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Bluestone and Section 16 Wildli(c Issues Report western Aggregates, Int. ' the year in response to snowmelt and rainfall recharge, with highest levels in late spring and early summer. Additional detailed background is available in SHB Agra (1994a). ' In 10 bore holes at the approved, but unbuilt, RFP Sanitary Landfill site, in the same ' formation, but on the opposite side of Rock Creek drainage from the existing Bluestone Aggregates operation and proposed Bluestone expansion, depth to groundwater at its highest annual level (late June and early July) varied from 33 to 54 feet below the surface (USDOE 1994a). Additional detailed hydrologic characterization of the area is available in USDOE (1994a). ' At the Section 16 site, depth to groundwater varies depending on time of year and proximity to RFP Reservoir and unlined irrigation ditches. The unreclaimed claypit, located in the ' middle of Section 16, supports a water level approximately 30-35 feet below the surface. However, this pond is hydrologically connected to the Fox Hill sandstone and Laramie Formations, both with high water transmissivity levels, possibly resulting in a water level ' greater than that of the adjacent Rocky Flats alluvium. Test holes randomly dug with a backhoe around the Section 16 site to evaluate gravel deposits and groundwater levels did ' not locate groundwater closer than at ]east 25 feet from the surface (R. Myers, WAI, pers. comm.), the maximum depth explored by the backhoe. ' Depth to groundwater in 10 bore holes at the alternative RFP landfill site, located in the same geologic formation just east of the proposed Section 16 mining area, is shallower, varying from 3.5 to 14.5 feet and averaging just over 8 feet USDOE (1994a). These ' groundwater measurements, taken in late June and early July, may have been influenced by concurrent up gradient operation of Smart Ditch and asouth-north lateral to Woman Creek. ' Because of (1) the flat topography atop pediments where mining is proposed, (2) the high permeability of soils and gravels atop pediments, and (3) minimal encroachment of mining ' into the extreme upper reaches of minor, ephemeral Rock Creek drainages, baseline surface runoff from proposed mining areas is thought to represent minimal contributions to the maintenance of down gradient, mesic vegetation along drainage bottoms inhabited by PJM. ' To avoid indirect impacts to occupied or potential PJM habitat, WAI will modify their ' mining proposal and commit to the following: 1. There would be no mining into the groundwater table at either the Bluestone or ' Section 16 sites. Data indicate the groundwater table is below the level of proposed n-lining. In the event the water table is encountered during mining, the local area would be backfilled so that evidence of the water table is not exposed on a seasonal o:r annual basis. This would result in a reduced depth of mining. As long as the groundwater table is not exposed, hydric, down-gradient vegetation, partially or wholly ' supported by groundwater, should not be affected. ' Western Ecosystems, Inc. t t December, 1994