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<br /> <br /> <br />I '~li,1,bt; <br /> <br />~ .c ''''- <br />\ ,,,"L <br />~.. <br />~~~~ Co: ~. , ) <br />\1' .:tL ..;lorf <br />>', '4"" <br /> <br />Berthoud <br /> <br />a problem of comprehensive land use <br />planning more than one of water resources <br />planning. Once the best uses of the lands <br />have been determined, water supplies can <br />be developed, managed, and preserved to <br />meet those needs. <br /> <br />WATER QUALITY <br /> <br />The total dissolved solids (TOS) for 2 years <br />of record (October 1971 through <br /> <br />September 1973) range from 24 milligrams <br />per liter (mg/I) in North St. Vrain Creek near <br />Lyons to 1,535 mg/I in the Big Thompson <br />River at the mouth near LaSalle. Thus, flows <br />originating in the upper reaches of the <br />drainage basins are excellent in quality but <br />deteriorate rapidly downstream due to use <br />and reuse on the lands and by municipal and <br />industrial effluents. <br /> <br />At the same time surface water is being <br />diverted for agricultural use, ground water <br />is being pumped for that purpose. A part of <br />the water applied to the surface finds its way <br />back into the ground-water aquifer, a portion <br />runs off, and some is lost to <br />evapotranspiration. Each time this use <br />pattern occurs, dissolved salts are <br />concentrated in the water. This reduces <br />water quality and limits its usefulness. <br /> <br />Trends in TOS content of ground water from <br />alluvial aquifers were investigated to <br />determine if degradation is occurring. The <br />increasing TOS content of ground water <br />indicated that degradation has occurred <br />throughout most of the South Platte River <br />Basin. <br /> <br />The alluvial aquifers are recharged by <br />surface water during periods of high <br />surface-water flows. However, at times of <br />low surface-water flows, the reverse <br />situation often occurs and ground water <br />enters the streams from seeps and springs <br />along the stream channels. The relationship <br />between surface- and ground-water quality <br />was investigated by comparing the average <br />TOS for each supply. Exhibit 111-2 shows the <br />results of that comparison. The average TOS <br />of the ground water shows close agreement <br />with the average high TOS of the surface <br />water. The average high TOS of the surface <br />water corresponds to periods of low flow <br />when seepage of ground water into the river <br />is significant. <br /> <br />Table 111-1 lists small communities in the <br />study area which obtain their water supply <br />from the ground-water aquifer. <br /> <br />111-3 <br /> <br />