2009-09-25_PERMIT FILE - M2009076 (42)

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SUBSTANTIALLY REDUCES RISK TO THE ENVIRONMENT. REPROCESSING: REPROCESSING WILL RESULT IN NEW TAILINGS THAT ARE NOT RCRA WASTES. HOWEVER, POTENTIAL LEACHATES FROM THE WASTE WILL EXCEED AWQC. REPROCESSING REDUCES MOBILITY, TOXICITY 10D VOLUME OF THE CONTAMINANTS. THIS ALTERNATIVE IS THE ONLY OPTION THAT REDUCES VOLUME. PROCESSING REDUCES EXISTING RISK TO HUMAN HEALTH AND THE ENVIRONMENT. THIS OPTION IS THE MOST EXPENSIVE OF THE SIX ALTERNATIVES EVALUATED EVEN CONSIDERING THE VALUE OF THE MINERALS EXTRACTED (SEE TABLE 2). OVERALL, REPROCESSING IS A PERMANENT SOLUTION THAT REDUCES EXPOSURE TO HUMAN HEALTH AND THE ENVIRONMENT. #RA SELECTED REMEDY DESCRIPTION OF SELECTED REMEDY THE SELECTED REMEDY FOR OPERABLE UNIT TWO OF THE CLEAR CREEK/CENTRAL CITY SITE CONSISTS OF SLOPE STABILIZATION AND RUNON CONTROL. THE REMEDIAL INVESTIGATION IDENTIFIED FOUR POTENTIAL EXPOSURE PATHWAYS BY WHICH THE TAILINGS AND WASTE ROCK PILES COULD IMPACT HUMAN HEALTH AND THE ENVIRONMENT. THESE POTENTIAL PATHWAYS ARE: - COLLAPSE OF TAILINGS AND WASTE ROCK PILES INTO STREAMS; - RUNOFF FROM TAILINGS AND WASTE ROCK PILES INTO STREAMS; - INHALATION OF DUST FROM THE PILES; AND - INGESTION OF MATERIAL FROM THE PILES. TWO SITES WERE IDENTIFIED THAT HAD TAILINGS AND WASTE ROCK PILES THAT HAD THE POTENTIAL TO LLAPSE INTO CLEAR CREEK OR NORTH CLEAR CREEK BECAUSE OF UNSTABLE SLOPES. THE TWO SITES ARE E BIG FIVE TUNNEL AND THE GREGORY INCLINE. THE ARGO TUNNEL TAILINGS AND WASTE ROCK PILE WAS ALSO IDENTIFIED AS BEING UNSTABLE BECAUSE OF BEING UNDERCUT. IF THE ARGO WASTE ROCK PILE FAILS, THE STRUCTURES BELOW IT WOULD BE AFFECTED, HOWEVER, THE WASTE ROCK WOULD NOT REACH CLEAR CREEK. BASED ON THE EFFECTS ON HUMAN HEALTH AND THE ENVIRONMENT FROM THE POTENTIAL COLLAPSE OF THE BIG FIVE WASTE ROCK PILE INTO CLEAR CREEK, IT IS RECOMMENDED THAT THE SLOPES ON BOTH SIDES OF THE CREEK BE REGRADED AND STABILIZED AND THAT ROCK RIP-RAP BE PLACED ON THE TOE TO PROTECT THE SLOPE FROM ERODING AND COLLAPSING INTO CLEAR CREEK. BASED ON THE EFFECTS ON HUMAN HEALTH AND THE ENVIRONMENT FROM THE POTENTIAL COLLAPSE OF THE TAILINGS AND WASTE ROCK PILE AT THE GREGORY INCLINE, IT IS RECOMMENDED THAT THE GABION-BASKET WALL BE MAINTAINED UNTIL MONITORING INDICATES REMEDIATION IS NECESSARY OR UNTIL THE TAILINGS ARE REMOVED FOR REPROCESSING. AT THAT TIME, A PERMANENT SOLUTION WILL BE IMPLEMENTED. SPECIFIC DETAILS CONCERNING THE STABILIZATION REMEDIAL ACTIONS WILL BE DEVELOPED DURING REMEDIAL DESIGN. THE COST OF THIS REMEDIATION IS PROVIDED IN TABLE 3. THE SECOND EXPOSURE PATHWAY IS CONTAMINATED WATER FROM BOTH RUNOFF AND RUN ON OVER THE TAILINGS AND WASTE ROCK PILES. RUNOFF CAN BE CONTROLLED BY ALTERNATIVES SUCH AS: CAPPING, CHEMICAL FIXATION, REPROCESSING, AND OFF-SITE DISPOSAL. BECAUSE OF THE HIGH COST TO CONTROL RUNOFF AND THE FACT THAT THE QUANTITY OF RUNOFF, AS OPPOSED TO RUNON, FROM THE FIVE SITES IS SMALL WHEN COMPARED TO THE TOTAL RUNOFF FROM THE MINING DISTRICT (LESS THAN 0.01 PERCENT OF THE TOTAL DURING STORM EVENTS), NO LARGE-SCALE REMEDIATION TO ELIMINATE RUNOFF IS PROPOSED. HOWEVER, RUNON CONTROLS (UPGRADIENT DITCHES) HAVE BEEN INCORPORATED INTO THE PROPOSED REMEDIATION. THE COSTS FOR RUNON CONTROL ARE SHOWN FOR ALL FIVE SITES IN TABLE 3. RUNON CONTROLS WILL SUBSTANTIALLY REDUCE THE QUANTITY OF WATER FLOWING OVER THE WASTE ROCK AND TAILINGS PILES. A DETAILED EVALUATION OF THESE QUANTITIES IS PROVIDED IN THE OPERABLE UNIT NO. TWO FS (APPENDIX J). BASED ON THE BENEFIT ACHIEVED BY PROVIDING RUNON CONTROL AND THE RELATIVELY SMALL COST OF THESE MEASURES, RUNON CONTROLS ARE RECOMMENDED. 10EN FINAL DESIGNS ARE COMPLETED TO TREAT ACID MINE DRAINAGE UNDER OPERABLE UNIT NO. ONE, COLLECTION AND TREATMENT OF RUNOFF FROM TAILINGS AND WASTE ROCK PILES AT THE TREATMENT FACILITIES WILL BE EVALUATED.