the value of the ground water resource. While the RFF study noted many uncertainties, those that pertain to the benefit side of the equation are substantial enough to warrant further research.

Canter, L. W., and D. A. Sabatini. 1994. Contamination of public ground water supplies by Superfund sites. International Journal of Environmental Studies, Part B 46:35-57.

Spofford, W. O., A. J. Krupnick, and E. F. Wood. 1989. Uncertainties in estimates of the costs and benefits of ground water remediation: Results of a cost-benefit analysis. Discussion Paper QE 89-15. Washington, D.C.: Resources for the Future.

The objective of this case study is to illustrate how incorporating the economic concepts and techniques developed in Chapters 1 through 4 of this report can assist in management of ground water resources over the long term. Unlike the previous case studies, which are limited to reviews of existing work and demonstrations of value of ground water in various contexts, the Tucson case study illustrates the application of the conceptual valuation framework described in Chapter 3.

The Tucson case study is notable both for the diversity of ground water services it illustrates as well as for the urgency of policy attention the area's water management system requires. The intent is not to calculate the incremental change in value of services provided by ground water in the "with treatment" and "without treatment" condition but to identify the steps required to implement the valuation process in a real-world context. This case study simplifies and abstracts information from the actual Tucson situation in order to better illustrate the role of economic valuation in improving management of ground water resources.

Ground water provides numerous extractive services in Tucson, including residential, commercial, agricultural, and industrial water uses. The region's ground water resources also provide a range of in situ services, such as prevention of land subsidence, reservoir functions that will buffer future drought associated with shortages in surface water supplies, bequest value, and ecological services such as maintenance of riparian habitat. Policy-makers in Arizona have struggled to reduce the extent to which ground water supplies in the region are mined. Ground water policies have been put in place as a mechanism to ration and conserve supplies for future use. Alternative renewable surface water sup-