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T830161 <br />' HYDROLOGY EXHIBIT G <br />I <br />All water involved in the quarry operation will be handled in accordance with all <br />applicable state and Federal laws. An NPDES Permit has been applied for and granted. <br />The following is a characterization of the local hydrology. <br />Surface I~~ater Hydrology <br />' Surface water in the area of the quarry site is concentrated in hvo channels. The <br />closest to the quarry is Coal Creek, a natural stream which flows along the west and <br />north sides of the site. Coal Creek is a braided stream which flows to the northeast in <br />a channel cut in the Pierre Shale. A thick (average 15'-20'), coarse saturated gravel <br />fills the stream bed. As Coal Creek's water level fluctuates seasonally in response to <br />water dr2~vn off by irrigation and seasonal changes, the gravels are probably recharged <br />' by the creek at high flow and contribute water to the creek at low flow. Upgradient <br />from the site, the creek probably contributes water to the Rocky Flats Alluvium <br />' seasonally through infiltration. <br />' The seco;td channel of concentrated surface water flow is a man-made channel, the <br />South Boulder Diversion Canal. This structure diverts water from Eldorado Canyon to <br />' the southeast and eventually back to the southwest where it empties into Ralston <br />Reservoir. At its closest it lies about 1/2 mile southwest of the site. This canal will <br />be unaffected by the quarry. <br />1 <br /> <br /> <br /> <br />1 <br />1 <br />Precipitation on the surficial materials in this area is likely to infiltrate the alluvium at <br />a high rate. Infiltration rates for the top 5 feet of soil were reported at 0.2 to 6.0 <br />inches per hour (Moreland and Moreland, 1975). Branson, Miller, and McQueen (1964, <br />Table 2) reported rates from 3.90 to 7.35 inches per hour for Roclry Flats Alluvium. <br />Sheet or overland flow probably occurs during precipitation events exceeding these <br />rates. Additional recharge to the gravels in this area probably occurs from Coal Creek <br />percolation, the McKay and Upper Church Ditches, and possibly minor amounts from the <br />South Bou;.der Diversion Canal. <br />-24- <br />1 <br />