Water in the Tucson region is a limited resource. Ground water has been developed in the past as a primary source of water to supply all uses, and the present possibility emerges that the output products of this system of uses can be salvaged and combined with the primary source for further use. A water-salvage industry is conceived in which the outputs of water uses, augmented by storm runoff, become the inputs to the industry; water treatment is the main activity of the industry; and water of improved levels of quality is its principal output. The regional sources of salvageable water are defined as 1) domestic-industrial effluents from the metropolitan sewage collection and disposal system, 2) domestic and industrial effluents from isolated locations, called discrete sources, and 3) storm runoff from both urban and non-urban watersheds. At the 1970 level the available quantity of such waters is estimated to be in excess of 35,000 acre-feet per year and increasing. Historically, only the first of these classes of water has been salvaged and reused in the Tucson region, and then only for irrigation of fiber, field, and forage crops. The current level of treatment technology is adequate to upgrade the quality of any or all of these salvageable waters to the requirements of additional agricultural as well as recreational and industrial uses. What needs to be determined is the degree of economic feasibility of allocating the salvaged waters to these uses under the prevailing institutional constraints. The selected types of potential uses in the water reuse subsystem are industrial uses as represented by power plants and by mining and milling operations, the recreational uses of urban fishing and boating activities and park irrigation, and agricultural uses in the form of irrigation of field and forage crops, cotton, orchard, and produce. Each of the classes of use is embodied in an industry which realizes a net return to the water input. An urban recreation survey indicates, for example, that under maximum intensity of use the net returns to water for fishing and boating might be as much as $500 per acre-foot. The objective relative to all uses is to maximize aggregate net returns to water from the combined supply, and the measure of effectiveness is a net benefit function representing the difference between gross benefit and incremental cost for water in each activity. The available salvaged waters are substituted incrementally for ground water in the total regional water supply function. Calculated numerical examples of allocation of combined supplies, in a linear programming format with restraining institutional conditions, demonstrate that under optimal allocation the treated municipal-industrial effluent would be used to some extent to serve not only agricultural but recreational and industrial uses. This result is attributable in part to the condition that the metropolitan water agencies bear the obligation of primary and secondary treatment at no direct cost to the user. Under benefit maximization this effluent also could serve a significant part of the water needs of the remote mining operations; under existing institutional arrangements, however, this industry is minimizing cost by pumping from the nearest available ground-water source. Preliminary calculations indicate that structural adjustments involving construction of new facilities in the Tucson region for the utilization of salvaged waters could be economically justified, their feasibility being highly sensitive to the extent of use for urban recreational activities.

Position paper.

Partial Technical Completion Report, Office of Water Resources Research, Project A-020-ARIZ / Grant Agreement No. 14-31-0001-3203 / Period of Investigation: 7/69-6/71 / Potential uses or reuses of salvageable waters in the Tucson region were examined, and costs and benefits related to such uses were evaluated. The quality of salvageable waters as determined in exploratory sampling was compared with water quality standards and criteria appropriate for agricultural, recreational and selected industrial uses. A tableau was then constructed which showed the type and estimated cost of conventional water treatment that would be required for each source-to-use combination. Finally, an estimate was made of unit net benefits to be anticipated from salvageable water input to these uses, and the net benefits were applied in several test calculations to illustrate mixed allocations of the various salvaged waters to the selected uses.

With the population of urban areas rapidly increasing, a much greater demand is being placed on existing water supplies. The arid southwestern region of the United States, in particular, is experiencing large population increases while possessing limited water resources. Tucson is a representative city in the region facing problems of providing an adequate water supply to the public in the future. Presently, Tucson is being supplied entirely with groundwater. Increases in population and industrial activities, however, have caused a steady decline of the groundwater table in the Tucson Basin. The reclamation of wastewater and the importation of water have been studied as alternatives in alleviating the annual decline of the groundwater table. Problems still exist, however, preventing the immediate use of both aforementioned supplies of water. In developing the water resources of an area, every possible source of water must be evaluated. A source which has not received much attention, but which merits much attention, is the water occurring as urban runoff following intense storms. In order to evaluate the potential of urban runoff as a water supply, the study includes investigations of water quality, water treatment through storage and coagulation, and problems involved with the utilization of storm water. Samples of runoff from three diversified urban watersheds in the Tucson area were analyzed for bacterial, mineral, pesticide, solids, and chemical oxygen demand concentrations. The watersheds were characterized according to the percentage of the total area devoted to a particular land use. In addition, the hydrologic characteristics of each storm were tabulated. Correlation coefficients were determined between the quality parameters and the watershed and hydrological characteristics. Development of regression equations equating quality parameters as a function of both watershed and hydrological characteristics was also undertaken. The final analysis of the quality study involved the determination of relationships between quality parameters of chemical oxygen demand, total coliforms and suspended solids and the point of time on the hydrograph at which runoff was sampled. Prior to beneficial use of the urban runoff, treatment to varying degrees will be required. In the second phase of this study, the efficiency of treatment by the simple methods of storage and alum coagulations was studied. Five gallon samples were collected from randomly selected storms and used either in the storage or coagulation study. Changes in chemical oxygen demand, solids and bacterial concentrations were evaluated at selected intervals during storage for a period of a week. Jar test studies utilizing varying doses of alum were undertaken on water collected from each of the watersheds, determining the efficiency of chemical oxygen demand, turbidity, and total coliform removals. The final phase of the study involved discussion of the problems attendant with the planning and design of treatment facilities. Included in this phase were sections involving water quality standards and the related treatment processes, waste sludge production and treatment methods, and costs pertaining to treatment. Legal aspects of appropriating the urban runoff were considered and the possible conflicts between upstream and downstream interests noted. The study concluded with a demonstration of the application of dynamic programming for optimally planning the location and capacity of storage treatment facilities at urban sites.

With groundwater resources becoming less available in the physical, economic, and legal senses, water reuse is rapidly gaining momentum in the arid West. An institutional assessment of water reuse in the Tucson Basin in Arizona indicates that despite institutional changes encouraging the substitution of effluent for native groundwater, many opportunities for water reuse are precluded by existing water rights arrangements and insufficient economic incentives. An economic assessment compares potential benefits and costs of implementing water reuse plans for the Tucson area with potential benefits and costs of alternative water-supply scenarios in which similar quantities of water are provided from other sources. Alternative water sources include pumping native groundwater, "reallocating" water saved through reduction in low value water uses, and importing surface water and groundwater from other basins. The results of this study indicate that at the present time, there is no convincing economic justification for increasing water reuse as planned by the City of Tucson. Not only are reduction in use and importation alternatives less costly to implement than increasing effluent use, they also save more groundwater. The results of the economic assessment indicate that the citizenry of the Tucson Basin would be better served if planned increases in the use of effluent in the Tucson metropolitan area were postponed until the costs become more competitive with the costs of alternatives.

Secondary effluent from the Roger Road Wastewater Treatment Plant undergoes tertiary treatment of dual media filtration and chlorination. The tertiary effluent is recharged and subsequently extracted for irrigation in Tucson, Arizona. The fate of chlorinated organics in this recharge system was investigated in this research. Nonpurgeable organic carbon was found to reach a constant level in the groundwater after being recharged. Not all of the organic carbon was removed from the water. Nonpurgeable organic halogens increased as they flowed away from the recharge basins. Reasons for this increase were not determined. Attempts were made to define the apparent molecular weight distribution of the NPOC and the NPOX. Measured values of the two parameters were consistently greater after the analytical processing than before, making the determination impossible.