Naval Air Station Lemoore

IRP Site 1 is a 39-acre regulated solid waste sanitary landfill located in the southern portion of NAS Lemoore. The landfill began operating in 1961 and was used as a municipal landfill exclusively for NAS Lemoore until 1991. Earliest disposal reportedly began in the southeast comer of the landfill and progressed to the north and west. From 1961 to 1967, refuse was burned in the trenches and then covered. After 1967, wastes were compacted and covered. According to disposal records, wastes placed in the landfill during this period included paint strippers, paint sludge, plating solutions, blasting sand, industrial sewer sludge, clarifier sludge, photo processing wastes, asbestos, capacitors, and miscellaneous solid wastes such as metal containers, wood, plastics, rags, paper, concrete, and asphalt.

Until 1978, commercial or industrial wastes disposed of at the landfill included approximately 2,000 to 4,000 gallons of liquid waste per year containing unknown concentrations of hazardous substances. Liquid wastes may have contained trichloroethene, trichloroethane, methyl ethyl ketone, plating solutions, acetone, paints, solvents, and waste oils possibly contaminated with polychlorinated biphenyls. Beginning in 1978, NAS Lemoore initiated a program to segregate wastes containing hazardous substances from other solid wastes. The landfill was issued a solid waste facility permit in 1979. Disposal of any hazardous waste other than infectious waste was specifically prohibited under the permit. Landfill use is currently restricted to the stockpiling of fill soils.

Previous investigations at the landfill include an initial assessment study in 1984, the confirmation study that followed in 1986, and an air and solid waste assessment test in 1988. The 1995 final report on a remedial investigation conducted at IRP Site 1 concluded that although no complete exposure pathways existed at the landfill, future human exposure to contaminants of concern may occur. Contaminants of concern included volatile and semi-volatile organic compounds, pesticides, petroleum products and constituents, and metals in soil or groundwater under the landfill.

A final 1996 feasibility study evaluated alternatives addressing future exposure to contaminants of concern at the landfill. Later in 1996 a proposed plan was released to the public identifying the preferred alternative. Landfill closure and post-closure care and monitoring were selected as the remedy for IRP Site 1, including a native soil cap, groundwater monitoring, landfill gas monitoring, and land use controls.

The Navy has conducted post-closure annual groundwater monitoring and sampling at IRP Site 1 since 1997. Every five years, a review of remedy performance and protectiveness is performed at the site in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act process. The first five-year review was conducted in 2002. The most recent review, conducted in 2017 and completed in 2018, found the land use control and institutional control remedy at IRP Site 1 to be protective of human health and the environment.

A 2018 post-closure monitoring program report recommended that landfill gas monitoring continue in wells installed around the IRP Site 1 landfill perimeter in case exceedances requiring a response occur, but that annual gas vent monitoring within the interior of the landfill be removed from the activities conducted at the landfill. Interior vents produced historically low detections of methane and were not providing useful information on potential methane migration at the facility boundaries. Regulatory agencies concurred in 2019 because methane gas was not detected in the landfill gas perimeter monitoring wells. The six perimeter landfill gas wells are still monitored annually.

A 2021 post-closure monitoring program report recommended that additional monitoring wells be installed to investigate hexavalent chromium exceeding California maximum contaminant levels in groundwater in three existing monitoring wells and to provide an additional upgradient point for groundwater contouring. After discussion with state regulatory agencies, the Navy will install one additional downgradient well for monitoring hexavalent chromium.

NAS Lemoore continues operating and maintaining monitoring systems and performing long-term monitoring at the landfill. The remedy is expected to be protective of human health and the environment throughout the life of the remedial action.

The 2020 per- and polyfluoroalkyl substances (PFAS) preliminary assessment report recommended further investigation at IRP Site 1 because plating solutions and industrial waste sludge disposed of at the landfill may have contained PFAS. Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations below project screening levels in groundwater samples for all three PFAS screening compounds used for making site management decisions.

PFAS concentrations reported in the PFAS site inspection report were rescreened in 2022 using new Department of Defense PFAS investigation guidance and the U.S. Environmental Protection Agency regional screening levels. Some concentrations for PFAS screening compounds were found to exceed screening levels and based on those results, IRP Site 1 was recommended for further evaluation as part of a PFAS remedial investigation. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 2 is a former pesticide rinse area located in the Administration Area in the southern part of NAS Lemoore. It consists of a fenced asphalt-paved storage yard area for Building 750, former Building 752, and a grassy area. Building 752, constructed in 1961, was one of the primary installation pesticide mixing and application equipment rinse-down areas, where pesticide containers and applicators were triple rinsed. Prior to demolition of the building in 1982, as much as 100,000 gallons of pesticide rinsate was discharged in this area.

A 1984 initial assessment study conducted by the Navy at NAS Lemoore included the Pesticide Rinse Area, Building 752, identified as IRP Site 2. Records examined during this study indicated that 10 to 18 chemicals were stored at the facility between 1979 and 1982. The most common pesticides discharged at Site 2 were the herbicides bromacil and diuron and the insecticides dursban, naled, and carbaryl. Because the site was an area with frequent human contact, a confirmation study was recommended.

A remedial investigation and ecological scoping assessment were completed in 1998. The ecological assessment concluded that IRP Site 2 contained such poor habitat that it could not support wildlife. During the remedial investigation, metals including arsenic were detected in soil samples, and low levels of pesticides and herbicides and elevated concentrations of metals were detected in the groundwater samples. However, the screening level human health risk assessment found that site contamination does not pose a significant threat to human health or the environment.

A 2010 arsenic confirmation sampling report found concentrations of arsenic during a 2007 confirmation soil sampling event to be within background levels at IRP Site 2. A screening level human health risk assessment, completed as part of the 2011 record of decision, updated the 1998 remedial investigation risk assessment by considering the new arsenic data. The human health risk at IRP Site 2 was found to be within acceptable limits. A record of decision recommending no further action was prepared. The Central Valley Regional Water Quality Control Board concurred in 2012 and the site was closed with no further action.

IRP Site 3 is a former pesticide rinse area located on the southern side of Building 50 in the Operations Area in the northern part of the air station. Between 1962 and 1975, pesticide containers and applicators were rinsed in an unpaved area adjacent to the southern side of Building 50. Approximately 65,000 gallons of rinsate containing about 130 gallons of pesticides were discharged onto the ground during this time according to personnel interviews. Reportedly, some of the rinsate occasionally ran into the street, where it may have entered a nearby storm drain.

A 1984 initial assessment study at NAS Lemoore recommended a confirmation study for IRP Site 3 because of the presence of potentially contaminated soil in an area where human contact was frequent. Soil sampling completed in 1991 as part of a remedial investigation found low concentrations of pesticides in shallow soil. No pesticides, polychlorinated biphenyls, or herbicides were detected in any of the groundwater samples.

The results of a human health risk assessment in a 1997 remedial investigation report indicated that the site posed no unacceptable risk to the environment or human health for occupational and construction workers. Residential use restrictions were required because arsenic concentrations in soil exceeded maximum background concentrations and slightly exceeded the U. S. Environmental Protection Agency’s target hazard index. No contaminants of concern were identified in groundwater.

A 1998 record of decision for IRP Site 3 prohibits residential land use. A land use control remedial design was finalized in 2012 to prevent other development and use of the site. Annual physical inspections of the site are required to confirm continued compliance with all institutional control objectives and land use restrictions. An October 2022 work plan outlined the current plans for annual inspection of land use control implementation.

In addition, five-year reviews of remedy performance and protectiveness are performed at the site in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act process. The most recent review was conducted in 2017 and found the land use control and institutional control remedy at IRP Site 3 to be protective of human health and the environment.

IRP Site 4, the Old Fire Training Area, is in the northern half of the air station in the Operations Area. From 1961 to 1965 the area was used to train fire-fighting personnel stationed at NAS Lemoore. During fire training exercises, waste fuel was ignited on the ground or spread over an old airplane fuselage to simulate a crash fire. The area was unpaved and measured 40 feet by 60 feet and records indicate that approximately 24,000 gallons of fuel were used for the fire training exercises.

A 1984 initial assessment study conducted by the Navy at NAS Lemoore included the Old Fire Training Area, identified as IRP Site 4, for further investigation. The Navy conducted a remedial investigation in 1998 at IRP Site 4, which included collecting additional soil and groundwater samples from both inside and outside the fire training area. The samples were analyzed for a variety of chemicals including volatile organic compounds (VOC), semi-volatile organic compounds (SVOC), fuel-related compounds, pesticides, and metals. Low levels of VOCs, fuel, and SVOCs associated with combustion of fuel were found in soils within the Old Fire Training Area and in groundwater beneath IRP Site 4. None were detected outside the fire training area.

Human health and ecological assessments evaluated the potential effects to human health and the environment from exposure to the chemicals identified at the sites. The risk assessments identified contaminants, exposure pathways, potential human and ecological receptors, and the possible risks of exposure to contaminants. IRP Site 4 was considered protective of human health and the environment for all reasonable anticipated future land uses.

Confirmation soil sampling conducted in 2007 found concentrations of arsenic to be within background levels at IRP Site 4. A 2011 screening level human health risk assessment completed by the Navy updated the 1998 remedial investigation risk assessment by considering the new arsenic data. The risk at IRP Site 4 was found to be within acceptable limits and a record of decision recommending no further action was prepared. The Central Valley Regional Water Quality Control Board concurred in 2012 and the site was closed with no further action.

Further Investigation for per- and polyfluoroalkyl substances (PFAS) was recommended in the 2020 basewide PFAS preliminary assessment report for soil and groundwater at IRP Site 4 because of the potential that aqueous film-forming foam, a PFAS-containing material known as “AFFF,” was used during firefighting training at this site.

Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in surface soil samples for two of three PFAS screening compounds used for making site management decisions. All three PFAS screening compounds were detected in groundwater samples, with concentrations exceeding project screening levels. IRP Site 4 was recommended for further evaluation. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

Firefighting School

IRP Site 5, the Firefighting School, is in the Operations Area in the northern part of NAS Lemoore. It was used from 1967 to 1988 to train firefighting personnel. Building 85 is located at the school and was used for classroom and administrative purposes. The main contaminants associated with historical operations at the IRP Site 5 are petroleum hydrocarbons.

IRP Site 5 consisted of a large gravel area, approximately 180 by 210 feet, with a central concrete fire pit. The fire pit was a concrete slab 30 feet by 30 feet with a 10-inch concrete curb. A subgrade concrete-lined sump, approximately 2 feet square and 2 feet deep, was at the center of the pit. Firefighting training activities were conducted at the area east of the building. After training exercises, excess unburned fuel was drained to an oil–water separator. After separation, fluids drained through an unlined open ditch into two unlined sumps where they infiltrated into the surrounding soils or evaporated.

In 1986, investigations for IRP Site 5 and IRP Site 9, the Sludge Drying Ponds, were combined because of proximity and similar contaminants.

After firefighting activities ceased in 1988, the area was modified. The fire pit was demolished, and the aboveground storage tank was removed. A new training facility located in the southern portion of Site 5 was used for fire training exercises until approximately 1994. At the new facility, fire training exercises were conducted within a bermed concrete area.

In 1997, the remaining IRP Site 5 structures and piping were removed from beneath the fire pit. Approximately 2,200 cubic yards of fuel-contaminated soil were excavated in 1999 to approximately 10 feet below ground surface and removed as part of a petroleum cleanup action. The soil was treated prior to using as backfill in the original excavation.

Naval Exchange Operations Gas Station (Building 59)

The Naval Exchange Operations (NEX OPS) Gas Station is in the Operations Area in the northern part of NAS Lemoore, within the northwest portion of combined IRP Sites 5 and 9. The NEX OPS Gas Station originally consisted of two 10,000 gallon underground storage tanks (USTs) and one fueling island. Another fuel island and 10,000 gallon UST were added in 1973 and 1974. One of the original USTs failed a 1986 leak test. The leaking UST and 164 cubic yards of impacted soil were removed in 1988. Subsequent investigations indicated that petroleum hydrocarbons were present in underlying groundwater. In 1995, the existing USTs were removed and replaced with two new USTs to supply gasoline to the station.

The NEX OPS Gas Station was added to the combined IRP Site 5 and 9 investigation in 2001 when commingled petroleum and hazardous constituents were identified. For investigation purposes, combined IRP Sites 5 and 9 were identified as Exposure Area A, and the NEX OPS Gas Station was called Exposure Area B.

Various remedial investigations performed from 1990 through 2009 verified the extent of the petroleum hydrocarbon impacts to human health and the environment. The 2017 feasibility study established remedial action objectives identifying chemicals, exposure pathways, and receptors for surface and subsurface soils, groundwater, and soil gas at Exposure Area A, and groundwater and soil gas at Exposure Area B. The preferred alternative is monitored natural attenuation, although the Central Valley Regional Water Quality Control Board requested additional data in support of natural attenuation model predictions. The Navy intends to prepare a proposed plan and record of decision but concluded in a 2022 draft groundwater investigation technical memorandum that additional assessment is necessary at IRP Site 5/9 prior to selecting a final remedy.

Further Investigation for per- and polyfluoroalkyl substances (PFAS) was recommended in the 2020 basewide PFAS preliminary assessment report for soil and groundwater at IRP Site 5 because of the potential that aqueous film-forming foam, a PFAS-containing material known as “AFFF,” was used during firefighting training at this site.

Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in surface and subsurface soil samples from the former fire pit and unlined sumps for two of three PFAS screening compounds used for making site management decisions. All three PFAS screening compounds were detected at concentrations exceeding project screening levels for groundwater in samples from and downgradient of the same two areas. IRP Site 5 was recommended for further evaluation. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 6 is a concrete-lined open ditch and three connecting tributary ditches east of Runway 32R that drain stormwater from the Operations Area in the northern part of NAS Lemoore. From 1961 to 1984, treated liquid effluent from the Operations Area Industrial Wastewater Treatment Plant (IWTP), treated liquids from the sanitary sewage treatment plant, and runoff from nearby agricultural fields flowed down the ditch to the nearby Kings River. The topography of the site is of low relief with very little change in elevation. IWTP liquid effluent discharge treatment activities were terminated in 1984 although this ditch continues to carry runoff from the storm sewer system. IRP Site 6 has been managed under the Navy’s ERP and was closed out with no further action required under a record of decision completed in 2003.

Aircraft Hangars 1 through 5 in the Operations Area in the northern part of the air station, also identified as Buildings 210, 240, 270, 300, and 330, contain aqueous film-forming foam (AFFF) fire-suppression systems. The hangars and Operations Area discharged waste into the IWTP and subsequently into the open ditch. Additionally, AFFF could have been released to the ground surface and subsequently flowed as surface runoff to the open ditch.

Further investigation was recommended in the 2020 per- and polyfluoroalkyl substances (PFAS) preliminary assessment report for soil and groundwater at IRP Site 6. Liquid waste containing PFAS, a substance that may be present in AFFF, had likely been disposed of to the IWTP, and subsequently to the open ditch. Other releases from AFFF fire suppression systems could have impacted the site through surface flow.

Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in groundwater samples for two of three PFAS screening compounds used for making site management decisions. IRP Site 6 was recommended for further evaluation. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 7 is an open unlined ditch constructed in the southern part of NAS Lemoore in 1960. It carries discharges from numerous Administration Area storm drains and sanitary sewer effluent from the Housing Area sanitary sewage treatment plant. Discharge from the ditch north of the NAS Lemoore Housing Area to the Kings River began in 1964.

The sanitary sewage system reportedly received some industrial wastes. About 100 gallons per year of lead-containing battery shop waste and 1,000 gallons per year of other chemicals such as solvents, paints, and thinners were disposed of by discharge to the sanitary sewer system. The sanitary sewage treatment plant was replaced in 1974, and the effluent discharge was diverted to evaporation ponds. Effluent from the storm drain system was also discharged directly to the Housing Area open ditch without treatment until 1974. Currently, discharges to the ditch are covered under a general industrial activity discharge permit. The only discharges are to avoid flooding from stormwater during extremely high flow.

The 1984 initial assessment study for IRP Site 7 recommended a confirmation study because some contamination may have been bound in sediments in the ditch, the ditch discharges to the river, and the ditch passes through the river’s floodplain.

Remedial investigation activities initiated in 1991 included extensive soil, sediment, groundwater, and surface water sampling. Based on the analytical results, human health risk assessments included in the 1998 report found that IRP Site 7 does not pose an unacceptable risk to human health. The ecological risk assessment found that the permanent habitat at the site is inadequate to support aquatic life, posing minimal ecological concern.

The Navy completed a record of decision in 2002, selecting no further action as the remedy at IRP Site 7. The Department of Toxic Substances Control Central Valley and Central Valley Regional Water Quality Control Board concurred by record of decision signature, and the site was closed with no further action in 2003.

From 1964 until approximately 1974, the trickling filter sanitary sewage treatment plant serving the Housing and Administration Area in the southern part of NAS Lemoore discharged sludge through a cast-iron pipeline to two unlined drying beds directly east of the treatment plant. Each pond was slightly less than 2 acres in size and approximately 4.5 feet deep.

The treatment plant may have received discharges of battery shop waste and solvents, paints, and thinners from the sanitary sewer. The sludge drying beds were cleaned out periodically and the dried sludge was taken to a permitted landfill. In 1974, the treatment plant was replaced with a new system and subsequently the drying beds were filled with clean soil. The area is now largely covered by concrete and asphalt.

A 1984 initial assessment study conducted at IRP Site 8 determined that no confirmation study was required because the sludge drying beds were periodically cleaned out and no accumulation over time of hazardous waste components was thought to have occurred.

Although not recommended in 1984 for additional confirmation study, remedial investigation activities were initiated at IRP Site 8 in 1991 that included soil and groundwater sampling. Based on the analytical results, the human health risk assessment included in the 1998 report found no unacceptable risk to human health for occupational and construction workers. However, residential use restrictions were required because of the risk posed by contact with and inhalation of chromium in soil, and ingestion of chromium in groundwater. An ecological risk assessment also completed in 1998 concluded that the permanent habitat at IRP Site 8 is inadequate to support aquatic life, posing minimal ecological concern.

A land use control remedial design was finalized in 2012 to provide long-term protectiveness of human health and the environment by restricting land use to industrial only. Annual physical inspections of the site are required to confirm continued compliance with all institutional control objectives and land use restrictions.

In addition, five-year reviews of remedy performance and protectiveness are performed at IRP Site 8 in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act process. The most recent review was conducted in 2017 and found the institutional control remedy at IRP Site 8 to be protective of human health and the environment.

IRP Site 9, the Sludge Drying Ponds, includes two unlined industrial waste treatment sludge ponds directly south of the Industrial Wastewater Treatment Facility (IWTF) in the south Operations Area, which is in the northern part of NAS Lemoore. Each pond is approximately 125 feet by 85 feet. Sludge was deposited in these two unlined ponds from 1961 to 1987. The west pond was closed in 1983 by excavating sludge and approximately 5 feet of soil. Discharges continued after 1984 at the east sludge drying pond only.

All discharge from the IWTF is regulated by the Central Valley Regional Water Quality Control Board, including discharge to the ponds. In 1985, a report on the investigation and preliminary engineering study on the IWTF was prepared in response to the lowering of the waste discharge standards. The report concluded the effluent from the IWTF frequently exceeded existing maximum allowable discharge limits for lead, pH, electrical conductivity and total suspended matter. The report recommended improvements to the facility and waste disposal practices.

In 1986, the Installation received a Cease and Desist Order (Order No. 86-174) from the Central Valley Regional Water Quality Control Board. The installation was ordered to stop sludge waste disposal to unlined ponds and conduct further assessment. The Regional Water Board determined the sludge to be a Class 1 waste because of high concentrations of heavy metals and the potential for contaminants to migrate through the soils to groundwater.

The east sludge drying pond underwent closure in 1987. Closure activities included excavation and disposal of 3,267 cubic yards of material, which was replaced by clean fill. Results of soil testing during excavation indicated that the primary components of the waste discharged were heavy metals and several organic compounds.

Analytical results for groundwater samples from IRP Sites 5 and 9 monitoring wells collected during 1992 and 1993 remedial investigations indicated that five volatile organic compounds (VOC) and the metals chromium and selenium were present above regulatory limits. The VOC plume in groundwater was found to extend east beneath IRP Site 5 from IRP Site 9, approximately 600 feet to the southwest. The former sludge drying ponds are the likely source of the VOCs dissolved in the groundwater at IRP Site 5 and all future investigations of groundwater were investigated under IRP Site 5.

Further investigation was recommended for IRP Site 9 in the 2020 per- and polyfluoroalkyl substances (PFAS) preliminary assessment report for soil and groundwater because the sludge drying ponds had received waste from the IWTF, which reportedly had received substances that may have contained PFAS from electroplating wastes or aqueous film-forming foam, a PFAS-containing material known as “AFFF.”

Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in groundwater samples for two of three PFAS screening compounds used for making site management decisions. PFAS compounds were not detected in subsurface soil samples collected down to 19 feet below ground surface, likely because of the soil removal actions in 1983 and 1987. IRP Site 9 was recommended for further evaluation. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 10 is approximately one mile north of the installation main gate in the Administration Area in the southern part of NAS Lemoore. The landing strip was reportedly oriented in an east-west direction on the northern side of a row of trees. According to a 1984 initial assessment study that included IRP Site 10, the landing strip was used by a private contractor from the mid-1960s until 1978. The site was considered a potential source of pesticide contamination resulting from spills or rinsing of pesticide application equipment, although these operations could not be confirmed through personal interviews. A dirt road used by farmers currently exists where the landing strip was reportedly located.

Soil analytical data collected from 1994 through 1997 during remedial investigation activities indicated that environmental contamination was present at low levels. Only 4,4'-DDE, a breakdown product of the insecticide DDT, was detected in samples collected from the upper 4 feet of soil within and adjacent to IR Site 10. Only the two pesticides/herbicides bromacil and diuron were present in groundwater samples collected from the site. Because IRP Site 10 is in an exclusively agricultural area, the detection of low levels of these compounds may be the result of long-term pesticide and herbicide usage for agricultural purposes and may not be directly related to former pesticide application landing strip activities.

The 1997 remedial investigation report human health risk assessment found no unacceptable risk to human health. An ecological risk assessment completed in 1998 concluded that the highly disturbed, poor-quality habitat at IRP Site 10 would not support wildlife, posing minimal ecological concern.

The Navy completed a record of decision in 1998, selecting no further action as the remedy at IRP Site 10. The Department of Toxic Substances Control Central Valley and Central Valley Regional Water Quality Control Board concurred by record of decision signature, and the site was closed with no further action.

IRP Site 11, the site of the transformer oil spill at Building 3, is on the northwestern side of the intersection of Skytrain Avenue and K Street in the Operations Area in the northern part of NAS Lemoore. Building 3 housed an electrical transformer. Sometime around 1968, about 1,000 gallons of dielectric waste oil material was drained from a transformer being serviced or replaced. The waste oil was spread on the ground surrounding Building 3.

The 1984 initial assessment study recommended a confirmation study to determine if polychlorinated biphenyls, common in transformers on the installation at the time, had contaminated soil in sufficient quantities to require remedial action. When transformers were removed from Building 3 in 1994, maintenance records were located and routine maintenance did not include draining transformer oil, making it unlikely that oil was spread on the ground outside the building at that point in time.

Remedial investigation activities initiated in 1991 included soil sampling to a depth of 6 feet. Based on the analytical results, the human health risk assessment, included in the 1996 report, found no unacceptable risk to human health. An ecological risk assessment completed in 1998 concluded that the highly disturbed, poor-quality habitat at IRP Site 11 would not support wildlife, posing minimal ecological concern.

The Navy completed a record of decision in 1997, selecting no further action as the remedy at IRP Site 11. The Department of Toxic Substances Control Central Valley and Central Valley Regional Water Quality Control Board concurred by record of decision signature, and the site was closed with no further action.

IRP Site 12, the site of the transformer oil spill at Building 468, is at the southern end of runway 32-L in the Operations Area in the northern part of NAS Lemoore. Building 468 housed electrical transformers. Sometime around 1968, about 2,220 gallons of dielectric waste oil material was drained from transformers being serviced or replaced. The waste oils were spread on the ground on the north side of Building 468, covering an area approximately 30 feet by 40 feet.

A 1984 initial assessment study recommended a confirmation study to determine if polychlorinated biphenyls, common in transformers on the installation at the time, had contaminated soil in sufficient quantities to require remedial action. When transformers were removed from Building 468 in 1994, maintenance records were located. Routine transformer maintenance did not include draining transformer oil, making it unlikely that oil was spread on the ground outside the building.

Remedial investigation activities initiated in 1991 included soil sampling to a depth of 8 feet. Based on the analytical results, the human health risk assessment, included in the 1996 report, found no unacceptable risk to human health. An ecological risk assessment completed in 1998 concluded that the highly disturbed, poor-quality habitat at IRP Site 12 would not support wildlife, posing minimal ecological concern.

The Navy completed a record of decision in 1997, selecting no further action as the remedy at IRP Site 12. The Department of Toxic Substances Control Central Valley and Central Valley Regional Water Quality Control Board concurred by record of decision signature, and the site was closed with no further action.

IRP Site 13 is in the Operations Area in the northern part of the air station. A concrete walled-in area next to Building 50 and the area adjacent to this building were used to store transformers from about 1972 until 1981. Up to 30 transformers at a time were in this area, which is about 50 feet by 50 feet within the concrete walls and 50 by 15 feet on the east side of the building. Some transformers were reportedly drained in the area, but no visible evidence remains.

A 1984 initial assessment study concluded that it was probable that the transformers held dielectric oil which contained polychlorinated biphenyls. The study report recommended a confirmation study to determine if polychlorinated biphenyls had contaminated soil in sufficient quantities to require remedial action.

Remedial investigation activities initiated in 1991 included soil sampling to a depth of 6 feet and groundwater sampling at two locations. Based on the analytical results, the human health risk assessment, included in the 1996 report, found no unacceptable risk to human health. An ecological risk assessment completed in 1998 concluded that the highly disturbed, poor-quality habitat at IRP Site 13 would not support wildlife, posing minimal ecological concern.

The Navy completed a record of decision in 1997, selecting no further action as the remedy at IRP Site 13. The Department of Toxic Substances Control Central Valley and Central Valley Regional Water Quality Control Board concurred by record of decision signature, and the site was closed with no further action.

IRP Site 14 is in the Operations Area in the northern part of NAS Lemoore and is composed of former jet engine test cells (JETC), maintenance buildings, hangars, and aircraft parking areas. A large, chlorinated solvent plume originates from several source areas that may include historical releases; industrial wastewater line (IWL), storm drain, wash rack, and former underground storage tank releases; and surface and aircraft maintenance related releases. The main source areas are identified as the Central/Northwest source area, evaluated as Exposure Area A in the human health risk assessment, and the Southeast source area, evaluated as Exposure Area B in the risk assessment.

Originally, only the small portion of IR Site 14 near the former JETCs was investigated. The findings from the original remedial investigation (RI) resulted in expansion of the boundary of IRP Site 14 to include buildings that are physically located above the chlorinated solvent groundwater plume and that discharge to the IWLs. Building 170 is a jet engine maintenance shop. Underground storage tanks 173A, 173B, 174A, and 174B used to store JP-5 jet fuel were located directly south of the JETCs. Operations at the JETCs ceased in 1998 and the test cells and tanks were removed in 2000.

An RI addendum was finalized for IRP Site 14 in 2017. Since then, additional post-RI sampling has occurred. Indoor air and subslab samples were obtained to refine potential vapor intrusion risks for the current industrial worker in several buildings at the site. Groundwater sampling was implemented in 2018 and 2019 to provide current groundwater data for evaluation of remedial alternatives.

In 2015, the Navy designated a portion of IRP Site 14 as IRP Site 18 for management purposes. Previous investigations and historical incidents of industrial wastewater overflows at IRP Site 18 suggest that the Southeast source area south of Building 170 is a potential separate source of volatile organic compounds in underlying shallow groundwater. IRP Site 14 is defined as the Central/Northwest source area of the diffuse, chlorinated solvent plume that lies beneath both IRP Sites 14 and 18. Although some overlap of data analysis and assumed plume interaction will occur, these areas will be addressed separately under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). IRP Site 14 is currently in the feasibility study phase of the CERCLA process.

Further investigation was recommended for IRP Site 14 in the 2020 basewide per- and polyfluoroalkyl substances (PFAS) preliminary assessment report because of the fire suppression system within the maintenance hangar that contained aqueous film-forming foam, a PFAS-containing material known as “AFFF.”

Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in groundwater samples for one of three PFAS screening compounds used for making site management decisions. IRP Site 14 was recommended for further evaluation.

The 2020 PFAS preliminary assessment report also identified the NAS Lemoore Operations Area Fire Station 62 in Building 190, just north of IRP Site 14, as the location of a suspected source area for PFAS releases to the environment. AFFF is known to be stored at the operational fire station building and in fire department vehicles. In addition, fire department vehicles were reportedly washed at the site, and PFAS may have been released from spills or leaks from the vehicles.

Results in the 2022 basewide PFAS site inspection report for Operations Area Fire Station 62 showed concentrations in surface soil samples exceeding project screening levels for two of three PFAS screening compounds. Detected concentrations of two of three PFAS screening compounds in groundwater samples from a temporary well also exceeded project screening levels.

For report tracking purposes, areas of interest (AOI) for PFAS, that were not already existing IRP sites, were labeled as AOIs. Operations Area Fire Station 62 was identified as AOI #14 in the PFAS preliminary assessment report and 2022 site inspection report. Because of its proximity and local groundwater flow direction, AOI #14 was added to IRP Site 14 for further evaluation as part of a PFAS remedial investigation. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 15, the Franklin Avenue pesticide rinse area, is south of Franklin Avenue and west of Enterprise Avenue in the Administration Area in the southern part of NAS Lemoore. Pesticide containers and applicators were rinsed in the vicinity of Building 765, although specific information pertaining to the rinsing operation is not available. Past handling practices of pesticides at the Franklin Avenue pesticide rinse area were probably similar to IRP Sites 2 and 3, where pesticide containers and equipment were rinsed onto paved and unpaved ground.

This site was first investigated during the 1986 verification phase/confirmation study that followed the 1984 initial assessment study at NAS Lemoore. Surface soil samples collected and analyzed for pesticides and dioxins did not find substantial contamination at the site. A 1991 remedial investigation initiated to determine the nature and extent of contamination included soil sampling and analysis for metals, pesticides, herbicides, and dioxins. Pesticide compounds and dioxins were detected in 2 of 61 soil samples, but no chemical constituent concentrations were reported to be above current regulatory levels. The distribution of contaminants at IRP Site 15 indicated that the previous pesticide rinse operations did not result in widespread pesticide or dioxin contamination in soil.

The Central Valley Regional Water Quality Control Board recommended additional groundwater sampling prior to consideration of no further action at IRP Site 15. The sampling was conducted in 1994 and there were no detections of any target analytes in groundwater samples.

Risk assessment results in a 1997 remedial investigation report indicated that no unacceptable risk to human health or the environment was present at the site. The 1998 final ecological scoping assessment report stated that because of the poor habitat quality, there is low potential for complete exposure pathways and no further ecological evaluations were recommended.

The Navy’s 1998 record of decision selected no further action as the remedy at IRP Site 15. The Department of Toxic Substances Control and Central Valley Regional Water Quality Control Board concurred by record of decision signature, and the site was closed with no further action.

IRP Site 16 consists of a large sludge drying bed immediately west of the intersection of Skytrain Road and L Street in the Operations Area in the northern part of NAS Lemoore. It is divided into 10 smaller compartments approximately 15 feet by 10 feet each and one large sludge pond approximately 40 feet by 40 feet in size. These drying beds and the pond were historically used to dewater municipal wastewater treatment sludge and are believed to be part of the original sewage treatment facility installed when NAS Lemoore began operations in the early 1960s. A 6-inch cast iron line led from the sewage treatment digesters to the sludge beds. The wet sludge was placed in the bed and pond and allowed to dry. A new sewage treatment system was installed at NAS Lemoore between 1981 and 1982 and the old sewage treatment plant and the sludge drying beds were abandoned.

In 1986, the sludge beds were investigated to determine if contaminants concentrated in the sewage sludge leached into the soil during the dewatering cycle. Soil samples were collected and analyzed for semi-volatile organic compounds, dioxins, and metals. Only metals were detected in the soil samples, but not above levels of concern at the time. The Department of Toxic Substances Control requested additional soil and groundwater sampling.

The 1997 final remedial investigation report for IRP Site 16 found no widespread or significant levels of contamination present in soil, although the volatile organic compound, 1,1-dichloroethane (1,1-DCA) was consistently detected in groundwater. These 1,1-DCA detections were attributed to contamination in a groundwater plume from IRP Site 5, located upgradient from IRP Site 16. Risk assessment results indicated no unacceptable risk to human health for occupational and construction workers. Residential use was prohibited because of risk of ingestion of a solvent and the presence of molybdenum in groundwater. The ecological assessment concluded that the poor habitat at the site could not support wildlife.

A 1997 IRP Site 16 record of decision selected a no action alternative. The Navy subsequently re-evaluated the need to act at IRP Site 16, and a land use control remedial design was finalized in 2012. The remedial design restricted land use to industrial only to provide long-term protectiveness of the remedy. Annual physical inspections of the site are required to confirm continued compliance with all institutional control objectives and land use restrictions. An annual inspection in 2021 verified that land use controls are in place. An October 2022 work plan further outlined the current plans for annual inspection of land use control implementation.

In addition, five-year reviews of remedy performance and protectiveness are performed at IRP Site 16 in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act process. The most recent review was conducted in 2017 and found the land use control and institutional control remedy at IRP Site 16 to be protective of human health and the environment.

IRP Site 17 is a grass-covered area between the east runway and the east taxiway located in the Operations Area in the northern part of the air station. In December 1987, a leak in a 16-inch diameter aluminum pipe carrying JP-5 jet fuel was discovered. The line connected a 119,478-gallon fuel storage tank to a series of refueling islands in the north end of the Operations Area.

The Navy initiated cleanup efforts shortly after the leak was discovered by conducting an excavation to uncover and repair the JP-5 pipeline. Following repair of the line, waste JP-5 fuel was removed from the excavation. The Navy opened a second excavation northeast of the leak site after fuel recovery declined in the initial excavation. Because of the extensive nature of the spill, the site was added to the Environmental Restoration Program for long-term remedial action.

Investigations of soil, soil vapor, and groundwater conducted in 1988 included sampling that indicated soil and groundwater contamination. JP-5 and trace levels of benzene, ethylbenzene, toluene, and xylene were present beneath IRP Site 17. Soil contamination was limited to the capillary fringe and water table interface. The groundwater plume was centered northeast of the original leak site and extended approximately 320 feet to the southwest and 400 feet to the northeast. A demonstration involving a steam injection and vapor extraction system was conducted at IRP Site 17 from June 1994 to October 1994. Product removal activities recovered approximately 218,000 gallons of JP-5 fuel.

Additional investigations were completed in 1996 and 1997 to determine the nature and extent of petroleum related contamination at IRP Site 17. A multi-phase extraction (MPE) system was pilot tested at the site in 1999 and was in full-scale operation for 30 months from 2002 to 2005 removing an additional 28,500 gallons of fuel. A significant reduction in the thickness of the free product plume and the diminishing monthly volume of product extracted from the subsurface resulted in termination of MPE operations 2 months early, and a bioventing test was conducted in early 2005. Full-scale bioventing began in August 2005 and remained in operation through 2007, and intermittently until 2010, resulting in the removal of approximately 1,000 gallons of fuel product. From 2005 to 2010, about 100 additional gallons of product were removed using absorbent socks and periodic manual skimming.

A 2011 corrective action plan included a risk screening based on prior data from soil, soil vapor, and groundwater sampling. The risk screening was used to develop corrective action objectives addressing the presence of apparent petroleum free product and potential vapor intrusion exposure from the migration into indoor air of volatile constituents in the subsurface. Vapor intrusion was found to be an incomplete exposure pathway due to the site location and lack of buildings in the area of concern.

The corrective action plan presented and evaluated three corrective action alternatives. The remedy selected for IRP Site 17 included free product removal, institutional controls, and monitoring to address the petroleum-contaminated soil and groundwater. The selected remedy received concurrence form the Department of Toxic Substances Control and Central Valley Regional Water Quality Control Board in 2011.

The MPE system at IRP Site 17 was activated again for five months in 2011, and an additional 1,500 gallons of product were removed. From 2014 through 2016, six additional free product removal events were conducted. Free product removal by skimming continued until 0.5-inch or less of product was observed in wells or an overall decline of free product was observed after six consecutive sampling events. The Central Valley Regional Water Quality Control Board concurred in 2017 with the Navy’s closure recommendation for groundwater contingent upon the destruction of all on-site monitoring wells and the continued implementation of institutional controls.

A land use control remedial design was finalized in 2019 for long-term monitoring at IRP Site 17. The remedial design included institutional controls in the form of land use restrictions to ensure that no buildings are constructed within the area without a soil gas investigation and vapor intrusion evaluation. Annual physical inspections of the site are required to confirm continued compliance with all institutional control objectives and land use restrictions.

An October 2022 work plan outlined the current plans for annual inspection of land use control implementation. In addition, a review of remedy performance and protectiveness is to be performed at IRP Site 17 every five years in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act process.

IRP Site 18 is in the central portion of the Operations Area in the northern part of the air station. This site was formerly part of IRP Site 14 and was identified for further investigation as a potential separate volatile organic compound (VOC) groundwater contamination source from that of IRP Site 14, potentially from a cracked stormwater catch basin located just south of the southeast corner of Building 170.

Review of the site history for IRP Site 14 as it relates to IRP Site 18 area indicates that spent solvents and rinsates used within flight operation buildings where aircraft maintenance and repair took place were discharged to the industrial wastewater line (IWL). Chemicals may have been released to the subsurface through identified breaks in the IWL. Previous investigations also identified breaks in the IWL at the site as the most likely source of the VOC contamination.

The entire site is paved, and relatively flat. Groundwater flow direction has historically been to the southeast. A preliminary assessment and site inspection were completed in 2018, and a remedial investigation at the site followed in 2022.

Further investigation was recommended for IRP Site 18 in the 2020 per- and polyfluoroalkyl substances (PFAS) preliminary assessment report because a cracked stormwater catch basin at the site, believed to be a distinct source of VOC groundwater contamination from that at IRP Site 14, could also represent a source for PFAS-containing materials entering subsurface soil and migrating into groundwater. IRP Site 18 has a similar history of groundwater contamination to that of IRP Site 14. PFAS releases may also be from other sources, such as the wash rack located near Building 188 and cracks in the stormwater drain lines in the vicinity of Building 170.

Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in a groundwater sample for one of three PFAS screening compounds used for making site management decisions. IRP Site 18 was recommended for further evaluation. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

A 2020 basewide per- and polyfluoroalkyl substances (PFAS) preliminary assessment (PA) report provided documentation of research that assessed whether PFAS have been or are suspected to have been released to the environment at NAS Lemoore. For tracking purposes, areas of interest that were not already existing IRP sites were labeled as areas of interest (AOI) in the PA report. The report identified the following AOIs for additional PFAS investigation.

• AOI #7, the March 6, 1969, Plane Crash, is located off the west side of Runway 32-R approximately 1,100 to 1,400 feet from the approach end. The Aviation Safety Network records list a March 6, 1969, Lockheed P-3B Orion aircraft crash that occurred on base. The crash report states that upon impact at the runway approach, the fuselage came to rest to the left side of Runway 32-R approximately 1,100 feet from the approach end, and the port wing separated and continued approximately 300 feet beyond the fuselage. Both the fuselage and separated port wing were engulfed in flames.

• AOI #9, Hangar 1, contains a fire-suppression system that uses aqueous film-forming foam (AFFF). The system includes an interior 1,200-gallon AFFF aboveground storage tank (AST) with associated piping. Building 210 is connected to the Operations Area industrial wastewater line (IWL) system. There are no known discharges or leaks of AFFF within or near Hangar 1.

• AOI #10, Hangar 2, contains five sets of independent AFFF fire suppression systems, each supplied from two ASTs with an associated AFFF monitor. Building 240 is connected to the Operations Area IWL system. Based on an interview, in the early 2000s AFFF leaked at Hangar 2 and overflowed into the IWL. Due to low release volume, the interviewee believed there was no discharge to the environment from the conveyance. In addition, during the December 2018 PA site visit, an area of staining leading to a floor drain was observed beneath one of two aboveground AFFF storage tanks within Hangar 2.

• AOI #11, Hangar 3, contains five sets of independent AFFF fire suppression systems, each supplied from two ASTs with an associated AFFF monitor. Building 270 is connected to the Operations Area IWL system. According to the interview with the Fire Inspector, a small leak or release occurred within Hangar 3 on October 5, 2018.

• AOI #12, Hangar 4, contains five sets of independent AFFF fire suppression systems, each supplied from two ASTs with an associated AFFF monitor. Building 300 is connected to the Operations Area IWL system. There are no known discharges or leaks of AFFF within or in close proximity to Hangar 4.

• AOI #13, Hangar 5, contains an AFFF fire-suppression system. The configuration of the system requires further confirmation. Building 330 is connected to the Operations Area IWL system. Other than a small leak from an AFFF storage tank that was easily contained and cleaned up, no discharges or leaks of AFFF within or near Hangar 5 are known to have occurred.

Results in the subsequent 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in groundwater samples for two of three PFAS screening compounds used for making site management decisions. As a group, these AOIs were recommended for further evaluation. As the Comprehensive Environmental Response, Cleanup and Liability Act process is implemented, they will collectively be identified as IRP Site 19. This grouping was based on proximity, groundwater flow direction, and potential PFAS source. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

A 2020 basewide per- and polyfluoroalkyl substances (PFAS) preliminary assessment report provided documentation of research that assessed whether PFAS have been or are suspected to have been released to the environment at NAS Lemoore. For report tracking purposes, areas of interest (AOI) for PFAS, that were not already existing IRP sites, were labeled as AOIs. The NAS Lemoore Administration Area Fire Station 61 is in the southern part of NAS Lemoore and is identified as AOI #15 in the PFAS preliminary assessment report and 2022 site inspection report.

According to an interview with the Fire Chief and research confirming the information, aqueous film-forming foam, a PFAS-containing material known as “AFFF,” is stored at Fire Station 61. In addition, fire engines at Fire Station 61 carry standard quantities of AFFF. No known releases of AFFF are documented at Fire Station 61, and no records are available documenting on-site equipment testing. Vehicles are washed at the fire station, and the Fire Chief stated that equipment testing did take place at Fire Station 61 and another fire station, likely at wash pads located adjacent to each station.

Results in the 2022 basewide PFAS site inspection report showed concentrations exceeding project screening levels in soil samples for one of three PFAS screening compounds used for making site management decisions. Two of three PFAS screening compounds were detected at concentrations exceeding project screening levels for groundwater in samples from a temporary well. AOI #15 was recommended for further evaluation.

As the Comprehensive Environmental Response, Cleanup and Liability Act process is implemented, this AOI will be identified as IRP Site 20. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

A 2020 basewide per- and polyfluoroalkyl substances (PFAS) preliminary assessment report provided documentation of research that assessed whether PFAS have been or are suspected to have been released to the environment at NAS Lemoore. For report tracking purposes, areas of interest (AOI) for PFAS, that were not already existing IRP sites, were labeled as AOIs. The South Evaporation Pond System, identified as AOI #16 in PFAS preliminary assessment and site inspection reports, is located on 430 acres of NAS Lemoore property approximately one-half mile south of the main air station southern boundary.

The South Evaporation Pond System consists of two stabilization ponds and three evaporation ponds. The evaporation pond system was constructed in 1974 when the Administration Area wastewater treatment plant was replaced with the current Operations Area Industrial Wastewater Treatment Plant (IWTP) to comply with a Central Valley Regional Water Quality Control Board cease and desist order to terminate discharge to the Kings River. Since 1984, treated waste effluent from the IWTP has been pumped through a 6-mile-long pipeline and discharged to the south evaporation pond system.

Discharge of substances potentially containing PFAS within Hangars 1 through 5 may drain to the IWTP through industrial wastewater line piping and subsequently to AOI #16. Fifteen-foot-high berms were constructed to contain wastewater effluent within the ponds. The remainder of the site is actively used for stabilization and evaporation pond activities. Surface soil within areas of the exposed pond bottoms consists of residual effluent solids that have settled out from the wastewater column.

Results in the 2022 basewide PFAS site inspection report showed concentrations below project screening levels in surface and subsurface soil samples for all three PFAS screening compounds used for making site management decisions. Soil samples were collected and evaluated to qualitatively assess PFAS in the effluent solids but were not necessarily intended to evaluate a potential PFAS release to soil. Two of three PFAS screening compounds were detected at concentrations exceeding project screening levels for groundwater in samples.

As the Comprehensive Environmental Response, Cleanup and Liability Act (CERCLA) process is implemented, this AOI will be identified as IRP Site 21. Although a recommendation for further evaluation was made in the basewide PFAS site inspection report because of exceedances of PFAS screening levels in groundwater samples, the site will not move forward to the remedial investigation phase of the CERCLA process at this point in time. The ponds at IRP Site 21 are still in operation and could potentially be receiving PFAS in effluent from the Industrial Wastewater Treatment Plant. Therefore, the site will remain in an “on hold” status until operations cease, at which time it will be reevaluated under CERCLA. More details on NAS Lemoore PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

Underground Storage Tank (UST) Site 01 is at the northwestern corner of Building 188, the Airframes Shop, which is an aircraft maintenance shop in the south-central portion of the Operations Area in the northern part of NAS Lemoore. UST 188-1 was installed in 1983 and removed from service in 1988. The tank itself was removed in 1994 and is considered closed under the Resource Conservation and Recovery Act Program closure plan approved by the Department of Toxic Substances Control (DTSC) in 1994.

The DTSC concurred in 2000 with the Navy’s request that contamination associated with UST Site 01 be addressed with IRP Site 14. Subsequent investigations are discussed in the IRP Site 14 site description.

Underground storage tank (UST) 188-2 was a 1,000-gallon-capacity fiberglass tank that was used in the plating shop of the Public Works Department for storage of generated plating wastes. UST 188-2 was within the boundary of IRP Site 14.

When UST 188-2 and the associated piping were removed, two soil samples were collected from below the UST and five soil samples were collected from below the area of associated piping. These soil samples were analyzed for heavy metals, cyanide, halogenated solvents, total petroleum hydrocarbons, and acidity. Analyses indicated that all samples contained concentrations either undetectable or below background.

A letter of acceptance of the removal action summary report and a signed final closure certification for UST Site 02 - UST 188-2 were received from the Department of Toxic Substances Control in 1996.

The former Naval Exchange Administrative Gas Station, located at the corner of Hancock Avenue and Hancock Circle in the Administration area in the southern part of the air station, was built in 1962 and contained four underground storage tanks (USTs) and one underground waste oil tank. Operations began in 1962 and continued until the gas station was closed in 2019.

A gasoline release of approximately 2,800 gallons from four USTs and associated piping was discovered in 1988. Free product was observed during a 1988 excavation and initial investigation. A 1994 remedial investigation and feasibility study further defined the areal extent of a dissolved fuel plume and was followed in 1995 by removal of existing USTs and installation of new USTs at the site.

Hydrocarbon-contaminated soil was excavated in 2006 from an area south of the fuel-dispensing islands. From 2000 through 2007, groundwater samples were collected quarterly from monitoring wells. A 2008 site characterization and analysis penetrometer system further delineated the extent of contamination at the gas station site. A 2010 groundwater monitoring report recommended additional remediation strategies for the free product and shallow benzene and unleaded gasoline additive methyl tert-butyl ether plumes at the site.

A site survey and inspection of the monitoring well network and several monitoring events were completed in 2018 and 2019. Tanks and fuel dispensing components were removed in 2020. Confirmation samples were collected from beneath the recent USTs and along the product lines, and no leaks from the recent USTs and associated piping were detected.

The 2020 site characterization report recommended excavation of soil as the corrective action for source area petroleum impacts with continued measurable levels of free product. Existing perimeter monitoring wells would be retained and sampled quarterly to monitor possible migration of the dissolved groundwater plume and to monitor natural attenuation. The Central Valley Regional Water Quality Control Board concurred with these recommendations, including excavation and monitored natural attenuation, with the addition of soil vapor and indoor air sampling.

A thorough review by Navy specialists from 2020 to 2021 recommended that the soil vapor and indoor air sampling results should be used to evaluate the overall threat, to determine if all or partial excavation would be cost effective, and to determine whether pursuit of low threat closure may be a more sensible and cost-effective approach. In March 2023, the Water Board conditionally concurred with the Navy's draft work plan to conduct sub-slab and indoor air sampling as part of remedial activities at the site. The corrective action plan for UST Site 03 will outline the path forward and will be completed following soil vapor and indoor air sampling.

Underground Storage Tank (UST) Site 765 is approximately 100 feet west of Building 765 in south NAS Fallon and is the site of a former service station constructed in 1962 that was active until 1988. The facility provided fuel for public works construction activities and included a fueling area and two 10,000-gallon steel USTs. The two USTs were removed in 1988 and the excavations backfilled after leaks were detected in tank-top bungholes and old vacuum fuel feed lines.

Groundwater monitoring wells were installed at the site from 1989 through 1995 in support of soil and groundwater investigations. Routine groundwater monitoring was conducted from 1999 through 2009. The Navy’s 2009 request for site closure was denied by the Central Valley Regional Water Quality Control Board because of benzene levels consistently above site-specific cleanup goals in one monitoring well and possible indoor air quality issues related to the proximity of Building 765.

The Navy performed four quarters of groundwater monitoring beginning in September 2010, repeating the fourth monitoring event because of a laboratory error related to sample handling. Results from the monitoring program reported petroleum hydrocarbons detections in only one well, the same monitoring well as before, with all concentrations including benzene below site-specific cleanup goals and maximum contaminant level drinking water standards.

In 2012, the Central Valley Regional Water Quality Control Board concurred with the Navy’s recommendation for no further action required status at UST Site 765, following documented destruction of all monitoring wells.

Underground Storage Tank (UST) Site 773 is the location of a jet fuel spill near Building 773 in south NAS Lemoore.

As of 2009, the Navy had compiled eight years of groundwater elevation data and analytical data for petroleum hydrocarbons and the volatile organic compounds benzene, toluene, ethylbenzene, and xylene in groundwater at UST 773. The results from 2009 samples showed low concentrations of petroleum hydrocarbons in monitoring wells and no detections of volatile organic compounds, including benzene. A risk assessment performed for the site using this data found that groundwater does not pose a risk to human health or the environment.

In 2013, the Central Valley Regional Water Quality Control Board concurred with the Navy’s recommendation for no further action required at UST Site 773, following documented destruction of all monitoring wells.

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