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<br /> <br />, <br /> <br />. <br /> <br />. <br /> <br />USGS Accomplishments <br /> <br />Well Inventory of the Lower Colorado River Flood Plain and Adjacent Areas in Arizona, <br />California, Nevada, and Utah <br /> <br />The U.S. Supreme Court decree, 1964, Arizona v. California, is specific about the <br />responsibility of the Secretary of the Interior to account for consumptive use of water from the <br />mainstream; consumptive use is defined to include "water drawn from the mainstream by <br />underground pumping." Water pumped from wells on the flood plain is presumed to be river <br />water and the accounting surface can be used to identify wells outside the flood plain in and <br />near the lower Colorado River valley that yield water that will be replaced by water from the <br />river. A well inventory of the lower Colorado River flood plain and adjacent areas in <br />Arizona, California, Nevada, and Utah is needed to locate wells, provide current information <br />for each well, and provide precise position information in order to apply the accounting- <br />surface method and include in the appropriate wells in water accounting along the river. The <br />objective of this project is to inventory wells on the flood plain of the lower Colorado River; <br />in the Yuma area downstream from Laguna Dam and in the area surrounding Lake Mead, <br />Moapa and the.. Virgin River Valleys within the river-aquifer boundary; and complete the well <br />inventory on tfle adjacent alluvial slopes and tributary valleys between Hoover Dam and <br />Laguna Dam within the river-aquifer boundary. <br /> <br />Project began in FY94 with data collection in the Yuma area. <br /> <br />~.... <br />W <br />~. <br />~ <br /> <br />Colorado <br /> <br />As part of the cooperative effort between the U.S. Geological Survey and the Bureau of <br />Reclamation to maintain and update a salinity data base and statistical analysis of data for the <br />Colorado River basin, a regression procedure was deve OPe9 to estimate dissolved-solids <br />concentration at the Station, Colorado River at Grand anyo (sampling was discontinued in '/ <br />1987). In addition, the following projects are ongoing. v;cfJ.V7 ~ <br /> <br />; <br />I <br />1 <br />I <br />, ' <br />i <br />The Dolores Project diverts water from the Dolores River (from McPhee Reservoir) for ! <br />irrigation..!n the San Juan Basin. The Project delivers water to areas that have never been <br />irrigated, including about 7,500 acres of land on the Ute Mountain Ute Indian Reservation, '( i , <br />and also delivers supplemental water to Montezuma Valley, which has been irrigated for ~'iL <br />nearly 100 years. Water-quality problems are related to the long-term irrigation in the pt}l TO"! J~j\ <br />McElmo Creek basi~. Fish samples collected in the study area indicate potential problems of ------ -to ,y-r.! <br />mercury contamInation. <br /> <br />Irrigation Drainage Reconnaissance Study of the Dolores Project <br /> <br />Samples collected in the spring of 1990 (pre-irrigation season), from old and new irrigated <br />areas and at background sites had dissolved-solids concentrations greater than 1,000 milligrams <br />per liter (mgiL). Selenium was greater than 10 micrograms per liter (ug/L) in only three <br /> <br />13 <br />