Naval Air Station Fallon

IRP Site 1 is in the southern portion of NAS Fallon. The site was used from the mid-1950s until 1988 for fire training and consisted of a former unlined earth-bermed pit and two aboveground storage tanks. Napalm, off-specification fuel, oil, and solvents were stored in the tanks before being poured into the pit and ignited to conduct the training. An estimated 1.1 million gallons of flammable liquid were released during training.

Contamination and exposure risks were evaluated in a 1988 remedial investigation. The Nevada Division of Environmental Protection requested that the Navy discontinue fire training exercises and the tanks and underground piping were removed. Contaminated soil associated with the burn pit was excavated in 1994. Approximately 900 gallons of free product were removed in 1996, and biodegradation remediation was implemented.

Pilot studies were conducted at IRP Site 14 in 2002 and 2003 to evaluate technologies for treating groundwater contaminated with volatile organic compounds. Several technologies were found to be effective technology for reducing the concentrations of volatile organic compounds in groundwater including in situ air sparging and soil vapor extraction, as reported in the 2004 groundwater pilot studies report.

Historical data and data from a 2007 site characterization and delineation of petroleum hydrocarbons in groundwater and soils were used to design a remedial investigation. The results were reported in a 2012 remedial investigation addendum and feasibility study that determined the nature and extent of contamination and evaluated remedial alternatives for site cleanup.

Remedial action for IRP Site 1 was outlined in the 2015 record of decision for the Southern Operable Unit, which includes IR Sites 1, 14, and 16, including excavation of fuel-impacted soil, free-product skimming, and long-term groundwater monitoring. Institutional controls were implemented to limit exposure to volatile organic compound-impacted groundwater. A 2019 five-year review reported that the remedy was functioning largely as intended. Volatile organic compounds above remediation goals were detected in groundwater in 2020, and continuation of planned monitoring was recommended.

Further investigation was recommended at IRP Site 1 for per- and polyfluoroalkyl substances (PFAS) in the 2019 basewide PFAS preliminary assessment report because aqueous film-forming foam, a PFAS-containing material known as “AFFF,” was potentially used to control fires ignited for training purposes.

Sampling results from the subsequent 2021 basewide PFAS site inspection showed concentrations exceeding project screening levels for all three PFAS screening compounds used for making site management decisions. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 2 is in the northwestern part of NAS Fallon and encompasses approximately 23 acres. The New Fuel Farm site stores jet fuel, diesel fuel, and motor vehicle gasoline fuel, and has served as the main fuel storage and distribution terminal since 1957. The site is the former location of various potential contaminant source areas including five underground storage tanks, a tank bottom disposal area and drainage swale, an oil/water separator and leach field, a bioslurp array, a truck washdown area and loading rack area, a fuel transfer area, and a weed control area.

A site inspection was conducted in 1988 and further investigation was recommended. Historical records indicate that up to 85,000 gallons of fuel or fuel and water mixture were released from the various source areas at the site. The Navy has removed approximately 78,700 gallons of fuel from the early 1990s through 2021. The remedial activities included underground storage tank removals and release containment and cleanup.

The remedial action at IRP Site 2 in the final 2016 record of decision for the Northern Operable Unit (NOU), which includes IR Sites 2, 3, and 4, consists of fluid level gauging in monitoring wells, recovery of fuel, and long-term monitoring with land use controls. A 2023 interim remedial action completion report documents completion of remedy construction and remedy operation., as well as the specific milestones for achieving site closeout. Free product recovery continues biweekly as needed.

An additional area known as the Hot Pit #3 is also included in the remedial action. The Hot Pits refueling area is east of NOU Sites 2 and 4, on the opposite side of the aircraft taxiway on the northeastern end of NAS Fallon. It contains nine direct or “hot” fueling areas used to train air crews on direct fueling of military aircraft. A 2014 to 2017 expanded site investigation (ESI) concluded that free product encountered in three monitoring wells at Hot Pit #3 originated from the NOU 2 Fuel Farm and that any monitoring of free product or corrective action at the site should be included in the remedial actions at NOU Site 2.

Further investigation was recommended at IRP Site 2 for per- and polyfluoroalkyl substances (PFAS) in the 2019 basewide PFAS preliminary assessment report because aqueous film-forming foam, a PFAS-containing material known as “AFFF,” was stored in a former 500-gallon aboveground storage tanks until 2014, when it was replaced by a new fire suppression system.

Results from the subsequent 2021 basewide PFAS site inspection showed concentrations exceeding project screening levels in shallow soil samples for two of three PFAS screening compounds used for making site management decisions. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 3 is composed of several small sites on 26 acres in the vicinity of Hangar 1, including two primary unpaved former source areas north and south of Hangar 1. The northern source area contains the northern aircraft fuel disposal area, the bowser disposal area, and an oil/water separator. The southern source area contains the southern aircraft fuel disposal area, the ground support equipment area, and the Wells Air Start building, currently known as the Wells Air Facility. Fluids released included jet fuel, hydraulic fluid, lube oil, organic solvents, and cleaning solvents. An estimated 25,600 gallons of waste aircraft fluid were released to unpaved surfaces at the various areas.

Soil sampling results from 1991 indicated the presence of low-level volatile organic compounds and petroleum hydrocarbon contamination. A bioslurper system installed in 1993 removed approximately 16,200 gallons of free product between 1993 and 2001. Approximately 130 cubic yards of soil were removed from an area of stained soil discovered by the Navy in 2006 during trench excavation and three groundwater monitoring wells were installed.

Chlorinated solvents were detected in groundwater at concentrations exceeding screening levels in 2014. Recent monitoring data indicates that a dissolved-phase groundwater plume at the site has decreased in size and concentration since the early 2000s.

The selected remedy for IRP Site 3 in the final 2016 record of decision for the Northern Operable Unit, which includes IR Sites 2, 3, and 4, included long-term groundwater monitoring and implementation of temporary land use controls. A report documenting the progress of remedial action implementation was submitted for review in 2021. Semi-annual groundwater sampling events continue.

Further investigation was recommended at IRP Site 3 for per- and polyfluoroalkyl substances (PFAS) in the 2019 basewide PFAS preliminary assessment report because aqueous film-forming foam, a PFAS-containing material known as “AFFF,” may have been stored and handled in large quantities and may have been used to control maintenance fires in a hangar at the site.

Results from the subsequent 2021 basewide PFAS site inspection showed concentrations exceeding project screening levels in groundwater samples for two of three PFAS screening compounds used for making site management decisions. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 4 consists of 7 acres and was used from 1976 to 1981 for vehicle maintenance, storage, painting, and light overhaul operations. An estimated 50 gallons of waste, including radiator fluid, were flushed into the drains in Building 378. Approximately 400 gallons of waste fluids may have spilled in the adjacent yard during vehicle repair from 1976 to 1981.

A 1988 site inspection conducted found that contamination in soil and groundwater was from disposal of waste liquids to a floor drain that exited Building 378; spills and releases of fuel and oils to unpaved ground surfaces during vehicle maintenance; and releases of fuel from transfer piping associated with a former aboveground storage tank.

In 2005 the Navy removed 280 cubic yards of total petroleum hydrocarbons-contaminated soil and associated piping between Building 333 and the location of a former aboveground storage tank. A final closure report submitted by the Navy concluded that no further action was necessary for soil.

A 2007 investigation delineated the extent of free product at the site. Soil, groundwater, and soil gas data were collected for an updated risk assessment and to identify a strategy for cleanup and site closure. Removal activities and product monitoring conducted from 2008 to 2013 indicated that product levels continued to decline, and that the amount of acreage impacted by free product contamination had been reduced by 89 percent since the 1990s.

The selected remedy for IRP Site 4 in the final 2016 record of decision for the Northern Operable Unit, which includes IR Sites 2, 3, and 4, includes fluid level gauging in monitoring wells, recovery of fuel, and long-term monitoring with land use controls.

Further investigation was recommended at IRP Site 4 for per- and polyfluoroalkyl substances (PFAS) in the 2019 basewide PFAS preliminary assessment report because liquids containing aqueous film-forming foam, a PFAS-containing material known as “AFFF,” may have been released to a building drain and outdoor vehicle maintenance yard.

Results from the subsequent 2021 basewide PFAS site inspection showed concentrations exceeding project screening levels in groundwater samples for the three PFAS screening compounds used for making site management decisions. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 5 consists of two adjacent metals and solid waste disposal areas on 8.5 acres in the northern portion of NAS Fallon. During a 1986 excavation for a utility line in the northern disposal area, abundant metal debris and several decayed 20-millimeter (mm) ammunition shells were found that were believed to have been buried in the 1950s. The material was excavated and removed to the base landfill, and the shells were disposed of offsite by explosive ordnance detachment personnel. The southern disposal area was used in the 1950s and 1960s for inert packing material disposal by burial of pallets, metal boxes, strapping, ammunition cans, and cardboard.

Hazardous material was not found at IRP Site 5 during the 1988 site inspection. The site was closed with state agency concurrence in 2001, although unexploded ordnance and land use control restrictions were implemented because limited quantities of 20-mm shells remained buried at the site. Land use controls include an 8-foot fence with barbed wire around the perimeter of the active ordnance area. Institutional controls restrict unauthorized access, development, or residential use of the site and unauthorized soil disturbance, excavation, or removal.

IRP Site 6 is near the eastern boundary of NAS Fallon, midway between the northern and southern boundaries, and is 11.5 acres in size. Two unlined pits were reportedly located at the site in two regions of relatively level, unpaved surface soils. The pits were estimated to have comprised a 500-foot by 500-foot area and were used from 1966 through 1972 for disposal of off-specification fuel. An estimated 70,000 gallons of primarily jet fuel were released at the site and allowed to infiltrate native soil.

A site inspection was conducted in 1988, followed by the initial remedial investigation in the early 1990s that identified a small area of free product in the form of fuel in the central portion of the disposal area. Additional investigations were conducted, and several monitoring wells were installed.

A 2007 soil gas survey in the northern portion of the site reported no significant soil gas detections, leading to a finding, with state concurrence, that disposal only occurred in the southern disposal area.

A 2012 study reported that concentrations of chemicals in soil did not exceed soil action levels and concentrations of chemicals in groundwater did not consistently exceed groundwater action levels. A human health remedial investigation risk assessment was reviewed as part of a 2013 corrective action plan. Based on review findings and because the site is within a secured military facility lacking receptors, the Nevada Division of Environmental Protection determined that no further assessment or remediation is required to be protective of human health and the environment. A no further action determination for IRP Site 6 is documented in a 2014 letter from the Nevada Division of Environmental Protection to the Navy.

IRP Site 7 is in the eastern-central portion of NAS Fallon and occupies 2.3 acres. The suspected source of contamination was napalm, a mixture of gelling agent and petroleum fuel, but no evidence was found supporting its presence. The 1988 site inspection team could not locate the site and the NAS Fallon Fire Chief testified in 1991 that napalm was not burned there and was instead burned at Site 1.

A 1994 remedial investigation recommended no action at the site because no evidence exists to support the presence of napalm. A record of decision signed by the Navy and the Nevada Division of Environmental Protection closed IRP Site 7 with no further action necessary to protect human health and the environment in 2002.

IRP Site 8 occupies 0.5 acres and is in east-central NAS Fallon. It was used from the 1940s to the 1960s for sighting in aircraft-mounted machine guns. The soil berm backstop, or Gunbutt, was removed in 1987 because of grading for a new runway. Because of the previous use of the site, the chemical of potential concern was lead. The grading of the site makes it unlikely that substantial amounts of lead remain because the soils in the area were likely removed and redistributed along the course of the runway.

A site Inspection was conducted in 1988 and again in 2001. A 2001 Nevada Division of Environmental Protection letter to the Navy states that no further remedial action is required at IRP Site 8 and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 9 occupies 21.5 acres in southeastern NAS Fallon and is the central treatment facility at the base, receiving wastes via the sanitary sewer. Wastewater treatment operations occurred from 1943 to the present. The plant consists of treatment basins, settling ponds, and sludge and grit disposal areas. Potential contaminants of concern include hazardous materials removed from the sanitary discharge as grit, tank sludge, and contaminants in treated effluent.

A 1988 site inspection found no contaminants at concentrations that would require remediation. Based on the results of the inspection and a 2003 soil and groundwater investigation, the Navy prepared a proposed plan and draft decision document recommending no further action at IRP Site 9. The Nevada Division of Environmental Protection concurred with the Navy’s recommendation in a 2003 letter and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

Further investigation was recommended at IRP Site 9 for per- and polyfluoroalkyl substances (PFAS) in the 2019 basewide PFAS preliminary assessment report because of a known release of wastewater containing aqueous film-forming foam, a PFAS-containing material known as “AFFF,” into sanitary sewers that enter the Wastewater Treatment Plant.

Results from the subsequent 2021 basewide PFAS site inspection showed concentrations exceeding project screening levels in groundwater samples for two of three PFAS screening compounds used for making site management decisions. The third PFAS screening compound was also detected in groundwater, but at concentrations below project screening levels. All three PFAS screening compounds were detected at concentrations below project screening levels in soil samples from and downgradient of the treatment plant sludge drying beds. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 10 occupies 1.1 acres in southern NAS Fallon, adjacent to IRP Site 9. Ten trenches at the site were used from 1960 to 1980 for solid and liquid waste disposal, including construction debris, trichloroethylene, and other liquid chemicals. Some liquid waste was reportedly received from both the Salt Wells and the China Lake Propulsion Laboratories.

A 1988 site inspection was followed by a 2003 soil and groundwater investigation. Based on results, the Navy prepared a final decision document recommending closure at IRP Site 9. The Nevada Division of Environmental Protection concurred with the Navy’s recommendation in 2005 and the site was closed with no further action required.

IRP Site 11 includes 0.5 acres in southern NAS Fallon. Paint wastes were disposed of or spilled on unpaved ground north of the paint shop. Disposal ceased in 1986 when the ground surface was paved with concrete.

Two subsurface soil samples collected during a 1994 remedial investigation showed very low concentrations of volatile organic compounds. A groundwater investigation was completed in 2003. Based on results of the investigations, the Navy prepared a final decision document recommending closure at IRP Site 10. The Nevada Division of Environmental Protection concurred with the Navy’s recommendation in 2005 and the site was closed in 2005 with no further action required.

IRP Site 12 includes 0.1 acres in southern NAS Fallon. Various pesticides were handled and stored at the site. Vehicles used for pest control application were also rinsed at the site and a former leach field received the runoff. Pest control operations have been moved and IRP Site 12 is no longer operational.

A 1988 site inspection was followed by a 2003 soil and groundwater investigation. Based on the results, the Navy prepared a proposed plan and draft decision document recommending no further action at IRP Site 12. The Nevada Division of Environmental Protection concurred with the Navy’s recommendation in a 2003 letter and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 13 occupies 0.06 acres in the southern NAS Fallon and included two 26,000-gallon underground storage tanks used to store fuel for the boiler plant. Potential contamination may have consisted of No. 6 fuel oil, waste lubrication oil, hydraulic fluid, JP-5, and diesel fuel and originated from spills during boiler plant tank filling. The tanks were used for intermittent storage of other fuels and oils after the storage of fuel for the boiler plant was discontinued in 1981.

A site inspection was conducted in 1988. During tank removal in 1992, the ground below the tanks was found to be covered with six to ten inches of asphaltic material formed by the overflow of the fuel oil. Soil samples contained very low concentrations of volatile organic compounds. A groundwater sample from the pit contained hydrocarbons but no detectable volatile organic compounds.

Environmental fate and transport data from a 1995 engineering evaluation revealed that soil contaminants exhibited low mobility due to high viscosity, low volatility, low solubility in water, and strong sorption to soils. The remedial alternatives analysis recommended no action as the best option for the site.

The Navy received a no further action determination in 1997 from the Nevada Division of Environmental Protection.

IRP Site 14 occupies 4.6 acres in south-central NAS Fallon and consists of a concrete slab that served as the foundation for a former mechanics bay, fueling area, and support building. The facility was in use between 1943 and 1971. The building reportedly served as the auto hobby shop from 1971 until 1973, when it was demolished. Two underground storage tanks removed in 1989 that stored leaded gasoline and diesel fuel were estimated to have leaked as much as 2,000 gallons of petroleum hydrocarbon fuel. Groundwater contaminants include 1,2 dichloroethane and benzene.

A basewide 1988 preliminary assessment and site inspection identified the Old Vehicle Maintenance Shop as IRP Site 14. Contamination and exposure risks were evaluated in a 1994 remedial investigation report and public health assessment.

Pilot studies were conducted at IRP Site 14 in 2002 and 2003 to evaluate technologies for treating groundwater contaminated with volatile organic compounds. Several technologies were found to be effective technology for reducing the concentrations of volatile organic compounds in groundwater including in situ air sparging and soil vapor extraction, as reported in the 2004 groundwater pilot studies report.

Historical data and data from a 2007 site characterization and delineation of petroleum hydrocarbons in groundwater and soils were used to design a remedial investigation. The results were reported in a 2012 remedial investigation addendum and feasibility study that determined the nature and extent of contamination and evaluated remedial alternatives for site cleanup.

Remedial action for IRP Site 14 was outlined in the 2015 record of decision for the Southern Operable Unit, which includes IR Sites 1, 14, and 16, and was implemented the same year. Excavation of 1,746 tons of fuel-impacted soils, treatment of 57,000 gallons of groundwater and removal of 130 gallons of free product was completed. Monitoring wells were gauged for free product in 2016 but none was detected. Sampling in 2020 detected 1,2-dichloroethane, benzene, chloroform, ethylbenzene, and vinyl chloride at concentrations above their respective remediation goals. Institutional controls were also implemented as part of the selected remedy to prevent exposure and to prohibit the domestic use of groundwater and the construction of residential buildings until action levels are met.

A 2019 five-year review concluded that the remedy for the site was functioning as intended. Groundwater monitoring and land use control monitoring will continue annually. An indoor air vapor intrusion study was completed in 2021, and a 2023 human health risk assessment found no significant risk from vapor intrusion associated with the groundwater contaminant plume at IRP Site 14.

IRP Site 15 occupies 0.15 acres in southern NAS Fallon and included a mechanic bay with lube pits, a fueling island, and two 7,760-gallon gasoline underground storage tanks (UST) identified as Tanks 62 and 62A. The two USTs were formerly referred to as IRP Site 62 and were part of UST R Site 3. The service station reportedly operated from 1944 through the early 1960s. Potential contaminants of concern included petroleum hydrocarbons from operations.

A site inspection was conducted in 1988. the contents of Tank 62 and Tank 62A were characterized for disposal in 1991 and found to contain diesel and water. Both tanks were removed under the UST Program in 1992.

IRP Site 62 was incorporated into IRP Site 15 in 1994 with Nevada Division of Environmental Protection (NDEP) concurrence. The Navy closed the tanks sites with NDEP approval in 1996. In 2001, a closure report was prepared recommending no further action at IRP Site 15. The NDEP concurred with the Navy’s recommendation in a 2001 letter. A 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 16 includes 0.9 acres at the Old Fuel Farm in southern NAS Fallon. It consisted of four concrete and steel underground storage tanks immediately east of Hangar 7. The Old Fuel Farm was the primary fuel storage and distribution area from 1943 until 1962. After the fuel farm moved, the four underground storage tanks were used from 1963 to 1985 for excess storage of various fuels. An estimated 9,000 gallons of petroleum fuel and 3 gallons of chlorinated solvents were released during operations.

A 1988 site inspection indicated that the tanks were leaking, and they were excavated and removed in 1992. A 1994 remedial investigation identified a chlorinated volatile organic compound plume in groundwater. Remedial actions were conducted, including a plume containment system constructed in 2004 to provide hydraulic control and prevent potential migration of site contaminants to the Stillwater Reservoir and Wildlife Preserve. A 2012 remedial action included treatment of groundwater affected by chlorinated volatile organic compounds using injection of ozone and hydrogen peroxide.

Remedial action for IRP Site 1 was outlined in the 2015 record of decision for the Southern Operable Unit, which includes IR Sites 1, 14, and 16, and included treatment of remaining chlorinated volatile organic compounds in groundwater with in-situ chemical oxidation, followed by monitored natural attenuation and institutional controls. The remedy is currently being implemented as described in the remedial design. In situ treatment consists of injection of sodium permanganate and sampling to monitor performance. A remedial action completion report describing the results of the remedial action implementation will be prepared when in situ treatment is completed. Long-term groundwater monitoring sampling results will be evaluated to determine whether additional treatment is needed and whether the remedy is operating properly.

IRP Site 17 occupies about 0.99 acres in southeastern NAS Fallon. Runoff from aircraft maintenance and cleaning from 1943 to 1987 was suspected to have contaminated soil and groundwater at the site. The chemical of concern was petroleum hydrocarbons.

A 1988 site inspection was followed by a 2003 soil and groundwater investigation. Based on inspection and investigation results, the Navy prepared a proposed plan and draft decision document recommending no further action at IRP Site 17. The Nevada Division of Environmental Protection concurred with the Navy’s recommendation in a 2003 letter and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 18 is near the southeastern corner of the wastewater treatment facility. The site is part of the Landfill Operable Unit, which includes IRP Sites 18, 20, 21, and 22. An estimated 18,000 tons of municipal refuse and industrial waste were reportedly buried in four disposal trenches at the 2.3-acre site from 1943 to 1946. Because the site was used as a landfill during World War II, it represents a cultural resource that is eligible to be included on the National Register of Historic Places. Site 18 has also been identified as a State Historical Site.

A site inspection was conducted in 1988. Although a 1999 preliminary decision document recommended no further action at this site, very low concentrations of pesticides were detected in groundwater in 2002. Wells were sampled again in 2010 and 2011 and pesticides were not detected. Elevated dioxin concentrations were detected in surface soils in 2011, and a human health risk assessment was conducted to address the elevated dioxin concentrations.

After completing a feasibility study in 2014, the Navy, with the concurrence of the State of Nevada, selected native soil cover, land use controls, and long-term groundwater monitoring as the remedy for the site. The final record of decision was signed in 2018. Landfill inspections are conducted annually and groundwater monitoring and sampling at the site will continue to be conducted every two years.

IRP Site 19 includes 3.9 acres and is in southern NAS Fallon. The area received an estimated 2,200 cubic yards of trash and other wastes generated during facility decommissioning activities between 1946 and 1949. Wastes, including vehicles, vehicle maintenance waste, wood, paints, thinners, and solvents, were reportedly buried in trenches less than 8 feet in depth.

A site inspection was conducted in 1988, followed by a 1994 remedial investigation that did not include soil and groundwater sampling because no contamination was observed. Since Site 19 does not pose a public health hazard, no corrective actions were recommended, and the site was closed in 2002.

IRP Site 20 is a former landfill covering 26 acres in southwestern NAS Fallon. The site is part of the Landfill Operable Unit, which includes IRP Sites 18, 20, 21, and 22. From 1951 through 1965, approximately 85,000 tons of solid wastes such as wet garbage, trash, and rubble, and 1,400 gallons of fuels, waste oil, and hydraulic fluid were buried in trenches. Sludge from the wastewater treatment plant was also reportedly buried at the site.

A site inspection was conducted in 1988. Additional investigations in 1994 and 2003 confirmed the presence of petroleum hydrocarbons in soil and the volatile organic compound chloromethane in groundwater. Remedial alternatives were evaluated, and a 2004 decision document selected land use controls, along with groundwater monitoring and landfill maintenance, as the site remedy.

Annual landfill inspections and/or groundwater monitoring were performed from 2007 to 2022, and soil cap sampling was conducted in 2012. A 2019 five-year review reported that the remedy in place at IRP Site 20 is functioning as intended and is protective of human health and the environment. Groundwater sampling has been discontinued with concurrence from the Nevada Division of Environmental Protection, although landfill inspections continue to be conducted annually.

Because the landfill received waste material which may have contained aqueous film-forming foam, a per- and polyfluoroalkyl substances (PFAS)-containing material known as “AFFF,” from wastewater treatment ponds, the 2019 basewide PFAS preliminary assessment report recommended further investigation at IRP Site 20.

Results from the subsequent 2021 basewide PFAS site inspection showed concentrations below project screening levels in groundwater samples for all three PFAS screening compounds used for making site management decisions. No further evaluation for PFAS was recommended. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

This former landfill site occupies 60 acres in east-central NAS Fallon. The site is part of the Landfill Operable Unit, which includes IRP Sites 18, 20, 21, and 22. IRP Site 21 was active from 1965 through 1980 and reportedly received both solid and liquid wastes from 1965 through 1975. Solid waste included garbage, trash, and rubble, and liquid waste may have contained jet fuel, gasoline, diesel fuel, waste oils, and hydraulic fluids. Only solid waste was disposed of at the site from 1975 until 1980, when landfill operations ceased. Approximately 96,000 tons of solid waste and 1,000 gallons of fuels, waste oil, and hydraulic fluid were buried in trenches or burned while the Receiver Site Landfill operated.

A site inspection was conducted in 1988. Additional investigations in 1994 and 2003 confirmed the presence of petroleum hydrocarbons in soil and the volatile organic compound trichloroethylene in groundwater. Remedial alternatives were evaluated, and a 2004 decision document selected land use controls, along with groundwater monitoring and landfill maintenance, as the site remedy.

Annual landfill inspections and groundwater monitoring were performed from 2007 to 2022, and soil cap sampling was conducted in 2012. A 2019 five-year review reported that the remedy in place at IRP Site 21 is functioning as intended and is protective of human health and the environment. Groundwater monitoring has been discontinued with concurrence from the Nevada Division of Environmental Protection. Landfill inspections continue to be conducted annually.

This former landfill site occupies 18 acres in eastern NAS Fallon. The site is part of the Landfill Operable Unit, which includes IRP Sites 18, 20, 21, and 22. Landfill disposal was transferred here from IRP Site 21 in about 1980, and operations continued until 1987. The site reportedly received approximately 60,000 tons of solid waste that was buried in trenches.

A site inspection was conducted in 1988. Additional investigations in 1994 and 2003 found no exceedances of action levels for any chemicals in soil or groundwater within the landfill boundary. Remedial alternatives intended to prevent future human exposure to landfilled material and to mitigate the potential for future leaching of possible contaminants from the landfilled material to groundwater were evaluated. A 2004 decision document selected land use controls, along with groundwater monitoring and landfill maintenance, as the site remedy.

Annual landfill inspections and/or groundwater monitoring were performed from 2007 to 2022, and soil cap sampling was conducted in 2012. A 2019 five-year review reported that the remedy in place at IRP Site 21 is functioning as intended and is protective of human health and the environment. Groundwater sampling has been discontinued with concurrence from the Nevada Division of Environmental Protection, although landfill inspections continue to be conducted annually.

IRP Site 23 occupies 4.9 acres in southern NAS Fallon and includes the shipping and receiving disposal area. Solid wastes were reportedly received at the site from 1968 to 1984, including trash and rubble. A burned-out fuselage was also reportedly buried in the southern portion of the site. Burn pits were observed at the site in the late 1990s. Asbestos was buried at one location but was later removed and properly disposed of at an off-site facility.

A 1988 site inspection was followed by a remedial investigation in 1994 and a soil and groundwater investigation in 2003. Based on investigations and evaluation of results, the site does not pose a public health hazard. No corrective actions were recommended, and the Navy prepared a proposed plan and draft decision document. The Nevada Division of Environmental Protection concurred in a 2003 letter with the Navy’s recommendation of no further action at IRP Site 23, and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 24 consists of Perimeter Road, which runs along the eastern boundary of the base and connected interior roads, and is about 26 acres in size. The Road Oiling Area, along the north, east, and southeast borders of NAS Fallon, consists of perimeter roads that were oiled with approximately 37,000 gallons of waste oils, fuels, and solvents for dust control. Dust control occurred between 1943 to 1946 and again from 1951 to 1981. Specific wastes used for dust control included hydraulic fluids, antifreeze, leaded gasoline, carbon tetrachloride, motor vehicle gasoline, jet fuel, trichloroethene, and trichloroethane. Some parts of the north perimeter roads are currently paved, although all roads were unpaved before 1981.

A 1988 site inspection was followed by a remedial investigation summarized in a 1994 report and a soil and groundwater investigation in 2003. Based on investigations and evaluation of results, the soil does not contain contaminants at harmful levels and the site does not pose a public health hazard. Additionally, access to the area is restricted. No corrective actions were recommended, and the Navy prepared a proposed plan and draft decision document. The Nevada Division of Environmental Protection concurred in a 2003 letter with the Navy’s recommendation of no further action at IRP Site 24, and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 25 occupies 4.5 acres in east-central NAS Fallon. Concrete, asphalt, and wood were reportedly buried in pits or ditches from 1970 to 1980. The material was generated from runway and road repair projects.

A site inspection was conducted in 1988 and no chemical contamination was reported. A 2001 Nevada Division of Environmental Protection letter to the Navy states that no further remedial action is required at IRP Site 25, and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 26 includes about 2 acres in northwestern NAS Fallon. Concrete, asphalt, and wood from runway and road repair projects were reportedly buried at the site.

A site inspection was conducted in 1988 and no chemical contamination was reported. A 2001 closure report was prepared recommending no further action at IRP Site 26, the Nevada Division of Environmental Protection concurred with the Navy’s recommendation in a 2001 letter, and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 27 is approximately 20 miles southeast of NAS Fallon and is 21,627 acres in size. Approximately 100 gallons of diesel fuel were reportedly spilled in 1987 along one of the access roads leading to the B-17 bombing range. Diesel fuel was the only contaminant.

A site inspection was conducted in 1988. Cleanup of the spill generated approximately 10 cubic yards of contaminated soil, which was relocated to a remote area of the bombing range. Closure approval for IRP Site 27 is documented in a 2001 letter from the Nevada Division of Environmental Protection to the Navy, and a 2005 NAS Fallon ERP overview presentation documents that the site was closed.

IRP Site 28 includes 0.5 acres in northern NAS Fallon. During investigations of nearby landfill Sites 21 and 22, increasing trends of hydrocarbons were detected in upgradient wells. The petroleum contamination was not a result of landfill constituents, and no nearby infrastructure or operations could be a source. Interviews with base personnel revealed that a fuel tank fell from an aircraft at this Northeast Runway area location in the late 1990s or early 2000s.

A 2017 investigation characterized the nature and extent of petroleum hydrocarbon contamination in the soil and groundwater at IRP Site 28. The investigation followed the underground storage tank corrective action process and consisted of systematic collection of soil samples at 16 grid locations distributed evenly across the site. Petroleum hydrocarbons were detected in select soil and groundwater samples but at concentrations significantly below Nevada Division of Environmental Protection closure levels.

The results of the 2017 investigation indicated that the site does not contain any obvious sources of petroleum hydrocarbon contamination, and that soil and groundwater do not represent a risk to human health or the environment. The site was closed in 2018 following Nevada Division of Environmental Protection concurrence with the Navy’s no further action recommendation.

IRP Site 29 occupies 1.53-acre in southwestern NAS Fallon, outside the perimeter fence line, but within the air station property boundary. A dumping area discovered by the installation’s archaeologist consisted of potential asbestos construction debris and possibly 55-gallon drums containing unknown substances. The area was covered with fragments of transite pipe, exterior roofing or wall tiles, roofing material, felt, tar, and possible asbestos-containing cellulose insulation.

No historical structures or operations were identified during a 2016 preliminary assessment, although review of mid-1940s to 1960 aerial photographs indicated a historical feature, possibly a previous excavation, in roughly the same area as the surficial asbestos-containing material. A 2018 site inspection found no indications of a chemical release to soil or groundwater from historical activities and recommended no further investigation of soil or shallow groundwater. Potentially friable asbestos-containing material (ACM) was observed within the boundary of a historical feature on the ground surface and to a depth of approximately 1 foot, and non-friable ACM was observed to a depth of approximately 2 feet.

An engineering evaluation was prepared in 2020, followed by a 2021 action memorandum that documented selection of a removal action. A 2022 removal action completion report details the surface removal of visible ACM from a 0.66 area surrounding the historical feature area and excavation of ACM and soil to a depth of two feet from the 0.87 acre historical feature area. Visible asbestos debris and excavated ACM and soil were transported off site to the appropriate disposal facility, and the excavation was backfilled with reusable stockpiled soil and imported soil.

Hazards to human health and environmental receptors from exposure to ACM in surface and shallow subsurface soil were sufficiently mitigated by the removal. The Navy requested site closure with no further action in the 2022 IRP Site 29 completion report. The Nevada Division of Environmental Protection concurred and the site was closed in May 2022.

A basewide preliminary assessment (PA) of per- and polyfluoroalkyl substances (PFAS) in soil and groundwater was conducted in 2019. Areas inclusive of existing IRP sites and unaffiliated areas at NAS Fallon with the potential for PFAS releases were identified during the PA for further investigation in a basewide PFAS site inspection (SI). The purpose of the SI was to determine, through sampling of soil and groundwater media, if a release of PFAS has occurred at the areas identified during the PA as areas where PFAS use, storage, or disposal may have occurred.

The results of soil and groundwater sampling conducted during the 2021 SI determined that PFAS were present at four unaffiliated areas identified as areas of concern (AOC), in addition to other IRP sites and areas. Based on proximity, these four AOCs were grouped together as IRP Site 30 for the purposes of a future PFAS remedial investigation. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 30 consists of the following four AOCs:

• April 2018 F-22 Belly Landing Crash Site (formerly AOC 1) is an area in the center of Runway 31L, the location of an F-22 aircraft crash in April 2018. Aqueous film-forming foam, a PFAS-containing material known as “AFFF,” was reportedly used at the scene to extinguish the fire that resulted from the crash. Results from the 2022 basewide PFAS SI showed concentrations above project screening levels in groundwater samples for one of three PFAS screening compounds used for making site management decisions.

• April 1961 Douglas R4D-5 (DC-3) Crash Site (formerly AOC 3) is an area in the center of Runway 31L and is the site of a Douglas R42-5 (DC-3) crash in April 1961. Protein foam, potentially a PFAS-containing material, was reportedly used at the scene. Results from the 2022 basewide PFAS site inspection showed concentrations above project screening levels in groundwater samples for all three PFAS screening compounds used for making site management decisions.

• September 2011 F/A-18 Crash Site (formerly AOC 4) is an area on the northern outboard side of Runway 31R/13L. An F/A-18 aircraft crashed in September 2011 during a landing attempt on Runway 31R/13L and flipped onto the other side of the runway, off the flight line, and into the dirt. AFFF was used at the scene to extinguish the fire. Results from the 2022 basewide PFAS SI showed concentrations above project screening levels in groundwater samples for two of three PFAS screening compounds used for making site management decisions.

• The Fire Truck Staging Area (formerly AOC 12) is between Runways 31R and 13L. Although fire trucks were reportedly not washed and no training was conducted at the Fire Truck Staging Area, flow checks releasing water potentially containing residual AFFF from hoses may have been conducted. Results from the 2022 basewide PFAS SI showed concentrations above project screening levels in groundwater samples for all three PFAS screening compounds used for making site management decisions.

IRP Site 31, formerly Area of Concern (AOC) 2, is northeast of Building 243. In March 2012, a Kfir F-21-C2 fighter jet crashed in the soil northeast of the building, lost its main gear, and crashed into the building. Because a known release of aqueous film-forming foam, a per- and polyfluoroalkyl substances (PFAS)-containing material used for firefighting known as “AFFF,” occurred, the 2019 basewide preliminary assessment of PFAS in soil and groundwater identified the site as AOC 2 and recommended further investigation in a basewide PFAS site inspection.

The purpose of the 2021 basewide PFAS site inspection was to determine, through sampling of soil and groundwater media, if a release of PFAS has occurred at the areas identified during the preliminary assessment as areas where PFAS use, storage, or disposal may have occurred. Results from the site inspection showed concentrations at IRP Site 31 exceeding project screening levels in groundwater samples for two of the three PFAS screening compounds used for making site management decisions. The site was recommended for inclusion in a PFAS remedial investigation. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

IRP Site 32, formerly Area of Concern (AOC) 10, is the Fire Pit Training Area associated with Building 492, the Mock-Up Training Aid Center, located in southwestern NAS Fallon. Potential releases of small quantities of aqueous film-forming foam, a per- and polyfluoroalkyl substances (PFAS)-containing material used for firefighting known as “AFFF,” were identified in the 2019 basewide PFAS preliminary assessment at AOC 10, now known as IRP Site 32. Potential impacts to soil and groundwater may have resulted from use of the site and residual AFFF discharged from fire truck hoses to the soil during operations at the site. The preliminary assessment recommended further investigation in a basewide PFAS site inspection.

The purpose of the 2021 basewide PFAS site inspection was to determine, through sampling of soil and groundwater media, if a release of PFAS has occurred at the areas identified during the preliminary assessment as areas where PFAS use, storage, or disposal may have occurred. Results from the site inspection showed concentrations at IRP Site 32 exceeding project screening levels in groundwater samples for all three PFAS screening compounds used for making site management decisions and for one PFAS screening compound in soil. The site was recommended for inclusion in a PFAS remedial investigation. More details on NAS Fallon PFAS investigations can be found on the PFAS Data Summary and PFAS Documents tabs.

MRP UXO Site 1, the Off-Range Ordnance area, is approximately 8,000-acres about 16 miles south of the NAS Fallon Main Station. The area is adjacent to the southern Range Bravo-19 boundary, an active range primarily used for both live and inert ordnance air to surface and close air support training. Range B-19 was established in 1953 and expanded in 1999. The accidental release of ordnance outside of the Range B-19 boundaries was first discovered in the late 1980s. Beginning in 1989, several munitions and munitions debris removal actions were completed on adjacent tribal land by the NAS Fallon Explosive Ordnance Disposal Unit. The potential for future off-range ordnance has been largely mitigated by modifying the aircraft training approach trajectories and relocating target areas at Range B-19.

A preliminary assessment of the Off-Range Ordnance Area is being conducted to investigate historical Range B-19 training activities and types and manner of ordnance used. Navy personnel and Walker River Paiute Tribe representatives knowledgeable of off-range ordnance on Tribal land were interviewed, and a site visit to observe the ground surface for the presence of munitions, munitions-related items, impacts to the land surface, and potential impacts to soil was conducted. The preliminary assessment report is currently under development.

UST-R-Site 1 is currently a paved government vehicle parking area and car wash pad in the Building 395 Area northwestern NAS Fallon that was formerly the site of a military gas station. Two underground storage tanks (UST) identified as UST 396A and UST 396B were installed at the site in 1976. UST 396A, a 3,000-gallon steel tank used to store diesel fuel, was removed in 1990 after it failed an annual tank tightness test. UST 396B, a 10,000-gallon steel tank used to store unleaded gasoline, was removed in 1994, along with the piping for both tanks and the fuel island. Approximately one-eighth of an inch of free product was observed in the excavation during removal of the two USTs. The Navy requested concurrence from Nevada Division of Environmental Protection (NDEP) that no further action be required for soils at the site. The NDEP replied in a 1999 letter that although characterization of soil contamination was not required, closure of both soil and groundwater at the site was preferred and sampling of downgradient wells on a semiannual schedule should be initiated.

A 2007 investigation delineated the extent of free product at UST-R Site 1. Soil and groundwater data were used to produce an updated risk assessment and identify a strategy for cleanup and site closure. The Navy recommended that a corrective action plan be developed for UST-R Site 1 to address floating free phase product in monitoring well (MW) 395F east and downgradient of former UST 395A and achieve closure at UST-R Site 1 with no further action required.

A corrective action plan completed in 2013 summarized active free product removal at UST-R Site 1, Building 395 Area UST, from 2007 through 2013. Additional groundwater and product monitoring and product removal with skimmers was recommended at MW 395F, where free product contamination had rebounded. The Navy concluded that further investigation was necessary.

A 2017 site investigation conducted to further define the nature and extent of petroleum hydrocarbon contamination at UST-R Site 1 found that residual petroleum contamination remains in the smear zone, the interface between free product floating on the water table and the overlying soil, at concentrations significantly lower than required by the NDEP for closure. Groundwater sampling results indicated that contamination from the former USTs is limited to the area near a boring approximately 90 feet east of former UST 395A. A 2020 supplemental investigation was conducted to better characterize the groundwater contamination.

Current site conditions at UST-R Site 1 and the results of the 2017 and 2020 investigations led the Navy to select a remedial approach consisting of monitored natural attenuation and quarterly groundwater monitoring, free product removal from MW 395F, and free product level monitoring in the existing monitoring well network.

The 2021 UST-R-Site 1 corrective action plan states that the Navy will request closure if after three years groundwater contaminant concentrations are stable or decreasing and have not rebounded; if contaminant concentrations are less than U.S. Environmental Protection Agency maximum contaminant levels for four consecutive quarters; or if free product is not observed at UST-R-Site 1 for four consecutive quarters.

UST-R Site 2 is in the Building 806 area in the southwestern corner of NAS Fallon. Building 806 is a former power plant built in 1962 to ensure power availability to the building and others in the vicinity in case the local grid was inoperable. Among the structures located in the vicinity of Building 806 were two 80,000-gallon aboveground storage tanks (AST) and fuel transfer station, one 1,000-gallon underground storage tank (UST), and two 12,000-gallon USTs identified as 806N and 806S.

The two 80,000-gallon ASTs were used to store fuel oil and were taken out of service in the mid-1980s. Th Navy disassembled and removed the tank, piping, fill port, and transfer station from the site in 2002. No evidence of petroleum contamination around the foundations of the tanks was observed. Soil samples from the excavation beneath the fill port indicated the presence of diesel-related petroleum hydrocarbon contamination.

The 1,000-gallon UST that was used to store lubrication oil was also excavated and removed in 2002. Soil samples from the excavation indicated the presence of diesel-related petroleum hydrocarbon contamination. Groundwater entered the excavation, and floating product was observed on the groundwater. Initial grab groundwater samples from the excavation also contained diesel-related petroleum hydrocarbons and heavier oils.

The two 12,000-gallon former USTs 806N and 806S were located east of Building 806 and provided fuel for power plant operations. Both tanks were removed and disposed of in 1992. Groundwater and petroleum product were observed in the excavation pit when the tanks were removed. Petroleum hydrocarbons were detected in soil samples at the excavation site and in groundwater samples from the excavation.

The Navy further investigated the extent of potential groundwater contamination associated with tanks 806N and 806S and installed monitoring wells in 1994 and 1996. A groundwater plume extending beyond the wells farthest downgradient from the excavation area was delineated but no free product was detected by 1996. The Navy employed fate and transport modeling to demonstrate that concentrations of fuel-related compounds in groundwater were decreasing. In addition, the ambient quality of shallow groundwater at the site precluded its beneficial use as a drinking water supply. The Navy recommended no further action and the Nevada Division of Environmental Protection (NDEP) concurred in 1998,

A 2007 investigation initiated by the Navy of IRP petroleum sites at NAS Fallon delineated the nature and extent of contamination in all media and assessed human health risks from the releases at the UST-R Site 2 Building 806 area. Data collected confirmed that petroleum-related compounds in the shallow groundwater downgradient from the Building 806 area are decreasing to levels below screening criteria or are no longer detectable. The primary sources of contamination, the former ASTs and USTs, were removed and no evidence of a secondary source exists.

Almost all locations where petroleum contamination was detected in shallow soil are currently covered by pavement and action levels are not consistently exceeded. Based on these findings, NDEP approved the Navy request for no further action for releases from UST-R Site 2, and the site was closed in 2012.

UST-R Site 3 included three former underground storage tank (UST) locations identified as Site 62, UST-R19, and UST-R220.

Site 62 was a former service station in southern NAS Fallon. Two 7,760-gallon gasoline USTs identified as Tanks 62 and 62A were located approximately 21 feet from the southwestern corner of Building 62. A site inspection was conducted in 1988. The contents of Tank 62 and Tank 62A were characterized for disposal in 1991 and found to contain diesel and water. Both tanks were removed under the UST Program in 1992. Site 62 was incorporated into IRP Site 15 in 1994 with Nevada Division of Environmental Protection (NDEP) concurrence and closed in 2001.

UST-R19 is outside the boundaries of NAS Fallon at Range B-19, approximately 13 miles south of NAS Fallon. It was the site of two 1,500-gallon diesel USTs identified as 19E and 19W, near the east and west range observation towers. Investigations were conducted concurrently in 1994 at UST-R19 and other UST sites associated with observation towers.

The NDEP stated in a 1994 letter that no further action was required for UST-R19W because the tank was removed in good condition, analytes in the soil sample collected from beneath the tank were below levels of concern, and groundwater was not encountered. Holes were reportedly observed in UST-R19W during removal prior to 1993. Although no groundwater was encountered, the field crew was unable to remove the concrete ballast slab, and petroleum hydrocarbon contaminated soil remained. The NDEP required that the Navy conduct additional investigations at the site.

UST-R220 was a 1,500-gallon diesel tank northeast of the intersection of Churchill Avenue and Carson Road approximately 7 feet from the southeastern corner of Building 220, the Airfield Lighting Standby Generator Building. Although the tank was reported to be in good condition when removed prior to 1993 and no groundwater was encountered, petroleum hydrocarbon contaminated soil remained at the site. The NDEP required that the Navy conduct additional investigations at the site.

NDEP reviewed the Navy’s 1995 report of findings from investigations at UST-R19E, UST-R220, and several other UST sites and concluded that the excavation and proper disposal of all significantly contaminated soil encountered was documented, and no significant groundwater contamination was detected at these sites. NDEP concurred in 1996 that no further action was required at UST-R19E and UST-R220.

Building 201 is within IRP Site 2 in northern NAS Fallon. It was built in 1955 as the Fuel Farm Operations Building and was originally heated using an oil-fired steam boiler. Fuel oil was supplied from a 750-gallon underground storage tank (UST) approximately 5 feet from the west wall of the building. The tank and associated lines were abandoned in place in approximately 1959 when the building was connected to the Central Heating Plant.

During a review of utility drawings in 2008, the NAS Fallon Environmental Division was notified of a possible UST in the subsurface at Building 201. Further investigation indicated that the tank had been removed, but it was suspected that residual fuel from the tank had leaked into the soil. Corrective measures taken included the excavation of approximately 3 cubic yards of soil. Soil samples from the site indicated the presence of residual petroleum hydrocarbon contamination.

A 2017 investigation included groundwater sampling from one temporary well, soil sample collection from direct-push borings, and laser-induced fluorescence screening for petroleum hydrocarbon contaminants. Results of the investigation identified residual contamination in groundwater in the immediate vicinity of the former tank basin. The volume of water produced for sampling by temporary well was sufficient for volatile organic compound analysis only. The estimated concentration of benzene, the only volatile organic compound detected, exceeded the maximum concentration level for groundwater. Although petroleum hydrocarbons were detected in soil samples collected at the site, concentrations were at levels low enough to achieve closure under Nevada Division of Environmental Protection requirements.

Because the results for the benzene concentration in groundwater from the temporary well were estimated, a 2020 supplemental investigation was performed at UST-R Site 4 which included installation and sampling of a new permanent monitoring well to better characterize the groundwater contamination. Benzene was detected in the sample at a concentration below the maximum concentration level for groundwater. No contamination above state action levels was identified in soil or groundwater and UST-R Site 4 was closed in 2021 with no further action required.

Building 314 was in northern NAS Fallon. It was built in 1957 as a central heating plant that provided high temperature hot water to several buildings on the north side of the station. A 13,800-gallon aboveground storage tank (AST) near former Building 314 and piping were removed in 2005. The tank was initially used for storing JP-5 fuel and later diesel fuel and was filled from a 2-inch underground fuel line near the building. A 1.5-inch boiler feed line ran parallel to the fill line before entering the building.

The NAS Fallon Environmental Division was notified in 2008 that a contractor demolishing Building 314 had encountered contaminated soil while capping off fuel lines. Subsurface stained soil and a fuel odor were discovered in the area where the tank and fuel lines were removed in 2005. Approximately 30 tons of contaminated soil was removed from UST-R Site 5. The NAS Fallon Public Works Center removed all associated piping from the area of the former building in 2010.

A 2017 draft site closure report found that soil and groundwater at UST-R-Site 5 has been adequately characterized and does not represent a risk to human health or the environment. No further action was recommended. The Nevada Division of Environmental Protection concurred in 2018 and the site was closed in accordance with applicable State of Nevada regulations.

UST-R Site 6, the Former Fuel Oil Pipeline Area, is in southern NAS Fallon and was discovered in 2013 when petroleum contamination was found downgradient of IRP Sites 14 and 16, which are immediately to the south. Historical information indicates that the contamination was most likely associated with a distribution system that supplied fuel oil to buildings in the southeast quadrant of the air station. All known petroleum containing tanks were removed and trenching activities have shown that the pipeline is no longer present.

A 2017 investigation conducted to define the nature and extent of petroleum hydrocarbon included groundwater sampling from temporary and existing wells, soil sample collection from direct-push borings, and laser-induced fluorescence screening for petroleum hydrocarbon contaminants. Results of the investigation identified residual petroleum hydrocarbon contamination and free product in temporary and existing monitoring wells. Analysis of the groundwater samples for petroleum hydrocarbons and volatile organic compounds detected estimated concentrations in one well exceeding maximum concentration levels for benzene and pentachlorophenol, an herbicide not related to the former fuel oil pipeline. Although petroleum hydrocarbons were detected in soil samples collected at the site, concentrations were at levels low enough to achieve closure under Nevada Division of Environmental Protection (NDEP) requirements. A 2020 supplemental investigation at UST-R Site 6 included installation of a new permanent monitoring well, which was sampled to better characterize the groundwater contamination.

Current site conditions at UST-R Site 6 and the results of the 2017 and 2020 investigations led the Navy to selected a remedial approach consisting of free product removal from a monitoring well in the central Former Fuel Oil Pipeline area, installation of two permanent monitoring wells, monitored natural attenuation and quarterly groundwater monitoring, free product characterization and level monitoring in the existing monitoring well network, and additional soil borings and sampling to evaluate the need for any soil excavation.

The 2021 UST-R-Site 6 corrective action plan states that the Navy will request closure if free product is less than 0.5 inches in all wells for four consecutive quarters; if after three years groundwater contaminant concentrations are stable or decreasing and have not rebounded; if contaminant concentrations are less than U.S. Environmental Protection Agency maximum contaminant levels for four consecutive quarters; or if petroleum hydrocarbon constituent concentrations in soil boring samples are below NDEP default screening levels protective of direct contact exposure and leaching to groundwater.

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