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<br />-z7- <br />1) Depletion of ground water from rock and alluvial aquifers; <br />2) Depletion of spring flows; <br />3) Depletion of water well yields; <br />4) Degradation of water quality in bedrock and alluvial aquifers; <br />and <br />5) Degradation of water quality through surface discharges of <br />aquifers (springs and base flow to streams). <br />These potential impacts are discussed by aquifer in the following <br />paragraphs. Aquifers not discussed will not be impacted by the proposed <br />Foidel Creek mine. <br />During mining, the applicant has predicted a depletion of the Wadge <br />coal-overburden aquifer and the dewatering of two fault zones due to <br />drawdowns of ground water into the mine workings. The applicant used two <br />mathematical models to obtain a projected combined mine inflow rate and <br />drawdown cone with the Wadge coal-overburden aquifer. These two models <br />were the GRWATER model, a finite difference, two dimension, digital <br />model, and a Line-Sink model. The GRWATER model was developed by <br />Colorado State University to predict steady-state dewatering of an <br />aquifer, while the Line-Sink model presented in McWhorter and Sunada <br />(1977) was used to predict the additional inflows resulting from the <br />dewatering of two fault zones. The resulting discharge rates and extent <br />of the drawdowns from the two models were added together to obtain a <br />total maximum predicted mine inflow of 608 gallons per minute (195 gpm <br />from the aquifer and 413 gpm from the two faults) and to develop a map of <br />the total projected water level decline in the affected aquifer (see <br />Figure 5). A description of the modeling can be found on pages 2.05-47 <br />to 2.05-49a within the revision application. <br />The applicant has projected that the ground water level declines within <br />the permit and adjacent areas will be confined to the Wadge <br />coal-overburden aquifer. This is supported by the thick shales and <br />siltstones separating the Wadge coal-overburden aquifer from the <br />underlying Trout Creek sandstone aquifer and overlying Twentymile <br />sandstone aquifer. <br />The maximum 608 gpm mine inflows projected by the applicant for the mine <br />after five years represents a removal of ground water stored within the <br />Wadge coal-overburden aquifer. Figure 4 shows the projected decline of <br />the piezometric surface within the Wadge coal-overburden aquifer. <br />The dewatering of the Wadge coal-overburden aquifer and the fault zones <br />by the mine workings may impact the recharge of the Fish Creek alluvial <br />aquifer and base flow in Fish Creek. However, during the five-year <br />permit period, the applicant projects only minor decreases. The <br />