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Record of Decision System (RODS)

HILL AIR FORCE BASE

Abstract

Site Name:  HILL AIR FORCE BASE
Address:  00-ALC/EM 
City & State:  HILL AFB  UT  84056
County:  DAVIS, WEBER
 
EPA ID:  UT0571724350
EPA Region:  08
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R08-91/049
ROD Date:  09/30/1991
Operable Unit(s):  02
 
Media:  SOIL GROUNDWATER
 
Contaminant:  VOCS, PCE, TCE, TOLUENE, XYLENES
 
Abstract:  THE 6,700-ACRE HILL AIR FORCE BASE (HILL AFB) SITE IS AN ACTIVE MILITARY FACILITY SITUATED BETWEEN THE CITIES OF OGDEN AND SALT LAKE CITY, COVERING PORTIONS OF DAVIS AND WEBER COUNTIES, UTAH. THIS RECORD OF DECISION (ROD) ADDRESSES PART OF OPERABLE UNIT 2 (OU2), WHICH CONSISTS OF TWO UNLINED DISPOSAL TRENCHES, SEEPS, AND SPRINGS, AND CONFINED AND UNCONFINED AQUIFERS. LAND USE IN THE AREA IS MAINLY AGRICULTURAL AND RESIDENTIAL. BOTH SOUTH WEBER AND HILL AFB OBTAIN DRINKING WATER FROM DEEP WELLS IN CONFINED AQUIFERS. BECAUSE THE BASE COVERS A LARGE AREA, THE AIR FORCE HAS GROUPED GEOGRAPHICALLY ADJACENT CONTAMINATED AREAS INTO SEVEN OUS. FROM 1967 TO 1975, HILL AFB DISPOSED OF WASTE SOLVENTS AND SLUDGE FROM DEGREASING OPERATIONS IN THE ONSITE DISPOSAL TRENCHES. IT IS ESTIMATED THAT 100,000 TO 1,000,000 GALLONS OF TCE BOTTOMS FROM THE SOLVENT RECOVERY UNIT, SLUDGE FROM VAPOR DEGREASERS, AND PLATING-TANK SLUDGE BOTTOMS WERE DISPOSED OF IN THESE TRENCHES. FEDERAL INVESTIGATIONS FROM 1983 TO 1986 IDENTIFIED VOC CONTAMINATION IN ONSITE AND OFFSITE GROUND WATER. AS A RESULT OF THESE INVESTIGATIONS, HILL AFB BEGAN COLLECTION AND TREATMENT OF CONTAMINATED GROUND WATER FROM SEEPS AND SPRINGS IN 1986. IN ADDITION, AN ALTERNATE WATER SUPPLY WAS PROVIDED TO FIVE PROPERTIES TO PREVENT THE USE OF CONTAMINATED GROUND WATER FROM SEEPS AND SPRINGS. THIS ROD ADDRESSES THE INTERIM REMEDIATION OF OU2 SUBSURFACE SOIL AND GROUND WATER BY REMOVING A DNAPL SOURCE AND THUS PREVENTING CONTAMINANTS FROM REACHING AQUIFERS CURRENTLY USED AS DRINKING WATER SOURCES. A SUBSEQUENT ROD WILL PROVIDE A FINAL REMEDY FOR OU2 SOIL, GROUND WATER, SURFACE WATER, AND AIR. THE PRIMARY CONTAMINANTS OF CONCERN AFFECTING THE SOIL AND GROUND WATER ARE VOCS INCLUDING PCE, TCE, TOLUENE, AND XYLENES.

THE SELECTED REMEDIAL ACTION FOR THIS INTERIM REMEDY INCLUDES INSTALLING AND MAINTAINING A SOURCE RECOVERY SYSTEM TO REMOVE DNAPL CONTAMINATION FROM THE SUBSURFACE; PUMPING DNAPL-CONTAMINATED GROUND WATER, WITH ONSITE DISCHARGE TO A PRETREATMENT FACILITY TO SEPARATE DNAPL FROM GROUND WATER USING A STEAM STRIPPER; TEMPORARILY STORING THE DNAPL ONSITE IN STEEL TANKS, FOLLOWED BY TRANSPORTING THE WASTE OFFSITE FOR INCINERATION; INSTALLING A PIPELINE FROM THE SITE TO THE BASE INDUSTRIAL WASTEWATER TREATMENT PLANT (IWTP); TREATING THE PRETREATED GROUND WATER AT THE IWTP USING AIR STRIPPING, FOLLOWED BY CARBON ADSORPTION; DISCHARGING THE TREATED WATER OFFSITE TO A PUBLICLY OWNED TREATMENT WORKS (POTW); AND MONITORING DNAPL COLLECTION AND TREATMENT DURING REMEDIATION ACTIVITIES. THE ESTIMATED PRESENT WORTH COST FOR THIS REMEDIAL ACTION IS $3,710,000, WHICH INCLUDES AN ANNUAL O&M COST OF $1,000,000 FOR 2 YEARS.

PERFORMANCE STANDARDS OR GOALS; ACTUAL CHEMICAL-SPECIFIC STANDARDS OR GOALS WILL BE SET IN A FUTURE ROD.
 
Remedy:  THIS INTERIM REMEDY ADDRESSES REMOVAL OF A SOURCE OF CONTAMINATION IN THE SUBSURFACE SOILS AND GROUND WATER AND REDUCTION OF THREAT OF CONTAMINATION OF AQUIFERS CURRENTLY USED AS A SOURCE OF DRINKING WATER BY ELIMINATING OR REDUCING THE RISKS POSED BY THE SITE THROUGH TREATMENT. THE CONTAMINATION ADDRESSED BY THIS INTERIM ACTION IS DENSE, NON-AQUEOUS PHASE LIQUID (DNAPL). THIS INTERIM ACTION IS CONSISTENT WITH ANY FUTURE ACTIONS TO COMPLETE CLEAN UP OF THE ENTIRE OPERABLE UNIT, AND IS A LOGICAL FIRST STEP IN THE CLEAN UP PROCESS. FUTURE CLEAN UP ACTIONS ADDRESSING FINAL REMEDIES FOR ALL CONTAMINATED MEDIA (SOIL, GROUND WATER, SURFACE WATER, AIR) WILL BE DETAILED IN A SUBSEQUENT RECORD OF DECISION (ROD). NO CHANGES HAVE BEEN MADE TO THE SELECTED REMEDY ORIGINALLY PRESENTED IN THE PROPOSED PLAN.

THE MAJOR COMPONENTS OF THE SELECTED REMEDY INCLUDE;
* INSTALLATION AND MAINTENANCE OF A SOURCE RECOVERY SYSTEM CAPABLE OF REMOVING DNAPL CONTAMINATION FROM THE SUBSURFACE.
* INSTALLATION AND MAINTENANCE OF AN ON-SITE GROUND WATER AND DNAPL PRETREATMENT FACILITY TO SEPARATE DNAPL FROM GROUND WATER AND TO TREAT CONTAMINATED GROUND WATER TO LEVELS WHICH CAN BE DISCHARGED TO THE BASE INDUSTRIAL WASTE WATER TREATMENT PLANT (IWTP).
* DISPOSAL OF DNAPL OFF-SITE BY INCINERATION IN ACCORDANCE WITH THE RESOURCE CONSERVATION AND RECOVERY ACT (RCRA).
* INSTALLATION AND MAINTENANCE OF A DOUBLE-WALLED PIPELINE FROM THE SITE TO THE BASE IWTP CAPABLE OF TRANSPORTING PRETREATED GROUND WATER.
* TREATMENT AND DISCHARGE OF THE PRETREATED GROUND WATER WITH OTHER BASE INDUSTRIAL WASTE WATERS AT THE IWTP AND DISCHARGE TO THE NORTH DAVIS COUNTY SEWER DISTRICT'S PUBLICLY OWNED TREATMENT PLANT IN ACCORDANCE WITH THE BASE'S INDUSTRIAL PRETREATMENT DISCHARGE PERMIT.
* MONITORING THE DNAPL COLLECTION AND TREATMENT SYSTEM DURING REMEDIATION ACTIVITIES.
 
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