Marine Corps Logistics Base Barstow

OU 1 comprises CAOC 37 and includes groundwater impacted by volatile organic compounds, primarily tetrachloroethylene and trichloroethylene, below and immediately surrounding Yermo at MCLB Barstow. The OU 1 groundwater plume has historically been divided into three comingled plumes: 1) the former CAOC 26 plume, 2) the former Yermo South plume, and 3) the Yermo North plume.

Remedial investigation activities for OU 1 groundwater were conducted between February and December of 1992. The phase I remedial investigation identified the presence of volatile organic compounds exceeding federal and state drinking water standards in the groundwater at Yermo Annex. The OU 1 groundwater volatile organic compound plumes were associated with potential sources identified as CAOCs 26, 15/17, 23, 26, and 35. Phase II remedial investigation activities conducted in 1994 focused on defining the vertical and lateral extent of the groundwater contamination.

In 1996, the Navy implemented administrative measures and installed active groundwater remediation systems pursuant to protectiveness measures and remedial action objectives specified in the OU 1 and 2 record of decision. Current remedial systems designed to treat OU 1 contamination primarily consist of downgradient groundwater extraction, both in-situ and ex-situ treatment, and upgradient reinjection of treated groundwater via the groundwater extraction and treatment system. While operation of these systems has satisfied remedial action objectives at the Yermo South and CAOC 26 plumes, remaining contaminants in the Yermo North plume may indicate additional source areas.

The Navy is currently pursuing additional site characterization activities targeting evaluations of the nature and extent of the emerging contaminants per- and polyfluoroalkyl substances, commonly referred to as PFAS. A preliminary assessment was conducted for OU1, followed by a 2019 site inspection. Based on the results, a draft remedial investigation work plan is currently under development for further investigation because PFAS-containing materials were potentially handled, stored, used, or released in specifically identified areas.

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OU 2 comprises CAOC 38 and includes groundwater impacted by volatile organic compounds underlying Nebo Main Base. OU 2 includes separate Nebo North and Nebo South dissolved volatile organic compound plumes.

Groundwater remedial investigation activities for OU 2 were conducted between February and December of 1992. The phase I remedial investigation identified the presence of volatile organic compounds exceeding federal and state drinking water standards in the groundwater at Nebo Main Base. The primary contaminants of concern are tetrachloroethylene in the Nebo North plume and trichloroethylene in the Nebo South plume. Phase II remedial investigation activities conducted in 1994 focused on defining the vertical and lateral extent of the groundwater contamination.

In 1996, the Navy implemented administrative measures and installed active groundwater remediation systems pursuant to protectiveness measures and remedial action objectives specified in the OU 1 and 2 record of decision. Concentrations of contaminants of concerns in the source area of the Nebo North Plume have been reduced to below applicable maximum contaminant levels, and groundwater remediation systems have been decommissioned. The Nebo South remediation system continues to operate to prevent the off-base migration of the remaining contaminant plume.

The Navy is currently pursuing additional site characterization activities targeting evaluations of the nature and extent of the emerging contaminants per- and polyfluoroalkyl substances, commonly referred to as PFAS. A preliminary assessment was conducted for OU1, followed by a 2019 site inspection. Based on the results, a draft remedial investigation work plan is currently under development for further investigation because PFAS-containing materials were potentially handled, stored, used, or released in specifically identified areas.

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OU 3 addresses shallow soil contamination at Yermo Annex. Within OU 3, there are four CAOCs: CAOC 18, CAOC 20, CAOC 23, and CAOC 34. Groundwater monitoring at CAOCs 20 and 23 is performed as part of OU 1 remedial activities. Additional information for the specific CAOCs within OU 3 is provided below.

CAOC 18 – Sludge Waste Disposal Area

CAOC 18, the Sludge Waste Disposal Area, is north of 12th Street and east of Building 573, on the eastern side of the Yermo Annex. The unpaved 6-acre area is adjacent to the eastern edge of OU 5, CAOC 36, the vehicle repair and storage area of the Central Repair Division. Potential sources of contaminants at CAOC 18 are miscellaneous industrial wastes from the Central Repair Division reportedly discharged between 1961 through the late 1970s directly to the bottom surface of an unlined channel that runs through the middle of CAOC 18. The area is currently used for vehicle storage.

In 1989, CAOC 18 was included as part of OU 3 remedial investigation and feasibility study. During the remedial investigation, human health and ecological risk assessments were conducted and were considered not to pose a significant potential risk to human health or the environment under the industrial land-use scenario. The remedy for CAOC 18 selected in the 1997 record of decision for OU 3 and 4 was the no action alternative and does not include land use controls.

CAOC 20 – Second Hazardous and Low-Level Radiological Area

CAOC 20 is located on the eastern side of the Yermo Annex. This site is bounded on the east and southeast by CAOC 21, the Industrial Waste Disposal Area and the CAOC 23 Landfill Area, and by railroad tracks to the north and south. CAOC 20 includes low-level radiological waste disposal wells capped by a concrete pad and surrounded by a chain-link fence, which is designated as S-596, and 31 uncapped nonradioactive waste disposal wells. The wells are approximately 30 feet deep and 4 feet in diameter. Potential sources of contaminants at CAOC 20 include low-level radiological waste, which was reportedly buried in S-596, and non-radioactive waste, which was buried in the 31 disposal wells between 1953 and 1975.

CAOC 20 was divided into three strata consisting of documented and suspected contamination sources. The remedial investigation was completed in a single-phase field investigation of the three strata from March to October 1992.

The remedy for CAOC 20 Strata 1 and 2 selected in the 1997 record of decision for OU 3 and 4 included land use controls as well as groundwater monitoring implemented under the record of decision for OU 1 and 2. Additional land use controls include maintaining drainage controls to promote surface runoff and minimize standing water directly above buried wastes. CAOC 20 is subject to the CERCLA five-year review process. A no further action remedy was selected for CAOC 20, Stratum 3 because it does not contain buried waste and thus requires no remedial action.

CAOC 23 – Landfill Area

CAOC 23, known as the Landfill Area, is an irregular L-shaped area located at the south to southeast corner of the Yermo Annex between the railroad tracks that serve the warehouse areas and the perimeter fence surrounding the industrial operations. This area is approximately 5,000 feet long, 400- to 500-feet wide, and comprises approximately 60 acres. The topography across the landfill area is slightly sloped and is generally shaped by landfill activities. Potential sources of contaminants at CAOC 23 include solid waste and some hazardous liquid wastes that were disposed of between 1946 and 1980 when the CAOC operated as a storage area for waste and rollback equipment.

CAOC 23 was divided into six strata consisting of documented and suspected contamination sources. Previous investigations confirmed that Stratum 2 and the southern portion of Stratum 1 were used in the past for landfilling activities. This area is referred to as Zone 1. Additionally, low levels of polychlorinated biphenyls and pesticides are in the surface soils of Stratum 5.

The remedy for CAOC 23 selected in the 1997 record of decision for OU 3 and 4 included construction of a concrete cap at Zone 1 and land use controls for the southern portion of Strata 1 only, as well as groundwater monitoring implemented under the record of decision for OU 1 and 2. Strata 1 is also subject to the CERCLA five-year review process.

CAOC 34 – PCB Storage Area

CAOC 34, the PCB Storage Area, is former Building S-345 located on the eastern side of the Yermo Annex adjacent to the western side of the MCLB Effluent Disposal Pond, the location of Building 426. The PCB Storage Area consisted of two separate concrete basins. The western basin is labeled Basin A and the eastern basin is Basin B. Both were constructed directly over the wastewater effluent ponds of the former MCLB Domestic Wastewater Treatment Facility. Potential sources of contamination at CAOC 34 included leakage or spillage from transformers and drums of polychlorinated biphenyl-contaminated sludges and oils stored within the basins.

CAOC 34 was divided into three strata consisting of documented and suspected contamination sources. A remedial investigation was conducted between March and October 1992 and in January 1994. The area adjacent to and surrounding CAOC 34 was selected in December 1994 as the site for construction of a new industrial wastewater treatment and recycling facility. A time critical removal action was implemented to excavate all soils in the basins and demolish the concrete basins.

Following the removal action, CAOC 34 was considered protective of human health and the environment because excavations removed the contaminated soil and the treatment plant foundation. The remedy for CAOC 34 selected in the 1997 record of decision for OU 3 and 4 was the no action alternative, which does not include institutional or engineering controls or containment, excavation, or treatment technologies.

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OU 4 addresses shallow soil contamination at Nebo Main Base. Within OU 4, there are four CAOCs. These include CAOC 2, CAOC 5, CAOC 9, and CAOC 11. Groundwater monitoring is not performed at OU 4. Additional information for the specific CAOCs within OU 4 is provided below.

CAOC 2 – Pesticide Storage and Washout Area

CAOC 2, the Pesticide Storage and Washout Area, is located on the north side of Nebo. The facility is bounded by an access road and railroad tracks on the south, oxidation ponds on the east, and an unlined drainage channel and the MCLB golf course on the west. CAOC 2 covers about 1.8 acres of relatively flat terrain. The surrounding yard is open, unpaved, and covers about 1.3 acres. At the time of the remedial investigation, the facility had 10 buildings and 2 rectangular, concrete 15- x 20-foot wash pads used for equipment storage, cleaning and repair, pesticide and herbicide storage, and other operations related to MCLB yard maintenance.

CAOC 2 was divided into four strata consisting of documented and suspected contamination sources, which include pesticide spills, wash pads, and drainage pathways. The remedial investigation at CAOC 2 was completed in a single-phased field investigation of the four strata between March and October 1992. Pesticides were detected in Strata 2 and considered a potential significant health threat to MCLB workers. A time critical removal action was completed at Strata 2 to excavate pesticide contaminated soil.

Following the removal action, CAOC 2 was considered protective of human health and the environment. The remedy for CAOC 2 soils selected in the 1997 record of decision for OU 3 and 4 was the no action alternative, which does not involve institutional or engineering controls or containment, excavation, or treatment technologies.

CAOC 5 – Chemical Storage Area

CAOC 5, the Chemicals Storage Area, is in the southeastern portion of Nebo, north of CAOC 7, the Drum Storage Area and Landfill, northwest of CAOC 6, the Original Trash Landfill, and south of Joseph Boll Avenue. The CAOC includes three lots, Lot 351, 352, and 357, which encompass a total area of about 50 acres. Interstate 40 crosses Lot 352, the southern part of the CAOC. From 1948 to 1978, the area was used to store rollback equipment and hazardous chemicals. A one-ton spill of the insecticide DDT was reported to have occurred at Lot 351 between 1976 and 1977.

CAOC 5 was divided into three strata consisting of documented and suspected contamination sources. The remedial investigation for CAOC 5 was conducted in two phases during 1992 and 1994. Phase I activities consisted of scoping, stratum definition, reconnaissance, and a soil and geologic investigation. Phase II activities were limited to field screening for polychlorinated biphenyls in Lots 351 and 357.

As a result of the findings of the remedial investigation, CAOC 5 was considered protective of human health and the environment because polychlorinated biphenyl levels were below regulatory levels and are similar to basewide levels. The remedy for CAOC 5 soils selected in the 1997 record of decision for OU 3 and 4 was the no action alternative, which does not include institutional or engineering controls or containment, excavation, or treatment technologies.

CAOC 9 – Fuel Disposal Area

CAOC 9, the Fuel Disposal Area, encompasses a small, unpaved area approximately 150 by 250 feet in the southwest corner of Nebo Main Base, just west of CAOC 7, the Drum Storage Area and Landfill, and the Amphibious Vehicle Testing Area also known as the Fish Pond. In the 1950s, waste fuel and oil were discharged to the ground surface in an arroyo along the south perimeter of Nebo Main Base. An estimated 120,000 gallons of gasoline, diesel fuel, and lubrication oil were disposed of by this method. The 1983 initial assessment study conducted at MCLB Barstow stated that the potential for off-site migration was low because of volatilization of the lighter fuel fractions, immobilization and biodegradation of the heavier fuel fractions, and overall site conditions, mitigating the threat to human health or the environment at CAOC 9.

The remedy selected for CAOC 9 soils in the 1997 OU 3 and 4 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The remedy is considered protective of human health and the environment because risk levels are below the target human health risk range, no groundwater impacts resulted from contaminant detections, and low levels of contaminants detected would not have an adverse impact on ecological receptors.

CAOC 11 – Fuel Burn Area

CAOC 11, the Fuel Burn Area, is in the southwest corner of the Nebo Main Base, between Structure S-189, the tank farm area, to the north and Structure-72, aboveground water storage tank to the south. The site is accessed via a dirt road off Guam Avenue. The area measures approximately 240 by 680 feet and is relatively flat with no structures or significant surficial features. The potential source of contaminants at CAOC 11 is the approximately 1,000 gallons per week of waste fuels and oils reportedly discharged to the ground and burned at the site from the 1940s to the 1960s.

A remedial investigation was conducted in two phases at CAOC 11 during 1992 and 1994. As a result of the findings of the remedial investigation, CAOC 11 was considered to be in a protective state. The remedy for CAOC 11 soils selected in the 1997 record of decision for OU 3 and 4 was the no action alternative, which does not include institutional or engineering controls or containment, excavation, or treatment technologies.

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OU 5 addresses shallow soil contamination at Yermo Annex. Within OU 5 there are 15 CAOCs. These include CAOCs 15/17, 16, 19, 21, 22, 24, 26, 27, 28, 29, 30, 31, 32, 35 (Stratum 2 and the eastern portion of Stratum 1), and 36. Groundwater monitoring at CAOCs 15/17, 16, 26, and 35 is performed as part of OU 1 remedial activities. Additional information for the specific CAOCs within OU 5 is provided below.

CAOC 15/17 – Oil Storage/ Spillage and Industrial Wastewater Treatment Plant Areas

CAOC 15, the Oil Storage/Spillage and Industrial Wastewater Treatment Plant Areas, is in the northern part of the Yermo Annex, north of Building 573. This CAOC was originally described in the 1983 initial assessment study at MCLB Barstow as an area that extended north and east of the temporary evaporation basin at CAOC 17. Defueling operations took place in this area, where an estimated 4,000 drums of waste oil from recommissioned vehicles and new lubricating oil were stored. CAOC 17 is directly south of CAOC 35, the Yermo Class III Landfill, and partially overlaps CAOC 15, the Oil Storage/Spillage Area. CAOC 17 encompasses 14 evaporation basins, four sludge drying beds, a temporary pond, three oxidation ponds, and the overflow area around the ponds. The combined size of CAOCs 15 and 17 is 13 acres.

Potential sources of contamination at CAOC 15/17 include the reported discharge of industrial wastes to unlined and lined ponds, and storage of sludge in the drying beds. CAOC 15/17 was divided into six strata consisting of documented or suspected contaminated sources. A remedial investigation was completed to collect additional soil samples. As a result of the findings of the 1996 remedial investigation, CAOC 15/17 was considered protective of human health and the environment. The remedy for CAOC 15/17 soils selected in the 1998 record of decision for OU 5 and 6 was the no action alternative and does not include institutional or engineering controls or containment, excavation, or treatment.

CAOC 16 – Building 573 and Perimeter Area

CAOC 16, Building 573 and Perimeter Area, located in the northeast quadrant of the Yermo Annex, consists of the Maintenance Center Barstow and its perimeter area comprising approximately 60 acres. Building 573 is the main facility of the Base Repair Division. The floor of Building 573 is approximately 10 acres in area and the perimeter area is covered by a concrete hardstand slab at least 10 inches thick. The hardstand provides an effective barrier from encountering any contaminated soils. In the past, most liquid waste generated during repair operations were transported from Building 573 to CAOC 15/17, the former Industrial Wastewater Treatment Plant. via an underground industrial drainage system. Sections of the pipeline leading to the former treatment plant were found to have been breached, allowing release of liquids into the subsurface. The broken pipeline sections are considered to be the main source of vadose zone and groundwater contamination at CAOC 16. Five underground storage tanks around Building 573, removed in 1992 as part of a separate program, were also found to have contributed to site contamination.

The 1996 remedial investigation findings identified volatile organic compound contamination believed to be present in the vadose zone beneath CAOC 16. In addition, there may be localized areas of non-volatile organic compound contamination such as metals, polychlorinated biphenyls, and semi-volatile organic compounds that were not specifically characterized as part of the remedial investigation.

The remedy for CAOC 16 soils selected in the 1998 record of decision for OU 5 and 6 was institutional controls put in-place to maintain the existing concrete hardstand. The record of decision stipulates that no breaching of the concrete hardstand may occur, except for routine maintenance purposes. Groundwater remedial actions are being performed under OU 1. CAOC 16 is subject to the CERCLA five-year review process.

CAOC 19 – First Hazardous and Low-Level Radiological Area

CAOC 19, the First Hazardous and Low-Level Radiological Area, is located near the center of the Yermo Annex southeast of Building 598. The CAOC consists of approximately 10,000 square feet on which hazardous materials and low-level radiation equipment such as luminous dials containing radium and tritium isotopes were previously stored. The 1983 initial assessment study performed at MCLB Barstow speculated that hazardous materials and low-level radiation equipment may have been buried here as well, although no documentation was discovered to verify any burial of wastes. The initial assessment study states that the site was not intended for permanent disposal of hazardous materials and materials were stored at the surface temporarily and removed during rollback operations after both World War II and the Korean conflict. Documentation was not available regarding the types or amounts of wastes and equipment that may have affected this CAOC.

The remedy selected for CAOC 19 soils in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 19 remedy is considered protective of human health and the environment because risk levels are below the target human health risk range, no groundwater impacts resulted from residual soil contamination, there is little evidence of radioactive contamination, and no sensitive species or sensitive habitats would be affected by the contamination at CAOC 19.

CAOC 21 – Industrial Waste Disposal Area

CAOC 21, the Industrial Waste Disposal Area, is located on a flat, open unpaved area near Gate 5 at the eastern perimeter of the Yermo Annex. The site contains several concrete pads from previously existing barracks and the S-530 electrical substation located in the eastern portion of the site. An unlined drainage channel borders the southern portion of CAOC 21. A UST in the western portion of CAOC 21 was removed in June 1992. CAOC 21 is not an active site.

CAOC 21 was divided into four main strata consisting of documented and suspected contamination sources, including an old firefighting area, an electrical substation, an underground storage tank, and a liquid waste discharge area. A removal action was completed in Strata 1, 1a, and the drainage channel to address residual polychlorinated biphenyl and furan contamination. All soils containing polychlorinated biphenyls at concentrations greater than 1 milligram per kilogram were excavated, removed, and transported off-site for disposal. Detections of polychlorinated biphenyls in Strata 1b, 2, and 4 were below the regulatory levels.

The remedy for CAOC 21 soils selected in the 1998 record of decision for OU 5 and 6 was the no action alternative, which does not include institutional or engineering controls, containment, excavation, or treatment.

CAOC 22 – Domestic Wastewater Disposal Area

CAOC 22, the Domestic Wastewater Disposal Area, is in the southeastern portion of the Yermo Annex, adjacent to the eastern property boundary. The site consists of three unlined percolation ponds that were used for disposal of treated wastewater at Yermo Annex. The ponds first received effluent from the old domestic wastewater treatment plant in 1952. Throughout their historical use, the unlined percolation ponds received treated effluent from both the old domestic wastewater treatment plant that operated from 1952 to 1976 and the new plant in operation since 1976. The three unlined percolation ponds and the associated overflow area of CAOC 22 comprise approximately 4 acres. The contaminants of potential concern at CAOC 22 included organic and inorganic domestic and industrial waste constituents and pesticides.

CAOC 22 was divided into two strata consisting of documented and suspected contamination sources, including the percolation ponds and the overflow area. Results of a 1996 remedial investigation sampling effort identified volatile organic compounds, pesticides, and metals as potentially site related contaminants. No polychlorinated biphenyls or semi-volatile organic compounds were detected.

The remedy selected for CAOC 22 soils in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 22 remedy is considered protective of human health and the environment because concentrations of metals were below background or would not impact groundwater, contaminants remaining in the soils do not threaten groundwater or surface water quality, risk levels are below the target risk range or within an acceptable range, and no species or sensitive habitats would be affected by the contamination at CAOC 22.

CAOC 24 – The Tracked Vehicle Test Area

CAOC 24, the Tracked Vehicle Test Area, is an elliptical area of approximately 4,500 by 500 feet in the southwestern portion of the Yermo Annex. The area was used to test drive various types of tracked vehicles. Waste oils and industrial wastewaters were sprayed onto the surface of the track area to control the wind erosion of the sandy subgrade, to suppress dust, and to help form the vehicle test track. These sprayed materials are referred to as "dust suppression" and "desert mix" materials. The contaminants of potential concern at this CAOC included the constituents of waste oils and solvents such as heavy metals, polyaromatic hydrocarbons, and possibly polychlorinated biphenyls.

A 1996 remedial investigation sampling effort identified semi-volatile organic compounds, one pesticide, and total petroleum hydrocarbons as diesel in soils at CAOC 24. The remedy for CAOC 24 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 24 remedy is considered protective of human health and the environment because no volatile organic compounds were detected in any of the soil samples, low levels of semi-volatile organic compounds were below risk-based criteria values, metals are present at concentrations below or of minor concern to human health, and low levels of contaminants would not impact groundwater.

CAOC 26 – Building 533 Waste Disposal Area

CAOC 26, the Building 533 Waste Disposal Area, encompasses Building 533 which is the Packaging and Maintenance Shop, and the area around the building. This CAOC is in the west-central portion of the Yermo Annex, south of CAOC 27 and east of CAOC 28. The shop consisted of a waterfall-type paint booth, several dip tanks for cleaning and preservation operations, a vapor degreaser, and a sandblasting unit. According to the 1983 initial assessment study conducted at MCLB Barstow, wastes generated at this site included petroleum solvents, trichloroethylene, waste oil, and preservatives. The perimeter area of Building 533 contains a steam cleaning rack, an oil/water separator, a concrete sump to the north, a pad area that formerly housed a transformer, and a French drain area. The French drain was removed in 1992.

CAOC 26 was divided into six strata consisting of documented and suspected contamination sources from Building 533 activities. A phase I soil sampling effort was performed and determined that further sampling was necessary to characterize the vadose zone in support of the OU 1 program. Following a remedial investigation, CAOC 26 soils were found to be protective of human health and the environment.

The remedy for CAOC 26 soils selected in the 1998 record of decision for OU 5 and 6 was the no action alternative, which does not include land use controls, containment, excavation, or treatment.

CAOC 27 – Building 436 Fuel Storage Area

CAOC 27, the Building 436 Fuel Storage Area, encompasses approximately 1.5 acres in the north-central portion of the Yermo Annex and includes the former location of Building 436 and the boiler plant, which has been decommissioned. Four underground storage tanks and associated underground piping were located in this CAOC. Three of these underground storage tanks were removed in 1992 under the base underground storage tank program. Other potential sources of contamination at the site included a steam cleaning pad, oil interceptor, and boiler blowdown sump. The contaminants of potential concern at CAOC 27 included petroleum hydrocarbons and heavy metals.

A phase I soil sampling effort was performed at CAOC 27. Volatile organic compounds, semi-volatile organic compounds, pesticides, and polychlorinated biphenyls were detected at levels lower than residential soils values.

The remedy for CAOC 27 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 27 soil remedy is considered protective of human health and the environment because contaminants in soil were detected at levels below screening values or are present at concentrations of minor concern, no groundwater impacts result from contaminant detections under CERCLA, and no sensitive species or habitat would be affected by CAOC 27.

CAOC 28 – West Lot, Dust Control Area

CAOC 28, the West Lot, Dust Control Area, is in the northwestern quadrant of the Yermo Annex, which is west of the main industrial facilities. Various storage activities took place at CAOC 28 between 1965 and 1978. A review of historical records revealed that the site was used for storage, maintenance-related activities, and railroad-related activities. Wastewater and waste oil were applied at this CAOC to suppress dust. The waste oil came from various operations at the Base. An asphalt-like material designated "desert mix” was also applied to the site for dust control. Additionally, wastewater from the ponds at the base sanitary wastewater treatment plant was sprayed on this site to control dust. The contaminants of potential concern at CAOC 28 included constituents of waste oils, solvents, heavy metals, polyaromatic hydrocarbons, and polychlorinated biphenyls.

A phase I soil sampling effort was performed at CAOC 28. Results indicated that that risk levels were below the target risk range. The remedy for CAOC 28 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 28 remedy is considered protective of human health and the environment because risk levels are below the target risk range, no sensitive species or habitat would be affected by the contamination, no risk to human health exists, and contaminants would not impact the groundwater.

CAOC 29 – Sludge Storage Area

CAOC 29, the Sludge Storage Area, is in the northwestern corner of Yermo Annex adjacent to CAOC 28. The site encompasses approximately 2.5 acres, including two unspecified 0.5-acre areas where sludge was stored. The sludge was generated from the ponds associated with the sanitary wastewater treatment plant, which was designed originally to treat domestic waste, although hazardous waste of unknown industrial origin and quantity eventually was taken to the plant and processed into the subject sludge. The contaminants of potential concern at CAOC 29 included organic and inorganic constituents of the sludge from the domestic waste ponds and the industrial hazardous waste.

A phase I soil sampling effort was performed for CAOC 29. No volatile organic compounds, polychlorinated biphenyls, or pesticides were detected in soil. The remedy for CAOC 29 soils selected in the 1998 record of decision for OU 5 and 6 was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 29 soils remedy is considered protective of human health and the environment because risk levels are below the target risk range, no sensitive species or habitat would be affected by the contamination at CAOC 29, and the contaminants would not impact the groundwater.

CAOC 30 – Locomotive Repair Shop Disposal Area

CAOC 30, the Locomotive Repair Shop Disposal Area, encompasses approximately 1 acre in the northwest portion of the Yermo Annex. This site contains the present location of Building 628, the Locomotive Repair Shop, and the now defunct Building 479, the former Repair Shop. Minor repairs to locomotives are performed at the facility inside Building 628. Repairs and maintenance include steam cleaning, draining fluids, lubricating parts, and changing oil. The facility includes a repair pit and a collection sump. A small woodshed was located south of Building 628 and prior to being dismantled covered an oil/water separator. An underground storage tank in the immediate vicinity but outside the CAOC 30 boundary was removed in 1992 under a separate program. The contaminants of potential concern at this CAOC included pesticides and petroleum hydrocarbons.

A phase I soil sampling effort was performed for CAOC 30. The results led to a finding that risk levels were below the target risk range. The remedy for CAOC 30 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 30 soil remedy is considered protective of human health and the environment because risk levels are below the target risk range, no sensitive species or habitat would be affected by the contamination at CAOC 30, and contaminants remaining in the soils do not threaten to impact the quality of groundwater or surface water.

CAOC 31 – North Vehicle Test Track Road

CAOC 31 is the North Vehicle Test Track Road, located within Lot 486 in the north-central portion of Yermo. This area is used to test various types of tracked vehicles. CAOC 31 consists of approximately 6,500 linear feet of unpaved test track to which waste oil and industrial wastewater effluent were applied to alleviate the dust, as was done at CAOC 28. The waste oil was spread throughout the area of the track and was used in road construction. The contaminants of potential concern at this CAOC included the constituents of waste oils such as heavy metals, polyaromatic hydrocarbons, and possibly polychlorinated biphenyls.

A phase I soil sampling effort was conducted for CAOC 31. No semi-volatile organic compounds, polychlorinated biphenyls, or cyanide were detected in soil. Only low levels of pesticides and total petroleum hydrocarbons as diesel were detected but all were below the target risk range.

The remedy for CAOC 31 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 31 soil remedy is considered protective of human health and the environment because risk levels are below the target risk range, no sensitive species or habitat would be affected by the contamination at CAOC 31, and contaminants remaining in the soils do not threaten to impact the quality of groundwater or surface water.

CAOC 32 – Preservation and Packaging Storage Area

CAOC 32, the Preservation and Packaging Storage Area, is in the north-central portion of the Yermo Annex and comprises approximately 1.5 acres. The CAOC encompasses Building 203, which is the Preservation Shop, and the perimeter, a drum storage area, an operating steam wash rack, a sump and associated piping, and the former location of an excavated underground storage tank. The area west of Building 203 was reportedly used to store drums containing hazardous materials. Operations at the facility consist of the preservation of military equipment for long-term storage using a light petroleum-based oil and de-preservation after long-term storage. Waste streams generated at this shop consist of diesel/preserving oil mixtures, waste automotive fluids, equipment steam cleaning wastes, and spill cleanup wastes. The contaminants of potential concern at this CAOC included constituents of waste oils and solvents, heavy metals, petroleum hydrocarbons, polyaromatic hydrocarbons, and polychlorinated biphenyls.

CAOC 32 was divided into four sampling strata where known or suspected sources of contaminants of potential concern have been identified. A phase I and II soil sampling effort was conducted. Findings indicated that no groundwater was impacted, and soil sample results were below the regulatory level.

The remedy for CAOC 32 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 32 soil remedy is considered protective of human health and the environment because detected polychlorinated biphenyl concentrations were below the guidance level, no groundwater impacts result from contaminant detections, and no sensitive species or sensitive habitats would be affected by the contamination found at CAOC 32.

CAOC 35 – Class III Landfill

CAOC 35, Class III Landfill, is an inactive 17.4-acre landfill in the northeastern portion of Yermo. The landfill was designated as Class III and was permitted to accept nonhazardous waste by the Regional Water Quality Control Board, Lahontan Region. The wastes deposited at the site consisted primarily of household refuse from the Yermo Annex and Nebo Main Base, with commercial and industrial waste consisting of wood, paper, and plastic packing materials. The primary contaminants of concern in soil at CAOC 35 are volatile organic compounds, semi-volatile organic compounds polyaromatic hydrocarbons, petroleum hydrocarbons, and polychlorinated biphenyls.

CAOC 35 was divided into two strata consisting of documented and suspected contamination sources, including the landfill area and adjacent anomaly area. The remedy for CAOC 35 selected in the 1998 record of decision for OU 5 and 6 included a soil cap for the western and central area of Stratum 1, also identified as Zone 1. After construction of the cap was completed, institutional controls were implemented at this site. The record of decision stipulates that land use at CAOC 35 Zone 1 is restricted to activities that cannot disrupt the physical or structural integrity of the soil cap. Further, no excavation of soils may occur at CAOC 35 Zone 1 below a 5-foot depth unless prior approval is obtained. The record of decision selected the no action alternative for Stratum 2 and the eastern portion of Stratum 1. CAOC 35 is subject to the CERCLA five-year review process.

CAOC 36 – Proposed Paint Combat Vehicle Maintenance Shop

CAOC 36, the Proposed Paint Combat Vehicle Maintenance Shop, is in the eastern portion of the Yermo Annex, approximately 200 feet northeast of Building 573 and southeast of the industrial waste treatment plant. This CAOC encompasses approximately 1.5 acres. The area was assumed to be associated with waste-handling and storage for activities associated with Building 573. Historic aerial photos from the 1960s to 1991 indicated that heavy equipment and drums were stored at the site. The site is covered with a 10-inch-thick concrete pad. The contaminants of potential concern at CAOC 36 included petroleum hydrocarbons.

A phase I soil sampling effort was performed. The presence of low-level phthalates, a single detection of trace-level pesticides, and metals were identified but all were below the regulatory level.

The remedy for CAOC 36 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 36 soil remedy is considered protective of human health and the environment because the results of the human health risk assessment found no risk to human health from the chemicals of concern in the soils at CAOC 36, the potential for leaching of the contaminants to groundwater would not impact the groundwater, and the low levels of organics and inorganics detected would not negatively affect the environment.

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OU 6 addresses shallow soil contamination at Nebo Main Base. Within OU 6 there are nine CAOCs. These include CAOCs 1, 3, 4, 6, 7, 8, 12, 13, and 14. Remedial action and groundwater monitoring at CAOC 6 is performed as part of OU 2 remedial activities. Additional information for the specific CAOCs within OU 6 is provided below.

CAOC 1 – Landfill North of Golf Course

CAOC 1, the Landfill North of the Golf Course, is in the northern portion of the Nebo Main Base. The site encompasses approximately 18 acres, including a reported sludge disposal area that was identified during a site visit. From the late 1940s to the mid-1970s the site was used as a landfill for disposal of road construction debris, concrete, asphalt, and other materials to prevent erosion and flooding from the Mojave River. Quantities of waste sludge reportedly disposed of at CAOC 1 could not be verified. The 1983 initial assessment study estimated that 900 tons of dry wastewater treatment plant sludge were disposed of in the area bounded by the golf course, the oxidation ponds, and the Mojave River.

CAOC 1 was divided into three strata consisting of documented and suspected contamination sources, including the landfill area, a suspected landfill area, and the sludge disposal area. A 1996 remedial investigation was completed and concluded that CAOC 1 soil was considered protective of human health and the environment. The remedy for CAOC 1 soils selected in the 1998 record of decision for OU 5 and 6 was the no action alternative.

CAOC 3 – Wastewater Disposal Area

CAOC 3, the Wastewater Disposal Area, is in the northern portion of Nebo, adjacent to the southern boundary of CAOC 1. The site includes the golf course and the evaporation and percolation disposal ponds with an overflow area. A third area, the surface water within the disposal ponds, was eliminated from further investigation. The evaporation and percolation disposal ponds are approximately 2,000 feet east of the golf course. A review of the 1983 initial assessment study revealed that wastewater was disposed of from 1942 to 1974 by evaporation and percolation in the disposal ponds. Secondary effluent was used to irrigate the golf course from 1952 to 1972, and from 1978 to the present.

CAOC 3 was divided into three strata consisting of documented and suspected contamination sources from the golf course, effluent disposal ponds, and the overflow area. A phase I soil sampling effort was performed and concluded that pesticide concentrations were similar to levels found basewide. The remedy for CAOC 3 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative.

CAOC 4 – The Old Trap and Skeet Range Areas

CAOC 4, the Old Trap and Skeet Range Areas, is in the northeastern quadrant of the Nebo Main Base. The site was used to store wooden containers of calcium hypochlorite. A review of historical records revealed that the calcium hypochlorite was originally stockpiled in CAOC 3, an area near the golf course, from the middle to late 1940s before its relocation to CAOC 4. These wooden containers of calcium hypochlorite were piled near a gully on CAOC 4 and were buried in the gully when they began to deteriorate and leak.

The original area identified as Stratum 1, formerly CAOC 4, consisted of an area between the oxidation ponds and the industrial and sanitary sewage disposal plant. During a site visit in 1990, the area east of the industrial and sanitary sewage disposal plant was observed to be littered with skeet debris. This area became Stratum 2. The site boundaries were further adjusted to include an aerial infrared anomaly. The area of the anomaly became Stratum 3, just north of the industrial and sanitary sewage plant and south of the wastewater treatment ponds. The contaminants of potential concern for CAOC 4 included constituents of calcium hypochlorite and polyaromatic hydrocarbons.

The remedy for CAOC 4 Strata 1 and 2 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 4 Strata 1 and 2 soils remedies are considered protective of human health and the environment because risk levels are below the target risk range or below the quantitation limit, no groundwater impacts resulted from contaminant detections, and low levels of contaminants detected would not have an adverse impact on ecological receptors. Stratum 3 of CAOC 4 is not included as part of OU 5 and 6 record of decision and was part on an investigation of CAOC 10.37, a decommissioned industrial wastewater plant with evaporation ponds that may have impacted the stratum. CAOC 10.37 is discussed under the OU7, Miscellaneous CAOCs, section.

CAOC 6 – The Original Trash Landfill

CAOC 6, the Original Trash Landfill, is north of Interstate 40 in the eastern portion of the Nebo Main Base. The site reportedly was used between 1946 and 1952 for disposing of approximately 20,000 cubic yards of lumber, building materials, empty paint cans, and other general trash. CAOC 6 was also used for storing approximately 80 tons of various formulations of the insecticide DDT and other unknown materials. These materials were stored in 13 revetments on and adjacent to the CAOC 6 landfill area. All revetments were bermed and opened away from the facility. The contaminants of potential concern at CAOC 6 included volatile organic compounds, semi-volatile organic compounds, pesticides, polychlorinated biphenyls, metals, and cyanide.

Results of the 1995 phase I remedial investigation sampling effort identified polyaromatic hydrocarbons and organochlorine pesticides as the only contaminants at significant concentrations in Strata 1, 2, and 3. Modeling indicated that these contaminants were not a threat to groundwater. The remedy for CAOC 6 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative with unrestricted future land use, and the site was closed out with no further action required. The CAOC 6 soils remedy is considered protective of human health and the environment because no evidence of landfilling was found, risk levels are below the target risk range, further action for groundwater is being taken as part of the OU 2 remedial action, and the low levels of contaminants detected would not have an adverse impact on ecological receptors.

CAOC 7 – Drum Storage and Landfill Areas

CAOC 7, the Drum Storage and Landfill Areas, is in the southwest corner of Nebo Main Base. The site consists of the western and eastern landfill areas with a former drum storage area located adjacent to the eastern landfill area. In addition to storing drums and other equipment, landfill operations consisted of the combustion of flammable liquids in trenches, followed by covering the resulting ash with soil. According to the 1983 initial assessment study, the estimated waste volume disposed of at the landfill is approximately 40,000 cubic yards.

CAOC 7 was divided into four strata consisting of Strata 1 and 2, the documented and suspected contamination sources from the landfill disposal area; Strata 3, the drum storage and spillage areas; and Strata 4, the former playground area. During the 1996 remedial investigation, polychlorinated biphenyls were detected at levels below regulatory levels in Strata 3 and 4 and trichloroethylene and tetrachloroethylene were detected at levels exceeding the regulatory levels in Strata 1 and 2.

In the 1998 OU 5 and 6 record of decision, the selected remedy for CAOC 7 Strata 1 and 2 was a single-layer native soil cap. The record of decision stipulates that future land use at Strata 1 and 2 is restricted to activities that cannot disrupt the physical or structural integrity of the soil cap, other than for purposes of cap maintenance activities, unless prior approval is obtained. The selected remedy for CAOC 7 Strata 3 and 4 in the OU 5 and 6 record of decision was the no action alternative, although groundwater monitoring at CAOC 7 is performed in accordance with the OU 2 record of decision. CAOC 7 is subject to the five-year review process under CERCLA.

CAOC 8 – Building 197 Wastewater Disposal Area

CAOC 8, the Building 197 Wastewater Disposal Area, is in the northeast corner of Building 197. Activities inside this machine shop building included plumbing, machining, and machine cleaning operations. Industrial wastes consisting of acid solutions, solvents, alkaline cleaners, and detergents were reportedly generated by cleaning operations in the building. Chemicals were reportedly discharged through a drain in the cleaning area slab and to a drainage swale east of the building. The 1983 initial assessment study reported that between 1959 and 1975 an estimated 2,000 gallons of hazardous waste were discharged to the ground at CAOC 8. The contaminants of potential concern comprising constituents of the waste stream include volatile organic compounds, semi-volatile organic compounds, polychlorinated biphenyls, metals, cyanide, pesticides, and total petroleum hydrocarbons such as diesel.

Results from 1996 phase I remedial investigation sampling identified semi-volatile organic compounds, xylene, and thallium as possible site-related contaminants in Strata 1 soils, but concentrations were below the target risk range. The remedy for CAOC 8 Strata 1 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative. The CAOC 8 soil remedy is considered protective of human health and the environment because risk levels are below the target risk range, no groundwater impacts result from contaminant detections, and low levels of contaminants detected would not have an adverse impact on ecological receptors.

CAOC 12 – The Radiator Cleaning Chemical Disposal Area

CAOC 12, the Radiator Cleaning Chemical Disposal Area, is an oval-shaped area in the southern portion of the Nebo Main Base. The 1983 initial assessment study describes the disposal area as being adjacent to and north of the above-grade fuel farm. During a 1991 preliminary review and visual inspection, the site was identified by MCLB Barstow personnel as being approximately 30 feet northeast of the existing aboveground fuel tank farm and adjacent to an existing underground storage tank. The underground storage tank, which contained waste fuel and oil, was removed in 1992 during the basewide tank removal program. The contaminants of potential concern at CAOC 12 included waste fuel and oil constituents including volatile organic compounds, semi-volatile organic compounds, polychlorinated biphenyls, metals, petroleum hydrocarbons, and pesticides.

Results of 1996 phase I remedial investigation sampling at CAOC 12 identified semi-volatile organic compounds and metals but were at levels below the target risk range. The remedy for CAOC 12 soils selected in the 1998 OU 5 and 6 record of decision was the no action alternative. This soil remedy is considered protective of human health and the environment because risk levels are below the target risk range, no groundwater impacts result from contaminant detections, and low levels of contaminants detected would not have an adverse impact on ecological receptors.

CAOC 13 – The Preservation and Packaging Storage Areaa

CAOC 13, the Preservation and Packaging Storage Area, is in the southern portion of Nebo, south of Interstate-40 and east of the main housing area. A review of the 1983 initial assessment study indicated that the Preservation and Packaging Division, currently known as the Preservation and Maintenance Support Section, maintained a storage building for paints, thinners, and other solvents at CAOC 13 prior to its destruction in a fire in 1957. The only remains of the former storage building are an 800 square-foot slab of concrete and perimeter foundation. The CAOC includes the former building area delineated by the perimeter of the concrete slab and approximately 400 square feet of surrounding soil. The contaminants of potential concern include solvents and the associated constituent semi-volatile organic compounds, petroleum hydrocarbons, polychlorinated biphenyls, metals, cyanide, and pesticides.

Results of 1996 phase I remedial investigation sampling did not identify any definitive, site related contamination in groundwater at CAOC 13. The remedy selected in the1998 OU 5 and 6 record of decision for CAOC 13 soils was the no action alternative. The soil remedy is considered protective of human health and the environment because risk levels are below the target risk range, no groundwater impacts result from contaminant detections, and low levels of contaminants detected would not have an adverse impact on ecological receptors.

CAOC 14 – Drainage Channels and Mojave Riverbed Outfalls

CAOC 14 consists of three main stormwater drainage channels that comprise the Nebo Main Base surface drainage system and four outfalls that discharge into the Mojave River. The channels, designated A, F, and G, and outfalls, designated B, C, D, and E, are essentially unlined trenches, although short segments are lined with concrete. Between the mid-1940s and 1974, industrial wastes from cleaning and plating operations in Buildings 2, 27, 50, and 53 were discharged through area drains, culverts, and ditches to the banks of the Mojave River. Waste streams included grease, oil, phenols, chromium phosphate, and detergents. The primary contaminants of concern are volatile organic compounds, polyaromatic hydrocarbons, and metals in soil.

CAOC 14 was divided into seven strata, assuming that each channel and outfall could have been impacted by different sources. Low levels of contaminants were detected in the soils that were within the risk range for site-related carcinogenic risks. Modeling conducted as part of the 1996 remedial investigation identified residual pesticides in Outfall E as a possible threat to groundwater. Further action for groundwater at CAOC 14 was included as part of the OU 2 remedial action. The selected remedy for CAOC 14 soils in the 1998 record of decision for OU 5 and 6 was the no action alternative.

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OU 7 addresses the remaining sites not covered by OUs 1 through 6. OU 7 includes 14 CAOCs from the Nebo Main Base identified as CAOCs 10, N-2, 10.38/10.39, NPZ-14, 7 (Stratum 1), 10.12, 10.27, 10.35, 10.37, 10.3, 10.4, 10.5, 10.49, 10.80; and three CAOCs from the Yermo Annex identified as CAOCs 9.6. 9.68, and Y-7 TA-12. Additional information for the specific CAOCs within OU 7 is provided below.

CAOC 10 – Sodium Valve and Metallic Debris Area

CAOC 10 is an approximately 5-acre north-northwest sloping area located in the southwest portion of Nebo, 250 to 300 feet to the northwest of the base residential area. The former waste area was historically used as a soil borrow source and for burial of metallic debris and sodium-filled valves. Fill soil currently covers the area to prevent exposure and drainage controls have been implemented. A lead “hot-spot area” approximately 15-foot by 10-foot by 5-foot-deep where soil concentrations exceeded cleanup levels was identified as part of the 2010 supplemental remedial investigation.

The selected alternative for CAOC 10 soil in the 2014 OU 7 record of decision was “hot-spot removal” with land use controls. The selected action includes excavation of approximately 30 cubic yards of soil in the defined lead contamination area, off-site disposal, and backfilling with imported clean backfill. Lead-impacted soil excavation and disposal was completed in 2019. Results from six confirmation soil sample indicated that post-excavation soil lead levels were less than the cleanup level, and the hot spot removal action was considered complete. The selected land use controls prevent other site uses and provide for maintaining drainage and erosion controls. CAOC 10 is subject to the CERCLA five-year review process.

CAOC N-2 – Area 1

CAOC N-2 Area 1 includes a 17.3-acre parcel in the south-central portion of Nebo previously used for equipment storage and as a trap and skeet shooting range. Waste oil containing polychlorinated biphenyls was reportedly applied to this area for dust suppression from the early 1950s until 1966, resulting in specific areas of polychlorinated biphenyl-impacted soil. The trap and skeet range were operated at CAOC N-2 Area 1 between 1982 and 1999 in an area that overlaps with the former equipment storage area. Lead shot and skeet target clay debris containing polyaromatic hydrocarbons has been identified throughout the former skeet and trap range area. A closed and capped landfill identified as part of CAOC 7 Stratum 7 overlies a portion of the shooting range. The former equipment area and trap and skeet range are currently unused desert vegetated land with remnant concrete walkways traversing the area. An unpaved access road also traverses the area and is periodically graded.

The selected alternative for CAOC N-2 Area 1 in the 2014 OU 7 record of decision includes surface vacuuming of lead shot and clay target material and off-site disposal, excavating polychlorinated biphenyl-impacted soil area “hot spots” and off-site disposal, and implementing land use controls. Excavation and disposal of soil containing visible clay target materials or known polyaromatic hydrocarbons or polychlorinated biphenyls above the cleanup levels was completed in 2019. Some additional excavation was required after contaminant concentrations at two suspect sample locations were found to be above cleanup levels. Results of additional confirmation samples determined that concentrations were below cleanup levels following the additional removal activities, and the excavation was considered complete.

Based on the results of the removal and excavation activities, the Navy recommended no further action, which will eliminate the need for land use controls at CAOC N-2 Area 1. Because CAOC N-2, Area 1 is subject to the CERCLA five-year review process, the Navy proposes to document formal removal of the land use controls during the next five-year review.

CAOC 10.38/10.39 – Unit 7

CAOCs 10.38 and 10.39 include former industrial operation areas in the central portion of Nebo. The CAOCs are divided into 7 individual units which include Units 1 through 6, which are domestic and industrial wastewater pipelines, and Unit 7, which are drainage ditches connected to industrial wastewater connection lines. Approximately 95,000 lineal feet of domestic wastewater pipelines included in Units 1 through 6 are active and operating under a California Regional Water Quality Control Board permit. From 1978 to 1990, industrial wastewater was transferred from Nebo to the industrial waste treatment plant through the former surface drainage ditches and industrial wastewater conveyance pipelines designated as Unit 7. Surface drainage trenches have been backfilled and the industrial wastewater conveyance lines have been plugged with concrete and are no longer in use.

Monitored natural attenuation with land use controls was selected for CAOC 10.38/10.39 Unit 7 in the 2014 OU 7 record of decision. The selected remedy includes monitoring the natural attenuation of volatile organic compounds in groundwater and implementing land use controls that restrict the site to industrial uses and prevent potable use of the groundwater within the plume area. CAOC 10.38/10.39 Unit 7 is also subject to the CERCLA five-year review process.

CAOC NPZ-14

NPZ-14 is a monitoring well installed in 1992 in a now vacant area previously used for equipment storage in the south-central portion of Nebo. The monitoring well was initially installed to measure groundwater levels in this portion of the base, but it is also located within one of Nebo’s two primary areas of concern for groundwater. Given its location within an identified groundwater plume, NPZ-14 was added to the OU 2 monitoring well network in 1998 and is monitored twice a year. Groundwater monitoring results indicate trichloroethylene at concentrations exceeding regulatory limits. Six additional monitoring wells were installed in 2011 and sampled in 2012 to delineate the contaminant impacts in the plume more narrowly. Analyses of samples collected from these wells suggest that trichloroethylene-impacted groundwater is localized to the NPZ-14 area and that the impacted groundwater plume does not extend off-base.

Monitored natural attenuation with land use controls was the selected alternative for NPZ-14 in the 2014 OU 7 record of decision. The selected action includes monitoring the degradation of volatile organic compounds in groundwater in the vicinity of NPZ-14 and land use controls to prevent potable use of the groundwater within the plume area. NPZ-14 is subject to the CERCLA five-year review process.

CAOC 7 Stratum 1 – Soil Vapor and Groundwater

CAOC 7 Stratum 1 is a capped waste disposal area in the southeastern portion of Nebo. The disposal area was a landfill operated as the principal solid waste landfill at MCLB Barstow from the early 1950s to 1964. The area was covered with approximately 2 feet of soil in 1964. The landfill cap and groundwater monitoring remedy for the site was instituted in 1998 under the OU 5 and 6 record of decision. Monitoring well NSP-2 was installed at the down-gradient end of CAOC 7 Stratum 1. Beginning in 2001, results from groundwater samples from the NSP-2 and other routinely monitored wells in the vicinity found trichloroethylene concentrations at or above regulatory limits. As a result, a remedy evaluation was conducted under the OU 5 and 6 record of decision which included the installation in 2011 of an additional upgradient groundwater monitoring well and two soil vapor wells through the cap. Volatile organic compound contamination was found in soil vapor samples below CAOC 7 Stratum 1 to a depth of at least 170 feet below ground surface.

The selected remedy in the 2014 OU 7 record of decision for soil vapor at CAOC 7 Stratum 1 was soil vapor extraction, and the selected remedy for groundwater at CAOC 7 Stratum 1 was monitored natural attenuation with land use controls. The selected action for the vadose zone soil includes removing volatile organic compounds by soil vapor extraction, treatment with granular-activated carbon, and disposal of the granular-activated carbon off-site. Land use controls for the soil vapor extraction remedy implemented for CAOC 7 Stratum 1 under the OU 5 and 6 record of decision include signage, fencing, and maintenance requirements and will be extended to include protection of monitoring and remediation systems and wells, as necessary. CAOC 7 Stratum 1 is subject to the CERCLA five-year review process.

To implement the record of decision remedies, soil vapor extraction wells were installed from November 2018 to January 2019. Additionally, a comprehensive monitoring program was implemented to verify that the remedy is mitigating further impacts to the groundwater by removing volatile organic compounds from impacted vadose zone soils. Annual evaluations of the effectiveness of the remedy are being performed. For the groundwater remedy, land use controls established in the OU 1 and OU 2 record of decision will be maintained at OU 7 to prevent potable use of groundwater until cleanup levels are met.

CAOC 9.60

CAOC 9.60 is the former location of underground storage tank T-530b in the east-central portion of Yermo. Former tank T-530b was reportedly a 40,000-gallon steel underground storage tank used to store used oil and other waste liquids from 1942 to 1960. The site is currently unpaved and used for parking. Future land use is an undefined industrial scenario. Previous soil and soil vapor investigations near the underground storage tank identified impacts in its vicinity. In response, tank T-530b and associated impacted soil were removed in 1992.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 9.60 and required that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes. CAOC 9.60 is subject to the CERCLA five-year review process.

CAOC 9.68

CAOC 9.68 consists of the former locations of underground storage tanks T-588A and T-588B adjacent to Building 588 in the northwest portion of Yermo. Investigations determined that underground storage tank T-588A was an oil-water separator and T-588B was a vertical French drain. These facilities may have been used to receive waste streams from vehicle maintenance and repair activities at Building 588. Both underground storage tanks were removed in 1992. CAOC 9.68 is currently unpaved with backfill gravel at the surface.

For CAOC 9.68, the 2014 OU 7 record of decision selected land use controls as the site remedy, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes. CAOC 9.68 is subject to the CERCLA five-year review process.

CAOC 10.12

CAOC 10.12 is the location of former Building 50 in the northwest portion of Nebo. Constructed in 1948, Building 50 was used for cleaning, painting, preservation, and packaging operations and general storage and vehicle repair. The building had contained a wash pad area, a drainage area, and a solvent still area. Waste from Building 50 was documented to have contained spent blast media, waste grease, oil, tetrachloroethylene, paint sludge, steam-cleaning wastewater, sodium hydroxide, heavy metals, and solvents. Building 50 was demolished in 1990. CAOC 10.12 currently consists of a partial concrete foundation and unpaved areas.

The 2104 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.12, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes and restrict use of groundwater. Volatile organic compounds detected in soil vapor and groundwater are being remediated under the OU 1 and 2 record of decision. CAOC 10.12 is subject to the CERCLA five-year review process.

CAOC 10.27

CAOC 10.27 includes Building S-338, which was used for fire-fighting training activities in the northeast portion of Nebo until 1975. Used oil and waste fuel were sprayed on wood and scrap metal materials and burned. The generated fire-fighting wastewater was discharged into a roughly 3-foot-deep subgrade concrete containment area, then discharged through a drainpipe to an unpaved railroad right-of-way located on the north side of the building. The building and wastewater containment area were demolished between 1998 and 1999, and the former subgrade containment area was backfilled with soil to current grade. The site is currently covered with asphalt pavement or has concrete aprons surrounding unpaved areas and is used for equipment storage and staging.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.27, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes. CAOC 10.27 is subject to the CERCLA five-year review process.

CAOC 10.35

CAOC 10.35 consists of the former domestic wastewater treatment plant in the north-central portion of Nebo that was in operation from 1942 to 1978. The plant included a pump station, clarifier, sludge drying bed, and four effluent disposal ponds that were converted into two sludge beds in 1948. The disposal ponds were located 2,500 feet east of the current disposal ponds. The disposal ponds were investigated as part of the OU 5 and 6 remedial investigation and feasibility study. The wastewater treatment plant building was demolished, and the area is currently used for temporary equipment storage and staging.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.35, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes. CAOC 10.35 is subject to the CERCLA five-year review process.

CAOC 10.37

CAOC 10.37 was an industrial wastewater treatment plant that operated between 1975 and 1990 in the northeast portion of Nebo. The plant has been decommissioned, the area is mostly paved and enclosed within a fence and is currently not in use. The former plant has a concrete pad with a drain that connects to a wet well, and a waste oil float tank, ferrous chloride tank, air flotation unit, two sludge drying beds, and five evaporation ponds. The evaporation basins are paved with concrete. Dewatered sludge was disposed of off-base and effluent from the air flotation unit was transferred to five concrete-lined evaporation basins.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.37, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes and restrict groundwater uses. CAOC 10.37 is subject to the CERCLA five-year review process.

CAOC 10.3 – Warehouse 2

CAOC 10.3, Warehouse 2, is a 2.9-acre concrete storage facility located in the northwest portion of Nebo that was constructed in 1942. It has a concrete floor with numerous floor drains and the surrounding outdoor area is covered in concrete pavement. The warehouse was used for vehicle repair from 1942 to 1961 and chemicals including fuels, oils, various greases, acids, vapor degreasers, radiator coolants, and antifreeze were likely used at this location. The building has been used for general storage of aircraft parts and equipment since 1961.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.3, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes and restrict groundwater uses. CAOC 10.3 is subject to the CERCLA five-year review process.

CAOC 10.4 – Warehouse 3

CAOC 10.4, Warehouse 3, is a general warehouse located in the northwest portion of Nebo that was constructed in 1942. The warehouse was used for storage and vehicle repair. An oil/water separator that was removed in 1999 and three cleaning tanks were formerly located in the northern portion of the warehouse. A steam-cleaning wash rack and sump used to clean small machinery is in the vicinity of the former oil/water separator. The warehouse includes a concrete floor, sumps, floor drains, and concrete pavement around the outside of the building. More recently it has been used for environmental staff office space, and storage of field equipment and equipment cleaning. Use of the warehouse used as office space ended in 2012.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.4, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes and restricts groundwater uses. CAOC 10.4 is subject to the CERCLA five-year review process.

CAOC 10.5 – Warehouse 4

CAOC 10.5, Warehouse 4, is in the northwest portion of Nebo and was previously used for general storage and vehicle repair. The warehouse is a concrete facility constructed in 1942 that encompasses approximately 2.9 acres. Vehicle repair activities were performed at the facility from 1942 to 1961. Circular concrete patches in the northwest corner of the building near the former locations of a battery shop and generator provide evidence of three former floor drains. The facility currently houses squash courts and is used for recreational activities and is also used for storage of aircraft parts and equipment.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.5, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes and restrict groundwater uses. CAOC 10.5 is subject to the CERCLA five-year review process.

CAOC 10.49 – Former Underground Storage Tanks T-27A, B, and C

CAOC 10.49 is on the south side of Building 27 and east of CAOC 10.12 in the northwest portion of Nebo. Underground storage tanks T-27A, T-27B, and T-27C were previously located in this area. Vent pipes for the three underground storage tanks were visually identified in 1992. A 1995 geophysical survey detected anomalies underlying the vent pipe locations, but no underground storage tanks were found during subsequent air-knifing in the area. The area is currently a paved parking lot for Building 27.

Volatile organic compounds were detected in samples collected during a 2002 investigation focused on potential soil contamination and impacts on underlying groundwater. Remedial action consisting of air sparging and soil vapor extraction was performed in this area between 2008 and 2012 as part of the Nebo North plume cleanup activities under the OU 1 and 2 ROD.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.49, requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. The land use controls restrict current and future land use to industrial purposes and restrict groundwater uses. CAOC 10.49 is subject to the CERCLA five-year review process.

CAOC 10.80 – Former Underground Storage Tank T-354

CAOC 10.80 is south of former Building 354 in the northwest portion of Nebo and is the location of tank T-354, a former 450-gallon fiberglass underground storage tank. It was reportedly a boiler blow-down tank that was removed in 1992. The location is currently a paved area. Records from MCLB Barstow indicate that no wastes were managed in underground storage tank T-354 and that no releases were recorded during its use. The land in the vicinity of former Building 354 in undeveloped. Future planned land use is unknown.

During investigations in 1992 when the tank was removed and again in 1998, elevated concentrations of total chromium were detected, and several other metals were detected above base background levels in soil, but below regional screening levels. Hexavalent chromium and volatile organic compounds were not detected in soil samples. Groundwater and soil vapor samples were not collected at CAOC 10.80. A risk evaluation based on the sample results found that there are no known human receptors or exposure pathways at CAOC 10.80, and there is no wildlife exposure pathway to chemicals in soil because there is no viable habitat for ecological receptors.

The 2014 OU 7 record of decision selected land use controls as the site remedy for CAOC 10.80. Although the site was determined to be non-actionable, the land use controls restrict current and future land use to industrial purposes and restrict groundwater uses because low levels of metals in soil remain at CAOC 10.80. An update to the base master plan was made requiring that any actions planned at this area or proposed changes in site use be coordinated through and reviewed by the MCLB Barstow Environmental Division. CAOC 10.80 is subject to the five-year review process under CERCLA.

CAOC Y-7 TA-12

CAOC Y-7 TA-12 is an approximately 260-foot by 360-foot area adjacent to the southeastern corner of a former 17-acre Class III landfill in the northeastern portion of Yermo. During an aerial thermographic survey in 1991, a suspected waste burial area was identified at the site, although subsequent field investigations did not identify buried waste or impacted soil. CAOC Y-7 TA-12 has been and is currently vacant, undeveloped land with sparse desert vegetation. Groundwater beneath CAOC Y-7 TA-12 is being addressed under OUs 1 and 2, although impacts to groundwater from this CAOC are not suspected. The contaminants of potential concern at CAOC Y-7 TA-12 included volatile organic compounds, semi-volatile organic compounds, polychlorinated biphenyls, and metals.

No contaminants of potential concern were detected in soil or soil gas samples exceeding background or regional screening levels. Groundwater at CAOC Y-7 TA-12 is currently being remediated via an air sparge and soil vapor extraction system under OUs 1 and 2 record of decision.

The no action alternative was selected for CAOC Y-7 TA-12 soils under 2014 OU 7 record of decision, and the site was closed out with no further action required. The soils remedy is considered protective of human health and the environment because risk levels are within the risk management range, no sensitive species or habitat would be affected by the contamination at the site, and groundwater underlying CAOC Y-7 TA-12 is being addressed under the OU 1 and 2 record of decision.

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CAOC 33 is not associated with an OU. CAOC 33, Rifle Range Disposal Area, was identified during the 1983 initial assessment study as a disposal area for miscellaneous industrial sludge, dried industrial waste treatment sludge, and waste oil. These wastes were disposed of at the rifle range at various times throughout the history of MCLB Barstow at an estimated volume disposed of approximately 100 cubic yards of sludge annually. The treatment plant study indicated that 6,000 gallons of industrial sludge and about 1,000 cubic yards of industrial waste treatment sludge and unknown quantities of waste oil were reportedly disposed of at this site. CAOC 33 was proposed for elimination from the remedial investigation to be conducted 1995 as not requiring further investigation. The Federal Facility Agreement stakeholders accepted this proposal, and CAOC 33 was removed from the IRP.

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Building 327, located in the northeastern corner of the Nebo Main Base, was constructed in 1975 to provide heat to MCLB Barstow. A large petroleum release affecting soil and groundwater originated from the Building 327 heating plant subgrade fuel delivery pipeline. The facility, which operated until 1997, included a heating plant with two 250,000 gallon above‐ground tanks and one 2,000-gallon underground storage tank for heating oil storage. The tanks were removed in 1998. All above‐ground facilities were demolished and removed by 2008 and the site is currently unused vacant land.

From 1994 to 2017, a series of investigations were conducted to determine the extent of contamination on-base and extending off-base from volatile organic compounds and petroleum hydrocarbons in soil and groundwater beneath the site. Samples were collected from soil borings and numerous monitoring wells were installed around the site during these investigations. In 2015, a corrective action plan was implemented for two additional years of groundwater monitoring in order for the site to meet the state’s 2012 criteria for a low‐threat case closure for a petroleum release.

A Navy evaluation in 2018 found that the site met the State’s 2012 criteria for a low‐threat case closure, and a request that the Regional Water Quality Control Board grant case closure was submitted. In 2019, the Water Board directed that that all groundwater monitoring wells associated with the site be destroyed before a no further action letter could be issued. All wells were destroyed except for three that are located off-base. Once the Navy obtains site access and the wells are destroyed, all requirements will be met for case closure and the Water Board will recommend no further action at the site.

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