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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />l <br />l <br />l <br />l <br /> <br />37~7 <br /> <br />The EPA effort more clearly defines salt loading sources <br />than does the USGS effort. It is important to note, however, <br />that the EPA study period covered one year while the USGS <br />utilized average salt yields covering a 43 year study period. <br />Data collected by the EPA could easily represent an unusually wet <br />year. <br /> <br />Evaluation of Ground Water Contribution to Salinity of <br />Streams in the Upper Colorado River Basin in Colorado is a joint <br />effort by the BLM and USGS. The reconnaissance level study <br />involved a one-time sampling program of baseflow during December <br />of 1977 and January of 1978. Groundwater inflow was considered <br />to represent the bulk of the stream flow during the low flow <br />winter months. It was also assumed that groundwater discharge <br />remains nearly constant during the year and remains nearly <br />constant from year to year. <br /> <br />The salt load estimates were derived from a mass balance <br />using measurements from the va~ious Colorado River system <br />subbasins in Colorado. The pe~cent of the total average annual <br />salt load contributed by ground water inflow varied considerably <br />from subbasin to subbasin. No real attempt was made to <br />distinguish between natural and man caused sources of salt <br />loading. <br /> <br />Six areas in Colorado have been autho~ized for planning or <br />construction by the Colorado River Basin Salinity Cont~ol Act. <br />Prior to developing a proposal to control salt loading in these <br />areas, the Bureau of Reclamation and Soil Conservation Service <br />conduct preliminary investigations to determine precisely the <br />sou~ce, location and magnitude of salt loading. This information <br />was utilized in all but the Yampa Subbasin. <br /> <br />-5- <br />