Laserfiche WebLink
r ' _ -• <br />mines. As such, effects on surface water are limited to the direct effects of <br />mining on surface water contained within the respective mine permit boundaries. <br />Each mine has provided a statement of probable hydrologic consequences as a <br />part of their individual permit applications. All three mines have identified <br />increased erosion rates from disturbed areas as the primary effect of mining. <br />A limited potential exists for increases in total dissolved solids <br />concentrations (TDS) in mine effluent. The increases in TDS mdy result from <br />dewatering of perched aquifers or subsidence related ground water discharge to <br />the surface water system or from contact of surface water with coal fines on <br />the mine benchs at these three mines. Any increases in TDS are expected to be <br />small since the dilution of surface water discharges with elevated TDS in the <br />volume of alluvial ground water is sufficient to limit the impact on the <br />receiving water. A small amount of acid drainage from the La Plata No. 1 Mine <br />has been documented to occur (4 to 3 gallons per minute), however a treatment <br />system will be installed to neutralize this water. Effects of mining on <br />surface water are controlled at each of-the three sites through the use of <br />sediment ponds and treatment systems. Cumulative impacts are limited to the <br />effects on ground water as discussed in the following section. <br />2. Ground Water Effects <br />As discussed in Section V-Ground Water of this document, the Menefee Formation <br />in 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 />overlie the operations. As these aquifers are not contiguous and are not put <br />to any use in this area, no impact to the hydrologic system will be realized. <br />Water from disrupted perched systems may discharge from up-dip mining entries <br />(La Plata No. 1 Mine). Water flowing into down-dip mining operations (King <br />Coal Mine, Blue Flame Coal Mine) will tend to flow away from the mine entries, <br />perhaps recharging the coal face when mining has ceased. <br />Due to the hydrologic and geologic characteristics of the Menefee Formation, <br />as welt as local topographic controls, no significant hydrologic impacts to <br />this system are anticipated. <br />The Hay Gulch Alluvial Valley Floor has been identified as an aquifer in the <br />study area. The Blue Flame Coal, La Plata No. 1 and King Coal Mines have been <br />designed to minimize, to the extent possible, impacts to the alluvial <br />aquifer. The sediment ponds at the King Coal Mine have never discharged into <br />the AVF. The proposed sediment pond at the Blue Flame site, as well as the <br />existing La Plata No. 1 Mine sediment pond, have been sized to treat the <br />runoff from a 10-year, 24-hour storm event. No discharge is expected from any <br />of these ponds due to a storm event of lesser magnitude or as a result of <br />snowmelt. Furthermore, monitoring of the alluvial aquifer downgradient from <br />the King Coal operation indicates that the quality of the alluvial aquifer is <br />not being diminished by coal mining operations. Alluvial water quality <br />monitoring programs committed to by both La Plata Coal Corporation and <br />National King Coal, Inc., will help delineate the potential for future impacts <br />to this alluvial system. <br />-20- <br />