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Geologic Conditions • The site of the proposed disposal operations shown on Map 24, Surface Facilities, is located adjacent to the Area Pit where the Wadge Seam was extracted by surface mining methods. The Wadge Seam and overburden are part of the Williams fork Formation of Cretaceous age. The littology, structure and stra[igraphy of the mine area are fully described in Rule 2.04.6. The lithology and stratigraphy of the N~'adge Seam and overburden are considered [o be very consistent over the mine area, as shown on Maps 7, 8, 9, Geologic Cross-Sections A-A', B-B' and C-C', respectively, and as documented in Rule ?.04.6. Geochemical concentrations are largely uniform in [he coal, roof and floor of the underground mine. A single drill hole was chosen for caring and testing the leaching potential of waste rock material, which is representative of the underground mine plan area. The location of the test hole 006-83-66 is shown on Map 5, Surface Geology. A lithologic log of the hole is presented in Exhibit 12, Lithology Core Logs. The hole was drilled into the strata 12 fee[ below the Wadge Seam. Core samples were collected from the roof material 7 feet above the coal want, from the coal seam itself, and from the floor material 5 feet below the coal seam. The core samples were delivered to dte lab for leachate testing. In addition to the core samples, aggregate samples of actual waste rock material were collected from the underground mine. The aggregate samples came from roof material entering the mine from roof falls, fault crossings, or overcast mining operations. The aggregate samples were also delivered to [he lah for leachate testing. Hydrologic Conditions • The proposed disposal site is in the Area 2 Pit, located adjacent to the Foidel Creek Mine portal area at the Energy No. I Minc. The Area 2 Pit is an open excavation with a bedrock highwall on [he north side and a spoil slope on the south side. The bedrock on the highwall side contains a sequence of saturated sandstone and siltstone units referred to as the "overburden aquifer". The characteristics of the overburden aquifer are fully described in Rule 2.04.7. The permeability and storativity of the overburden aquifer have been determined by conducting pump tests at several locations in the permit area. At the Energy No. I Mine, average horizontal permeability is 2.9 gallons per day per square toot, vertical permeability is 0.1 gpd/ft2, and storativity is 1.7 x 10-4 (unitless). The average yield of wells penetrating the overburden aquifer is 17.6 gpm. Hydraulic conductivities in the overburden aquifer are therefore very low, except in localized areas where the aquifer has been extensively fractured by joints and faults. The spoil material up-dip from [he pit forms an unconfined aquifer which serves [o recharge [he local ground water system. Water from snowmelt and rainfall infiltrates into the spoils, and Flows down-dip along the pit Floor where i[ pools up against the highwall. The head of water in the pit exceeds the elevation of the piezometric surface in the adjacent overburden aquifer and ground water Flows into the highwall providing recharge to the overburden aquifer. Ground water flows to the north under the gradient of piezometric surface as shown in Map 13, Twentymile Park Hydrology. Strip mining operations at [he Energy No. I Mine ceased in 1980. During the mining operations, ground water inFlow from the overburden in the highwall was minimal. Since that time, infiltration of water from rainfall and snowmelt inro the reclaimed spoils has ceased leaching of the spoil materials, and this leachate has accumulated in the final pi[ at the bottom of the dipslope. The chemistry of the leachate water, as well as the water level and • chemistry of ground water in the overburden aquifer, have been monitored on a monthly basis from 1979 to the present. MR 97- I ~4 2.0?-94 Revised 9/9/97