Laserfiche WebLink
hydrogeologic model. The mine flow estimates assist in identifying the <br />magnitude of mine discharge and to assess the potential impact on <br />natural patterns of groundwater recharge and discharge. <br />In the past, the West Elk Mine has experienced three types of mine <br />inflows. The first type of inflow is due to primary permeability which <br />is groundwater flow through the competent portions of the F Seam and <br />lower Barren Member. The second type of inflow occurs in the coal <br />seam and overlying Barren Member in areas of shallow overburden. <br />This is secondary permeability and is the result of groundwater flow <br />through the fractured and weathered portions of these strata. The <br />fractured rock acts as a conduit to the surface colluvial aquifers. The <br />third type of inflow is also due to secondary permeability and it is the <br />result of groundwater flow along fault zones. These fault zones may be <br />in contact with surface aquifers with water bearing zones in the <br />overburden, or with deep-seated sources of groundwater. The streams <br />in the North Fork area are generally fault controlled and may be a <br />source of recharge for fault related inflows. Prior [o the construction of <br />the mine entries, piezometers were installed in the colluvial/landslide <br />strata immediately .upslope of the entries. All piezometers but one were <br />destroyed during construction of the entries. <br />The operator at the West Elk Mine expects that mine inflows will <br />increase at a rate slower than the McWhorter model predicted for <br />advancing mine workings. Most of [he inflow has occurred along the <br />subcrop in the same location each year. The inflow is seasonal and <br />varies with the magnitude of seasonal precipitation. The experience <br />near the F Seam subcrop indicates that the colluvium, coal and bedrock <br />are recharged locally. In prior years, inflow to [he advancing mine <br />workings has been minimal and unmeasurable. However, in March <br />1996, MCC experienced a large inflow of water in the B East Mains <br />while mining through afault/fracture system. In April 1996, MCC <br />encountered the same fault in a subsequent entry, the inflow was <br />estimated to be a maximum of 2,500 gpm. The flows have since <br />receded. In May 1996, the flow was measured at approximately 240 <br />gpm and had diminished to less than 100 gpm by December 1998. <br />Three of the five entries experienced inflows during construction, <br />which began in September of 1981. Adit entry No. 4 experienced the <br />greatest inflow, about 5 gpm, which decreased to less than 1 gpm and <br />dried up within a week. The No. 1 entry produced a small quantity of <br />water from the bottom of the coal at a rate of less than 1 gpm and dried <br />up within two weeks. However, the sandstone roof at entry No. 1 was <br />dry. Entry No. 5 produced drips, approximately 0.1 gpm, for about <br />one week. The other two entries were dry. During the period from <br />August to December 1981 water levels dropped in some of the <br />35 <br />