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. 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