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C> N 1-'0 ~ Basin Salinity Control Program. In addition, the Secretary was authorized and directed to expedite completion of planning reports on 12 other units, one of which was the Glenwood-Dotsero Springs Unit. Among the natural sources of dissolved solids to the Colorado River, the largest of the point- source contributors (e.g., springs. geysers, mine drainage, and wells) to the upper Colorado River is in the reach between the mouth of the Eagle River near Dotsero and the mouth of South Canyon Creek west of Glenwood Springs. In this area, it has been estimated prior to this study thermal springs rising in or near the riverbed and associated ground-water systems contribute about 27,100 to 37,000 cu m (22 000 acre-it) of saline water containing 399,161 metric tons (440,000 tons) of salt annually. The PIQR (problem Identification and Qualification Report) identified concentrations of 9295 mg/L salt averaged annually at Dotsero Springs and 18,648 mg/L at Glenwood Springs. In this study, estimated flow weighted average values of 9954 mg/L for DS and 18,780 mg/L for Glenwood Springs were found. Of this amount, approximately 50 percent was contributed by known surface springs while the remaining tonnage was from subsurface inputs. Prior studies of the Glenwood- Dotsero Springs Unit indicated that salinity control measures have the potential of reducing the salt contribution to the Colorado River by at least 190,000 metric tons (209,000 tons) annually from the surface springs alone. Our study recently estimated the salt contribution as 174,700 metric tons (192,200 tons). This would result in a salinity reduction of more than 19 mg/L at Imperial Dam. Because of the significant salt contribution to the river, the salinity control program focused on the Glenwood Springs and Dotsero Springs point sources. Studies were initiated by CRWQO (Colorado River Water Quality Office) to characterize, quantify, identify beneficial uses, and find ways of preventing these waters from entering the Colorado River. A plan of study was initiated by the Bureau's UCR (Upper Colorado Region) in a report titled' 'Glenwood-Dotsero Springs Unit. Colorado, .Plan Formulation Draft Appendix". A characterization and application stucy of Glenwood Springs and Dotsero Springs waters was made by the Bureau's Engineering and Research Center, Division of Research. In anotner study, the Bureau's UCR contracted URS Corporation to make an investigation of the control and disposal of hot saline water from springs in the area of Glenwood Springs and Dotsero, Colorado. The results of this study were published in a report titled' 'Final Report, Phase I - Salinity Investigation of Glenwood-D.otsero Springs Unit". The UCR and URS chemical and physical data were consolidated with water analyses obtained by the Chemical Engineer- ingUnit. The Colorado River drains a total of 663,000 sq km (256,000 sq mi) in the United States and Mexico and carries a salinity burden that has historically averaged about 10 million metric tonnes ( 11 million English tons) annually. A number of sources contribute to this high salinity level. Approxi- mately half of Ihe present salt concentration in the Colorado River is man-induced (Le., irrigation return flow, reservoir evaporation, exports of water, municipal and industrial consumption, or con- tamination), and the other half is due to natural sources (Le., direct salt loading from natural springs and weathering of mineral-bearing rocks). At its headwaters in the mountains of north-central Colorado, the Colorado River has a salinity of only about 50 mg/L. However, the salinity progressively increases downstream as a result of water diversions and salt contributions from a variety of sources. In 1977, salinity averaged about 820 mg/L at Imperial Dam, the last major diversion point in the United States. Unless control mea- sures are taken, concentration will continue to increase, reaching levels, estimated by the USBR, of 1150 to 1210 mg/L at Imperial Dam by the year 2000. Water of 1000 mg/L or less salinity is gener- ally considered to be satisfactory for irrigating most crops, although con-centrations of 500 mglL can have detrimental effects on salt-sensitive crops. The U.S. Public Health Service recommends that public drinking water supplies contain less than 500 mglL. A-2