PUBLIC HEALTH ASSESSMENT
HANSCOM FIELD/HANSCOM AIR FORCE BASE
BEDFORD, MIDDLESEX COUNTY, MASSACHUSETTS
Hanscom Field/Hanscom Air Force Base (HF/HAFB) is a 1,120-acre site located 14 miles northwest of Boston in the towns of Bedford, Concord, Lincoln, and Lexington in central Middlesex County, Massachusetts. The site comprises Hanscom Air Force Base (HAFB)an active U.S. Air Force (USAF) baseand L.G. Hanscom Field (HF), an adjacent civilian airport owned by the Commonwealth of Massachusetts and operated by the Massachusetts Port Authority (Massport) and the Federal Aviation Administration (FAA). Light industry, residential areas, and open space surround HF/HAFB; and the headwaters of the Shawsheen River, one of the 27 major watersheds in Massachusetts, are on site.
A public airfield was built on the site in 1941. Military flying activities began in 1942. From 1942 to 1973, HAFB's primary mission was operational maintenance of fighter aircraft and research and development support. In 1973, military flight operation ceased and in the following year, the airfield was returned to state control for operation as a civilian airfield, the USAF retaining the remainder of the property. Today the USAF principally uses the 826 acres that remain under its control to support the Electronic Systems Center (ESC) of the Air Force Materiel Command.
Routine operations at HAFB have throughout its history generated wastes, including paint waste, chlorinated solvents, fuel, aromatic solvents, and polychlorinated biphenyls (PCBs). These wastes were often burned during fire training exercises, buried in landfills, or discharged to adjacent wetlands and streams. In addition, the handling and storage of fuels in underground storage tanks (USTs) and aboveground storage tanks (ASTs) have released contaminants to the soil and to groundwater.
In the early 1980s, the USAF initiated site investigations under the Department of Defense's Installation Restoration Program (IRP). The investigations initially identified 13 areas of potentially contaminated soil and groundwater. During subsequent investigations, USAF located a total of 22 potential contaminant source areas.
On May 31, 1994, the U.S. Environmental Protection Agency (EPA) placed HF/HAFB on the National Priorities List (NPL) because of contamination found in groundwater and subsurface soil. Using remedial investigation findings, the USAF selected and is conducting ongoing remedial actions to address site contamination and protect public health at eight IRP sites. The other 14 potential contaminant source areas have been closed out with regulatory approval.
In 1994 and again in 2003, ATSDR conducted site visits at HAFB. Although no imminent public health hazards were present at the site, ATSDR did identify three exposure pathways for additional evaluation: 1) potential exposure to site-related contaminants via groundwater, 2) potential contact with contaminants from former landfills, and 3) potential exposure to surface water and sediment.
ATSDR evaluated available environmental sampling data from long-term monitoring and individual IRP site investigations. Overall, HF/HAFB poses no public health hazard. On the basis of its evaluation, ATSDR reached the following conclusions regarding the three exposure pathways:
Groundwater: Volatile organic compounds (VOCs) have been detected in groundwater beneath and immediately downgradient of HF/HAFB. However, groundwater beneath and immediately downgradient of HF/HAFB is not used as a drinking water source. Using groundwater flow models and off-site monitoring well data, ATSDR has concluded that public and private wells located downgradient of HF/HAFB have not been affected by site-related contamination.
Surface Soil: Most soil contamination areas at HF/HAFB were beneath the ground surface, thus generally inaccessible to the public. ATSDR evaluated the three areas where surface contamination was possibleIRP Sites 4, 6, and 8. Given the limited contamination found in these soils, previous and ongoing remedial actions, and institutional controls in place; no current or future health hazards are associated with these areas. Due to a lack of past monitoring data, whether people were exposed to harmful levels of contamination prior to remediation is unknown. However, human contact with these areas is infrequent and incidental and; therefore, is not expected to cause a health hazard.
Surface Water and Sediment: Expected doses from exposure to concentrations of contaminants measured in the Shawsheen River and surrounding wetlands are not expected to have caused adverse health effects. Consequently, no public health hazards are associated with using the Shawsheen River or surrounding wetlands for recreational purposes.
Hanscom Air Force Base (HAFB) is an active military base located 14 miles northwest of Boston, in central Middlesex County, Massachusetts (Figure 1). HAFB is currently charged with research and development of command and control systems for the U.S. Air Force (USAF) (HAFB 2002b). L.G. Hanscom Field (HF) is an adjacent civilian airport owned by the Commonwealth of Massachusetts. It is operated by the Massachusetts Port Authority (Massport) and the Federal Aviation Administration (FAA) (HAFB 2002b). Together they comprise a 1,120-acre site known as Hanscom Field/Hanscom Air Force Base (HF/HAFB). HF/HAFB occupies a low-lying basin in the towns of Bedford, Concord, Lincoln, and Lexington and is surrounded by light industry, residential areas, and open space. The headwaters of the Shawsheen River, one of the 27 major watersheds in Massachusetts, are located on site (HAFB 2002b).
In 1941, a public airfield was built on the site and in 1942, military flying activities began. In 1952, the USAF acquired 396 acres from the Commonwealth of Massachusetts and leased an additional 641 acres, including the runways and flight line. The primary mission of HAFB during that time was operational maintenance of fighter aircraft and research and development support (HAFB 2002a). Military flight operations continued until 1973. The following year the airfield was returned to state control, but the USAF retained the remainder of the property (HAFB 2002a). During the 31 years of field operation, the USAF serviced and repaired a variety of aircraft on site (HAFB 2002a).
Since transfer back to state control in 1974, Massachusetts Port Authority (Massport) has operated HF as a civilian airport. The 826 acres of HF/HAFB that remain under USAF control are used principally to support the Electronic Systems Center (ESC) of the Air Force Materiel Command, which is the acquisition and development center for command and control systems (HAFB 2002a), and is the major tenant on the base. Other on-site organizations include the 66th Air Base Wing, the MITRE Corporation, sections of the Air Force Research Laboratory, and the MIT Lincoln Laboratory.
Throughout HF/HAFB's history, routine operations resulted in the accumulation of assorted industrial wastes in several areas within and adjacent to the site. Support operations generated paint waste, chlorinated solvents, fuel, aromatic solvents, and polychlorinated biphenyls (PCBs), all of which were usually burned during fire training exercises, buried in landfills, or discharged to adjacent wetlands and streams. In addition, the handling and storage of fuels in underground storage tanks (USTs) and aboveground storage tanks (ASTs) released contaminants to the soil and groundwater (HAFB 2002b).
In the early 1980s, the USAF initiated site investigations under the Department of Defense's Installation Restoration Program (IRP) (HAFB 2002a). In the 1980s and early 1990s, the Massachusetts Contingency Plan (MCP), with oversight by the Massachusetts Department of Environmental Protection (DEP), regulated HAFB's IRP (Baker 1998). Since the inception of the IRP, the USAF has undertaken a number of investigation and restoration activities.
The investigations began in the summer of 1982, identifying areas where soil and groundwater had been contaminated with jet fuel and other wastes (HAFB 2002a). In 1984, the IRP identified 13 sites that were thought to contain potentially contaminated soil or groundwater on either HAFB property or HF property. The IRP initiated an investigation and clean up of these sites (Baker 1998). During subsequent investigations, the USAF identified a total of 22 potential contaminant source areas (IRP Sites), divided into four NPL operable units (OUs 1-4) and 11 additional IRP Sites (Table 2) (Figure 2). Since their identification, each of these areas has undergone a variety of investigations to determine the extent of the contamination, and each is in various stages of removal and remedial activity. Oil, drums, USTs, and contaminated soil have been removed; and at a number of the sites, groundwater collection systems have been installed as needed.
On May 31, 1994, the U.S. Environmental Protection Agency (EPA), citing chlorinated solvents, jet fuel, and other petroleum-related compounds in the groundwater and subsurface soil, placed HF/HAFB on the National Priorities List (NPL). The NPL is EPA's list of the most serious uncontrolled or abandoned hazardous waste sites in the United States. The NPL is authorized by the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), commonly known as "the Superfund law," and is updated on a regular basis. Since HAFB's addition to the NPL, EPA now regulates the investigation and clean up of 11 of the 22 IRP sites under CERCLA (Baker 1998). The MCP continues to regulate the remaining 11 IRP sites.
Using investigative data and remediation activities, it was determined that 14 of the 22 potential source areas require no further action (NFA). Remedial actions have been selected and are in place at the remaining eight sites, and their effectiveness is periodically monitored. Six of the eight sites are classified as CERCLA sites with on-going remedial actions. Feasibility studies to determine appropriate action alternatives have been completed at the six CERCLA sites, each is at a different stage of remedial activity. The two additional areas (Sites 13 and 22) have petroleum-related contamination (excluded by CERCLA) and are; therefore, regulated by the MCP.
ATSDR is required by law to conduct a public health assessment (PHA) at each of the sites on the NPL. As part of the PHA process in 1994, ATSDR conducted an initial site visit to HF/HAFB. The visit's purpose was to collect information necessary to rank the site according to the potential public health hazard it represented and to identify public health issues related to environmental contamination. During the visit, ATSDR met with USAF and HAFB personnel and representatives from federal and state agencies. After identifying past, current, and future exposure pathways, ATSDR determined that no imminent public health hazards existed (ATSDR 1994).
In April 2003, ATSDR revisited HF/HAFB to obtain updated information about ongoing environmental activities. Again, ATSDR met with USAF personnel and toured the site. Discussions, the site visit, and data reviews, again, led ATSDR to conclude that there was little opportunity for public contact with site contaminants and no immediate threats to public health. ATSDR did, however, identify three exposure pathways for additional evaluation: 1) potential exposure to site-related contaminants via groundwater, 2) potential contact with contaminants from former landfills, and 3) potential exposure to surface water and sediment. In this PHA, ATSDR further evaluates these pathways.
ATSDR examines demographic and land use data to identify sensitive populations, such as young children, the elderly, and women of childbearing age, and to determine whether these sensitive populations are exposed to any potential health risks. Demographics also provide details on population mobility and residential history in a particular area. This information helps ATSDR evaluate how long residents might have been exposed to contaminants.
In 1992, HAFB employed 17,216 military and civilian personnel. By 1997, that number declined 22% to approximately 13,364 people working on site (Baker 1998). Over 800 military personnel and 1,000 dependents lived on site in 1997, while an additional 1,000 and 2,400, respectively, lived off site. About 200 of the 826 acres at HAFB are devoted to housing; 80 acres are community, commercial, and services areas. One hundred fifty acres are open space and recreation areas. The remainder of the base is industrial, research and development facilities, and administrative areas. On-site housing consists of 850 family housing units, 98 mobile home park spaces, 220 unaccompanied enlisted dormitory rooms, and 17 bachelor officer quarters (HAFB n.d.). A child development center, primary school, middle school, youth center, and medical center are all on site. A mobile home park and FamCamp area affiliated with HAFB are north of Hanscom Field. VIP housing is east of these areas. Fencing surrounds HAFB property and secured entrances restrict public access.
HF/HAFB is located approximately 14 miles northwest of Boston, in central Middlesex County. Middlesex County is home to about 1.5 million people, 6.3% of whom are under the age of 5, and 12.8% are over 65. The county has a population density of about 1,800 persons per square mile (Bureau of the Census 2000). Figure 3 shows the demographics within one mile of HF/HAFB.
Land use in the vicinity of HF/HAFB includes civilian and military residential areas, commercial land, light industrial zones, and open space. An important water resource, the Shawsheen River, passes through HF/HAF. The headwaters of the Shawsheen River, one of 27 major watersheds in Massachusetts, are located on HF/HAFB. From its origin in the on-site wetlands, the river flows approximately 25 miles north/northeast to the Merrimack River in Lawrence, MA. Near the site, the river is generally too shallow for recreational use, but farther downstream it is used for boating and fishing.
Adjacent to the site are the Naval Weapons Industrial Reserve Plant and Raytheon research facility to the north, the Bedford Forest (a conservation area) and residential property to the northeast, light industrial parks to the east, residential areas to the southeast, and the Minuteman National Historic Park to the south. HF/HAFB occupies land in four adjacent towns: Bedford, Concord, Lexington, and Lincoln. Each town has slightly differing land uses:
- Bedford. Of the approximately 13,000 people living in Bedford, 810 are under 5 years of age (Bureau of the Census 2000; MADHCD 2003). Bedford lies north of HF/HAFB and comprises residential areas, open space, and industrial and commercial areas. The residential areas are separated from commercial and industrial areas by woods and marshes; conservation land separates the town from the northern portion of HF (Baker 1998).
- Concord. Located west of HF/HAFB, approximately 17,000 people reside in Concord, 970 of whom are under 5 years of age (Bureau of the Census 2000; MADHCD 2003). Wetlands and wooded areas separate Concord residential areas from HF. Near HF/HAFB in Concord are large tracts of conservation land, several parcels of office space, and a few small farms (Baker 1998).
- Lexington. The most populous of the four townswith approximately 30,000 persons, 1,710 of whom are under 5 years of ageLexington is east of HF/HAFB and is home to office space, residential areas, part of the Minuteman National Historic Park, wetland areas, and historic districts (Baker 1998; MADHCD 2003).
- Lincoln. Aside from a small area of commercial property, Lincoln comprises almost entirely single-family homes, conservation areas, and some agricultural areas (Baker 1998). There are approximately 8,000 residents of whom 745 are under 5 years of age (Bureau of the Census 2000; MADHCD 2003).
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 the USAF under CERCLA, under the Resource Conservation and Recovery Act (RCRA), or from MCP. ATSDR has found that the HAFB environmental data are of adequate quality for public health determinations.
ATSDR's PHAs focus on the potential for human exposure, or in other words, contact with environmental contaminants. Chemical contaminants released into the environment have the potential to cause adverse health effects. That said, however, a release does not always result in human exposure. People can only be exposed to a contaminant if they come in contact with itthat is, if they breathe, eat, drink, or come into dermal (skin) contact with a substance containing the contaminant.
ATSDR scientists evaluate site conditions to determine if people could have been, are currently, or could in the future 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 through ingestion, dermal contact, or inhalation exposure to contaminated media (soil, sediment, water, air, or biota) has occurred, is occurring, or will occur.
If exposure was, is, or could be possible, ATSDR scientists consider whether the exposure-causing 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 various media and reflect an estimated contaminant concentration that is not expected 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 in 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), cancer risk evaluation guides (CREGs), and EPA's maximum contaminant levels (MCLs). EMEGs, RMEGs, and CREGs are non-enforceable, health-based CVs developed by ATSDR for screening environmental contamination for further evaluation. MCLs are enforceable drinking water regulations developed by EPA to protect public health.
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 or duration of exposure (how long), the route or pathway of exposure (breathing, eating, drinking, or dermal contact), and the multiplicity of exposure (combination of contaminants). Once exposure occurs, characteristics such as a person's age, sex, nutritional status, genetics, lifestyle, and health status influence how they absorb, distribute, metabolize, and excrete the contaminant. Together, these factors and characteristics determine the health effects that could occur.
In almost any situation, the true level of exposure to environmental contamination involves considerable uncertainty. 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 are usually much higher than the levels to which people are actually exposed. If the exposure levels indicate that adverse health effects are possible, ATSDR performs a more detailed review of exposure, also consulting 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 HF/HAFB: 1) potential exposure to contaminants in groundwater on site and off site, 2) potential exposure to on-site surface soil, and 3) potential exposure to contaminants in surface water and sediment.
ATSDR's assessment focuses on public exposure and; therefore, does not consider exposure of site personnel who could have contacted contaminated media as part of their job. Occupational exposure situations are regulated under the oversight of the Occupational Safety and Health Administration (OSHA) and National Institute for Occupational Health and Safety (NIOSH).
In addition, USAF operation of the airfield and flight line from 1942 to 1973, generated wastes that were disposed of in areas located outside the existing boundaries of HAFB, but within the area currently operated by Massport as HF. These suspected or confirmed fire training areas, waste burial sites, and surface spills have been evaluated as part of the IRP and have been designated IRP Sites 1, 2, 3, 4, 5, 11, 19, and 20. ATSDR evaluated potential past, current, and future public exposures to contamination at the NPL site (HF/HAFB), including contamination in those areas located outside HAFB but on HF. The evaluation of the current use of HF as a civilian airport is beyond the scope of this PHA.
Former operations and waste disposal practices at HAFB have contaminated the groundwater beneath the site with volatile organic compounds (VOCs), metals, and pesticides. The plumes are primarily located within site boundaries, but some VOC contamination, at relatively low levels, has extended beyond the site's northern boundary into the Bedford Forest. However, community members living near HF/HAFB and base residents do not use groundwater beneath or immediately downgradient of the site; therefore, no exposures are occurring to site-related groundwater contamination. Thus, exposure to groundwater is an incomplete pathway.
Groundwater is water present beneath the ground surface; it moves through cracks and spaces in porous units of rock and sediment known as aquifers. The porosity, or permeability, of the rock layer determines the speed at which the groundwater flows. Often impermeable layers of rock separate permeable layers. These impermeable (non-porous) layers, known as aquitards, not only prevent water from moving between layers above and below them, they can also separate two distinct aquifers. There are three aquifers beneath the HAFB region: the bedrock aquifer and two other aquifers made up of sandy sediments from an ancient glacial lakebed. The sediments comprising the two upper aquifers are separated by a semi-confining clay unit (CH2MHILL 1997a). The four layers beneath the site, beginning with the one closest to the surface, are:
- Surface Aquifer: The uppermost layer is made up mostly of fine sand and varies from 0 to 30 feet thick. This near-surface aquifer is unconfined. The surface aquifer generally flows in a northeasterly direction from the highlands (e.g. Hartwells Hill) to the lowlands and discharges to Elm Brook, to the Shawsheen River, and to wetlands within the Bedford Town Forest (CH2MHILL 1997a).
- Aquitard: This semi-confining layer is made up of relatively impermeable silt and clay that is difficult for groundwater to penetrate. This layer separates the surface and lower aquifers. In some areas it has been pinched out or eroded away and has ceased to exist, particularly on the hills and under Elm Brook north of Hartwells Hill. The thickness of this layer can be anywhere from 0 to 50 feet.
- Lower Aquifer: This semi-confined aquifer is made up of sandy glacial till on top to the underlying bedrock. It ranges from 0 to 60 feet thick, and pinches out at the bases of the hills to the north and west.
- Bedrock Aquifer: Groundwater can flow in the fractured and weathered bedrock. The bedrock is mostly granite with areas of gneiss, schist, and diorite. The depth of bedrock areas with groundwater is unknown. Wells drilled into this layer vary in depth from approximately 70 to 1,000 feet (CH2MHILL 1997a; Haley & Aldrich 1998).
The town of Bedford Aquifer Protection District has under its bylaws classified groundwater beneath and downgradient of the site as GW-1 (a potential future water supply). Additionally, DEP under state drinking water regulations has assigned the area east of runway 5-23 in the eastern portion of OU-1, as an approved Zone II. Zone II is an area where water contributes to a drinking water well under the most severe pumping and recharge conditions possible. The area north of runway 5-23 has been classified as a "potentially productive aquifer," meaning the U.S. Geological Survey (USGS) delineated it as a medium or high yield aquifer. Consequently, according to DEP, the area is of "high use and value" (CH2MHILL 2000a).
Groundwater beneath and immediately downgradient of HF/HAFB is, however, not used as a drinking water source, nor are there currently any plans to do so in the future. No drinking water wells are located either on site or immediately bordering the site.
In 1992, HAFB conducted a well inventory as part of the IRP Stage 2 Remedial Investigation (RI) for OU-3. All private and public wells within a 3-mile radius of the site used for irrigation, monitoring, or drinking were identified. Also, in 2000, HAFB met with the town of Bedford Department of Health to determine whether the inventory was still current or whether additional wells had been drilled since the 1992 inventory. Results indicate that 5 private wells are located within 1.4 miles of the northeast corner of HAFB, the closest being 1.2 miles north-northeast (HAFB 2002b).
- Bedford. In 1983, the town of Bedford began drawing drinking water from the Hartwell Road well field, located 1.2 miles northwest of HF. The well field was closed in 1984, after elevated levels of VOCs and dissolved iron were detected in the wells (CDM 1984c). Today, about 85 percent of the drinking water for the town of Bedford comes from the Massachusetts Water Resources Authority (MWRA) via the town of Lexington municipal system. The source of this water is the Quabbin Reservoir in western Massachusetts. Bedford augments this supply with water from the Shawsheen well field, which is 2.3 miles northeast of HAFB (HAFB 2002a, 2002b). Although the well field contains three wells, only one well is currently operational (personal communication with the Bedford Department of Public Works, December 2003).
- Concord. The Water/Sewer Division of Concord Public Works is responsible for delivering potable water to approximately 95% of Concord. The system is composed of eight separate pumping/treatment stations and a high-pressure water distribution system (Concord Public Works 2002).
- Lexington. The town of Lexington purchases approximately 2 billion gallons of treated water from MWRA annually (Lexington Water and Sewer Division 2004). The source of this water is the Quabbin Reservoir in western Massachusetts.
- Lincoln. The Lincoln Water Department supplies safe drinking water to Lincoln residents by adhering to EPA and DEP regulations. The source of the water is the Flint's Pond Watershed and the Tower Road Well recharge area (Lincoln Water Department 2004).
- HAFB receives its water from the towns of Lexington and Bedford.
Following a discovery of contaminants in the Hartwell Road well field in 1983, the USAF undertook a hydrogeologic investigation to determine the nature and extent of groundwater contamination resulting from former HAFB activities. The long-term monitoring program was initiated in January 1986, to determine the nature and extent of groundwater contamination, and later to examine the effectiveness of groundwater treatment systems (CH2MHILL 2000a). The monitoring program continues today; 15 rounds of sampling for 61 organic compounds have been conducted. Investigations have been inconclusive in identifying a specific source of the contamination that caused the well field to be shut down (EPA 2003a). ATSDR's evaluation of past and future use of the Hartwell Road well field is discussed in the Community Health Concerns section.
Long-term monitoring and IRP site-specific monitoring conducted since 1986, indicate several plumes within the HF/HAFB boundary as a result of former waste management practices at HAFB. Chlorinated solvents; benzene, toluene, ethylbenzene, and xylenes (BTEX compounds); and polycyclic aromatic hydrocarbons (PAHs) have been detected above health-based CVs in many of the monitoring wells located on site, and areas of petroleum product floating on the water table have been identified in several locations. With the exception of OU-1, these plumes appear to remain within site boundaries. The nature and extent of these plumes is described below.
- OU 1: Several locations of HF were used as disposal and fire training areas prior to 1974 when leased by the USAF. These activities left four general source areas with the potential for soil and groundwater contamination:
- Site 1: Fire Training area II
- Site 2: Paint Waste Disposal Area
- Site 3: Jet Fuel Residue/Tank Sludge Disposal Area
- Site 5: Fire Training Area I (Haley & Aldrich 1998).
- Site 4. Elevated concentrations of metals, VOCs, and semi-volatile organic compounds (SVOCs) have been found in the upper aquifer. Trace levels of VOCs and SVOCs have been found in the lower aquifer beneath Site 4, a sanitary landfill, which was capped in 1988 (Environmental Resources Management 1992). Long-term groundwater monitoring was conducted between December 1989 and September 1992, and supplemental sampling was conducted from 1994 to1996. This long-term monitoring indicated no contaminants at levels of concern, thus obviating any significant risk of harm to human health or to the environment, as well as the need for any further action (HAFB 2002b).
- Site 6. Site 6 is a former landfill site comprising two separate hillside construction debris disposal areas and a former filter bed area used in the 1940s and 1950s. Groundwater investigations surrounding the site have revealed chlorinated VOCs, aromatic solvents, and metals present in the groundwater. To prevent potential health effects from exposure to the groundwater, remedial actions were conducted and include a permeable cap, natural attenuation, long-term monitoring, and institutional controls (CH2MHILL 2000b).
- Site 13. In 1981, a leaking gasoline UST was found at the Base Motor Pool. The tank and three adjacent fuel storage tanks were replaced and a scavenger recovery system installed during the replacement operation recovered approximately 5 gallons of gasoline. In 1993, the tanks were replaced again. During this replacement activity, 986 tons of petroleum-contaminated soil were removed and 450,000 gallons of groundwater with low concentrations of petroleum contamination were pumped through a treatment system prior to discharge into the storm drainage system. Subsequent investigations revealed a limited pocket of groundwater contamination remain and in January 1999, HAFB selected monitored natural attenuation as the final remedial action alternative for this MCP regulated site (HAFB 2002a).
- Site 16. Site 16 includes contamination at Building T-860. In 1993, a site investigation found low levelsof chlorinated- and petroleum-related compounds in soil and groundwater samples, and in surface water from the Shawsheen River. A source could not be identified. Two abandoned USTs near Building T-860 were removed in 1990. No visible contamination could be seen under the USTs after removal. Groundwater well data indicated low levels of TCE near the river. In 2001, HAFB and DEP made a determination of no significant risk and no further action (HAFB 2002a).
- Site 21. Site 21 is an 7.5-acre area adjacent to Site 6 formerly used for the storage, off-loading, and dispensing of jet fuel from 1955 to 1973, and Number 2 fuel oil in the early 1970s. Fuels were stored in USTs and ASTs. Cleaning solvents and other aircraft maintenance products were also stored there. In 1990, HAFB discovered evidence of a past release of Jet Propellant #4 (JP-4). Investigations confirmed multiple locations of petroleum-contaminated soils and groundwater, in addition to the presence of three distinct, light non-aqueous phase liquid (LNAPL) pools floating on top of groundwater. Groundwater contamination consists of numerous VOCs such as benzene, toluene, naphthalene, 1,4-dichlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, vinyl chloride, cis-1,2-DCE, and TCE.
- Site 22. In 1991, during the replacement of gasoline and diesel USTs at the Base Service Station, approximately 2,600 cubic yards of petroleum-contaminated soil were removed. In 1990 and 1991, petroleum-contaminated soil was also found during the removal of two abandoned 500-gallon waste oil storage tanks and a 1,500-gallon fuel oil tank. Subsequent investigations between 1992 and 1996, found that some soil and groundwater contamination existed on site. In September 1997, HAFB selected monitored natural attenuation as the final remedial action alternative for this MCP regulated site (HAFB 2002a).
A remedial investigation, conducted for OU-1 in 1988, identified VOCs in the aquifers beneath the airfield. The primary contaminants were trichloroethylene (TCE) and cis-1,2-dichloroethene (cis-1,2-DCE) (Haley & Aldrich 1998). Buried drums and contaminated soil were removed from IRP Sites 1, 2, and 3 in 1988; a groundwater treatment system began operating in 1991 (IT 2002a) to contain and limit off-site migration of groundwater contamination (Haley & Aldrich 1998). The system is made up of interceptor wells and collection trenches at Site 1, 2, and 3, and four interceptor wells along the HF/HAFB boundary with the Bedford Forest (IT 2002a). In 1997, a vacuum-enhanced recovery system with four wells began operating to collect water from the bedrock. Contaminated groundwater collected from the system is pumped to a treatment facility with an air-stripping tower and discharged into adjacent wetland areas (Haley & Aldrich 1998). By March 2000, a total of 1 billion gallons of groundwater had been treated (CH2MHILL 2000a).
The bedrock aquifer has been monitored since 1986, through the Bedford Community Gardens well(1). Surface and lower aquifer sampling began in 2000. No VOCs have been detected above CVs in the surface aquifer. But TCE has been measured above CVs (5 parts per billion [ppb]) in all 17 samples collected from the bedrock aquifer since 1986, and in the lower aquifer in all four samples collected since 2000. Concentrations ranged from 35 to 330 ppb in the bedrock aquifer and 18.6 to 29.4 ppb in the lower aquifer. TCE has not been detected in the surface aquifer.
Additionally, since 1998, a cluster of wells has been sampled northeast of the airfield, farthest off site in the direction of flow, along the leading edge of the plume. No contaminants have been detected above CVs in either the surface or bedrock aquifers. That said, the lower aquifer has contained TCE above its CV in all but 1 of the 7 samples collected. Concentrations (ranging from 2.2 ppb to 25 ppb) have been gradually increasing since 1998 (IT 2002a).
In 1993, a soil vapor extraction system and groundwater recovery system were operated for four months and eight months, respectively. Similar systems were operated from September 1995 until October 1998. In 1999, a follow-on, vacuum-enhanced recovery system was installed and operated until 2003, when replaced by the final remedy. Several remedial investigation phases were performed and a final report was submitted in 2000 (CH2MHILL 2000b). In August 2002, a combination of interceptor trenches, recovery wells, removal of saturated soil, a variety of groundwater treatment, monitoring, and institutional controls was selected as the final remedy for the area (HAFB 2002b). Remedy construction began in June 2003, and was substantially completed in August 2003. On September 15, 2003, the remedy entered the long-term operation, maintenance, and monitoring phase (USAF 2003).
Because there are no drinking water or irrigation wells beneath and immediately downgradient of HF/HAFB, contact with on-site groundwater is an incomplete exposure pathway. To prevent the pathway from becoming complete in the future, drinking water and irrigation wells should not be installed in the area. Currently, the nearest drinking water well is located 1.2 miles north/northeast of the site. The single contaminant detected above CV in a monitoring welllocated between the plume and downgradient drinking water wellsindicates that chemicals are not present in sufficient concentrations to produce adverse health effects. Nevertheless, levels of TCE have been increasing in the lower aquifer since it was first sampled in 1998. Thus, ATSDR concurs with the continued sampling of the monitoring wells. As noted earlier, the town of Bedford's public water supply is MWRA and the Shawsheen River well field, which is located beyond the contaminant plumes, where groundwater contamination has not affected it. These wells are monitored for contaminants in accordance with federal and state regulations to ensure the water is safe to drink.
There is no current or future public health hazard associated with surface soil contact at HF/HAFB. Most source areas at HF/HAFB are buried and; therefore, constitute no potential contaminant exposure. ATSDR examined the three landfills where current or future surface soil exposure is possible and determined that contaminant concentrations are not expected to produce adverse health effects. Due to lack of past sampling data, it is unknown whether a potential hazard existed prior to remediation. But the levels detected and the infrequent and incidental exposure that is expected to have occurred, is not expected to have presented a public health hazard.
Many of the source areas at HAFB are located undergroundthe sources were buried wastes or underground releases. In addition, most areas with potential surface contamination are located in areas inaccessible to the public. There are three former landfill areas (IRP Sites 4, 6, and 8), which have been capped and/or covered with clean soil and converted to alternative uses. Site 4 is currently an open grass area with a section used as a ball field for HAFB personnel and area residents. Site 6 is surrounded by a fence to prevent access, but had encroached on off-site areas. It has recently been capped and covered with grass, and off-site debris has been removed. Site 8 is an open grass recreational area located between the HAFB clinic, military family housing areas, child development center, and elementary and middle schools.
This 10½-acre site, located in the southwestern corner of HF/HAFB, was used as a landfill from 1964 to 1974. During this time, the landfill primarily accepted solid waste, but HAFB personnel indicate that wastes from site shops and research laboratories were also routinely disposed of there. Contaminants possibly deposited include battery acid, bonding compounds, fuels, medical wastes, inks and paints, mercury, photographic chemicals, solvents, spent acids, TCE, and other cleaning solvents (O'Brien & Gere 1996). Prior to the opening of the landfill, topographic maps show a wetland area at this location (HAFB 2002b). The landfill is approximately 10 to 15 feet deep and is estimated to encompass about 210,000 cubic yards (HAFB 2002b). Site 4 is owned by the Commonwealth of Massachusetts and currently utilized by Massport. It was leased to the USAF from 1952 to 1974.
Site 4 was capped in 1988. Most of the site is covered with grass with small areas of brush and woodland vegetation. The land gently slopes from northeast to southwest, with depressions resulting from settling fill. The southeastern corner is used as a softball field in warm weather months, but the access road is fenced to prevent public automobile traffic (O'Brien & Gere 1996). Portions of the area are wetlands associated with adjacent Elm Brook. Drainage ditches encircling the site carry runoff into Elm Brook (O'Brien & Gere 1996).
No surface soil sampling is available prior to capping, and current topsoil is uncontaminated (clean) soil from another location. Therefore, potentially contaminated soil is not accessible to the public. Two surface soil samples were collected in April 1995, from two areas along the side slopes of the landfill where uncapped fill was exposed. Benzo(a)pyrene (0.45 ppm) was detected above its CV in one of the two samples. Arsenic (15 ppm) was the only metal detected above its CV (Table 3), but it was within the range of background concentrations for arsenic in Massachusetts soil (MADEP 2002).
This approximately 15-acre site is located in the northeastern portion of HF/HAFB. It is bounded by the Shawsheen River to the north, commercial properties to the northeast/east, a service road to the south, and IRP Site 21 to the west (IT 2002b). Site 6 is comprised of an upper (south) landfill that received site-related construction debris until 1995, a suspected ash-disposal area, and filter beds used from 1947 to the mid 1950s to de-water sewage and industrial waste sludge. Later the beds were covered with about 5-18 feet of municipal waste, construction debris, and soil. A non-contiguous western landfill is also investigated as part of Site 6 because it is believed that site-related construction debris disposal occurred there, as well. This area is adjacent to an area still used for construction materials and road salt storage (in a storage building referred to as a "salt dome") (EA 1998). In addition, in the late 1940s, it is believed that approximately 200 canisters of dichlorodiphenyltrichloroethane (DDT) were buried in the former filter bed area. Most of these canisters were reportedly removed in the early 1970s, and shipped off site for disposal. But about 1/4 of them were too deteriorated to remove and were left in place (EA 1998). The debris buried in the former filter bed area extended beyond the fenced boundary of HF/HAFB property into an area known as Debris Excavation Area #1.
Multiple phases of investigations have occurred at this site, but the first surface soil samples were not collected until 1996, when 15 surface soil samples were collected to characterize VOC, SVOC, PAH, total petroleum hydrocarbons (TPH), metals, pesticides, and PCB concentrations in surface soil near the former filter beds area (EA 1998). Results indicated that benzo(a)pyrene (to 1.1 parts per million [ppm]) was often detected above its CV of 0.1 ppm. Arsenic was also detected regularly above its CV of 0.5 ppm to a maximum concentration of 11.1 ppm, and lead (470 ppm) was found above its 400 ppm CV in one sample. Because no surface soil samples were collected at the former ash disposal area, the topmost sample from the soil borings (0-2 feet below ground surface [bgs]) were evaluated. Benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, dibenzo[a,h]anthracene, indeno[1,2,3-cd]pyrene were all detected at concentrations above their CVs (Table 4) (CH2MHILL 2000b).
The Site 6 Record of Decision (ROD), finalized in September 2000, called for containment of the three landfill areas with a permeable cap, removal of debris located in off-site areas, implementation of institution controls to prevent exposures to groundwater, long-term surface and groundwater monitoring to determine effectiveness of natural attenuation, a contingency groundwater remedy in the event that the selected remedy is not effective, and 5-year reviews (IT 2002b).
Debris deposited outside the fence line in Debris Excavation Area #1 was removed in 2001. Three confirmation soil samples were collected from the excavated area. Samples were analyzed for VOCs, SVOCs, metals, pesticides, and PCBs (IT 2002b). Arsenic was the only contaminant detected above its CV (but well below the MCP standard of 30 ppm). Also in 2001, a pervious cap was placed over the three landfill areas at Site 6 as part of the final remedy to prevent access to contamination. The area is now covered with grass and remains fenced and locked (HAFB 2002b).
Site 8, the Scott Circle Landfill, is surrounded by the HAFB clinic, an elementary school, a vegetable garden, and residential areas. It is bounded by an unnamed stream in the west and the Shawsheen River in the east. The two streams join north of the site. Construction material and debris were buried in the landfill from the early 1950s to 1973. The landfill was originally two landfills: north and south. The north landfill was about 2.5 acres. The south landfill was excavated in 1986, during the development of a military housing complex at Site 8 (JRB Associates 1984 as cited in Metcalf & Eddy 1990). While both landfills were used primarily for construction materials, personnel report the burial of potentially hazardous substances during the 1960s, including paint, paint thinner, solvents, waste oils, laboratory chemicals, aircraft, and automobiles (Metcalf & Eddy 1990). No surface soil sampling is available, but 21 near surface samples(2) were collected in 19899 from the south landfill and 12 from the north landfill (Metcalf & Eddy 1990). Site 8 was capped with clean fill and seeded in 1991 (personal communication with the Air Force, October 2003).
Because this area is located in close proximity to child care facilities and schools, because children use it recreationally, there potential for other users come contact with any contaminants that might be on the original surface under clean fill. ATSDR evaluated available sampling data prior landfill being capped determined arsenic was only contaminant detected above its CV of these near samples (Table 3).
No surface soil sampling is available from the area outside the fence at IRP Site 6 prior to the removal at Debris Excavation Area Number 1, or from Sites 4 and 8 prior to capping. Therefore, whether people from nearby residents or passers-by might have been exposed to unsafe levels of contaminants is unknown. The lack of available data makes past exposure to surface soil at Sites 4 and 8 and beyond the Site 6 fence an indeterminate public health hazard. It is not expected, however, that the limited frequency of exposure and the contaminant concentrations would have been sufficient to produce adverse health effects.
Because surface soil is inaccessible (due to fencing and to the fact that the soil at all three sites has now been capped) there is no current or potential future exposure to surface soil contaminants. Using conservative exposure assumptions for both adults and children who could use the former landfill areas for recreational purposes, ATSDR further evaluated the potential for health effects from contact with surface soil by estimating doses to those contaminants present above CVs. None of the contaminants were present in sufficient quantities to produce adverse health effects for the expected duration and frequency of use. Consequently ATSDR determined that there is no current or future public health hazard associated with surface soils from these landfills. Please see Appendix C for a complete evaluation of this exposure pathway.
There is no public health hazard associated with the surface water and sediment pathways. No adverse health effects are expected given conservative recreational exposure estimates and given the contaminant concentrations found in surface water and in sediment on and surrounding HF/HAFB.
HF/HAFB is located at the headwaters of the Shawsheen River, one of 27 major watersheds in Massachusetts. From its origin in the on-site wetlands, the river flows approximately 25 miles north/northeast to the Merrimack River in Lawrence, MA. Near the site, the river is generally too shallow for recreational use, but it is used for boating and fishing farther downstream (MRWC 1999). Because the Shawsheen River drains HF/HAFB and many HF/HAFB outfalls flow directly into the river or the wetlands that feed the river, there is potential for surface water contamination by site-related chemicals. Although there is no official surface water monitoring program at HAFB, surface water samples have been collected during the various remedial investigations of IRP Sites (e.g., Sites 4, 6, 8, and 21).
HF/HAFB is located on an ancient lakebed known as glacial Lake Concord, which filled with sediment following the last glaciation in New England (Haley & Aldrich 1998). The basin is 120 to 130 feet above mean sea level (msl) and is surrounded by low-lying hills of glacial till and gravel. In addition, the larger hills (Pine Hill to the west and Hartwells Hill to the north) rise about 100 feet above the plain (Haley & Aldrich 1998) and consist of bedrock covered with glacial till (CH2MHILL 1997a). The southern portion of glacial Lake Concord, including HF/HAFB, drains into the Shawsheen River. The river begins on site and flows through the main housing and administration area of HAFB through open channels and culverts. It flows from a final culvert north of Katahdin Hill to an open channel past the runway, and then off site. From HF/HAFB the river travels about 25 miles, then empties into the Merrimack River (CH2MHILL 1997a).
The northern and western portions of the glacial lakebed drain into Elm Brook. Elm Brook begins southwest of HF/HAFB and encircles the site, flowing north past Pine Hill and east past Hartwells Hill before joining the Shawsheen River northeast of HF (CH2MHILL 1997a).
Prior to construction of HF/HAFB, most of the area south of the airfield was wetland. While an extensive storm drainage network has been created, there are still pockets of wetlands on HF/HAFB. Many surrounding wetland areas are off site as well. Northeast of HF is a large wetland located in the Bedford Forest Conservation area. A network of drainage channels flow across the wetland area, the largest of which, Hartwell Brook, flows northeast through the forest to Elm Book, just upstream of the confluence with the Shawsheen River (CH2MHILL 1997a).
Due to the low topographic relief, the infilling of wetland areas, and the disruption of drainage patterns for construction purposes, drainage at HF/HAFB is mostly controlled through a system of drains, pipes, and culverts (Dynamac 1988). Surface runoff from HF/HAFB collects in a drainage network that flows into the Shawsheen River, Elm Brook, and the wetlands in the Bedford Forest (Haley & Aldrich 1998). Surface runoff tends to be highest in the spring and lowest in the summer and winter. Consequently, levels of the Shawsheen River fluctuate seasonally (Dynamac 1988).
Both Elm Brook and the Shawsheen River near HF/HAFB are too small for recreational uses such as fishing or swimming (MRWC 1999). But people could engage in passive recreation along the shores of surface water bodies located off site. For instance, people from the adjacent office park take their lunch break near a pond northeast of Site 6 (Metcalf & Eddy 1992). Although the pond is not conducive to swimming or wading, incidental exposure is possible.
Farther downstream the Shawsheen River becomes a recreational resource where people do swim, wade, fish, and canoe. Sport fishing is popular at the Shawsheen River, but the Massachusetts Department of Public Health has posted a fish consumption advisory at the river due to elevated mercury concentrations in its fish (MADPH 2003).
In addition, the city of Burlington, located about 10 miles downstream, uses the Shawsheen River as part of its water supply. Water from the Shawsheen is directed to the Mill Pond Reservoir, which is treated prior to its use as a portion of the city's municipal supply. While no other city directly draws surface water from the Shawsheen River as part of its drinking water, the cities of Bedford, Burlington, and Tewksbury have installed drinking water wells near the river or near one of its tributaries (SASR 2001).
HAFB has a National Pollutant Discharge Elimination System (NPDES) Multi-Sector Discharge Permit requiring monitoring (but not periodic sampling and analysis) of storm water discharges to surface waters. As of July 2003, HAFB is covered by the NPDES Municipal Separate Storm Sewer System (MS4) permit which includes sampling and analysis of storm water discharges into the Shawsheen twice a year. In addition, HAFB has a Basewide Quality Assurance Project Plan (QAPP), which specifies the monitoring program for IRP Sites with on-going remedial actions (IT 2003). While primarily addressing groundwater sampling and analysis the QAPP also includes the periodic analysis of surface water (Shawsheen River and other wetland areas). The following samples have been/will be collected as part of the storm water and IRP investigations and the IRP long-term monitoring program.
- In 1996, 1997, 2001, and 2002, stream Gauge 3 in the Shawsheen River, adjacent to IRP Site 21 was sampled for VOCs as part of a long-term monitoring program (IT 2002d). This sampling point is included in the monitoring program for IRP Site 21 with a semi-annual frequency of analysis for VOCs and TPH.
- Five surface water and sediment samples were collected from the Shawsheen River as part of a remedial investigation for IRP Site 6. Samples were analyzed for VOCs, SVOCs, pesticides, and metals.
- Seven surface water and sediment samples were collected from the Shawsheen River and its unnamed tributary surrounding IRP Site 8. Samples were analyzed for VOCs and metals.
- In 2001, three surface water samples were collected from the Shawsheen River as part of the long-term monitoring program for IRP Sites 13 and 22(3). The samples were analyzed for volatile petroleum hydrocarbons (VPH) with target analytes.
- The River Catch Basin accesses the Shawsheen River, which flows in culverts in the vicinity of IRP Site 22. In November 2002, surface sampling of this location was added to the monitoring program for IRP Site 22 and will continue in the future on an annual basis. The sample was analyzed for VPH with target analytes.
- Surface water entering the wetlands and in the wetlands of the Bedford Forest has been sampled for VOCs since 1986, as part of the long-term monitoring program for OU-1. One of the initial sampling point continues to be sampled and analyzed quarterly (Haley & Aldrich 1998; IT 2002a, 2003). In 1996, sampling was expanded to include selected trace metals. During three sampling events from 1996 to 1998, samples were collected and analyzed for VOCs (and selected metals in 1996 and 1998) at a total of five points within the adjacent wetland (CH2MHILL 2000a).
- Seven rounds of long-term monitoring were conducted at two surface water sampling locations in Elm Brook at Site 4 from December 1989 to September 1991. Samples were analyzed for seven VOCs, four metals, and water quality parameters (e.g., chloride, sulfate, and pH). Two rounds also analyzed for 15 metals and two SVOCs (Environmental Resources Management 1992).
- Eight surface water and eight sediment samples were collected in the vicinity of Site 6 during investigations from 1986 to 1996 (CH2MHILL 1999).
- A sampling point where the surface water exits the wetlands adjacent to Site 6 is included in the monitoring program for IRP Site 6 (IT 2003). Since 2001, annual samples have been collected from this location and were analyzed for VOCs, SVOCs, pesticides, PCBs, and metals (dissolved-phase & total) (Shaw 2003).
- In 2001, surface water from two separate wetland locations immediately adjacent to Site 6, which appeared to be discolored liquid seeping from Site 6, was collected and analyzed for VOCs, SVOCs, pesticides, PCBs, and metals (dissolved-phase & total). Subsequently, in 2003, in accordance with a Five-Year Review recommendation (HAFB 2002b), these two surface water sampling points were added to IRP Site 6's annual monitoring program (Shaw 2003).
- Discharges to the Shawsheen River were measured during the Water Quality Assessment Plan conducted by HAFB in November 1995. The assessment analyzed stormwater runoff sampled at three locations within the HF/HAFB drainage system prior to reaching the Shawsheen River. Samples were analyzed for 10 metals, PAHs, VOCs, and nitrate, in addition to other water quality parameters (Rizzo 1996).
Surface water and sediment on and adjacent to HF/HAFB could have become contaminated as a result of site-related runoff or discharge from contaminated groundwater. Tables 5 through 9 list the contaminants detected above CVs in the Shawsheen River and wetlands throughout the site.
Site-wide, seven organics, two pesticides, and six metals were detected in surface water above CVs. Not every site contained all of the contaminants. At the Shawsheen River, six contaminants were detected above CVs in less than half of the 18 samples collected (Table 5). Wetlands near OU-1 contained vinyl chloride and TCE in the late 1980s, and concentrations have been decreasing over time. Other VOCs were detected only in early sampling years. Selected metals were sampled in 1996 and 1998; less than half the time during those years lead was detected above EPA drinking water action level of 15 ppb (Table 6). Arsenic, iron, and manganese were each detected above CVs in Elm Brook and surrounding wetlands near Site 4 (Table 7). These metals are naturally occurring in the environment and cannot necessarily be attributed to the Site 4 landfill. Methylene chloride was also detected above CV in 6 of the 23 samples collected, but each time it was detected, it was also detected in the laboratory blank, indicating that the contaminant might not have been present at that concentration, if at all, in the environmental sample. Benzene, benzo(a)pyrene, chloromethane, and heptachlorepoxide were detected above CVs in at least one of the samples collected in the wetlands in the vicinity of Sites 6 and 21 (Table 8). Six metals were detected above CVs, each less than 50% of the time. The only contaminant considerably above its CV was arsenic.
Discharges from the HF/HAFB drainage system sampled during the 1995 assessment contained no VOCs, PAHs, or petroleum hydrocarbons. Silver (90 ppb) in one of the three samples was the only contaminant detected above its CV (50 ppb). Still, the detection limits for antimony, arsenic, and thallium were all slightly above their respective CVs (Rizzo 1996).
Throughout the site, 10 contaminants were detected above CVs in sediments. Five PAHs, PCB-1260, and arsenic were above CVs in at least 1 of the 12 sediment samples collected from the Shawsheen River (Table 9). Arsenic and iron were the only two contaminants detected above CVs in any of the 13 samples collected from Elm Brook and the wetlands surrounding Site 4 (Table 10). Benzo(a)pyrene, heptachlor epoxide, PCB-1248, arsenic, and iron were each detected above CVs in the sediments from wetlands surrounding Site 4 (Table 10).
ATSDR evaluated those contaminants detected above health-based CVs by assuming conservative exposure scenarios based on incidental ingestion of surface water and sediments while using the river and wetlands for recreational purposes. When these exposure estimates were taken into consideration, none of the chemicals were present at levels that would be expected to cause adverse health effects in the past, currently, or in the future. See Appendix C for a complete exposure assessment.
Furthermore, people are not expected to come in contact with harmful levels of these contaminants. Any skin contact with contaminants in surface water or sediment is expected to be limited in frequency and duration, and not of health consequence. Natural processes, such as dilution and mixing, is expected to further reduce concentrations of any migrating contaminants before they reach the Shawsheen River, thus precluding the buildup of harmful levels of site-related contaminants in Shawsheen River surface water, sediment, or fish. As a result, ATSDR determined that there is no public health hazard associated with recreational use of the Shawsheen River and surrounding wetlands in the vicinity of HF/HAFB.
ATSDR identified community health concerns by contacting community members, state and local officials, boards of health, and HAFB personnel. ATSDR also conducted a thorough review of site documents.
Community members surrounding HF/HAFB are concerned about the effects of current and potential increased use of HF as a civilian airfield.
The current and potential future uses of HF as operated by Massport (or another entity) are beyond the scope of this PHA. In this PHA, ATSDR evaluated exposures to contaminants resulting from operation of HAFB. No public health hazards were identified. Concerned community members should contact local community officials for more information regarding the use of HF as a civilian airfield.
Community members are concerned about potential future contamination of the Bedford Shawsheen River well field, located downstream of HF/HAFB.
The Bedford Shawsheen River well field is located along the Shawsheen River, approximately 2.3 miles northeast of HF/HAFB. Groundwater contamination from OU-1 has flowed beyond HF/HAFB boundaries to the north. However, to prevent further impact to off-site groundwater, the USAF installed a treatment system. The USAF also monitors groundwater in all three aquifers.
Because the well field is next to the Shawsheen River, pumping the wells could draw in surface water from the river. Although certain contaminants have been detected above CVs in the surface water, by the time they reach the well field several miles downstream, contaminants are expected to have dispersed to below concentrations expected to cause adverse health effects. To verify this conclusion, ATSDR evaluated well data from the most downstream sampling point collected during surface water evaluations. SWR-01 was collected 1 mile downstream of IRP Site 6 in 1996. This location is just upstream of the Shawsheen River confluence with Elm Brook and ½ mile upstream of Bedford's Shawsheen River well field (Dynamac 1988). Although a number of SVOCs were detected in this sample, no contaminants were present above health-based drinking water CVs, indicating that although site contaminants could be affecting the river, they are present in low quantities and are not expected to cause adverse health effects. Nevertheless, until contaminant concentrations in groundwater, which discharges to the surface water, have been sufficiently reduced as to be incapable of contaminating the river and entering the water supply, monitoring of the water and sediment would provide assurance that contamination does not increase to levels of concern.
Further, due to the discontinuation of military flight operations, no fuel or aircraft are stored at HAFB, thus the potential for future contamination is limited. Additionally, Bedford monitors the water from their well field as part of the Clean Water Act, and will continue to do so in the future. This monitoring will ensure that no site-related contaminants are making their way into the drinking water supply.
Residents of Bedford were concerned that groundwater wells used in the past to irrigate their gardens may have contained harmful levels of TCE.
In the past, a few community members dug shallow groundwater wells in the Bedford Community Gardens to irrigate their gardens. However, municipal water is supplied to the Bedford Community Gardens and most, if not all, of the residents use this water supply for their gardens.
During an initial groundwater analysis in 1986, TCE, from an unknown source, was found in a monitoring well within the bedrock aquifer under the Bedford Community Gardens. However, this well has never been used to supply irrigation water and none of the privately dug wells drew water from the bedrock aquifer. TCE has not been detected in the surface aquifer, where the irrigation wells were dug (personal communication with the Air Force, October 2003).
Therefore, there is not a completed pathway. The wells that were used in the past to irrigate residents' gardens did not draw water from the contaminated aquifer. Additionally, TCE is not expected to be taken up by and accumulated in plants and infrequent incidental exposure by dermal contact or inhalation would not be sufficient to pose a public health hazard.
Residents of Bedford are concerned that the past use of the Hartwell Road well field may have resulted in exposure to harmful levels of chemicals.
In April 1983, the town of Bedford began operating three water wells at the Hartwell Road well field, using them as a source for the town's drinking water. The well field is located 1.2 miles northwest of HF. Sampling of the well water in October 1983 identified organic solvents and dissolved iron at levels above current drinking water standards (Table 11; CDM 1984a, 1984b, 1984c). Following further sampling, the town of Bedford closed the municipal well field in April 1984, and they have since provided Bedford residents with a safe alternate water supply. Investigations have been inconclusive in identifying a specific source of the contamination that caused the well field to be shut down (EPA 2003a).
Residents who used water from the well field during its operation were possibly exposed to the contaminants when they drank the water or used it for other domestic purposes. ATSDR reviewed the environmental data and possible exposures to the well water for Bedford users. Through this review, ATSDR determined that no ill effects would be expected for people who used the water until the wells were closed in April 1984, a period of less than 1 year. Because the wells have not been used since 1984, no exposure is occurring now or expected to occur in the future (see next concern). Please see Appendix C for a complete evaluation of this past exposure pathway.
The Bedford Department of Health expressed the concern that one of the conditions of MWRA Water Division membership was to maintain and restore local water supplies to the extent possible.
ATSDR contacted the Bedford Department of Public Works and verified that there are not currently any plans to begin using the Hartwell Road well field in the near future (personal communication with the Bedford Department of Public Works, December 2003). ATSDR was assured that a complete chemical analysis of the water would be conducted before the wells are put back into production to ensure that the water, treated if necessary, will meet all Safe Drinking Water requirements set by EPA and will be safe for human consumption.
ATSDR received several comments during the public comment period (February 26, 2004, to April 12, 2004). Most of the comments were suggestions to revise the text for clarification and accuracy, which ATSDR completed in this final version of the health assessment.
What seems to be missing or given only minimal recognition in the Assessment is that the groundwater in the subject area has been used in the past as a public drinking water supply. The Town of Bedford is required to consider and plan for the potential resumption of utilizing this aquifer as a drinking water supply at some time in the future. As a condition of the Town's membership in the Massachusetts Water Resources Authority (MWRA) Water Division, the Town entered into a formal agreement with the MWRA agreeing to take steps to further protect this aquifer. This requirement was based on the possibility that the cost to treat the groundwater for future drinking water supply may at some future time become less costly than purchasing water from the MWRA. This is why the Town of Bedford established an Aquifer Protection District partially encompassing the airfield and base property. So in conclusion, there are public health risks continuing most notably into the future.
Groundwater beneath HAFB is addressed in the Potential Exposure to Contaminants in Groundwater section (pages 9-14). Several plumes of chlorinated solvents, BTEX compounds, and PAHs exist within the HF/HAFB boundary. Areas of petroleum product floating on the water table have also been identified in several locations. However, groundwater beneath and immediately downgradient of HF/HAFB is not used as a drinking water source, nor are there currently any plans to do so in the future.
ATSDR addressed past exposure to drinking groundwater from the Hartwell Road well field in Community Health Concern #4. Appendix C contains additional details on the methods and assumptions ATSDR used to estimate past human exposure doses and determine health effects. VOCs were detected in the wells, however, the levels were too low and the length of exposure was too short to be of health concern. The potential future use of the Hartwell Road well field is addressed in Community Health Concern #5. ATSDR was assured by the Bedford Department of Public Works that a complete chemical analysis of the water would be conducted before the wells are put back into production.
ATSDR agrees that before the groundwater is used to supply drinking water, it should be thoroughly tested and treated, if necessary, to ensure the water meets all federal and state Safe Drinking Water requirements and is safe for human consumption. ATSDR also concurs with the continued treatment of the groundwater to reduce the contamination currently present beneath the site.
ATSDR's PHAs are exposure driven. For adverse health effects to occur, people must be exposed to harmful levels of chemicals. Given the extent of regulatory oversight by DEP and EPA and the Bedford Department of Public Works' and Board of Health's awareness of the groundwater contamination and responsibility of ensuring public water supplies are safe to drink, ATSDR does not believe that any of these local, state, and federal agencies would knowingly allow people to be exposed to harmful levels of chemicals in their drinking water.
In communities faced with air, water, or food contamination, the many physical differences between children and adults demand special emphasis. Children could be at greater risk than adults from certain kinds of exposure to hazardous substances. Children play outdoors and sometimes engage in hand-to-mouth behaviors that increase their exposure potential. Children are shorter than are adults; this means they breathe dust, soil, and vapors close to the ground. A child's lower body weight and higher intake rate results in a greater dose of hazardous substance per unit of body weight. If toxic exposure levels are high enough during critical growth stages, the developing body systems of children can sustain permanent damage. Finally, children are dependent on adults for access to housing, medical care, and risk identification. Thus adults need as much information as possible to make informed decisions regarding their children's health. Therefore, ATSDR is committed to evaluating their special interests at sites such as HAFB as part of the ATSDR Child Health Considerations.
ATSDR has attempted to identify populations of children in the vicinity of HF/HAFB. Approximately 4,230 children under the age of 5 years live within the four towns surrounding the site (Bureau of the Census 2000). A child development center, an elementary school, and a Youth Activities Center are all located on site (HAFB n.d.).
Like other people living or working at or near HF/HAFB, children may contact contaminated site media. As discussed in the Evaluation of Environmental Contamination and Potential Exposure Situations section of this PHA, past, current, and future exposures for children could include contact with surface soil or exposure to contaminated surface water and sediment from rivers or wetlands.
To evaluate whether children might experience adverse health effects through past, current, or future exposures to site contaminants, ATSDR estimated potential doses for children. To estimate these doses, ATSDR used protective assumptions that overestimate the levels of actual exposure. Appendix C describes in greater detail the methods and assumptions ATSDR used to estimate childhood exposure doses and determine health effects.
ATSDR concluded that exposure to site contamination at HF/HAFB does not pose unique health hazards for children. Current and future exposures to surface soils and past, current, and future exposures to surface water and sediment are too low to be of health concern for children. Although exposure to surface soil in the past is indeterminate, since sampling data prior to remediation is not available, ATSDR does not expect that the potential, infrequent exposure to contaminants in the soil would have had adverse health effects.
After evaluating available environmental information, ATSDR finds that the overall, exposure situations at HF/HAFB pose no apparent public health hazard, with the exception that past exposure to surface-soil contamination is an indeterminate public health hazard due to the lack of sampling data. Conclusions regarding medium- and site-specific exposures are as follows:
Groundwater in the vicinity of HF/HAFB poses no public health hazard because groundwater on site and immediately off site is not used as a drinking water source and is; therefore, an incomplete exposure pathway.
Because of lack of sampling data prior to remediation activities, past exposure to surface soil is unknown. That said, infrequent exposure to potential contamination during recreation or trespassing is not expected to have had adverse health effects. But given the lack of sampling data, ATSDR finds that past exposure to surface-soil contamination is an indeterminate public health hazard.
Current and future contact with surface soil and HF/HAFB poses no public health hazard because:
- Soil at Site 4 has been capped with clean fill to prevent exposure to potential contaminants. Quantities measured in uncapped soil were not present in sufficient quantities to pose adverse health effect.
- Contamination located at Site 6 is inaccessiblethe area has been capped and continues to remain fenced and posted to prevent access.
- Soil at Site 8 has been capped and contains no contaminants above levels expected to cause adverse health effects.
Contaminants in surface water and sediment in the Shawsheen River and in wetlands and other water bodies surrounding HF/HAFB are not present in sufficient concentrations to pose adverse health effects in the past, currently, or in the future. As a result, the surface water/sediment pathway poses no apparent public health hazard. This means that exposure is possible, but is not expected to result in harmful health effects.
The Public Health Action Plan (PHAP) for HF/HAFB contains a description of actions taken and to be taken by ATSDR, the USAF, EPA, and DEP subsequent to the completion of this PHA. The purpose of the PHAP is to ensure that this PHA not only identifies potential and ongoing public health hazards, but provides a plan of action designed to mitigate and prevent adverse human health effects resulting from exposure to hazardous substances in the environment. The completed, ongoing, or planned public health actions are listed below.
- In 1982, a hydrogeologic investigation was conducted at HF to evaluate potential contamination in Bedford's Hartwell Road well field.
- An installation assessment/records search was conducted in 1984, to identify potential contamination, to evaluate migration potential, and to assess potential hazards. Thirteen sites were identified for further investigation. Subsequent investigations have identified 22 IRP Sites.
- Between 1985 and 1988, investigations were conducted and remedial action plans were developed for IRP Sites 1-5.
- In 1988, contaminated soil and drums at IRP Sites 1, 2, and 3 were excavated. These areas are located in the airfield and were the location of former fire training and disposal areas. A removal action was also conducted for the mercury release site (IRP Site 10) in 1988. The site was closed out in 1990.
- In 1988, the final remedial action was completed for IRP Site 4. The IRP Site 4 Landfill was capped with a low permeability cap. Additional investigations indicated that this measure was sufficient to protect human health and the environment. Inspections are performed quarterly. The IRP Site 4 Remedial Action was evaluated during a CERCLA 5-year review in 1997. The review established that the cap was protective of human health.
- In 1994, HF/HAFB was added to the NPL.
- Interim remedial actions (soil vapor extraction and groundwater collection or vacuum-enhanced recovery systems and monitoring) were conducted at IRP Site 21 from 1993 to 2003.
- Natural attenuation and monitoring was established as the final remedial action for IRP Site 22 in 1997, and IRP Site 13 in 1999.
- A ROD for a final remedy for OU-3/IRP Site 6 was finalized in 2001. The ROD called for containment of three landfill areas with a permeable cap, removal of debris located in off-site areas, implementation of institution controls to limit groundwater and land use, and for long-term surface and groundwater monitoring to determine the effectiveness of natural attenuation. Remedial plans also called for a contingency groundwater remedy in the event that the remedy is not effective, and 5-year reviews. The remedial design and construction was completed for the final remedy at IRP Site 6 in 2001. Off-site debris was removed, the landfill areas were capped, institutional controls were put in place, and the long-term monitoring program was initiated.
- In 2001, an Interim ROD was issued for OU-1 (IRP Sites 1, 2, and 3) selecting continued operation of the groundwater collection and treatment system as well as institutional controls and long-term monitoring.
- Investigations of all relevant remedial activities establishes that all required actions have been completed at IRP Sites 5, 7, 8, 9, 10 11, 12, 14, 15, 16, 17, 18, 19, and 20. These sites have been closed out with regulatory concurrence and require no further action.
- In 2002, the Second Five-Year Review for the HF/HAFB Superfund Site was completed. This five-year review concluded that the remedies in placed or programmed for the NPL OU-1, OU-2, OU-3/IRP Site 6 and OU-3/IRP Site 21 are, or are expected to be, protective of human health and the environment. Also in 2002, the Periodic Evaluation (5-Year Review) of the MCP regulated sites (IRP Site 13 and IRP Site 22) was completed which recommended continued monitoring of both sites.
- In 2002, a ROD for a final remedy for OU-3/IRP Site 21 was finalized. The selected remedy includes construction of interceptor trenches (with associated removal and disposal of petroleum contaminate soil), installation of a network of recovery wells (active and passive) connected to the existing oil-water separator and groundwater treatment system, enhancement of biodegradation of dissolved-phased contaminants (VOCs and fuel compounds) by the application of Oxygen Release Compound® (ORC®) in all trenches, and a long-term monitoring program to confirm that the groundwater contaminant plume is being remediated and/or contained and is not adversely impacting the Shawsheen River. The selected remedy also includes groundwater containment/treatment and vacuum-enhanced recovery contingencies, land use controls/institution controls to ensure that groundwater is not used for human consumption and that future land use does not increase the risk of exposure to contaminants remaining on site, and 5-year reviews.
- In 2003, the remedial design and construction was completed for the final remedy at IRP Site 21. Four interceptor trenches (475 LF) with ORC® added were constructed, 2,800 tons of petroleum-contaminated soil was recycled off site, and a network of recovery wells (10 active and 7 passive) were installed and connected to the reactivated existing oil-water separator and groundwater treatment system.
- Long-term monitoring was instituted at OU-1 in 1986, to determine the nature and extent of groundwater contamination and to monitor the migration of the contaminant plume. A groundwater pump-and-treat system became operational in 1991, to decontaminate water beneath the airfield. New wells were added and the system became automated in 1996. Vacuum-enhanced recovery was incorporated in 1999.
- Because there is groundwater contamination in several plumes beneath the site, the USAF has enacted institutional controls to prevent drinking water or irrigation wells from being drilled on site. ATSDR concurs with this action to ensure that groundwater beneath the site remains an incomplete exposure pathway.
- To ensure the remedy remains protective of human health and the environment, 5-year reviews are required at all sites where hazardous substances, pollutants, or contaminants remaining at the site are above levels that allow for unlimited use and unrestricted exposure. ATSDR concurs with continued use of 5-year reviews to ensure that remedies, which are in place, are operated, maintained, and monitored to continue to protect public health.
- Surface water monitoring is conducted in the Shawsheen River and wetlands surrounding OU-1 and OU-3 (IRP Sites 6 and 21) in accordance with the Basewide QAPP for Long-Term Monitoring at OU-1 and OU-3. Because on-site groundwater plumes can discharge toand potentially impactsurface water quality, ATSDR concurs with the action of continued monitoring of surface water quality until groundwater concentrations have decreased to levels that would not adversely impact the Shawsheen River or surrounding wetlands.
- Yearly monitoring is ongoing at IRP Sites 13 and 22, which are MCP-regulated sites where natural attenuation and monitoring was chosen as the selected remedy.
- HAFB conducts periodic inspections and maintenance of landfill caps. ATSDR concurs with this action to ensure that the protective caps remain in place.
- In 1996, long-term monitoring of groundwater contaminant concentrations and the thickness of the light non-aqueous phase liquid (petroleum product) was instituted at OU-3/IRP Site 21. Earlier interim recovery actions were replaced by the final remedy (petroleum product/groundwater recovery and treatment system) which became operational in 2003. ATSDR concurs with continued long term monitoring and petroleum product/groundwater recovery and treatment of OU-3/IRP Site 21 to monitor and prevent contamination from migrating offsite and adversely impacting the Shawsheen River.
- HAFB will continue to operate, maintain, and monitor the remedies for OU-1, OU-2, OU-3 (Sites 6 and 21), and the MCP sites (Sites 13 and 22) in accordance with RODs and other Air Force Decision Documents.
Its assessment of environmental data and potential exposure scenarios leads ATSDR to make the following recommendations:
- ATSDR concurs with continued treatment beneath OU-1 to prevent contamination from migrating further off site, as well as continued long-term monitoring north of the site in the Bedford Forest. In light of the increasing trend in TCE contamination in the lower aquifer, ATSDR suggests that if site-related contaminants continue to increase in off-site monitoring wells, drinking water wells within 1.5 miles downgradient of HF/HAFB should be tested to ensure that well water is within drinking water standards.
- On-site groundwater plumes can discharge to and potentially impact surface water quality. ATSDR therefore concurs with the USAF's continued monitoring of the groundwater quality. This will assure that levels do not increase to the point that contamination could reach the Shawsheen River or surrounding wetlands at levels that could present a public health hazard.
- ATSDR recommends that before groundwater beneath or immediately downgradient from HF/HAFB is used to supply drinking water, it should be thoroughly tested and treated, if necessary, to ensure the water meets all federal and state Safe Drinking Water requirements and is safe for human consumption.
Environmental Health Scientist
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry
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1 The Bedford Community Gardens well is not part of OU-1. The source of the TCE is unknown. HAFB monitors the well as a courtesy to the Bedford community (personal communication with the Air Force, October 2003).
2 Near surface samples were collected from "generally less than five-foot depth" (Metcalf & Eddy 1990). Ideally, ATSDR would evaluate exposure to surface soil samples collected from a depth less than 6 inches.
3 The Shawsheen River flows in three culverts through part of HAFB and discharges into open channel flow north of IRP Sites 13 and 22. The 2001 samples were collected from the discharge of the three culverts (IT 2002e).