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"'.)" :~-"".. .-;y.:;.. .- m C\l r-.. CHAPTER I INTRODUCTION f.':; o o A monitoring plan for Stage One was developed by the Bureau in October 1980 as a guide for the acquisition and analysis of data to determine the effects of Stage One construction on the salinity of the Colorado River. Measurements and samples taken bi-monthly from observation wells provide base data for evaluating the effects of the unit on ground-water flows and quality. Seven of these wells have continuous water-level recorders. In addition to ground-water monitoring, the program includes weekly measurements of water quantity and quality in tributary drains. Samples are also taken from canals where they enter and leave the Stage One area. The results from the water quality monitoring will be used by the Sec- retary of the Interior to assess the effectiveness of the Stage One devel- opment in reducing salt loading to the Colorado River. The Secretary's findings will form the basis for reconunendations to the Congress concerning further construction on the Grand Valley Unit. Wildlife resources are also being monitored in the Stage One area to determine the project I s effect on wildlife habitat, recreational use of wild- life, and wildlife populations. Studies were initiated in 1981 under con- tract with the Colorado Division of Wildlife. Annual reports will be prepared with completion of the final report scheduled in September, 1984. Background If salinity increases in the Colorado River are not controlled, expen] sive associated problems will continue to occur and opposition to develop- ment of compact-apportioned water by the Upper Basin States could occur. The Colorado River, at its headwaters in the mountains of north-central Colorado, has a salinity of only about 50 mg/L which progressively increases downstream as a result of water diversions and salt contributions from a variety of sources. In 1979 the salinity averaged about 809 mg/L at Imperial Dam, the last major diversion point in the United States. Without control measures the concentration at Imperial Dam is expected to increase and could reach 1,150 to 1,210 mg/L by the year 2000. ,later of 1,000 mg/L or less is satisfactory for irrigating most crops, although concentrations of 700 to 800 mg/L can have detrimental effects on salt--sensitive crops. The Environmental Protection Agency (EPA) reconunends that public drinking water supplies contain less than 500 mg/L. Water users in the Las-Vegas-Los Angeles-San Diego area and irrigators in southern California and Arizona are affected most by this salinity. Mu- nicipal and industrial water users experience economic losses in the form of increased water treatment costs, accelerated pipe corrosion and appliance wear, increased soap and detergent needs, and decreased drinking water pal- atability. For irrigators, the higher concentrations cause decreased crop yields, altered cropping patterns, increased leaching and drainage re- quirements, and increased management costs. Quantified losses in the Lower 3