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<br />. <br /> <br />. <br /> <br />tI) <br />00 <br />....J <br />0)' <br /> <br />. <br /> <br />I <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />as a water supply for irrigated agriculture. As far back as 1903, some <br /> <br />limited sampling was performed in order to determine acceptable salinity <br /> <br />levels for maintenance of crop production. Since 1941, fairly complete <br /> <br />records of flow and water quality conditions have been maintained at <br /> <br />some 17 stations throughout the Basin by the U. S. Geological Survey. <br /> <br />These stations and available records are identified in Figure IV ~2 <br /> <br />(V. S. DOL, 1973). As part of particular studies, many other stations <br /> <br />have been established and monitored for various constituents and periods <br /> <br />of time. A summary of these records on the EPA STORET System for <br /> <br />stations having more than 25 observations (usually at least 2 years record) <br /> <br />is presented in Appendix IV ~A. In addition there are numerous sampling points <br /> <br />throughout the basin at which there are less than 25 observations. <br /> <br />While there baa been accumulation of water quality data, the first <br /> <br />comprehensive studies of water quality conditions in .the Colorado River <br /> <br />were accomplished in 1964. Salinity has long been recognized as the major <br /> <br />quality problem of the Colorado, and since 1970, a number of studies have <br /> <br />been completed which have examined the mineral quality (salinity) problem. <br /> <br />A summary of these reports is presented in Table IV -1. As noted in the <br /> <br />table, some of these studies have attempted to identify sources of salinity <br /> <br />and to project future levels of concentrations based on proposed water <br /> <br />development. <br /> <br />That salinity has been the over-riding water quality concern from a <br /> <br />5 <br />