2010-12-17_REVISION - C1981019 (140)

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Model development DRAFT 13 • Layer 9 - bottom of Gc coal to mid distance between bottom of Gc coal and top of Fab coal; • Layer 10 - mid distance between top of I sequence and bottom of Gc coal to bottom of Gc coal; • Layer 11 - top of I sequence to mid distance between top of I sequence and bottom of Gc coal; • Layer 12 - top of KM to top of I sequence; • Layer 13 - bottom of KM to top of KM; • Layer 14 - top of Trout Creek Sandstone to bottom of KM; • Layer 15 - middle of Trout Creek Sandstone to top of Trout Creek Sandstone; and • Layer 16 - bottom of Trout Creek Sandstone to middle of Trout Creek Sandstone. Valley fill layers The valley fill deposits are included as the upper two layers (Layers 1 and 2) in the model. The bottom elevation of the valley fill (top of bedrock) is estimated from the bedrock surface in the KEC geological model and the estimated thickness of valley fill deposits based on borehole data and professional judgment from projects with similar geomorphic characteristics. Figure 3.9 shows the thickness of valley fill represented in the model. The top of the valley fill layer is the ground surface in the streams drainage valleys. 3.3.1 Hydraulic conductivity Prior to model calibration, initial estimates of the hydraulic conductivity of the bedrock hydrogeological units were assigned based on values measured from individual well tests and the pilot dewatering test. Initial estimates are described below: • Transmissivity estimates from the pilot -dewatering test average about 15 ft2/d over the saturated bedrock interval from the Gc to the water table. Based on flow meter tests conducted in the pilot dewatering well, a transmissivity of about 10 ft2/d is attributable to the F/G sequence (this value was assigned to layers 8 and 9 in the model) and about 5 ft2/d to units above the Fab seam (this value was assigned to layers 3 through 7 in the model). • Based on the type of units that are present, the transmissivity of the sequence below the Gc to the KM (model layers 10 through 12) was considered to be similar to the transmissivity of the sequence above the Fab and was set at the same value as layers 3 through 7 (i.e., 5 ft2/d). 2572-R3 Colowyo Coal Company, L.P. Water Management Consultants