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Pikeview Quarry Environmental Assessment <br /> <br />1 <br /> <br /> <br />Page 29 <br />concrete lined channel that continues for about 2/3 mile to the confluence with Douglas <br />Creek, which is also contained in a concrete lined channel downstream to its confluence <br />with Monument Creek. <br />The mean monthly precipitation at the neazest weather station in Colorado Springs is <br />presented in Table 3.1. While this data is not directly applicable to the project site, due <br />primarily to differences in elevation, the quarry receives about 2 to 3 inches more <br />precipitation per year than Colorado Springs, but follows the same monthly pattern (Castle <br />Concrete Company, 2000a). <br />Table 3.1-Average monthly precipitation (1950-1997) <br /> <br />r <br /> <br /> <br /> <br />1 <br /> <br /> <br />Month Precipitation (inches) <br />January 0.28 <br />February 0.34 <br />March 0.88 <br />April 1.32 <br />May 2.33 <br />June 2.30 <br />July 2.84 <br />Augur[ 2.87 <br />September 1.33 <br />October 0.84 <br />November 0.51 <br />December 0.35 <br />Source: Colorado Climate Center, Colorado State University <br />(h ttp://ccc.atmos. colostate. edu) <br />Mining at the quarry has changed the flow paths of the stream channels within the <br />quarry's boundazies, but water enters and exits the quarry's permit boundaries at the same <br />places it has historically done so. The drainage channels have become longer as water is <br />routed azound active mine operations and through sediment ponds, resulting in less energy <br />per foot of stream channel available for erosion. The water now runs across baze soil, which <br />requires less energy than the original vegetated surface to erode soil particles. The <br />availability of a lazge sediment source more than offsets the reduced channel slopes. <br /> The mine's stormwater management plan (Castle Concrete Company, 2000) utilizes <br /> four sediment retention ponds within the permit azea to prevent sediment from moving off <br /> the site. A lazge collection basin (# 1) is located west of the stockpile and processing azea, <br /> and adjacent to the azea on private land proposed for the layback reclamation; collection <br /> basins # 2 and #3 aze located west of the main office; and collection basin #4 is located <br /> northeast of the main office, at the east permit boundary. Stormwater drainage and sediment <br /> retention basins aze illustrated in Figure 3.1. <br />' Stormwater facilities at Pikeview Quarry were designed to handle a ]0-yeaz, 24-hour <br /> storm event, and they have been effective at controlling a significant amount of sediment <br />' generated by the operation through a series of sediment basins and energy dissipation drop <br /> structures. Some additional sediment has been dischazged as a result of large <br />' Hydrosphere Resource Consultants, 1002 Walnut Sveet $uhe 200, Boulder, CO 80302 <br />