and livestock) uses approximately two-thirds of the total ground water withdrawn in the United States, with public supply (including domestic withdrawals) accounting for nearly a quarter of the total.

In the late 1970s and early 1980s, the U.S. Environmental Protection Agency (EPA) began to direct attention toward ground water pollution studies, emphasizing the identification and evaluation of pollution sources and source categories and subsurface transport and fate processes for both inorganic and synthetic organic chemicals. Also in the early 1980s, the inception of the Superfund program brought attention to the need to clean up contaminated soil and ground water and led to major remediation programs by EPA and the Departments of Defense and Energy. In 1984 EPA adopted a ground water protection strategy that focused on land use planning, engineering control measures, and management practices that could be used to prevent ground water contamination and thus protect ground water quality.

The Safe Water Drinking Act of 1986 included a wellhead protection program to further encourage such pollution prevention efforts by state and local governments. EPA has continued to promulgate policies and related guidance to stress the importance of protecting renewable ground water resources from contamination and thus minimize the need for remediation efforts (U.S. EPA, 1991).

Ground Water Valuation Terminology

The inherently interdisciplinary nature of the ground water valuation problem becomes obvious in the confusion about terminology used to describe it. There is no commonly used ground water valuation terminology and no one set that is obviously superior. Two different sets of valuation terminology are displayed in Table 1.3. The first is based upon the physical state of the ground water from which value is derived. The primary distinction is between extractive values, which occur as a result of the extraction of ground water and subsequent consumptive use, and in situ values, which occur as a consequence of leaving the water in the aquifer. Extractive values include municipal, agricultural, and industrial uses of water, uses that nearly always include a sizable component of consumptive use. In situ values are derived from the services provided by leaving water in the aquifer and typically do not involve consumptive transformation of the water. In situ values include ecological values, buffer values, values associated with the avoidance of subsidence, recreational values, existence values, and bequest values.

The second set of terminology comes from the economic literature or the valuation of ground water resources which classifies ground water values in terms of use values and nonuse values. This distinction acknowledges that use values are associated with both consumptive and nonconsumptive uses of water, including ecological uses, buffering, subsidence avoidance, and recreation. By contrast, nonuse values, including existence and bequest value, may occur when



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