilution in an
aquifer are well construction and local pumping patterns.
The AGMA has strict guidelines for the upper construction of
a well, mandating skin-tight seals and approved materials.
However, the law does not dictate the depth from which the
water may be pumped. Depth may determine quality if
wastewater is widely used and the upper regions of the
aquifer are heavily contaminated by saline recharge.
The intensity of pumpage in the city service area is
very high. Wastewater recharged to the south of the city
has little likelihood of leaving the basin via the only
major drain, the Santa Cruz River. However, not all wells
158
will capture saline recharge, only those down gradient or
very close to wastewater irrigation sites. The placement of
pumps is crucial. Wells close to wastewater recharge sites
should have the pumps placed as deep as possible. Monitoring salinity at the well site will reveal saline groundwater
areas; blending, even if it is uneconomical in the
short-term, may be necessary in those areas to improve the
quality of wastewater and decrease the compounding effect of
the salinity cycle.
Time of Recharge Arrival in the Aquifer
A final factor which affects the salinity cycle is
the percolation time required for the water applied at the
surface to reach the aquifer. Percolation time is a
function of the downward velocity of recharge water and the
depth to the aquifer from the surface.
Estimates of the downward velocity of recharge water
vary greatly. Postillion (1985) calculated the downward
velocity of recharging water in the Green Valley area to be
10 feet per year. The average depth to water in the Tucson
basin is over 200 feet; using these figures, 20 years is the
expected lag period before the salinity of the CAP water
reaches the aquifer. The depth to water in the Santa Cruz
River channel is very shallow, perhaps 50 feet, whereas in
the central Tucson well field depths to water go as high as
300 feet. A recent study by Bowman and Rice (1985)
159
intimates the 10 feet per year average downward velocity
underestimates the actual speed of recharging waters. They
conclude that the standard estimators of semi-saturated and
saturated flow underestimate by a factor of three to six
times the velocity they observed. Downward velocity can be
as great as 30 to 60 feet per year. The actual velocity is
a function of soil characteristics such as porosity, which
has been recognized, and homogeneity, a recent point of
discussion in the study of the vadose zone between the
surface and the aquifer.
The downward velocity of recharge is difficult to
predict because of the diversity of materials in the vadose
zone. The time of arrival of recharging water is critical
in the estimation of economic impacts generated by salinity
degradation of the aquifer. Estimates of the impacts are
limited by this unknown.
Figures 9, 10, and 11 show the lag time effect over
a one hundred year period for various salinity pick-up rates
as they affect the overall TDS concentration in the
aquifer. It is evident that an annual salinity pick-up rate
of 3 percent will have grave consequences over the 100-year
period; the zero year lag results in a concentration of
nearly 5,000 mg/1, the 10-year lag in a concentration of
3,800 mg/1, and the 20-year lag in a concentration of 2,400
mg/l. For the annual salinity pick-up rates of 1 and 2
percent the consequences are much less dire. At 2 percent
160
(spuusnotu)
T/ 2m '44TuT1PS
161
-:t
csi
res
(sviresnou)
T/ 211 `.&qTuTTE'S
••n
162
0
clt)
CS 4.,
CS
(spuesno41)
11 2m '/Ç4TuT1eS
163
the one hundred year TDS concentrations are approximately
2,200, 1,800, and 1,500 mg/1 for the zero year, 10 year, and
20 year lag periods, respectively. And for a one percent
annual salinity pick-up rate the TDS concentrations range
from a high of slightly over 800 mg/1 for the zero year lag
period to about 670 mg/1 for the 20 year lag period.
Over the shorter time period considered in Chapter
7, 1991-2025, the salinization of the aquifer seems less
acute. The salinity levels range from 820 mg/1 for the
worst-case scenario where there is zero lag time and a 3
percent annual salinity pick-up rate for aquifer recharge,
to 350 mg/1 for the best case where there is a 20 twenty
year lag period and a one percent pick-up rate.
It is generally recognized that the salinity of the
basin will increase because of the groundwater conservation
policies which promote the importation of Colorado River
water and wastewater reuse. As was shown here, there is a
potential for serious salinity loading of the aquifer; the
costs of salinity loading were not included in the calculus
of the conservation policies. Confining ourselves to
analyses of the short-term implications of groundwater
conservation can be misleading as to the policy's long-term
implications. In the long-term, Tucson must either end its
reliance on groundwater or suffer the costs of a greatly
degraded water supply.
164
Summary
Because of the physical properties of the Tucson
basin, salts from CAP water will increase the salinity of
the aquifer. Drainage of the salinity out of the basin and
dilution with natural recharge and existing groundwater
storage will not solve the problem. How large the increase
in TDS concentration over time will be depends in large part
on how much salt is brought into the basin and on the scale
and location of wastewater reuse.
The incidence of degradation will not be homogenous
within the basin. Areas of high TDS concentrations occur in
various levels of the aquifer. Blending of the saline water
with good quality water can ameliorate user damages to a
degree, but if a well site were to become too saline, and
the costs associated with salinity damage were to exceed its
production value, abandonment might be the only recourse.
Given there are a limited number of well sites because of
policy and physical constraints, the costs of providing
water must increase as water providers are forced to find
alternative well sites. Identifying well sites with
potential quality problems and evaluating them with respect
to the costs of alternative sources of water is necessary in
the economic assessment of the salinity cycle. Research
focusing on the economic costs of salinity needs to move
from merely estimating the direct costs of damage to the
examination of long-term costs of water supply degradation.
165
Estimates of aquifer degradation are based on
approximated hydrological properties. The estimates of
degradation made by the Bureau of Reclamation (1984) and
CH2M Hill/Rubel and Hager (1983) have been criticized in
previous discussions for not incorporating realistic
hydrologic assumptions. However, as was noted above, the
hydrologic parameters needed for a realistic estimate are
difficult to obtain and evaluate.
The costs of saline water use will continue to
increase for water users whose supplies are caught in the
cycle. The cycle will result in decreased groundwater
quality and higher user costs as will be discussed in the
following chapter.
CHAPTER 7
COSTS OF GROUNDWATER CONSERVATION
In this chapter, the costs of proposed conservation
policies are estimated. Direct and indirect costs generated
by salinity in municipal water supplies which accrue to
single-family residences are evaluated with respect to
alternative groundwater conservation policies. The salinity
damage costs are then compared to the expenditures and a
class of consumer costs for the groundwater conservation
programs.
Projecting the Economic Costs of Salinity Damage
The planning horizon of 1991 to 2025 was chosen
because it is the period during which CAP water inflows and
AGMA programs are to be used to achieve safe-yield.
Conservation policies are represented by thirteen scenarios.
The scenarios were chosen to represent feasible policies for
Tucson's groundwater conservation programs. Some of the
scenarios are designed to separate out the effects of combinations of policy instruments. For example, desalination of
CAP water is considered in two scenarios to estimate the
effects of wastewater reuse, alone, on groundwater
degradation.
166
167
A water supply and use model was used to compute
flow-weighted average annual salinity in water supplied to
single-family residences. The average annual salinity is
the sum of the flow-weighted salinity load carried in each
water source divided by the sum of water amounts from each
water source. The water use is calculated as the population
of single-family residences times the estimated use per
single-family household.
Water use was adjusted to meet the projected annual
water requirements for the City of Tucson. The per capita
water requirements are assumed to be 140 gallons per capita
per day for the service population of the City of Tucson in
all scenarios, except 8a and 8b. The size of the population
of the City of Tucson is from estimates by the Department of
Economic Security for the 1984 base year with growth rates
and service populations as estimated by Beck and Associates
(1984) for TWD.
Wastewater reuse projections are from the City of
Tucson Wastewater Reuse Report (CH2M Hill/Rubel and Hager,
1983). The salinity of reclaimed wastewater is assumed to
be 242 mg/1 greater than municipal service water (CH2M
Hill/Rubel and Hager, 1983). Wastewater discharges are
adjusted to account for the City of Tucson's
responsibilities to provide wastewater to the Tohono
O'odaham Indians under the Southern Arizona Water Settlement
Act in the amount of 30,600 acre-feet per year, including
168
transmission losses (CH2M Hill/Rubel and Hager, 1983). For
all scenarios, it is assumed that increases in salinity
concentration in the aquifer as the result of factors not
included in this analysis are negligible.
The total water use summed over the study period for
the city of Tucson is about 5.35 million acre-feet under
present population projections. Groundwater pumpage
accounts for about 53 percent of the projected water use and
CAP for about 47 percent. Wastewater reuse summed over the
study period is projected to be about 890 thousand acrefeet. The scenarios will modify these projections under
various policies.
Calculation of Total Annual Costs
The costs of household damage to water-using
appliances for a Tucson single-family residence are a
function of the lifetimes and original costs of the
appliances weighted to represent the typical household's
number of appliances. The estimate of household damages is
weighted by the projected number of single-family residences
to calculate the total annual costs of salinity damage. The
total annual cost of damage to single-family residences is
calculated as the product of three elements: (1) the flowweighted average salt concentration in time period t; (2)
the damage function relating salt concentration to annual
169
household costs; and (3) the number of single-family
residences in time t.
Policy Scenarios
The first scenario is the base case which assumes no
imported water, present wastewater reuse volumes, and no
artificial recharge. The second scenario conforms to
current plans for CAP deliveries and wastewater reuse for
the City of Tucson.
Scenario 1. No CAP importation and no wastewater
reuse beyond the present 452 acres. Total water use is
calculated as the service population for the TWD times the
per captia use rate of 140 gallons per capita per day. This
scenario is hereafter referred to as the base case.
Scenario 2. CAP water is brought on line in 1991
and is blended with groundwater prior to delivery as shown
in Table 15. The average share of CAP water over the entire
study period is 48 percent of total water requirements for
the city with an average annual delivery of 73.4 thousand
acre-feet. The salinity of CAP water is as projected in the
Bureau of Reclamation model CAPSIM (see Figure 1).
Wastewater reuse for acreage and amount per acre is as
projected in the City of Tucson Wastewater Reuse Report
(CH2M Hill/Rubel and Hager, 1983), increasing from 4,200
acres in 1990 to 7,315 in 2025 (see Table 28). This
scenario is hereafter referred to as the City Report Plan.
170
Scenario 3a. Same as 2, but the CAP water to
groundwater blend is adjusted to 50 percent or greater in
favor of CAP. All values for the blend of CAP to
groundwater in Table 15 less than 50 percent are set equal
to 50 percent and those greater than 50 percent in the table
are unchanged, the groundwater blend values are adjusted
accordingly. The average annual share of CAP water over the
entire study period is 54 percent of the total water supply
of the city with mean annual deliveries of 81.3 thousand
acre-feet.
Scenario 3b. Same as 2, but the CAP water to
groundwater blend is 60 percent or greater. All values of
CAP blend in Table 15 less than 60 percent are set equal to
60 percent and those greater than 60 percent are unchanged.
The average share of CAP water over the entire study period
is 60 percent of the total city water supplies with mean
annual deliveries of 91.4 thousand acre-feet.
Scenario 4a. Same as 2, but the CAP water is
partially desalted to a constant salinity concentration of
500 mg/l.
Scenario 4b. Same as 2, but the CAP water is
desalted to the level of present municipal water supplies
and contains a constant salinity concentration of 300 mg/l.
Scenario 5. The CAP water blending schedule and the
TDS concentration are the same as 2, but wastewater reuse
for municipal acreage does not expand to the projected
171
levels. Wastewater reuse acreage remains constant at
present levels, 452 acres.
Scenario 6. Same as 2, but the per acre wastewater
allotment for municipal irrigated acreage is increased 10
percent.
Scenario 7. Same as 2, but the municipal acreage
irrigated with wastewater is 10 percent greater than
projected.
Scenario 8a. The CAP water to groundwater blend
and the wastewater reuse are the same as in 2, but the per
capita water requirements are lowered from 140 gallons per
capita per day to 120 gallons per capita per day.
Scenario 8b. No CAP importation and no wastewater
reuse beyond the present 452 acres, the same as the base
case described in scenario 1, but the per capita water
requirements are lowered from 140 gallons per capita per day
to 120 gallons per capita per day.
Scenario 9a. Same as 2, but 50 percent of the
wastewater which is not used for irrigation and is normally
discharged into the channel of the Santa Cruz River is
artificially recharged.
Scenario 9b. Same as 2, but 100 percent of the
water normally discharged into the channel of the Santa Cruz
River is artificially recharged.
The projected average annual pick-up rates are
presented in Table 33. The costs of damage generated by CAP
172
and by salinity pick-up are calculated separately in Tables
35 and 36.
Assumptions and data used in the projections
are discussed below.
Description of Data
Population. Population is used in the cost
computations to estimate water requirements and aggregate
damage. The population used in this evaluation is only that
of single-family residences. This partial damage estimate
is used because, although we know damages will occur to
other municipal water-use sectors such as multi-family
residences, industry and horticulture, there are no reliable
estimates of the effects of salinity on these sectors. The
estimates of single-family population are from the reports
on water rates for Tucson Water (Black and Veatch, 1982;
Beck and Assoc., 1983; Beck and Assoc., 1984).
Historical
population levels are presented in Table 11 and projected
population levels in Table 12. The number of single-family
households is estimated to increase by about 2.3 percent per
year (Beck and Associates, 1984).
Municipal water use. Municipal target use rates for
water providing agencies in the Tucson Active Management
Area (TAMA, 1984) are listed in Table 31. They represent
maximum rates during the period indicated. Water use rates
for single-family residences in the projections were assumed
173
Table 31. Tucson Active Management Area Water-Use Targets
for Water Providing Agencies, First Management
Plan Targets.
Period
Gallons per Capita per Day
(GPCD)
150
1990
-
1999
2000
-
2009
145
2010
-
2025
140
174
to be constant, at the lowest target rate, except when
modified in scenarios 8a and 8b.
CAP to groundwater blend. The blend of CAP and
groundwater is central to the calculation of salt
concentration in municipal water. Estimates of the future
blend rates are published in the Tucson Metropolitan
Wastewater Reuse Assessment (CH2M Hill/Rubel and Hager,
1983). The blend estimates are presented in Table 15.
Future Salinity Inflows. Salinity concentrations in
the Colorado River are not constant. In this century, the
salt content of the Colorado River increased steadily up
until the last few years, when it has decreased due to high
runoff. Studies by the Bureau of Reclamation indicate that
the future salinity levels in the river can be expected to
range from less than 600 mg/1 to more than 900 mg/1 below
Parker Dam. The expected average reported by the Bureau is
about 747 mg/1 (Bureau of Reclamation, 1984). The average
of the 15 runs presented in the salinity load model, CAPSIM,
are graphically represented in Figure 1. The annual
averages shown in Figure 1 are assumed to be equal to the
annual salt concentration of the CAP on arrival in Tucson.
Rate of Aquifer Degradation
Evaluation of the rate of salinity pick-up which
results from groundwater degradation is calculated in a
175
flow-weighted average to evaluate the effects of groundwater
pumpage volume, effective mixing volume of the aquifer, and
incidental and natural recharge amounts. The principal
recharge sources are municipal irrigation, local
agricultural irrigation, and river releases of treated
wastewater from treatment plants. The analysis is based on
the mass balance of salinity and the water balance of
inflows and outflows.
The salinity pick-up rates which characterize the
scenarios are presented in Table 32. Pick-up rates are
expressed as the mean percentage increase in groundwater
salinity within the Tucson basin over the previous year.
The estimates in Table 32 are given for three aquifer
dilution volumes which represent effective aquifer volumes
for the City of Tucson service area: 2 million acre-feet,
5 million acre-feet and 10 million acre-feet. There are
approximately 10 million acre-feet of water in an aquifer
covering 160 square miles that is 1000 feet thick with a
specific yield of 0.10. Recharges into the 10 million acrefeet of aquifer volume are assumed to mix completely with
groundwater to 1000 feet. The 5 and 2 million acre-feet
estimates represent cases of incomplete dilution where the
mixing only occurs in the upper 500 and 200 feet of the
aquifer, respectively. All estimates assume complete and
instantaneous mixing in the assigned aquifer volumes.
176
Table 32. Projected Average Annual Salinity Pick-Up Rate
for Various Policy Scenarios. -- 1991-2025.
Available Dilution Volumes in the Aquifer
Million Ac-Ft
Scenario
2
5
10
Percent 1
1.33
0.62
0.33
2
2.67
1.41
0.80
3a
2.71
1.44
0.82
3b
2.75
1.48
0.84
4a
2.36
1.22
0.68
4b
2.07
1.05
0.58
5
1.81
0.93
0.52
6
2.76
1.46
0.83
7
2.70
1.43
0.81
8a
2.44
1.28
0.72
8b
0.91
0.41
0.22
9a
2.79
1.54
0.89
9b
2.91
1.66
0.97
177
The dilution volumes were chosen arbitrarily to
illustrate the dependence of pick-up rates on dilution
volumes. The range of dilution volumes demonstrates the
effect of decreasing well field areas. As restrictions on
expansion increase, the available dilution volume
decreases. Actual salinity pick-up rate for an individual
well is determined by the location of the well relative to
recharge sites and the hydrogeological conditions of the
well location.
Table 33 lists the mean TDS concentration of the
Tucson basin for the year 2025, given the various
scenarios. Zero lag time is assumed in this table. A
10-year lag would generate the same TDS concentrations but
would add 10 years to the dates given in Table 33.
Salt concentration in municipal water supplies is
affected by various policy actions. The main difference
among the policies is caused by the effects of various
recharge salinity and amounts which affect the salinity
cycle. Policies with CAP water as a major water supply
create a higher salt load in the aquifer when employed in
conjunction with expanded wastewater reuse.
Costs of Salinity Damage
Computation Method for Present Value of Total Costs
The present value of the annual salinity damage
costs for the study period are presented as the discounted
178
Table 33. Estimated Mean TDS Concentrations in the Tucson
Basin Aquifer for the Year 2025 Given Various
Policy Scenarios.
Available Dilution Volumes in the Aquifer
Million Acre-Feet
Scenario
2
5
10
mg/1 1
476
372
336
2
754
490
396
3a
765
495
399
3b
775
501
402
4a
678
459
380
4b
613
432
367
5
562
415
359
6
777
498
400
7
760
493
394
8
698
468
388
8b
437
357
330
9a
788
512
409
9b
817
533
421
Note: A zero lag time is assumed for arrival of the
recharged water to the aquifer.
179
sum of annual damage costs. The present value is calculated
as:
P —
2025
E
t=1986
[D(t)] fit
where:
P
—
the discounted sum of annual damage costs or
the present value;
D(t) = the annual damage cost in year t;
0
—
the discount factor, 1/(1+r);
r
=
the discount rate.
Present Value of Costs Generated by Salinity
The present value of single-family residence damages
associated with the direct use of CAP water are shown in
Table 34. Damages from the use of degraded groundwater are
shown in Table 35. The total damages from both water
sources are shown in Table 36.
Various discount rates are presented to demonstrate
the effects the discount rate on the present value of the
damages. The costs in the first year (1991) are discounted
5 years and the costs in the last year (2025) are discounted
40 years.
180
Table 34. Present Value of Damage Costs to Single-Family
Residences Generated Directly by CAP Salinity
under Various Scenarios. -- 1986 Dollars.
Tucson, Arizona.
Scenario
Discount
Rate
Present Value
Percent
Millions of Dollars
1
O
4
8
0.0
0.0
0.0
2
O
4
8
188.6
67.8
28.4
3a
O
4
8
208.6
80.3
36.4
3b
O
4
8
232.2
91.8
42.6
4a
O
4
8
91.9
34.7
15.7
4b
0
4
8
0.0
0.0
0.0
5
O
4
8
188.6
67.8
28.4
6
O
4
8
188.6
67.8
28.4
7
0
4
8
188.6
67.8
28.4
181
Table 34--Continued.
8a
8b
9a
9b
O
4
8
188.6
67.8
28.4
O
4
8
0.0
0.0
0.0
O
4
8
188.6
67.8
28.4
0
4
8
188.6
67.8
28.4
182
Table 35. Present Value of Costs Associated with Salinity
Damages Resulting from Groundwater Degradation
for Single Family Residences for Various
Scenarios, Given Various Discount Rates. -1991-2025. 1986 Dollars. Tucson, Arizona.
Aquifer Dilution Volume
Million Acre-Feet
Discount
Rate
Scenario
Percent
5
2
--
10
Present Value
Millions of Dollars ----
1
0
4
8
89.9
29.3
10.7
44.2
14.9
5.7
27.1
9.4
3.8
2
0
4
8
102.1
34.9
13.5
44.4
15.4
6.1
24.8
8.8
3.6
3a
0
4
8
107.1
37.0
14.5
46.7
16.4
6.6
26.0
9.4
3.9
3b
0
4
8
110.5
38.3
15.1
48.5
17.0
6.8
27.0
9.7
4.0
4a
0
4
8
89.6
31.0
12.2
39.4
13.9
5.6
22.3
8.1
3.4
4b
0
4
8
77.6
27.1
10.8
34.6
12.3
5.0
19.9
7.3
3.1
5
0
4
8
61.0
21.1
8.4
28.7
10.2
4.1
17.1
6.3
2.7
6
0
4
8
107.1
36.7
14.3
46.3
16.1
6.4
25.8
9.2
3.8
183
Table 35--Continued
0
4
8
103.9
35.6
13.9
0
4
8
45.3
15.8
6.3
25.3
9.0
3.7
91.3
31.5
12.3
40.4
14.1
5.7
22.9
8.2
3.4
0
4
8
63.9 22.0
8.9
33.1
11.8
5.0
21.8
8.1
3.6
9a
0
4
8
110.2
37.3
14.7
48.7
16.9
6.7
27.2
9.6
3.9
9b
0
4
8
124.6
43.2
17.1
56.0
19.5
7.8
31.2
11.1
4.6
7
8a
8b
184
Table 36. Present Value of Total Damage Costs Generated by
Salinity under Various Scenarios. -- Flow Period
1991-2025.
1986 Dollars.
Tucson, Arizona.
Aquifer Dilution Volume
Million Acre-Feet
Scenario
Discount
Rate
Percent
2
5
10
Present Value
of Dollars
-- Millions
----
1
0
4
8
89.9
29.3
10.7
44.2
14.9
5.7
27.1
9.4
3.8
2
0
4
8
290.6
102.6
41.9
232.9
83.1
34.5
213.3
76.6
32.0
3a
0
4
8
315.7
117.3
51.0
255.3
96.6
43.0
234.6
89.6
40.3
3b
0
4
8
342.7
130.0
57.7
280.7
108.8
49.4
259.2
101.5
46.6
4a
0
4
8
181.5
65.7
27.9
131.3
48.6
21.3
114.2
42.8
19.1
4b
0
4
8
77.6
27.1
10.8
34.6
12.3
5.0
19.9
7.3
3.1
5
0
4
8
249.5
88.9
36.8
217.2
77.9
32.6
205.7
74.0
31.1
6
0
4
8
295.7
104.5
42.7
234.9
83.9
34.8
214.3
77.0
32.2
185
Table 36--Continued
0
292.4
7
4
103.4
8
42.3
233.8
83.5
34.7
213.9
76.8
32.1
8a
0
4
8
279.9
99.2
40.8
229.0
81.9
34.1
211.4
76.0
31.9
8b
0
4
8
63.9
22.0
8.9
33.1
11.8
5.0
21.8
8.1
3.6
9a
0
4
8
298.8
105.1
43.1
237.3
84.6
35.1
215.7
77.4
32.4
0
4
8
313.2
110.9
45.5
244.5
87.2
36.2
9b
219.8
78.9
33.0
186
Discussion of the Scenario Results
To simplify comparison, a discount rate of 4 percent
and a dilution volume of 5 million acre-feet are assumed.
Additionally, the costs of the base case, scenario 1, are
subtracted from scenarios 2 through 9b to give the
differential or net costs of the policy changes.
Scenario 1.Water requirements for the City of
Tucson are met entirely from groundwater in scenario 1, the
base case. However, it is assumed that the municipal water
use per household is constant and reflects the TAMA gallons
per person per day target level. The low annual salinity
pick-up rate in scenario 1, 0.62 percent, reflects no
salinity increases due to CAP water salts and minimal
compounding effects in the salinity cycle due to wastewater
reuse. The cost generated by groundwater degradation is
$14.9 million. There is no CAP salinity damage cost. The
present value of the costs in scenario 1 are the
no-policy-action baseline costs against which the other
scenarios are to compared.
Scenario 2. Scenario 2 represents the projected
wastewater reuse and CAP water delivery plans as presented
in the City of Tucson Wastewater Reuse Report (CH2M
Hill/Rubel and Hager, 1983), referred to as the City Report
Plan. The wastewater reuse and CAP groundwater conservation
activities of this scenario more than double the base case,
scenario 1, pick-up rate of the salinity cycle, bringing it
187
to 1.41 percent (Table 32). The results show the salinity
of the aquifer rising from 300 mg/1 to 490 mg/l. The total
net damage costs are $68.2 million of which $67.8 million
are associated with direct use of CAP water and $0.5 million
are associated with groundwater degradation. Because 48
percent of all municipal water is from the CAP, scenario 2
generates fewer groundwater degradation costs (but more
groundwater degradation) than the base case, scenario 1, but
higher total costs.
Scenarios 3a and 3b. Scenarios 3a and 3b, in which
the CAP share of the water blend is 50 and 60 percent,
respectively, show that small increases in CAP water
deliveries do not affect the pick-up rate in the salinity
cycle in a disproportionately large manner when compared to
the City Report Plan (scenario 2), Table 32. The costs
associated with use of degraded groundwater are smaller than
in scenarios employing less CAP water. Costs associated
with direct CAP use increase significantly for the case 3b
because a larger proportion of Tucson municipal water is
comprised of CAP water and less groundwater is used.
However, the rate of degradation increases as CAP water use
increases. The pick-up rates for scenarios 3a and 3b are
1.44 percent and 1.48 percent, respectively. The total net
damage costs for scenario 3a are $81.7 million of which
$80.3 million are associated with CAP and $1.5 million are
associated with groundwater degradation. The total net
188
damage costs for scenario 3b are $93.9 million of which
$91.8 are associated with CAP and $2.1 million are
associated with groundwater degradation.
Scenarios 4a and 4b. In scenarios 4a and 4b, CAP
water is desalted to concentrations of 500 and 300 mg/1 to
capture the magnitude of groundwater degradation costs
resulting from wastewater reuse alone. The salinity pick-up
rates for scenarios 4a and 4b are 1.22 and 1.05,
respectively. The total net damage costs for scenario 4a
are $33.7 million with $34.7 associated with CAP.
Groundwater degradation as well as the cost of using
degraded groundwater decreases from the estimates in the
base case, scenario 1, by $1.0 million because the CAP share
of water used never degrades. The total net damage costs
for scenario 4b is lower than the total damage costs in the
City Report Plan (scenario 2) by $2.6 million. The costs
can be interpreted as the groundwater degradation costs to
single-family households caused by the planned wastewater
reuse program of the City of Tucson Wastewater Reuse Report
(CH2M Hill/Rubel and Hager, 1983).
Scenario 5. Scenario 5 captures the effect of the
CAP imports alone when wastewater reuse is held at 1983
levels, 452 acres of landscape irrigation. If most of the
wastewater is directly discharged without reuse, the pick-up
rate is 0.93 percent. The total net damage costs for
scenario 5 are $63.0 million.
There are $67.8 million
189
associated with direct use of CAP water and a net decrease
of $4.7 million in groundwater degradation costs. The
decrease in groundwater degradation cost is due to the
decreased use of wastewater for municipal irrigation.
Scenarios 6 and 7. The assumptions in scenarios 6
and 7 represent 10 percent increases in the amount of
reclaimed wastewater for municipal irrigation applied per
acre and in the acreage of municipal landscaping irrigated
with reclaimed wastewater, respectively. The results show
the salinity pick-up rate for the increased irrigation
apllication rate, 1.46 percent, to be slightly larger than
for the increased acreage irrigated, 1.43 percent. This
higher pick-up rate is due to the increased aquifer recharge
stemming from over-irrigation when the per acre allotment is
increased. The increased amount of wastewater use when
summed over the study period, 1991-2025, is about 891
thousand acre-feet for both scenarios. The total net damage
costs for scenario 6 are $69.0 million, of which $67.8
million are associated with CAP and $1.2 million are
associated with groundwater degradation. The total net
damage costs for scenario 7 are $68.6, where $67.8 million
are associated with CAP salinity and $0.9 million are
associated with groundwater degradation.
Scenario 8a. Scenario 8a, reduces per capita water
use to 120 gallons per capita per day, approximately a 14
percent reduction. CAP deliveries and wastewater reuse are
190
the same as in the City Report Plan, scenario 2. The
reduced annual per capita use generate a salinity pick-up
rate of 1.28 percent which is lower than the scenario 2, the
City Report Plan, pick-up rate of 1.41 percent. With less
consumption there is less water and less salt in the
salinity cycle. Since the model blends groundwater and CAP
water in fixed proportions (see Table 15), a reduction in
municipal water use means a reduction in the amount of CAP
water required. The total damage costs for scenario 8a are
$67.0 million. There is a net decrease of $0.8 million in
the costs associated with groundwater degradation. Of
course there is an additional loss in consumer utility due
to reduced water use which will be discussed later.
Scenario 8b. This scenario imposes the same
restrictions on municipal per capita use as scenario 8a but
employs no CAP or wastewater expansion. This scenario
generates the least degradation costs because there is no
salinity inflow from the CAP and very limited wastewater
reuse. The costs associated with groundwater degradation
decrease in the amount of $3.1 million. Under this
scenario, the aquifer salinity is near a steady-state and
changes only slightly over time.
Scenarios 9a and 9b. The final scenarios, 9a and
9b, estimate the effects of artificial recharge of 50
percent and 100 percent of surplus wastewater, respectively,
on the salinity pick-up rate. The results of the flow-
191
weighted calculations show that recharge affects the pick-up
rate only slightly. Recharge of 50 percent of the surplus
wastewater results in a pick-up rate of 1.54 and recharge of
100 percent results in a pick-up rate of 1.66 percent. The
net costs associated with scenario 9a total $69.7 million
with $67.8 resulting from direct CAP use and $1.5 million
associated with groundwater degradation. The total net
costs associated with scenario 9b are $72.3 million, $67.8
million from CAP direct use and $4.6 million from
groundwater degradation.
Since artificially recharged wastewater is assumed
to have the same TDS concentration as wastewater delivered
for irrigation and it is assumed that no evaporation losses
occur in recharge, the artificially recharged water is of
low salt concentration as compared to irrigation recharge.
There are no data available on the evaporation losses in
recharge; the treatment of water for recharge and
evaporation during recharge will raise the salinity load but
the degree of increase is not known and is here assumed to
be zero. The results for scenarios 9a and 9b should be
applied cautiously because of these assumptions. Any
increase in evaporation would increase the salinity of the
recharge and increase degradation.
192
Amounts of Groundwater Conserved
Groundwater conservation is defined here to mean the
decrease in net groundwater withdrawals. The major means of
achieving groundwater conservation is by the substitution of
CAP water for groundwater and by artificial recharge of
wastewater. The conservation amount realized under the
policies and programs in a scenario is subtracted from the
amount of groundwater pumped to meet the water requirements
of the base case (scenario 1). Artificial recharge amounts
are subtracted from withdrawals to yield the amount of net
withdrawals. Wastewater reuse offsets groundwater
withdrawals for municipal irrigation in all cases except
scenario 5. However, wastewater is counted against total
municipal requirements since it is not regulated under the
AGMA. Wastewater reuse is considered a luxury water use
which allows the expansion of turf areas that would
otherwise be limited under the gallons per capita water
requirements in all scenarios except 5. Scenario 5
represents increased groundwater pumpage to meet increased
municipal irrigation demands and is included analyze the
effects of increased municipal irrigation with higher
quality water. Table 37 presents the amounts of net
withdrawal for each scenario.
193
Table 37. CAP Water Use, Groundwater Use, and Total Water
Use Summed over the Study Period. -- 1991-2025.
Tucson, Arizona. a
Scenario
CAPb
-
-
Groundwater
Total
Million Acre-feet ---
1
0.00
5.35
5.35
2
2.58
2.77
5.35
3a
2.88
2.47
5.35
3b
3.23
2.12
5.35
4a
2.58
2.77
5.35
4b
2.58
2.77
5.35
5
2.58
3.27
5.85
6
2.58
2.77
5.35
7
2.58
2.77
5.35
8a
2.21
2.38
4.59
8b
0.00
4.59
4.59
9a
2.58
2.77
5.35
9b
2.58
2.77
5.35
a.
Total water use is calculated as the gallons per capita
per day municipal target of the Tucson Active Management
Area times the population projections of the Department
of Economic Security.
b.
CAP to groundwater blend ratio CH2M Hill/Rubel and
Hager, 1983.
194
Salinity Damage Costs per Acre-foot
of Decreased Groundwater Withdrawals
The degree of groundwater conservation for each
scenario differs because the water supply alternatives
employed in the scenarios are distinct. The scenarios are
now analyzed for costs per acre-foot of groundwater pumpage
decreased by the various conservation efforts. Decreased
pumpage is defined as net groundwater withdrawals and is
considered to be the amount of groundwater conserved under
the policies and programs of the scenarios 2 through 9b.
The groundwater withdrawals of scenarios 2 through 9b are
subtracted from the amount of pumpage withdrawals of the
base case (scenario 1) to yield net withdrawals. Net
withdrawals are divided into the net change in salinity
costs (net of the base case in scenario 1) to calculate the
net per acre-foot salinity costs associated with alternative
groundwater management options, scenarios 2 through 9b. The
salinity costs associated with each acre-foot of water
conserved are shown in Table 38.
Scenario 2, representing the City Report Plan, has
the eighth highest cost. This scenario offsets groundwater
pumpage by about 48 percent.
The scenarios with the least salinity cost per acrefoot of offset groundwater withdrawals are scenarios 8b and
4b. Both scenarios generate less net costs than the base
case, scenario 1, and are shown as negative costs. Scenario
195
Table 38. Average Present Value of Salinity Damage per
Acre-foot of Decreased Groundwater Withdrawals.
1986 Dollars Discounted at Four Percent.
Aquifer Dilution Volume Assumed as
5 Million Acre-feet.
Scenario
Present Value
per Acre-foot
Dollars
1
0.00
2
26.49
3a
28.40
3b
29.06
4a
13.08
-
4b
1.00
37.40
6
26.78
7
26.64
8a
22.55
8b
- 4.00
9a
21.04
9b
17.84
5
Note: Artificial Recharge is considered to offset
groundwater withdrawals.
196
8b has the same assumptions as scenario 1, no CAP use and no
expansion of wastewater reuse, with the further assumption
that the municipal water use requirements are reduced by
about 14 percent. The low salinity degradation cost in
scenario 8b is the result of reduced groundwater pumpage and
reduced incidental recharge from municipal irrigation.
Scenario 4b is based on desalting CAP water to 300 mg/1
which holds CAP water at a constant; it is a low-salt water
supply which experiences no degradation due to salinity
pick-up. Scenario 4b is the third lowest cost scenario, and
like scenario 4a, is based on desalting.
The increase in salinity damage costs per acre-foot
of decreased groundwater pumpage associated with increasing
CAP allotments, scenarios 3a and 3b, is small because the
increased salinity costs are offset by proportional
decreases in groundwater withdrawals.
Scenario 5 does not increase wastewater reuse from
1983 levels and employs CAP water supplies. This scenario
shows salinity damage costs per acre-foot conserved to be
slightly greater than scenario 2, the City Report Plan.
Decreased wastewater irrigation causes about 890 thousand
acre-feet more groundwater to be pumped to make-up the
irrigation requirements for the acreage to be irrigated with
wastewater as described in the City Report (CH2M Hill/Rubel
and Hager, 1983). The decrease in groundwater withdrawals
197
for this scenario as compared to the pumpage requirements in
the base case, scenario 1, is about 31 percent.
Artificial recharge offsets groundwater pumpage in
scenarios 9a and 9b and thus decreases net groundwater
withdrawals. The costs per acre-foot are low because the
implied quantity conserved is high.
Costs of Conservation Programs
Water Supply Cost Estimates
Groundwater Water Pumpage. Groundwater conservation
programs offset the costs of pumpage. Changes in pumpage
costs resulting from decreased groundwater withdrawals are
subtracted from each of the total costs of each of the
scenarios to represent the net change in costs associated
with groundwater conservation scenarios 2 through 9B. The
costs of pumpage for the city of Tucson include electric
power, maintenance, and the capital costs of the pumps. The
total costs associated with pumpage for the city of Tucson
in 1986 are estimated to be $8.2 million for the pumpage of
80.8 thousand acre-feet of groundwater (Beck and Assoc.,
1986). The average cost per acre-foot for 1986 is
calculated to be $101.47 per acre-foot. The costs of
distribution and administration are not included in the
following discussion because the effects of groundwater
conservation programs on them is not clear. These costs are
198
therefore assumed to remain the same regardless of water
source.
Central Arizona Project Water. CAP water costs are
determined by three factors: capital costs, unit costs, and
treatment. In the City of Tucson Wastewater Reuse
Assessment (CH2M Hill/Rubel and Hager, 1983), CAP costs were
estimated to be about $210.00 per acre-foot for the schedule
of delivery shown in Table 15. Inflating these 1983 costs
to 1986 dollars results in an estimated pre-distribution
cost for treated CAP water of $231.11 per acre-foot per
year.
Wastewater. Wastewater offsets pumpage when it is
used to supply municipal irrigation. CH2M Hill/Rubel and
Hager (1983) estimated that treated wastewater for reuse
will cost about $200.00 per acre-foot, which when inflated
to 1986 dollars is $220.00 per acre-foot.
This ignores the
costs associated with construction of a wastewater
distribution system and storage. In the city wastewater
reuse study, distribution and storage increased the costs of
wastewater reuse over simple reclamation costs by 50 to 250
percent.
Artificial Recharge. Artifical recharge costs are
greatly affected by land costs since recharge requires large
plots for surface basin systems which infiltrate water.
Orange County, California has a large recharge project with
a capacity of 15 million gallons per day. Similarities
199
exist between the Orange County project and proposed Tucson
projects because both have similar requirements for highquality, treated water. The Orange County cost in 1978-1979
was about $200.00 per acre-foot for the recharge activity
(Asano, 1985). Inflating the Orange County costs to 1986
dollars and including cost of recovery, yields a cost of
about $310.00 per acre-foot recharged. It is assumed that
reclaimed wastewater which otherwise would be discharged
into streambeds can be used as source water. Because there
is excess wastewater, no costs are included for water
acquisition.
Desalting Treatment. Desalting is not a groundwater
conservation program but it has been investigated by the
city of Tucson because of concerns about salinity
(Montgomery-Johnson-Brittain (1983). In this study,
desalting was included as a scenario for two reasons, to
evaluate the salinity damages from CAP and to measure the
effects on salinity pick-up rates resulting from wastewater
reuse alone. Desalting costs are highly dependent on energy
costs since the technology requires large expenditures of
power. Asano (1985) estimated the costs of desalting to be
about $411.00 per acre-foot (1984 dollars inflated to 1986
dollars). The desalting process removes 87 percent of the
salt concentation.
Only a portion of the CAP water need be desalted
because the process removes 87 percent of the salt from
200
water. The average salinity of CAP water is estimated to be
720 mg/l. To desalt to 500 mg/1, only 31 percent of the CAP
water would require treatment at an average cost per acrefoot for the total CAP allotment of $127.38. Desalting to
300 mg/1 requires that 58 percent of the CAP allotment be
desalted at a cost of $238.00 per acre-foot.
Total Expenditures for Conservation
Applying the above costs to the schedules of water
uses in the average-flow model for pick-up rate yields a
rough estimate of the total costs of conservation projects.
The costs in Table 39 are the estimated total expenditures
made to provide water and to replace damaged water-using
appliances. The estimates represent the present value of
costs discounted at 4 percent and summed over the study
period.
Expenditures per Acre-foot of Groundwater Conserved
Table 40 shows the present value of expenditures and
salinity costs per acre-foot of decreased groundwater
withdrawals and the percentage of groundwater withdrawals
offset by the actions of these scenarios. Groundwater
conservation is high in scenarios 9a and 9b because
artificial recharge is counted against withdrawals.
Scenario 9b has the second highest total costs but yields
the lowest expenditure per acre-foot. The next lowest
201
Table 39. Estimated Present Value of Total Expenditures for
Water Acquisition and Net for Groundwater
Conservation Under Various Scenarios.
-- 1986 Dollars Discounted at 4 Percent Summed
over the Study Period.
Scenario
Total
Expenditures
Net
Expenditures
- Million Dollars 1
226.9
0.0
2
430.7
203.8
3a
455.5
228.6
3b
478.4
251.5
4a
590.9
364.0
4b
730.5
503.6
5
469.4
242.5
6
439.1
212.2
7
439.1
212.2
8a
380.2
153.3
8b
194.5
- 32.4
9a
518.7
291.8
9b
606.7
379.8
Note: Net expenditures are the total water acquisition
costs for each scenario minus the water acquisition
costs of the base case, scenario 1.
202
Table 40. Present Value of Expenditures for Groundwater
Conservation Programs per Acre-foot of
Groundwater Conserved. -- Present Value in 1986
Dollars, Discounted at 4 Percent, and Summed Over
the Study Period.
Scenario
Present Value
Per Acre-foot
Dollars
1
2
79.12
3a
79.44
3b
.
77.84
4a
141.31
4b
195.48
5
143.91
6
82.38
7
82.38
8a
51.57
8b
-
42.41
9a
88.03
9b
93.69
203
expenditure per acre-foot is scenario 9a, which has the
fifth highest total costs.
The Value of Groundwater Conservation
to the Consumer
Changes in Consumer Surplus
Consumer surplus, as discussed in Chapter 4, is
equal to the difference between the amount of money that a
consumer actually pays to buy a certain quantity of water,
and that amount the consumer would be willing to pay rather
than to go without it.
The reduction-in-use from the target of 140 gallons
per capita per day (GPCD) to 120 GPCD is a decrease of about
14 percent. Single-family residences in the TWD service
area paid $206.54 on average for 95.9 hundred cubic-feet
(ccf) of water in 1986 (Beck and Assoc., 1986). A 14
percent decrease from this average annual use rate would
result in an average water use per single-family residence
of 82.2 ccf per year.
The price elasticity of demand for water is
difficult to measure. However, for policy assessment
purposes Martin and Thomas (1986) suggest that a long-run
price elasticity of about -0.5 is a good rough estimate.
Their estimate is for arid regions and their study data set
includes Tucson. A constant price elasticity of -0.5 over
the 14 percent reduction in quantity implies a marginal
204
willingness-to-pay at the lower quantity of $265.59 per year
per single-family residence.
The light shaded area in Figure 12 is the change in
consumer surplus generated by a change quantity, OQ to OQ'.
The dark shaded area is the cost of production for the
Tucson Water Department. The cost of production is assumed
constant per unit provided, with current price set at
average cost, $206.57.
The loss in consumer surplus is $404.28 per
residence per year, represented by the lightly shaded area
in Figure 12. The loss in consumer surplus per acre-foot of
decreased groundwater pumpage is $12,855.20.
Discussion of Consumer Surplus
In light of the analysis of salinity damages and
groundwater expenditures, the reduction-in-use programs are
the lowest capital cost alternatives to groundwater
conservation. However, the consumer is carrying the costs
of conservation for the reduction in the quantity of water
which can be consumed. This loss is not reflected in the
expenditures for groundwater conservation activities (Table
39) because it is in the form of utility losses resulting
from reductions in water use. A problem exists in measuring
these losses. Consumer surplus is the economist's answer to
that problem.
205
$/Unit
Demand for
Municipal
Water
P
'
Quantity
of Water
Figure 12. Loss in Consumers Surplus for a
Reduction-in-Use.
206
There is a controversial history for the use of
consumer surplus as a measurement of utility loss. Paul
Samuelson (1977) takes a critical stance on the
admissibility of consumer surplus as a meaningful measure of
utility change. Samuelson notes the use of consumer surplus
measures is based on the assumptions that the marginal
utility of income is constant and that the utilities of all
other goods are independent. The change in consumer surplus
evaluated here, $404.28 per residence per year ($12,855.20
per acre-foot per year), is not an insignificant change in
real income. Therefore, the requirement of constant
marginal utility of income is likely to be violated. Baumol
(1977) notes, "Only if the variation in the money measure is
small, i.e. if the indifference curves [between money and
the good in question] are nearly parallel, can one calculate
the consumers' surplus from a demand curve with any
confidence." If these proposals are ignored, Baumol claims
the measurement of consumer surplus is a "rubber yardstick."
While the elasticity of Marshallian demand is a useful tool
for estimating price to quantity demanded relationships, it
is not an income compensated measurement.
Policy itself may change preferences. Tucson has
reduced its per capita use of water over the last decade
(Martin et al., 1984) partially due to price response and
partially due to changes in attitude as the result of
education and the introduction of inexpensive water-saving
207
devices. A change in attitude or preferences which result
in voluntary lower water-use will tend to make the
measurement of consumer surplus an overestimate.
Summary
Salinity in municipal water supplies generates
resource user costs. Water-supply policies, wastewater
reuse, reduction-in-use programs, service area restrictions,
and artificial recharge are the policy instruments for
groundwater conservation. The relation between policy and
user cost was evaluated. Policies which increase the
groundwater salinity, in terms of salinity pick-up, are
artificial recharge with wastewater, over irrigation with
wastewater, and the percentage of CAP water which comprises
municipal water supplies.
The physical factor which influences groundwater
quality most in this analysis is the effective dilution
volume of the aquifer. When the incidental recharge
resulting from the use of wastewater does not fully mix with
large volumes of groundwater, the rate of salinity pick-up
increases greatly. Service area restrictions which limit
the expansion of city well fields constrain the effective
mixing volume of the aquifer. These restrictions do not
conserve groundwater. They serve to protect other
groundwater rights from the water table drawdown as urban
areas seek more water supplies. The placement of wells and
208
wastewater irrigation sites are one of the few solutions
available to counteract the effects of service area
restrictions if wastewater reuse is to be expanded without
suffering increasing costs in the form of salinity damage.
The influence of service area restrictions is reflected in
the different dilution volumes. The effect of limited
dilution greatly increases salinity damage costs. The
magnitude of the total capital costs associated with
groundwater conservation programs overwhelms the total costs
of salinity damage. However, on the margin, the effects of
salinity damage are important. The decision to undertake a
groundwater conservation project is usually made at a given
cost assumption. If the decision for the project scale is
made on the margin and the marginal salinity damage costs
are large and uncounted, then the project scale will be too
large.
Because groundwater conservation is a popular policy
with many local governments and persons in the private
sector, the future value of the aquifer must be perceived to
be great. Viewing the aquifer as a capital resource, its
value will be determined by its role as an insurance against
drought, a low-cost water supply, and a high-quality water
supply. The imputed value of the resource services is as
least as great as the expenditures undertaken for
conservation.
CHAPTER 8
WEIGHING THE COST OF GROUNDWATER CONSERVATION
PROGRAMS: CONCLUSIONS
Municipal water-users in Tucson will suffer
increased costs generated by salinity as groundwater supply
alternatives are employed. Policies enacted to preserve the
diminishing groundwater supplies contribute to the salinity
degradation of municipal water. Assurance of secure
supplies is perceived as crucial for long-term prosperity in
Tucson and the policy-makers responsible for water supplies
are planning extensive groundwater conservation programs.
These programs include the importation of Colorado River
water via the CAP, wastewater reuse for irrigation,
artificial recharge of wastewater, service area
restrictions, and reduction-in-use.
The hydrogeologic characteristics of the basin
restrain the flow of groundwater. Growing water demands
have exploited the aquifer beyond its capacity to balance
inflows and withdrawals. Thus, the aquifer is a stock
resource that receives only limited recharge. The quality
of the recharge has been the focus of this study.
The major contribution of this research has been to
identify and characterize the compounding of salinity in the
209
210
hydrologic cycle as it relates to groundwater conservation
policy. A partial costing of salinity damages reveals that
these damages, though modest in present value terms, grow in
current values over time and should be considered in policy
decisions.
The Municipal Water-Salinity Cycle
Concentrations of conservative elements such as
salinity will rise as water cycles through successive uses.
Water evaporates during use and in treatment processes
leaving less water carrying the same salt load.
Just as groundwater pumpage is out of balance
because demands for groundwater exceed natural
replenishment, the introduction of highly saline recharge
water outstrips the natural capacity of the aquifer to
mitigate salinity increases through dilution and drainage.
Groundwater salinity and its accompanying damages to
groundwater users rise as the opportunity to exploit the
aquifer stock for dilution decreases. Service area
restrictions on the expansion of municipal well-fields were
enacted to restrain cities from encroaching on agricultural
water rights. However, these restrictions limit the
potential to dilute degraded recharge water and partially
offset the benefits generated by groundwater conservation.
Service area restrictions are seen as perhaps the
single most damaging policy in this study. When applied in
211
concert with other groundwater conservation activities, the
restrictions increase the costs of groundwater salinity
degradation significantly. The costs of service area
restrictions were reflected in the study as differences in
dilution volumes. Well placement opportunities are bounded
by the restrictions forcing well siting to be near locations
experiencing incidental recharge. Salinity in pumped water
will rise because the final water quality of such recharge
is degraded and dilution and mixing potential is limited.
This indicates that service area restrictions and the
related factor of well placement are important and neglected
areas of conservation policy.
The Responsibility for Salinity Degradation
Authority for water quantity and water quality is
fragmented. Those responsible for achieving sufficiency in
water supply are employing water supply policies that result
in the introduction of large quantities of salts into the
Tucson basin. Since these public officials are not
responsible for water quality, they have not taken the
degradation effects of their water supply policies into
account in this policy consideration.
The provisions of the AGMA drive groundwater
conservation programs in directions that may have costly
consequences for water quality. Incentives to import water
from outside the basin and to reuse wastewater are central
212
to the conservation effort. These water supply alternatives
have been shown to be very damaging especially when used
together. Such policies are popular with decision-makers
because they generate lower regulatory costs than more
coercive programs such as demand management. Because the
water supply decisions are costless to the policy-makers, in
terms of water quality, they have no motivation to consider
the tough decisions necessary to provide integrated quantity
and quality management.
Summary of the Costs of
Groundwater Conservation
The total capital value of groundwater conservation
activities represent the costs of salinity damage and
conservation programs. In current period dollars, the
salinity damage costs associated with groundwater
degradation are overshadowed by the salinity damage costs
associated with the direct use of imported water. The
expenditures for groundwater conservation activities are far
greater than the damage cost estimates. There is a problem
of perspective in weighing the magnitude of these cost
estimates. Each conservation activity must be looked at
separately and in light of the overall objectives of water
management.
213
Salinity Damage Costs
Partial Costs. The salinity damage cost estimates
made here are only for a single class of water-users,
single-family residences. Multi-family residences,
industry, and horticulture were excluded from the analysis.
Even for the single family residence, only a fraction of the
water-using appliances are included in the cost analysis.
In this limited perspective, it was calculated that
increased salinity costs will cost each residence about
$0.125 per mg/1 per year. If a residence were to receive
unblended CAP water at over 700 mg/1, the annual increment
to costs is over $50.00. On average, the blend assumptions
for CAP and groundwater used here resulted in salinity
damage costs for CAP water alone at $25.00 per residence per
year.
Rate of Degradation. The costs associated with
salinity degradation of groundwater are not as easy to
characterize for a single time period. The rate of salinity
pick-up is slow, less than 3 percent per year in most cases,
but the consequences for the long-term are great. At an
average annual rate of pick-up of 2 percent, the groundwater
in the aquifer would degrade to 1000 mg/1 of salinity in 61
years. However, in the first year under this assumed
degradation rate, the increase is only 6 mg/l. Rate of
change is a complex idea and does not lend itself to easy
interpretation with a single cost estimate.
214
Present Value. The costs of salinity damage in were
presented under a range of discount rates. The annual costs
in the year of damage occurence is the same for all discount
rates, only the calculation of the time value of money
changes. The range of discounted costs for a scenario vary
by factors of six to nearly nine depending on whether the
zero percent discount rate or the eight percent discount
rate is chosen. For any discount rate greater than zero the
present value of salinity damage costs are small since the
costs are discounted to 1986 dollars and the effects begin
after 1991. The discount rate is applied to weigh
alternative investments which seek to maximize returns on
scarce investment resources. Decisions about the value of
preserving irreplaceable natural resources may not be made
merely on the basis of maximizing present value of returns.
This is clearly the case with groundwater conservation
activities. If the large expenditures for conservation now
being considered were weighed against discounted future
benefits and the present costs of water acquisition, under
the criterion of maximum present value, groundwater
depletion is an attractive policy. The social discount rate
for conservation activities appears to be very low because
the perceived value of future benefits for secure water are
held very high. If the social discount rate for
conservation benefits is lower than the one used for this
study, the present value of degradation costs is
215
underestimated. Finally, referring back to the discussion
of the rate of change of salinity degradation, the present
value in current dollars of salinity degradation does not
include the costs associated with salinity in 2025 and
beyond.
Investments in Groundwater Conservation
Groundwater conservation expenditures were estimated
for imported water, wastewater reuse for irrigation, and
artificial recharge of wastewater. The expenditure
estimates are very rough but give an idea of the magnitude
of conservation activities. In present dollars, current
water-supply practices, represented in the base case
(scenario 1) with no imported water or other large
conservation activity, have a present value of costs
discounted at 4 percent over the study period of $226.9
million. Adoption of the conservation plan represented by
the City Report Plan (scenario 2) increases present value of
study period expenditures by $203.8 million. The scenario
which makes full utilization of wastewater by recharging all
excess wastewater, scenario 9b, increases these expenditures
$379.8 million. The cost of these water-substitution
conservation programs is over twice current water costs. If
these costs are passed on to the consumer in the form of
increased prices, the losses in consumer welfare will be
large and may outweigh the benefits.
216
Loss in consumer welfare was examined for a single
type of program, reduction-in-use (scenarios 8a and 8b).
The case evaluated, which cut water use by 14 percent
involved over $12,000 per acre-foot per year in estimated
consumer utility losses. Comparing this with a present
valued net increase in expenditure of $79.12 per acre-foot
of groundwater conserved under scenario 2, shows that large
uncounted utility losses may be expected under the
reduction-in-use programs.
Expenditures for desalting CAP water were calculated
and were found to be high. Desalting has been discussed as
a means to reduce potential salinity damage but as it is
seen here, the costs probably exceed any benefit which may
be generated. Desalting is no panacea for reducing the
costs of the salts in imported water. Salinity degradation
seems to defy technological remedies.
Terminal Value and Conservation
At the end of the study period, 2025, the quality of
the groundwater will be degraded and we will have made large
groundwater conservation expenditures. Table 41 presents a
summary of the both the total and per acre-foot expenditures
for alternative water supplies, the amount of groundwater
conserved, and the salinity in the aquifer in 2025 for the
scenarios evaluated.
217
Table 41. Estimated Present Value of Total Costs of
Salinity Damage and Total Expenditures for
Groundwater Conservation Under Various
Scenarios. -- 1986 Dollars Discounted at
4 Percent and Summed Over the Study Period.
Scenario
Salinity
Expenditures
Million Dollars
Total Cost
1
14.9
229.6
244.5
2
83.1
485.4
568.5
3a
96.6
509.3
605.9
3b
108.8
657.5
766.3
4a
48.6
610.1
658.7
4b
12.3
718.3
730.6
5
77.9
391.7
469.6
6
83.9
498.7
582.6
7
83.5
498.7
582.2
8a
81.9
434.0
566.6
8b
25.3
205.5
230.8
9a
84.6
636.3
720.9
9b
87.2
787.1
874.3
218
The implied loss in capital value of the resource
should be considered in choosing among polices with similar
conservation effects but different terminal values. The
terminal value of the aquifer is comprised of quality and
quantity. Scenario 4b, desalting CAP water to 300 mg/1,
generates the highest total costs and costs per acre-foot,
conserves no more groundwater than the City Report Plan
(scenario 2), but ranks among the lowest in final salinity.
The decision to adopt this program of desalting, costs over
$500 million more than the base case and keeps the terminal
date increase in salinity down to 60 mg/1 over the base
case. Comparing desalting to 300 mg/1 with the City Report
policy shows desalting to cost $300 million more than the
City Report Plan and to have a terminal salinity value of 58
mg/1 less.
For the scenario with artificial recharge of all
excess wastewater, (scenario 9b), the increased capital and
salinity costs are $380 million. This scenario yields the
largest amount of groundwater conserved but also generates
the highest final salinity, 533 mg/l. It should be asked:
Is 1.47 million acre-feet in conserved groundwater worth the
increases over the base case of $380 million in conservation
expenditures plus the 161 mg/1 in salinity degradation of
this scenario?
The total capital costs per acre-foot of groundwater
conserved are arrayed by percent groundwater conserved in
219
Figure 13. Reasons behind the low cost per acre-foot for a
reduction-in-use groundwater conservation program with
alternative water supplies (scenario 8a) when compared to
the City Report Plan are evident, less water is pumped and
less CAP water is purchased. The reduction-in-use program
without alternative water supplies (scenario 8b) is negative
in both change salinity concentration and capital cost per
acre-foot and does not appear in the figure. The loss in
consumer surplus associated with the reduction-in-use
scenarios 8a and 8b is very high, however. On a per acrefoot conserved basis, it may exceed $12,000.
The groundwater conservation programs which employ
the artificial recharge of excess wastewater (scenarios 9a
and 9b) show the highest conservation potential because of
the addition of recharged wastewater which offset the
pumpage account. The groundwater conservation amount is
high and spreads out the costs on a per acre-foot conserved
basis.
There are 5 scenarios that conserve 48 percent of
the groundwater pumped in the base case, the lowest-cost one
is the City Report Plan (scenario 2). The programs which
increase CAP water deliveries (scenarios 3a and 3b) conserve
more groundwater in proportion to the increased deliveries
of CAP water. The scenarios which employ alternative water
supplies and do not increase wastewater irrigation
(scenarios 2, 3a, 3b) or which artificially recharge large
220
4b El
200 59
4a9
3a
6,7 ii D
O
0 9a gb 0
3b
2
1 00 -
D
8a 9
1
o a
o
i
.
.
20
40
60
80
Percentage Groundwater Conserved
Costs per
Acre-foot by Percentage Groundwater Conserved.
Figure 13. Distribution of Total
221
amounts of artificial recharge (scenarios 9a and 9b) all
seem, on the basis of average cost per acre-foot conserved,
to be the least expensive alternatives and indeed are all
under consideration by the city. However, this figure does
not portray long-run consequences of salinity degradation.
Salinity values in 2025 for these policies are 490 mg/1 for
the City Report Plan, 495 mg/1 for a 6 percent increase in
CAP deliveries, 501 mg/1 for a 12 percent increase in CAP
deliveries, 512 mg/1 for artificial recharge of 50 percent
of excess wastewater supplies, and 533 mg/1 of 100 percent
of excess wastewater supplies.
Recommendations for Further Research
The analysis presented here of the costs of
groundwater conservation programs was limited to a partial
evaluation of the damages. A complete costing of the
damages generated by salinity degradation for all water
using sectors would allow more complete evaluation and a
clearer comparison of choices. The costs should include not
only the value of capital recovery but also the value to the
consumer.
The hydrologic evaluation was based on a simplified
mass balance model. The sensitivity of salinity degradation
to effective aquifer volume suggests that attention to well
field placement and wastewater reuse is merited. Given
conservation goals, these spatial policy parameters appear
222
to have the greatest potential for reducing the degradation
side-effects of conservation. Hydrologic modelling of the
water cycle in the Tucson Basin is a necessary tool to
integrate policy goals and the physical constraints of the
region.
Lastly, avenues need to be explored to find
institutional means to integrate quantity and quality
considerations in policy formulation. It is a truism that
maximizing a single variable at the expense of all other
considerations will not yield a global maximization. To
make policy and only consider quantity goals at the expense
of all else will, in all eventuality, generate costly
mistakes.
REFERENCES
Anderson, Jay C., and Alan P. Kleinman, "Salinity Management
Options for the Colorado River", Utah Water Research
Laboratory, Utah State University, Water Resources
Planning Series Report, June 1978.
Anderson, Lee G., and Dwight R. Lee, "Optimal Governing
Instrument, Operation Level and Enforcement in
Natural Resource Regulation: The Case of the
Fishery", American Journal of Agricultural
Economics, August 1986.
Arrow, K. J. and Fisher, A. C., "Environmental Preservation,
Uncertainty, and Irreversibility", Quarterly Journal
of Economics, May 1974.
Arrow, K. J. and Lind, R. C., "Uncertainty of the Evaluation
of Public Investment Decisions", American Economics
Review, Vol. 40, June 1970.
Babcock, J. A. and Hix, G. L., "Annual Static Water Level,
Basic Data Report: Tucson Basin and Avra Valley,
Pima County, Arizona for 1981", City of Tucson,
Tucson Water, Planning Division, 1981.
Baumol, William J., Economic Theory and Operations Analysis,
Prentice-Hall Inc., Englewood Cliffs, New Jersey,
1977.
Baumol, William J. and Wallace E. Oates, The Theory of
Environmental Policy: Externalities, Public
Outlays, and the Quality of Life, Prentice-Hall,
Inc., Englewood Cliffs, New Jersey, 1975.
Beck, R. W. and Associates, "Water Rates Report for Tucson
Water, City of Tucson, Arizona", March 1983 and 1984
(two separate reports).
Beck, R. W. and Associates, "Final Water Rates Report for
Tucson Water", May 1986.
223
224
Black and Veatch, Engineers, "Economic Effects of Mineral
Content in Municipal Water Supplies", Research
Development Program Report, Office of Saline Water,
Washington, D.C., 260:42-47, May 1967.
Black and Veatch, Engineers, "Report on Water Rates for
Tucson Water", Kansas City, Missouri, 1982.
Bookman-Edmonston Engineering, Inc., "Report on Use of
Reclaimed Water for Irrigation", Phoenix, Arizona,
1978.
Bouwer, Herman, "Wastewater Reuse in Arid Areas", In
Wastewater Reuse, Editor:
E. J. Middlebrooks, Ann
Arbor Science Publishers, Inc., Ann Arbor, Michigan,
137-180, 1982.
Bowman, R. S., and R. C. Rice, "Chemical Tracers--Their Use
in Measuring Deep Percolation Rates", In Proceedings
of the Third Deep Percolation Symposium, Arizona
Department of Water Resources, Phoenix, Arizona,
November 7, 1984.
Buchanan, J. M., "External Diseconomies, Corrective Taxes
and Market Structure", American Economic Review,
59:174-177, 1969.
Bureau of Reclamation, "Draft: Environmental Impact
Statement, Tucson Aquaduct--Phase B, Central Arizona
Project", Filing Date: December 18, 1984.
Lower
Colorado Region. U.S. Department of the Interior.
CH2M Hill/Rubel and Hager, "Tucson Metropolitan Wastewater
Reuse Assessment", City of Tucson, 1983.
Citizens Water Advisory Committee, "Summary Report on Water
Policy and Issues", September 1977.
City of Tucson, "Wastewater Division Annual Reports, 19511952 to 1974-1975."
Coase, R. H., "The Problem of Social Cost", Journal of Law
and Economics, 3:1-44, 1960.
Colorado River Basin Salinity Control Forum, "Water Quality
Standards for Salinity: Colorado River System",
July 9, 1981.
Colorado River Study Commission, "Report on Colorado River
Water Quality", March 1981.
225
Colorado River Water Quality Office, "Evaluation of Salinity
Control Programs in the Colorado Rive Basin",
submitted to Robert A. Olson, Acting Commissioner of
Reclamation, Department of the Interior, October
1984.
Condit, Robert, Personnel Communication and Review of
"Annual Water Reports", 1985.
Connell, Desmond D., Jr., "A History of the Arizona
Groundwater Management Act", Arizona State Law
Journal, 313, 1982.
D'Arge, Ralph C. and Larry Eubanks, "Municipal Damage
Estimation" and "Appendix 4, Municipal and
Industrial Consequences of Salinity in the Colorado
River Service Area of California", in Anderson, J.
C. and A. P. Kleinman, Salinity Management Options
for the Colorado River, Utah Water Research
Laboratory Report, 78-003, 1978.
Davis, Stephen E., "Tucson Needs for Central Arizona project
Storage", in Hydrology and Water Resources in
Arizona and the Southwest. Proceedings of the 1984
Meetings of the Arizona Section--American Water
Resources Association and the Academy of Science.
Davidson, E. S., "Geohydrology and Water Resources of the
Tucson Basin, Santa Cruz and Pima Counties,
Arizona", Geological Survey Water Supply Paper 1939, U.S. Government Printing Office, Washington,
D.C., 1973.
bavis, S. E., "Tucson's Needs for Central Arizona Project
Storage", in Hydrology and Water Resources in
Arizona and the Southwest, Volume 8, 1981.
DeBoer, L. M., and Larson, T. E., "Water Hardness and
Domestic Use of Detergents", Journal of the AWWA,
Volume 53:829, July 1961.
Gordon, Arthur J., Debra L. Daniel, and Terry M. Turner,
"Effects of Arizona's 1980 Ground Water Code on the
Prevention of Ground Water Degradation from
Agricultural Practices", Arizona Department of
Health Services, Unpublished, 1985.
Griffin, Adrian H., "An Economic and Institutional
Assessment of the Water Problem Facing the Tucson
Basin", Ph.D. Dissertation, University of Arizona,
May 1980.
226
Ingram, Helen M. and Scott J. Ullery, "Policy Innovation and
Institutional Fragmentation", Policy Studies
Journal, Volume 8:5, Spring 1980.
Johnson, R. Bruce, "Hydrologic Factors Affecting Ground
Water Management for the City of Tucson, Arizona",
Hydrology and Water Resources in Arizona and the
Southwest, 8:1-8, 1978.
Kneese, Allen, "The Environmental Decade (Action Proposals
for the 1970's)", U.S. Congress, House of
Representatives, Subcommittee on Government
Operations, 91st Congress, 2nd Session, U.S.
Government Printing Office, Washington, D.C., 190197, 1970.
Laney, R. L., "Chemical Quality of Water in the Tucson
Basin, Arizona", U.S. Geological Survey Water Supply
Paper 1939-D, 1972.
Martin, Peter, "Evaluation of Ground Water Quality in the
Cortaro Area", M.S. Thesis, The University of
Arizona, unpublished, 1980.
Martin, William E. and Helen M. Ingram, Planning for Growth
in the Southwest, National Planning Association,
1985.
Martin, William E., Helen M. Ingram, Nancy K. Laney, and
Adrian H. Griffin, Saving Water in a Desert City,
Resources for the Future, Washington, D.C., 1984.
Martin, William E. and John F. Thomas, "Policy Revelance in
Studies of Urban Water Demand", American Journal of
Agricultural Economics, Volume 22, Number 13,
December 1986.
McGuckin, J. Thomas, and Young, Robert A., "On the Economics
of Desalination of Brackish Household Water
Supplies", Journal of Environmental Economics and
Management, Volume 8, 1:79-96, 1981.
McLean, Thomas M. and Stephen E. Davis, "The Alternatives
and Impacts Associated with a Future Water Source
Transition for Tucson Water", Hydrology and Water
Resources in Arizona and the Southwest, Proceedings
of the 1981 Meeting of the Arizona Section of the
American Water Resources Association and the
Hydrology Section of the Arizona Academy of
Sciences, 11:59-65, 1981.
227
Metcalf and Eddy, Engineers, "The Economic Value of Water
Quality", Research Development Program Report No.
770, Office of Saline Water, Washington, D.C., 3369, January 1972.
Montgomery-Johnson-Brittian, Appendix A to Water Quality
Objective Report, Data Base memorandum, 1983.
Orange County Water District, Water Quality and Consumer
Costs, Santa Ana, California, 45-63, May 1972.
Patterson, W. L., and Banker, R. F., "Effects of Highly
Mineralized WAter on Household Plumbing and
Appliances", Journal of the AWWA, September 1968.
Pima Association of Governments, "Assessment of Nitrates",
Upper Santa Cruz Basin Mines Task Force, 1983.
.
"Green Valley-Cortaro
Area Management Plan", Draft, January 1985.
Postillion, Frank G., "Evaluating Alternatives for
Groundwater Quality Management in Green Valley-Sahuarita, Arizona", Masters Thesis, Department of
Wastershed Management, December 1985.
Randall, Alan, Resource Economics: An Economic Approach to
Natural Resource and Environmental Policy, Grid
Publishing, Columbus, Ohio, 1981.
Randall, Richard and Bruce Johnson, "A Demonstration
Recharge Project in Tucson, Arizona", in Proceedings
Second Symposium on Artificial Recharge in Arizona,
Floyd L. Marsh (Editor), Water Resources Research
Center, University of Arizona 252-262, September
1985.
Samuelson, Paul Anthony, Foundations of Economic Analysis,
Atheneum, Inc., 1979.
Siemak, Robert "Water Treatment Presentation", in Tucson
Water Treatment Plant Project--Phase I Preliminary
Investigations, Appendix C to Water Quality
Objective Report. Montgomery-Johnson-Brittain.
Report reproduced by City of Tucson, 1984.
Snow, Lester, "Role of the First Management Plan", Statement
to GUAC, August 13, 1983.
TAMA, Annual Report, Computer Printout (unpublished) of
Pumpage, 1985.
228
Tihansky, Dennis P., "Economic Damages from Residential Use
of Mineralized Water Supply", Water Resources
Research, Volume 10, 2:145-154, April 1974.
Tinney, J. Craig, "Summary of Agricultural Planning Unit
Acreage", Tucson AMA/Arizona Department of Water
Resources, Presented to the Agricultural Technology
Advisory Group, Unpublished, September 26, 1985.
Todd, D. K., Ground Water Hydrology, John Wiley, New York,
1976.
.
"Ground Water", in Handbook of Applied
Hydrology, Chow, V. T. (Editor), McGraw-Hill Co.,
pages 12-1 to 12-30, 1964.
Todd, D.K. and D. E. O. McNulty, "Polluted Ground Water",
Water Information Center, Port Washington, New York,
1976.
Tucson Active Management Area, "Management Plan for First
Management Period 1980-1990", Arizona Department of
Water Resources, December 1984.
"Inventories of Irrigated
.
Farmlands by Planning Unit Obtained from Irrigation
Grandfathered Rights Applications", Arizona
Department of Water Resources, Unpublished data,
1984b.
Turvey, Ralph, "On Divergences Between Social Cost and
Private Cost", Economica, Vol. XXX:309-313, 1963.
U. S. Geological Survey, "Southwestern Basins and Ranges",
Atlas HA-55, U.S. Geological Survey, undated.
Weinberger, L. W., D. G. Stephan and F. M. Middleton,
"Solving our Water Problems--Water Renovational
Reuse", Annual of the New York Academy of Science,
136:131-154, 1966.
Wilson, C. G., "Cortaro Area Pollution Source Assessment",
Water Resources Research Center, University of
Arizona, Tucson, Arizona, April 1983.
Wilson, L. G., and K. J. DeCook, "Ground WAter Recharge from
Cuban Runoff and Irrigation Returns", Proceedings of
the First Deep-Percolation Symposium, May 1-2, 1980.
229
Yu, John, "A Multi-Criteria Water Quality Index for Optimal
Allocation of Reclaimed Municipal Wastewater", Ph.D.
Dissertation, University of Arizona, unpublished,
1977.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement