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N .....' --1 ,,(,;,. COLORADO As part of the cooperative effort between the U.S. Geological Survey and the Bureau of Reclamation to maintain and update a salinity data base and statistical analysis of data for the Colorado River basin. a regressi on procedure was developed to estimate dissolved-solids concentration at the Station, Colorado River at Grand Canyon (sampling was discontinued in 1987). In addition, the following projects are ongoing: Irrigation Drainage Reconnaissance StUdy of the Dolores Project The Dolores Project diverts water from the Dolores River (from McPhee Reservoir) for irrigation in the San Juan Basin. The Project delivers water to areas that have never been irrigated, including about 7,500 acres of land on the Ute Mountain Ute Indian Reservation, and' also delivers supplemental water to Montezuma Valley, which has been irrigated for nearly 100 years. Water- quality problems are related to the long-term irrigation in the McElmo Creek basin. Fish sampl es colI ected in the study area indicata potential problems of mercury contamination. Samples collected in the spring of 1990 (pre-irrigation seasonl, from old and new irrigated areas and at background sites had dissolved-solids concentrations greater than 1,000 milligrams per liter (mg/L). Selenium was greater than 10 micrograms per liter (ug/Ll in only three samples, The highest selenium concentration (88 ug/L) was a sample from Navajo Wash near Towaoc, which drains some of :the area of long-term irrigation south of Cortez, All data collection has been completed, and the final report is being prepared, Irrigation Drainage Reconnaissance of the Pine River Area, Southern Ute Indian Reservation Large concentrations of selenium in ground water have been reported on parts: of the Southern Ute Indian Reservation. A documented case of human selenium poisoning caused by drinking well water occurred in 1962. Livestock poisoning is reported occasionally on the reservation. These areas also receive irrigation water from the Federal Pine River Project. This study will evaluate the Pine River Project to determine if irrigation drainage is contributing selenium. other trace elements, and pesticides to water, bottom sediments, and biota. Ground water in the Ignacio-Oxford area and near Arboles will be sampled for selenium. ,:J l~ . ,"."-." ",.d/;,>T. __'" : ''''''. '" ...hJ!