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Record of Decision System (RODS)

ROCKY MOUNTAIN ARSENAL (USARMY)

Abstract

Site Name:  ROCKY MOUNTAIN ARSENAL (USARMY)
Address:  IMMED N STAPLETON INTL ARPT 
City & State:  ADAMS COUNTY  CO  80022
County:  ADAMS
 
EPA ID:  CO5210020769
EPA Region:  08
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R08-90/039
ROD Date:  02/26/1990
Operable Unit(s):  19
 
Media:  GROUNDWATER
 
Contaminant:  DBCP
 
Abstract:  THE ROCKY MOUNTAIN ARSENAL (RMA) (OPERABLE UNIT 19) SITE COMPRISES PART OF THE 17,000-ACRE RMA SITE, WHICH IS A FORMER US ARMY CHEMICAL WARFARE AND INCENDIARY MUNITIONS MANUFACTURING AND ASSEMBLY PLANT IN ADAMS COUNTY, COLORADO. FROM THE 1950S UNTIL LATE 1969, THE US ARMY USED THE RMA FACILITY TO PRODUCE THE NERVE AGENT GB (ISOPROPYLMETHYL PHOSPHONOFLUORIDATE). IN ADDITION, BETWEEN 1947 AND 1982, PRIVATE INDUSTRIES LEASED MAJOR PORTIONS OF THE PLANT FACILITIES TO MANUFACTURE VARIOUS INSECTICIDES AND HERBICIDES. SINCE 1970, FACILITY OPERATIONS PRIMARILY HAVE INVOLVED THE DESTRUCTION OF CHEMICAL WARFARE MATERIALS. BECAUSE FINAL REMEDIATION OF THE RMA SITE WILL TAKE MANY YEARS TO COMPLETE, THIRTEEN OTHER CONTAMINATION SOURCES INTERIM RESPONSE ACTIONS (IRAS) WERE DETERMINED NECESSARY PRIOR TO IMPLEMENTING THE FINAL ONPOST RECORD OF DECISION (ROD). OPERABLE UNIT 19 (RAIL CLASSIFICATION YARD) IS ONE OF THE AREAS INCLUDED IN THE IRAS. IN 1980, THE PESTICIDE 1,2-DIBROMO-3-CHLOROPANE (DBCP) WAS DETECTED IN THE ALLUVIAL GROUND WATER NEAR THE RAIL CLASSIFICATION YARD OF RMA. TO PREVENT OFF-POST MIGRATION OF DBCP IN THE GROUNDWATER, THE IRONDALE CONTROL SYSTEM (ICS) WAS INSTALLED IN THE RAIL CLASSIFICATION YARD IN 1981. THIS SYSTEM, WHICH HAS BEEN EFFECTIVE IN PREVENTING OFF-POST MIGRATION, INVOLVES PUMPING AND TREATMENT OF CONTAMINATED GROUND WATER FOLLOWED BY REINJECTION. SITE INVESTIGATIONS BY THE US ARMY INDICATE DBCP CONTAMINATION IN UNSATURATED SOIL AND SEDIMENT, POSSIBLY FROM LEAKING RAIL CARS, TO BE POTENTIAL SOURCES OF GROUND WATER CONTAMINATION. THIS ROD ADDRESSES INTERIM MANAGEMENT OF MIGRATION OF THE CONTAMINATED GROUND WATER PLUME. THE PRIMARY CONTAMINANT OF CONCERN AFFECTING THE GROUND WATER IS DBCP.

THE SELECTED INTERIM REMEDIAL ACTION FOR THIS SITE INCLUDES INSTALLING A GROUND WATER INTERCEPTION/CONTAINMENT SYSTEM PARALLEL TO THE CONTAMINANT FLOWPATH, INCREASING THE TREATMENT CAPACITY OF THE ICS AND CONSTRUCTING PIPELINES TO CONVEY EXTRACTED GROUNDWATER TO THE ICS; GROUND WATER PUMPING AND TREATMENT USING CARBON ADSORPTION AT THE ICS FOLLOWED BY REINJECTION; CONDUCTING GROUND WATER MONITORING. THIS INTERIM REMEDIAL ACTION WILL BE IMPLEMENTED JOINTLY WITH THE RMA MOTOR POOL IRA. THIS ESTIMATED PRESENT WORTH COST OF THIS INTERIM REMEDIAL ACTION IS $2,662,000, WHICH INCLUDES AN ANNUAL O&M COST OF $183,000 FOR FIVE YEARS.

PERFORMANCE STANDARDS OF GOALS; THE CHEMICAL-SPECIFIC GOAL FOR GROUNDWATER TREATMENT OF DBCP IS 0.2 UG/L BASED ON THE PROPOSED MCL. CHEMICAL-SPECIFIC GOALS FOR OTHER POTENTIAL CONTAMINANTS ARE BASED ON MCLS AND COLORADO BASIC STANDARDS FOR GROUNDWATER (CBSG) AND INCLUDE BENZENE 5 UG/L (MCL), TOLUENE 2,420 UG/L (CBSG), AND TCE 5 UG/L (MCL).
 
Remedy:  SEE ABSTRACT
 
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