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SUMMARY (Continued) . Problems and Needs At its headwaters in the mountains of north-central Colorado, the Colorado River has a salinity concentration of 50 milligrams per liter (mg/L). The concentration progressively increases downstream because of water diversions and salt contributions from a variety of sources. In 1985, salinity averaged 607 mg/L at Imperial Dam, the last major diver- sion point in the United States. Without any control measures and in combination with future development in the Colorado River Basin, Recla- mation estimates the concentration will increase, reaching levels of 963 mg/L at Imperial Dam by the year 2010. In response to the Federal Water Pollution Control Act and its amendments, the seven Colorado River Basin States adopted and the Environmental Protection Agency (EPA) approved numeric criteria for three locations on the Colorado River, as listed in the table below. The goal of the salinity control program is to maintain concentrations at or below these criteria. Numeric on the criteria for salinity lower Colorado River Annual flow-weighted concentration (mg/L) 723 747 879 . Station Below Hoover Dam Below Parker Dam At Imperial Dam The Dirty Devil River Basin contributes about 150,000 tons of salt annually to the Colorado River System. The Dirty Devil River is formed by the confluence of the Fremont River and Muddy Creek and flows gener- ally in a southerly direct ion to the upper arm of Lake Powell. The river drains a total of approximately 4,300 square miles. For the water years 1977 through 1980, an annual average of approximately 150,000 tons of salt and 75,000 acre-feet of surface water, as measured at Poison Springs, left the Dirty Devil River Basin. As shown in the figure on the following page, the Muddy Creek tributary contributes an annual average of 86,000 tons of salt transported by 25,000 acre-feet of water. The Fremont River tributary annually contributes 51,000 tons of salt transported by 47,000 acre-feet of water. Below the confluence of the Fremont River and Muddy Creek, small springs and surface runoff contrib- ute an estimated 13,000 tons in 3,000 acre-feet of water. . Sources of salt in the Fremont River are primarily from natural sur- face runoff and irrigation return flow. A few small springs'contribute insignificant quantities. The waters from these sources are all low in concentrations of total dissolved solids. Sources of salt in Muddy Creek, mainly derived from the dissolution of salt from geologic formations, are irrigation and coal mine return flows near Emery, natural surface runoff, and saline springs primarily in Emery South Salt Wash and Hanksville Salt Wash. Unit studies focused on Muddy Creek and its tributaries because of the large salt load and small water volume, indicating salinity control may be accomplished more economically here than on the Fremont River. 002310 S-2