2011-12-06_REVISION - C1980001 (3)

Home Browse Search

`Discharge ofleachate froni pit TDS loading of Trout Creek immediately downstream froni the 'Edna Mine and the formation of spoil springs indicate leachate is discharging from pits at the mine =`(PAP, page'2.SB -1 of Appendix 2.-5B) 5. , Leachate impacts on bedrock-ground water — Mining operations left a wedge'of unmined bedrock-les's than 1,000 feet wide at the toe of the pits that lies between the the of the pits and Trout Creek. This unmined rock is believed to transmit leachate from the backfilled pits to the rock's outcrop next to Trout Creek and to its subcrop beneath Trout Creek, resulting in the leachate flowing into the creek's.surface water and alluvium, rather -than to bedrock downdip.ifrotn the creek. Consequently, no impacts to bedrock ground water are :suspected.: Substantial leachate discharge to bedrock in the bottom of Edna's‘pits would notbe possible due to the impermeable shale and siltstone that underlies the Wadge seam as shown on iithologic and geophysical logs in - Section 2.2.4.1 of the PAP. The mining operation can be expected to be in compliance with the basic standards for ground water for a compliance point in - any stratigraphic unit at the permit boundary. Monitoringdata from well TCS, immediately, downdip from the permit boundary, indicates the Trout Creek Sandstone has not been affected by: the mining operation at that location. 6. :Leachate impacts on alluvial.water — TDS°concentrations in the two alluvial monitoring wells downstream from the Edna Mine have risen from around 500 to over 900 mg/1 since 1996. This may be an impact from spoil leachate, but a number of other reasons ` might bear on the rise. 7. .• , Leachate impacts on surface water— Monitoring .. data through 2006 indicate spoil leachate has increased the TDS levels in Trout Creek immediately downstream from the mine (sites TR -C and D). Concentrations reached a maximum of =about 1400 mg/l - iri'one sample in 1995. Since then, the annual maximum has declined to less-than the ;predicted - maximum of:_ :1,186 mg/l,-and continues to - showa decrease with time: The increased TDS in Trout Creek caused by the _ leachate has not caused an exceedance of the instreain" standards. •The Colorado Water Quality Control Division (CWQCD)'has not .found the mine's discharges Trout Creek to be in violation of the discharge permit limitations. There were several exceedances :o f the discharge permit's sulfate limitations in 1999 through 2001. CWQCD has enforcement authority for the 'discharge permit and' noted some of those.exceedances in the -discharge permit when. the :permit was issued in 2000. 8. Pre -law leachate vs. post -law leachate Pre -SMCRA spoil springs have hindered recognition of.the hydrologic inipacts.resulting ;from C1980 -001 Edna Mine Permit Renewal No. 6 ° 25 •2