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La Plata Coal Draft Finings - 9 - May 18, 1987 <br />manner so as to minimize impacts to the prevailing hydrologic balance within <br />the alluvial aquifer. La Plata Coal Corporation has committed to sealing the <br />sediment pond with a non-toxic substance to minimize the infiltration of <br />holding water into the alluvial material in which the pond is incised. <br />Furthermore, the sediment pond, which is adequately sized to contain the <br />runoff from a ten year, 24-hour storm, will not discharge until a storm event <br />of this magnitude has been exceeded. <br />In order to document that the sediment pond does not degrade the quality of <br />the Hay Gulch aquifer, La Plata Coal Corporation has committed to completing a <br />monitoring well immediately down-gradient from the sediment pond. This well <br />will be monitored for depth-to-water and water quality as explained in <br />Section V of this document. <br />The La Plata Mine No. 1 will operate a leach field within the bounds of the <br />Hay Gulch alluvial valley floor. The La Plata Coal Corporation has <br />demonstrated to the satisfaction of the San Juan Basin Health Unit that the <br />area in which the leach field will be constructed does not contain ground <br />water within eight (8) feet of the AVF surface. As the leach field is small <br />in size, and the depth-to-water is more than two (2) feet below the bottom of <br />the leach field, the Division has approved construction of this facility. <br />In order to verify the water table elevation in this area, the La Plata Coal <br />Corporation has committed to constructing a ten (10) foot deep, two (2) inch <br />diameter monitoring well ten (10) foot down gradient from the leach field. <br />Depth-to-water measurements will be taken during periods of snowmelt runoff <br />and during the wet months of September or October. <br />B. Cumulative Hydrologic Impact Assessment <br />The Division has made an assessment of the probable cumulative hydrologic <br />impacts of anticipated and permitted mining operations within the ground water <br />and surface water study areas. <br />The purpose of the cumulative hydrologic impact assessment is to determine the <br />cumulative impacts to the hydrologic system from all existing and anticipated <br />coal mining operations within the ground and surface water study areas. <br />The surface water study area is defined as the Hay Gulch drainage basin from <br />about Hesperus, Colorado, to its' confluence with the La Plata river, near <br />Kline, Colorado. The ground water study area is defined at the Menefee <br />Formation and Hay Gulch alluvial aquifer in the immediate vicinity of the <br />existing and anticipated mining activities. <br />The coal mining operations which are considered in this cumulative assessment <br />include the La Plata No. 1 (permit application submitted; inactive), King Coal <br />11ine (permit issued; active), and the Blue Flame Coal Mine (permit issuance <br />pending; inactive). <br />Ground Water <br />As discussed in Sections V and IX of this document, the Menefee Formation in <br />the vicinity of Hay Gulch is essentially dry. Due to lithologic and <br />topographic variables, limited perched aquifers will exist within the <br />formation. Mining activities will dewater those perched aquifers which <br />