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COLLAPSE OF TAILINGS AND WASTE ROCK PILES INTO CLEAR CREEK AND NORTH CLEAR CREEK; <br />- RUNOFF FROM THE WASTE ROCK AND TAILINGS PILES CONTAMINATING CLEAR CREEK AND NORTH <br />CLEAR CREEK; AND <br />- INHALATION OR INGESTION OF MATERIAL FROM THE PILES. <br />THE IMPACT DUE TO POTENTIAL COLLAPSE OF THE BIG FIVE AND GREGORY INCLINE WASTE ROCK/TAILINGS <br />PILES WERE EVALUATED IN THE SECTION ENTITLED "SITE CHARACTERISTICS". AS DISCUSSED IN THAT <br />SECTION, BOTH AWQC AND MCLS WOULD BE EXCEEDED IN CLEAR CREEK AND NORTH CLEAR CREEK. <br />THE SITE CHARACTERISTICS SECTION ALSO SUMMARIZED THE EFFECTS OF RUNOFF DURING STORM EVENTS. <br />ACTUAL DATA INDICATE THAT AWQC ARE EXCEEDED IN CLEAR CREEK AND NORTH CLEAR CREEK. <br />IN ADDITION TO POTENTIAL IMPACTS DUE TO RUNOFF AND COLLAPSE, THE ADVERSE EFFECTS OF INHALATION <br />OF INGESTION OF MATERIAL FROM THE PILES WERE EVALUATED AND SUMMARIZED IN THE SITE <br />CHARACTERISTICS SECTION (TABLE 1). UNDER CURRENT (EPISODIC EXPOSURE) WORST CASE CONDITIONS, THE <br />RISK FOR INGESTION OF SOIL WAS 1 X 10-4 (ONE EXCESS CANCER DEATH IN 10,000 PEOPLE OVER A <br />LIFETIME). UNDER AVERAGE CONDITIONS, THE RISK WAS 2 X 10-5. INHALATION OF DUST UNDER AVERAGE <br />AND WORST CASES INDICATED RISKS OF 5 X 10-6 TO 1 X 10-4. UNDER A POTENTIAL FUTURE USE <br />RESIDENTIAL SCENARIO, THE RISK OF INGESTION UNDER AVERAGE CONDITIONS RANGED FROM 8 X 10-5 TO <br />1 X 10-4. UNDER MAXIMUM PLAUSIBLE EXPOSURE CONDITIONS THE RISK RANGED FROM 4 X 10-4 TO <br />9 X 10-4. <br />SLOPE STABILIZATION AND RUNON CONTROL ALTERNATIVE: BASED ON THE DETAILED EVALUATION OF CRITERIA <br />CITED PREVIOUSLY, SLOPE STABILIZATION AT THE BIG FIVE WASTE ROCK PILES WOULD BE ACCOMPLISHED BY <br />EXCAVATION, SLOPE CUTBACK AND TOE RIP-RAP TO PREVENT EROSION AND TAILINGS COLLAPSE INTO CLEAR <br />CREEK. BASED ON DETAILED EVALUATION AT THE GREGORY INCLINE, THE CURRENT GABION WALL WOULD BE <br />MAINTAINED UNTIL MONITORING INDICATES REMEDIATION IS NECESSARY OR UNTIL THE TAILINGS ARE REMOVED <br />FOR REPROCESSING. AT THAT TIME, A PERMANENT SOLUTION WILL BE IMPLEMENTED. RUNON CONTROLS SUCH <br />DIVERSION DITCHES OR CULVERTS WOULD BE PLACED ON THE UPGRADIENT SIDE OF ALL SITES. <br />SLOPE STABILIZATION WOULD BE A PERMANENT SOLUTION THAT ELIMINATES COLLAPSE OF THE TAILINGS AND <br />WASTE ROCK PILES. THE POTENTIAL FOR CATASTROPHIC CONTAMINATION OF CLEAR CREEK AND NORTH CLEAR <br />CREEK WOULD BE ELIMINATED. THE RUNOFF WOULD ALSO BE REDUCED BY ELIMINATING RUNON AT THE <br />UPGRADIENT SIDES OF THE PILES. NO REDUCTION IN IMPACT DUE TO DUST OR INGESTION WOULD BE <br />ACHIEVED. <br />CAPPING ALTERNATIVES: RESULTS OF THE SCREENING ANALYSIS INDICATED THAT BECAUSE OF THE STEEP <br />SLOPES ONLY TWO TECHNICALLY FEASIBLE CAPPING ALTERNATIVES EXIST FOR WASTE PILES AT THE NATIONAL <br />TUNNEL AND ARGO TUNNEL: SYNTHETIC LINERS OR SOIL CEMENT COVERS. BECAUSE OF THE STEEP SLOPES AT <br />BOTH SITES, A SOIL COVER WOULD NOT REMAIN ON A SYNTHETIC LINER. A BARE LINER WOULD BE EXTREMELY <br />SUSCEPTIBLE TO DAMAGE AND/OR VANDALISM WITH FREQUENT REPLACEMENT REQUIRED. THE SOIL CEMENT <br />COVER RETAINS THE NATURAL COLOR OF THE TAILINGS AND WASTE ROCK MATERIAL AND IS PROBABLY <br />PREFERRED BY THE COLORADO HISTORICAL SOCIETY AND LOCAL RESIDENTS OVER A LINER. THUS, A SOIL <br />CEMENT COVER IS THE PREFERABLE CAPPING ALTERNATIVE WHICH COULD BE IMPLEMENTED AT THE NATIONAL <br />TUNNEL AND ARGO TUNNEL WASTE PILES. <br />BEFORE THE GREGORY INCLINE CAN BE CAPPED, THE TEMPORARY GABION WALL WOULD BE REPLACED. A TIMBER <br />CRIB WALL IS PRICED COMPARABLY WITH OTHER ALTERNATIVES AND WOULD PROBABLY BE PREFERRED BY THE <br />COLORADO HISTORICAL SOCIETY. ALTERNATIVES EVALUATED FOR CAPPING WERE A SYNTHETIC LINER AND SOIL <br />CEMENT COVER. THE SOIL CEMENT COVER IS A PERMANENT COVER AND IS PROBABLY PREFERRED BY THE <br />COLORADO HISTORICAL SOCIETY OVER OTHER CAPPING ALTERNATIVES. <br />THE BIG FIVE WASTE ROCK PILE PROVIDES A TECHNICAL CHALLENGE FOR CAPPING AND PROTECTION AGAINST <br />FLOOD EROSION. PHYSICAL CONSTRAINTS IMPOSED BY THE ORIGINAL TOPOGRAPHY AND THE LOCATION OF <br />CLEAR CREEK ALONG ONE SIDE OF THE PILES DICTATE THAT PILES WOULD BE REGRADED AND RIP-RAP WOULD <br />* PLACED FOR FLOOD PROTECTION. THE REGRADED PILES WOULD THEN BE COVERED BY A SOIL CEMENT CAP. <br />SYNTHETIC LINER COULD BE PLACED, BUT NO SOIL COVER COULD BE PUT ON THE LINER. <br />CAPPING OF THE QUARTZ HILL WASTE ROCK PILE WAS EVALUATED FOR THREE AREAS: PARKING LOTS WITH <br />ADJOINING SIDE SLOPES, AN AREA NEAR THE TUNNEL ENTRANCE, AND ALL REMAINING AREAS FROM THE <br />PARKING LOTS TO THE TUNNEL PORTAL. THE SCREENING ANALYSIS INDICATED THAT SOIL CEMENT COVERS