2008-09-17_REVISION - M1980244 (28)

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• CC&V has committed to installing additional compliance monitoring wells near the base of ECOSA as described in MC report (Page 49). I. The Division is aware that some of these monitoring wells will no longer be available when the WHEX portion of the East Cresson is developed. The DRMS proposes to set numeric protection levels on the ones to be in place even after the mine expansion is completed, based on the current available data, which is more than five quarters. If after some years of monitoring, the DRMS concludes impacts to the hydrologic balance to be minimal, CC&V can submit a revision to the permit to lower the # of monitoring wells. Is CC&V going to continue to monitor the surface water in Grassy Valley at locations GV-01 AND GV-02? Given the operators own long term prediction that states in 50 years approximately 23gpm could be discharged from the ECOSA, post closure, how would this discharge be addressed if the predicted happens and the discharge does not meet the water quality standards for Grassy Valley?. Since DRMS, does not have the statutory authority to bond for water treatment, are there plans to obtain a NPDES discharge permit from CDPHEE at that time? Please explain Response: CC&V understands DRMS' plan to set numeric protection levels and would work with DRMS on such levels as part of this Amendment No. 9. CC&V intends to continue monitoring the surface water in Grassy Valley at locations GV-01 and • GV-02. As noted in the response to Adequacy Comment VI (E)(a) above, CC&V also proposes to monitor GV-03, and a new monitoring location at the downstream edge of the diatreme to be designated GV-04. The predicted long term flow of 23 gpm migrating through the base of the ECOSA will be easily accommodated as infiltration to the underlying alluvium and bedrock. The water will pass into the diatreme, and will eventually migrate to the regional ground water table that is intersected by the Carlton Tunnel. It will undergo the same geochemical processes as are described in the MLE Project Application (and prior submittals such as Amendment No. 8). Runoff from a reclaimed ECOSA would only include diffuse storm water runoff, which is not a point discharge and would not require a NPDES-style permit. The reclamation includes a clay cover, growth medium, and revegetation. J. Given the lack of adequate ground water monitoring well data in Poverty Gulch (North Cresson Mine), with the exception of PGMW-2 which has been dry since construction in 2001, the Division requests at least two more additional wells be drilled and completed prior to initiating impacts in the area. The Division allowed the current monitoring with limited data to be in place, since the plugging of the two monitoring wells (PGMW-1A &1B), because there are no current active Cresson Project disturbances in the area and none were proposed under AM-08. The current mining plan proposes to disturb a considerable • amount of acres as part of the mine life extension. Even though there is a lack of measurable drainage, except in association with a heavy precipitation event, and a few wet areas down gradient, which may or may not get shallow ground water flow from upgradient areas, there is still the potential for some adverse effect to the overall hydrologic balance. That is why the Division recommended to CC&V, in the reclamation and mining portions to ?h