REP28646 - Laserfiche WebLink

Home Browse Search

J Hydrologic Data Interpretation and Impact Assessment for the Permit and Adjacent Areas Thissec-iun focuses on three areas. First, it analvr es the hydrologic data gathered during water year 1992. Second, it assesses impacts of mining on thg quality and gnontity of water in surface streatnsa spsint,~, gYOUntlwater aquifers, mine inflows, antk mine discharges daring water year-1992. Lastly, ita estimates puteatial impacu uC.mirting on these waters daring water year 1943., Surface water, springs, and groundwater are consid- ered separately even though they are interrelated. The report attempts to show the interrelationships that are significant or could be expected. Because mine water and groundwater are so interrelated, they are discussed together. same as previous years. Separate estimates arc provided fur low [low conditions and spring runoff conditions. Table 6 shows total estimated sustained mine inflows for the 1992 water year. The seasonal pattern u( mine inflows observed at the main portal area and along Sylvester Gulch indicates the colluvium, coal, and bedrock recharee locally. The area along Sylvester Gulch contains many naturally occurring fractures. Water moves down slope through the colluvium and fracture zones and discharges as springs and seeps. Water inflows appear to be controlled by the amount of precipitation (mostly snowmclt), dcplh of overbur- den, and location and extent of fracture zones and nut by the extent of the underground ~wrkings. Assessment of Mine Water and Groundwater Mine Water The underground mining methods in use at the West Elk Mine can affect groundwater in essential- ly two ways. First, development mining in areas where groundwater is present in or near the coal seam can cause localized movement of this water into the mine workings. To date, groundwater movements of this type have occurred in areas of low cover which are highly fractured (near out- crops and near stream channels) and where sandstone channels bearing water immediately overlie the coal seam. Secondly, retreat mining can cause subsidence and the fracturing of overlying groundwater formations. Again, water usually moves inw the mine workints. At the West Elk Mine, the permeability of the "F' scam and overlying strata is vero low and the areal extent and quantity of water stored in these units are small. During 1992, the mine workings located near the outcrop, the main portal area, and along Sylvester Gulch behaved similarly to previous years, relative to inflows. follows occurred primarily from the roof in areas of low overburden and near the "F" seam outcrop. Inflow locations were essentially the Mine water inflows (or the 199? water year in the Sylvester Gulch and the main portal areas arc expected to be similar w those of the 1991 and 1992 water years. However, precipitation could have an impact on inlluw rates if there is a dramat- ic change in 199?. Data from NOAA's Somerset lE Station and Colorado Climate Report indicate precipitation during 1992 was similar to that in 1990 and 1991. - ~,~ Mine water inflows fur other areas of the mine arc related to particular geologic and topographic Features as well as water-bearing formations. In the "F' seam, these areas include the 1st West Submain, Panels I W 15, 1 W2S, l W?S, 1 W'JS. 1 WSS, 1 W6S, 1 W 1 N, 2W 1 N, the 1st East Submain. the 1 Northwest and 2 Northwest Submains, and Panels NW1S and NW2S. In the "B" scam, the areas include the West Mains. Because of theac local features, each area is Discussed separatey. "F" Seam No mining occurred in the "F" seam in 1992. The firer west Submains and crosscuts one and two were completed during the first yuaner of 1992. r 1 J