GENERAL32613 - Laserfiche WebLink

Home Browse Search

• -25- The depletion of ground water from aquifers may impact the discharge of over and underlying aquifers by drying up springs and seeps. The applicant has identified only two springs, SP-1 and SP-2 in the permit and adjacent areas. The drying up of these springs will slightly reduce surface flow during high flow periods and also improve water quality, since these springs are intermittent and have poor water qualities. The net impact of drying up these springs will be minimal and even beneficial since the water quality of these springs is poor. The•depletlon of bedrock ground water in the mine area will not impact any wells within the permit and hydrologically adJacent areas. Water depleted from ground water aquifers will be replenished upon closure of the mine. The depletion will continue until the mine working fill and an equilibrium is established between the mine workings and the overlying and underlying strata. All underground mines that induce subsidence have the potential to Increase mine inflows particularly if the subsidence occurs within a 'u' Significant source of water (ex. stream, pond, alluvial aquifer). However coal mine subsidence does not seem to be a source of Significant inflows into the North Thompson Creek Mines. Areas which have undergone longwall and pillar extraction (e.g., areas of controlled subsidence) do not pontrlbute significant inflows. This can be attributed to the fact that these mine areas are not under perennial stream valleys, but under the ' steep h111slopes. Limited extraction is planned under Middle and North Thompson Creeks in the future. This limited extraction will minimize the impacts of subsidence on the hydrolpgtc balance of the overlying stream and aquifers. Future monitoring of mine Inflows will enable the ' quantification of the effects of subsidence on the quantity of ground and surface waters. The applicant has submitted analyses of the coals, roof, and floor strata. The analyses of the roof dnd floor materials performed by the So11s Laboratory of Colorado State University (Appendix 3-I) indicate that these units contain Insufficient carbonate minerals to buffer the iron sulfide (e.g., pyrite) contained in these strata. These analyses Indicate that these strata are acid-forming and potentially toxic. The inactive North Thompson Creek No. 2 Mine contains both acid and toxic mine waters (see laboratory analysis of Portal No. 2 Mine, dated June 22, 1982). This analysts shows that mine water in the No. 2 Mine exceeds ` receiving stream standards for the following ions: aluminum, cadmium, chloride, copper, iron, manganese, anmtonla, sulfate, zinc, and total dissolved solids. Afield measurement of pH by MLRD staff obtained a pH -, value of 2.5 for the No. 2 Mine water. It must be noted that this mine is abandoned and "pre-law"; it is not proposed to be reopened not permitted under this proposed decision. During mining, water which collects in the mine has limited exposure to the affected strata prior to discharge to the surface. Thus, there 1s little degradation of water quality. However, upon completion of mining, there is a potential for the formation of acidic and toxic mine waters. This degradation of water quality would result from the prolonged ekposUre of water to fractured roof strata and to the exposed coal and' floor strata once the mine pumps are shut off.