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18 Estimating Economic Impacts of Salinity... (37 percent). Irrigated farming leaches salts from the saline soils found in the Basin. N m CJ:) 0) The salinity of the Colorado has both regional and national implications. RegionaUy, irrigation of crops with excessively saline water may reduce yields or even prohibit growing of certain types of crops. Domestic use of saline water can require extra treatment to meet secon- dary drinking water standards (500 mgiL) or to improve palatability for drinking or cooking. Saline water can also damage plumbing and uten- sils and a1fect discretionary purchases of householders. These regional penalties of saline water use are described and quantified in sub- sequent chapters of this report. Nationally, the impact of Colorado River salinity affects our relations with the nation of Mexico. Minute 242 of the International Boun- dary and Water Commission of the United States and Mexico addressed the problem in 1973 with the result that the United States agreed to deliver an average of 1.36 maf of Colorado River water each year at Morales Dam which is at an average annual salinity no greater than 115 ppm :t 30 ppm more than that measured at Imperial Dam. Salinity Control Programs and Legislation The Bureau of Reclamation began a general investigation program (Colorado River Water Quality Improvement Program) in 1971. The next year, a cooperative program was under- taken by the Departments of the Interior and Agriculture, the U.S. Environmental Protection Agency (EP A), and the seven states of the Colorado River Basin to maintain salinity levels at or below the levels then existing on the Colorado main stem. Three major legislative acts subsequently have dermed and implemented this broad salinity control program. In 1972, Public Law 92-500, the Federal Water Pollution Control Act as amended ("The Clean Water Act") was inter- preted by EP A as requiring water quality stand- ards for salinity in the Colorado River. In 1973, the Colorado River Basin Salinity Control Forum was organized as a mechanism to establish salinity standards and to promote inter- state cooperation in the Basin and, among other purposes, to develop numeric criteria and a plan of implementation for salinity control for the river, to be recommended to each state for its adoption. Subsequently, the seven Colorado River Basin (CRB) states adopted the criteria and a plan of implementation for maintaining salinity at the numeric criteria for Hoover, Parker, and Imperial Dams and the EPA approved the plan. In 1974, Public Law 93-320, the Colorado River Basin Salinity Control Act, established the Colorado River Basin Advisory Council, made up of representatives of the seven Basin states, to make recommendations to the three named federal agencies of the progress of implementa- tion of the program. P.L. 93-320 also authorized construction of four salinity control units and studies of another twelve units. In 1984, the Congress passed Public Law 98- 569, amending P.L. 93-320. The amended law authorized two additional salinity control units and directs the Secretaries of the Interior and Agriculture to give preference in construction to those salinity control projects that reduce salinity at the least cost per unit of salinity reduction. A major component of the Act was authorization of a voluntary onfarm program within the USDA program. Past and Anticipated Future Salinity Levels of the Colorado River, 1973-2010. The Bureau of Reclamation in 1985 developed the data shown in Figures 3, 4, and 5, Salinity Projections at the three stations for which numeric criteria have been adopted. These graphs illustrate flow-weighted average annual estimates of salinity levels (in mgiL of total dissolved solids) at each of three major points of diversion along the Colorado River, i..e., Hoover, Parker, and Imperial Dams. Both the past and future salinity values are flow- weighted average annual estimates. Future estimates have been developed by simulation using the Colorado River Simulation System (CRSS).