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o l\;) ,.... u"t From Eisenhauer -- Salinity not only has economic effects on water users in the lower basin States, but it is also an important factor in international relations with Mexico, which is guaranteed an annual supply of 1.85 billion cu m (1.5 million acre-ft) of Colorado River water, by a 1944 treaty. in 1973, the United States and Mexico agreed that water delivered to Mexico from the main system of the river would have a salinity of no more than 145 mg/L greater than the average salinity of the water at Imperial Dam. Before this study. it had been estimated that in this area thermal springs-rising in or near riverbed and associated ground-water systems contribute about 27,137,000 cu m (22, 000 acre-ft) of saline water, containing 399,161 metric tonnes (440,000 English tons) of salt annually. A PIQR (Problem Identification and Qualification Report) 12) identified average annual concentrations of 18,648 mg/L salt at GS (Glenwood Springs) and 9295 mglL at DS (Dotsero Springs). In this study, estimated flow-weighted average values of 18,780 mg/L for GS and 9954 mg/L for DS were found. Of this amount, approximately 50 percent was contributed by known surface Prior studies of the Glenwood-Dotsero Springs Unit indicated that salinity control measures can reduce salt contribution to the Colorado River by at least 190,000 t (209,000 tons) annually from surface springs alone. 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 for, and find ways of preventing these waters from entering the Colorado River. A characterization and application study of Glenwood and Dotsero surface springs water was made by the USBR Engineering and Research Center. Division of Research. In another study, the Bureau of Reclamation's UCR (Upper Colorado Region) contracted to investigate the control and disposal of hot saline water from springs near Glenwood Springs and Dotsero, Colorado. Chemical and physical data obtained were consolidated with water analyses obtained by the Chemical Engineering Unit. This study showed that 14 GS identified springs ranged in dissolved salt content from 16,670 mg/L to 21,850 mg/L, and that 11 DS identified springs ranged in dissolved salt con-tent from 8300 mg/L to 10,670 mg/L. Most Glenwood-Dotsero springs emerge in and along the Colorado River at ground eleva- tions lower than river surface. Apparently, springs originate from saltier aquifers and are diluted by surface water and by river water before emerging. A test program was needed to locate and charac- terize Glenwood aquifer water. 2. Regional Hydrogeology FlVm Geldon -- Paleozoic rocks in northwestern Colorado were investigated during the U.S. Geological Survey's Regional Aquifer-System Analysis of the Upper Colorado River Basin. Paleozoic rocks in the study area are grouped into 11 hydrostratigraphic units on the basis of lithologic and hydrologic properties. Devonian and Mississippian carbonate rocks and Pennsylvanian and-Pennian sandstone are regional aquifers, with natural discharges that commonly exceed 50 gallons per minute. Discharges from the Devonian and Mississippian carbonate rocks to artesian wells and springs can be as much as 3,200 gallons per minute. Other hydrostratigraphic units in the area are either local aquifers or confining A-3