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~ Hydrologic Data Interpretation and Impact Assessment for the Permit and Adjacent Areas • This sect.jon focuses on three areas. first, it analyze es the hydrologic data gathered during water year 1992. Second, it assesses impacu of mining on thg quality and quantity of water in surfscc streams springs, groundwater aquifers. mine inflows, antb mine discharges during water year 1992. Lastly, it_ estimates ptxential impacts of mining on these waters daring water year 1993. , Surface water, springs, and groundwater arc wnsid- ered separately even though they are interrelated. The report at[empts to show the interrelationships that are significant or could he expected. Because mine water and groundwater are so interrelated, they are discussed together. 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 totalized movement of this water imo the mine workings. To date, groundwater movements of this type have occurred in areas of low cover which are highly Iractured (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 Cormations. Again, water usually moves into the mine workings. At the West Elk Mine, the permeability of the "F' seam and overlying strata is very low and the areal extent and quamity 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 simiWrly to previous years, relative to inflows. lnllows occurred primarily from the roof in areas of low overburden and near the "F" seam outcrop. Inflow locations were essentially the same as previous years Separate estimates arc provided fur bw flow conditions and spring runoff conditions. Table 6 shows total estimated sustained mine inflows fur the 1992 water year. The seasonal pattern of mine in0uws observed at the main portal area and along Sylvester Gulch indicates the colluvium, coal, and bedrock recharge locally. The area along Sylvester Gulch contains many naturally occurring fractures. Water moves down slope through the colluvium and Iracture runes and discharges as springs and seeps. Water inflows appear to he controlled by the amount of precipitation (mostly snowmelt), depth of uverbur- den,and location and estcnt of fracture zones and not by the extent of the underground workings. Mine water in0uws fur the 1993 water year in the Sylvester Gulch and the main portal areas arc expected ut be similar to 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 1993. Data from NOAA's Somerset lE Station and Colorado Climate Repun indicate precipitation during 1992 was similar w that in [990 and 1991. - ~ .l,~ S 7 , ! i~ Mine water inflows for other areas of the mine are related w particular geologic and topographic features as well as water-bearing formations. [n the "F' seam, these areas include the Ist West Submain, Panels 1 W 1S. 1 W2S, I W3S, I W'-!S, 1 WSS, f W6S, 1 W 1N, 2W 1N, the lst East Submain, the 1 Northwest and 2 Northwest Submains, and Panels NWIS and NW2S. In the "B" scam, the areas include the Wcst Mains. Because of these local features, each area is discussed separatcy. "F" Seam No mining occurred in the "F' seam in 199'_. The lust west Submains and crosscuts one and two were completed during the first quancr of 1992. •