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Overburden monitoring wells have varied, depending on location. Hydrographs for Wells 006- 82 -74C south of <br />the portal and 009 -79 -4 south of the SWMD show little change other than small seasonal fluctuations. <br />However, hydrographs for Wells 006 -87 -01 and 91M006 near the Northeast Mains and Well 93M001 near the <br />southwestern corner of the EMD show significant declines since the early- to mid- 1990s, presumably in <br />response to mine dewatering. The water -level in Well 91M006 declined about 600 feet between 1992 and 2005, <br />and an additional 125 feet between 2005 and 2010, but between 2010 and 2013, the water level recovered about <br />40 feet. The water level in Well 93M001 declined about 440 feet between 1995 and 2002, but only an <br />additional 28 feet between 2002 and 2013. <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. This does not, however, 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) as shown on Figure 13, Predictive Analysis After 5 Years of Mining. This figure <br />indicates that drawdown effects may extend to the outcrop areas of the overburden units at the margin of the <br />Twentymile Park Basin. The permeability of the Wadge /Wolf Creek Interburden and Wolf Creek Seam, as <br />measured in recently - installed monitoring wells WC008 and WC013, is 0.0016 ft/d, or about 25 times lower <br />than that of the Wadge Overburden. Given the extremely low permeability of the Wadge /Wolf Creek <br />Interburden and Wolf Creek Seam, mining of the Wolf Creek Seam is not anticipated to result in any significant <br />incremental impacts on ground water levels or occurrence beyond those that have already occurred in <br />conjunction with the Wadge Seam mining activities. <br />Recovery of potentiomctric levels within the overburden units will occur following mining, through recharge of <br />the units, primarily at the basin margins. Subsidence effects will cause fracturing and rubblization of the <br />overburden units, so that 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 up -dip spoils area of the adjacent Eckman Park <br />surface 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 potentiornetric head will be at <br />the elevation of the base of the mined zone. The spoil at the old highwalls is expected to be fully saturated <br />under reclaimed conditions, as is the case near the Foidel Creek Mine Portal Area. The effective potentiometric <br />head in the spoils in these areas is therefore near the land surface elevation. The head differential across the <br />unmined 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 />in any given area is governed by the distance between the two areas, the transmissivity of the unmined material <br />in this interval, the head differential across the interval, and the length over which these conditions prevail. The <br />total recharge rate is given by the standard steady -state flow equation. <br />Q= �l <br />D <br />where: Q = recharge rate (ft3 /day) <br />T = Transmissivity of un -mined interval (ft2 /day) <br />h, = potentiometric head in spoils (ft) <br />hz = potentiometric head in workings (ft) <br />D — distance between spoil and workings (ft) <br />L — length perpendicular to flow over which above conditions prevail (ft) <br />The head differential between the spoils and the Wadge Seam underground workings is approximately 300 ft (h, <br />— 112). The distance between these two areas in the southeastern part of the permit a -rea is about 1,000 feet (D), <br />and the length over which these conditions prevail is about 5,000 feet (L). Further to the west, the distance <br />between existing or proposed spoils and the proposed underground workings increases rapidly due to the <br />PR14 -10 2.05 -140 12/18/14 <br />