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N 0') Ut ;-. significant incre~sing costs as salinity levels surpass 500 mg/l." the maximum recommended in the U.S. Environm.ental Protection Agency Secondary Drinkirig Water Standards.2 Alternatives suggElsted for salinity control in the Colorado River Basin include (1) augmentation of the basin water supply, (2) reduction of salt loads by structural measures as well as management alternatives. and (3) curtailment of future water resource development. The feasibility and desirability of these three salinity control alternatives are influenced by the economics of such actions; e.g.. the relative justification from a benefit versus cost viewpoint. the reqognition of water rights. and the political and institutional forces surrounding each alternative. It is therefore n!lCeSSa ry from the nationa I economic efficiency viewpoint to estimate. as accurately as posSible, the economic impacts of changes in salinity levels upon users of the waters of the Colorado. The economic value of the reduction in salinity levels resulting From mitigation measures is necessary to judge the desirability of such measures. Similarly. the negative economic value of increases in salinity resulting from the salt loading effect of return flows of water development projectS is necessry to judge the desirability of such development plans. It is recognized that more than economic impacts result fr<i)m changing salinity. such as fish and wildlife. recreation. and environmental impacts. While recognizing that many other effects of salinity do exist. the overriding concern addressed here deals with the monetary effects upon direct users of Colorado River water. Potential damages or total penalty costs from adverse salii:lity .conditions can be defined as the sum of direct penalty costs incurred by water users and indirect penalty costs imposed on the economy of the region. 2 Pursuant to Safe Drinking Water Act approved December 16. 19741Public Law 93-523. 88 Stat. 1660). III. PHYSICAL IMPACTS OF SALINITY Evaluation of possible salinity effects on basin water users indicates that the major quantifiable adverse effects are primarily limited to agricultural. municipal. and industrial uses. Each of these uses is physically affected in different ways and consequently has singular alternatives available to mitigate adverse conditions. The following describes the significant physical effects. outlines feasible alternatives used to minimize losses. and presents the procedures implemented in this study to quantify the resultant impacts in preparation for economic analysis. A. Agriculture Salinity effects on agricultural uses are manifested primarily by limitations on the types of crops that may be irrigated with a given water supply and by reduction of crop yields as salinity, levels increase. Other conditions being equal. as salinity levels increase in applied irrigation water. salinity levels in the root tone of the soil also increase. Because different crops have different tolerances to salts in the root zone. limits are placed on the types of crops that may be grown. When salinity levels in the soil increase above the threshold levels of a crop. progressive impairment of crop growth and yield results. Irrigation water which has a high percentage of sodium ions may also affect soil structure and cause adverse effects on crop production. B. Municipal Domestic uses comprise the major utilization of. municipal water supplies. Total hardness. a parameter closely related to salinity, is of considerable interest in assessing water quality effects on these uses. Increases in the concentration of salinity and hardness lead to added soap and detergent consumption. corrosion. and scaling of metal water pipes and water heaters. accelerated fabric wear. added water softening costs. and in extreme cases. abandonment of a supply. According to measurements of hardness. raw water supplies derived from the Colorado River at or below Lake Mead would be classified as very hard. A 3 oi.