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areas, west of Trout Creek and above TR <br /> 1.5 <br />209186 domestic, SWNESec14T4NR86W alluvial, appears to be out of specified <br /> household azea, west of Trout Creek. and above TR <br /> 1.5 <br />63790 domestic NENESec25T5NR86W alluvial, appears to be out of specified <br /> area, west of Trout Creek, 1.5 mile below <br /> minin activi <br />84697 domestic SENWSec36T5NR86W bedrock, appears to be the Trout Creek <br /> Sandstone monitorin well TCS-1 <br />There aze no known domestic or agricultural uses of groundwater from the Trout Creek alluvial <br />or spoil aquifer specified azeas. The use of shallow wells developed in backfill spoil areas would <br />be of limited value due to the small quantities of water available within this spoil aquifer. By <br />observed values of spoil spring and alluvial water quality, a classification of potentially usable <br />quality is selected for these two specified azeas in this review. The TDS level criteria of <br />potentially usable quality is 10,000 mg/1 for both of these specified areas. Post mining spoil water <br />was expected to have average TDS values of 3,000 mg/I (PAP page 2.5-96). However, discharges <br />from sedimentation ponds fed by spoil springs have TDS values in the 4,000s, and at times <br />approach 5,000 mg/l. Water from the spoil aquifer would be expected to have TI)S levels that <br />correspond to the spoil springs. Values of TDS in monitoring well WR-1, a spoil sampling point, <br />have ranged as high as 4570 mg/1 to date. [This prediction is called to the attention of the <br />operator in an adequacy letter.] As indicated above, spoil spring discharges appear to have an <br />impact on specified Trout Creek alluvium with TDS values in the 4,000s. All these values aze <br />less than ] 0,000 mg/1. Thus the Edna mine is in compliance with potentially usable quality <br />criteria with regard to Trout Creek alluvial and spoil aquifer specified areas. <br />There is a known domestic use of the Trout Creek Sandstone within a zone of potential impact, <br />and this aquifer could possibly serve as a ground water supply for the postminin€; rangeland <br />use. However, the potential impact from mining activities to the Trout Creek Sandstone is <br />limited. The shale bedrock in the low-wall of the mine pit may be a permeability barrier to <br />subsurface discharge of leachate. The Trout Creek is a few hundred of feet deeper than the <br />mined coal sequence, and most likely is not in hydraulic communication with the bottom of the <br />pits due to relatively impervious intervening layers. In addition, leachate has lower head than <br />adjacent bedrock in most place, and there is minimal opportunity for leachate to infiltrate these <br />bedrock units. Regional hydrology indicates ambient head in any permeable bedrock unit can <br />be expected to be several tens of feet above the elevation of the unit; the head exerted by spoil <br />leachate ranges between only 25 ft. and 50 fr. In addition, there has been no change in the <br />range, and no indication of rising values in, the monitored well TCS-I. The TDS threshold for <br />this classification is also 10,000 mg/1. The maximum TDS value in TCS-1 was 860 (except for <br />an abnormal reading) during the monitoring period 7/1995 through 10/2003. There was no <br />sample taken during 2004.monitoring. Thus the mining activity is considered to be in <br />compliance with this rule for this specified azea. <br />Colorado Dischazge Permit System <br />Page 8 <br />