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Groundwater Points of Compliancess <br />Page 10 <br />Whereas the Trout Creek Sandstone is believed to be the first unit below the lowest pit <br />disturbance (Wadge Coal) with any significant potential as an aquifer, that there is approximately <br />200 feet of relatively impermeable strata between the spoil groundwater of the former mine pits <br />and the Trout Creek Sandstone, and that the piezometric surface within the Trout Creek <br />Sandstone is higher than the free water surface of the spoil groundwater (springs and seeps), the <br />Division concludes that there is no potential to negatively impact the quality of groundwater in <br />the Trout Creek Sandstone. Therefore, a point(s) of compliance is not required for bedrock <br />groundwater at the Edna mine (Permit C-1980-001). <br />The alluvium of the Trout Creek alluvial valley floor (current flood plain) is hydrologically down <br />gradient of mining activity within the permit area. A barrier of undisturbed, relatively <br />impermeable strata was left between the mine pit(s) of the Edna mine and the alluvium. Spoil <br />groundwater manifests itself in springs and seeps in the vicinity of the former pit low walls <br />(uphill side of the barrier), and these spring and seep flows are collected and discharged to Trout <br />Creek. The potential for breach of the barrier, providing a direct source of impact from lazge <br />flows of spoil ground water to the adjacent alluvial waters of Trout Creek, is considered by the <br />Division to be remote. However, a by-pass of the bamer at the south end of the permit azea may <br />have occurred, allowing underground spoil groundwater to flow to TR-1.5. Concentrations of <br />TDS at TR-1.5 have reached the levels of those concentrations found in spoil groundwater. There <br />has additionally been a slight rise in the concentrations of TDS at TR-3 and at TR-4 since 1994. <br />Another source of impact, considered by the Division to be very limited, is infiltration of <br />sediment pond outfall discharges from the two unlined ditches across the alluvial valley floor to <br />Trout Creek. <br />A third potential impact is Trout Creek itself. Dischazges from the sedimentation ponds have an <br />impact on the water quality of Trout Creek. In turn, the waters of Trout Creek could have the <br />potential, through recharge, to impact the alluvial ground water. However, the Division <br />concludes that Trout Creek is a gaining stream in the specified area (ground water flow is from <br />alluvial areas to creek surface flow), and, without drawdown of alluvial water within the flood <br />plain, surface Trout Creek flow does not (significantly) recharge the adjacent alluvial areas. <br />The mine operator considered monitoring well TR-3 to be the best indicator of the baseline <br />quality of alluvial waters that have a potential for being affected by mining in the Moffat area.sb <br />Although there are numerous references (in the PAP) to possible sources of impact on alluvial <br />ground water, there appeazs to be the potential for an impact to alluvial ground water From spoil <br />ground water. Designation of TR-3 as a point of compliance may be appropriate. <br />ss C WQCCR 41 page 17 (41.66) <br />se PAP page 2.5-75 <br />