Naval Air Facility El Centro

IRP Site 1 is an approximately 6.8-acre inactive, former municipal landfill located southeast of the intersection of Magazine Road and Patrol Road in the northern portion of the NAF El Centro that operated from 1965 to 1983 and remained inactive thereafter. Waste disposed at the unlined landfill included household rubbish with lesser amounts of construction debris and some industrial waste. Waste management practices included periodic burning to reduce waste volume.

The IRP Site 1 landfill was characterized in a 1987 basewide site investigation and a 1993 solid wastewater quality assessment test. Groundwater monitoring at the site began in 1991. A landfill cap and associated civil improvements were constructed in 1998 as an interim remedy to prevent possible human or ecological exposure to the potentially contaminated. As part of the interim remedy, the Navy ceased irrigation in the field adjacent to the east and south of IR Site 1 to lower groundwater levels beneath the base of the landfill waste to prevent soil and landfill wastes from leaching and migrating into groundwater. In 2000, a post-closure maintenance plan was prepared, and a long-term monitoring and reporting program was instituted.

A 2001 remedial investigation concluded that potential risks to human health and the environment at IRP Site 1 were low and that exposure to site contaminants was prevented by the landfill cap, site security measures, and low groundwater levels because of elimination of irrigation operations in agricultural fields directly adjacent to the site. A 2002 feasibility study also found that low groundwater levels minimized the potential for contaminants of concern to migrate from landfill wastes into groundwater.

In 2009, a record of decision established a remedy at IRP Site 1 consisting of institutional controls in the form of land use restrictions on future irrigation of the adjacent agricultural fields to maintain water levels below the bottom of the landfill wastes, controls to protect the integrity of the landfill cap, and continuation of a groundwater monitoring and reporting program. The Navy continues to perform semiannual groundwater monitoring, landfill inspection, and maintenance at IR Site 1 along with monthly visual inspections of the landfill cap and associated civil improvements including fencing, signs, and drainage. Although the selected remedy did not require landfill gas monitoring, the Navy has continued due diligence methane gas monitoring concurrent with other semiannual events. The Navy will however assess the need to continue monitoring for landfill gas monitoring in the future.

The most recent five-year review of the remedy completed in 2020 found the remedy for IR Site 1 to be protective of human health and the environment. Land use restrictions, controls to protect the integrity of the landfill cap, and the long-term monitoring and reporting that documents no impact to groundwater from the landfill program continues. The next five-year review will be conducted by 2025.

IRP Site 2 is an approximately 39-acre former landfill located in the northwest portion of NAF El Centro on the south side of Patrol Road. The site consists of Unit 1, the Western Area, and Unit 2, subdivided into Unit 2 East and Unit 2 Asphalt Cap Area. Unit 1 comprises approximately 16 acres and was a borrow pit area for runway fill material. The area was filled with irrigation return flow from adjacent agricultural fields after completion of the runway extension in approximately 1955, creating three ponds. In 1962, the ponds were drained and the borrow pits were filled with construction and demolition debris, primarily concrete rubble. Unit 2 was a municipal landfill from about 1946 until 1965, when landfill operations were transferred to the Magazine Road Landfill, now IRP Site 1. The landfill received household rubbish, paint, solvents, photographic chemicals, asbestos, various fuels and oils, mercury amalgam, batteries, empty 55-gallon drums, parachutes, spray cans, spray paint filters, demolition debris, pesticide shop waste, tires, asphalt, and wood.

The IRP Site 2 landfill was characterized in a 1987 basewide site investigation. As part of the 1998 interim remedy at nearby IRP Site 1 landfill, the Navy ceased irrigation in an adjacent agricultural field. This lowered groundwater levels beneath the base of the IRP Site 1 landfill waste and caused groundwater level elevations below IR Site 2 to also decline. A 2004 IRP Site 2 remedial investigation documented the collection of soil, soil-gas, surface debris, and groundwater samples, and recommended additional actions at the site. An IRP Site 2 feasibility study evaluated potential remedial action alternatives and in 2012 a record of decision established the remedy for the site.

The remedy includes “hot spot” excavation and off-site disposal of construction debris at Unit 1 and surface debris at Unit 2, an asphalt cap at Unit 2, long-term post-closure groundwater and landfill gas monitoring, and land use controls. The IRP Site 2 remedial action was completed in 2018 in accordance with the requirements of the ROD. The Navy continues to perform semiannual groundwater monitoring, landfill inspection, and maintenance at IR Site 2 including inspections of the landfill cap and associated civil improvements such as signs, drainage, asphalt cover, monitoring wells, and settlement monuments.

The most recent five-year review of the remedy completed in 2020 found the remedy for IR Site 2 to be protective of human health and the environment. The removal of the “hot spot” in Unit 1, excavation of all surface debris at Unit 2, installation of a landfill cap at Unit 2, and institutional controls in the form of land use restrictions have made potential exposure pathways incomplete, and the long-term monitoring and reporting program continues. The next five-year review will be conducted by 2025.

IRP Site 3 is an approximately 0.1-acre area located at the northwestern corner of NAF El Centro, east of the sewage stabilization ponds and north of Patrol Road. In 1986, approximately 800 cubic feet of sewage sludge were dumped into an unlined pit 20-foot by 10-foot by 5-foot-deep. The pit was closed with a soil cover following disposal activities, and the site was graded.

IRP Site 3 was first characterized in a 1987 basewide site investigation. The results of site investigation activities included drilling and sampling soil borings, installing and sampling one groundwater monitoring well, and sampling nearby surface water led to the finding that the contaminants of concern extended beyond the original confines of the burial pit. Data from sampling in 1999 led to a recommendation of no further action for groundwater and destruction of the well.

A removal action was conducted in 1998 for approximately 1,950 cubic yards of contaminated soil from IRP Site 3. Following excavation, confirmation sampling results indicated that concentrations of contaminants in soil were below cleanup levels. The site was closed in 1999, following Department of Toxic Substances Control concurrence by letter.

IRP Site 4 is an approximately 0.03-acre area located south of 4th street in the northwestern portion of NAF El Centro. From 1963 to 1975, the site consisted of fire-fighting training areas and a fuel farm where reported waste streams consisted of petroleum hydrocarbons. IRP Site 4 is associated with IRP Sites 5, 6, 7, and 11.

IRP Site 4 was first characterized in a 1987 basewide site investigation. Monitoring indicated that groundwater had not been contaminated at the site and cleanup was not required. Based on concentrations of metals and petroleum in soil consistent with base and regional background concentrations and other non-petroleum contaminants reported at concentrations below the detection limit, a recommendation for no further action under CERCLA was made for IRP Site 4. Regulatory agency concurrence for closure of the site was received in June 1998.

IRP Site 5 is an approximately 0.01-acre area located in the central portion of NAF El Centro, west of runway 12/30. From 1958 to 1963, the site consisted of fire-fighting training areas and a fuel farm where reported waste streams consisted of petroleum hydrocarbons. IRP Site 5 is associated with IRP Sites 4, 6, 7 and 11.

IRP Site 5 was first characterized in a 1987 basewide site investigation. Based on concentrations of metals in groundwater and petroleum in soil and groundwater consistent with base and regional background concentrations and other non-petroleum contaminants reported at concentrations below detection limits, a recommendation of no further action under CERCLA was made for IRP Site 5. Regulatory agency concurrence for closure of the site was received in June 1998.

IRP Site 6 is an approximately 0.4-acre area in the northwestern portion of NAF El Centro, off Patrol Road. From 1946 to 1958, the site consisted of fire-fighting training areas and a fuel farm where reported waste streams consisted of petroleum hydrocarbons. IRP Site 6 is associated with IRP Sites 4, 5, 7 and 11.

IRP Site 6 was first characterized in a 1987 basewide site investigation. Based on concentrations of metals in groundwater and petroleum in soil and groundwater consistent with base and regional background concentrations and other non-petroleum contaminants reported at concentrations below detection limits, a recommendation of no further action under CERCLA was made for IRP Site 6. Regulatory agency concurrence for closure of the site was received in June 1998.

IRP Site 7 is an approximately 23-acre area located in the northwestern portion of NAF El Centro, along Runway 08/26. From 1942 until 1958, the site consisted of a fuel farm where reported waste streams consisted of petroleum hydrocarbons. IRP Site 7 originally consisted of eleven 50,000-gallon and twelve 25,000-gallon concrete underground storage tanks, along with eight dispenser stations for trucks. The underground storage tanks were reportedly emptied, crushed in place, and backfilled with sand. The eleven 50,000-gallon underground storage tanks located in the southeastern portion of the site were subsequently removed in 1993 and 1994. Investigations have confirmed that the remaining twelve 25,000-gallon concrete underground storage tanks and associated piping were abandoned in place, and that the piping did not contribute to fuel contamination at IRP Site 7.

IRP Site 7 was first characterized in a 1987 basewide site investigation. Numerous investigations have been conducted at the site and the surrounding area since then. A 1999 petroleum plume investigation and a 2000 groundwater pilot study presented comprehensive investigation data and documented site conditions prior to site remediation. In 1994, in addition to the UST removal and abandonment, approximately 4,000 cubic yards of soil inclusive of approximately 1,500 cubic yards of contaminated soil were excavated. Pilot testing on remediation wells was conducted in 1999 and 2000.

Since 2001, a long-term groundwater monitoring program in support of remediation activities has been conducted using wells at and downgradient of IRP Site 7. From 2000 to 2008, a full-scale vacuum-enhanced pumping remediation system was operated in the southern portion of the source area. In 2008, a new vacuum-enhanced pumping remediation system was installed in the northern portion of the source area and remained operational until it was shut down in 2012 because of technical issues.

In 2010, a three-phase corrective action plan consisting of active remediation, verification monitoring, and request for closure was developed to address fuel hydrocarbon constituents in groundwater at IRP Site 7. The overall corrective action and exit strategy includes additional monitoring dissolved contaminants of concern to evaluate whether the target cleanup goals are met.

The Navy initiated discussions in 2018 with the Regional Water Quality Control Board concerning site closure. Concentrations of chemicals of concerns have continuously been below the cleanup goals in 38 of 40 monitoring wells. In the other two wells, concentrations of benzene, 1,2-dichlorethane, and total petroleum hydrocarbons as gasoline have exceeded cleanup goals at over the last four sampling events. As a result, sampling was reduced during the fall of 2019 to only these two wells with the concurrence of the Water Board. Based on sampling results, the Navy recommended in a 2020 long-term monitoring report that monitoring continue in pursuit of a response complete determination under the State Water Resource Control Board’s Low Threat Closure Policy.

IRP Site 8 is an approximately 2.2-acre area located in the northwestern portion of NAF El Centro, off Patrol Road and adjacent to IRP Site 2. The site was constructed in 1958 to store salvaged metals prior to their resale. In 1982, the site was cleared by an outside contractor, but only selected materials were removed, and the remaining materials were abandoned onsite. In 1983, five empty transformers were removed and disposed of off base. An estimated 200 gallons of transformer fluid may have leaked onto the ground prior to removal of the transformers. In addition, an unknown quantity of paint in the form of discarded paint cans and spray paint cans was also disposed of at the site.

IRP Site 8 was first characterized in a 1987 basewide site investigation. A 1991 site inspection assessed the potential for the release of hazardous substances and evaluated the nature of contamination if a release had occurred. Contaminants in soil, including polychlorinated biphenyls were identified, and a removal action was performed in 1998. Approximately 5,500 tons of soil were excavated from the site. All contaminant-impacted soils were transported off-site for disposal and analytical results from confirmation sampling were below cleanup goals. In September 1999, the California Department of Toxic Substances Control approved the no further action recommendation, and the site is closed.

IRP Site 9 is an approximately 0.7-acre area located on the northeastern corner of B Street and North Street. From 1963 to 1983, the site was used to store transformers. IRP Site 9 consists of UST 144 and a portion of Building 744.

IRP Site 9 was first characterized in a 1987 basewide site investigation. A site inspection and data gap study were performed at the site and the data were used in a development of screening risk assessment. Contaminated soil limited to the upper 1-foot of soil was removed from the site, and groundwater was not a medium of concern. Based on the analytical results from the site inspection and risk assessment, the Navy recommended closure of IRP Site 9 with no further action. The Regional Water Quality Control Board concurred with the recommendation for site closure in June 1998.

IRP Site 10 is an approximately 6-acre area located in the northwestern corner of the facility, outside the main boundary fence and immediately north of the operating NAF El Centro sewage and wastewater treatment plant. The site consists of three unlined ponds with earthen-bermed sides. From the 1940s until 1976, the ponds functioned as the only sewage treatment for NAF El Centro. Domestic and industrial sewage flowed into Pond 1, where most solids settled out. The effluent would continue to flow into Ponds 2 and 3, and then to the New River. There is no record that accumulated sludge was removed from the pond bottoms. The ponds were partially covered with thick vegetation until early 2007 when it was removed in preparation for soil sampling activities. Currently, all of the ponds are dry.

IRP Site 10 was first characterized in a 1987 basewide site investigation. A 2004 extended site inspection assessed potential risks to human health and the environment based on analysis of soil samples within the former stabilization ponds and groundwater quality. Cleanup alternatives were evaluated and excavation with offsite disposal was selected as the preferred remedy. A removal action was performed and documented in a 2009 closure report. The Department of Toxic Substances Control concurred for site closure in an October 2009 letter.

IRP Site 11 is an approximately 0.2-acre area located in the southeastern portion of NAF El Centro, south of Runway 12/30. Additional information on the history of the site is not available.

IRP Site 11 is an approximately 0.2-acre area located in the southeastern portion of NAF El Centro, south of Runway 12/30. Additional information on the history of the site is not available.

IRP Site 12 is an approximately 0.04-acre area located in the eastern boundary of NAF El Centro, off Patrol Road. The site was used from 1986 to 1987 as an open burn pit for a variety of debris, resulting in contamination from burned household debris, such as wood, pipes, cans, and jars. The debris was doused with jet fuel, ignited, and allowed to burn to completion.

IRP Site 12 was first characterized in a 1987 basewide site investigation. The result was a recommendation of no further action because the water-bearing fuel was applied immediately before burning and the contents were allowed to burn completely, leading to the finding that any hazardous constituents were burned or volatilized. The human health risk screening in a 1998 data gap study conducted to support the IRP Site 12 recommendation indicated that dioxins were present in the soil at concentrations that potentially cause adverse effects to human health and the environment.

A remedy was recommended to remove the dioxin-contaminated soil. A 2001 removal action report documents the excavation and disposal off-site of approximately 100 cubic yards of dioxin-impacted soil. Confirmation samples from soil and groundwater samples collected following the removal action confirmed that all concentrations of contaminants in both media were below preliminary remediation goals. The site was backfilled with clean, imported soil, and IRP Site 12 was officially closed in 2001 with letters from the Department of Toxic Substances Control and the Regional Water Quality Control Board.

IRP Site 13 is an approximately 0.2-acre area located in the northern portion of NAF El Centro, off Patrol Road. The site was used from 1942 to 1953. Additional information on the history of the site is not available.

IRP Site 13 was first characterized in a 1987 basewide site investigation. A subsequent site inspection and data gap study produced data that were incorporated into a screening risk assessment used to make determinations concerning the presence of contamination at the site. Neither soil nor groundwater contamination was identified, and no cleanup was required. The Navy requested site closure, which was granted in a June 1998 letter from the Regional Water Quality Control Board.

IRP Site 14 is an approximately 16-acre area located in the fuel farm in the southeastern portion of NAF El Centro, off Patrol Road. The site was used from 1960 to 1985 as a fuel farm tank rinsate disposal area where rinsate water and sludge from the tanks were allowed to drain. IRP Site 14 is collocated with IRP Site 15.

IRP Site 14 was first characterized in a 1987 basewide site investigation and then in a 1991 site inspection, which indicated that the site was contaminated solely with petroleum products. This finding placed the site under the CERCLA Petroleum Exclusion, effectively transferring it to the underground storage tank program under Regional Water Quality Control Board oversight. A portion of the site was excavated, and contaminated soil and groundwater were treated using a multiphase extraction system.

Data were collected to assess the effectiveness of soil and groundwater remediation at the fuel farm, concentrations of contaminants were below detection limits, and the site was recommended for closure. The Regional Water Quality Control Board concurred in October 1999 with the Navy’s recommendation for site closure at IRP Site 14.

IRP Site 15 is an approximately 16-acre area located in the fuel farm in the southeastern portion of NAF El Centro, off Patrol Road. The site was used from 1958 to 1981 as a filter cleaning area where spilled fuel was collected in small sumps. IRP Site 15 is collocated with IRP Site 14.

IRP Site 15 was first characterized in a 1987 basewide site investigation and subsequently in a 1991 site inspection, which indicated that the site was contaminated solely with petroleum products. This finding placed the site under the CERCLA Petroleum Exclusion, effectively transferring it to the underground storage tank program under Regional Water Quality Control Board oversight. A portion of the site was excavated, and contaminated soil and groundwater were treated using a multiphase extraction system.

Data were collected to assess the effectiveness of soil and groundwater remediation at the fuel farm, concentrations of contaminants were below detection limits, and the site was recommended for closure. The Regional Water Quality Control Board concurred In October 1999 with the Navy’s recommendation for site closure at IRP Site 15.

IRP Site 16 is an approximately 0.03-acre area located in the southern portion of NAF El Centro, immediately north of Building 565 and south of the medical/dental facility. In 1981, a 130-gallon aboveground storage tank of spent potassium ferricyanide bleach used in color photo processing ruptured and spilled approximately 100 gallons onto the ground. The site was reportedly cleaned up in 1983, but a 1992 investigation reported a bluish-green staining of the soil.

IRP Site 16 was first characterized in a 1987 basewide site investigation. Soil sampling results from a 1992 site inspection detected petroleum hydrocarbons, cyanide, and polychlorinated biphenyls, although none of these contaminants of potential concern were detected at concentrations above levels of concern and no further action was recommended for the site. A 1997 technical memorandum that documented a preconstruction assessment of the vertical and lateral extent of contamination at the site reported concentrations of the contaminants of potential concern below established risk-based action levels.

After soil sampling activities from the preconstruction assessment were completed, the area was restored to original grade with approximately 130 cubic yards of clean, native soil. The site was capped with asphalt and became part of the parking lot adjacent to Building 565. The Department of Toxic Substances Control concurred in a May 1997 letter with a recommendation for site closure at IRP Site 16.

IRP Site 17 is an approximately 0.03-acre area located in the western portion of NAF El Centro, south of 4th Street. The site contains a firefighting pit that was built in 1980 and was used for training sessions approximately once per month until an unknown date. Each session involved several fires and maneuvers, and each fire required several hundred gallons of fuel from a mobile 1,000-gallon tank adjacent to the pit to ignite. Most of the contents of the tank were reportedly used during each session. Although jet fuel was primarily used to ignite and fuel the fires, motor gas, aviation gas, diesel fuel, stove oil, and hydraulic fluid were reportedly also disposed of in the firefighting training area. Approximately 25 gallons of aqueous film-forming foam were used during each session to extinguish the fires.

IRP Site 17 was first characterized in a 1990 preliminary assessment that recommended further action at the site. A human health risk screening from a subsequent 1992 hydrogeological assessment that examined the migration potential of hazardous waste constituents indicated that reported concentrations of contaminants had the potential to cause adverse effects on human health and the environment and recommended further action at the site. A 1998 data gap study followed included analyses for dioxins, a contaminant not previously included. Dioxins were reported at levels above preliminary remediation goals and a remedy that removed dioxin-contaminated soil present at IRP Site 17 was recommended.

A 2001 removal action resulted in excavation of approximately 3,000 cubic yards of contaminated soil and then backfilling of the site with clean, imported soil. Groundwater sampling results were below the maximum contaminant levels, showing that contaminants in soil had not migrated. In December 2001, the Department of Toxic Substances Control concurred that all response actions had been completed and that no further removal or remedial action was necessary, and the site was closed.

IRP Site 18 is an approximately 9.7-acre area located in the northwestern portion of NAF El Centro, west of the sewage stabilization ponds. From the mid-1940s to the mid-1970s, the site was used as the primary disposal area on base for burning and dumping waste materials generated at the installation. IRP Site 18 was reportedly heavily used until 1965 when the Magazine Road Landfill (IRP Site 1) was opened, then sporadically afterward until the mid-1970s.

Environmental investigations at IRP Site 18 began with a 2005 preliminary assessment. Elevated concentrations of metals were detected in soil samples and further investigation was recommended. The results of risk assessments from the preliminary assessment and a 2011 site inspection found that soil at the site posed a potentially unacceptable risk to human health and ecological receptors. A 2016 remedial investigation and 2017 feasibility study evaluated the nature and extent of contamination at the site, potential risks to human health and the environment, and the feasibility of various remedial actions. As a result of the feasibility study, the preferred remedial alternative selected was excavation and offsite disposal of contaminated soil.

A record of decision documenting the Navy’s plan for excavation, disposal, and backfilling at IRP Site 18 was finalized in August 2020. The IRP Site 18 remedial action was completed in 2021. Once the site cleanup objectives are achieved through the selected remedy, a final closure report will be prepared to document the remedial action.

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MRP Site 1 is an approximately 4-acre area located north of the runways in the northeastern corner of NAF El Centro. The range was used on an almost daily basis from 1971 to 1988 by the base skeet club for recreational purposes. Military personnel concurrently used the range for shotgun proficiency and moving target orientation training. The site consisted of a firing arc, target area, and impact area. MRP Site 1 is no longer used, and desert scrub vegetation has been re-established approximately 200 feet northeast of the firing arc.

MRP Site 1 was first characterized in a 2005 basewide range preliminary assessment. A 2009 site inspection of NAF El Centro ranges assessed whether historical range activities had affected MRP Site 1 and three other ranges, resulting in the release of munitions constituents, including explosives and metals, and whether further response actions would be required. The site inspection report concluded that the detections of metals, specially lead and arsenic, at concentrations above the project action limits were localized.

A 2018 remedial investigation evaluated the nature and extent of contamination at the site and potential risks to human health and the environment. The investigation report found no unacceptable risks to human health or the environment under current and potential future use scenarios at MRP Site 1, and recommended no further action, and the Navy published a proposed plan in 2019 documenting the recommendation for the site. The no further action record of decision was finalized in 2020 for unrestricted use and unlimited exposure at MRP Site 1.

MRP Site 2 is an approximately 4-acre area located north of the runways along the northern boundary of NAF El Centro. The site consisted of 10 firing positions and targets located at various fixed distances and was used from 1942 to the 1980s for small arms training and periodic requalification. Desert scrub vegetation has been reestablished on most of the former range, which is closed and no longer in use.

MRP Site 2 was first characterized in a 2005 basewide range preliminary assessment. A 2009 site inspection of NAF El Centro ranges assessed whether historical range activities had affected MRP Site 2 and three other ranges, resulting in the release of munitions constituents, including explosives and metals, and whether further response actions would be required. The site inspection report concluded that lead detected in two locations at concentrations above preliminary remediation goals did not appear to be widespread, although further investigation of lead debris observed at the site was recommended.

A 2018 remedial investigation evaluated the nature and extent of contamination at the site and potential risks to human health and the environment. The report recommended an evaluation of remedial or removal action alternatives that address lead in soil that may pose unacceptable risk to hypothetical future residents. Because a removal action was determined to be appropriate, the Navy prepared an evaluation/cost analysis for a non-time critical removal action to address lead-containing soil at MRP Site 2. The preferred alternative was determined to be excavation and offsite disposal. The Navy’s removal action work plan was approved by the Department of Toxic Substance Control in July 2022.

MRP Site 3 is an approximately 640-acre area located northwest of NAF El Centro. The site comprises the Navy-owned portion of the Carrizo Impact Area, of which 26,360 acres was transferred to the State of California. MRP Site 3 was used for a variety of both small arms and various explosive ordnance target practice. Dates of operation are unknown, although sweeps of the impact area by Navy explosive ordnance disposal personnel that located munitions and explosives of concern were first conducted in 1959 after the site was closed and were repeated periodically into the 1990s. Referred to as the Carrizo Impact Area 2, the larger State of California-owned tract that is northwest of the smaller MRP Site 3 is being addressed under the federal Formerly Used Defense Site Program.

MRP Site 3 was first characterized in a 2005 basewide range preliminary assessment and subsequently in a 2007 site-specific assessment. A 2007 airborne geophysical survey located munitions-related materials and detected a total of 1,438 magnetic anomalies. A 2008 site inspection provided a comprehensive review of the former Carrizo Impact Area concluded that munitions and explosives of concern and contamination from munitions constituents were present and recommended further investigation. The Navy plans to coordinate with the State of California to adopt similar remedial investigation approaches for both MRP Site 3 and Carrizo Impact Area 2, the two contiguous portions of the former total Carrizo Impact Area.

MRP Site 4 is an approximately 10-acre area located north of the runways, near the boundary of NAF El Centro. The site consists of a turret range and a skeet range and was used from 1943 to 1952 for small arms training, including machine gun familiarization, shotgun proficiency, and moving target orientation. The turret range included several truck-mounted turrets and fixed mounted machine gun positions, with firing directed north from the firing line. The skeet range was a single field shotgun range, with skeet shooting to the north of the firing arc. The ranges were closed following the end of World War II, and the demolition and removal of the range structures occurred prior to 1977.

MRP Site 4 was first characterized in a 2005 basewide range preliminary assessment. A 2009 site inspection of NAF El Centro ranges assessed whether historical range activities had affected MRP Site 1 and three other ranges, resulting in the release munitions constituents, including explosives and metals, and whether further response actions would be required. The site inspection report concluded that metals detected at concentrations were above the project action limits at three locations and polycyclic aromatic hydrocarbon concentrations exceeding regulatory limits were widespread throughout the site.

A 2018 remedial investigation evaluated the nature and extent of contamination at the site and potential risks to human health and the environment. The investigation report recommended an evaluation of remedial alternatives that address antimony, arsenic, lead, and polycyclic aromatic hydrocarbon compounds in soil at concentrations that may pose unacceptable risk to human health and ecological receptors. A 2023 feasibility study proposed five remedial alternatives that will be presented to the public for comment in a proposed plan. The Navy is proceeding with the CERCLA process at MRP Site 4, which is expected to a record of decision for the selected remedy.

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