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w o to C.j( Salinity in the Navajo aquifer may have been derived from upward movement of saline water from the upper Paleozoic aquifer or possible from localized dissolution: of evaporates that were present in the Navajo aquifer. Apparent increases and decreases in salinity of water from selected wells could be caused by pumping or wellbore effects. Potential upward movement of water from the upper Paleozoic aquifer into the Navajo aquifer may take place in an area near Aneth where the hydraulic head in the upper Paleozoic aquifer exceeds that in the Navajo aquifer. Mixing model results indicate that the bromide-and iodide-to-chloride weight ratios characteristic of oil-field brine in the study area decrease with increasing chloride concentration in water from the Navajo aquifer, and generally follow the end-member mixing lines constnlcted with the mean non-oil field brine and the upper Paleozoic aq\lifer end"member water compositions. Neither oil- field brine nor comingled injection water is the source of salinity to the Navajo aquifer. The del oxygen-I 8 (0"0) and del deuterium (oD) values of water samples from the Navajo aquifer north of the San Juan River are distinctly lighter than the 0"0 and oD values of water samples from the Navajo aquifer east and south of the San Juan River. This difference is possible caused by geographic segregation of water in the aquifer and not by mixing with oil-field brine. The del Strontium-87 (o"Sr) values of oil-field brine samples are substantially. smaller than the values of water samples from the Navajo aquifer, indicating that oil field brine is nota source of salinity. The 087Sr values of 'water samples from the upper Paleozoic aquifer are similar to the mean isotopic composition of the more saline water from the Navajo aquifer and indicate that the upper Paleozoic aquifer is a possible source of salinity. Hierarchical cluster analysis using chemical constituents in 43 water samples from the Navajo aquifer, 4 water samples from the upper Paleozoic aquifer, and 5 oil-field brine samples indicates that oil-field brine is not the salinity source to the Navajo aquifer and that water from the upper Paleozoic aquifer may be a source of salinity. Irrigation Drainage and Selenium--Middle Green River Basin Detailed study of wildlife areas in the middle Green River Basin of Utah during 1986-1990 has shown that concentrations of selenium in water and biologic tissues were harmful to wildlife at the Ste)Vart Lake Waterfowl Management Area, lower Ashley Creek, and the Ouray National Wildlife Refuge.. The sources of seleniumat Stewan Lake is irrigation drainage from the Bureau of . Reclamation Jensen Unit which drains sedimentary deposits of marine and nonmarine origin. A significant linear reiation (R2 of 0.65) exists between concentrations of dissolved selenium. discharge to Ashley creek and concentrations of dissolved solids, but no relation (R2 <0.01) exists between loads of selenium and loads of dissolved solids. This indicates that salinity controls that are chosen only to treat large sources of salt loading may fail to control loads of selenium. The largest source of selenium contamination in the area is seepage originating from the Ashley Valley sewage lagoons. Water in the lagoons is free of selenium, but passes through fractured Mancos shale and discharges to Ashley Creek carrying selenium load in excess of I kilogram per day. Seepage from the sewage lagoons also contribute about 9,000 tons per year of salt to Ashley Creek. There is no direct involvement of a Department of the Interior (DOl) selenium project associated with the sewage lagoons. Currently, the U.S. Fish and Wildlife Service (FWS) is preparing litigation under "take" provisions of the Endangered Species Act against the local sewer board, State of Utah, and possible the Environmental Protection Agency. 11