Laserfiche WebLink
a) Longwall operation induced subsidence creates a zone of increased permeability <br />above the mined -out area and within a 15 to 25 degree angle of draw. <br />b) Cracking and opening of fissures at the ground surface can occur within the zone of <br />tensile strain. However, the depth of such subsidence fractures is limited. <br />c) The zone of increased permeability above the longwall operation is typically 30 to <br />50 times the thickness of the removed strata. <br />d) The thickness of the zone of increased permeability is dependent on the thickness of <br />the removed strata; speed of mining; and geologic character of the overburden. <br />After completion of mining, the permeability of the disturbed strata is predicted to <br />return to close to pre -mining conditions. <br />Subsidence impacts to alluvial water quantity <br />Alluvial waters should not be impacted due to mining and subsidence, due to the presence of <br />a 500-600 foot thick marine shale above the mined Wadge seam and deeper Wolf Creek <br />seam which acts as an aquiclude and minimizes the disruption in the near surface. Previous <br />subsidence along Fish Creek in the Western Mining District recorded only minimal changes <br />in the water levels in the alluvial aquifer in Fish Creek. <br />Subsidence impacts to ,ground water quality <br />The mine predicts that subsidence fracturing could cause a new hydrologic communication <br />between bedrock units with different quality. However, the applicant states that monitoring <br />do not indicate any substantial intercommunication of bedrock or alluvial aquifers. <br />Compliance with Basic Standards for Ground Water (Regulation 41 of the Colorado Water <br />Quality Control Commission) <br />Section 4.05.13(1) of the Regulations requires the establishment of one or more ground <br />water points of compliance (well) for an operation which has the potential to negatively <br />impact the quality of groundwater. The Wadge overburden and the Twentymile Sandstone <br />are the two major aquifers most likely to be affected by the Foidel Creek Mine. The <br />following wells serve as the Foidel Creek Mine's groundwater points of compliance: <br />97013TM (Twentymile sandstone), 008-77-58 (Wadge overburden), 008-AU3 (Fish Creek <br />alluvium), and 008 -AT -1 (Trout Creek alluvium). The mine's annual hydrology reports <br />contain long-term data from these wells. These data show Foidel Creek Mine is in <br />compliance with the Basic Standards for Ground Water at the groundwater points of <br />compliance. <br />Surface water <br />Several possible effects on the surface water system have been identified: <br />Discharge of mine inflow water to surface water drainages <br />Mine water discharged to the surface system will increase the conductivity, total dissolved <br />solids (TDS), and sulfate and iron concentrations in the streams receiving the discharge. <br />Foidel Creek Mine 20 August 10, 2018 <br />