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Record of Decision System (RODS)

SILVER BOW CREEK/BUTTE AREA

Abstract

Site Name:  SILVER BOW CREEK/BUTTE AREA
Address:  BUTTE TO MILLTOWN RESERVIOR 
City & State:  BUTTE  MT  59750
County:  SILVER BOW, DEER LODGE
 
EPA ID:  MTD980502777
EPA Region:  08
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R08-90/030
ROD Date:  09/28/1990
Operable Unit(s):  04
 
Media:  SOIL SEDIMENT GROUND WATER SURFACE WATER
 
Contaminant:  METALS, ARSENIC, LEAD
 
Abstract:  THE SILVER BOW CREEK SITE IS A MINING AND PROCESSING AREA IN THE UPPER CLARK FORK RIVER BASIN, DEER LODGE COUNTY, SOUTHWESTERN MONTANA. THIS RECORD OF DECISION (ROD) DOCUMENTS THE SELECTED INTERIM REMEDIAL ACTION FOR ONE OF ELEVEN OPERABLE UNITS FOR THE SITE, THE WARM SPRINGS PONDS OPERABLE UNIT, WHICH COVERS APPROXIMATELY 2,500 ACRES JUST ABOVE THE BEGINNING OF THE CLARK FORK RIVER. SEVERAL ONSITE CREEKS (E.G., WARM SPRINGS, SILVER BOW, MILL, WILLOW) AND A STREAM BYPASS (MILL-WILLOW BYPASS) SERVE AS PRINCIPAL HEADWATERS TO CLARK FORK RIVER. THREE SETTLING PONDS (I.E., WARM SPRINGS PONDS), AN AREA BETWEEN THE NORTHERN MOST POND AND THE CLARK FORK RIVER'S BEGINNING POINT, AND A SERIES OF WILDLIFE PONDS ARE LOCATED IN CLOSE PROXIMITY TO THE STREAMS. CONTAMINATION AT THE SITE IS THE RESULT OF OVER 100 YEARS OF MINING AND PROCESS OPERATIONS IN THE AREA. MINING, MILLING, AND SMELTING WASTE WERE DUMPED DIRECTLY INTO SILVER BOW CREEK AND TRANSPORTED DOWNSTREAM TO THE CLARK FORK RIVER WITH FINAL DEPOSITION DOWNSTREAM AS FAR AS 130 MILES. THE THREE SETTLING PONDS, WHICH COVER OVER FOUR SQUARE MILES, WERE BUILT TO ALLOW WASTES FROM SILVER BOW CREEK TO SETTLE OUT BEFORE DISCHARGE TO THE CLARK FORK RIVER. AN ESTIMATED 19 MILLION CUBIC YARDS OF TAILINGS AND HEAVY METAL-CONTAMINATED SEDIMENT AND SLUDGES HAVE COLLECTED IN THE PONDS. AN ESTIMATED 3 MILLION CUBIC YARDS OF CONTAMINATED TAILINGS REMAIN UPSTREAM OF THE PONDS, ALONG THE BANKS OF SILVER BOW CREEK. PRINCIPAL THREATS FROM THE SITE INCLUDE THE POSSIBILITY OF POND BERM FAILURE DUE TO FLOOD AND EARTHQUAKE DAMAGE THAT COULD RELEASE MILLIONS OF CUBIC YARDS OF TAILINGS AND SEDIMENT TO THE RIVER. FURTHERMORE, THE CREEKS ARE CONTAMINATED WITH DISSOLVED METALS, AND EXPOSED SOIL AND TAILINGS ARE CONTAMINATED WITH ELEVATED LEVELS OF SEVERAL METALS. THE PRIMARY CONTAMINANTS OF CONCERN AFFECTING THE SOIL, SEDIMENT, GROUND WATER, AND SURFACE WATER ARE METALS INCLUDING ARSENIC, CADMIUM, COPPER, LEAD, AND ZINC.

THE SELECTED REMEDIAL ACTION FOR THIS SITE INCLUDES RAISING AND STRENGTHENING ALL POND BERMS; INCREASING THE CAPACITY OF POND 3 TO RECEIVE AND TREAT (USING METALS PRECIPITATION) FLOWS UP TO A 100-YEAR FLOOD LEVEL, AND CONSTRUCTING NEW INLET AND HYDRAULIC STRUCTURES TO PREVENT DEBRIS FROM PLUGGING THE POND 3 INLET; UPGRADING THE TREATMENT CAPABILITY OF PONDS 2 AND 3 TO TREAT ALL FLOWS UP TO THE 100-YEAR PEAK DISCHARGE, AND CONSTRUCTING SPILLWAYS FOR ROUTING EXCESS FLOOD WATER INTO THE BYPASS CHANNEL; FLOODING (WET-CLOSURE) ALL DRY PORTIONS OF POND 2; RECONSTRUCTING THE MILL-WILLOW BYPASS CHANNEL, AND REMOVING ALL REMAINING TAILINGS AND CONTAMINATED SOIL FROM THE BYPASS, FOLLOWED BY CONSOLIDATING THESE WITH DRY TAILINGS AND CONTAMINATED SOIL WITHIN THE DRY PORTION OF POND 1 AND POND 3, CAPPING AND REVEGETATING THE CLOSURE AREAS; DEWATERING WET PORTIONS OF POND 1, COVERING THE AREA WITH A RCRA-TYPE CAP AND REVEGETATING; CONSTRUCTING INTERCEPTION TRENCHES TO COLLECT CONTAMINATED GROUND WATER IN AND BELOW POND 1, THEN PUMPING THE WATER TO POND 3 FOR TREATMENT; ESTABLISHING SURFACE AND GROUND WATER QUALITY MONITORING SYSTEMS; AND IMPLEMENTING INSTITUTIONAL CONTROLS AND SITE RESTRICTIONS. DECISIONS CONCERNING REMEDIATION OF CONTAMINATED SOIL, TAILINGS AND GROUND WATER IN THE AREA BELOW POND 1 WILL BE MADE WITHIN ONE YEAR, PENDING EVALUATION OF VARIOUS WET- AND DRY-CLOSURE ALTERNATIVES AND PUBLIC REVIEW. UNTIL THESE DECISIONS ARE MADE, SOIL CLEANUP LEVELS CAN NOT BE DETERMINED. THREE CHEMICAL- AND LOCATION-SPECIFIC ARARS PERTAINING TO WATER QUALITY STANDARDS AND POTENTIAL SOLID WASTE DISPOSAL REQUIREMENTS WILL BE WAIVED IN THIS REMEDY. THE PRESENT WORTH COST FOR THIS REMEDIAL ACTION IS $57,416,000 WHICH INCLUDES AN ESTIMATED ANNUAL O&M COST OF $379,000 FOR 5 YEARS.

PERFORMANCE STANDARDS OR GOALS; ALL EXPOSED TAILINGS AND CONTAMINATED SOIL IN THE MILL-WILLOW BYPASS HAVE ALREADY BEEN REMOVED AND PLACED IN THE CLOSURE AREA BEHIND THE POND 3 BERM. FINAL SOIL CLEANUP LEVELS WILL BE SET WITHIN ONE YEAR OF THIS ROD. GROUND WATER PUMPING AND DISCHARGE FOR TREATMENT IN THE POND SYSTEM WILL COMPLY WITH STATE STANDARDS, WITH THE EXCEPTION OF ARSENIC (0.02 MG/L) AND LEAD (0.05 MG/L). STATE SURFACE WATER CONCENTRATIONS OF ARSENIC AND MERCURY REQUIRE AN ARAR WAIVER BASED ON TECHNICAL IMPRACTICABILITY AND THE FACT THAT THIS IS AN INTERIM REMEDY. THE REPLACEMENT CRITERIA ARE ARSENIC 0.02 MG/L AND MERCURY 0.0002 MG/L AT THE BEGINNING OF THE RIVER.
 
Remedy:  THE WARM SPRINGS PONDS OPERABLE UNIT IS LOCATED WITHIN DEER LODGE COUNTY, APPROXIMATELY 27 RIVER MILES NORTHWEST OF BUTTE AND JUST ABOVE THE CONFLUENCE OF THE MILL-WILLOW BYPASS AND WARM SPRINGS CREEK. SILVER BOW, MILL, WILLOW AND WARM SPRINGS CREEKS ARE PRINCIPAL HEADWATERS STREAMS OF THE CLARK FORK RIVER, WHICH BEGINS AT THE NORTHERNMOST BOUNDARY OF THE WARM SPRINGS PONDS OPERABLE UNIT.

THE SELECTED REMEDY FOR THE WARM SPRINGS PONDS OPERABLE UNIT MAY BE SUMMARIZED AS FOLLOWS;
ALLOW THE PONDS TO REMAIN IN PLACE; PONDS 2 AND 3 WILL CONTINUE TO FUNCTION AS TREATMENT PONDS UNTIL UPSTREAM SOURCES OF CONTAMINATION ARE CLEANED UP;
* RAISE AND STRENGTHEN ALL POND BERMS ACCORDING TO SPECIFIED CRITERIA, WHICH WILL PROTECT AGAINST DAM FAILURE IN THE EVENT OF MAJOR EARTHQUAKES OR FLOODS, AND INCREASE THE STORAGE CAPACITY OF POND 3 TO RECEIVE AND TREAT FLOWS UP TO THE 100-YEAR FLOOD;
* CONSTRUCT NEW INLET AND HYDRAULIC STRUCTURES TO PREVENT DEBRIS FROM PLUGGING THE POND 3 INLET AND TO SAFELY ROUTE FLOWS IN EXCESS OF THE 100-YEAR FLOOD AROUND THE PONDS;
* COMPREHENSIVELY UPGRADE THE TREATMENT CAPABILITY OF PONDS 2 AND 3 TO FULLY TREAT ALL FLOWS UP TO 3,300 CFS (100-YEAR PEAK DISCHARGE) AND CONSTRUCT SPILLWAYS FOR ROUTING EXCESS FLOOD WATER INTO THE BYPASS CHANNEL;
* REMOVE ALL REMAINING TAILINGS AND CONTAMINATED SOILS FROM THE MILL-WILLOW BYPASS, CONSOLIDATE THEM OVER EXISTING DRY TAILINGS AND CONTAMINATED SOILS WITHIN THE POND 1 AND POND 3 BERMS AND PROVIDE ADEQUATE COVER MATERIAL WHICH WILL BE REVEGETATED;
* RECONSTRUCT THE MILL-WILLOW BYPASS CHANNEL AND ARMOR THE NORTH-SOUTH BERMS OF ALL PONDS TO SAFELY ROUTE FLOWS UP TO 70,000 CUBIC FEET PER SECOND (ONE-HALF OF THE ESTIMATED PROBABLE MAXIMUM FLOOD);
* FLOOD (WET-CLOSE) ALL DRY PORTIONS OF POND 2;
* CONSTRUCT INTERCEPTION TRENCHES TO COLLECT CONTAMINATED GROUND WATER IN AND BELOW POND 1 AND PUMP THE WATER TO POND 3 FOR TREATMENT;
* DEWATER WET PORTIONS OF POND 1 AND COVER AND REVEGETATE (DRY-CLOSE) ALL AREAS WITHIN THE POND 1 BERMS;
* ESTABLISH SURFACE AND GROUND WATER QUALITY MONITORING SYSTEMS AND PERFORM ALL OTHER ACTIVITIES NECESSARY TO ASSURE COMPLIANCE WITH ALL APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS;
* IMPLEMENT INSTITUTIONAL CONTROLS TO PREVENT FUTURE RESIDENTIAL DEVELOPMENT, TO PREVENT SWIMMING, AND TO PREVENT CONSUMPTION OF FISH BY HUMANS; AND
* DEFER, FOR NOT MORE THAN ONE YEAR AFTER THE EFFECTIVE DATE OF THIS DOCUMENT, DECISIONS CONCERNING THE REMEDIATION OF CONTAMINATED SOILS, TAILINGS, AND GROUND WATER IN THE AREA BELOW POND 1, PENDING EVALUATION OF VARIOUS WET- AND DRY-CLOSURE ALTERNATIVES AND A PUBLIC REVIEW.
 
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