WSP08886 - Laserfiche WebLink

Home Browse Search

to.) o t~ ~ Utah Aneth Ground-Water Salinity Study The summary report for this project was published and released to the public in September 1996 by the U.S. GeologicalSurvey. The study was guided by the Aneth Technical Committee, which is composed of representatives of State, Navajo Nation, and federal government agencies as well as. private oil companies. Represented ort the Aneth Technical Committee are the Bureau of . Reclamation; the Bureau of Land Management; U.S. Environmental Protection Agency; the Bureau of Indian Affairs: Texaco Exploration and Production, Inc.; Mobile Exploration and Producing U.S., Inc; Phillips Petroleum, Inc., the Utah Division of Oil, Gas, and Mining; the Navajo Environmental Protection- Administration; Navajo Nation Water Resources Management Department; and U.S, Geological Survey. Because of the concern of potentially increasing salinity in freshwater aquifers in the vicinity of the Greater Aneth Oil Field in southeastern San Juan County, Utah, a hydrologic and geochemical study was done to determine the extentand concentrations of salinity in the freshwater aquifers,to document changes in the salinity throughout time, and to identify, if possible, the source. and potential pathways of the;, saline water. The Navajo aquifer is the principal bedrock aquifer in the vicinity of the Gre;,ater Aneth Oil Field and includes the Entrada, Navajo, and Wingate Sandstones. The Navajo aquifer is confined in this area, and wells typically discharge water at land surface. The Navajo aquifer generally ranges from 750 to I ,000 feet in thickness, with the top of the aquifer averaging 550 feet below land surface. The Navajo aquifer is recharged along the flanks of the Abajo Mountains, Sleeping Ute Mountain, . and Carrizo Mountains, to the north, east, and south of the study area, respectively. Potentiometric contours, increasing hydraulic head with depth, and. gains in discharge indicate that water in the Navajo aquifer moves down gradient from these recharge areas and discharges into the San Juan River. . Water from the Navajo aquiferisdischarged primarily from water wells, and dry holes and previousiy producing oil wells that were plugged back to water-bearing formations-. -Measured discharge from flowing wells during the study ranged from less than 1 to as much as 150 gallons per minute. About 600 acre-feet of water discharged from the Navajo aquifer from wells during 1992-93. Water-level declines in some navajo aquifer wells have been as much as 178 feet since the 1950s. Dissolved-solids concentrations in water from 56 wells in the Navajo aquifer ranged from 145 milligrams per liter (fresh) to as much as 17,300 milligrams per liter (very saline). Water from most wells shows less than to-percent variation in salinity with time; however, increases of greater than 50 percent have been documented for selected wells. Water with dissolved-solids concentrations greater than 10,000 milligrams per liter may be less than 500 feel below land surface in the Aneth area. High levels of salinity in water from some water wells prior to the late 1950s indicate that saline water was present in the Navajo aquifer before development of the Greater Aneth Oil Field. 10