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o C'lJ r-- ~...::- CHAPTER I INTRODUCTION o '-', ~. Basin States attributable to ~rease of 1 mg/L of salinity uary 1981 prices. ------- salinity average $472,000 annually for each in- in the range of 875 to 1,225 mg/L based on Jan- -- The United States is obligated to an annual delivery of 1.5 million acre- feet of Colorado River water by a 1944 treaty with Mexico. In 1973 the United States and Mexico agreed that the total dissolved solids concentration of water delivered to Mexico would have a salinity of no more than 115 2: 30 parts per million greater than the average salinity of water at Imperial. Dam. The seven-state Colorado River Basin Salinity Control Forum has numerical salinity criteria for three points on the lower mainstem of the river. These standards have been adopted by each of the Basin States and are approved by EPA. If these standards are to be met, about 2.8 million tons of salt will have to be removed from the system annually soon after the turn of the century. The criteria for the three locations are as follows: Below Hoover Dam Below Parker Dam Imperial Dam 723 mg/L 747 mg/L 879 mg/L In recognition of these facts, Congress passed the Colorado River Basin Salinity Control Act (Public Law 93-320) on June 24, 1974, .mich directed the Secretary of the Interior to construct the Grand Valley and the other units and to expedite the investigation, planning, and implementation of the salin- ity control program as described in Chapter VI of the Secretary's report enti- tled Colorado River Water Quality Improvement Program, February 1972. The Secretary was also directed to implement a salinity control policy for the Colorado River. This implemented policy essentially adopted the "Conclusions and Recommendations" published in the Proceedings of the Reconvened Seventh Session of the Conference in the Matter of Pollution of the Interstate Waters of the Colorado River and Its Tributaries in the States of California, Colo- rado, Utah, Arizona, Nevada, New Mexico, and Wyoming. The conference was held in Denver in April 1972 under the authority of Section 10 of the Fed- eral Water Pollution Control Act (33 U.S.C. 1160) and the policy was approved by the Administrator of the Environmental Protection Agency in June, 1972. In addition, the Secretary was instructed to carry out the completion of planning reports on 12 units (a thirteenth was later added). Feasibility level inves- tigations for 10 of the 13 planning units were specifically authorized by Pub- lic Law 96-375 (October 3, 1980). J Level of Detail The Grand Valley Stage Two investigations will be conducted on the pre- mise that the salt reduction efforts on Stage One will be successful and are , cost effective. Cost effectiveness, the major economic determinant of the ~ value of a salinity control plan, is the annual cost of reduoing the salinity 4