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<br />Water QLSlity <br /> <br />Water quality in the South Platte River near the site is <br />generally poor. This stretch of the river has been classified <br />by the state as C, Dl, indicating that water in the river is <br />suitable for industrial and irrigation uses. Tests conducted <br />by the Colorado Department of Health in January through August <br />of 1975 at Henderson indicate tkiat average temperature, pg and <br />oxygen levels generally are conducive to certain species of <br />fish life. Dissolved nutrien*_s, however, are quite high which <br />indicates a condition detrimental to fish life but beneficial <br />to irrigation usage. There are many municipal ar:d industrial <br />wastewater treatment plants that discharge to the South Platte <br />River above the mining ..ite. The discharges of thes_ treatment <br />plants degrade the natural quality of water in the river. <br />Ground water quality from the sands and gravels near the <br />mining site ranges from good to fair. The water contains con- <br />centrations of sulfate and dissolved solids which in places, <br />may be above the Colorado Department of Health drinking water <br />standards. The pH of the water ranges from 7.2 to 7.6. <br />Drainage <br />The principal surface water feature in the area is the <br />South Platte River. It is a snowmelt stream, and approximately <br />75% of the flow is derived from snowmelt, the remaining 25% is <br />composed of runoff from precipitation, discharged ground water <br />from shallow alluvial aquifers west slope •.:ater imported for <br />municipal use, and return flows from irrigation. Floors in the <br />South Platte River can range from a low of 4.4 cfs recorded <br />during April, 1951 to as much a. 33,000 cfs during May, 1973. <br />The peak flow recorded during May, 1973 approximated the 100 - <br />year flood. Aerial photographs of the flood were used t~ define the 100- <br />year flood plain and floodway (Figure 3). <br />Dikes along the southern boundary and the west bank of the <br />South Platte River control the amount of overbank flow during <br />the 100-year flood. It is estimated that 15,000 cfs will pass <br />through th.: site as overbank flow during the 1,, .,-yeas flood. <br />It will back up behind and pass over Henderson P,oad. Flow lepths <br />will average Lhree to four feet and velocities two to three feet <br />per second upstream of Henderson Road. Downstream of Henderson <br />-5- <br />