2021-01-28_REVISION - C1982057 - Laserfiche WebLink

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Ground Water Effects (South Extension Area Addendum) Probable hydrologic consequences to the ground water regime as a result of mining the Wadge, Sage Creek and Wolf Creek coal seams within the south extension area have been assessed. Localized effects to the hydrologic system will include: 1) The drawdown of ground water, due to pit dewatering. 2) The establishment of a relatively unconfined aquifer of poor quality in the backfilled pits. Spoil discharge may increase the TDS of the overburden ground water system With respect to both the overburden and coal seam ground water systems, elevated levels of TDS and individual constituents will be localized. The impact of localized water quality degradation in the coal and overburden aquifers is minimal, given that the aquifers do not yield volumes sufficient for irrigation purposes, baseline ground water quality in these systems is marginal to unsuitable for stock watering and/or irrigation, and there are no wells completed in the overburden or coal units in the mine vicinity. Regarding drawdown for the Wadge ground water system, the largest estimated radial distance will occur in the overburden aquifer, where a one-foot drawdown is predicted. For the Sage Creek/Wolf Creek systems, drawdown in the overburden is predicted. No pre-existing water sources with registered water rights including water wells were identified in the south extension area. The maximum radius of influence for one foot of drawdown over the predicted life of mine for the south extension area will not extend beyond the permit area boundary. Because drawdown will be limited to areas within the permit boundary, there is no anticipated impact to adjacent water users due to drawdown. Surface Water Effects The majority of runoff from disturbed areas within the original permit area during the mine life will be diverted to Sediment Ponds 005 and 006, prior to release off site. Effluent from Ponds 005 and 006 flows to unnamed ephemeral gulches, and ultimately Dry Creek. The majority of runoff from disturbed areas in the south extension area during mine life will be diverted to the Sediment Pond 016/016A series or to Sediment Pond 017, prior to discharge. Effluent from the ponds will flow into Hubberson Gulch, and ultimately Dry Creek. Effects of mining on Hubberson Gulch and Dry Creek will involve changes in quantity and quality, which are further described below. A negligible acreage affected by the extreme eastern extension of the south area pits and the neck pits between the north and south mining areas will drain to Sediment Ponds 009 and 015, and eventually to Sage Creek. Measurable effects on Sage Creek water quality or quantity are not projected, due to the small disturbance acreage and the fact that there will be no spoil water flow to the Sage Creek watershed. The mining and reclamation activities will result in changes to the geomorphic characteristics of ephemeral stream channels within the 005, 006, 016 and 017 drainage Page 25 of 37