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PUBLIC HEALTH ASSESSMENT

BARSTOW MARINE CORPS LOGISTICS BASE
(a/k/a MARINE CORPS LOGISTICS BASE BARSTOW)
BARSTOW, SAN BERNARDINO COUNTY, CALIFORNIA


SUMMARY

Marine Corps Logistics Base Barstow (MCLB) is located approximately 135 miles northeast of Los Angeles in the central Mojave Desert in San Bernardino County, California. MCLB consists of three separate areas: the Nebo Main Base, the Yermo Annex, and the Rifle Range. The Nebo Main Base (1,571 acres), adjacent to U.S. Interstate 40, is 3.5 miles east of the city of Barstow and contains base housing, administrative buildings, and covered storage for warehousing activities. The Yermo Annex (1,680 acres), located 7 miles east of Barstow, is used for the storage of supplies and the maintenance, repair, overhaul, and reassembly of vehicles and weapons. The Rifle Range (2,438 acres) is a secure area adjacent to the southern boundary of the Nebo Main Base used for practicing marksmanship skills.

The United States Environmental Protection Agency (EPA) placed MCLB on the National Priority List on November 15, 1989, as a result of potential soil and groundwater contamination throughout the base. A Federal Facilities Agreement was signed on October 24, 1990, by the Marine Corps, the EPA (Region 9), the California Regional Water Quality Control Board (Lahontan Region), and the California Environmental Protection Agency (Region 4), Department of Toxic Substances, to establish a schedule for environmental investigations and required remedial actions at the site.

The Agency for Toxic Substances and Disease Registry (ATSDR), headquartered in Atlanta, Georgia, is a federal agency within the U.S. Department of Health and Human Services. ATSDR, under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) conducts public health assessments for sites that the U.S. Environmental Protection Agency (EPA) has listed on its National Priority List (NPL). In response to the placement of MCLB on the NPL, ATSDR evaluated the public health significance from environmental contamination at MCLB. For this evaluation, ATSDR conducted a site visit in March 1991 and March 1997 and evaluated the available environmental information for MCLB. Based on this review, ATSDR has identified and evaluated the following six completed or potential exposure pathways of concern. This evaluation is summarized below by pathway with ATSDR public health conclusion categories.

Exposure to Contaminated Groundwater

  1. Past use of the Nebo Main Base production wells for on-base drinking and production (No Apparent Public Health Hazard, see Appendix D for a definition of this phrase).
  2. Past use of the Nebo Main Base production wells for irrigation (No Apparent Public Health Hazard).
    Current and Future use of the Nebo Main Base production wells for irrigation (No Public Health Hazard).
  3. Past use of off-site private wells southeast of the Nebo Main Base (No Apparent Public Health Hazard).
  4. Past use of the Yermo Annex production wells for on-base drinking and production (No Apparent Public Health Hazard).
  5. Past use of off-site private wells east of the Yermo Annex (No Apparent Public Health Hazard).

Potential Exposure to Contaminated Soils

  1. Past, current, and future exposure to soils at the rifle range given present land use (No Public Health Hazard).

These exposures are discussed in detail in this report and are summarized below.

Nebo Main Base Production Wells
Prior to 1977, the Nebo Main Base obtained potable water from six on-base production wells for drinking and operations. People working and living on-base used this water. ATSDR evaluated the human exposure to this water because these wells had the potential to be impacted by the Nebo Main Base - northern plume and the Barstow area wide groundwater contamination. The northern plume is an area of groundwater contamination caused by historical disposable practices at Warehouse 2 and surrounding buildings. This Warehouse was built in 1942, and the wells were installed from 1942 to 1969. The predominant contaminant is tetrachloroethene. In 1997, MCLB stopped using the wells for drinking water and production water because of high levels of total dissolved solids. Water was then obtained from the City of Barstow. The production wells were used after 1977 to irrigate the golf course.

The Barstow area wide groundwater contamination is a regional area of groundwater contamination identified by high total dissolved solids caused by off-base upgradient municipal and industrial-waste discharges and upgradient recharge of the aquifers by irrigation.

Prior to 1994, limited well data are available. The data that does exist includes the analysis of water quality parameters such as major cation, anions, and a few other chemicals such as phenols, trihalomethanes, and mercury. Prior to 1994, the well water was not analyzed for the type of chemicals found in the Nebo Main Base - northern plume. After 1994, the production wells were sampled once in 1994 and 1999 for the contaminants found in the northern plume. Of the chemicals analyzed for, only trichlorobenzene was found in the 1994 samples and it was below levels of public health concern

MCLB has investigated the Nebo Main Base - northern plume since 1983 and found that the plume is limited in the upper 20 feet of the aquifer and extends to the edges of the Mojave River. Concentrations at the Mojave River are below EPA Maximum Contaminant Levels (MCLs). MCLB is currently cleaning up the groundwater. Additional details of the plume are found in this report.

For this Public Health Assessment (PHA), ATSDR evaluated the data from the MCLB investigation of the northern plume and sampling data from the production wells. We have concluded that there is No Apparent Public Health Hazard for past use of the wells for drinking, production, and irrigation.

For current and future use of the wells for irrigation, ATSDR assigned the hazard category of No Public Health Hazard because volatile organic compounds (VOCs) were found below levels of concern in samples collected in 1994 and below levels of detection in samples collected in 1999.

Yermo Annex Production Wells
Historically, the Yermo Annex at MCLB used five groundwater wells to obtain water from the Mojave River Aquifer. This water was used by people working on-base. After 1975, only three of the five wells were active (Wells 3, 4 and 5). In 1988, MCLB found groundwater contamination (volatile organics) in each of the three active wells. The highest concentration detected was 25 microgram per liter (µg/L) trichloroethene (TCE) in Yermo Well 3 in 1988. The MCL for TCE is 5 µg/L. MCLB decommissioned Well 3 at this time. Contaminants in the other two wells were below MCLs. The wells were also monitored for other water quality parameters. Both Wells 4 and 5 are continually monitored and are currently being used. Based on the length of exposure and the concentration of contaminants in the wells, ATSDR concluded that there is no public health hazard. Therefore, we have assigned the ATSDR hazard category of No Apparent Public Health Hazard since people were exposed to concentrations below levels of concern.

Off-Site Wells at the Nebo Main Base and Yermo Annex
Private wells, used for drinking water, adjacent to and off-site of the Nebo Main Base and Yermo Annex were impacted by VOCs. Human exposures at these locations pose no apparent public health hazard because of the short duration of exposure and low levels. Currently, the wells at the off-base sites near the Nebo Main Base are no longer used while carbon filters (with monitoring) have been placed on the off-base wells near the Yermo Annex. Future use of the off-base groundwater is regulated by the San Bernardino County Department of Health Services which has been notified of the groundwater contamination.

Soils at the Rifle Range
The rifle range is used by the Marine Corps for target practice. The local police have also used the range. Based on sampling data, elevated lead levels are present in the soils at the firing range. However, past and current health hazards from these soils are not likely because the area is secured from the public and its current use does not involve contact with the soil. Health hazards from future land use changes are prevented by Department of Defense (DOD) policy on the environmental requirements prior to property transfers. ATSDR includes this exposure pathway in this report to stress the importance of proper handling of the property because of the elevated lead levels in the soils.


I. BACKGROUND

A. Site Description and Operational History

Marine Corps Logistics Base Barstow (MCLB) is located approximately 135 miles northeast of Los Angeles in the central Mojave Desert in San Bernardino County, California (Figure 1). MCLB consists of three separate areas: the Nebo Main Base, the Yermo Annex, and the Rifle Range. The Nebo Main Base (1,571 acres) is adjacent to U.S. Interstate 40, 3.5 miles east of the city of Barstow and contains base housing, administrative buildings, and covered storage for warehousing activities. The Yermo Annex (1,680 acres), located 7 miles east of Barstow, is used for the storage of supplies and the maintenance, repair, overhaul, and reassembly of vehicles and weapons. The Rifle Range (2,438 acres) is a secure area adjacent to the southern boundary of the Nebo Main Base, and is used for practicing marksmanship skills.

The Marine Corps established MCLB at the site of the Nebo Main Base in 1942 as a storage area for supplies and equipment for the Marine Corps forces serving in the Pacific during World War II. Between 1943 and the present, MCLB provided logistical support to Marine Corps commands stationed throughout the western United States and the Pacific.

The Yermo Annex was acquired in 1946 when the Nebo Main Base operation outgrew its facilities. A large amount of additional capacity for repairing and rebuilding vehicles and weapons was added to the Yermo Annex with the addition of the Central Repair Shop (Building 573) in 1961.

The Rifle Range was purchased in the mid-1950s to provide a secure area for marksmanship practice.

Vehicle assembly and maintenance activities over the past 50 years at MCLB generated large quantities of waste such as: waste oils, fuels, solvents, paint residues, grease, hydraulic fluids, battery acids, various gases, and low-level radiation sources. Other hazardous substances used or generated on the base included pesticides, herbicides, polychlorinated biphenyls (PCBs), calcium hypochlorite, and sodium. Past waste disposal practices reflected the accepted procedures at the time and included disposal in landfills, burn trenches, and other miscellaneous sites on the base (Jacobs Engineering Group, 1995b).

B. Remedial and Regulatory History

Since 1983, MCLB has implemented the U.S. Department of Defense's Installation Restoration Program (IRP) to identify, investigate, and clean up contamination that originated from the base. In 1984 and 1985, MCLB and the United States Geological Survey (USGS) identified trichloroethylene (TCE) in groundwater monitoring wells at both the Nebo Main Base and the Yermo Annex. Additional investigations during this time identified chlorinated solvents, including TCE in the monitoring and drinking water supply wells at the Yermo Annex and in monitoring wells at the Nebo Main Base. The contaminated water supply wells (production wells) were subsequently connected to a carbon adsorption treatment system (Jacobs Engineering Group, 1995b).

As a result of these investigations, the United States Environmental Protection Agency (EPA) placed MCLB on the National Priority List (NPL) on November 15, 1989, because of soil and groundwater contamination. A Federal Facilities Agreement (FFA) was signed on October 24, 1990, by the Marine Corps, the EPA (Region 9), the California Regional Water Quality Control Board (Lahontan Region), and the California Environmental Protection Agency (Region 4), Department of Toxic Substances, to establish a schedule for environmental investigations and required remedial actions at the site.

The FFA grouped 38 IRP areas of concern (known as CERCLA areas of concern or CAOCs) (Figures 2 and 3) into seven operable units (OU).

  • Operable units 1 and 2 (OU-1, OU-2) address groundwater contamination at the Yermo Annex and the Nebo Main Base, respectively.


  • Operable units 3 and 4 (OU-3, OU-4) address soil contamination investigated through the first remedial investigation (RI) for the Yermo Annex and the Nebo Main Base, respectively.


  • Operable units 5 and 6 (OU-5, OU-6) address soil contamination identified during the investigation of operable units 3 and 4.


  • Operable unit 7 (OU-7) will eventually address additional areas of concern where hazardous materials may have been released to soils (Jacobs Engineering Group, 1995b).

A Phase I groundwater investigation was performed in 1992 at MCLB to define the regional conditions and to provide a preliminary assessment of groundwater quality at both the Nebo Main Base and the Yermo Annex. Elevated TCE concentrations were detected in a monitoring well (NEP-4) at the southeast corner of the Nebo Main Base during Phase I investigations. The Marine Corps initiated an effort to identify potential receptors of contaminated water and identified four off-base private wells that were affected at the Nebo Main Base and Yermo Annex. These wells were sampled and either taken off line or modified with carbon filters. Phase II groundwater investigations focused on characterizing the extent to which contamination was detected in Phase I, and to determine the need for removal actions in these areas.

A Record of Decision (ROD) was signed for OUs 3 and 4 in May 1996 and for OUs 5 and 6 in December 1997. An additional ROD was signed for OUs 1 and 2 in March 1998. The actions recommended in the RODs are summarized in Appendix E. Additional investigations will be conducted as needed under OU-7 for 247 Solid Waste Management Units (SWMUs) under the RCRA Corrective Action Plan (Appendix F). Of the 247 SWMUs, 19 require additional investigation under RCRA.

C. ATSDR Activities

The Agency for Toxic Substances and Disease Registry (ATSDR) conducted an initial site visit in March 1991. During the second site visit, conducted in March 1997, ATSDR met with representatives from the U.S. Navy Environmental Health Center, the California Department of Health, the California Department of Toxic Substances Control, the Lahontan Regional Water Quality Control Board, the USGS, and the County of San Bernardino Health Services. ATSDR also met with several citizens during the second site visit who expressed concerns about groundwater quality in the area that was not related to activities at MCLB.

D. Demographics

The on-base residential areas at MCLB are located at the Nebo Main Base. The population of the Nebo Main Base is 1,459 people (U.S. Census, 1990), of which 56.5% is male (Figure 4). The population of the base is primarily white (67.8%) and children under the age of 10 comprise 28.7% (419 children) of the population. The population density is 493 people per square mile. There are 369 households on the base, but this figure does not include group quarters such as military barracks. The average tour of duty at MCLB is 2 to 3 years.

An additional 21,472 people live in the city of Barstow and surrounding area (U.S. Census, 1990). Barstow is the center of commercial and public services for the area. The communities surrounding MCLB include Daggett (2,000 residents), Yermo (2,300 residents), and Newberry Springs (3,000 residents) (Jacobs Engineering Group, 1995a). The population density within one mile of MCLB varies from 0 to 772 people per square mile.

E. Land Use and Environmental Description

The Nebo Main Base and the Yermo Annex areas are located in the central part of the Mojave Desert in Southern California. More specifically, the Base and Annex are located in the Mojave River groundwater basin with the Calico Mountains to the north and the Daggett Ridge to the south (U.S. Geological Survey, 1997). Precipitation in the area averages about 5 inches per year.

The Mojave River flows east along the northern boundary of the Nebo Main Base. Flooding occasionally occurs in this area from heavy rainfall in the San Bernardino Mountains, 50 miles to the southwest, where the headwaters of the Mojave River are located (U.S. Geological Survey, 1997).

Groundwater recharge in the Mojave River Basin is due primarily to the precipitation on and runoff from the San Bernardino Mountains, which receive significantly more precipitation (75 inches) than other areas of southern California.

Agriculture activities in the area include 130 acres under cultivation for alfalfa located approximately 1.5 miles northwest of the Nebo Main Base. There are also some agricultural activities several miles downgradient of the Yermo Annex. The closest irrigation well is also several miles downgradient of the Yermo Annex (U.S. Marine Corps, 1998).

F. Quality Assurance and Quality Control

In preparing this public health assessment (PHA), ATSDR relied on information provided in the referenced documents and contacts. The agency assumes quality assurance and control measures were followed with regard to chain of custody, laboratory procedures, and data reporting. The validity of analyses and conclusions drawn in this document is determined by the reliability of the information referenced in this report.


II. ENVIRONMENTAL CONTAMINATION AND POTENTIAL EXPOSURE PATHWAYS

In this section, exposure pathways are evaluated to determine whether people accessing or living near or at MCLB could have been (a past scenario), are (a current scenario), or will be (a future scenario) exposed to site-related contaminants. When evaluating exposure pathways, ATSDR identifies whether exposure to contaminated media (soil, water, air, waste, or biota) has occurred, is occurring, or will occur through ingestion, dermal (skin) contact, or inhalation (Figure 5). If exposure was or is possible, ATSDR then considers whether contamination is present at levels that might affect public health.

ATSDR evaluates these contamination levels by comparing them to comparison values. Comparison values are developed by ATSDR from scientific literature available on exposure and health effects. These comparison values are derived for each of the different media and reflect the estimated contaminant concentration that is not likely to cause adverse health effects for a given chemical, assuming a standard daily exposure (e.g., ingestion rate, inhalation rate) and standard body sizes. ATSDR comparison values are designed to be many times lower than levels at which no effects were observed in experimental animals or epidemiologic studies. Therefore, exposure to chemical concentrations above comparison values does not necessarily produce health effects. If contaminant concentrations are above comparison values, ATSDR further analyzes exposure variables (for example, duration and frequency) and the toxicology of the contaminant before making conclusions and recommendations.

Comparison values used in this document include EPA's maximum contaminant levels (MCL), ATSDR's environmental media evaluation guides (EMEG), reference dose media guides (RMEG), and cancer risk evaluation guides (CREG). MCLs are enforceable drinking water regulations developed to protect public health. They also consider economic and technological factors. CREGs, EMEGs, and RMEGs are strictly health-based comparison values developed by ATSDR that are not enforceable. A glossary of environmental and health terms and descriptions of the comparison values used in this public health assessment are provided in Appendix A and Appendix B, respectively.

ATSDR reviewed the environmental data generated from investigations of the 38 IRP sites and 247 Resource Conservation and Recovery Act (RCRA) Solid Waste Management Units at MCLB to determine if there are any associated past, current, or future public health hazards. ATSDR also evaluated other pertinent environmental data such as production well monitoring data. From this review, ATSDR identified and evaluated the following six completed or potential exposure pathways of concern (Table 1):

Exposure to Contaminated Groundwater

  1. Past use of the Nebo Main Base production wells for on-base drinking and production (No Apparent Public Health Hazard, see Appendix D for a definition of this phrase).
  2. Past use of the Nebo Main Base production wells for irrigation (No Apparent Public Health Hazard).
    Current and future use of the Nebo Main Base production wells for irrigation (No Public Health Hazard).
  3. Past use of off-site private wells southeast of the Nebo Main Base (No Apparent Public Health Hazard).
  4. Past use of the Yermo Annex production wells for on-base drinking and production (No Apparent Public Health Hazard).
  5. Past use of off-site private wells east of the Yermo Annex (No Apparent Public Health Hazard).

Potential Future Exposure to Contaminated Soils

  1. Past, current, and future exposure to soils at the rifle range given present land use (No Public Health Hazard).

These six exposure pathways are discussed in the following sections with justifications for our conclusions.

A. Exposure to Contaminated Groundwater

Through the DOD Installation Restoration Program, MCLB has identified five plumes of contaminated groundwater at MCLB: two at the Nebo Main Base and three co-mingled plumes at the Yermo Annex (See Figure 1). The two Nebo Main Base plumes consist of the northern plume located between the A.T. and S.F. Railroad tracks and the Mojave River and the southern plume located near the southeastern corner of the base beneath and downgradient of CAOC 6. The northern plume had the potential for impacting one or more of the on-base production wells in the past while the southern plume had impacted two off-base private wells in the past. The three co-mingled plumes at the Yermo Annex impacted on-base production wells and two off-base private wells in the past.

ATSDR has evaluated these groundwater plumes in five exposure scenarios as listed below:

  1. Past use of the Nebo Main Base production wells for on-base drinking and production (Section II.A.1).
  2. Past, current, and future use of the Nebo Main Base production wells for irrigation (Section II.A.2).
  3. Past use of off-site private wells southeast of the Nebo Main Base (Section II.A.3).
  4. Past use of the Yermo Annex production wells for on-base drinking and production (Section II.A.4).
  5. Past use of off-site private wells east of the Yermo Annex (Section II.A.5).

1. Past use of the Nebo Main Base production wells for on-base drinking and production

Summary

Prior to 1977, the Nebo Main Base obtained potable water from six on-base production wells for drinking and operations. The water was used by people working and living on-base. ATSDR evaluated the human exposure to this water because these wells had the potential to be impacted by the Nebo Main Base - northern plume and the Barstow area wide groundwater contamination. The northern plume is an area of groundwater contamination caused by historical disposable practices at Warehouse 2 and surrounding buildings. This warehouse was built in 1942 and the wells were installed from 1942 to 1969. The predominant contaminant in the northern plume is tetrachloroethene. In 1997, MCLB stopped using the wells for drinking and production water because of high levels of total dissolved solids. Water was then obtained from the City of Barstow. The production wells were used after 1977 to irrigate the golf course.

The Barstow area wide groundwater contamination is a regional area of groundwater contamination identified by high total dissolved solids caused by off-base upgradient municipal and industrial-waste discharges and upgradient recharge of the aquifers by irrigation.

Prior to 1994, limited well data are available. The data that does exist includes the analysis of water quality parameters such as major cation, anions, and a few other chemicals such as phenols, trihalomethanes, and mercury. Prior to 1994, the well water was not analyzed for the type of chemicals found in the Nebo Main Base - northern plume. After 1994, the production wells were sampled once in 1994 and in 1999 for the contaminants found in the northern plume. Of the chemicals analyzed for, only trichlorobenzene was found in the 1994 samples and it was below levels of public health concern

MCLB has investigated the Nebo Main Base - northern plume since 1983 and found that the plume is limited in the upper 20 feet of the aquifer and extends to the edges of the Mojave River. Concentrations at the Mojave River are below MCLs. MCLB is currently cleaning up the groundwater.

For this PHA, ATSDR evaluated the data from the MCLB investigation of the northern plume and sampling data from the production wells and has concluded that there is No Apparent Public Health Hazard for past use of the wells.

Discussion

The six Nebo Main Base production wells were constructed from 1942 (Nebo Well 1) to 1969 (Nebo Well 6). These wells provided water for base activities at Nebo including administrative offices, bachelors' quarters, officer's housing, and other on-base family housing. Wells 3 and 6 currently provide irrigation water for the base golf course.

The production wells vary in depth from 192 feet below ground surface (bgs) to 467 feet bgs (Almgren and Koptionak, 1986, See Table 2). Nebo Well 1 was abandoned in the 1950s for unknown reasons, and the remaining wells were taken out of service in 1977 due to groundwater degradation from high levels of total dissolved solids (TDS). The TDS contamination was caused by on-base irrigation of the golf course with treated wastewater and the Barstow area wide groundwater contamination. The Barstow area wide groundwater contamination was caused by off-base upgradient municipal and industrial-waste discharges and upgradient recharge of the aquifer by irrigation (U.S. Geological Survey, 1997). The Nebo Main Base has obtained its drinking water from the City of Barstow since December 7, 1977 (Western Division Naval Facilities Engineering Command, 1977). Nebo Wells 2, 3, and 6 were used after 1977 for irrigating the golf course. Nebo Well 2 was discontinued from use in 1993 (ATSDR, 1999).

Besides the TDS levels, limited data are available to determine if the Nebo Main Base production wells were impacted by the Nebo Main Base - northern plume in the past. Groundwater data from the wells are available from three sources: 1) inferred information from the IRP groundwater monitoring for the Nebo Main Base - northern plume, 2) limited sampling of the production wells that was part of the wastewater monitoring program, and 3) sampling of the production wells in 1994 and 1999.

The IRP groundwater monitoring program has defined the nature and extent of the Nebo Main Base - northern plume. This plume is contained within the base and appears to be the result of historical disposal activities at Warehouse 2 and surrounding buildings. Warehouse 2 was constructed in 1942 and operated as a repair facility until 1961 when operations were suspended and transferred to the Yermo Annex. The plume contains various volatile organic compounds (VOCs) with tetrachloroethene (PCE), benzene, and 1,2-dichloroethene exceeding EPA's MCLs.

Based on well data and groundwater modeling, the Nebo Main Base - northern plume extends 1,500 feet by 4,000 feet from these buildings and appears to be limited to the upper 20 feet of the aquifer (40 to 60 feet below ground surface, See Figure 7). The edge of the plume has reached the river, but VOC concentrations are below EPA's MCL at this edge. The maximum TCE and PCE concentrations detected in this plume are 6 µg/L and 80 µg/L, respectively (Southwest Division Naval Facilities Engineering Command, 1998). The maximum concentrations of benzene (1.2 µg/L) and 1,2-DCA (3 µg/L) were detected above ATSDR CREGs but below EPA MCLs. Chloromethane (8.9 µg/L) was detected above EPA's Life Time Health Advisory for drinking water (LTHA). The plume has remained stable and has not increased in size in the 12 quarterly sampling events since 1992 (Southwest Division Naval Facilities Engineering Command, 1998). Fate and transport studies indicated that the shallow groundwater (20 to 30 feet), high fluctuation in water table elevations, and sandy soil may all be contributing to the natural degradation of this plume (Southwest Division Naval Facilities Engineering Command, 1998).

The plume extent shown in Figure 7 was determined using existing groundwater monitoring wells, piezometers, hydropunch data, and scientific judgment. Based on Figure 7, it doesn't appear that the plume has impacted the production wells. However, there are limited groundwater data between the identified plume and the base production wells, horizontally and vertically. One permanent piezometer (NPZ-8) and two hydropunch locations (NHP-11 and NHP-15) identify the area between the southern boundary of the plume and the production wells. NPZ-8 was sampled only once in June 1994 with a detection of 1,2-dichloroethane at 0.8 µg/L. The total depth of NPZ-8 is 55 feet below ground surface (bgs). The hydropunch locations are NHP-11 and NHP-15 with a depth of 33 to 37 feet. The hydropunch locations were sampled in August 1994. Of the VOCs analyzed for, the only detected compound was chloroform in NHP-15 at 0.7 µg/L (estimated). Although these chemicals at these concentrations do not present a health concern, ATSDR was concerned that the depth of these sampling points may not represent the groundwater that the deeper production wells would draw from. Nebo Well 3, closest to Warehouse 2, was screened from 37 to 280 feet bgs. The next closest wells to Warehouse 2 are Nebo 1 and 6, which were screened beginning at 70 and 109 feet bgs, respectively. The hydropunch depths may have been adequate for Nebo Well 3 but not for the other wells. Furthermore, the pumping action of the production wells prior to 1977 would have lowered the surface of the water table and changed the groundwater flow direction, creating a sinkhole effect. Based on an aquifer test performed by the USGS, the area affected by the drawdown (equal to or greater than 0.25 feet) was approximately 0.8 square miles (U.S. Geological Survey, 1975). Current groundwater flow is easterly. If the source of groundwater contamination came from Warehouse 2 and the contamination did not spread laterally, north to south, the groundwater contamination would have missed the production wells. However, the pumping of the production wells could have spread the contamination southeast. The sampling results discussed in the next few sections indicate that it has not spread in this direction.

From the IRP Administrative Record, ATSDR found limited data from direct sampling of the production wells prior to the beginning of the IRP program in 1983. These sample dates include 1970, 1976, 1981 and 1982. The parameters and wells sampled are shown in Table 3. The 1970 data were limited to Nebo Wells 2, 3, 4, 5, and 6; parameters included a few ions (e.g., sodium sulfate), phenols, chromium, total dissolved solids, and methylene blue active substances (measures anionic surfactants, a type of detergent). The 1976 data were limited to total phenols in Nebo Well 6 and Yermo Well 3. In 1981, MCLB sampled the Nebo Main Base production wells 2, 3, and 6 for major cations and anions (e.g., ammonia and bicarbonate), other water quality parameters (e.g., pH), several minerals (e.g., silica), 11 metals, radionuclides, pesticides and herbicides, and trihalomethanes. In 1982, these wells were sampled again for radionuclides and trihalomethanes.

Of the chemicals analyzed, ATSDR considered the following chemicals of concern: phenols measured in 1976, mercury measured in 1981, and alpha radionuclide particles measured in 1982. The concentrations of these compounds are discussed in the following sections and their impact on public health is discussed in the following Public Health Implications section.

Phenols
The data available for 1976 included data on only phenols from Nebo Well 6 and Yermo Well 3. The concentrations in the Nebo Well (Table 4), varied from 2 ppb in May to 180 ppb in November and dropped to 9 ppb in a second measurement in November (the reason for this variation was not reported). The Yermo Well data are discussed in Section II.B. Phenols consist of different compounds consisting of phenol and other compounds with phenol the core of the compound (e.g., 2,4-dinitrophenol). This list may vary depending on the analytical method used. The composition of the phenols analyzed for in the 1976 data was not identified and may have only included phenol. However, for purposes here, we are defining the phenols to be the sum of 11 compounds measured by U.S. EPA Method 604 (See Table 5, U.S. Code of Federal Regulations (CFR) 40, Parts 136 - Revised as of July 1, 1995). The ATSDR comparison values of these eleven compounds vary by three orders of magnitude from 0.3 ppb (CREG) for pentachlorophenol to 200 ppb for 2,4-dimethylphenol (Chronic RMEG Child). In 1970, phenols were measured in Nebo Wells 2, 3, 4, 5, and 6 with concentrations of 8 and 3 ppb in wells 3 and 4 and non-detect in wells 2, 5, and 6. Also in 1970, MCLB analyzed water from their chlorinated water supply reservoir and the phenol concentration was below levels of detection.

Beginning in 1992, MCLB, through the IRP groundwater monitoring program, analyzed groundwater samples for the 11 phenol compounds discussed above and listed in Table 5. Results were below levels of detection. The smallest detection limits for these compounds were 10 ppbs. One of the 11 compounds has a CREG below these detection limits: pentachlorophenol (CREG 0.3 ppb). Therefore, one of the phenol compounds could possibly be present and above our screening values. ATSDR discusses the health implications of this compound in the following section titled "Public Health Implications."

Mercury
In 1981, mercury exceeded the MCL of 2 ppb at 2.6 µg/L in Nebo Main Base Well 3 and below the MCLs in Wells 2 (1.2 ppb) and well 6 (0.5 ppb) (Environmental Research Laboratory, 1981).

Radionuclides
Alpha radionuclide activity was detected above the MCL (15 pCi/L) in March 1982 in Nebo Well 3 at 21.1 pCi/L. Subsequent sampling of Well 3 in June 1982 showed alpha radionuclide activity at 4.4 pCi/L.

MCLB sampled the production wells for additional parameters of concern in 1994 and 1999 (Law/Crandall, 1994 and Foster Wheeler, 1999). In 1994, MCLB sampled Nebo Wells 2, 3, and 6 for 59 volatile organic compounds (VOCs) such as tetrachloroethene and trichloroethene, 11 metals, 19 pesticides, 8 Aroclors, and about 15 water quality parameters such as hardness, dissolved solids and pH. Of the VOCs, 1,2,3-trichlorobenzene (0.33 µg/L) and 1,2,4-trichlorobenzene (0.25 µg/L) were detected in 1994.

In 1999, MCLB sampled Nebo Wells 3 and 6 for 10 metals, 65 VOCs, and 7 water quality parameters. The analysis of VOCs included tetrachloroethene and trichloroethene. Of the VOCs analyzed for, none were detected. Well 2 was not sampled because it is no longer being used.

Public Health Implications

ATSDR evaluated the health implications from use of the on-base production wells at Nebo Annex using the limited direct sampling data and indirect groundwater monitoring data. From this data, we identified potential concerns with TCE, phenols, mercury, and radionuclides. Our concerns and evaluation of these chemicals are described below.

Phenols
The phenols identified in Nebo Well 3 and 4 in 1970 and in Well 6 in 1976 are difficult to evaluate because phenols consist of different compounds, each with a different toxicity as discussed previously. Moreover, we do not know if the analysis was for phenol or if it included the sum of different phenol compounds. We have assumed that the analysis was the sum of the individual compounds to be more protective of human health. In 1992, MCLB sampled for these individual compounds and they were not detected. However, the detection limit for one phenol compound was higher than ATSDR's comparison value. MCLB did not locate any sources of this type of contamination at the base, but the contaminants may have been part of the Barstow area groundwater contamination (U.S. Geological Survey. 1975). Nonetheless, ATSDR concludes that exposure to phenols is not a public health hazard since the 1970 data showed that the drinking water reservoir did not contain phenols although Wells 3 and 4 had values of 8 and 3 ppb, respectively. The water from the individual wells was mixed in a reservoir before distribution. Therefore, this indicates that the mixing with the other wells reduced the concentrations to levels below detection. We assume that in 1976 and in other years for which we don't have data, the water from the wells was similarly mixed and the results similar to those from 1970.

Mercury
The level of mercury of 2.6 ppb (MCL = 2 ppb) detected in the well water is not a public health hazard. Although mercury exceeded the MCL in Well 3, mercury was below the MCL in Wells 4 and 5 because in part, the water from these wells was mixed prior to distribution lowering the total level to safe concentrations. The mixing ratio when this sample was taken is not known. However, if the groundwater from Well 3 mixed with Well 2 (1.2 ppb) and Well 6 (0.5 ppb) on a 33/33/33 part by volume, the combined mercury concentration would have been below the MCL at 1.4 ppb. In fact, Well 3 had the lowest pumping rate of the Nebo Main Base wells so this ratio is probably conservative.

Other factors we considered about exposure are the concentration of mercury in Well 3 over time and the speciation of mercury. We do not have that trend data or speciation of mercury. We assumed the mercury was mostly inorganic mercury since the water was obtained from groundwater. Based on the mixtures, ATSDR concludes that mercury in the well water was not a public health hazard.

Radionuclides
Alpha radionuclide activity was measured in Nebo Main Base Well 3 (21.1 picocuries per liter (pCi/L) above the MCL (15 pCi/L) in March 1982. In subsequent sampling, the value dropped below the MCL. ATSDR concludes that this one time concentration above the MCL is not a public health hazard for two reasons:

  • Water from Well 3 was mixed with other wells. Alpha radionuclide activity in Nebo Wells 2 and 6 was below the MCL in the March 1982 samples. Hence, the dilution would have reduced the value to below the MCL. Although we don't know the dilution ratio, Well 3 is the lowest producing well at Nebo. A contribution of 1/3 of the water from each well would have reduced the concentration to 1.8 pCi/L. This value is below the MCL of 15 pCi/L.


  • If mixing of the water from different wells did not occur, a health impact is still not expected. The health endpoint for alpha radionuclide activity is cancer and the MCL is devised on multiple years of exposure. Nebo Well 3 was sampled in June 1982 and the alpha radionuclide activity was 4.4 pCi/L after being 21.1 pCi/L in March. Since exposure above the MCL occurred for at most three months, the additional risk for getting cancer is negligible.

Volatile Organic Compounds
Prior to 1994, MCLB sampled the Nebo Main Base production wells for VOCs consisting of trihalomethanes. In 1994 and 1999, MCLB sampled the Nebo Main Base production wells for many other VOCs including all the chemicals detected in the Nebo Main Base - northern plume. This chemical list included TCE and PCE. MCLB detected trihalomethanes in the pre-1994 samples and 1,2,3-trichlorobenzene (0.33 µg/L) and 1,2,4-trichlorobenzene (0.25 µg/L) were found in the 1994 samples.

The concentrations of trichlorobenzene and trihalomethanes detected are below ATSDR's environmental risk evaluation guidelines (EMEGs) for water. Therefore, ATSDR concludes that past uses of the Nebo Main Base production wells were probably not a health hazard based on the limited piezometer and hydropunch data collected during the Installation Restoration Program and direct sampling of the wells in 1994 and 1999. Therefore, the use of these wells in the past are assigned an ATSDR hazard category of no apparent public health hazard.

Although the use of the production wells poses no apparent health hazard, the population that would have been affected included people working and living at the Nebo Main Base prior to 1977. The earliest population data we have of MCLB are from 1988. In 1988, the population working and living on base was approximately 5,000 (Nebo and Yermo): 885 working and living on base and additional 4,115 working and living off-base. If we assume that 1,300 people were working at the Yermo Annex in 1988 (based on 1990 data, Jacobs Engineering Group, 1990a), then 3,700 worked at Nebo with 885 of these people also living on base. It is not clear from this data if the number of dependents is included in the 885 people. It is very likely that the population changed regularly due to rotations and the amount of military activity.

Conclusion

Overall, we have assigned the ATSDR hazard category of No Apparent Public Health Hazard for past use of these wells for drinking water and production because indirect evidence indicates that they were probably not contaminated above levels of concern in the past. The indirect evidence consists of piezometers and deep wells that may not be in any flow paths between the source area and the production wells. The deep wells are located laterally and downgradient of the production wells and the piezometers are not as deep as the production wells. Other indirect evidence of past water quality includes sampling of the production wells in 1994 and 1999 for VOCs. All of the VOCs analyzed for were not detected except for two compounds in 1994. The concentrations of these two compounds were at least 10 times below levels of health concern.

2. Past, current, and future use of the Nebo Main Base production wells for irrigation

In Section II.A.1, we discussed the general groundwater quality, well sampling data, and the public health impacts from ingesting the water from the Nebo Main Base production wells. These data also apply to evaluation of the public health impact of using the wells for irrigating the golf course. In this case, the potential existed for past, current, and future exposure to volatile organic compounds such as TCE and PCE, the highest VOCs measured in the groundwater. These compounds, if present, could volatilize during irrigation and people could be exposed via inhalation.

For past exposure, ATSDR doesn't have direct evidence of TCE and PCE in the production wells. As stated in the beginning of Section II.A.1., the piezometers and deep wells that were installed may not be in any flow paths between the source area and the production wells. The deep wells used in the IRP monitoring program are located laterally and downgradient of the production wells and the piezometers are not as deep as the production wells. Nonetheless, for this evaluation of past exposure prior to 1994, we assumed the VOCs were present.

ATSDR examined this past exposure route through the following steps:

  • We assumed that TCE and PCE are the only volatile organic compounds present in the production wells and they are present at the highest concentrations measured (6 µg/L TCE and 80 µg/L PCE) during the IRP monitoring program. Although other VOCs were present, TCE and PCE are compounds with the highest concentrations detected and the most toxic. If these compounds can be shown to be safe, the other compounds detected will also be safe.


  • The irrigation water is piped to an open reservoir. The pipe that discharges the groundwater into the reservoir is elevated above the surface of the water. Hence, the water is aerated as it splashes into the reservoir. This aeration would enhance the volatilization of these compounds reducing their concentration in the water. Further volatilization occurs from the water as it is stored in the open reservoir for a variable period of time.


  • People would be exposed to the VOCs, downwind of the reservoir or during irrigation. ATSDR's Cancer Risk Evaluation Guide for TCE is 0.6 ug/m3 and 2 ug/m3 for PCE. To calculate a concentration that would over estimate the actual concentration present and be overly protective of human health, we assumed that all of the TCE and PCE volatilize during irrigation. Further, we assumed that the water is applied at a rate of 1000 liters/minute (264 gallons/minute) for one hour and the volatilized TCE and PCE stays in a box. This box is the approximate length and width of the golf course (2,500 feet by 500 feet) with a ceiling height of 15 feet. We then find the concentrations in the box are 0.07 ug/m3 PCE and 0.005 ug/m3 TCE. These values are 100 times below the CREGs. Furthermore, the assumptions used in these calculations overestimate exposures. Hence, actual concentrations would be even lower based on these assumptions. Therefore, past use of the water for irrigating the golf course is not an apparent public health hazard.

For current and future exposure, we evaluated exposure based on the analysis of the production well water in 1994 and 1999 which showed all of the VOCs analyzed for were not detected except for two compounds: 1,2,3-trichlorobenzene (0.33 µg/L) and 1,2,4-trichlorobenzene (0.25 µg/L). Both of these compounds were detected in Nebo Well 2 in 1994. The concentrations of these two compounds if released to the air would also be below levels of concern for inhalation because they would move through the atmosphere in the same manner as TCE and PCE and are at least 20 times lower in concentration. Furthermore, MCLB discontinued the use of Nebo Well 2 in 1993. Therefore, ATSDR classifies these wells as no public health hazard for current and future use for irrigation.

Conclusion

Overall, ATSDR assigns the hazard category of No Apparent Public Health Hazard for past use of these wells for irrigation based on our assumptions, risk calculations, and existing data and No Public Health Hazard for current and future use of the wells based on the 1994 and 1999 sampling data.

3. Past use of off-site private wells southeast of the Nebo Main Base

Summary

Two private off-base wells, used in the past, were contaminated by TCE from the Nebo Main Base - southern plume. Based on ATSDR's evaluation described in this section, past consumption of the groundwater is not likely to result in health problems. Therefore, ATSDR assigned the hazard category of No Apparent Public Health Hazard. Furthermore, current and future uses of these wells are Not a Public Health Hazard since the wells are no longer used.

Discussion

The Nebo Main Base - southern plume, located at the southeastern corner of the Nebo Main Base, has migrated approximately 600 feet off-base. The plume is about 800 feet by 1,000 feet and migration is limited by low aquifer conductivity and the high organic carbon content of the soil (Southwest Division Naval Facilities Engineering Command, 1996). This plume is believed to originate from the historical use and disposal of solvents at CERCLA Area of Concern 6 (CAOC 6), Original Trash Landfill (Southwest Division Naval Facilities Engineering Command, 1998) or from a drainage channel that extended between IRP sites 5 and 6 that may have been used for the discharge of solvents, oils, and fuels (Jacobs Engineering Group, 1993).

The maximum TCE and PCE concentrations detected in the southern plume were 422 µg/L and 17 µg/L, respectively (Southwest Division Naval Facilities Engineering Command, 1998). Maximum concentrations of 1,2-DCA (4 µg/L), chlorodibromomethane (3.0 µg/L), and bromodichloro-methane (4.0 µg/L) were detected above ATSDR's CREG but below EPA's MCL. The southern plume is downgradient the former base production wells. The plume has moved east, away from the base.

MCLB discovered groundwater contamination at the Nebo Main Base - southern plume in 1992 after installing and sampling monitoring well NEP-4. TCE was the only detected volatile organic in 1992 at 290 ppb (accuracy of this value was in doubt because it did not pass quality assurance and quality control protocols). Also in 1992, MCLB identified two wells on private property adjacent to the southeast corner of the base near NEP-4 that was used by families in one house and two mobile homes. The closest well was sampled in November 1992 and found to be contaminated with TCE at 11 ppb (CERCLA Level 3 QA/QC). The well was resampled in December 1992 and found to contain 9 ppb TCE (preliminary data, CERCLA Level 4 QA/QC). The families were provided with bottled water four days after MCLB obtained the first sample result (Jacobs Engineering Group, 1993a). In June 1993, the homes were connected to the MCLB water supply (Jacobs Engineering Group Inc., 1993b).

The second well, approximately 750 feet downgradient of the first well, was used for irrigation and has never been sampled (ATSDR, 1999). ATSDR assumes the well is contaminated based on contaminated downgradient monitoring wells. MCLB reports that this irrigation well is no longer used.

We estimate the affected population to be about 12 people and assume that the wells are no longer being used for any purpose (ATSDR, 1999).

Extrapolation of the two sample results to historic concentrations is difficult because groundwater concentrations may have fluctuated. ATSDR does not know, with complete certainty, if the two samples sufficiently represent exposure. The private well has not been resampled since 1992 and the construction of the well is not known. However, it is very likely that the more highly contaminated groundwater is closer to NEP-4. Hence, the TCE concentrations were probably never as high as 290 ppb as detected in NEP-4. Since the plume appears to have limited longitudinal and lateral migration and the concentration decreases east of well NEP-4, ATSDR assumes that the highest concentration in the private well was 11 ppb TCE.

Public Health Implications

The maximum TCE concentration detected in the first private well (11 ppb) adjacent to the Nebo Main Base's southeast boundary is above both ATSDR's CREG and EPA's MCL. Since the CREG is a screening tool, exposure to TCE concentrations above the CREG are not necessarily associated with health effects. ATSDR evaluated the potential for adverse health effects from exposure to TCE-contaminated groundwater. Accounting for sensitive subpopulations (i.e., children), ATSDR estimated that adults drank and otherwise ingested (including inhalation due to cooking and showering) 4 liters of well water each day and weighed 70 kilograms (kg). We assumed children drank and otherwise ingested 3 liters of well water each day and weighed 10 kg. To calculate a conservative exposure dose, ATSDR used the exposure period of 30 years and the maximum contaminant concentrations. As a result of this assessment, ATSDR concludes that consumption of TCE in off-site drinking water from the first private well did not and will not result in health problems for the off-site residents using the affected well for home use in the past. The calculations are presented in Appendix C.

ATSDR has also determined that the use of the second private well is not a health hazard because of lower concentrations and its use as an irrigation well. Although the second private well has not been sampled, we are confident that the concentrations would be lower than the first private well for two reasons. First, the second private well is farther downgradient from the source area, and second, the contaminant concentrations, as indicated by the monitoring wells, become lower as one moves downgradient from the source area. Besides these lower concentrations, the use of the water for irrigation results in a lower exposure than consumption of the water from the first well. Since use of the water in the first private well is not an apparent public health hazard, we conclude that use of water from the second well for irrigation is not an apparent public health hazard.

Future monitoring and restrictions on the use of the groundwater will be accomplished through MCLB's Long Term Groundwater Monitoring Plan as required by the Record of Decision (ROD) for Operable Units 1 and 2. The plan is updated annually. As required by the ROD, MCLB has notified the San Bernardino County Department of Health Services of the groundwater contamination. San Bernardino County is responsible for approval of new well drilling and has been provided information on the groundwater contamination.

Overall for this exposure, ATSDR assigns the hazard category of No Apparent Public Health Hazard.

4. Past use of the Yermo Annex production wells for on-base drinking and production

Summary

Historically, the Yermo Annex at MCLB used 5 groundwater wells to obtain water from the Mojave River Aquifer. After 1975, only three of the five wells were active. In 1988, MCLB found groundwater contamination (volatile organics) in each of the three active wells. The highest concentration detected was 25 µg/L TCE in Yermo Well 3 in 1988. The MCL for TCE is 5 µg/L. MCLB decommissioned Well 3 at this time. Contaminants in the other two wells were below MCLs. The wells were also monitored for other water quality parameters as discussed in this section. Based on the length of exposure and the concentration of contaminants in the wells, ATSDR concludes that there is no public health hazard. Therefore, we have assigned the ATSDR hazard category of No Apparent Public Health Hazard since people were exposed to concentrations below levels of concern.

Discussion

Historically, the MCLB Yermo Annex used five groundwater wells to obtain water for drinking and production. Yermo Well 1 was taken out of service in the 1950s while Yermo Well 2 was taken out of service in 1975. The locations of these wells are shown in Figure 6.

Yermo Well 3 was discontinued in 1995 because of groundwater contamination. Yermo Wells 4 and 5 are still in use. MCLB plans to install a sixth well outside of the groundwater plume. This plume is discussed on the next page. The status of these wells, pumping rates, and screen depths are summarized in Table 2.

In 1988, MCLB found TCE contamination in Well 3 exceeding MCLs. TCE was detected at 5.7 µg/L in March 1988 and subsequently at 25 µg/L in November 1988 (Jacobs Engineering Group, 1990b). During this same time, TCE contamination was found below MCLs in Yermo Well 4 at 1.5 µg/L and in Well 5 at 1.7 µg/L (Jacobs Engineering Group, 1992).

Since TCE in Well 3 exceeded the MCL of 5 µg/L, MCLB decommissioned the well but reactivated it in 1989, after installation of an activated carbon water treatment system. The well was taken off-line permanently in 1995 because of deterioration of the wellhead and collapse of the well casing. The well was sealed and closed in 1997 (ATSDR, 1999).

MCLB continues to use Well 4 since the TCE concentrations are below MCLs and it is upgradient of the currently defined plumes. The source of contamination in the well was not discussed in the Administrative Record. Well 4 has been monitored quarterly since 1997 and the results have been below detection levels.

MCLB continues to use Yermo Well 5. An activated carbon treatment system was installed on it in 1989. The system was installed as a precautionary measure due to its close proximity to Building 573 and a landfill.

The groundwater contamination that has impacted the Yermo Annex wells is described as one plume composed of three co-mingled plumes that arise from different sources. The contaminants of concern in all three plumes are volatile organic carbons (VOCs), with TCE and PCE the predominant compounds.

The first plume, or Yermo Annex northern plume, impacted Yermo Annex Well 5. This plume is beneath and downgradient of CAOCs 15/17, 16, 18, and 35. The plume extends 5,000 feet downgradient of its sources and has migrated off-base. Maximum concentrations of TCE and PCE are 77 µg/L and 230 µg/L, respectively.

The second plume, or Yermo Annex southern plume, is downgradient of CAOCs 22 and 23 and has impacted Yermo Annex Well 3. The southern plume is co-mingled with the northern plume, resulting in a combined area, 8,000 feet long and 2,000 feet wide, extending about one mile beyond the base boundary. The maximum TCE and PCE concentrations detected within this plume are 34 µg/L and 18 µg/L, respectively.

The third, or CAOC 26 plume, is downgradient of CAOC 26. This plume mingles with the northern and southern plumes and may have contributed to contamination detected in Wells 3 and 5. TCE and PCE were detected in the CAOC 26 plume at concentrations of 141 µg/L and 31 µg/L, respectively.

The groundwater flow direction is to the east, with the groundwater at the southwestern corner of the base flowing northeast and then becoming east as it flows under the central part of the Yermo Annex. The maximum concentrations detected at the eastern base boundary are 74 µg/L for TCE and 66 µg/L for PCE. Contaminant levels above drinking water standards have been detected off-base about 2,000 feet downgradient of the base boundary.

The existing data indicate that the VOC contamination is located primarily within the upper 40 feet of the groundwater table (Southwest Division Naval Facilities Engineering Command, 1996).

ATSDR does not have the exact date Yermo Wells 3, 4, and 5 became contaminated since sampling before 1988 was limited. In 1985, MCLB sampled groundwater from Yermo Wells 3, 4, and 5 for volatile organic compounds, semivolatile organic compounds (SVOCs), herbicides and pesticides. Concentration values were below detection (MCLB, 1985). One could conclude from these data that wells 3, 4, and 5 were not contaminated prior to this date. However, this conclusion holds some uncertainty for two reasons. First, the detection limits for this analysis were not available and second, definitive conclusions are usually drawn from several consecutive samples over several months.

Prior to 1985, ATSDR found limited data from the Yermo Annex production wells. From the IRP Administrative Record, ATSDR found sample results from 1970, 1976, 1981, and 1982. The dates, wells sampled, and constituents analyzed for in the Yermo Annex production wells are presented in Table 3. TCE and PCE were not analyzed for during these times, so these data will not help us determine when the wells became contaminated with these compounds. On the other hand, these data showed the groundwater contained phenols in 1976 (3 ppb to 83 ppb in Well 3) and chloroform in 1982 (0.1 µg/L in Well 3 and 0.5 µg/L). Other constituents were present but were below levels of concern.

Phenols were singled out because the data did not indicate if phenol or a class of phenol compounds were present. As discussed in Section II.A.1, the phenols present a range of toxicity. The evaluation of these concentrations is presented in the next section. Phenol and phenolic-type compounds were not detected in groundwater samples taken during the IRP groundwater monitoring after 1992. In addition, phenols were not detected in samples taken in 1970, although the detection limits were not reported.

Chloroform was singled out as a possible indicator of other contamination, such as the TCE plume. However, the highest concentration of chloroform detected from the IRP monitoring program was 1 µg/L. Therefore, the presence of chloroform probably does not indicate that TCE contamination is present.

Based on the evaluation of these data, ATSDR assumes for the purposes of this report that the Yermo Annex wells were not contaminated prior to 1985.

Public Health Implications

ATSDR evaluated the health implications of using the on-base production wells at the Yermo Annex. ATSDR evaluated the exposure to TCE and phenols.

Phenols
The phenols identified in Yermo Well 3 in 1976 are difficult to evaluate because phenols consist of different compounds, each with a different toxicity. Moreover, we do not know if the analysis was for phenol or if it included the sum of different phenol compounds. We have assumed that the analysis was the sum of the individual compounds. The IRP sampled for these individual compounds and they were not detected. However, the detection limit for one compound was higher than ATSDR's comparison values. MCLB did not locate any sources of this type of contamination at the base, but the contaminants may have been part of the Barstow area groundwater contamination (U.S. Geological Survey. 1975). Nonetheless, ATSDR concludes that exposure to phenols is not an apparent public health hazard since Yermo Annex Well 3 was used sporadically and the IRP program has not found a source of phenol type contamination.

TCE
Short-term exposure to TCE may have occurred for workers at the Yermo Annex from 1985 to 1988 when contamination was detected in Yermo Annex Wells 3, 4, and 5. The exact extent of the exposure is not known because Well 3 was used sporadically for unknown periods of time as a backup supply. Wells 4 and 5 were contaminated but at levels below MCLs. Since TCE was the only contaminant above MCLs detected in Well 3, we evaluated the health implications of exposure to TCE for 3 years.

Since the Yermo Annex was a work environment, we did not evaluate children. ATSDR assumed that adults weighed 70 kilograms and drank and otherwise ingested (including inhalation from volatilization of TCE from the water) 4 liters of well water each day for 3 years. From the calculations presented in Appendix C, ATSDR does not expect past use of the water to cause noncarcinogenic health effects nor an increased risk of cancer.

There is no potential for present or future exposures to workers at the Yermo Annex, because the base's drinking water supply is in compliance with state and federal standards.

As a result of this assessment, ATSDR concludes that consumption of TCE or phenols in on-site drinking water at the Yermo Annex in the past is Not an Apparent Public Health Hazard. Current and future exposure to contaminants from well 5 does not pose a public health hazard because the water from this well is treated prior to distribution and the water is monitored monthly for organics. Current and future exposure of water from Well 4 is not a health hazard because monitoring from 1997 had shown levels below detection.

5. Past use of off-site private wells east of the Yermo Annex

Summary

TCE levels found in two off-base wells were below MCLs. Carbon treatment units have been installed on the two wells. Past use of the ground water is Not an Apparent Public Health Hazard. Current and future use of the wells is Not an Apparent Public Health Hazard because the groundwater is treated prior to use.

Discussion

In 1995, elevated levels of TCE (5 µg/L) and PCE (5 µg/L) were detected in monitoring well Y15-1, which is upgradient from two private wells adjacent to the Yermo Annex. Sampling at the two private wells indicated that low levels of TCE (0.6 µg/L) and PCE (0.8 µg/L) were present. MCLB initiated a time-critical action and provided bottled water to the residents until a carbon treatment unit could be installed on each well. Three additional active drinking water wells are located about 2 miles downgradient of the Yermo Annex. Groundwater sampling indicates that the water quality of these wells has not been affected by activities on the base. Fate and transport modeling of the groundwater indicates that it will take about 30 years for the plume to reach these wells and that the maximum concentration expected to reach the well will be below drinking water standards (Southwest Division Naval Facilities Engineering Command, 1998).

Although past exposures to TCE may have occurred at two private wells adjacent to the Yermo Annex, the levels of TCE were well below MCLs and no health hazards are expected. The wells currently have carbon-activated absorption treatment units to remove organic contaminants, so there is no risk for present or future exposures. These treatment units are monitored by MCLB quarterly for VOCs and the results show that the carbon filters have been treating the water to non-detect levels.

Public Health Implications

In summary, there is No Apparent Public Health Hazard from past consumption of groundwater from these two private wells. Additionally, current and future use of the wells is Not an Apparent Public Health Hazard since the water is treated prior to use. Future monitoring and restrictions on the use of the groundwater will be accomplished through MCLB's Long Term Groundwater Monitoring Plan as required by the Record of Decision (ROD) for Operable Units 1 and 2. The plan is updated annually. As required by the ROD, MCLB has notified the San Bernardino County Department of Health Services of the groundwater contamination. San Bernardino County is responsible for approval of new well drilling and has been provided information on the groundwater contamination.

B. Past, current, and future exposure to soils at the rifle range.

The rifle range is used by the Marine Corps for target practice. The local police have also used the range. The rifle range consists of three areas: the rifle range impact area, the pistol range impact area, and the machine gun impact area. The rifle and pistol ranges are operational, while the machine gun impact area was last used in 1960. At the rifle range impact area, 50,000 rounds of ammunition are fired annually and at the pistol range impact area 30,000 rounds are fired annually. Unexploded and defective devices are removed from the practice areas after shooting exercises. The surface soil in the area is contaminated with lead from spent bullets or bullet fragments. Lead concentrations of up to 17,300 milligram per kilogram (mg/kg) have been detected on the rife range (Southwest Division Naval Facilities Engineering Command, 1996). The past and current use of the site does not pose a human health hazard because access is restricted, but this could change with future land use changes. Land use changes and future needed cleanup are regulated under the Department of Defenses' Environmental Restoration Program and the proposed Range Rule (Code of Federal Regulation, Volume 32, Section 339) addressing firing ranges. In short, past, current, and future use of the rifle range is not a public health hazard with present land use.


III. COMMUNITY HEALTH CONCERNS

Two series of public interviews have been conducted by the Marine Corps for a Community Relations Plan. The first interviews were conducted in February and March 1990 and involved 35 community members. A second set of interviews involving 12 community members was conducted in June 1994 for an updated version of the Community Relations Plan. All respondents expressed general concerns regarding the existence of contaminated areas at MCLB. One third of the interviewees were aware that the major area of concern was the contaminated groundwater beneath the base. Some of the respondents (primarily in the first round of interviews) felt that the base was too secretive about its cleanup operations. In response, the base conducted two open houses to discuss cleanup activities and provide fact sheets. In addition, MCLB is publishing a quarterly newsletter addressing IRP activities. Residents of Barstow, which is located upstream from MCLB, did not express public health concerns. The residents of the communities of Daggett, Yermo, and Newberry Springs, which are located downstream from Barstow, expressed concern about potential contamination of their drinking water supplies (Jacobs Engineering Group, 1995a). During the 1997 site visit, ATSDR met with several citizens who expressed concerns about area groundwater quality not related to activities at MCLB.


IV. ATSDR CHILD HEALTH INITIATIVE

ATSDR recognizes that infants and children may be more sensitive to environmental exposure than adults in communities faced with contamination of their water, soil, air, or food. This sensitivity is a result of the following factors: 1) children are more likely to be exposed to certain media (e.g., soil or surface water) because they spend more time outdoors than most adults; 2) children are shorter than adults, which means that they can breathe dust, soil, and vapors close to the ground; and 3) children are smaller; therefore, childhood exposure results in higher doses of chemical exposure per body weight. Children can sustain permanent damage if these factors lead to toxic exposure during critical growth stages. ATSDR is committed to evaluating special interests at sites such as MCLB, as part of the ATSDR Child Health Initiative.

ATSDR evaluated the likelihood that children living on MCLB may have been or may be exposed to contaminants at levels of health concern. ATSDR did not identify any situations in which children were likely to be or have been exposed to chemical contaminants at levels of health concern. Although the children may have been exposed to elevated levels of TCE in drinking water, conservative exposure estimates indicate that the maximum detected concentrations do not pose a health concern. It is unlikely that the children would have come into contact with other on-site contaminated media because these sites are not close to the residential housing on the base and have restricted access due to their industrial nature.


V. HEALTH OUTCOME DATA

ATSDR conducts a review of existing health outcome data (e.g., birth and death certificates, birth defects registries, cancer registries, etc.), when available, if people have been exposed to site contaminants or if the community has concerns related to specific health outcomes. The evaluation of health outcome data may give a general picture of the health of a community, or it may confirm the presence of excess disease or illness in a community. However, elevated rates of a particular disease may not necessarily be caused by hazardous substances in the environment. Other factors such as personal habits, socioeconomic status, and occupation, also may influence the development of disease. In contrast, even if elevated rates of disease are not found, a contaminant may still cause illness or disease.

At MCLB, ATSDR did not review health outcome data because the exposures identified were at levels that would not cause adverse health effects.

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