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• Hydrologic Data Interpretation and Impact Assessment for the Permit and Adjacent Areas L_I This section focuses on three areas. First, it analyzes the hydrologic data gathered during WY 1993. Second, it assesses impacts of mining on the quality and quantity of water in surface streams, springs, groundwater aquifers, mine inflows, and mine discharges during WY 1993. Lastly, it estimates po- tential impacu of mining on these waters during WY 1994. Assessment of Mine Water and Groundwater Mine Water The underground mining methods in use at the West Elk Mine can affect groundwater in essentially two ways. First, development mining in areas where groundwater is pres- ent in or near the coal seam can cause local- ized movemen[ 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 immedi- ately overlie the coal seam. Secondly, re- treat mining can cause subsidence and the fracturing of overlying groundwater forma- tions. Again, water usually moves into the mine workings. At the West Elk Mine, the permeability of the "F" and "B" seams and strata of the Mesa Verde Foundation overly- ing the "F" seam and located between the "F" and "B" seams is very low, and the areal extent and quantity of water stored in these units are small. During WY 1993, the mine workings locat- ed near the outcrop, the main portal area, and along Sylvester Gulch behaved similarly to previous years, relative to inflows. In- flows occurred primarily from the roof in areas of low overburden and near the "F" seam outcrop. Inflow locations were essen- tially the same as previous years. Separate estimates are provided for low flow condi- tions and spring runoff conditions. Estimat- ed sustained mine inflows (5 acre-feet) for the WY 1993 water year are shown in Ta- ble 6. The seasonal pattern of mine inflows ob- served at the main portal area and along Sylvester Gulch indicates that the colluvium, coal, and bedrock recharge locally. The area along Sylvester Gulch contains many natu- rally 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 snowmelt), depth of overburden, and location and extent of fracture zones, and not by the extent of the underground workings. Mine water inflows for other areas of the mine are related co site specific geologic and topographic features as well as water-bear- ing formations. No measurable inflows of water (mine inflows requiring conveyance to a sump and pumping from the mine) were detected with mining in the "B" Seam. The observation is that mining activity continues to dewater the coal seam as mined, and local areas of roof and floor fractures. Once initial dewatering is complete, there appears to be no sustained (recharge) flows. There appears to be no correlation with seasons or precipitation events. The interpretation is that migration of water from overlying and underlying formations is very low. These low quantities are thought to be from a 11