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the storage pools are now being pumped intermittantly to maintain water levels below these maximum water <br />level elevations. Timing and water quality issues related to mine water discharge are discussed in "Effects on <br />Ground Water Quality of Aquifers and Surface Water Systems Impacts of Mine Water Discharge ". <br />Dewaterin2 and Potentiometric Drawdown in Bedrock Units <br />Projected inflows to the mine from the Wadge overburden unit will cause dewatering and potentiometric <br />drawdown in the unit. Wlie- e`Tlf�'�i'WLTitymite g"a —dstone directly overlies the mine }worlc"ing � Ott vviiYl also' b <br />of ef- cted.- To date,"no measurable impact to the Trout Creek Sandstone has been observed; an water quality <br />data ✓from mine inflows does not indicate any significant connection to either the overlying Twentymile <br />Sandstone or the underlying Trout Creek Sandstone. Well 006- 82 -48A, completed in the Twentymile <br />Sandstone, showed a rapid water level decline before being rendered inoperable due to being undermined by a <br />longwall panel. Other Twentymile Sandstone wells, however, which are not directly underlain by mine <br />workings, do not show any direct impact from mining. <br />Ma1or fault zones are not expected to .provide significant conduits for around water flow through the marine <br />shale in the part of the basin underlain by the proposed mining activities. This is due to the nature of the marine <br />s, es and the high overburden stress in this area, which would tend to keep the fault zones closed. Appreciable <br />ground water flows through fault zones has only been observed at the basin margins where overburden stress is <br />relieved. Well BRDH -7 is located approximately one -half mile from the mine workings and has not shown any <br />significant water level decline (Figure 12a). Futurree_minin is eg x �ected to have one localized impA.ct..on .y r <br />levels in the Twentymile Sandstone. <br />T_he _proximity of the Wadge overburden unit to the mined zone and the, expectation of subsidence - induced <br />fracturing will result in dewatering of the unit immediately above _and_ adjacent to active mine areas. Drawdown <br />of potentiometric levels in this unit will occur beyond the area of active mining as a result of lateral movement <br />of ground water toward these areas. <br />The extent of potentiometric lowering was investigated using the finite- difference simulation model described in <br />Exhibit 13, Ground Water Model Documentation. The model did not account for mine inflow derived from <br />dewatering of the overburden directly above active mining areas. However, this does not invalidate the <br />prediction of drawdown effects as this is based on the estimates of lateral movement toward mined areas which <br />was correctly assessed. The extent of potentiometric lowering is illustrated by predicted drawdown after 5 years <br />of mining (starting in 1983) and it is shown on Figure 13, Predictive Analysis After 5 Years of Mining. This <br />figure indicates that drawdown effects will extend to the outcrop areas of the overburden unit at the margin of <br />the Twentymile, Park Basin. Evaluation of data from observation wells indicates that these predicted effects are <br />probably overestimated. <br />Recovery of potentiometric levels within the overburden unit will occur following mining through recharge of <br />the unit, primarily at the basin margins. Subsidence effects will cause fracturing and rubblization of the <br />overburden unit, so that its postmining permeability will initially be much higher than typical premining values. <br />Consequently, the rate of potentiometric recovery will primarily be governed by the rate of recharge. <br />Recharge to the mine workings will primarily be from the updip spoils area of the adjacent Eckman Park surface <br />mine. During mining, and for most of the recovery period following mining, the workings and overlying <br />overburden adjacent to these spoils areas will not be saturated i.e. the effective potentiometric head will be at the <br />elevation of the base of the mined zone. The spoil at the old highwalls is expected to be fully saturated under <br />reclaimed conditions, as is the case near the Foidel Creek Mine portal area. The effective potentiometric head in <br />the spoils in these areas is therefore near the land surface elevation. The head differential across the unmined <br />interval during and following mining is considerably higher than under premining conditions due to the <br />dewatering of the mined zone and overlying overburden unit. This situation induces recharge at a <br />proportionately higher rate than under baseline conditions. The rate of recharge to the workings from the spoils <br />at any given area is governed by the distance between the two areas, the transmissivity of the unmined material <br />PR09 -08 2.05 -139 04/27/09 <br />