2008-03-03_PERMIT FILE - C2006085 (16)

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Ms. Angela Bellantoni Apri125, 2007 Page 5 The nearby water supply wells, including residential wells, have low reported yields. The Northfield monitoring wells also have low reported yields and conditions encountered during the drilling of permit number 222887-A recently confirmed low yields in the area. The nearby wells are completed in shallower stratigraphic intervals within the Vermejo formation and based on the geology and the well completion information; the local wells are verb likely hydraulically disconnected from the Ocean Wave coal seam. The permeabilities of the Vermejo sediments including the coal seam are very low. Based on information available from the on-site monitoring well, geologic logs and geophysical logs, there is little vertical seepage in this geologic unit. The results of drawdown calculations, based on the hydrologic properties of the Vermejo formation, indicated that there are no significant water level changes projected in the intervals above and below the coal. Projections of water level changes in the coal were made utilizing common ground water equations and the hydraulic properties determined from previous analyses and published reports. We used the Theim equation and the following aquifer parameters to quantify potential impacts to the well. Hydraulic conductivity: Range from 1 to 5 gpd/ft? Horizontal distance from mine boundary to well: 2500 ft Starting head (ft above coal seam): 200 ft Estimated inflow: 30 gpm Radius of mining operations: 3000 ft Unconfined /confined conditions, steady state conditions Note that hydraulic conductivity value is supported by published reports (Horizontal Hydraulic Conductivity Estimates for Intact Coal Barriers Between Closed Underground Mines, Environmental and Engineering Geoscience; August, 2006; v. 12; no. 3; P. 272 -282). Specific capacity data from nearby wells suggest lower hydraulic conductivity values in the Vermejo formation. The projected water level change in this one well (Permit No. 222887-A) ranges from 0 to 15 feet based on information available on the hydrologic properties of the Vermejo sediments. Water level change projected for other nearby wells will be less than this amount due to the greater distances from the mine. Even if water level changes of this magnitude do occur, the slight change in water level is not expected to impact the performance of the well. Water levels in wells are constantly changing due to well pumping and natural hydrologic cycles. The well should be able to tolerate the slight change. It is recognized that subsidence of the mine will result in localized fracturing above the mine cavity. A rubble zone likely to form above the mine is projected to extend less than 100 feet vertically above the mine and is projected to be isolated to the area within the angle of draw, as presented in Figure 2. In order to determine the potential for impacts to wells in and near the rubble zone, a well inventory and drawdown analyses were P~ ~i~ ~r~ • completed for wells in and near the rubble zone. The well inventory indicated that there