2018-02-05_PERMIT FILE - C1981019

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October 19, 2017 Table 1. Simulated Collom Area Layers Layer No. Layer Description 1 Surface to top of Dl Seam 2 Dl -D2 Seam 3 Bottom of D2 Seam to top of E2 Seam 4 Top of E2 Seam to top of F6 Seam 5 F6 Seam 6 Bottom of F6 Seam to top of FA Seam 7 FA -FB Seam 8 Bottom of FB Seam to top of G7 Seam 9 G7-09 Seam 10 Bottom of G9 Seam to top of GA Seam 11 GA -CB Seam 12 Bottom of GB Seam to top of H2 Seam 13 Top of H2 Seam to top of I3 Seam 14 Top of I3 Seam to top of J2 Seam 15 Top of J2 Seam to top of Km Layer 16 Top of Km to bottom of Km Layer 17 Bottom of Km Layer to Model Bottom Page 8 balance calculations performed by WMC (2006). For perspective, the average recharge rate of 2 inches per year represents a recharge rate of 150 gpm over the entire surface area of the Collom Pit. The drainages within and around the Collom Pit--Collom Gulch, Little Collom Gulch, and Jubb Creek—were assigned high floor conductance, also for conservatism. The vertical side boundaries of the model represented no -flow boundaries. The Km bed was assigned a hydraulic conductivity of le -5 ft/day for computational efficiency, even though it has demonstrated lower saturated permeability (2.2e-6 ft/day) in the laboratory. This was done because too high of a contrast between neighboring low -permeability and high -permeability zones leads to numerical instabilities. The calibration was carried out in two steps. First, an initial set of hydraulic conductivities (two horizontal and one vertical component) and storage coefficients were assigned to each individual layer in the model, and the model was cycled to steady-state equilibrium, with the pilot well pump turned off in the model. In the second step, once steady- state equilibrium was achieved, the pump at the pilot well was turned on using the pumping schedule (Table 2) based on the pumping test data. In this step, draw -down response was observed in the model for 37 days of pumping, and the rebound response for the following 20 days for each observation point (stand pipe and piezometer) was compared to the model response for those observation points. The calibration was achieved by iteratively modifying the hydraulic conductivities and storage coefficients for all the modeled layers until best fits were obtained for Layers 4, 5, 6, 7, 9, 11, 12, and 13. These were the only layers that had any observation points and associated data available. (Note that layers 1 through 3 are located above the water table and are therefore unsaturated. Flow [infiltration] in the unsaturated (or vadose) zone depends on other properties of the porous medium besides the permeability and hydraulic gradient and, given the 350 -ft depth to the water table, can be ignored.) Layers 8 and 10 were modeled as similar to layers 12 and 13 as will be seen in the discussion that follows. Agapito Associates, Inc.