2010-01-25_PERMIT FILE - C1981044A (4)

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declines in the levels in Wells 81-01 and 83-O1 between 1988 and 1990 appear to have leveled off since the middle of 1990. Water levels in these two wells and in Well TR-7A measured during 1991 are similar to the levels measured in 1983 and 1984. The slight recovery from 1984 through 1988 is apparently the result of a shift in the location of mining to an area further up dip. Water level fluctuations since 1983 are greater in Well 81-O1 as compared to Wells TR-7A and 83-01 as would be expected since this well is closer to the location of mine dewatering. The water levels in Well 83-02 show a different pattern. The water level decline of about 150 feet from 1987 to mid 1989 in Well 83-02 is determined to be related to mine dewatering as No. 5 Mine workings approached the location of the well. The more abrupt 200 foot decline in water levels observed near the end of 1989 and beginning of 1990 is thought to be a drawdown response due to subsidence as its location is only a few hundred feet horizontally from as F seam longwall panel, which was mined in a similar time frame. Wells TR-4 and 83-03 are located at greater distance horizontally from the active operations for Mines 5 and 6. Water levels in Well TR-4 appear to be related to the fluctuations observed on all three of the down gradient Middle Sandstone wells, 81-O1, 83-O1, and 83-02. The water level decline in TR-4 prior to 1984 and [he subsequent recovery up to 1988 closely parallels the trends observed in wells 81-O1 and 83-01. The decline during the first part of 1991 also parallels the [rend in these two wells. However, the rapid decline during the last part of 1989 and the first part of 1990 appears to follow the trend observed in well 83-02 although the magnitude of decline is considerably less. Well 83-03 is the Middle Sandstone monitoring well located furthest (more than 1.5 miles) from active underground operations for Mines 5 and 6. The water levels in Well 83-03 show pattern that requires further explanation given that potentiometric levels at the well are under flowing artesian conditions. The overall trend for this well from 1984 through 1992 suggests a decline in potentiometric levels in this well of about 25 feet based on the linear regression line included on Figure 17, Section 2.04-7, Hydrology Information. However, the occasional sharp decline followed by rapid recovery which appear in the time plot are likely the result of errors in obtaining an accurate measurement of equilibrium artesian pressures within the well. The long-term decline could be a pressure response due to the overall drop in piezometric levels in the Middle Sandstone in the vicinity of Mines 5 and 6. On the other hand, there was no apparent relationship between the fluctuations observed in Well 83-03 with the fluctuations observed in other Middle Sandstone wells due perhaps [o possible pressure measurements fluctuations and the further distance [o the well. Based upon the 1992 piezometric map (Map 13), the ground water gradient in [he Middle Sandstone ranges from 120 feet per mile to the southwest to 60 feet per mile to the southwest. The drop in piezometric levels in the Middle Sandstone unit above the subsided longwall mine panels in the F and E coal seams has created a potentiometric gradient to the south in the vicinity of the longwall panels. The rock slope entries between the "E" and the "H" seams are not anticipated to significantly modify the probable hydrologic consequences. The rock slopes will be approximately 1,650 feet long, starting in the `B" seam at an elevation of 5,147 feet, and ending in the "H" seam at an elevation of 5,622 feet. The ramps will be mined at a 15% grade. Geologic characteristics of the area are known from borehole 94-08. The ramps penetrate a series of coal seams (E, F, and H seams), shales and sandstones. Three sandstone strata separated by shales will be encountered in the rock slopes at the following intervals (from the bottom of the rock slopes in the "E: seams): • 254-528 feet (sandstone 275 feet thick); • 828 - 962 feet (sandstone 134 Feet thick); • 1,039 - 1,180 feet (sandstone 141 feet thick). These three sandstones form the Middle Sandstone, which in several other exploration boreholes is composed of only one strata. The sandstone is water bearing and the static water level (potentiometric surface) is at an elevation of 6,100 feet in the general area of the rock slopes. Hydraulic conductivity of the sandstone strata was estimated as 1.42 ft/day (5x10° cm/sec). This estimate is based on permeability testing in other boreholes in the mine permit area. Although some ground water inflow during [he rock slopes excavation could occur from the shales and coal seams, Permit Renewal No. 4 2.05-41 Revised 3/5/03