Laserfiche WebLink
post-mining water quality in Ward Creek (see page 68 of <br />Volume 8 of the application, September 9, 1982, addendum). <br />This change in water quality could affect water-use patterns <br />in the vicinity of the mines. A TDS of 900 mg/1 is high for <br />domestic uses. Information in the application indicates that <br />there is little domestic use of ground water in the area. <br />Most domestic water users obtain their water supply from the <br />Colby municipal water line. Other users of water (stock, <br />irrigation, and industrial) should not be significantly <br />affected by the predicted water quality change. Monitoring <br />of water will be conducted to verify these predictions. <br />i. Impacts from Coal Mine Waste Disposal on Groundwater <br />The applicant placed mine development waste in old <br />abandoned strip mine pits (see Map 2.05.3(2)(b)-1 of the <br />permit application). Some additional disturbance was <br />proposed but never occurred. The underground development <br />waste pile is completely underlain by bedrock and will <br />not be in direct contact with the unconsolidated <br />glacial/alluvial material. The applicant has determined <br />that significant vertical permeabilities do not exist in <br />the strata near the mine (see pages 20-35 of Volume 8). <br />Therefore, vertical infiltration of leachate from the <br />refuse pile into underlying aquifers should not be a <br />significant problem. <br />No predictions of specific quality are available; <br />however, experience at backfilled areas in northwestern <br />Colorado suggest that a rough estimate of volume can be <br />calculated from an acreage analysis. Given 21 acres of <br />disturbance at Red Canyon, peak spoils discharge could <br />reach 30 gallons per minute following snowmelt. This <br />value probably overestimates the discharge, given the <br />lower precipitation regime near Cedaredge. <br />b. Surface Water Effects and Mitigation <br />Three probable impacts to the surface water regime have been <br />identified by the applicant. During the active mining phase, <br />mine dewa tering may have lessened the volume of water dis- <br />charging to the streams from the alluvium and could poten- <br />tially have caused a gradient reversal. The discharge of <br />mine inflow water would change the location of groundwater <br />discharge to the surface water system and result in a <br />degradation of water quality. Following sealing of the mine, <br />and the reestablishment of the coal aquifer, discharge of the <br />mine water to the glacial-alluvial aquifer could result in a <br />diminution of water quality of the adjacent streams. <br />Some depletion of the stream/alluvial aquifer system could <br />occur through the coal seams themselves which subcrop beneath <br />21 <br />