2018-01-03_REVISION - C1994082 (29)

Home Browse Search

F. Probable Hydrologic Consequences Probable hydrologic consequences of the Tab 17 of the permit application package. presented here. Groundwater Yoast mining operations are discussed in A summary of that discussion is The probable hydrologic consequences to groundwater resulting from coal extraction at the Yoast Mine include drawdowns to aquifers from pit inflows, and subsequent pit dewatering and production well pumping as well as impacts to groundwater quality resulting from flow through mine spoil. As the Yoast Mine is now reclaimed, pit dewatering and production well pumping will not occur during the 2015-2020 permit term. Seneca's predictions of the magnitude of these impacts are discussed below. Groundwater Inflows to Pits and Associated Drawdowns The Yoast Mine intercepted the following hydrologic units: the Wadge Overburden, Wadge Coal, Wolf Creek Overburden, and Wolf Creek Coal. Seneca Property, LLC used two models to predict pit inflows as a result of mining activities. The models were the McWhorter (1982) method and the Theis equation, both of which are described in detail in Tab 17 of the PAP. The Theis equation, which was also used to predict drawdowns, consistently predicted higher discharges for each aquifer with the exception of the Wolf Creek Coal than did the McWhorter method. The more conservative estimates of pit inflows from each aquifer in cubic feet per day were 365 for the Wadge Overburden, 160 for the Wadge Coal, and 745 for the Wolf Creek Overburden, and 499 for the Wolf Creek Coal. Variability in aquifer characteristics in the Grassy Creek and Sage Creek drainages cause variation in the predicted drawdowns. The radial distance to a one -foot drawdown in the Wadge Overburden was predicted to be 401 feet in the Grassy Creek drainage and 564 feet in the Sage Creek drainage. The one -foot drawdown radius in the Wadge Coal was predicted to be 369 feet in the Grassy Creek drainage and 468 feet in the Sage Creek drainage. Radial distances to the one -foot drawdowns in the Wolf Creek Overburden and Wolf Creek Coal in the Sage Creek drainage were predicted to be 452 and 491 feet, respectively. Because the drawdowns due to pit inflows were to be mostly contained within the leasehold area, and adjacent water users are located beyond the one -foot drawdown contours, no significant impact on groundwater use due to pit inflows was predicted. Impacts of Production Well Seneca Property, LLC predicted that maximum drawdowns in the Trout Creek aquifer resulting from nine years of pumping in the Yoast Production Well would 21