PUBLIC HEALTH ASSESSMENT
EDWARDS AIR FORCE BASE
EDWARDS AIR FORCE BASE, KERN COUNTY, CALIFORNIA
Edwards Air Force Base (EAFB) occupies 470 square miles in southern California, approximately 100 miles northeast of Los Angeles. Since the base was established in 1933, the U.S. Air Force and the National Aeronautics and Space Administration have used EAFB facilities to conduct aircraft research, which has included development and testing of airplanes, rockets, and rocket fuels. A number of chemicals, primarily fuels and solvents, are needed to operate and maintain the aircraft tested at EAFB. EAFB has identified past practices that resulted in chemical contamination of the environment. Because of the presence of contamination in groundwater, landfills, and soils on base, the U.S. Environmental Protection Agency (EPA) placed EAFB on the National Priorities List on August 30, 1990. Site investigations, remediation, and preparation of a Record of Decision are in progress to address known and potential contamination (AFFTC 1998b).
This public health assessment (PHA) presents the Agency for Toxic Substances and Disease Registry's (ATSDR's) evaluation of whether past, current, or future practices at EAFB could cause people who live or work on base, or nearby community members, to be exposed to unhealthy levels of environmental contamination. To prepare this PHA, ATSDR reviewed available environmental sampling data from EAFB, EPA, the U.S. Geological Survey, the North Edwards Water Quality Board, and the California Department of Toxic Substances Control. ATSDR also consulted with community members, base personnel, and regulatory agency officials. From this data review, communication with people knowledgeable about EAFB, and site visits conducted in 1998, 2001, and 2002, ATSDR was able to evaluate three potential exposure pathways and four community concerns related to EAFB.
ATSDR's conclusions related to the three potential exposure pathways follow and are summarized in the table at the end of this section.
- Potential exposure to contaminants in drinking water. As a result of past practices at EAFB, contamination has been released to groundwater at hundreds of Environmental Restoration Program (ERP) sites throughout the base. Although EAFB ERP investigations have revealed petroleum hydrocarbons, volatile organic compounds, and semi-volatile organic compounds in groundwater throughout the base, contaminants have not migrated to on-base or to off-base drinking water supply wells. ATSDR evaluated groundwater sampling data for both on-base and off-base private and public drinking water wells. ATSDR determined that no humans have been exposed to contaminants via drinking water supplied by EAFB drinking water supply systems, off-base community supply systems, or off-base private wells--drinking water supplies are safe. The groundwater contamination at EAFB is therefore not a public health hazard, and remediation and monitoring programs are in place to ensure that it does not become a future hazard.
- Potential exposure to chemical warfare materiel (CWM). A U.S. Army report released in 1993, as part of an Army-wide investigation effort, listed EAFB as likely to have buried CWM. As a result, in 1994, an archival research program and subsequent site investigations were initiated at EAFB to identify potential locations of CWM. Based on community concerns, ATSDR evaluated potential exposures to CWM that could have been located in soil or soil gas at four sites (Sites 426, 427, 429, 445) on base. Through site investigations, EAFB has found no evidence of buried CWM in soil at any of the locations. ATSDR determined that no human exposure to CWM and/or CWM degradation products has occurred on base. Therefore, CWM is not a past, present, or future public health hazard.
- Potential exposure to dioxins in air from Sites 16 and 18. Petroleum and halogenated hydrocarbon releases to soil and groundwater at Sites 16 and 18 have prompted EAFB to install soil vapor and groundwater extraction systems (dual extraction systems, or DESs) to clean up contamination. These DESs have the potential to emit dioxins in the air because of the combustion processes they use to destroy contaminant particles. ATSDR examined stack emission, ambient air, and dispersion modeling data for dioxins produced by the DESs at Sites 16 and 18. ATSDR determined that predominant wind directions blow contaminants away from residences and off-base populations, so the potential for exposure to dioxins from Sites 16 and 18 is limited. ATSDR also evaluated concentrations of dioxins in ambient air and determined that they are lower than levels that would be expected to produce adverse health effects. ATSDR concludes that exposure to dioxins from DESs at Sites 16 and 18 is not likely to result in adverse health effects.
One well at EAFB, well N-2, has contained elevated levels of arsenic at various times during its use (1964-1995). Arsenic in this well is likely due to naturally occurring background concentrations. ATSDR examined arsenic monitoring data and the likelihood of exposure to drinking water from this well. ATSDR determined that arsenic concentrations in well N-2 were not high enough and exposures were not of sufficient duration to result in adverse health effects. Well N-2 has not been in use since 1995.
|Exposure Scenario||Time Frame||Exposure||Public Health Hazard?||Actions Taken/Recommended|
|Residents and workers drinking groundwater from on-base supply wells.||Past||Yes||No||
|Off-base residents drinking groundwater that supplies private and community supply wells near the North Base boundary.||Past||No||No||
|Base residents and workers coming in contact with chemical warfare materiel (CWM) in soil or soil gas on base.||Past||No||No||
|Base residents and workers breathing dioxins in air from two dual extraction remediation systems at Sites 16 and 18.||Past||Yes||No||
Edwards Air Force Base (EAFB) is located in California approximately 100 miles northeast of Los Angeles (see Appendix B, Figure 1). The base is situated within three counties: Kern, Los Angeles, and San Bernardino. Nearby communities include Boron, California City, Kramer Junction, Lancaster, Mojave, North Edwards, and Rosamond. The base occupies 470 square miles, including all of Rosamond and Rogers Dry Lakebeds (AFFTC 1998b).
Military activity began in the EAFB area in 1933, when the Army Air Corps set up the Muroc Bombing and Gunnery Range on the eastern side of Rogers Dry Lakebed. In the early 1940s, troops were moved to an area across the lakebed, now known as South Base. The Army Air Corps used the range to the east of the lakebed to train fighter pilots and bomber crews during World War II. By 1946, all activities were under the control of the Muroc Army Airfield. In 1948, the Muroc Army Airfield became a U.S. Air Force (USAF) facility. The facility was named "Edwards Air Force Base" on December 8, 1949 (AFFTC 1998a).
On June 25, 1951, the U.S. Air Force Flight Test Center (AFFTC) was opened to support aircraft test flights, operate test facilities, and provide facilities for contractors. Between 1952 to 1955, facilities were moved from South Base to the present Main Base area (AFFTC 1998a).
Today the host units of the base are the AFFTC 412th Test Wing, the 95th Air Base Wing, and the USAF Test Pilot School. The major associate units include the National Aeronautics and Space Administration's (NASA's) Dryden Flight Research Center (DFRC), the Air Force Research Laboratory--Propulsion Directorate (AFRL), the Defense Commissary Agency, the Air Force Operational Test and Evaluation Center, the 31st Test and Evaluation Squadron, the 602nd Training Support Squadron, the Army Air Force Exchange Service, and the Utah Test and Training Range (AFFTC 1998b).
Activities at EAFB, such as development and testing of airplanes, rockets, and rocket fuels, aircraft operation and maintenance, and bombing range use, have focused on supporting aircraft research as the base's primary mission (AFFTC 1998b).
A number of chemicals, primarily fuels and solvents, are needed to operate and maintain the aircraft tested at EAFB. Currently, use and disposal of these chemicals are strictly regulated to prevent releases to the environment. EAFB, however, has identified past practices that may have resulted in known or potential chemical contamination of the environment. These practices included:
- Use of underground and above-ground storage tanks (USTs and ASTs) and pipelines to store and transport fuels and liquid chemicals. Large amounts of petroleum, oils, and lubricants (POLs) have been used to support aircraft testing. Much of these chemicals was stored in USTs and ASTs, which can leak. POLs were also unintentionally spilled during storage, transport, and use, as well as intentionally released for dust control and during aircraft operation.
- Use of cleaning agents (solvents and corrosives) and coating-related materials (paints, thinners, strippers, and plating materials) in aircraft operation and maintenance. Until the 1970s, when more stringent disposal controls were implemented, base personnel may have disposed of these chemicals by pouring them directly onto the ground or into dry wells.
- Disposal of wastes in sanitary landfills and hazardous waste disposal areas. Domestic garbage, industrial wastes, and hazardous materials were commonly placed in landfills for disposal. At bombing ranges, munitions burial pits were used for disposal of spent ordnance.
- Collection of wastewater and surface-water runoff in stormwater retention ponds, evaporation ponds, and test stand catchment basins. At AFRL, solvents and cooling water were disposed of in catch basins that drained to the desert.
- Fire training using fuels and flammable liquids. The USAF released fuels and other flammable liquids to practice firefighting techniques. Materials were released to the ground and ignited.
EAFB's Environmental Restoration Program (ERP) began in 1980. The first preliminary assessment study, published in 1981, identified nine sites with potential groundwater contamination. Another 31 ERP sites were identified during the 1980s.
The U.S. Environmental Protection Agency (EPA) placed EAFB on the National Priorities List (NPL) on August 30, 1990. A Federal Facility Agreement (FFA) was signed on September 25, 1990, by USAF, EPA (Region 9), and the California EPA's (CALEPA's) Department of Toxic Substances Control (DTSC). On October 16, 1990, the California Regional Water Quality Control Board, Lahontan Region, signed the FFA. The FFA requires compliance with the National Contingency Plan; Resource Conservation and Recovery Act (RCRA); Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA); Superfund Amendment and Reauthorization Act (SARA); and applicable state law. The agreement instituted a process through which federal and state agencies, as well as the public, could be involved in the cleanup of EAFB.
A Comprehensive Remedial Investigation/Feasibility Study Management Plan was published in 1991. The Plan organized the 40 sites identified during the 1980s into seven operable units (OUs). An Expanded Source Investigation/RCRA Facility Assessment was carried out from 1991 to 1993, resulting in the identification of additional sites. Each of these was placed in one of 10 OUs (see Appendix B, Figure 2). The 10 OUs represent primarily geographic areas:
- OU 1: Main Base Flight Line
- OU 2: South Base
- OU 3: Base-Wide Water Wells
- OU 4: Air Force Research Laboratory
- OU 5: Jet Propulsion Laboratory
- OU 6: NASA Dryden Flight Research Center
- OU 7: Base-Wide Miscellaneous
- OU 8: Northwest Main Base
- OU 9: East Air Force Research Laboratory
- OU 10: North Base
A total of 471 sites have been identified on the base (EAFB 2002a). In 1993, the FFA schedule was renegotiated (AFFTC 1998b). In 1988, an EAFB tank removal program began that was designed to remove all USTs that did not meet EPA requirements. A total of 409 tanks were removed before the program was completed in 1996. Records of Decision (RODs) will be completed for each of the ten operable unites by 2007.
ATSDR conducted an initial site scoping visit in 1991. The purpose of the visit was to:
1) identify information necessary for initiating the public health assessment process at the base; 2) determine whether exposure to hazardous materials at levels of concern for short and long term health effects were occurring; 3) collect available information to prioritize ATSDR health assessment activities. ATSDR staff met base representatives, toured the installation and surrounding areas, and collected community health concerns. ATSDR identified past, current and future exposure pathways and determined that no immediate or long-term public health hazards existed.
ATSDR performed a follow-up site visit in September 1998 to confirm that EAFB posed no immediate health threats to the public, meet with government and community representatives, visit contaminated areas, and determine information needs. ATSDR completed a health consultation following a February 2001 site visit. The health consultation documented issues that were identified as requiring detailed evaluation in this public health assessment (PHA) and concluded that site conditions did not pose an immediate public health hazard (ATSDR 2001). During preparation of this PHA, ATSDR visited the site again in May 2002 to collect additional information and evaluate site conditions.
During the site visits, ATSDR met with representatives of EAFB, the California Department of Health Services (CADHS), DTSC, EAFB's Restoration Advisory Board (RAB), and community members to identify community concerns. Concerns and comments raised during these site visits are discussed in the "Evaluation of Environmental Contamination and Potential Exposure Situations" and "Community Health Concerns" sections of this PHA.
People on and near EAFB use the area's land and natural resources in many ways. ATSDR examines land and natural resource use to determine which of these activities might put people at risk for exposure to environmental contaminants. This information is important because land use affects people's exposures to contamination by controlling the types and frequencies of activities in those areas. ATSDR uses this information as part of the evaluation of contamination and exposure in this document.
EAFB is located east of Rosamond, approximately 100 miles north-northeast of Los Angeles. The base occupies about 470 square miles of high desert in portions of three counties (Kern, Los Angeles, and San Bernardino). Most of the base, including all of the developed areas, is located in Kern County. The far eastern portion is in San Bernardino County, and some of the southwestern portion is in Los Angeles County. Highways and railroads run near or along three of the base's four sides: U.S. Route 395 runs along the eastern border; State Route 58 and the Burlington Northern Santa Fe Railroad run along the northern border; and State Routes 14/138 and the Union Pacific Railroad parallel the western border (AFFTC/EM 1993). Communities located near EAFB include Boron, California City, Kramer Junction, Lancaster, Mojave, North Edwards, and Rosamond (see Appendix B, Figure 1).
EAFB is situated in the Antelope Valley within the Mojave Desert. It is bounded to the northwest by the Tehachapi Mountains and the south-southwest by the San Gabriel Mountains. This area of the Mojave Desert is characterized by broad alluvial (river) valleys of relatively high elevation with interior surface drainage. Seasonal runoff forms ephemeral (seasonal) lakes, or playas, at topographic lows along the valley axis (e.g., Rosamond and Rogers Dry Lakebeds). The playas form a dry hardpan surface most of the year, ideal for aircraft testing (AFFTC/EM 1993).
Before the military began to use EAFB, the base area and its environs were used for ranching, agriculture, and mining. Military activity began in the EAFB area in 1933 on the eastern side of Rogers Dry Lakebed. In the early 1940s, troops were moved to the area now known as South Base (see Appendix B, Figure 1). The North Base area was developed between 1942 and 1945 as a secret test facility for aircraft. As operations at North Base were reduced in the 1960s, many of the original facilities were demolished. The North Base was used only sparingly through the 1970s and into the mid-1980s, when activity again increased, mainly for high-security programs. Also located on North Base is the former Jet Propulsion Laboratory (JPL) complex, occupied by NASA from 1945 to 1995 for rocket engine and propellant testing (AFFTC/EM 1993; AFFTC 1998a).
DFRC, just north of the Main Base, was established in 1946. Construction of the AFRL, located east of Main Base, across Rogers Dry Lakebed, began in the early 1950s. Between 1952 to 1955, facilities were moved from South Base to the present Main Base area and most of the South Base structures were demolished. Since 1955, most activity at EAFB has centered around the Main Base area with various parts of North Base, NASA, JPL, and AFRL consisting of secure, restricted areas (AFFTC/EM 1993; AFFTC 1998a).
The Main Base is used primarily for aircraft research, development, and testing programs. To support these programs, the Main Base runway, numerous hangars, fuel storage and delivery systems, and maintenance and repair facilities have been constructed. In addition to test-related structures, the base housing areas, commercial facilities, hospital, administration buildings, and physical plant maintenance facilities are located at Main Base. Other miscellaneous facilities included those operated by the base's Morale, Welfare, and Recreation departments, including indoor and outdoor pools, a golf course, a rod and gun club, riding stables, and community activity and skills development centers (AFFTC/EM 1993, EAFB 2002a). The Wildlife Conservation Program issues permits, in accordance with state regulations, to EAFB workers and residents for fishing in the artificially stocked Branch Memorial Pond, located on Main Base, and for waterfowl hunting at Piute Ponds, a 560-acre area of treated effluent ponds located in the southwest corner of the base (AFFTC/EM 1995).
ATSDR examines demographic data (i.e., population information) to determine the number of people potentially exposed to environmental chemicals and to determine the presence of sensitive populations, such as children (ages 6 and younger), women of childbearing age (ages 15 to 44), and the elderly (ages 65 and older). Demographic data also provide details on population mobility, which, in turn, helps ATSDR evaluate how long residents might have been exposed to environmental chemicals (see Appendix B, Figure 3).
The daytime population at EAFB comprises the Combined Test Forces, which include military and civilian personnel and their dependents. An estimated 3,850 military personnel, including officers and enlisted members, work at the base. The civilian population working on base numbers 7,835 and the dependent population is approximately 4,290. The estimated total daytime population at EAFB is approximately 15,980 (EAFB 2001).
Family housing units at EAFB consist of 310 units for officers and 1,360 for enlisted members. EAFB maintains a 188-space mobile home park for privately owned mobile homes; two- and three-story dormitories for 32 to 84 members in single and double rooms; bachelor officer housing of 62 apartment-style units; and 16 apartment-style units available for senior non-commissioned officers (EAFB 2002a). According to the 2000 census, EAFB supports an on-base residential population of approximately 5,900 people (U.S. Census Bureau 2000).
Four schools are located on base: Bailey Elementary school for students in kindergarten, first, and second grades, Branch Elementary school for students in third, fourth, and fifth grades, and Edwards Middle School for those in grades six, seven, and eight (EAFB 2002a). In addition, Desert High School is located on base, with approximately 420 students in grades 9 through 12 (Desert High School 2002). EAFB houses a child development center for children 6 weeks to 5 years old, a Teen Center, a Youth Activities Center, and a Boy Scout camp on South Base (EAFB 2002a).
In preparing this PHA, ATSDR reviewed and evaluated information provided in the referenced documents. Documents prepared for the CERCLA program must meet standards for quality assurance and control measures for chain-of-custody, laboratory procedures, and data reporting. The environmental data presented in this PHA come from site characterization, remedial investigation, and groundwater monitoring reports prepared by EAFB under CERCLA and RCRA. Based on our evaluation, ATSDR determined that the quality of environmental data available for EAFB is adequate for making public health decisions.
ATSDR's PHAs are driven by evaluation of the potential for human exposure, or contact with environmental contaminants. Chemical contaminants released into the environment have the potential to cause adverse health effects. However, a release does not always result in human exposure. People can only be exposed to a contaminant if they come in contact with it--if they breathe, eat, drink, or come into skin contact with a substance containing the contaminant.
ATSDR scientists evaluate site conditions to determine if people could have been, are, or could be exposed (i.e., exposed in a past scenario, a current scenario, or a future scenario) to site-related contaminants. When evaluating exposure pathways, ATSDR identifies whether exposure to contaminated media (soil, sediment, water, air, or biota) has occurred, is occurring, or will occur through ingestion, dermal (skin) contact, or inhalation.
If exposure was, is, or could be possible, ATSDR scientists consider whether contamination is present at levels that might affect public health. ATSDR scientists select contaminants for further evaluation by comparing them against health-based comparison values (CVs). These are developed by ATSDR from available scientific literature related to exposure and health effects. CVs are derived for each of the different media and reflect an estimated contaminant concentration that is not likely to cause adverse health effects for a given chemical, assuming a standard daily contact rate (e.g., an amount of water or soil consumed or an amount of air breathed) and body weight.
CVs are not thresholds for adverse health effects. ATSDR CVs establish contaminant concentrations many times lower than levels at which no effects were observed in experimental animals or human epidemiologic studies. If contaminant concentrations are above CVs, ATSDR further analyzes exposure variables (for example, duration and frequency of exposure), the toxicology of the contaminant, other epidemiology studies, and the weight of evidence for health effects.
Some of the CVs used by ATSDR scientists include ATSDR's environmental media evaluation guides (EMEGs), reference dose media evaluation guides (RMEGs), and cancer risk evaluation guides (CREGs) and EPA's maximum contaminant levels (MCLs). MCLs are enforceable drinking water regulations developed to protect public health. CREGs, EMEGs, and RMEGs are non-enforceable, health-based CVs developed by ATSDR for screening environmental contamination for further evaluation.
You can find out more about the ATSDR evaluation process by consulting Appendix C, reading ATSDR's Public Health Assessment Guidance Manual at http://www.atsdr.cdc.gov/HAC/HAGM/, or contacting ATSDR at 1-888-42ATSDR.
Exposure does not always result in harmful health effects. The type and severity of health effects a person can experience because of contact with a contaminant depend on the exposure concentration (how much), the frequency and/or duration of exposure (how long), the route or pathway of exposure (breathing, eating, drinking, or skin contact), and the multiplicity of exposure (combination of contaminants). Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, lifestyle, and health status of the exposed individual influence how the individual absorbs, distributes, metabolizes, and excretes the contaminant. Together, these factors and characteristics determine the health effects that may occur.
In almost any situation, there is considerable uncertainty about the true level of exposure to environmental contamination. To account for this uncertainty and to be protective of public health, ATSDR scientists typically use worst-case exposure level estimates as the basis for determining whether adverse health effects are possible. These estimated exposure levels usually are much higher than the levels that people are really exposed to. If the exposure levels indicate that adverse health effects are possible, ATSDR performs a more detailed review of exposure, also consulting the toxicologic and epidemiologic literature for scientific information about the health effects from exposure to hazardous substances.
ATSDR identified three potential exposure situations at and near EAFB for further evaluation: potential exposure to contaminants in drinking water on base and off base, potential exposure to chemical warfare materiel (CWM) on base, and potential exposure to dioxins in air from Sites 16 and 18 on base. Table 1 provides a summary of potential exposure situations evaluated in this PHA. Appendix C describes the evaluation process ATSDR used to identify potential exposure situations at EAFB.
|Pathway Name||Exposure Pathway Elements||Comments|
|Contaminant||Environmental Medium||Point of Exposure||Route of Exposure||Time of Exposure||Exposed Population|
|Completed Exposure Pathways|
|On-base drinking water||Arsenic||Groundwater||On-base drinking water supply well N-2||Ingestion||Past
|On-base workers, residents||Arsenic contamination was of limited duration and magnitude and would not be expected to produce adverse health effects.|
|Dioxins in air from Site 16 and Site 18||Dioxins||Air||Air in the vicinity of dual extraction systems at Site 16 and Site 18||Inhalation||Past
|On-base workers near Site 16 and Site 18||Wind patterns typically blow dioxins away from workers and residents. Levels are low enough that they would not be expected to result in adverse health effects.|
|Potential/Eliminated Exposure Pathways|
|On-base drinking water||Refer to Appendix A, Table 4||Groundwater||On-base drinking water supply wells||Ingestion||Past
|On-base workers, residents||There is no evidence of contaminant migration to on-base drinking water wells.|
|Off-base drinking water||Refer to Appendix A, Table 4||Groundwater||Off-base private or community supply wells||Ingestion||Past
|Off-base residents||There is no evidence of contaminant migration off base.|
|Chemical warfare materiel in soil or soil gas||Chemical warfare agents and their degradation products||Soil
|Potentially contaminated soil at Sites 426, 427, 429, and 445||Dermal (skin) contact, inhalation||Past
|On-base workers, residents||There is no evidence of contamination in surface or subsurface soil or soil gas.|
Have past EAFB activities affected base and community drinking water supplies? Are chemical contaminants present in drinking water at harmful levels?
EAFB receives drinking water from two sources--groundwater wells on base and the Antelope Valley East Kern Water District (AVEK). Historically, the EAFB water supply came from groundwater; in March 1993, EAFB also began using AVEK-supplied water (EAFB 2002d). The drinking water supply wells at EAFB include eight potable wells in South Base and four potable wells at the AFRL (EAFB 1999, 2002d). These wells draw water from the deep aquifer of the Antelope Valley groundwater basin (AFCEE 1996). AVEK operates under the State Water Project and obtains surface water from the Delta (between Sacramento, Stockton, and Concord) that is treated before distribution (AVEK 2001). Nearby off-base communities receive their drinking water from private and community supply wells that also draw water from the Antelope Valley groundwater basin.
As a result of past practices at EAFB, contamination has been released to groundwater at hundreds of ERP sites throughout the base. To date, 29 contaminant plumes have been identified and characterized, located in OUs 1, 2, 4, 5, 6, and 8 (JT3/CH2MHill 2002) (see Appendix B, Figure 6). Plumes mainly consist of solvents and petroleum products used in aircraft operation and maintenance. These plumes are located within base boundaries; no plumes have been found migrating toward on-base supply wells or beyond base boundaries (AFFTC 1998b) (see Appendix B, Figure 7).
ATSDR determined that no human exposure to environmental contaminants has resulted from drinking water supplied by EAFB supply systems, off-base community supply systems, or off-base private wells. EAFB ERP investigations have revealed petroleum hydrocarbon, volatile organic compound (VOC), and semi-volatile organic compound (SVOC) contamination throughout the base, but no contaminants have migrated to on-base or off-base drinking water supply wells. One well at EAFB, N-2, has contained elevated levels of arsenic at various times during its use (1964-1995), but the levels and duration of exposure were too low to result in adverse health effects. ATSDR reviewed environmental data and potential exposure situations and concluded that no adverse health effects are likely to result from the low-level exposure to arsenic found in groundwater at EAFB.
The Antelope Valley is a closed alluvial basin containing 5,000 to 10,000 feet (ft) of alluvial fill. The Antelope Valley groundwater basin underlying EAFB is composed of two groundwater subbasins, the Lancaster subbasin and the North Muroc subbasin. The Lancaster subbasin underlies most of the Main Base and South Base areas, while the North Muroc subbasin underlies North Base. The Lancaster subbasin is divided into two aquifers--an unconfined principal aquifer (beginning at approximately 35 to 95 ft below ground surface [bgs]), and a partly confined, deep aquifer (beginning at approximately 70 to 200 ft bgs). The two aquifers are separated by low-permeability sediment deposits of locally variable thickness. The aquifer in the North Muroc subbasin (beginning at approximately 95 to 130 ft bgs) is unconfined (USGS 1992).
The principal source of recharge to the Lancaster subbasin is infiltration of rainfall and runoff through the alluvial fans of Big Rock, Little Rock, and Amargosa Creeks (south of EAFB, at the base of the San Gabriel Mountains). Recharge to the North Muroc subbasin prior to development of the valley occurred as groundwater flow from the Lancaster subbasin. As the valley has become populated, groundwater levels have declined in the Lancaster subbasin to the point that groundwater no longer flows from it into the North Muroc subbasin. There is a groundwater divide, oriented east-west across the north-central part of Rogers Dry Lakebed, that hydraulically separates the North Muroc subbasin and the Lancaster subbasin. Recharge to the subbasins from infiltration in the bedrock hills on the eastern and northwestern parts of EAFB is minimal. Some recharge within the valley from storm runoff has been observed, but infiltration is limited by low permeability sediments near the ground surface (USGS 1992).
The drinking water supply wells at EAFB include eight potable wells (built between 1951 and 1994) in South Base that supply the Main Base area (see Table 2). These wells draw water from the deep aquifer of the Lancaster subbasin at screen intervals ranging from 216 to 833 ft bgs. Water from the wells is pumped directly into two storage tanks, where chlorine is added for disinfection. The North Base supply system previously consisted of one well, N-2, that was installed in 1964 (drawing water from the unconfined aquifer of the North Muroc subbasin) but was taken off line in 1995 due to elevated arsenic concentrations. Water purchased from AVEK has replaced the water formerly provided by that well. AVEK water enters the base near the North Gate, where chlorine and polyphosphate are added for disinfection and corrosion control. The water then flows into two storage tanks for subsequent distribution across the base. AVEK water can be, and often is, mixed with EAFB groundwater to provide additional water to the Main Base area. Water can also be exchanged from south to north, through valve rearrangement (EAFB 1999, 2002d).
AFRL receives its water supply from four groundwater wells (built in 1964) that also draw water from the deep aquifer of the Lancaster subbasin. Water from these wells is treated (through addition of chlorine) at AFRL before being distributed (see Table 2) (EAFB 2002d). AFRL also receives water through base-wide AVEK distribution (EAFB 1999).
EAFB has three non-potable wells (built between 1946 and 1990) on base. One well fills the Branch Park pond, while the other two are chlorinated prior to use at Camp CORUM, the West Gate guard shack, the rod and gun club, the firing range, and two remote sites on the west side of the base. The non-potable wells are used for washing and cleaning only (EAFB 2002d).
|Drinking Water Source||Dates of Use||Screen Interval
(Feet Below Ground Surface)
|AVEK Water District supplies North Base, Main Base, AFRL|
|South Base wells supply Main Base and South Base areas|
|Former North Base well supplied North Base areas|
|Well N-2 (no longer in use)||1964-1995||N/A|
|Air Force Research Laboratory (AFRL) wells supply AFRL|
Source: EAFB 2002d
AFRL Air Force Research Laboratory
AVEK Antelope Valley East Kern Water District
N/A Not applicable
The eastern and western boundaries of EAFB are more than 5 miles from occupied portions of the base and base operations, but base operations at JPL occur within ½ mile of the northern base boundary. Off base, there are 19 private (4 residential, 3 trailer park, 12 commercial) and 5 community supply (North Edwards, Boron, and Desert Lake) wells located 0 to 2 miles from the north boundary that could potentially be influenced by EAFB groundwater contamination (see Table 3 and Appendix B, Figure 7) (AFFTC/EMR 2002c; JT3/CH2MHill 2002). Groundwater flow at North Base varies from northeasterly to northwesterly, but groundwater generally flows north from Rogers Dry Lakebed, off base, toward the North Edwards community (AFFTC/EMR 2002a, 2002c) (see Appendix B, Figure 7).
Through site investigations and sampling, EAFB has discovered and characterized 29 groundwater plumes that contain a variety of VOCs and SVOCs, including: benzene/toluene/ethylbenzene/xylene (BTEX), carbon tetrachloride, 1,2-dichloroethane (1,2-DCA), cis-1,2-dichloroethene (1,2-c DCE), 1,4-dioxane, ethylene dibromide, methyl-tert-butyl ether (MTBE), N-nitrosodimethylamine (NDMA), tetrachloroethylene (PCE), perchlorate, and trichloroethylene (TCE)(see Appendix A, Table 4). Groundwater plumes are located in OUs 1, 2, 4, 5, 6, and 8 (see Appendix B, Figure 6). All plumes are within base boundaries and are located between 8 and 130 ft bgs (see Appendix A, Table 3)(JT3/CH2MHill 2002).
During site investigations conducted since 1990, EAFB has installed and sampled hundreds of monitoring wells on base. Select groundwater monitoring wells are also sampled semi-annually to assess long-term migration of contaminant plumes in groundwater, estimate trends of contaminant plumes, establish groundwater gradients, provide warning in the case of any off-base contaminant migration, and make recommendations for future groundwater sampling events (AFFTC/EMR 2002c). Samples from these wells have served to define the extent of groundwater plumes (see Appendix B, Figure 6).
|Well Name||Description||Date Well Use Began||Screen Interval
(Feet Below Ground Surface)
|Desert Lake Community Services District #2||Drinking water production
(community water system)
|Chas Raycroft||Private well
(use status unknown)
|Boron Water District #15||Drinking water production
(community water system)
|Boron Water District #13||Drinking water production
(community water system)
|Jay's Trailer Park #1||Trailer park well||1956||Unknown|
|Williamson Trailer Park #1||Trailer park well||1981||100-200|
|North Edwards Water District #-2||Drinking water production
(community water system)
|North Edwards Water District #1||Drinking water production
(community water system)
|Dunes Apartments #1||Drinking water production
(non-community water system)
|Fountain Trailer Park #1||Drinking water production
(non-community water system)
|Burlington Northern Santa Fe Railroad||Drinking water production
(private water system)
|Stubborn Mule Ranch||Business/private
(private water system)
|Old Mud Camp Area||Industrial water supply
(private water system)
Sources: AFFTC/EMR 2002e; JT3/CH2MHill 2002
Contaminant plumes are located between 2.5 and 15 miles from any actively used drinking water supply wells and have not reached the deep aquifer from which drinking water is obtained (plume depths are 8 to 130 ft bgs, while the drinking water aquifer is 175 to 700 ft bgs) (JT3/CH2MHill 2002). EAFB's Civil Engineering department coordinates an active water sampling program that includes monthly bacterial and chloroform testing, inorganic chemical and VOC testing every 3 years, radioactivity testing four times during every 4-year period, and taste, odor, and appearance factor testing quarterly. EAFB has been in compliance with all federal, state, and local safe drinking water requirements (EAFB 2000).
EAFB's only North Base well, N-2, was removed from service in 1995 because of elevated levels of arsenic. The well began operating in 1964 (AFFTC/EMR 2002e). Arsenic is a naturally occurring mineral that is present in high concentrations across the Antelope Valley due to erosion of natural deposits (EAFB 2000). Well N-2 was sampled for arsenic concentrations either monthly or quarterly between 1983 and 1998, in accordance with regulatory requirements (EAFB 2002e). Most arsenic concentrations in well N-2 ranged from 10 parts per billion (ppb) to 50 ppb,(1) however, sporadic spikes in arsenic levels occurred throughout the years. The maximum value detected was 81 ppb in October 1992 (EAFB 2002e).
EAFB is currently conducting a study of treatment options that will allow for the removal of arsenic from base well water before that water is introduced into the water distribution system. The results of this study will enable EAFB to meet the newest arsenic standard in drinking water of 10 ppb in all of its drinking water supply wells by 20061 (EAFB 2002d).
In addition to five community supply wells, there are residences, trailer parks, and commercial properties located just north of the EAFB boundary. Most of these off-base properties obtain their drinking water from groundwater. The closest groundwater plumes to the North Base boundary are a series of four perchlorate plumes in OU 5, Sites 282 and 285, that contain perchlorate at concentrations of up to 160,000 ppb (see Appendix B, Figure 7). Because of the close proximity to off-base drinking water wells at the northern portion of the base, EAFB has installed two rows of groundwater monitoring wells between the contaminated areas and the base boundary. Monitoring of these wells is conducted semi-annually and enables EAFB to track contaminant migration and anticipate and prevent contamination of drinking water supply wells. Sampling in the monitoring wells has never detected any perchlorate contamination (AFFTC/EMR 2002c).
In addition, modeling of the perchlorate plume has indicated that it would take 700 years for the plume to reach the base boundary (largely due to the slow rate of groundwater flow in the area) (D. Steckel, AFFTC/EMR, personal communication, May 2002). EAFB is currently evaluating remediation options for the perchlorate plumes at Sites 282 and 285 to remove the possibility of any future contaminant migration (P. Schiff, AFFTC/EMR, personal communication, May 2002).
Community members have expressed concern that perchlorate contamination in North Base groundwater might be migrating off base and could contaminate their drinking water wells. CADHS and EAFB conducted a well survey, in April 1998, to address those concerns. The well survey consisted of perchlorate sampling in all private and commercial wells located within 2 miles of the northern base boundary (see Appendix B, Figure 7). No off-base wells were found to be contaminated with perchlorate (AFFTC/EMR 2002e).
The community of North Edwards began monitoring groundwater for perchlorate in 1998, in accordance with EPA's Unregulated Contaminant Monitoring Rule for Public Water Systems. In November 2001, the perchlorate result for Well 1 was an unquantifiable detect below the detection limit of 8 ppb, which means that perchlorate was not detected at a detection limit of 8 ppb. EAFB's Restoration Advisory Board, concerned with the analytical results, requested re-sampling of the two community supply wells in North Edwards (NEWD 2002). In May 2002, the Antelope Valley Laboratory and an EAFB contractor obtained samples from each of the two community supply wells within 5 minutes of one another. Neither laboratory found perchlorate above detection limits (< 4 ppb) at either well (NEWD 2002).
Although groundwater at EAFB is contaminated by various organic and inorganic compounds, these chemicals have not contaminated on-base or off-base drinking water wells and there is consequently no exposure to them. Arsenic was detected at elevated levels in one EAFB drinking water supply well (well N-2) between 1964-1995. ATSDR evaluated the duration and levels of exposure to arsenic from well N-2. Arsenic exposures had a short enough duration, and involved low enough levels, that no adverse health effects would be expected. ATSDR concluded that past, present, and foreseeable future drinking water use from on- and off-base wells is not expected to result in adverse human health effects.
Arsenic was detected in well N-2 at levels above ATSDR's noncancer (3.0 ppb) and cancer (0.02 ppb) CVs at various times during the well's use (1964-1995). Because ATSDR's CVs are screening tools based on very protective assumptions about exposure and toxicity, exposure to arsenic in well N-2 at concentrations above the CV would not necessarily result in harmful health effects. To further evaluate whether health effects may result from arsenic in this well, ATSDR derived exposure doses using additionally conservative assumptions about how often and how much water a person might drink from a well containing the maximum detected arsenic concentration (though most concentrations were below half of the maximum). ATSDR assumed that an adult consumed water containing 81 ppb arsenic for 30 years and a child for 6 years. These protective estimates allow ATSDR to safely evaluate the likelihood, if any, that arsenic in well N-2 could cause harm. ATSDR's review of the toxicologic literature for arsenic suggests that the levels in the N-2 well water are at least 10 times lower than arsenic levels shown to cause cancer or other adverse health effects in humans exposed through their drinking water (ATSDR 1998a). Appendix D provides more information about arsenic and ATSDR's evaluation of arsenic exposures.
Are people living or working on base likely to contact CWM in nearby disposal areas?
In response to Congressional direction, the U.S. Army released a report listing areas throughout the United States where CWM may be located. Locating and safely handling CWM is currently a high priority for the military because CWM is designed to be very hazardous to humans and health hazards could be serious if exposures occur (EAFB 1998; HAZWRAP 1998).
The U.S. Army listed EAFB as likely to have buried CWM. As a result, an archival research program was initiated at EAFB in 1994 to identify potential locations of CWM. The program identified 25 potential CWM sites, all of which were assigned to Operable Unit 7. Sites 426, 427, 429, and 445 were prioritized for investigation based on proximity to housing (Site 426), proximity to base operations (Sites 427 and 429), and public concern (Site 445). The remaining 21 sites are located in remote areas of the base that are not expected to be frequented by people (AFFTC 1998b).
ATSDR evaluated geophysical, soil, and soil gas data to determine if potential current and future exposure to CWM is likely for on-base residents and workers. ATSDR determined that no human exposure to CWM and/or CWM degradation products has occurred on base because CWM is not present. Therefore, CWM is not a public health hazard.
Site 426, located within the Main Base area, was identified in 1996 as a former toxic gas storage yard. Subsequent non-intrusive field assessment surveys strongly suggested that disposal activities occurred at this facility during its operational period, i.e., the mid-1940s through the early 1950s. The current boundaries of Site 426 include Popson Avenue to the north and Rosamond Boulevard to the east and south (see Appendix B, Figure 8) (HAZWRAP 1998). Two older dormitory buildings, housing approximately 600 Marine and Air Force personnel, are located approximately 400 ft northwest of the site. About 100 to 150 Air Force personnel live in a newer dormitory complex, built in 1997, located west of the site (AFFTC/EMR 2002d). Irrigation ditches, concrete foundations, an abandoned water well filled with soil and debris, and contaminated soil and groundwater from a UST (removed in July 1995) are currently present within the site (EAFB 2002c).
Site 427, located at South Base, is identified as a bomb storage magazine on several historic maps. The facility is located within the area known today as the Munitions Maintenance and Storage Branch (a secure, gated area). The magazine reportedly was used to store bomb shells, but no live explosives, from 1942 to 1946 (AFFTC 1998b; EAFB 2002c).
Site 429 is located at South Base. The former Chemical Storage Area was active from 1943 to 1946. It consisted of two chemical warfare magazines and a chemical gas instruction building. The facilities were located approximately 1,700 ft north of the east section of the South Base runway. The facilities were razed in the mid-1950s when the present-day Main Base was created (EAFB 2002c).
Site 445 was identified in the 1994 U.S. Army Corps of Engineers Archives Search Report as a biological warfare testing location. It was specifically used to test the dissemination and dispersion of simulant material, and to verify cloud detection devices, from 1966 to 1968. The site, which is presumed to have a 1-mile radius, is located in the southwest corner of Rosamond Dry Lakebed, northeast of Piute Ponds. There are no known activities (military or civilian) currently occurring at the site. Land currently used for agricultural purposes is approximately 2.5 miles from the site boundary (AFFTC/EMR 2002b; EAFB 2002c).
A number of investigations have been conducted at Site 426 to identify and evaluate the potential presence of CWM or CWM degradation products. These efforts have included archival research (1994-1997), aerial photograph search (1997), geophysical surveys (1996-1997, 2000), drilling and soil sampling (1997, 2000), active and passive soil gas surveys (1997, 2000), and soil excavation (2002) (AFFTC/EMR 2001, 2002d; ATSDR 2002; EAFB 2002c). Groundwater sampling was also conducted in conjunction with a UST at Site 426. (No CWM or CWM degradation products were detected in groundwater samples [AFFTC/EMR 2002d]. UST-related groundwater contamination is addressed in Section 3.2.)
Archival research and aerial photograph search indicated that the yard may have been used for storing CWM.
Geophysical surveys included electromagnetics, magnetics, ground-penetrating radar, and induced polarization and resistivity. The surveys identified numerous anomalies that EAFB interpreted to be four trenches filled with metal objects and other debris. The trenches were each estimated to be 150 to 160 ft long and 12 ft wide, spaced approximately 23 ft apart from one another. The soil cover above the trenches was estimated to be approximately 3 to 4 ft deep. Maximum depth of potentially buried CWM was estimated at approximately 9 to 10 ft bgs (AFFTC/EMR 2002d).
Drilling and soil sampling were conducted in January 1997 to determine if CWM or CWM degradation products were migrating from the presumed trenches to the west toward the dormitory complex. During drilling, the workers' breathing zone above the boreholes was continuously monitored to identify any potential CWM release as a result of drilling activities. Soil samples were pre-screened in the field to ensure they did not contain CWM above action levels. The air monitoring during drilling, soil sample pre-screening, and laboratory analysis of the soil samples did not detect any CWM or CWM degradation products. Soil samples did not contain any CWM or CWM degradation products. One composite subsurface sample contained elevated concentrations of arsenic, a potential CWM degradation product and also a naturally occurring mineral (AFFTC/EMR 2001). Additional boreholes were similarly drilled and sampled in March 2000. Laboratory analysis detected no CWM or CWM degradation products in the soil samples. UST-related hydrocarbon contamination was detected (AFFTC/EMR 2002b). A composite surface soil sample collected northeast of the trenches contained high concentrations of sulfur (31,000 mg/kg), but did not contain any other anomalous concentrations of inorganic compounds. Arsenic was not detected above background concentrations (AFFTC/EMR 2001).
EAFB conducted three rounds of soil gas surveys at Site 426, in July 1997, October 1997, and February/March 2000. The July 1997 sampling event consisted of active soil gas sampling to determine if petroleum hydrocarbon wastes were disposed in the trenches; all analytes were below detection limits. The first round of passive soil gas sampling was conducted in October 1997; analyses from this round detected potential mustard degradation products 1,4-thioxane and 1,4-dithiane in 15 of the 25 samples collected (HAZWRAP 1998).
EAFB conducted additional soil gas sampling in February and March 2000 to corroborate the results of the first sampling effort and collect background samples for comparison of CWM degradation products. This round of sampling used two different methods at overlapping locations. No CWM was found, but traces of 1,4-thioxane and 1,4-dithiane were detected at both Site 426 and the background location using one of the sampling techniques. Because they were detected by only one of the sampling techniques and were also detected at the background location, EAFB hypothesized that the presence of these compounds was caused by something other than a release of mustard (AFFTC/EMR 2001). U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) confirmed that 1,4-thioxane and 1,4-dithiane can be found as remnants of diesel fuel (ATSDR 2002).
Based on the evidence of trenches and the continued possibility that CWM might be present in soil, EAFB conducted an interim removal action (IRA) at Site 426 from July to October 2002. The primary objective of the IRA was to remove, if present, all CWM-contaminated soil and debris. All excavation was performed under a 50-foot-wide, 80-foot-long containment structure, mounted on rails, that moved along the length of each trench. The air within the containment structure was maintained at a negative pressure. The air exhaust from the structure was also filtered to prevent a release of any CWM that might be present, and monitored to verify that CWM was not released (AFFTC/EMR 2002d).
No CWM or CWM-contaminated soil or debris was found in the trenches. UST-related soil contamination was removed. The containment structure was demolished in November 2002 and the site was back-filled and re-graded in December 2002 (ATSDR 2002).
Site 427 was formerly used for the storage of CWM during WW II and is currently used for conventional munitions storage. Chemicals that may have been kept in the storage magazine could have included mustard, lewisite, phosgene, white phosphorus, hydrogen cyanide, and cyanogen chloride (EAFB 2002b). Site 427 is in an access-restricted (fenced and guarded) area that requires clearance for entrance, so it is unlikely to be frequented by any non-military personnel.
Site investigations at Site 427 have included archival research (1993), field reconnaissance (1999), and a passive soil gas survey (2001). Archival research demonstrated that the location of the facility has not changed since it was first seen in a 1942 aerial photograph. There was no aerial photographic or archival evidence of burial at the site (AFFTC/EMR 2002b).
Field reconnaissance (October 1999) found that the facility (currently Building 643) appeared to be intact and used for storage of conventional ordnance, though nothing was being stored in the building at the time of reconnaissance. The area surrounding the facility was surveyed for evidence of burial or debris; nothing was observed on the ground surface. Neither a geophysical survey nor a subsurface investigation was conducted because of the lack of physical or archival evidence of burial at the site (EAFB 2002c).
A passive soil gas survey was conducted at Site 427 in July 2001. Soil gas points were placed in an area (70 ft by 80 ft) surrounding the former bomb storage magazine. The compounds undecane, tridecane, and pentadecane were detected in low levels in four samples. A pesticide, p-chloro, was detected in two samples, and 1,1,1-TCA, 2-MeNAPH, and 2,6-DNT were also detected at low concentrations. The low levels of fuel-related compounds and the solvent TCA may be related to past or current maintenance activities at the facility, and the explosive DNT is most likely from conventional ordnance. Based on these data, there appear to be no residuals from the storage of CWM at the site (AFFTC/EMR 2002f).
The facilities at Site 429 were among those referred to in a 1943 memorandum that called for adequate storage of CWM, in particular mustard gas. Chemical Agent Identification Set kits containing mustard, lewisite, phosgene, and chloropicrin are among the containers possibly stored at Site 429 facilities. In addition, there is a possibility that tear gas cylinders, smoke pots, and smoke grenades were being stored in the facilities. Because the facilities were used to store CWM, it is possible that training kits containing glass vials of live agents may have been buried nearby after the training unit was deactivated (particularly near the Chemical Gas Instruction Building). Disposal practices may have also released contamination to soils surrounding the facilities. Investigations at Site 429 have included archival research and aerial photograph examination (1993), field reconnaissance (1999), geophysical surveys (2000), and a passive soil gas survey (2001) (EAFB 2002c).
Archival research and aerial photographs revealed three possible CWM burial locations. (They were identified as such because of a lack of vegetation and apparent human-made relief or disturbance.) Field reconnaissance conducted in October 1999 revealed the building foundations identified as the Chemical Gas Instruction Building and the Chemical Warfare Magazines. Adjoining the concrete foundations was weathered asphalt. The soils immediately surrounding the facilities appeared undisturbed, and with no evidence of staining at the ground surface. The site was littered with debris (e.g., clay pigeons, metallic scraps, tin cans) unrelated to former activities (EAFB 2002c). Site 429 is located under the flight line, along the edge of Rosamond Dry Lakebed, beyond an airplane graveyard and refueling station, and would not be expected to be frequented by many people.
Geophysical surveys at Site 429 were conducted between February and May 2000, and included a magnetic reconnaissance survey, a detailed magnetic survey, and an electromagnetic induction survey. The geophysical surveys revealed a featureless pattern of anomalies (i.e., no indication of trenches or consolidated dumping areas) in an area south of the former Chemical Gas Instruction Building, extending east towards the Rogers Dry Lakebed. All anomalies were evaluated as having low likelihood of representing buried CWM. A ground penetrating radar survey was conducted in October 2000; it indicated that most of the debris present at the site was less than 2 ft deep, with a few isolated anomalies 3 ft deep (EAFB 2002c).
A passive soil gas survey was conducted in July 2001. Soil gas points were placed at 50-foot intervals surrounding the former Chemical Warfare Magazines and Chemical Gas Instruction Building, the area of small metal debris, and a background location approximately 400 ft northwest of the site. The compounds undecane, tridecane, and pentadecane were detected in seven samples. 2-MeNAPH was detected in four samples, and toluene was detected in one. P-chloro, benzene, and 2,6-DNT were detected in two samples each. A tear gas called 2-chloro was detected in one sample at a low concentration (AFFTC/EMR 2002f).
The tear gas residual is likely related to past gas training activities. The low levels of fuel-related compounds may be related to maintenance activities at the facility or off-gassing of asphalt debris. The explosive DNT is most likely from conventional ordnance. Based on these data, there appear to be no residuals from the storage of CWM (mustard or lewisite) at the site (AFFTC/EMR 2002f).
Site 445 is a 1-mile radius area where simulants (Bacillus subtilis var. niger and Serratia marcescens) were sprayed throughout the presumed site from a vehicle, creating an aerosol for the purpose of measuring dispersion distance and testing various detection equipment. The primary objective of past testing activities was to verify detection methods, not to measure any effects of the simulants used.
Aerial photographs from 1928 to the present were reviewed prior to conducting field reconnaissance to look for indications of burial trenches or debris. However, no aerial photographs exist of the area for the period between 1963 and 1992, when simulant testing would have occurred. Field reconnaissance was conducted in October 1999, at which point no evidence of burial trenches or debris was observed on the Lakebed surface. No domestic (homestead) or military debris was observed at the site (EAFB 2002c).
There is no evidence that any materials were left on the site, either as surface debris or in disposal trenches. In addition, any simulants used 30 years ago probably would have degraded due to the harsh desert environment. The site was approved for "no further investigation" status by EAFB oversight regulatory agencies in February 2001 (EAFB 2002c).
ATSDR determined that possible CWM burial sites 426, 427, 429, and 445 have not yielded any evidence of the presence of chemical warfare agents and/or their degradation products. The only site that presented any potential evidence of buried CWM has been excavated and no CWM was found. Consequently, all four sites represent an eliminated exposure pathway and ATSDR concludes that CWM at EAFB poses no public health hazard because there is no opportunity for exposure.
Are people being exposed to harmful levels of dioxins in air emitted from the dual extraction remediation systems at Site 16 and Site 18?
Petroleum and halogenated hydrocarbon releases to soil and groundwater at Sites 16 and 18 have prompted EAFB to conduct non-time-critical removal actions to clean up contamination. Soil vapor and groundwater extraction systems--DESs--have been installed to clean soil and groundwater at Sites 16 and 18. These extraction systems have the potential to emit dioxins into the air because of the combustion processes they use to destroy the contaminant particles.
ATSDR has evaluated stack emissions, ambient air, and dispersion modeling data related to dioxins produced by the DESs at Sites 16 and 18. ATSDR has determined that levels are not high enough, and exposures are not likely to last long enough, for adverse health effects to result.
Sites 16 and 18 are located near the U.S. Army Aviation maintenance hanger along the Main Base Flight Line in OU1 (see Appendix B, Figure 11). Past remedial investigations have identified soil and groundwater hydrocarbon contamination associated with leaks along the former JP-4 pipeline, industrial waste lines, and USTs. To treat the contamination, EAFB has installed a DES at each site (i.e., a combination of soil vapor and groundwater extraction systems). Vapors produced by the extraction system are treated using catalytic oxidation, a process that uses high temperatures to destroy chemicals. Dioxins/furans may be produced as a result of this process (AFFTC 2001; Weston 1998a, 1998b). Operation of the DES at Site 16 began in March 1997. The DES at Site 18 uses a thermal oxidizer instead of a catalytic oxidizer, but is otherwise comparable to the Site 16 DES. The DES at Site 18 began operating in April 2000 (AFFTC 2001).
When examining potential exposures to contaminants in ambient air, one must understand the prevailing wind patterns for a given location: wind patterns largely determine how contaminants move through the air. EAFB has summarized the wind speed and direction data for the vicinity of Sites 16 and 18 in a format known as a windrose. Windroses display the statistical distribution of wind speeds and directions in a single plot. Five-year (1992-1997; see Appendix B, Figure 12) and single sampling event windroses (from 1997 and 2001) all show that wind patterns in the vicinity of Sites 16 and 18 are from south and west to north and east. In fact, data indicate that winds blow from west-southwest to east-northeast more than 75 percent of the time. These wind patterns would predominantly blow contaminants that might be present in ambient air toward the eastern and northeastern portions of EAFB--away from populated and residential areas.
Due to community concerns, EAFB has conducted three rounds of dioxin/furan (henceforth, "dioxin") sampling at Sites 16 and 18 since May 1997 (when the first DES started operating). Samples have been collected from both the systems' exhaust stacks and ambient air, and dispersion modeling based on stack emissions and wind patterns has been performed (AFFTC 2001; Weston 1998a, Weston 1998b).
EAFB, in conjunction with EPA Region 9 and their subcontractors, conducted the first round of dioxin air sampling at the Site 16 DES in June 1997. Ambient air concentrations were measured for two separate, but consecutive, 36-hour periods at two upwind locations, two downwind locations, and within the fence line of the DES. During the first sampling period, the total dioxins at one of the downwind locations (0.064 picograms per cubic meter, or pg/m3) and one of the upwind locations (0.044 pg/m3, measured at the location approximately 70 meters upwind) just slightly exceeded the dioxin CV of 0.042 pg/m3 (see Appendix A, Table 4). However, the maximum level of dioxins detected during the second sampling period was 0.026 pg/m3 (measured at the second upwind location, approximately 80 meters from the DES)--well below the CV (Weston 1998a).
EAFB and EPA noted significant variability in the sampling results at the emission stack sampler during the June 1997 sampling round. In addition, laboratory analysis detected dioxins in some of the field blanks (Weston 1998a). To verify the results of the initial sampling, EAFB conducted a second round of dioxin sampling in November 1997. Some modifications were made to the DES in the interim (Weston 1998b).
During the November sampling round, dioxin concentrations in ambient air at the DES (0.101 pg/m3) and approximately 70 meters upwind (0.138 pg/m3) both exceeded the CV (0.042 pg/m3). Ambient air concentrations 70 and 115 meters downwind of the DES also slightly exceeded the CV, with dioxin levels at 0.059 pg/m3 and 0.047 pg/m3 (see Appendix A, Table 4). Dispersion modeling based on measured stack emissions of 3.0 to 9.0 pg/m3 showed that the maximum potential average annual impact of the DES approximately 600 meters downwind (or 300 meters upwind) was 0.0023 pg/m3 dioxins (Weston 1998a). Because the maximum concentrations of dioxins were detected upwind of the DES, it seems unlikely that the Site 16 DES is the dominant source of dioxins in the area.
EAFB expanded the Site 16 DES in August 1999 to include a total of 18 dual extraction wells. During EAFB's April 2001 sampling event, only stack emission samples were collected at Site 16. (Though ambient air measurements better represent the contaminants that someone would be likely to breathe, stack emission data can provide some perspective on the possibility for elevated contaminant concentrations in ambient air from a specific source.) When the DES was sampled in April 2001, at its higher rate of operation, stack emissions were 67.1 to 93.7 pg/m3, up from 3.0 to 9.0 pg/m3 in 1997. ATSDR expects maximum potential average annual impact from the DES to increase with an order of magnitude similar to that of the stack emissions' increase. The impact of the DES 600 meters downwind, or 300 meters upwind, should thus be approximately 0.023 pg/m3. This level is 10 times higher than the modeled 1997 concentration of 0.0023 pg/m3 , but is still well below the CV.
EAFB, in conjunction with EPA Region 9 and their subcontractors, conducted one round of dioxin air sampling at the Site 18 DES in April 2001. Ambient air concentrations were measured at one upwind location, at two downwind locations, and within the fence line of the DES. All sampling results were non-detect (AFFTC 2001). However, it should be noted that the detection limits used for analyzing dioxins from this event were higher than the CV. Consequently, it is difficult for ATSDR to make any definitive public health statements in relation to dioxins in ambient air from Site 18.
In attempting to come to some conclusions regarding dioxins in air near Site 18, ATSDR has employed the protective public health assessment practice of assuming that contaminants may be present at up to half the reported detection limit, even when not detected. ATSDR applied this practice to the detection limits used in analyzing the April 2001 ambient air results and calculated an estimated maximum dioxin concentration of 0.375 pg/m3. This estimated concentration is close to an order of magnitude higher than the CV of 0.042 pg/m3. (Again, ATSDR is not contending that dioxins were present in air at 0.375 pg/m3--dioxins were not detected. Rather, ATSDR is using that concentration solely for the purposes of conducting a protective public health evaluation.)
ATSDR examined stack emission, ambient air, and dispersion modeling data for dioxins produced by DESs at Sites 16 and 18. ATSDR determined that predominant wind directions blow away from residences and off-base populations, so the potential for exposure to contaminants from Sites 16 and 18 is limited. ATSDR also evaluated concentrations of dioxins in ambient air and determined that levels are lower than those that would be expected to produce adverse health effects. ATSDR concludes that exposure to dioxins from Sites 16 and 18 DESs is not likely to result in adverse health effects.
Dioxins are present in air at EAFB near Sites 16 and 18. However, the 5-year windrose for the area in the vicinity of Sites 16 and 18 shows that predominant wind directions are between southwest and west--toward the Main Base runways and Rogers Dry Lakebed, but away from population centers. Therefore, though people may occasionally be exposed to dioxins in air, any exposure would be expected to be of limited duration.
Nonetheless, ATSDR evaluated the likelihood of adverse health effects from the maximum levels of dioxins detected. The highest measured concentrations of dioxins near Sites 16 and 18 were found upwind of the DES: 0.138 pg/m3. The maximum level estimated for Site 18 was 0.375 pg/m3. Typical levels of dioxins in outdoor air in urban and industrial areas in the United States average around 2.3 pg/m3 (ATSDR 1998b). Though dioxins are extremely toxic, adverse health effects have been observed in people exposed to dioxins at levels at least 10 times higher than background levels (ATSDR 1998b). Because maximum dioxin concentrations found at EAFB are close to 100 times lower than urban-area background levels, ATSDR does not believe exposure to dioxins at EAFB is likely to produce adverse health effects. See Appendix E for more information about dioxins and their toxicity.
1. Until 2002, EPA's maximum contaminant level (MCL) for arsenic was 50 ppb. Following an extensive review of toxicologic literature, EPA proposed a new MCL for arsenic of 10 ppb that will go into effect in 2006.