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' Annual Hydrology Report April 28, 1988 Page 13 1 adjacent to the coal seam can cause localized movement of this water into the mine workings. 7b date, groundwater movements of this type have occurred in ' areas of low cover which are highly fractured (near outcrops and near stream channels) and where sandstone channels bearing water immediately overlie the coal seam. Sewndly, retreat mining, which causes subsidence, can fracture ' overlying groundwater formations causing movement of the water, usually into the mine workings. The permeability of the F seam and overlying strata is very low and the areal ' extent and quantity of water stored in these units is small. 4 The mine workings located near the outcrop, the main portal area, and along ' Sylvester Gulch behaved similarly to previous years with respect to inflows. Inflows occurred primarily from the roof in areas of lchi overburden and near the F seam outcrop. Inflow locations are essentially the same as previous years and ' are shown on Exhibit II. The estimated flows at these locations are also shown on Exhibit II for low flow conditions as well a~ spring runoff conditions. Table 1.4-3 shows total estimated sustained mine inflows for the 1987 water year. ' The seasonal pattern of mine inflows observed in the mine working at the main portal area and along Sylvester Gulch indicate that the wlluvium, coal, and ' bedrock recharge locally. The area along Sylvester Gulch wntains many naturally occurring fractures. Water groves down slope through the colluvium and fracture zones and discharges as springs and seeps. Water inflows appear to be ' controlled by precipitation (rtgstly snowmelt), depth of overburden, location and extent of fracture zones and not by the extent of the underground workings. Increased mine discharges during water year 1987 in the Sylvester Gulch fan area can be attributed to a concerted effort by WECC to keep the fan entries ' dewatered to a larger extent. This was done to prevent standing water from interfering with mine ventilation and to try to cut down on floor heave problems ' in the area. It is not likely higher in 1987 than in 1986, but that that mine inflow rates in a trade off occurred. Sylvester Gulch were The trade off being that water normally lost through seepage was actively pumped out of the mine. ' Mine water inflows for the 1988 water year in the Sylvester Gulch area and the main portal area are expected to be similar to those of 1986 and 1967 water years; however, precipitation wind have an impact on inflow rates if there is a ' dramatic change in 1988. Mine water inflows for other areas of the mine, namely the 1st West Submain, ' Panels 1W25, 1W3S, 1W45, and the 1st East Submain are related to particular geologic and topographic features as well as water bearing formations in these areas. Fach area will be discussed in detail. ' 1st West Submain The 1st West Submain was not actively mined during 1987. Areas previously ' mapped as wet or damp are shown on Exhibit II. This area remained somewhat damp during 1987, but did not produce any measureable flows. The wet areas of the 1st West Submain are thought to be associated with sandstone channels which immediately or closely overlie the wal seam and with ' fracture zones in the Inane Pine Gulch area.