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Pikeview Quarry Environmental Assessment <br />Page 30 <br />thunderstorms, but the volume has been greatly reduced due to the addition of a final <br />sediment basin neaz the east permit boundary. Additional sediment control is being <br />established as revegetation efforts take place. <br />Stormwater dischazges are caused by erosion from cut slopes, raw and processed <br />material stockpiles located on the site, occasional runoff from haul road through the <br />property, arJd stockpiles of materials. <br />Hydrosphere conducted an analysis of potential gross erosion at the Pikeview Quatry <br />(see Appendix D} and estimated that under current conditions gross erosion rates aze about <br />75,495 cubic yards per year. Potential gross erosion is the total amount of material that <br />moves during a storm event or year. The gross erosion does not include soil that may be <br />deposited due to changes in topography or stored in sediment retention ponds. Given the <br />uncertainty of the final contours, maximum slopes, operation of sediment detention ponds <br />and other details of the reclamation plan, the sediment yield from the site (net erosion} was <br />not calculated in this EA. <br />Runoff is caused both by thunderstorms, frequent during the summer months, and 1>y <br />water use in the quarry for dust suppression on roads and on spray bazs for the processing <br />equipment, and general plant use. Runoff from thunderstorms was calculated for the <br />Pikeview Quarry as described in the hydrologic analysis presented in Appendix D. Table 3.2 <br />summarizes the run off estimates at Pikeview Quarry under the current conditions. <br />Table 3.2 -Instantaneous Peak and Total Runoff Volume <br />Estimates at Pikeview Quarry <br />Storm Peak Runoff (cfs) Total RunofT(AF) <br />2-yr, 24hr 0 0 <br />10-yr, 24-hr 11 38 <br />100-yr, 24-hr 87 428 <br />Water use in the quarry is approximately 5,287,000 gallons per yearlo, of which 3,000 <br />to 6,000 gallons a day are used for dust abatement operations. <br />3.2.4 Water Quality <br />No water quality data is available for the unnamed tributary which drains the basin <br />where the quarry is located. Possible sources of contaminants to the tributary• include <br />sediment fi•om mining and reclamation activities at the quarry, development to the north and <br />east of the quany, and other pollutants associated with urban runoff Urban runoff can <br />contaminate streams with oil from vehicles, and sand and salt used to help remove snow <br />10 Data provided by Banks and Gesso (letter November 27, 2000), for the period July 1999 to July 2000. <br />Hydrosphere Resource ConsulumLS, 1002 Walnut Street Suite 200, Boulder, CO 80302 <br />u <br /> <br />1 <br /> <br />~J <br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br /> <br />1 <br /> <br /> <br /> <br />1 <br />1 <br />