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<br />• AQUIFER CHARACTERISTICS <br />The Rocky Flats aquifer is composed of Quaternary unconsolidated deposits. The ground water <br />genera Ily flows eastward, but is controlled by topography and ground water will flow laterally <br />into drainages. The hydraulic conductivity for [his aquifer ranges from 0.03 to 0.003 feet/day <br />(10-~ to 10'6 cm/sec). The permeability of the underlying Arapahoe Formation ranges from <br />0.0003 to 0.00003 feet/day. This unit acts as a hydraulic barrier and impedes downward flow <br />of ground water resulting in a predominantly lateral flow regime (Wright Water Engineers, <br />1991). <br />The Laramie-Fox Hills Aquifer ranges up to 200 Ceet thick and is used as a ground water source <br />in the Denver Basin east of the site. The aquifer is confined by the Arapahoe and Laramie <br />formations which are predominantly claystones. The confining pressures result in water levels <br />that rive hundreds of feet above the aquifer when it is penetrated by wells in the Denver Basin <br />(Hillier et.al., 1983). We11s that fully penetrate the aquifer generally yield 100 gallons per <br />minute:, but may yield as much as 900 gpm. The water in this aquifer may exhibit elevated <br />concentrations of methane, iron, fluoride and hydrogen sulfide (Romero et.al., ]972). <br />Recha:-ge to the Rocky Flats Alluvium occurs From precipitation, seepage, and overland and <br />basal flow. Basal flow and precipitation are the predominant forms of recharge in the spring <br />• and summer. Fall and winter recharge generally is a result of baseflow. <br />GROUNDWATER QUALITY <br />Background ground water quality data has been established using wells constructed, monitored <br />and sampled by the Environmental Monitoring and Assessment Division of EG&G. These wells <br />are located upgradient of the Rocky Flats Plant but downgradient of the proposed mine area. <br />Data from the monitoring and sampling program indicates that the groundwater in the mint <br />area is not affected by contamination at the plant site. <br />SURFACE WATER <br />The source of water in the ephemeral drainages east of the site is principally precipitation but <br />groundwater also is known to discharge to the surface water as springs and seeps. Seeps occur <br />primarily at the contact between the Rocky Flats Alluvium and the underlying bedrock, or <br />where paleo channels in the Arapahoe Formation are exposed in the sides of stream valleys. <br />• <br />