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ARCOSA topography and the surficial geology of the region, as described in Exhibit D, the stormwater flows from the affected lands will likely not Impact waters of the South Boulder Diversion Canal. The McKay Ditch is a drainage feature located within 2 miles south and southeast of the affected lands boundary The ditch conveys water southwest from the nearby Rocky Flats area to where it is Intercepted by the South Boulder Diversion Canal. Topographically, this ditch is upgradient of the affected lands. The Upper Church Ditch is located more than 2 miles east of the affected lands and is likely a regional contributor to water in Coal Creek, however, this drainage feature is not topographically connected, and likely not hydraulically connected to the affected lands other than both being contributors to Coal Creek Rocky Flats Lake is located within 2 miles of the southern-most boundary of the affected lands and approximately 2 8 miles from the quarry area. Given the distance from the quarry, regional topography and the surficial geology of the region, as described in Exhibit D, the stormwater flows from the affected lands will likely not impact waters of Rocky Flats Lake. As discussed in Exhibit D, the surficial materials (i e , alluvial material overlaying Pierre Shale) around and within the affected lands boundaries are intermittently saturated' Precipitation is likely to infiltrate the alluvium at a high rate given the coarse-grained nature of the materials. Infiltration rates for the top 5 feet of soil were reported at 0.2 to 6 0 inches per hour (Moreland and Moreland, 1975) Branson, Miller, and McQueen (1964) reported rates from 3.90 to 7.35 inches per hour for Rocky Flats Alluvium Sheet or overland flow probably occurs during precipitation events exceeding these rates Additional recharge to the gravels in this area probably occurs from Coal Creek percolation, the McKay and Upper Church Ditches, and possibly minor amounts from the South Boulder Diversion Canal A ditch constructed around the southern quarry slope and along the gravel/shale interface will be installed for the purpose of intercepting groundwater seeps and surface water runoff from the alluvium overlaying the Pierre Shale The ditch will direct flows around the slope, along the road and to the pond Site Stormwater Similar to the regional surface water hydrology discussed above, surface water hydrology for the affected lands is shown on the Exhibit G-3 map. The affected lands area, and thus the stormwater conveyance, is divided by State Highway 93. Stormwater including surface runoff and snow melt on the west side of Highway 93 is directed to the quarry where it is contained within the quarry area. Runoff from the process area on the east side of Highway 93 either sheet flows to an onsite ditch that conveys water alongside the haul road beneath Highway 93 and into the quarry, or it is collected in the roadside diversion channels parallel to Highway 93 that convey water either away from the affected lands or to the onsite ditch that conveys water beneath the highway Surface water gathered in the quarry is collected in a sump within the quarry. The sump is located at the northeast corner of the quarry, and water from the sump is discharged in accordance with Colorado Discharge Permit System (CDPS) requirements (Permit No. COG-501573), if needed. The current permit imposes a report only limit for selenium to gather data with the possible addition of a selenium limit in the Z Reference Figure 6 2 1 1-1 of the Engineering Design and Operations Report,prepared by Sergent, Hauskins&Beckwith in 1992 for the Western Aggregates, Inc(former owner)proposed Shale Mine Ash Backfill Project