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Subsidence impacts to alluvial water auantit <br />Alluvial waters should not be impacted due to mining and subsidence, due to the presence of a 500-600 foot <br />thick marine shale above the mined Wadge seam which acts as an aquiclude and minimizes the disruption in the <br />near surface. Previous subsidence along Fish Creek in the Western Mining District recorded only minimal <br />changes in the water levels in the alluvial aquifer of Fish Creek <br />Subsidence impacts to ground water quality <br />The mine predicts that subsidence fracturing could cause a new hydraulic connection between bedrock units <br />with different quality. However, the applicant states that monitoring data recorded does not indicate any <br />substantial intercommunication of bedrock or alluvial aquifers. <br />Compliance with Basic Standards for Ground Water (Regulation 41 of the Colorado Water Quality Control <br />Commission) <br />Section 4.05.13(1) of the Regulations require the establishment of one or more ground water points of <br />compliance (well) for an operation which has the potential to negatively impact the quality of groundwater. The <br />Wadge overburden and the Twentymile Sandstone are the two aquifers most likely to be affected by the Foidel <br />Creek Mine. The 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 alluvium), and 008- <br />AT-1 (Trout Creek alluvium). The mine's annual hydrology reports contain long-term data from these wells. <br />These data show Foidel Creek Mine is in compliance with the Basic Standards for Ground Water at the <br />groundwater points of 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 water system will increase the conductivity, total dissolved solids (TDS), <br />sulfate, and iron concentrations in the streams receiving the discharge. Total suspended solids, SAR, and pH <br />could also increase due to these discharges. SAR may reach up to 6.2 in Fish Creek and 3.0 in Trout Creek. <br />Sulfate and conductivity impacts are predicted for various segments of the stream system to be affected. TR-32 <br />approved a plan which will allow the mine to discharge considerable volumes of degraded water during high <br />flow (great dilution capacity) and lesser or no discharge during periods of low flow (minimal dilution capacity). <br />Lower Middle Creek - Impacts in this segment will be pronounced due to relatively small instream flows. <br />There is no sulfate or irrigation standard over this reach. However, due to standards on Trout Creek <br />immediately below this segment, impacts will be minimized during most times of the year. <br />Lower Fish Creek - The potential for significant impacts to lower Fish Creek, from mine water discharge site <br />115 (Fish Creek dewatering facility) downstream to the confluence with Trout Creek, exists. Although no <br />sulfate standard applies over this reach, Fish Creek and adjacent alluvial valley floor areas are held to a 1500 <br />umhos/cm material damage standard for irrigation waters. Modeling indicates that during low flow periods, <br />the instream conductivity limit of 1500 umhos/cm could be exceeded. Therefore, the applicant has <br />committed to maintain its mine water discharge rate from site 115 at a level which would prevent material <br />damage (<1500 umhos/cm) by measuring upstream flow and quality and computing a discharge rate which <br />would prevent downstream exceedance of the conductivity limit for irrigation waters. The sulfate standard <br />for drinking water of 250 mg/1 does not apply over this reach. <br />13