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Record of Decision System (RODS)

ROCKY FLATS PLANT (USDOE)

Abstract

Site Name:  ROCKY FLATS PLANT (USDOE)
Address:  HWY 93 BETWEEN GOLDEN&BOULDER 
City & State:  GOLDEN  CO  80402
County:  JEFFERSON
 
EPA ID:  CO7890010526
EPA Region:  08
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R08-91/054
ROD Date:  01/25/1991
Operable Unit(s):  02
 
Media:  SURFACE WATER
 
Contaminant:  VOCS, CARBON TETRACHLORIDE, PCE, TCE, RADIOACTIVE MATERIALS
 
Abstract:  THE ROCKY FLATS PLANT (USDOE) SITE IS PART OF THE 6,550-ACRE NUCLEAR WEAPONS RESEARCH, DEVELOPMENT, PRODUCTION, AND PLUTONIUM PROCESSING COMPLEX IN JEFFERSON COUNTY, COLORADO. THE PLANT IS COMPOSED OF THE 450-ACRE ROCKY FLATS PLANT (RFP) SECURITY AREA AND THE REMAINING BUFFER AREA. LAND USE IN THE AREA IS PREDOMINANTLY RURAL AND AGRICULTURAL WITH SEVERAL NEW RESIDENTIAL AREAS UNDER DEVELOPMENT. THIS RECORD OF DECISION (ROD) ADDRESSES OPERABLE UNIT 2 (OU2), WHICH INCLUDES THE 903 PAD AND LIP, AND MOUND AND EAST TRENCHES AREAS, WHICH ARE LOCATED SOUTHEAST OF THE RFP. THE SITE LIES WITHIN THE SOUTH WALNUT CREEK AND WOMAN CREEK DRAINAGE BASINS. THE SOUTH WALNUT CREEK BASIN AND WOMAN CREEK SURFACE WATER SERVE AS A SOURCE OF DRINKING WATER. SINCE 1951, THE DEPARTMENT OF ENERGY (DOE) USED THE SITE FOR MANUFACTURING COMPONENTS FOR NUCLEAR WEAPONS, PROCESSING PLUTONIUM, AND FABRICATING, MACHINING, AND ASSEMBLING COMPONENTS FROM METALS. A NUMBER OF PAST ONSITE STORAGE AND DISPOSAL ACTIVITIES ARE POTENTIAL SOURCES OF CONTAMINATION. FROM 1958 TO 1967, DRUMS CONTAINING RADIOACTIVELY CONTAMINATED OILS AND SOLVENTS WERE STORED ONSITE, WITH SOME OF THE DRUMS CORRODING AND LEAKING APPROXIMATELY 5,000 GALLONS OF LIQUID INTO THE SOIL. DURING A CLEAN-UP AND REMOVAL EFFORT OF THE DRUM STORAGE AREA, WINDS DISTRIBUTED PLUTONIUM TO THE SOUTH AND EAST. PRIOR TO 1968, SANITARY SEWAGE SLUDGE AND FLATTENED DRUMS CONTAMINATED WITH URANIUM AND PLUTONIUM WERE DISPOSED OF IN ONSITE TRENCHES, AND DRUMS OF URANIUM-CONTAMINATED OIL WERE BURNED IN ONSITE PITS. DURING THE 1950'S AND 1960'S, REACTIVE METALS INCLUDING LITHIUM, AND SOLVENTS WERE DESTROYED ONSITE. IN ADDITION, VARIOUS BOTTLED GASES WERE DETOXIFIED ONSITE BETWEEN 1982 AND 1983. CURRENT WASTE HANDLING PRACTICES INVOLVE ONSITE AND OFFSITE RECYCLING OF HAZARDOUS MATERIALS, AND OFFSITE DISPOSAL OF SOLID RADIOACTIVE MATERIALS AT ANOTHER DOE FACILITY. DOE HAS CONDUCTED A NUMBER OF INVESTIGATIONS THAT REVEALED VOCS, METALS, AND RADIONUCLIDES ABOVE BACKGROUND LEVELS IN SOIL, SEDIMENT, GROUND WATER, AND SURFACE WATER. A 1969 CLEAN-UP ACTION ATTEMPTED TO REMOVE CORRODED AND LEAKING DRUMS OF RADIOACTIVE WASTE FROM AN ONSITE AREA, REMOVE CONTAMINATED SOIL, AND CAP THE SOIL. IN 1970, APPROXIMATELY 1,405 DRUMS CONTAINING RADIOACTIVE WASTE WERE REMOVED AND DISPOSED OF OFFSITE. A 1990 RECORD OF DECISION (ROD) ADDRESSED CONTAMINATED GROUND WATER. THIS ROD PROVIDES AN INTERIM REMEDY FOR CONTAMINATED SOUTH WALNUT CREEK BASIN SURFACE WATERS AS PART OF OU2. THE PRIMARY CONTAMINANTS OF CONCERN AFFECTING THE SURFACE WATER ARE VOCS INCLUDING CARBON TETRACHLORIDE, PCE, AND TCE; AND RADIOACTIVE MATERIALS.

THE SELECTED REMEDIAL ACTION FOR THIS INTERIM REMEDY INCLUDES COLLECTING SURFACE WATER USING DIVERSION; TREATING SURFACE WATER USING PRECIPITATION AND CROSS-FLOW MEMBRANE FILTRATION TO REMOVE SUSPENDED SOLIDS AND RADIONUCLIDES, FOLLOWED BY LIQUID-PHASE ACTIVATED CARBON TO REMOVE ORGANIC CONTAMINANTS; DISCHARGING THE TREATED WATER ONSITE TO SOUTH WALNUT CREEK; CONDUCTING TREATABILITY STUDIES; AND MONITORING SURFACE WATER. THE ESTIMATED PRESENT WORTH COST FOR THIS REMEDIAL ACTION IS $4,850,600, WHICH INCLUDES AN ANNUAL O&M COST OF $361,600.

PERFORMANCE STANDARDS OR GOALS; CHEMICAL-SPECIFIC SURFACE WATER CLEAN-UP GOALS WILL BE BASED ON THE MOST STRINGENT OF STATE AND FEDERAL ALLOWABLE LIMITS AS SET FORTH IN ARARS, AND WILL APPLY TO THE FINAL REMEDIAL ACTION.
 
Remedy:  THE OVERALL OBJECTIVE OF THE SOUTH WALNUT CREEK BASIN IM/IRA AT OU 2 IS THE MITIGATION OF DOWNGRADIENT CONTAMINANT MIGRATION WITHIN SURFACE WATER BY MEANS OF THE COLLECTION AND TREATMENT OF CONTAMINATED SURFACE WATER TO ACHIEVE, TO THE EXTENT PRACTICABLE, ARARS (SEE SECTION 3.3). ARARS ARE USED IN DEFINING THE REMEDIATION GOALS FOR THE INTERIM ACTION. BASED ON THE MEETINGS BETWEEN DOE, CDH, AND EPA DURING FEBRUARY AND MARCH 1990, AND COMMENTS RECEIVED DURING THE PUBLIC COMMENT PERIOD, DOE IS PROPOSING THIS IM/IRA PLAN WHICH SPECIFIES POINT SOURCE LOCATIONS FOR THE COLLECTION OF CONTAMINATED SURFACE WATER, AND PROVIDES FOR THE COLLECTION AND TREATMENT OF FLOWS EXCLUSIVE OF THOSE RESULTING FROM HIGH PRECIPITATION EVENTS. THE COLLECTION SYSTEMS ARE DENOTED CS-59, CS-61, AND CS-132. COLLECTED SURFACE WATER IS AUTOMATICALLY TRANSFERRED TO THE TREATMENT SYSTEM BY PIPELINE. FLOWS AT STATIONS SW-56, SW-60, SW-101, AND SW-133 WILL BE COLLECTED AT THE DOWNSTEAM STATION SW-61 BY A NEW SURFACE WATER DIVERSION WEIR AND PUMP STATION. THE WEIR WILL SERVE TO DIVERT UP TO 37.5 GPM (14 GPM AVERAGE ANNUAL WITHDRAWAL RATE) FROM THE DRAINAGE. CONTAMINATED SURFACE WATER WILL BE DIVERTED UPSTREAM OF THE WEIR INTO A 1,000-GALLON PRECAST CONCRETE SUMP PROVIDED WITH A SCREEN, WHERE LARGE DEBRIS IS SEPARATED FROM THE FLOW. THIS SCREEN WILL REQUIRE MANUAL CLEANING TO REMOVE DEBRIS. WATER WILL BE PUMPED FROM THE MANHOLE TO THE TREATMENT FACILITY. WHEN THE INFLOW INTO THE SUMP EXCEEDS THE PUMPING RATE, THE EXCESS FLOW WILL RETURN THROUGH OVERFLOW PIPING TO THE DRAINAGE BELOW THE WEIR.

THE SEEP FLOW FROM SW-59 WILL BE ISOLATED FROM THE SOUTH WALNUT CREEK DRAINAGE AND COLLECTED SEPARATELY FROM CS-61 USING A 500-GALLON, PRECAST CONCRETE SUMP. THE SUMP AND INSTALLED PUMP WILL BE DESIGNED TO COLLECT AND TRANSFER THE DESIGN FLOW OF 4.5 GPM (1 GPM AVERAGE ANNUAL WITHDRAWAL RATE). FLOWS IN EXCESS OF 4.5 GPM WILL BE DISCHARGED TO SOUTH WALNUT CREEK, VIA AN OVERFLOW PIPE, TO THE DRAINAGE. THE OVERFLOW WILL ENTER SOUTH WALNUT CREEK UPGRADIENT OF CS-61 AND WILL EITHER BE COLLECTED BY OR ALLOWED TO PASS CS-61, DEPENDING ON WHETHER THE CREEK FLOW IS LESS THAN OR GREATER THAN THE 37.5 GPM DESIGN FLOW FOR CS-61. UPPER SOUTH WALNUT CREEK FLOW WILL BE COLLECTED AT SW-132 BY A NEW SURFACE WATER DIVERSION WEIR AND PUMP STATION. THE WEIR WILL SERVE TO DIVERT UP TO 18 GPM (5 GPM AVERAGE ANNUAL WITHDRAWAL RATE) FROM THE DRAINAGE. CONTAMINATED WATER WILL BE DIVERTED INTO A 1000-GALLON PRECAST CONCRETE SUMP. FLOW IN EXCESS OF THE DESIGN FLOW (18 GPM) WILL BE PERMITTED TO OVERFLOW THE DIVERSION WEIR.

THE SURFACE WATER COLLECTED WILL BE TREATED USING CROSS-FLOW MEMBRANE FILTRATION (FOR SUSPENDED SOLIDS AND RADIONUCLIDE REMOVAL), FOLLOWED BY LIQUID-PHASE ACTIVATED CARBON (FOR ORGANICS REMOVAL) (FIGURE 6-1). THE RESPECTIVE UNITS AND APPURTENANCES WILL BE HOUSED IN THREE 48-FOOT TRAILERS TO PROTECT WEATHER- OR TEMPERATURE-SENSITIVE COMPONENTS. FIRE PROTECTION WITHIN THE TRAILERS WILL BE PROVIDED BY TWO WALL-MOUNTED, 25-POUND, DRY CHEMICAL-TYPE FIRE EXTINGUISHERS. THE TRAILERS AND ALL TREATMENT UNITS ARE CONSTRUCTED OF NON-COMBUSTIBLES. OTHER THAN MINIMAL FILES AND RECORDS, NO COMBUSTIBLE MATERIALS WILL BE MAINTAINED WITHIN THE TRAILERS. EXTERNAL WATER PIPES WILL BE ABOVE GROUND AND HEAT TRACED TO PROTECT AGAINST FREEZING. ALL TANKS, PIPING AND SUMPS WILL BE EQUIPPED WITH SECONDARY CONTAINMENT TO COMPLY WITH 6 CCR 1007-3 AND 40 CFR 264.193.
 
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