IRP Site 3, the former Firefighting Training Area, is an approximately 1.1 acre undeveloped property in the central part of the southern half of Rough and Ready Island, the location of NCTS Stockton, along the northern part of the agricultural area. It bounded to the west by Daggett Road and to the north by an unlined drainage channel that flows east to west. The training area contained an equipment and fuel storage shed, a 3 to 5 feet deep unlined earthen burn pit roughly 30 feet wide by 100 feet long, two large aboveground storage tanks (AST) with open tops, and several drums. The Navy used IRP Site 3 as a firefighting training area from 1950 to 1978. Use of the burn pit was most frequent during the 1950s, with up to 20 fires per day. Between the 1960s and 1978 the burn pit was used twice per year. In 1978, use of IRP Site 3 for firefighting training activities stopped.
During training operations, the open ASTs were filled with water, floating fuel was placed on top, lit on fire, and extinguished. Advanced firefighting training simulations were also conducted in the burn pit, where fuel was poured directly onto the soil, lit on fire, and extinguished using water or foam fire retardants. Based on information provided by the Navy, fuels ignited in the former burn pit area included bunker oil, contaminated gasoline, contaminated aviation fuel, lube oil, crank case oil, lacquer thinner, kerosene, and solvents including trichloroethene.
Following the Navy’s initial assessment study at NCTS Stockton in 1984, the open tanks were removed and stored in the southwestern corner of the site, adjacent to the fuel storage area. One to two feet of visibly contaminated soil was removed from the burn pit in 1984. Analysis of two confirmation samples detected volatile organic compounds (VOC) and metals.
Beginning in 1986, investigations of environmental media at IRP Site 3 identified a VOC groundwater plume originating at the burn pit, as well as dioxin and furans, total petroleum hydrocarbons (TPH), and VOCs in soil at concentrations consistent with the presence of non‐aqueous phase liquid. In 1988 a verification study conducted by the Navy recommended additional investigation at the site.
A site investigation and aerial photograph review were conducted In 1992. Soil samples were collected and analyzed for VOCs, semivolatile organic compounds, organochlorine pesticides, polychlorinated biphenyls, TPH, metals, and dioxins and furans. In 1993, a high‐density polyethylene cap was installed to prevent rainwater infiltration through contaminated soil to groundwater.
The Navy identified the site as requiring a time-sensitive removal action in 1993 and estimated in a 1994 action memorandum that 2,500 cubic yards of contaminated soil remained at IRP Site 3. The burn pit was excavated to a depth of approximately 12 feet, backfilled with pea gravel, drain rock, and engineered fill, creating the “backfill pit.” The excavated soil was placed in a stockpile at IRP Site 45 and the burn pit was dewatered over the course of several weeks.
From 1997 to 2012 investigations and removal actions were ongoing at the site. A background water quality study, surface water and sediment site investigation, soil removal, remedial investigation and associated groundwater monitoring and risk assessment were all performed. A 2012 remedial investigation report and feasibility study incorporating findings from these prior activities concluded that sufficient data exists to identify VOCs as the primary concern at IRP Site 3, and that because VOCs have been decreasing over time and do not pose such a threat to human health or the environment, site risks can be managed by land use controls. The next step in the CERCLA process is to draft a proposed plan for public review identifying a preferred remedial alternative for IRP Site 3.
In 2018, groundwater samples were collected from four monitoring wells at IRP Site 03 for the Port of Stockton, the landowner at the time, under a non-Navy contract for per- and polyfluoroalkyl substances (PFAS) analyses. The PFAS perfluorooctanoic acid, known as PFOA, was detected in one well at a concentration above regional screening levels during the initial event and again when resampled to confirm the result. Under the 2003 Environmental Services Cooperative Agreement governing the transfer of NCTS Stockton properties located on Rough and Ready Island to the Port of Stockton, the Navy retained responsibility for any Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) actions. Based on the results for groundwater and in agreement with the Port of Stockton, the Navy moved forward with the investigation of PFAS under the CERCLA process.
A 2021 report on the Navy’s PFAS preliminary assessment presented the results of the 2018 sampling events, results of the site research, and interviews with persons knowledgeable of the site and identified IRP Site 3 as an area of concern (AOC). Aqueous film-forming foam, a PFAS-containing material referred to as “AFFF,” was potentially released at IRP Site 3 former burn pit, fuel storage area, and equipment shed. Because groundwater from IRP Site 3 is collected in Rough and Ready Island drainage channel system and conveyed to the stormwater pump house area, sediment and groundwater samples were taken during the site inspection.
Analytical results in the 2023 PFAS site inspection report from IRP Site 03 showed concentrations in groundwater samples exceeding regional screening levels for four of six PFAS screening compounds used for making site management decisions. Concentrations detected in soil samples exceeded regional screening levels for two of six screening compounds. Results from the stormwater pump house area showed no exceedances in sediment concentrations and only a slightly exceeding regional screening level in two groundwater samples.
The site inspection recommended further PFAS remedial investigation activities at IRP Site 3, with the stormwater pumphouse area investigated as part of IRP Site 3. More details can be found on the PFAS Data Summary and PFAS Documents tab.
IRP Site 45 is an approximately 400 feet wide and 600 feet long undeveloped 5.5-acre parcel located in the northern half of the west end of the Central Island Area. A chain‐link fence within the site encloses a partially covered stockpile from IRP Site 3 consisting of approximately 2,500 cubic yards soil.
The Navy began investigating IRP Site 45 in 1996 by collecting soil and groundwater samples because of the presence of soil mounds of unknown origin and apparent soil staining. Total petroleum hydrocarbons as motor oil, volatile organic compounds, and metals have been detected in groundwater.
From July 2000 through 2010, the Navy transferred properties in four phases to the Port of Stockton. An environmental services cooperative agreement was negotiated between the Navy and the Port of Stockton whereby the Port of Stockton is responsible for performing all environmental services except those deemed “Navy-Retained Conditions” as defined in the agreement. The Port of Stockton and the Navy continue to cooperate in managing the environmental condition of property at the former NCTS Stockton.
A 2021 report on the Navy’s potential per- and polyfluoroalkyl substances (PFAS) preliminary assessment identified IRP Site 45 as an area of concern because PFAS was detected in groundwater at IRP Site 3, and the soil stockpiled at IRP Site 45 is from the burn pit excavation at IRP Site 3. Soil sample collection from the 2,500-cubic yard stockpile and groundwater sampling of existing nearby downgradient wells for PFAS analysis was recommended.
Three borings were advanced at Site 45 during the 2021 PFAS site inspection and soil and groundwater samples were collected. Analytical results presented in the 2023 site inspection report showed concentrations in soil and sediment samples exceeding regional screening levels for three of six PFAS screening compounds. Analytical results for groundwater showed concentrations exceeding regional screening levels for two of six PFAS screening compounds. The site inspection recommended further PFAS remedial investigation activities at IRP Site 45. More details can be found on the PFAS Data Summary and PFAS Documents tab.