Marine Corps Air Station Yuma

OU 1 Area 1 is in the northern portion of MCAS Yuma, underlying an area of approximately 60 acres that extends from the Building 230 area to the northwestern station boundary, and consists of a chlorinated hydrocarbon-contaminated groundwater plume. Previous investigations have described the plume as consisting of the Hot Spot Area near Building 230, the interior Central Plume Area near the northeastern portion of the runway, and the Leading Edge Plume Area near the northwestern boundary of the station.

Following removal of two underground storage tanks (UST) from the vicinity of Building 230 in 1989, trichloroethylene was detected in soil beneath one of the USTs, which collected discharges from the floor drain of the Building 230 paint shop. Results of subsequent sampling found no remaining source of chlorinated hydrocarbons in the zone between the surface and groundwater in the Building 230 area. Although there is no conclusive evidence, the source of the chlorinated hydrocarbon plume appears to be related to Building 230 activities.

Groundwater sampling at deep wells in Area 1 during a 1996 remedial investigation confirmed that concentrations of chlorinated hydrocarbons exceeding maximum contaminant levels did not extend deeper than the top of the water table. Chlorinated hydrocarbons were also identified in groundwater beyond the western boundary of MCAS Yuma beneath property controlled by the Yuma Airport Authority. A 1999 technical memorandum prepared in support of the OU 1 remedial design and feasibility study fully delineated the horizontal and vertical extent of trichloroethylene- and 1,2-dichloroethane-impacted groundwater in the deep aquifer below the groundwater table.

A 1996 Area 1 in-situ source treatment and reduction alternatives plan evaluated the use of in-situ groundwater treatment technologies to address contamination in the Building 230 Hot Spot Area and Leading Edge Plume Area. In 1999, remedial action conducted at the HSA included installation of an air sparging and soil vapor extraction system. Operations ended in 2014 with regulatory concurrence that requirements in the 2000 Record of Decision were met. A remedial action initiated in 2000 at the Leading Edge Plume consisted of a vertical circulation treatment system. Based on contaminant concentrations and groundwater modeling results, the system was shut down with regulatory concurrence in 2018. The air sparging and soil vapor extraction and vertical circulation treatment systems began decommissioning activities in 2022 and are still underway.

Long-term monitoring of concentration trends for contaminants of concern in groundwater has been conducted at Area 1 since 1998 to verify progress toward achieving remedial action objectives. Institutional controls to prevent changes in land use, limit property access, and control the off-site migration of chemicals of concern are currently in place to prevent use of contaminated groundwater beneath OU 1 Area 1. No land use control deficiencies were noted during the inspections conducted in May 2022.

As a result of the 2020 basewide investigation of per- and polyfluoroalkyl substances (PFAS) at MCAS Yuma, Operable Unit 1 Area 1 was also designated as Installation Restoration (IR) Site 19 because of the presence of PFAS. A remedial investigation for PFAS is in progress at IR Site 19. The results of the human health risk assessment included in the remedial investigation will provide a basis for decisions regarding further action, if necessary, to address PFAS contamination at the site.

OU 1 Area 2 is northeast of the flight line along the easternmost taxiway, northwest of the Fuel Farm area and Building 303, a jet engine testing cell. The groundwater plume covered approximately 4 acres confined on station. The source area for the Area 2 plume was a suspected leach field associated with Building 303. Area 2 contamination consisted primarily of 1,1-dichloroethene, detected in consecutive Underground Storage Tank Program sampling events.

Since contaminant concentrations at the Area 2 plume were near regulatory limits, monitored natural attenuation was adopted to show that contaminant concentrations would be reduced through natural processes. Long-term monitoring of groundwater continued until plume concentrations decreased below regulatory limits. Area 2 was closed in 2006 with regulatory concurrence, and no further action is required for this area.

OU 1 Area 3 is north of the Combat Aircraft Loading area near a former unlined fire training pit, which was used from 1976 to 1985 to practice extinguishing fires. The groundwater plume covered approximately 10 acres and did not migrate off-station. The contamination at Area 3 was primarily trichloroethylene and 1,1-dichloroethenefound in the immediate vicinity of the former fire pit.

After the 1996 remedial investigation, monitored natural attenuation was adopted at the Area 3 plume to show contaminant concentrations would be reduced through natural processes. Long-term monitoring of groundwater continued until contaminant concentrations decreased below regulatory limits. Area 3 was closed in 2006 with regulatory concurrence, and no further action is required for this area.

OU 1 Area 4 was a non-CERCLA area in the Fuel Farm, with groundwater contamination primarily consisting of fuel components and a benzene plume that exceeded regulatory maximum contaminant levels. Corrective action pilot tests and pilot system operations began in 1995 and quarterly monitoring of wells installed under the Underground Storage Tank (UST) Program was conducted under the station-wide quarterly monitoring program. Area 4 was assigned to the State of Arizona’s Leaking UST Program during the 1996 remedial investigation and corrective actions and closure for this area were completed under that program.

OU 1 Area 5 was a non-CERCLA area in the Motor Transportation Pool, with groundwater contamination primarily consisting of fuel components and a benzene plume that exceeded regulatory maximum contaminant levels. Corrective action pilot tests and pilot system operations began at the Motor Transportation Pool in 1995, and quarterly monitoring of wells installed under the Underground Storage Tank Program was being conducted under the station-wide quarterly monitoring program. Area 5 was assigned to the State of Arizona’s Leaking UST Program during the 1996 remedial investigation and correction actions and closure for this area were completed under that program.

OU 1 Area 6 is south of Building 328, the Central Receiving Warehouse, where a small plume of primarily tetrachloroethylene was detected near three suspected diesel-fuel USTs associated with former Building 335. The footprint of the plume was less than 1 acre and contaminant concentrations were considered stable with no evidence of migration.

Following the 1996 remedial investigation, monitored natural attenuation was adopted at the Area 6 plume to show contaminant concentrations were being reduced through natural processes. Long-term monitoring of groundwater continued until contaminant concentrations decreased below regulatory limits. Area 6 was closed in 2003 with regulatory concurrence, and no further action is required for this area.

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CAOC 1 consists of a pre-1960 flight line that included tarmac, runways, aprons, taxiways, and associated aircraft-maintenance hangar facilities. This area is within the existing flight line in the north-central portion of MCAS Yuma and occupies approximately 170 acres. From the 1940s to the early 1970s, waste fuel and oil was routinely drained from aircraft engines directly to the ground where aircraft were parked, and waste oil was also used for dust control. The 1996 remedial investigation focused on the flight line areas, the suspected source areas for contamination, such as aircraft and vehicle wash racks, oil/water separators, fuel storage bladder locations, dry wells, miscellaneous stained soil areas, and maintenance and storage yards.

The OU 2 remedial investigation revealed widespread detection of total petroleum hydrocarbons and polycyclic aromatic hydrocarbons in surface soils and localized areas around the flight line. Polychlorinated biphenyls used in electric transformers, were reported at the northern edge of the flight line and existing wash rack. Solvents, pesticides, and metals were reported in shallow soil throughout the flight line. The investigation, however, did not find significant soil contamination in suspected source areas near specific units included in the investigation.

The remedy selected for CAOC 1 in the 1997 OU 2 Record of Decision was land use controls (LUCs) that restrict land use to Industrial/Commercial use. No deficiencies were noted during the May 2022 LUC inspections. The remedial actions for CAOC 1 will continue to be evaluated in five-year reviews, with the next review planned for 2025.

CAOC 2 occupied approximately 28 acres in the northeastern corner of the station, bordered by Worley Street to the south, Building 603 to the west, Shaw Avenue to the east, and the flight line to the north. The area was used from the 1940s to the early 1980s for public works shops and vehicle maintenance, and several specific spill locations have been identified. In addition, two underground fuel storage tanks found to be leaking were removed in 1981 and later replaced. One of the two tanks has been out of service since 1990 after failing a tank integrity test. This area of MCAS Yuma is largely developed and paved with asphalt and concrete and continues to be used as an industrial shops area.

The 1996 OU 2 remedial investigation found isolated detections of residual total recoverable petroleum hydrocarbons and polycyclic aromatic hydrocarbons, as well as volatile organic compounds, semivolatile organic compounds, benzene, toluene, ethylbenzene and xylene, pesticides, metals, and organic lead in shallow soils underlying the area. Significant soil contamination was not found around suspected source areas such as drywells, oil/water separators, and former buildings that were included in the investigation.

Based on the data collected at the OU 2 sites, no further action was recommended in the 1997 Record of Decision for CAOC 2 because no contaminants are present at this site that pose a threat to human health or the environment.

CAOC 3 includes the Auto Hobby Shop, Building 561, and its immediate surroundings covering an approximate 0.3 acre fenced area. This highly developed area of MCAS Yuma is used for vehicle and aircraft maintenance. Much of the area is paved with asphalt or concrete, although the area east of Building 561 is unpaved.

The unpaved area was reportedly used from 1960 to the early 1980s for disposal of vehicle wastes directly to the ground, including waste oil and Stoddard solvent. The 1996 OU 2 remedial investigation detected volatile organic compounds and residual total recoverable petroleum hydrocarbons in shallow soils underlying the area.

Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 3 because no contaminants are present at this site that pose a threat to human health or the environment.

CAOC 4, the Radar Hill Disposal Area, is adjacent to Buildings 040 and 1229, located south of Radar Hill within the central portion of MCAS Yuma. The area was used during the 1940s and 1950s for burning or burying trash, which at the time was anything that could not be used or recycled (e.g., waste paint, thinners, solvents, oils, and their containers). Unrinsed, empty pest control containers from frequent fogging to control flies and gnats were also disposed of in this area. More recently the area was used for construction debris disposal, consisting mostly of broken concrete slabs.

The 1996 OU 2 remedial investigation found residual total recoverable petroleum hydrocarbons and isolated detections of polycyclic aromatic hydrocarbons and lead in shallow soils underlying the area. Although surface soil samples collected from CAOC 4 during the remedial investigation did not contain detectable asbestos, potential asbestos-containing materials (ACM) were observed in debris piles and analysis confirmed the presence of asbestos in the materials.

Based on the results of the OU 2 remedial investigation and the feasibility study issued in 1996, the 1997 Record of Decision for CAOC 4 recommended removal of visible ACM, excavation of surface soil mixed with ACM, off-site disposal, and verification inspections. A final 1999 remedial action report recommended that no further action be required for the area following remedial action completion.

CAOC 5, the Light Anti-Aircraft Missile Battalion compound, is in the south-central portion of MCAS Yuma. From the late 1960s until 1974, this area was used as a vehicle maintenance and storage yard. Routine vehicle service, maintenance, and fueling operations resulted in disposal and release of fuels, oil, and various solvents onto the ground. Although the 1996 OU 2 remedial investigation primarily detected residual total recoverable petroleum hydrocarbons in shallow soils, none of the individual component hydrocarbons were detected.

Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 5 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 6, the Old Sewage Treatment Area, is west of County Road 3E and south of Loesch Street in an area currently used for military family housing. In the early 1940s, station sewage was treated in two Imhoff tanks and discharged to an unlined evaporation/infiltration lagoon and sludge beds. Approximately 100 to 200 million gallons of sewage were processed at the site, along with other wastes including oils, solvents, and thinners. The treatment facility was closed in 1943 and the sludge buried in place. In the early 1970s, a housing development was built over the buried lagoon and sludge beds.

Although a 1996 OU 2 remedial investigation primarily detected residual total recoverable petroleum hydrocarbons in shallow soils, none of the individual component hydrocarbons were detected. Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 6 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 7, the Fire Training School, is divided into two subunits: CAOC 7A, the northern unit, and CAOC 7B, the southern unit. CAOC 7A, occupying approximately 40 acres, is southwest of Radar Hill and north/northwest of the Combat Aircraft Loading Apron. During the 1996 OU 2 remedial investigation fieldwork, only CAOC 7A was investigated. Investigation of CAOC 7B was documented in the results of a 1995 MCAS Yuma asbestos survey.

CAOC 7A consists of 16 unlined fire pits in the northern portion of the site that were used between 1952 and 1985 for fire training. Facility 1220, the current lined fire pit, has been used since 1985, and seven former fuel bladder areas were used between 1967 and 1984. Fire training at the site involved floating flammables on water in shallow, unlined pits, with water and unburned flammables washed into the surrounding soil.

The 1997 OU 2 remedial investigation primarily detected widespread residual total recoverable petroleum hydrocarbons, generally in former fire pits and fuel bladders. Small broken pieces of asbestos-containing materials (ACM) were identified south and east of the active fire-training pit in an approximate 170,000 square-foot area. In one approximately 1,200 cubic yard area near the active burn pit, ACM contamination in soil reached a maximum of one foot deep. The remedial investigation concluded that asbestos is the only chemical of potential concern at the site that may pose a risk to human health or the environment.

CAOC 7B is south of the combat aircraft loading apron and consists of debris piles used for dumping construction debris. Seven sites within this area consist of isolated, coherent piles confirmed to contain one or more types of ACM with a total volume of approximately 10 cubic yards.

Based on the results of the 1996 OU 2 remedial investigation and feasibility study, the 1997 Record of Decision recommended removal of visible ACM, excavation of surface soil mixed with ACM, off-site disposal, and verification inspections. A final remedial action report for OU 2 following completion of the remedial action in 1999 required no further action at CAOC 7.

As a result of the 2020 site inspection of per- and polyfluoroalkyl substances (PFAS) at MCAS Yuma, CAOC 7 was reopened as Installation Restoration (IR) Site 7 to further investigate PFAS contamination in groundwater. A remedial investigation for PFAS is in progress at IR Site 7. The results of the human health risk assessment included in the remedial investigation will provide a basis for decisions regarding further action, if necessary, to address PFAS contamination at the site.

CAOC 8A is in the southeastern portion of MCAS Yuma, between North Ordnance Road and the southern MCAS Yuma property line. It is the site of a former landfill and surface disposal areas where wastes were burned prior to disposal in 10 to 20 pits. The site is currently vacant land except for ordnance and munitions storage bunkers within the Ordnance Distribution Facility. The disposal pits were backfilled and no longer provide for direct human exposure to contaminated soil.

During the 1996 OU 2 remedial investigation, this area was investigated as part of CAOC 8, a 68-acre area used primarily for disposal of MCAS Yuma municipal wastes from 1953 to 1961. A portion of the area was also used for rubble disposal and as a borrow area. The human health risk assessment performed during the remedial investigation recommended subdividing CAOC 8 into CAOC 8A and 8B, based on current and anticipated future land use, and evaluated each separately.

Drilling at CAOC 8A for sample collection within the landfill was not performed during the remedial investigation because of drilling conditions and potential hazards. OU 2 remedial investigation surface soil sampling detected total recoverable petroleum hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and metals.

Although the residential exposure risk from surface soil is at the high end of the acceptable range, exposure does not pose an unacceptable risk under an Industrial/Commercial land-use scenario. A risk management decision was made in the 1997 Record of Decision (ROD) to implement land use controls (LUCs) as the remedial alternative at CAOC 8A, restricting use to the current use at the time of ROD signing, which is an inactive landfill, surface storage, and roads. Any land use that could disturb the landfill contents is strictly prohibited to minimize potential health risks.

MCAS Yuma has proposed the installation of a southern perimeter entrance gate that would overlap portions of CAOC 8A. A 2021 remedy optimization study was conducted in support of the construction project to collect additional soil, soil vapor, and groundwater data from the subsurface. A human health risk assessment was performed using the newly collected data to evaluate if LUCs can be removed or changed to Industrial/Commercial use over portions of the site, which would facilitate the construction project. The draft remedy optimization report supports the changes to LUCs and is currently under review by the regulatory agencies.

During the remedy optimization study, a small subarea (identified as Site A) was discovered which contained munitions debris later characterized as inert; however, the planned sampling was not completed. The DON will conduct a site assessment of this area in 2023. A ROD Amendment or Explanation of Significant Differences document will be developed to update LUC requirements, as needed, after finalization of the CAOC 8A draft remedy optimization report.

No LUC deficiencies were observed during the May 2022 inspections. The remedy for CAOC 8A as currently implemented, or as revised by any amendment or other changes to the ROD will continue to be evaluated in five-year reviews, with the next review planned for 2025.

CAOC 8B is the MCAS Yuma residential housing area that now covers the area north of North Ordnance Road to Loesch Street. The remedial investigation risk assessment estimated human health risks at CAOC 8B for both Residential and Industrial/Commercial scenarios to be within the acceptable range. Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 8B because this site does not pose a threat to human health or the environment.

CAOC 9, the Southwest Sewage Lagoon, is within the southeast corner of MCAS Yuma, southwest of the intersection of North Ordnance Road and County Highway 3E. This approximately 14-acre area formerly consisted of two Imhoff tanks, sludge drying beds, and six unlined lagoons used for wastewater treatment from 1944 until 1970. The lagoons were closed in 1970 when the station began discharging to the Yuma wastewater treatment plant. The sludge was left in place and covered with fill materials.

The 1996 OU 2 remedial investigation reported detections of residual total recoverable petroleum hydrocarbons in near-surface soil and isolated detections of polycyclic aromatic hydrocarbons. Although asbestos was detected in samples from one debris pile north of the horse stables, it was not detected in surface soil samples. The remedial investigation concluded that the asbestos was the only chemical of concern at CAOC 9 that may pose a risk to human health or the environment.

The 1997 OU-2 Record of Decision for CAOC 9 recommended cleanup of visible asbestos-containing materials (ACM), excavation of surface soil mixed with ACM, off-site disposal, and verification inspections. A final 1999 remedial action report following completion of the remedial action required no further action at CAOC 9.

As a result of the 2020 site inspection of per- and polyfluoroalkyl substances (PFAS) at MCAS Yuma, CAOC 9 was reopened as Installation Restoration (IR) Site 9 to further investigate PFAS contamination in groundwater. A remedial investigation for PFAS is in progress at IR Site 9. The results of the human health risk assessment included in the remedial investigation will provide a basis for decisions regarding further action, if necessary, to address PFAS contamination at the site.

CAOC 10, the Ordnance Munition Disposal Area, consists of subareas 10A and 10B. CAOC 10A lies within the existing, secured Ordnance Distribution Facility and CAOC 10B lies within the fenced area adjacent to CAOC 8A in the southeastern portion of MCAS Yuma. Two disposal operations took place at CAOC 10A in the mid-1970s, when approximately 250 to 300 pounds of .50 caliber ammunition were buried north of Building 2114, and rinsate from napalm mixing was discharged to the ground. General trash from the ordnance area was reportedly buried at CAOC 10B between the late 1960s and 1970s.

CAOC 10 was used during World War II as a shooting range for bomber gun crews. From the early 1950s until approximately 2010, ordnance materials were stored in magazines around the central portion of Ordnance Loop Road. Surface tanks and drums have also been stored in the area and surface spills, including liquid residues from ordnance-mixing operations, have been reported. The area continues to be used for storage and handling of ordnance.

The primary findings for CAOC 10 from the 1996 OU 2 remedial investigation included detections of total recoverable petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), and one anomalous lead detection in shallow surface soil. Follow-up sampling conducted later in 1996 and in 1997 found PAHs at much higher total concentrations over a wider area than indicated by the remedial investigation. Supplemental soil sampling to fully define the extent of PAHs in the soil was conducted.

Although the remedial investigation risk assessment found the residential exposure risk to be higher than the acceptable range, exposure under an Industrial/Commercial land use scenario was in the middle of the acceptable range. A risk management decision was made in the 1997 Record of Decision to implement land use controls (LUCs) as the remedial alternative at CAOC 10, restricting future land use to the existing industrial/commercial use. During the May 2022 inspections, no LUC deficiencies were noted.

CAOC 11, the Radiation Disposal Pipes, is near the south-central boundary of the station. In the 1950s, the area was used for a one-time burial of two sealed iron pipes containing radioactive materials that included electron tubes, luminous markers, and radium dials and knobs. These pipes were excavated and removed in 1980.

A radiological characterization survey performed by the Department of Navy’s Radiological Affairs Support Office after pipe excavation indicated no significant differences in radioactivity in the burial pit soils when compared to soil from 20 feet and 200 feet away. Swipe tests of the excavated pipes for radiation measurement were low enough to permit unrestricted access at CAOC 11.

Because the characterization survey detected no radiological contamination, CAOC 11 does not pose a threat to human health or the environment. The 1997 OU 2 Record of Decision recommended no further action at the site.

CAOC 12, the Tear Gas Burial Area, is in the southwest part of MCAS Yuma, about 550 feet west of Building 1597, and on the southern edge of the concrete combat loading apron. In the late 1970s, numerous sacks of approximately 300 pounds of dry crystalline chemicals used in tear gas generation were reportedly buried in the area. Earthmoving operations in 1984 failed to uncover this material, and disposal activities at COAC 12 remain unconfirmed. No evidence of tear gas materials was found during previous investigations in the area.

The primary findings for CAOC 12 from the 1996 OU 2 remedial investigation were detections in shallow soil of volatile organic compounds and semi-volatile organic compounds below risk-based concentration values. Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 12 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 13 is a former drain field now covered by a 14-inch-thick concrete apron. The drain field is adjacent to the fenced area used for Marine Wings Weapons Unit operations from 1962 to 1985. The unit provided ordnance support for aircraft training, such as filling aircraft wing tanks with napalm and tear gas. The drain field was used for the disposal of rinsate from filling and mixing equipment and consisted of three joined septic tanks with four 125-foot clay tile leach lines set in gravel trenches covering about 0.25 acres. Approximately 1 million gallons of wastewater and chemicals are thought to have been discharged during active operations.

The OU 2 remedial investigation detected polycyclic aromatic hydrocarbons, pesticides, and metals in shallow soils underlying the site. Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 13 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 14 is northwest of Building 40 and south of Building 97 and consists of a lagoon that collected drainage from the hangar at Building 97. From 1973 to 1985, discharges consisted of water from oil/water separators, washdown from the hangar floor, and rinse water from removable fuel tank interior cleaning.

Although the 1996 OU 2 remedial investigation primarily detected residual total recoverable petroleum hydrocarbons and isolated polycyclic aromatic hydrocarbons in shallow soils, none of the individual component hydrocarbons were detected. Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 14 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 15 is within the Fuel Farm in the northeastern corner of MCAS Yuma, east of the flight line. The area formerly contained two underground storage tanks, occupying an area of approximately 0.3 acres. The tanks were installed in 1943 and removed in 1987 after they failed tank integrity tests. Waste materials stored in the tanks include various solvents and thinners, waste oil, paint wastes, other degreasing and stripping wastes, diesel fuels, and jet fuels.

The 1996 OU 2 remedial investigation indicated the presence of total petroleum hydrocarbons, semi volatile organic compounds, and metals in shallow soils below health-based guidance levels. Based on the investigation data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 15 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 16, which is in the highly developed flight line area of the station, consists of two underground storage tanks, each with a capacity of 1,000 gallons. The tire shop area of Building 230 reportedly drained to Tank No. 2, and the paint booth and other Building 230 maintenance facilities drained to Tank No. 4. The tanks both leaked and were removed in 1989.

Although the 1996 OU 2 remedial investigation primarily detected residual total recoverable petroleum hydrocarbons in shallow soils, none of the individual component hydrocarbons were detected. Trichloroethene was detected in one sample only. Semi-volatile organic compounds and metals were also detected, but metals were within background levels. Based on the investigation data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 16 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 17 is the former location of an underground storage tank in a remote area of MCAS Yuma, adjacent to Building 1708, about 1 mile southwest of the main Station. The tank was installed in 1985 to collect rinsate from a decontamination pad adjacent to Building 1708. The tank was abandoned in 1988 and removed in 1995.

During removal, three soil samples were collected from beneath the underground storage tank. No rinsate related contaminants were detected, indicating that tank leaks had not occurred.

Although the 1996 OU 2 remedial investigation primarily detected residual total recoverable petroleum hydrocarbons, none of the individual component hydrocarbons were detected. Semi-volatile organic compounds, pesticides, and metals were also detected, but metals were within background levels. Based on the investigation data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 17 because there are no contaminants present at this site that pose a threat to human health or the environment.

CAOC 18, comprising approximately 0.45 acres, is the Old Drum Storage Area within the northeastern corner of MCAS Yuma, north of the Fuel Farm. Numerous (approximately 102) 55-gallon drums were stored in a fenced area between 1987 and 1989. The drums, which contained investigation-derived wastes and waste personal protective equipment, were removed, and crushed in 1990, and the area is currently vacant.

Although the 1996 OU 2 remedial investigation primarily detected residual total recoverable petroleum hydrocarbons and isolated polycyclic aromatic hydrocarbons in shallow soils, none of the individual component hydrocarbons were detected. Solvents, pesticides, and metals were also detected at isolated locations in the shallow soils underlying this area. Based on the data collected at this site, no further action was recommended in the 1997 Record of Decision for CAOC 18 because there are no contaminants present at this site that pose a threat to human health or the environment.

As a result of the 2020 site inspection of per- and polyfluoroalkyl substances (PFAS), IR Site 20, a newly developed site, was identified because of the presence of PFAS in groundwater. The site is in the southwestern portion of the South Airfield Operations Area and includes the ARFF fire training area and emergency response sites. A remedial investigation for PFAS is in progress at IR Site 20. The results of the human health risk assessment included in the remedial investigation will provide a basis for decisions regarding further action, if necessary, to address PFAS contamination at the site.

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MRP Site 1 encompasses 370 acres in the southeast corner of MCAS Yuma and consists of three former small arms ranges, identified as the former Moving Base Range, Skeet Range, and Tower Trap Range. Residential facilities currently occupy approximately 25 acres in the northeastern portion of the site.

The Moving Base Range was established in 1942 and consisted of an oval track and 48 trap houses. Training was conducted by placing an aerial gunner in a vehicle driven around the track, while the gunner fired at clay targets launched from the trap houses. By 1952, ammunition storage buildings had been constructed on the site. The Skeet Range, which consisted of 16 firing semicircles, was established in 1942 and was used through at least 1946. The Tower Trap Range was established in 1942 and used through approximately 1946 and consisted of five firing positions with trap houses. Both the Skeet Range and Tower Trap Range were used for gunner training and recreation.

During the 2014 remedial investigation for MRP Site 1, no munitions and explosives of concern were identified. Lead shot and clay target fragments were observed on the ground surface throughout the site. MRP Site 1 was divided into MRP Site 1A and MRP Site 1B in 2015.

A 2015 time-critical removal action was conducted at MRP Site 1B in support of a planned microgrid energy facility. Sample results indicated that only the top 0.5 foot of soil required excavation, resulting in excavation of approximately 4,433 tons of non-hazardous soil that was disposed of at the South Yuma County Landfill. Post-excavation soil samples confirmed that soil with contaminant concentrations exceeding residential remediation levels had been removed. Regulatory concurrence for no further action was received in 2015 and MRP Site 1B was closed.

A 2018 non-time-critical removal action was conducted at MRP Site 1A in preparation for a potential future renewable energy project on the western half of the site. Excavation of soil impacted with polycyclic aromatic hydrocarbons (PAH), antimony, and lead resulted in the removal and off-site disposal of approximately 21,709 tons of non-hazardous soil and 7,445 tons of Arizona Special Waste soil from an approximate 25-acre area. A closure report was finalized for the removal action and the western half of the site was closed with regulatory concurrence in 2019.

In response to an emerging need for residential and recreational development at MRP Site 1A, a final action memorandum outlined a time-critical removal action for excavation of soil impacted by PAHs and lead on the remainder of the site. The removal action was performed, and regulatory agencies approved a completion report in September 2020.

Following completion of the removal actions, a Record of Decision that provides the details of final remedies for the site was developed and is being finalized. The selected remedy for the three Decision Units (DU) evaluated at MRP Site 1A consists of institutional controls that restrict land use to industrial or commercial use in two of the three DUs, and the selected remedy for the residential and recreational area, the third DU, will be no further action.

MRP Site 2 was the location on a 1952 preliminary Base Master Plan map proposed for construction of a small arms range. The site is currently part of the Yuma County Airport. Most of the site is currently paved and is used as a taxiway and parking apron for small planes. Hangars and buildings have been constructed at the site to provide administrative and operations facilities for the airport.

A 2010 site investigation at MRP Site 2 was followed by an expanded site investigation in 2014. Metals concentrations detected in surface and subsurface soil samples were below MCAS Yuma background values and human health screening levels. The Arizona Department of Environmental Quality concurred in 2015 with the Department of Navy’s no further action recommendation for MRP Site 2.

MRP Site 3 is a former small arms range that used a berm/backstop to reduce the hazard distance. The site was remediated and closed in 2003 as part of the Arizona Department of Environmental Quality Voluntary Remediation Program.

MRP Site 4 is a former small arms range in the north-central portion of MCAS Yuma that overlaps the boundaries of OU 2’s CAOC 1. Approximately 198 acres of the 240-acre site is highly developed and almost completely covered by buildings and concrete paving, including runways, taxiways, parking aprons, and parking lots. The source of potential munitions constituents in subsurface soil at MRP Site 4 is ammunition use during its operation as a small arms range. Cartridge, ball, and rifle-related munition types were used at the site.

A site investigation at MRP Site 4 did not include sampling because it is primarily located within CAOC 1, which was investigated during the 1996 OU 2 remedial investigation. Arsenic, cadmium, copper, lead, and zinc were detected at concentrations above background values during the remedial investigation at CAOC 1. The remedy selected in the 1997 OU 2 Record of Decision addresses metals-impacted soils at MRP Site 4 that are part of CAOC 1 through in-place institutional controls that restrict land use to Industrial/Commercial use.

The 2016 Record of Decision for MRP Site 4 documents selection of a land use control (LUC) remedy that expands the intuitional control boundaries to the remainder of MRP Site 4 outside of CAOC 1. No deficiencies were noted during the May 2022 LUC inspection conducted at the site.

MRP Site 5 is south of, and adjacent to, a combat aircraft loading area and covers less than 1 acre. It was formerly a firing-in buttress range built prior to 1952 that was removed in 1955. Because of the historical use of munitions with explosives at the site, munitions and explosives of concern (MEC) and munitions constituents were thought to potentially be a hazard at the site.

Following a 2010 site inspection at MRP Site 5, an additional assessment for MEC and arsenic in soil was recommended. A 2013 remedial investigation included a digital geophysical mapping survey and intrusive investigations across the entire site. The results of the survey were inconclusive due to interference from extensive metallic debris in the subsurface.

A 2016 expanded remedial investigation to complete characterization of the nature and extent of MEC at the site included excavating soil to remove metallic debris, screening excavated soil for MEC and material potentially presenting an explosive hazard, digital geophysical mapping of the entire site after excavation, identifying and removing all targets of interest, collecting, and analyzing samples beneath targets for explosives and metals, and backfilling the site. No contaminants at concentrations above residential use levels were detected in soils at MRP Site 5 following completion of expanded remedial investigation activities.

Results from an updated risk assessment performed in 2016 indicated that metals present in soils at MRP Site 5 do not pose an unacceptable risk to human health or the environment. The 2019 MRP Site 5 Record of Decision documented a no further action remedy based on the findings of the extensive site investigations completed at the site.

MRP Site 6, the former Firing-in Buttress Range 1295, is in the south-central portion of MCAS Yuma, beneath the southeastern runway area. The approximately one-acre range was built prior to 1955 in order to zero in fixed aircraft guns and was removed in 1985. The site is located entirely within the restricted area of the airfield east of, and adjacent to, a combat aircraft loading area.

A 2010 site inspection conducted at MRP Site 6 detected no metals in soil at concentrations exceeding project-screening levels, and no explosive constituents. Multiple, expended 20-millimeter (mm) projectiles that were observed during the inspection were classified by a qualified unexploded ordinance technician items as munitions debris and explosively non-hazardous. Because of the presence of the 20-mm projectiles, a digital geophysical mapping investigation was recommended to determine if munitions and explosives of concern (MEC) were present at the site.

Because of pending military construction project at MRP Site 6, the MCAS Yuma Ordnance Disposal group performed a sweep of the site prior to grading activities, and wood, metal and concrete debris were removed. No explosive hazards were identified during debris removal activities, although the potential for MEC and munitions constituents in the subsurface was not ruled out because of the historical use of projectiles at the site.

A 2013 feasibility study evaluated remedial alternatives for MRP Site 6. The 2017 MRP Site 6 Record of Decision documented a selected remedy of land use controls (LUC) consisting of engineering controls and institutional controls. As a result of the construction project, the site is covered by 3-feet of clean, imported soil overlain by a concrete apron, and engineering controls are effectively in place. Institutional controls are implemented through base planning processes, which require approval for any construction involving below ground activities. No LUC deficiencies were noted during the May 2022 inspection.

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