Marine Corps Air Station Yuma

Marine Corps Air Station Yuma - runway

Superfund Site | Marine Corps Air Station Yuma: Page 2 of 4

OU-1

The OU-1 Remedial Investigation (RI) report identified six areas (Areas 1 through 6) with fuel related and/or chlorinated aliphatic hydrocarbon groundwater contamination. Areas 4 and 5 were later identified as fuel sites, rather than CERCLA sites, and were assigned to ADEQ’s Leaking Underground Storage Tank Program. Areas 2, 3 and 6 have all achieved the EPA Maximum Contaminant Level (MCL) goals and have been closed with concurrence by EPA and ADEQ — no further action (NFA) is required in these areas.

OU-1 Area 1

The OU-1, Area 1 Record of Decision (ROD) Contaminants of Concern (COCs) are DCE, PCE and TCE. The site is divided into three areas: the “Hot Spot” source area, the “Central Plume Area” downgradient of the source, and the “Leading Edge Plume Area (LEPA)” at the base boundary at the downgradient edge of the contaminant plume.  A newer investigation into per- and polyfluoroalkyl substances (PFAS) contamination was begun in 2019.

“Hot Spot” source area:

  • Groundwater modeling performed in 2015 concluded TCE and 1,1-DCE (DCE) concentrations above the MCL would not migrate beyond the boundary of OU-1 Area 1.  Concentrations remain slightly above the MCLs in two Hot Spot area wells.
  • Air Sparging/Soil Vapor Extraction in the Hot Spot source area, began in 1999, was permanently shut down in 2019 due to asymptotic concentrations and declining water levels.

“Leading Edge Plume Area”:

  • A Vertical Circulation Treatment (VCT) system in the LEPA began operation on June 16, 2000. The system was shut down in December 2005 and restarted in July 2011. The VCT system was placed in temporary shutdown on Nov. 20, 2018. The VCT system currently remains shut down.
  • Groundwater monitoring has continued on a semiannual basis since the VCT system was shut down in November 2018. COC concentrations have been below the Environmental Protection Agency (EPA) MCLs in all LEPA wells since 2015.

A 1,4-dioxane investigation was completed in 2020, based on the results no further characterization is needed in OU-1 Area 1.

OU-2

OU-2 consists of the upper 10 feet of soil at 18 CAOCs where hazardous substance disposal actions or releases may have occurred. Twelve of the CAOCs were closed with NFA and three CAOCs were remediated to residential land use standards in 1999. The remaining three CAOCs (1, 8A and 10) were described in the December 1997 Final OU-2 ROD as requiring institutional controls (ICs) to prevent unlimited use and unrestricted exposure due to remaining soil contamination. The base has placed a fence around the site and listed land use controls in the base master plan. Two treatment systems have significantly lowered contaminant levels in affected soil. The main base system is an air-sparging/pump-and-treat system that attacks the main plume and a LEPA system that remediates contaminants beyond the main base system.

CAOC 1 (Flight Line)

CAOC 1 consists of the pre-1960 flight line (runways, aprons, and taxiways) and associated aircraft maintenance hangar facilities. CAOC 1 is located in the north-central portion of MCAS Yuma and occupies approximately 170 acres. The RI focused on the flight line areas where source areas of contamination were suspected (e.g., aircraft and vehicle wash racks, oil/water separators, fuel storage bladder locations, dry wells, miscellaneous stained soil areas, and maintenance and storage yards). Results of the RI did not reveal significant soil contamination. Chemicals evaluated in the Human Health Risk Assessment (HHRA) included PAHs, PCBs, pesticides, and metals.  ICs are in place to restrict the land use of CAOC 1 to industrial/commercial use. A change in land use from industrial to residential use will require re-evaluation of the remedy. The institutional controls are implemented through the Land Use Control Implementation Plan (LUCIP) and the Base Master Plan.

CAOC 8A (Southeast Station Landfill)

CAOC 8A is located in the southeastern portion of MCAS Yuma. This area is a former landfill that was used from 1953 to 1961 primarily for disposal of municipal wastes. The landfill’s disposal pits were backfilled and no longer provide an opportunity for direct human exposure to contaminated soil. CAOC 8A is entirely enclosed by chain-link fencing; access for vehicles is limited to those authorized to open the locked gates. The COCs are TRPH, PAHs, PCBs, and metals in surface soil.  An HHRA performed for CAOC 8A indicated that direct exposure to the site surface soil does not pose an unacceptable level of risk under an industrial land use scenario.  Risk associated with subsurface soil was not evaluated in the risk assessment.  The OU-2 ROD remedy is ICs to prohibit continued disposal or any activities that disrupt the landfill cover.

During 2021, an investigation of the closed landfill CAOC 8A began which included soil, soil gas and groundwater sampling.

CAOC 10 (Ordnance Munitions Disposal Area, Composed of Subareas 10a and 10b)

CAOC 10 was used during World War II as a small arms shooting range for bomber gun crews. From the early 1950s to 2010, ordnance materials were stored in the magazines around the central portion of Ordnance Loop Road. The area has also been used for surface tank and drum storage. Surface spills, including liquid residues from ordnance mixing operations, were reported within this area. Suspected waste associated with this area included used oils, ordnance waste associated with nitroaromatics, fuel-related wastes, and metals. During the RI, the primary findings of the field sampling and analysis program were TRPH and PAHs in surface soil, and one anomalous lead concentration.  ICs are in place to restrict the land use of CAOC 10 to industrial/commercial use. A change in land use from industrial to residential use will require re-evaluation of the remedy. The institutional controls are implemented through the Base Master Plan.