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particulate matter before being released to Arroyo "E." The Pond will provide sufficient storage for the <br />entire 25 -year, 24 -hour flood event, plus sediment loads. Stored runoff will be tested for pH and reported <br />annually in accordance with GCC's Colorado Discharge Permit. <br />Manage Process Water <br />GCC does not use water to wash limestone or otherwise generate process water. However, the Colorado <br />Department of Health and Environment considers any stormwater that has contacted active mining areas <br />to be "process water." This stormwater is collected in the in -pit sumps discussed previously. The <br />stormwater is temporarily held for the purpose of settling out solids. Prior to discharge to the permitted <br />outfall, the water is tested in accordance with GCC's Colorado Discharge Permit for discharges from sand <br />and gravel mining and processing. <br />Manage Domestic Wastewater <br />A domestic wastewater treatment system consisting of a septic system with a leach field is located north <br />west of the plant area. GCC has obtained a permit from the Colorado Department of Health and <br />Environment authorizing the operation of this system. <br />Mining Activities <br />Mining activities include the initial box -cut, temporary stockpiles, blasting, removal of resource material, <br />backfill, and reclamation of the land surface. Management of surface runoff from these activities will <br />include detention, sediment ponds, and diversion ditches with the following goals and objectives: <br />Control Storm Water Within Active Mining Area. <br />Storm water generated in the pit (and including tributary area outside the pit boundary) will be conveyed <br />by ditches to an "in -pit detention /sediment pond." The in -pit ponds are sized to store storm runoff from <br />the 10 -year, 24 -hour event and for sediment. Runoff from larger floods will still be contained within the <br />pit area, because the low -wall is anticipated to be at least 15 -feet above the pit floor. This arrangement <br />provides even greater flood protection to areas outside of the mining limits. <br />For mining block years 1 through 5, the drainage area is 85 acres, requiring a pond with storage for 9 acre <br />feet. The pond has been constructed below the pit floor to avoid interference with mining operations. <br />During mining block years 6 through 10, the existing Arroyo E Stock Pond and Diversion Ditch #3 will <br />limit the drainage area tributary to the active mine area to 210 acres. These facilities minimize the volume <br />of runoff draining into the active mine area. During this mining period, an intermediate size, in -pit <br />detention /sediment pond can be constructed with a volume of 22 acre feet <br />As the mining progresses above the Arroyo "E" Stock Pond, the in -pit detention /sediment pond will be <br />increased to accommodate the larger drainage area of 470 acres during block years 11 through 25. This <br />tributary area requires a pond with a volume of approximately 49 acre feet. The Arroyo "E" Stock Pond <br />will be replaced during reclamation (see below). <br />When mining progresses to block years 26 through 50, a new, in -pit detention /sediment pond will be <br />constructed (see Exhibit D -3). The pond sizes during this mining block can also be staged, according to <br />tributary drainage area. For instance, up to block year 40, the eastern branch of Arroyo "I" can continue to <br />bypass the mining operation, reducing the tributary area for the pond from 740 acres to 500 acres. <br />Control Storm Water Discharges from Active Mine Area <br />Technical Rev No 4 <br />April 26, 2013 <br />D -10 <br />