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<br /> <br />customarily used, except primary contact recreation:' Analysis <br />of water samples from nearby wells collected by the U.S. <br />Geological Survey in 1960 indicates the ground water in the <br />vicinity of the mining site is of moderate to poor quality. <br />Due to high concentrations of calcium, magnesium, sodium <br />potassium, sulfate, and chloride, the dissolved solids concen- <br />trations and hardness content were reported to be 2290 and 1280 <br />parts per million respectively. Extensive experience in de- <br />watering sand and gravel mines indicates that water quality is <br />not adversely affected by the dewatering process. Dewatering at <br />East Rigden is not expected to adversely affect water quality <br />of the Cache la Poudre River. - <br />Flood Plain <br />The U. S. Army Corps of Engineers (USAGE), Omaha District, <br />delineated the flood plain of the Cache la Poudre River in this <br />vicinity in a report called "Flood Plain Information, Cache <br />la Poudre River, Colorado, Volume 3, Fort Collins - Greeley, <br />Larimer - Weld County," in October, 1975. The report identifies <br />the flood plains of the intermediate regional flood (100 year) <br />and the standard project flood. Figure 8 is reproduced from <br />their report. According to the flood plain information report, <br />the 100 year flood plain is defined using peak discharge rates <br />of 16,600 to 17,500 cfs upstream of Boxelder Creek and 28,500 <br />cfs below Boxelder Creek. Utilizing flood profiles from the <br />Flood plain information report and Corps of Engineers' cross- <br />sections which are identified on official Larimer County <br />G-9 <br />