PUBLIC HEALTH ASSESSMENT
DOVER AIR FORCE BASE
DOVER, KENT COUNTY, DELAWARE
The Agency for Toxic Substances and Disease Registry (ATSDR) prepared this public health assessment (PHA) to evaluate potential health hazards from past, current, and future exposures to contaminants originating from Dover Air Force Base (DAFB). DAFB is an active U.S. Air Force (USAF) base located about 3.5 miles southeast of the city of Dover in Kent County, Delaware. In addition to the main base, DAFB includes two annexes: the Eagle Meadows Housing Annex (77.51 acres), located 1 mile southeast of DAFB in Lebanon, Delaware; and the Port Mahon Petroleum, Oil, Lubricant Annex (2.14 acres), located 3 miles northeast of Little Creek, Delaware. Including annexes, easements, and leased property, the base encompasses roughly 4,000 acres.
Over the years, materials used in industrial or general base support operations spilled or were released to the soil or the underlying groundwater due to accidents and/or waste management practices. These materials came primarily from aircraft and vehicle maintenance and repair activities; they included waste fuel, oils, solvents, pesticides, plating wastes, and paint. The primary contaminants of concern are volatile organic compounds (VOCs) and fuel-related compounds in groundwater. On March 13, 1989, because of environmental releases and the presence of contamination, the U.S. Environmental Protection Agency (EPA) put DAFB on its National Priorities List of sites to be investigated. In coordination with the Delaware Department of Natural Resources and Environmental Control (DNREC) and the U.S. Environmental Protection Agency (EPA), the USAF has been investigating and remediating known sources of environmental contamination on the base.
To evaluate possible health hazards associated with environmental contamination at DAFB, ATSDR conducted a comprehensive public health assessment (PHA). ATSDR's PHA process identifies populations who may have been or are exposed to hazardous substances and determines the public health implications of those exposures. As part of the process, ATSDR conducted site visits and met with representatives from DAFB in 1991 and 2003. Using information gathered during site visits and findings of site investigations conducted at DAFB, ATSDR examined the nature and extent of contamination associated with the site. ATSDR considered past, current, and potential future exposure situations in its evaluation.
Based on this evaluation, ATSDR identified five exposure situations for evaluation. Three of these are associated with industrial releases from DAFB and two potential environmental exposure situationslead in housing and arsenic in the drinking waterare not. ATSDR evaluated possible hazards associated with these exposures and concluded that they are not of health concern as follows.
- Contaminants in off-base drinking supply wells. ATSDR determined that no harmful exposures have occurred in the past from drinking water from off-site private wells. In 1984, VOCs were detected in water supply wells at a residential trailer park and other off-site private properties located southwest of the base. Although well water contaminants were below levels at which adverse health effects have been reported in the toxicologic literature, DAFB began providing drinking water to the residents of the trailer park in 1984. In addition, sources (e.g., local gas station and dry cleaning operations) other than DAFB may have contributed some contaminants to the well water. Construction to connect Gooch Trailer Park, the P&F Motorcycles business, and a residence to Tidewater Municipal Water Service began in September 2003. Because the residential trailer park was taken off its well system and placed on the DAFB drinking water system, no exposure to site-related contaminants has occurred since 1984. Therefore, drinking water from the trailer park now or in the future also poses no public health hazard.
- Arsenic in DAFB drinking supply well water. ATSDR has determined that arsenic levels in one of the base's drinking water wells are not hazardous. Routine testing over the years has shown that water from DAFB's drinking water wells has met state and EPA safe drinking water standards. Recently, EPA lowered its safe drinking water standardor maximum contaminant levelfor arsenic from 50 ppb to 10 ppb in light of recent findings of possible health effects from long-term exposure to arsenic. Arsenic was detected at levels up to 19 ppb in a DAFB water supply well that draws from the deep Piney Point Aquifer. Arsenic in the Piney Point Aquifer is believed to have originated from non-site sources, such as natural deposits in the earth's crust. The drinking water distribution system that supplies DAFB and the Eagle Heights Housing Area has two wellsD and Ein the Piney Point Aquifer. Even though arsenic exceeded the new standard, drinking base water or otherwise using it in the home is not expected to harm residents or base personnel. This is because the water is mixed with water from other wells before being distributed base-wide and exposure from the drinking the water is most likely to be short-term rather than over a lifetime. In addition, DAFB plans to stop drinking water use in Well D and abandon Well E in late 2003. These actions will prevent any future exposures.
- Lead exposures in DAFB housing. ATSDR has confirmed with DAFB personnel that, although some housing units have interior and exterior lead-based paint, no cases of childhood lead poisoning associated with DAFB housing have been reported at the base. Lead-based paint was used in base residences prior to 1978. Because young children are prone to hand-to-mouth activities they could eat lead paint chips or lead-contaminated dust, increasing their risk of developing lead poisoning. As part of the base's lead program and the state of Delaware's regulations, children living on base are tested for lead exposure at their 12-month well baby checkups. Additional testing is provided as needed for children who have not been tested, who have elevated blood lead levels, or who are at high risk for lead exposure. To date, no cases of lead poisoning have been confirmed. In addition, DAFB is removing lead hazards as the units are vacated, and residents are told about the potential hazards of lead when they first move into base housing.
- Possible vapors in DAFB homes located above the Area 6 VOC plume. ATSDR determined that people living in Eagle Heights Housing units above the Area 6 plume are not expected to encounter harmful levels of indoor air contaminants or develop adverse health effects. Some housing units in the Eagle Heights Housing Area sit above a VOC-contaminated groundwater plume that has migrated from the main portion of the base. Because VOCs in groundwater can travel through the soil into overlying buildings, ATSDR conducted conservative indoor air modeling for the potentially affected residential units using the maximum levels found in the shallow groundwater to create a worst-case evaluation. This modeling showed that VOC contaminants could be present in the air inside certain buildings, but at levels far below those associated with known adverse health effects. And because residents generally stay in base housing for a short period of time rather than over a lifetime, the exposure is minimized. In addition, groundwater contamination in the housing area is expected to decrease as a result of DAFB's ongoing remedial efforts, further reducing the risk of future indoor air contamination.
- Current use of a former landfill. ATSDR has determined that no harmful exposures are occurring at ball fields and a school located at or near a former base landfill. Land previously used for the former Landfill D-11 (called LF26) is now used for three ball fields and is located northwest of the nearby Welch Elementary and Middle School. This 2-acre landfill was used for disposal of construction debris and household refuse in the 1950s and 1960s. The former landfill has been covered with soil and grass that prevent contact hazards. Field investigations indicate that the contaminant levels are so low as to warrant no further action. In addition, the landfill is most likely beyond the stage at which soil gases are created and emitted.
ATSDR also assessed the exposure to VOCs moving from the water to the air during showering. Using a protective screening model, ATSDR predicted air concentrations based on the highest levels of VOCs found in the water. ATSDR also assumed that all of the VOCs volatilized to air and that no dissipation occurred. Using these assumptions, ATSDR concluded that, in the past, VOCs would not have reached levels in indoor air that would cause adverse health effects.
Dover Air Force Base (DAFB) is an active base located in Kent County, Delaware, approximately 3.5 miles southeast of the city of Dover. The site includes two annexes: DAFB's Eagle Meadow Housing Annex (77.51 acres), located 1 mile southeast of Lebanon, Delaware, and the Port Mahon Petroleum, Oil, Lubricant Annex (2.14 acres), located 3 miles northeast of Little Creek, Delaware. Including annexes, easements, and leased property, the base encompasses approximately 4,000 acres of land. DAFB is surrounded by cropland and wetlands, and bounded to the southwest by the St. Jones River (see Figure 1).
DAFB began operating at the Dover Municipal Airfield in December 1941. The U.S. Army Air Corps leased the partially constructed airfield for use as a coastal patrol base for the Eastern Defense Command. The facility expanded in early 1942, making the airfield more suitable for heavy aircraft such as B-25 Mitchell medium bombers. The airfield became an operational base for combat training of P-47 fighter pilots in August 1943 (Dames & Moore 2001).
The Dover Airfield became a Pre-Separation Processing Center for personnel leaving the service at the close of World War II and was subsequently deactivated in September 1946. The Air National Guard occasionally used the facility for training exercises. In July 1950, the facility was reactivated and officially designated Dover Air Force Base.
DAFB was used for air/land defense operations from early 1951 until March 1952, when it came under the command of the Military Air Transport Services (MATS). This made DAFB the East Coast terminal for cargo operation missions. From 1954 to 1965, many aircraft were used in these missions, including C-154, C-124, C-133, and C-141 cargo planes. A detachment of KC-97 tanker aircraft from the Strategic Air Command was located at the base from 1960 until 1965. MATS was re-designated as the Military Airlift Command in 1966, and then renamed again in 1992 as the Air Mobility Command.
DAFB is the base for the operations of the 436th Airlift Wing, whose primary mission is to provide immediate airlift of troops, cargo, and military equipment. The wing's secondary mission is to support tactical forces by participating in air-land or airdrop operations involving troop equipment and supplies. DAFB also serves as the joint services port mortuary. In addition, DAFB is the home terminal for the C-5 Galaxy aircraft on the East Coast. The C-5 Galaxy, a cargo plane, is the largest aircraft in the U.S. Air Force (USAF). DAFB is one of the few military bases with hangers and runways that will accommodate the C-5. DAFB is expected to remain an active military facility in the future.
A number of activities at DAFB generated hazardous wastes and released them into the environment. Contaminated process waters were either discharged into the base's drainage systems or treated. Other wastes were disposed of on site in landfills, discharged to surface water (with or without pretreatment), discharged to treatment plants, or burned during fire training exercises. These wastes came primarily from aircraft and vehicle maintenance and repair activities; they included waste fuel, oils, solvents, pesticides, plating wastes, and paint.
Environmental investigations began at DAFB when the U.S. Environmental Protection Agency (EPA) investigated the presence of an on-site landfill (LF13) that had been used for disposal of construction debris and rubble. The USAF continued environmental investigations at DAFB in 1983 under the Department of Defense's Installation Restoration Program (IRP). Most investigations at DAFB focused on former waste disposal practices, seeking to determine if they posed any threats to public health or the environment. Through these investigations, USAF found contamination, including solvents, metals, and polychlorinated biphenyls (PCBs), in groundwater and/or soil at several locations (USAF 2003).
On March 13, 1989, because of the contamination detected at DAFB, EPA added DAFB to the National Priorities List (NPL) of sites to be investigated. (The NPL is part of EPA's Comprehensive Environmental Response, Compensation, and Liability Act, or CERCLA, which is commonly known as "Superfund.") USAF then entered into a Federal Facility Agreement (FFA) with EPA Region III and the Delaware Department of Natural Resources and Environmental Control (DRNEC) to outline a comprehensive strategy for conducting environmental investigations and complete remedial actions on DAFB property where hazardous materials might have been disposed of, spilled, or stored.
DAFB evaluated environmental conditions through a 1993-1994 base-wide remedial investigation (RI) at 59 IRP sites identified as having hazardous or potentially having hazardous contamination. Most sites at DAFB were investigated at least once before the RI activities. Those investigations included the initial IRP investigations, a number of subsequent site investigations, and an Ecological Assessment (EA) of the base. The IRP sites have been grouped into four major management units: the East Management Unit, the North Management Unit, the West Management Unit, and the South Management Unit (Dames & Moore 2001). Nine areas of groundwater contamination (called Areas 1 through 9) have also been identified and grouped into the management units. Each IRP site has been addressed in the RI process based on its grouping in one of the four units. The four management units and associated areas of groundwater contamination are shown in Figure 2 and described below.
- North Management Unit. DAFB has identified only one IRP site, SD12, in this unit. SD12 is a drainage ditch with a history of receiving raw industrial wastes in the 1950s and industrial wastewater in the 1960s. Since 1969, the ditch has only been used for storm-water runoff from the North and West Management Units (Dames & Moore 1997a). Other features of the unit include runways, taxiways, access roads, and open fields.
- East Management Unit. This unit contains nine IRP sites and Area 1, a groundwater plume that has been related to past disposal activities. Although some fuel-related compounds were detected in the groundwater, the primary constituents of interest are chlorinated solvents. Other sites within this unit are the Ammunition Storage Facility, the Receiver Station, and the Hazardous Cargo Storage Facility (Dames & Moore 1997a).
- South Management Unit. Ten IRP sites identified at the South Management Unit include landfills, a fire training area, fuel releases, oil/water (O/W) separators, underground storage tanks (USTs), and a hazardous waste storage area. In addition, the South Management Unit contains Areas 2, 3, and 9. Areas 2 and 9 are each associated with distinct groundwater plumes of chlorinated solvents and Area 3 is associated with a groundwater plume of vinyl chloride and benzene (Dames & Moore 1997b).
- West Management Unit. As the largest unit, the West Management Unit contains 39 IRP sites and five Areas of associated constituents (Areas 4 through 8). The type of IRP in this unit varies: landfills, a fire training area, fuel releases, O/W separators, a pesticide shop, USTs, the former industrial waste basins (IWBs), the industrial waste collection drain (IWCD), and the former wastewater treatment plant . The aircraft parking apron, shops, offices, part of the golf course, and DAFB housing also are found within this unit. Each of the five areas within the West Management Unit is associated with particular groundwater constituents. Areas 4, 7, and 8 are each associated with fuel-related constituents (as well as some isolated areas in Area 6). Areas 5 and 6 are each associated with chlorinated solvent plumes (as well as a solvent source in Area 7) (Dames & Moore 1997c; Dames & Moore 2001).
DAFB has undertaken interim removal actions or remedial actions at some sites to control or reduce the spread of contamination from these areas. These measures include:
- Removal of petroleum hydrocarboncontaminated soil from a fire training area (FT03) in the East Management Unit.
- Removal of soil from a landfill (LF18) in the South Management Unit in 1996.
- Excavation of buried drums from at a fire training area (FT01) in the East Management Unit.
- Removal of a concrete basin and soils from WP21 in the West Management Unit in 1999.
- Removal of O/W separator systems at several locations throughout the base.
- Initiation of natural attenuation 1 or bioremediation at several Areas where volatile organic components (VOCs) have contaminated the groundwater.
To date, 33 IRP sites at DAFB have been recommended for no further action: 31 of them required no remediation because they were not hazardous to human health, and the other 2 have been remediated to cleanup standards (USAF 2003). Ten other sites are currently undergoing actions to mitigate groundwater pollution through monitored natural attenuation of chlorinated solvents or fuel-related products, free-phase jet fuel recovery, or accelerated anaerobic bioremediation (USAF 2003). Implementation of measures to clean up contamination at the remaining 16 sites will begin after DNREC and EPA approve the feasibility studies (FS) and sign the records of decision (RODs) that outlines the selected remedial action for a particular site (USAF 2003).
Through the public health assessment (PHA) process, ATSDR assesses conditions at a site from a public health perspective to determine whether people can be exposed to site-related contaminants through contact with the site's groundwater/drinking water, surface water, soil, biota , or air. As part of the PHA process, ATSDR conducted an initial visit to the DAFB in 1991. The purpose of the visit was to collect information necessary to rank the site according to its potential public health hazard, to identify public health issues related to environmental contamination at the facility, and to identify community health concerns. During the visit, staff met with USAF and DAFB personnel and representatives from federal and state agencies.
ATSDR visited DAFB again in February 2003 to obtain updated information related to environmental studies at the base. ATSDR met with USAF personnel and toured the base. Based on discussions, the site visit, and data reviews, ATSDR concluded at the time that there was little potential for immediate threats to human health. ATSDR did, however, identify several exposure pathways that required further evaluation, including ingestion of VOC-contaminated water from off-base drinking water supply wells, ingestion of arsenic-contaminated drinking water from the DAFB water supply, inhalation of indoor air contaminants from soil vapor intrusion, incidental ingestion of lead (from lead-based paint), and contact with contaminants in a former landfill. ATSDR prepared this PHA to further evaluate these pathways.
ATSDR examines demographic information, or population information, to identify the presence of sensitive populations, such as young children (age 6 and under), the elderly (age 65 and older), and women of childbearing age (age 15 to 44). 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 environmental contaminants.
More than 6,800 active duty and reserve military personnel work at the base. Ten dormitories on base provide 704 single occupancy accommodations. Approximately 1,000 military personnel and their family members live in one of 1,023 units at either the Eagle Heights housing development, located across U.S. Route 113 from the main base, or the Eagle Meadows housing annex, located 4 miles southwest of the main base in the village of Lebanon (DAFB 2003). Upgraded playgrounds are located throughout these housing areas.
Children living in base housing and lodging attend schools in the Caesar Rodney School District. On-base schools at the Eagle Heights Housing Development within this district are the Welch Middle School (157 students), the Welch Elementary School (340 students), and the Arnold Elementary School (133 students) (DAFB School Department 2003). A child development center located in Building 292 on Chad Street provides developmental care and educational services for up to 250 children between 6 weeks and 5 years old.
Approximately 39,000 people live within 3 miles of the site. The closest resident lives about ½ mile away. The city of Dover accounts for about 60% of the local population. The DAFB housing area is the second largest community and makes up approximately 11% of the local population. The city of Dover has the largest population between the ages of 5 and 18 years in the area, while the DAFB housing has the highest percentage of children age 5 and under. Other nearby towns include Little Creek, about 1 mile northeast of DAFB, and Camden, about 2 miles west (Dames & Moore 1997a). The town of Little Creek has the highest percentage of adults over 65 years of age in the area. Figure 4 shows 2000 demographics information for the population near DAFB. As the figure indicates, about 7,500 people live within a 1-mile buffer of the site, including 1,201 children under the age of 7 years and 303 adults aged 65 years and older.
ATSDR examines land use to determine what activities might put people at risk for exposure to contaminants related to DAFB. Land at DAFB is used primarily for operations to support the base's mission. A regularly patrolled perimeter fence surrounds DAFB. Access to the base is restricted to military personnel, base residents, and civilian employees. A member of the general public could enter by passing security guard stations located at the main entrance and another site entrance, registering his or her vehicle, and obtaining a pass. Certain sites under CERCLA investigations are fenced off to deter access.
Land use controls have been in place and enforced at DAFB since 1997 as part of a remedial action in the RODs signed for three East Management Unit sites: FT03, LF13, and WP14/LF15. Land use controls at the base include physical and administrative mechanisms to limit access to, and restrict the use of, property to prevent or reduce risks to human health. Physical controls include fencing around the industrial area of the base and the controlled-entry gates that are manned 24 hours a day, 7 days a week. Administrative controls include the DAFB General Plan, which prohibits use of groundwater from the Columbia Aquifer anywhere on base and restricts the digging or disturbing of soil at contaminated sites. DAFB, EPA Region III, and DNREC have been developing a base-wide land use control strategy that will essentially formalize the land use controls that have been in place since 1997.
In addition to the land use controls maintained by DAFB, DNREC has recently established a Groundwater Management Zone (GMZ) that encompasses all of DAFB as well as downgradient off-base properties. The GMZ is used to ensure that no well permits are issued for this area without prior written approval from DNREC's Site Investigation and Restoration Branch. The GMZ is typically coupled with deed restrictions for any affected non-federal property (DAFB 2003).
Land use surrounding DAFB consists of civilian and military single- and multi-family residential areas, commercial land, industrial zones, and large areas of agricultural and open land. Gooch Trailer Park is a small trailer park located southwest of the main portion of DAFB. The park provides 11 lots for year-round residential trailers. The size of the trailer park has remained the same since the 1980s.Two large industrial areas are located just north of DAFB and numerous commercial areas are found along the major highways north and west of DAFB. Agricultural areas and open spaces are concentrated to the south and east of the base, although they can be found all around the remaining perimeter (Dames & Moore 1997a). A nine-hole golf course also is situated along the southwestern boundary of the installation. Some anglers fish the St. Jones River, which flows along the western boundary of the base.
Natural resources used in the vicinity of DAFB include groundwater for drinking water and surface-water bodies for recreational uses. Some of the key exposure concerns associated with DAFB pertain to chemical contamination in the shallow aquifer (groundwater) and releases to the St. Jones River. For information on how contaminants might migrate to and/or accumulate in these media, ATSDR obtained background information on the local groundwater hydrogeology and surface-water hydrology.
Groundwater is found within four water-bearing subsurface formations, or aquifers, in the DAFB area. These aquifers are the Columbia, Frederica, Cheswold, and Piney Point Aquifers. The unconfined Columbia Aquifer is the uppermost, or shallowest, aquifer beneath DAFB. It holds the water table, which ranges from 29 feet below ground surface (bgs) to within a few feet near the St. Jones River (Dames & Moore 1995). Because this aquifer is so close to the surface, it is recharged by storm-water flow from the base. Local farmers use water drawn from the Columbia Aquifer for irrigation and/or drinking water. Most of these irrigation wells are located upgradient of the DAFB to the east and south (Dames & Moore 1997a; DNREC 2003).2 Other residential or commercial wells along the southern and western boundaries of the site also rely on water from the Columbia Aquifer. Some of these wells are downgradient of or have been impacted in the past by the Area 5 plume originating in the West Management Unit. (ATSDR evaluates public health hazards from exposure to contamination in drinking water supply wells affected by the Area 5 plume in the "Evaluation of Environmental Contamination and Potential Exposure Pathways" section of this PHA.)
The Frederica Aquifer, approximately 22 feet thick, is located beneath a confining layer (the Kirkwood Formation) that separates itand limits flowfrom the Columbia Aquifer. Although high levels of iron in this aquifer preclude its use by DAFB and the city of Dover as a source of drinking water, it is used by the towns of Fenton, Frederica, Harrington, and Milford, as well as a few food processing and poultry businesses located more than 8 miles away from DAFB (Dames & Moore 1997a).
The Cheswold Aquifer occurs at a depth of about 125 feet bgs at DAFB, separated from the Frederica Aquifer by a "90-foot silt, clay, siltey clayey sand layer" (Dames & Moore 1997a). Recharge of this aquifer comes from a narrow outcrop near the city of Smyrna and, to a limited extent, from leakage from the overlying Columbia Formation. Beneath the Cheswold Aquifer lies the Piney Point Aquifer, about 330 to 580 feet bgs. This aquifer is recharged by the overlying Cheswold Aquifer in response to heavy withdrawal on the Piney Point Aquifer. Together, the Cheswold and Piney Point aquifers provide 80% of the municipal and industrial water supply for the Dover area, including DAFB.
Two groundwater divides that represent areas of high or low water levels influence groundwater flow at DAFB. One divide associated with a groundwater high runs parallel to the northwest/southeast runway. The other divide, representing a groundwater low, is perpendicular to the first divide. The two divides segment the base into four areas, which were used to determine the boundaries of the current management units at DAFB (Dames & Moore 1995). In general, groundwater is known to flow southwest toward the St. Jones River and its tributaries in the South and West Management Units (the most industrial portion of the base) and to the on-base drainage channels, the North Drainage Ditch, and Pipe Elm Branch in the North and East Management Units (Dames & Moore 1997a).
The St. Jones River, which flows along the southern boundary of the base, and the Little River, which flows through the northern portion, are the two predominant river systems near DAFB. A drainage system at DAFB consisting of ditches and below-ground pipes diverts surface-water runoff on the base into tributaries of these rivers. Storm-water drainage along the northern and eastern portion of the base drains into three major drainage systems, then into the Pipe Elm Branch near the base boundary, and eventually into the Little River. Drainage from the southernmost portion is diverted by one of two drainage ditches that both eventually discharge into the St. Jones River (Dames & Moore 1995). Drainage in the western portion of DAFB is transported along subsurface drainpipes that discharge into an open trench east of U.S. Route 113. The ditch flows beneath the highway, through the DAFB golf course and ultimately into the St. Jones River (Dames & Moore 1995).
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 USAF site and remedial investigations. ATSDR has determined that the data's quality is adequate for making public health decisions.
ATSDR's PHAs are exposure (or contact) driven. People who work or live in area of an environmental release can only be exposed to a contaminant if they come in contact with it. Exposure might occur by breathing, eating, or drinking a substance containing the contaminant or by skin contact with a substance containing the contaminant. Therefore, a release does not always result in exposure.
ATSDR evaluates site conditions to determine if people could have been (a past scenario), are (a current scenario), or could be (a future scenario) exposed to site-related contaminants. When evaluating exposure pathways, ATSDR identifies whether exposure to contaminated media (soil, water, air, waste, or biota) has occurred, is occurring, or will occur through ingestion, dermal (skin) contact, or inhalation. ATSDR also identifies an exposure pathway as completed or potential, or eliminates the pathway from further evaluation. Completed exposure pathways exist if all elements of a human exposure are present. (See "Exposure Pathway" in Appendix A for a description of the elements of a completed exposure pathway.) A potential pathway is one in which one or more of the pathway elements cannot be definitely proved or disproved. A pathway is eliminated if one or more of the elements are absent.
More information about the ATSDR evaluation process can be found in ATSDR's Public Health Assessment Guidance Manual at http://www.atsdr.cdc.gov/HAC/HAGM/ or by contacting ATSDR at 1-888-42ATSDR.
Exposure and Health Effects
Given sufficient exposure levels, chemical contaminants disposed of or released into the environment can cause adverse health effects. The type and severity of health effects that occur in an individual from 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 (the 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 might occur as a result of exposure to a contaminant in the environment.
ATSDR selects contaminants for further evaluation by comparing them against health-based comparison values, or CVs. CVs are developed by ATSDR from the available scientific literature on exposure and health effects. They are derived for each of the different 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., amount of water or soil consumed or amount of air breathed) and body weight. In order to be conservative and protective of public health, ATSDR CVs are generally based on contaminant concentrations many times lower than levels at which no effects were observed in experimental animals or human epidemiologic studies. ATSDR's CVs are not used to predict the occurrence of adverse health effects, but serve as a protective screen and first step in evaluation of public health implications.
CVs include ATSDR's environmental media evaluation guides (EMEGs), reference dose media evaluation guides (RMEGs), and cancer risk evaluation guides (CREGs). CREGs, EMEGs, and RMEGs are non-enforceable, health-based CVs developed by ATSDR for screening environmental contamination for further evaluation. In addition, ATSDR uses EPA's maximum contaminant levels (MCLs). MCLs are enforceable drinking water regulations developed to protect public health. (See Appendix B for a further description of the CVs.)
If contaminant concentrations are above CVs, ATSDR then analyzes exposure variables (for example, duration and frequency), the toxicology of the contaminant and epidemiology studies for possible health effects. Figure 3 provides an overview of ATSDR's exposure evaluation process.
Possible Exposure Situations at Dover Air Force Base
ATSDR reviewed data for DAFB's 59 IRP sites in the four management units and other environmental issues to determine if they are associated with past, current, or future public health hazards. (Table 1 describes each site and briefly summarizes the evaluation.) When evaluating these areas, ATSDR assessed the level of contamination present or degree of physical hazard, the extent to which individuals come into contact with the contamination or hazard, and whether this contact would result in a public health hazard. The review indicated that most sites at DAFB are not associated with any known public health hazards because: (1) no site-related contaminants are present, (2) contaminant concentrations detected are too low to pose a health hazard, or (3) past and current exposure to the general public has been prevented.
In this review, however, ATSDR did identify several completed and potential exposure situations at DAFB for further evaluation. Exposure situations considered in this PHA include:
- Completed exposures:
- Ingestion of VOC-contaminated water from off-site, neighboring drinking water supply wells.
- Ingestion of arsenic in DAFB drinking water.
- Potential exposures:
- Breathing in vapors, possibly in base buildings overlying groundwater plumes.
- Childhood exposure to lead-based paint in DAFB housing.
- Hazards from use of land at a former base landfill.
Exposure situations at DAFB are evaluated in detail in the following discussion and summarized in Table 2. To acquaint the reader with terminology and methods used in this PHA, Appendix A provides a glossary of environmental and health terms presented in the discussion, Appendix B describes the CVs ATSDR used in screening contaminants for further evaluation, Appendices C and D describe the methods ATSDR used to evaluate whether health hazards exist, and Appendix E provides ATSDR's responses to comments received during the public comment review period (September 25 to November 17, 2003) for this PHA.
Testing of the well water at Gooch Trailer Park and other neighboring properties to DAFB in 1984 showed VOCs at levels above current safe drinking water standards. Following the detection, the trailer park well was closed in 1984, and DAFB supplied the trailer park and other affected properties with an alternate water supply. Some VOCs associated with solvents and perhaps fuel-related compounds at DAFB have contributed to groundwater contamination that has migrated as a plume beyond the base's southwestern boundaryand near these properties. Recent monitoring suggests, however, that commercial properties along Highway 113 (i.e., gas station and dry cleaning business) are partially or predominantly responsible for the off-site well water contamination. People possibly exposed to the contaminants from ingesting drinking water or from other domestic uses in the past are not expected to develop ill effects because the levels are below those shown to cause adverse health effects. No exposure has occurred since 1984. DAFB is currently pursuing plans to connect the residents to a utility service.
Off-Base Groundwater/Drinking Water Supply Contamination
In 1983, in accordance with RCRA regulations, DAFB sampled groundwater under unlined waste lagoons at the corner of Atlantic Street and 4th Street. These lagoons received discharges from on-base painting, aircraft washing facilities, and from Building 719 which housed a degreasing operation in the 1960s and 1970s (DAFB 1984a; DNREC 2003). Waste disposed of in the lagoons is believed to have seeped into the soil and the underlying groundwater. The monitoring efforts found that the groundwater of the Columbia Aquifer contained high levels of industrial chemicals, such as TCE and PCE. Fuel constituents, such as toluene and benzene, also were detected.
Groundwater in this area of DAFB flows typically southwest, toward the St. Jones River. Several drinking water supply wells are located downgradient of the lagoons, across U.S. Highway 113. Water supply wells identified in the area included the water supply well for the Gooch Trailer Park and wells at several neighboring properties (see Figure 5).
After DAFB detected the site-related contaminants in the Columbia Aquifer, Delaware's Division of Public Health (DPH) conducted sampling in June 1984 at downgradient, off-base drinking water supply wells that draw from the same Columbia Aquifer (DNREC 1984a). Table 3 summarizes DPH's well monitoring data. Results of the DPH sampling indicated that the well supplying the Gooch Trailer Park with drinking water contained organic industrial solvents (PCE at 231 parts per billion [ppb] and TCE at 7.2 ppb) and dissolved hydrocarbons (benzene at 175 ppb and toluene at 5.9 ppb). DPH also sampled wells at the P&F Motorcycles business and the Paradee Gulf Gas Station/Restaurant situated north of the base housing area along Highway 113and directly upgradient of the Gooch Trailer Park. These wells were also found to be contaminated with TCE (4.2 ppb and 20 ppb) and PCE (813 ppb and 3.6 ppb) (DNREC 1984a). Available information did not mention if other VOCs were detected in these two wells. A well serving a home associated with P&F Motorcycles property was also sampled, but, according to DNREC, contained no substantial contamination (1984c). Less is known about the wells at the nearby Giacomos Pizza, Texlers Exxon, and Hastings Dry Cleaners, located further south on Highway 113, nearer to the DAFB Main Gate. Limited available information suggests that the well water at these properties also contained VOC contamination, and was subsequently deemed by the Centers for Disease Control and Prevention (CDC) to be unfit for human consumption (CDC 1985). Table 4 provides a chronology of sampling events and public health actions related to contamination affecting the Gooch Trailer Park well and neighboring wells. 3
The concentrations of TCE, PCE, and benzene in Gooch Trailer Park well exceed the current ATSDR CVs and EPA safe drinking water standards, and were higher than concentrations in other affected neighboring water supply wells (DNREC 1984a). Based on detected concentrations, the DPH issued a public notice informing Gooch Trailer Park residents to refrain from drinking water from the affected well. Even though the source of the contamination had not been established, DAFB provided an emergency water tank supply to the trailer park in July 1984 (DNREC 1984a). Later that year, they connected the Gooch Trailer Park, the P&F Motorcycles business, a residence, and Paradee Gulf Gas Station to the base water supply because no municipal water service was available. The base's drinking water supply comes from the deeper confined (uncontaminated) Cheswold and Piney Point Aquifers (USAF 1984; DAFB 2003). Information was not available on whether Giacomos Pizza, Texlers Exxon, and Hastings Dry Cleaners were provided with an alternate water supply. However, Delaware Department of Transportation (DelDOT) acquired and subsequently demolished the properties in the early 1990s for the SR-1 highway construction. The Hastings site was listed as a Superfund site because of chlorinated solvent releases. It is currently undergoing a cleanup remedy under DNREC authority (DAFB 2003).
Groundwater Investigations Dover AFB
At the time of the 1984 state investigation of the water supply wells, there was very little hydrogeologic data available, and DNREC assumed that the former lagoons were the source of contamination in the Gooch Trailer Park well because it was the only known source of contaminants in the vicinity at that time. DNREC therefore recommended the closure of the unlined lagoons at the base (DNREC 1984b). Subsequent investigations by both the DelDOT and DAFB, however, revealed that the waste lagoons were not the source of the contamination. Their investigations suggested that the groundwater flow direction from the lagoons would carry contaminants far south of the Gooch Trailer Park, and away from the drinking water well (DAFB 2003). These investigations are described in further detail below.
DAFB CERCLA Investigations
DAFB investigated groundwater conditions at the base in accordance with CERCLA requirements. Through these investigations, DAFB identified nine areas of groundwater contamination on the base property associated with releases at IRP sites or other on-site areas. The groundwater contamination in these areas has formed plumes in the Columbia Aquifer beneath DAFB. Table 1 describes areas of IRP sites and areas of groundwater contamination beneath the base in further detail.
Monitoring conducted as part of the West Management Unit RI shows that groundwater contaminants in the Columbia Aquifer along the southwestern boundary form a plume referred to by DAFB as Area 5. The Area 5 plume originates near the aircraft maintenance area (OT51) and covers about 30 acres. The plume appears to cross the base boundary at U.S. Route 113 near the Gooch Trailer Park as it extends southwest toward the St. Jones River. Major components of the groundwater plume in Area 5 are TCE, PCE, 1,2-dichloroethylene (1,2-DCE), and vinyl chloride. Localized areas of BTEX components also exist. Businesses along the U.S. Route 113, such as the former Paradee Gulf Gas Station and P&F Motorcycles, were other sources of solvents and fuel-related compounds within the off-site portion of the Area 5 flow path (see discussion below) (Dames & Moore 2001).
On-site sources suspected of contributing VOCs and BTEX to the groundwater plume in Area 5 (see Table 5) are:
- An O/W separator (OT44), which is a source of TCE and 1,2-DCE.
- Former maintenance hangars (Buildings 794, 789, 790, and 791 at OT51). OT51 is believed to be a source of 1,2-DCE and vinyl chloride. Buildings 789, 790, and 791 are suspected sources of TCE and 1,2-DCE.
- A fuel-related site near Building 639 (SS20), believed to be a source of PCE, TCE, and 1,2-DCE.
- The IWCD (OT41) near the motor pool.
- An O/W separator (OT43) that appears to be a source of BTEX compounds (Dames & Moore 1997c).
VOC contamination in the shallow portion of the Columbia Aquifer of Area 5 is relatively limited. Small amounts of the contamination are localized to areas primarily beneath or near the suspected source areas. In the deeper portion of the Columbia Aquifer, however, contamination is more extensive. Contaminants from the multiple IRP sources seeped down to the deeper aquifer within Area 5 where they have mixed together, forming an elongated plume of varied VOC constituents that appears to emanate from a source near Building 794 at OT51 and migrates southwestward with the direction of groundwater flow past Building 639 at SS20 and the base motor pool. As of the 1997 RI, the downgradient extent of the plume had not been fully delineated because access could not be secured to private property (Dames & Moore 1997c).
Fuel-related BTEX compounds have been detected in the shallow Columbia Aquifer at several on-base IRP sites within Area 5. BTEX compounds were detected less frequently and at lower concentrations than the VOC contaminants, and extend only a short distance from the source area. In the deeper portion of the aquifer, concentrations are lower than those found in the shallower portion (Dames & Moore 1997c).
DAFB has instituted remedial actions in several of these areas, such as monitored natural attenuation or removal of contaminated soil, the suspected source, to within DNREC guidance levels. DAFB is currently overseeing a remediation project at Building 639 (Dames and Moore 2001). Through the Air Force Research Laboratory and Battelle of Columbus, Ohio, DAFB is testing a pilot-scale permeable barrier system. The barrier was installed in January 1998 in the parking lot west of Building 639 to allow treatment of the Area 5 plumes that migrate past Building 639. The barrier, however, does not address contaminants already in the groundwater downgradient of the barrier or those originating in the motor pool (Dames & Moore 1997c, DAFB 2003).
DelDOT Investigations at Off-Site Properties
In 19891990, DelDOT conducted an environmental investigation at off-site properties near DAFB in preparation for acquiring land for the SR-1 highway construction. Some of these properties included the Paradee Gulf Gas Station and the P&F Motorcycles property. The DelDOT investigation showed that there was a fuel-related source of contamination at the former Paradee Gulf Gas Station and a shallow PCE source at the P&F Motorcycles property. Both of these properties are north and upgradient of the Gooch Trailer Park and within the off-site portion of the Area 5 flow path (Dames & Moore 2001). Based on the locations and levels of contamination found at these sites, however, these properties are believed to be partially responsible for contaminants found in the off-base drinking water wells.
DelDOT acquired a portion of the P&F Motorcycles property and the Paradee Gulf Gas Station for the SR-1 highway construction that was eventually completed in the late 1990s. The P&F Motorcycle site is currently listed under the state of Delaware's Hazardous Substance Cleanup Program. No further investigations or cleanup actions are believed to have taken place at the P&F Motorcycle site since the DelDOT investigation in 19891990. The Paradee Gulf Gas Station was eventually demolished for the highway construction project (DAFB 2003). It is unknown whether any cleanup actions occurred at the Paradee Gulf site.
The off-base contamination of Area 5 will be addressed under the Delaware Hazardous Substance Cleanup Act with DNREC as lead authority. DNREC plans to notify the potentially responsible parties, which will presumably include DAFB, the owner of P&F Motorcycles, and DelDOT. DAFB will take appropriate action when DNREC completes the notification process (DAFB 2003).
Public Health Implications of VOCs in Off-Base Drinking Water Wells
Sampling in 1984 found VOCs in the drinking water supply well that serves Gooch Trailer Park at levels above ATSDR's current CVs (DNREC 1984a). Other drinking water wells in the area also contained VOCs, but either located at industrial or commercial properties or contained contaminants at lower levels than what were measured at the trailer park. People could have been exposed to VOCs in the past while drinking the water or using it for other domestic purposes. ATSDR examined the possibility of harmful health effects from using water from the affected wells at the trailer park or at other neighboring property in the past. ATSDR focused its public health evaluation on possible past exposures because no exposure has occurred since 1984 when DAFB provided the trailer park with drinking water. DAFB continues to supply water to the Gooch Trailer Park and the P&F Motorcycles property (Paradee Gulf has since been acquired and demolished by the DelDOT for the SR-1 highway construction).4
Past Exposure to VOCs from Ingestion of Drinking Water
ATSDR estimated the potential exposure dose for adults and children who drank water originating from the Gooch Trailer Park well to determine if a health hazard existed. ATSDR incorporated information about the frequency (how often) and duration (how long) of potential contaminant exposure. When site-specific information about exposure was lacking, ATSDR used assumptions that are considered protective of public health. For example, because it is not known when migrating VOCs first reached the Gooch Trailer Park well, ATSDR used an exposure period of 30 years for adults (and 6 years for children) to calculate a theoretical maximum exposure dose. ATSDR also assumed that the drinking water pumped to residential taps contained the maximum concentrations of VOCs in the well. This method is very protective because, in most exposure situations, it is highly unlikely that a person will be continuously exposed to the highest concentration detected. This approach provides an evaluation of whether a contaminant is likely to pose a health concern. Appendix C describes in detail the method ATSDR used to estimate exposure doses for past ingestion of water from the Gooch Trailer Park well and other affected off-base wells.
ATSDR compared the estimated exposure doses with standard health guidelines, such as ATSDR's oral minimal risk levels (MRLs) and EPA's reference doses (RfDs), if available, to determine the likelihood that adverse health effects will occur. The MRLs and RfDs provide a protective estimate of daily exposures to non-cancer agents that are not likely to result in adverse health effects, even for the most sensitive members of a community (e.g., pregnant women, children). The estimated exposure doses for ingestion of water from the Gooch Trailer Park well are provided in Appendix C, Table C-1.
Estimated exposure doses for an adult or child exposed to the detected levels of the VOCs found in the well are below corresponding MRLs/RfDs or several times lower than the levels at which effects were observed in the laboratory animal studies.5 Current toxicologic literature suggests that the detected levels of VOCs are also below levels thought to cause cancer via the oral route of exposure (ATSDR 1997a, 1997b, 1997c). Considering this information, no health effects are expected for people drank water from the VOC-affected wells in the past.
Past Exposure from Breathing in VOCs Released While Showering
Normal household usesuch as washing and bathingof water contaminated with VOCs at the detected levels might result in vapors being released. The primary way some VOCs enter the body is through inhalation of air contaminated with the chemical, therefore, residents of Gooch Trailer Park using the water for domestic purposes could have been exposed to VOC-contaminated vapors. Because some information suggests that highest levels of inhalation exposure to VOCs in the home occurs during showering (Lindstrom 1994), ATSDR assessed exposures to VOCs moving from the water to air during showering. To be protective, ATSDR used a screening level model to predict air concentrations based on the maximum detected VOCs in water. ATSDR also assumed that 100% of the VOCs volatilized to air and that no dissipation occurred. ATSDR's assumptions, methods, and the estimated doses are further described in Appendix C. Using these assumptions, ATSDR found no evidence that VOCs would have reached levels in indoor air in the past associated with adverse health effects.
Routine testing over the years has shown that water from DAFB's drinking water wells has met state and EPA safe drinking water standards. Recently, EPA lowered its safe drinking water standardor maximum contaminant levelfor arsenic from 50 ppb to 10 ppb in light of recent findings of possible health effects from long-term exposure to arsenic. Arsenic was detected at levels up to 19 ppb in a DAFB water supply well that draws from the deep Piney Point Aquifer–and above the new standard. Arsenic in the Piney Point Aquifer is believed to have originated from non-site sources, such as natural deposits in the earth's crust. The drinking water distribution system that supplies DAFB and the Eagle Heights Housing Area has two wellsD and Ein the Piney Point Aquifer. Even though arsenic exceeded the new standard, drinking base water or otherwise using it in the home is not expected to harm residents or base personnel. This is because the water is mixed with water from other wells before being distributed base-wide and exposure from drinking the water is most likely to be short-term rather than over a life-time. In addition, DAFB plans to either stop using the two Piney Point Aquifer wells for drinking water or abandon the wells in late 2003, which will prevent any future exposures.
Drinking Water at DAFB
The DAFB base water system, which relies on groundwater, serves about 10,000 people. Institutional controls prevent the use of groundwater from the contaminated shallow Columbia Aquifer beneath the base. Table 6 summarizes the drinking water wells used by DAFB. Drinking water for the main base at DAFB and the Eagle Height Housing Area has been obtained from three wells that draw water out of the Cheswold Aquifer and two wells that draw from the Piney Point Aquifer. These wells, located in different parts of the base property, feed into a common distribution system where the water is treated with fluoride and disinfected with chlorine (DAFB 2001a).
Residents of the Eagle Meadows Housing Annex obtain drinking water from two other wells in the deep Piney Point Aquifer. The water from these two wells feeds into a distribution system separate from the main base. In addition to the fluoride and chlorine treatment, water delivered to Eagle Meadows Housing Annex is treated with a corrosion-control inhibitor intended to prevent lead from leaching out of household water pipes (DAFB 2001a).
Arsenic in Drinking Water
DAFB has routinely monitored its drinking water in accordance with requirements set by EPA and the state of Delaware since the 1980s. Historical testing of the water supply indicated that the base's drinking well water met state and federal safe drinking water standards for contaminants, including those released to the groundwater from DAFB site operations.
EPA recently reduced its safe drinking water standard for arsenicits maximum contaminant level, or MCLfrom 50 ppb to 10 ppb in light of new information about possible long-term health effects from prolonged exposure to arsenic. It is the inorganic form of arsenic that is most commonly found in groundwater sources and drinking water supplies. Studies link ingestion of inorganic arsenic in drinking water to both non-cancer health effects and cancer.
EPA's MCLs, set under the Safe Drinking Water Act, are standards that limit the amount of certain contaminants in water provided by public water systems. MCLs are developed to protect individuals who could be exposed over a lifetime (70 years). Public drinking water suppliers must ensure that the quality of their drinking water meets these standards. Water that meets the standards is generally considered safe to drink, but it does not necessarily follow that any concentration that exceeds the MCL is expected to produce adverse health effects in a community. Protective, health-based standards and guidelines are derived to enable health professionals to recognize and resolve potential public health problems before that potential problem is realized.6
Arsenic exists in the Piney Point Aquifer beneath DAFB. Arsenic occurs naturally in rocks and soil; when these erode over time, arsenic can be released into surface water and underlying groundwater. Drinking water systems that rely on groundwater in areas of natural arsenic deposits can have high arsenic levels.
Results of the water quality monitoring were available in the Air Force Institute for Environment, Safety, and Occupational Health Risk Analysis (AFIERA) report (2001) and in Annual Consumer Reports on the quality of tap water at DAFB. ATSDR summarizes the monitoring results for the main base/Eagle Heights system and for the Eagle Meadows system in the discussion that follows and in Table 7.
Main Base and Eagle Heights Housing Area
The main base and the Eagle Heights Housing Area have obtained their drinking water from five water supply wells located within the base boundaries. Wells A, B, and C draw water from the Cheswold Aquifer and Wells D and E draw from the Piney Point Aquifer. Tests of the well water since the 1980s show that water in Well D reached a maximum arsenic concentration of 19 ppb (see Table 7). (Although concentrations above 10 ppb exceed the new EPA MCL, the arsenic concentration was below the established EPA MCL of 50 ppb at the time of the testing.) Water from Well D, however, is blended with water from the other wells before it is distributed to base personnel and Eagle Heights residents. This mixing of the water from various wells lowers the concentration of arsenic in the water ultimately delivered to users at the main base and at Eagle Heights. Limited available sampling of the distribution systems shows that the arsenic concentrations in the distribution system water have been below 10 ppb (AFIERA 2001).
Eagle Meadows Housing Annex
Water from the two Eagle Meadows Housing Annex wells contained arsenic at concentrations up to 10 ppb, the level established for the new MCL (see Table 7). Data were collected from individual wells and from the distribution system (DAFB 2003). DAFB is working to achieve arsenic levels no higher than 10 ppb in Eagle Meadows Housing Annex wells by 2006.
Public Health Implications of Arsenic in the DAFB Drinking Water Wells
The arsenic concentrations in DAFB's Well D (19 ppb) exceeded EPA's new MCL for arsenic of 10 ppb, while concentrations in other wells were at or below the new MCL. The arsenic concentrations also exceeded ATSDR's CREG of 0.02 ppb. ATSDR uses CVs and MCLs to select contaminants for further evaluation in cases where exposure is possible. Concentrations below CVs or MCLs are not expected to cause harmful effects; concentrations above CVs or MCLs will not necessarily lead to adverse health effects. That is because CVs and MCLs are established at concentrations generally many times lower than levels at which no effects were observed in experimental animals or human epidemiologic studies. Given this, the arsenic CV and MCL reflect an estimated contaminant concentration that is not likely to cause health effects in humans.
In June 2001, when the MCL's reduction to 10 ppb had been proposed but not finalized, AFIERA's Health Risk Assessment Branch evaluated potential health risk to residents and base personnel from drinking water containing the maximum concentration (19 ppb) of arsenic detected in Well D (AFIERA 2001). Using a risk assessment methodology consistent with EPA's Risk Assessment Guidance for Superfund and 20 years of data for Well D (but only 3 years of data for the base distribution system), AFIERA determined that arsenic was not at levels that could cause health effects or increase one's likelihood of developing cancer (AFIERA 2001). AFIERA recommended that DAFB determine the source of arsenic in Well D.
In follow-up to AFIERA evaluation, ATSDR evaluated exposure to arsenic in the base water supply wells. For arsenic in drinking water from the base wells, the primary exposure of concern is ingestion. People can also come in contact with water via skin contact and inhalation of vapors while using the water for domestic purposes. Neither skin contact nor inhalation of vapors is expected to pose harm: arsenic is not volatile, nor is it readily absorbed to any great extent through the skin. ATSDR focused, therefore, on the health effects that could result from drinking water containing arsenic at the detected levels.
ATDSR derived exposure doses to determine the extent to which drinking water containing the maximum detected concentration of arsenic in the base wells might be associated with adverse health effects. Note this assumption overestimates true exposures because people at DAFB do not obtain their water directly from the wells. Rather, water from a well is mixed and diluted with water from with other wells and then fed into the distribution system that ultimately leads to water taps at DAFB. Because of the dilution effect, drinking water reaching base residents and personnel contains a lower concentration of arsenic. ATSDR uses assumptions that are considered protective of public health. This approach allows ATSDR to estimate the highest possible exposure dose and determine any corresponding health effects. ATSDR compared these doses to the available MRLs and further reviewed the scientific literature about the toxicity and potential health effects of these contaminants. A further description of the assumptions used in estimating exposures is presented in Appendix C.
ATSDR found that an adult drinking water containing the highest concentration of arsenic detected in DAFB's wells was likely to be exposed to 0.0005 milligrams per kilogram per day (mg/kg/day) of arsenic. A child was likely to be exposed to 0.001 mg/kg/day. Both doses exceed the MRL for arsenic of 0.0003 mg/kg/day. ATSDR further reviewed scientific literature on arsenic to evaluate whether health effects would be likely to occur at the estimated doses. The threshold for arsenic effects is somewhere between 0.003 and 0.007 mg/kg/day (Marcus and Rispin 1988 as reported in ATSDR 2000). ATSDR's estimated doses based on arsenic levels in base drinking water wells are far below the levels required to saturate the body's detoxification mechanism. As a further comparison, the lowest dose (0.014 mg/kg/day) shown to cause adverse health effects (skin and gastrointestinal effects) in humans drinking arsenic-contaminated water for up to 45 years is 28 times higher than the estimated dose for adults and 14 times higher than the dose for children (ATSDR 2000).
EPA has classified arsenic as a human carcinogen. The arsenic lifetime exposure dose for cancer, based on the maximum arsenic concentration (0.00003 mg/kg/day), was below the Cancer Effect Level (CEL) of 0.0011 mg/kg/day, or the lowest level shown to cause cancer as been reported in toxicologic literature. ATSDR finds that, even considering very protective assumptions, the levels of exposure are very unlikely to lead to either long-term adverse health effects or cancer.
Although no adverse health effects are expected from arsenic in the DAFB drinking water supply, the base is pursuing measures to ensure that their water supply meets EPA's new arsenic standards of 10 ppb. They plan to use the existing Well D to fill tanks for fire suppression instead of drinking water and drill a new well into the Cheswold Aquifer to supply drinking water along with wells A, B, and C. DAFB also plans to abandon Well E as a drinking water supply well (DAFB 2003).
Contaminated groundwater from leaks and spills at the base has migrated beneath the Eagle Heights Housing Area. The most common contaminants in the groundwater are the VOCs TCE, PCE, and DCE. Under some conditions, VOCs can travel upward from the groundwater, through the soils, and into the air of subsurface spaces of buildings. For example, vapors can seep into basements through cracks in foundations or around sump pumps. People in affected residences could then breathe the VOCs. No indoor air sampling has been conducted to determine whether contaminants associated with the groundwater plumes have entered the buildings and adversely affected indoor air quality. ATSDR estimated indoor air concentrations for a typical unit at the Eagle Heights Housing Area. The maximum level of VOCs estimated in indoor air is much lower than the levels at which adverse health effects would be expected. Homes above the plumes, therefore, are not expected to accumulate indoor air contaminants to levels that could pose harm to residents.
Eagle Heights Housing Area and VOC Groundwater Contamination
The Eagle Heights Housing Area serves 2,289 military personnel and their family members. It is located in the West Management Unit, west of State Route 1. Area 6 in the West Management Unit of DAFB, an 80-acre area of contaminated groundwater in the Columbia Aquifer, extends 4,600 feet southwest across the highway beneath part of the Eagle Heights Housing Area (Dames & Moore 1997c, 2001). The Columbia Aquifer is the uppermost, or shallowest, aquifer beneath DAFB.
No drinking water supply wells are located in the Eagle Heights Housing Area that could become contaminated by the VOC plume. In some cases, however, VOCs in groundwater can evaporate, travel upward through the soil, and, by seeping into the cracks in foundations or through other means, reach the air inside homes. In this section, ATSDR evaluates the potential for VOCs to seep into homes in the Eagle Heights Housing Area located above the Area 6 plume.
The Sources of Area 6 VOC Contamination
Contaminants in the Area 6 plume came from many separate sources in the West Management Unit. Sources include some of the IRP sites, as well as paint stripping, maintenance, and plating shops and hangars where solvents were used (USAF 2003). The contaminants from various sites form plumes that commingle with contaminants from other sites, creating the larger area of groundwater contamination that has moved southward with the groundwater flow toward the housing area, and ultimately to the St. Jones River.
Between 1993 and 1999, as part of the RI activities and other investigations, DAFB collected groundwater data from a network of 54 groundwater monitoring wells in Area 6, some of them located in the housing area. The results show that the plumes contain mostly chlorinated solvents. The highest levels of contamination have been detected in a portion of the Area 6 plume known as Target Area 2 (see below) during the 1993 RI. TCE was reported on base at a maximum concentration of 15,000 ppb, and 1,2-DCE was reported at a maximum concentration of 2,600 ppb (Dames & Moore 2001). PCE and vinyl chloride were also detected but at lower concentrations.
As the contaminants migrate downward in the groundwater they disperse and commingle with contaminants from other source areas (Dames & Moore 2001). At the base boundary, VOC concentrations are much higher in the deeper monitoring wells than in the shallow wells. Isolated areas of the plume contained BTEX compounds related to fuels used at the base. A plume of the pesticide lindane was also located along the western boundary of Area 6.
DAFB originally identified four regions in Area 6 within the base boundaries that contained a combined concentration of VOCs at levels above 1,000 ppb. These regions, or Target Areas, are described below:
- Target Area 1. This area of contamination originates at the Paint Washout Area (Site SS59) along the eastern portion of the open storage yards, and extends south about 800 feet to 8th and 9th Streets.
- Target Area 2. Target Area 2 is elliptical and is approximately 13.1 acres in size. Early investigations suggested that this area of contamination was related to the Civil Engineering Shops Area. More recent investigations indicate that it originates from Building 719, the same source as Target Area 3. A portion of the Industrial Waste Collection Drain (IWCD) (OT41), running below and parallel to the northeast side of Building 719, is thought to have been the source of contamination for Target Areas 2 and 3. Building 719 is a jet engine inspection/maintenance shop. During the early 1940s, and again from 1951 to the present, it has been used as a cleaning room where a variety of solvents are used. Pipes from one room in the building once discharged to an outside underground storage tank/acid neutralization tank, which is no longer used. Another cleaning room contained an aboveground TCE dip tank. A third room formerly drained to an oil/water separator and its 500-gallon holding tank.
- Target Area 3. Located just north of Target Area 1, this area originates at Building 719, the Jet Engine Repair Shop.
- Target Area 4. This area is located north-northwest of Target Area 3 at an ISO-Dock (Building 715) and an engine storage facility (Building 716). This area is being investigated under OT50.
In addition to the on-base sources associated with the Area 6 plume, other off-base sources have contributed to the downgradient portion of the plumes. These sources include a former dry cleaning business (Hastings Dry Cleaners) and gas stations (Dames & Moore 2001).
Today, DAFB enforces land use restrictions that prohibit the use of the contaminated Columbia Aquifer beneath the base. DAFB has prepared a FS outlining remedial measures intended to reduce the concentration of groundwater contaminants associated with the Target Areas. Based on comments received from EPA, DAFB will conduct groundwater treatment to reduce the concentration of VOCs to meet EPA's drinking water standards, or MCLs, so as to prevent off-base migration of contaminants to areas where DAFB groundwater use restrictions cannot be enforced (Dames & Moore 2001, DAFB/CEV 2003).
Remedies proposed to reduce groundwater contamination in Area 6 are as follows:
- Natural attenuation at Target Area 1. Semiannual monitoring indicates that the natural processes of dilution, dispersion, and degradation of contaminants in groundwater has resulted in reduced levels of PCE and TCE and their breakdown products, DCE and vinyl chloride.
- Accelerated anaerobic biodegradation at Building 719 (Target Areas 2 and 3). Groundwater is extracted, injected with a carbon source and nutrients, and then reinjected into the groundwater, creating an anaerobic environment that encourages native microorganisms to break down the VOC contaminants (USAF 2003).
- Removal of O/W separators (OT46), concrete basins, and contaminated soil near WP21.
- Removal and capping of pesticide-contaminated soil at SS59 (Dames & Moore 2001).
Also, DNREC has approved natural attenuation as a groundwater remedy for contamination from the non-base sources (the dry cleaners and the gas stations) to the Area 6 plume (Dames & Moore 2001).
Contamination beneath the Eagle Heights Housing Area
Eight of the monitoring wells in the Area 6 network are located in the Eagle Heights Housing Area: DM350, DM353, DM354, DM355, DM360, IR06D, IRO7D, and DM397 (Dames & Moore 2001). VOCs have been detected in the deep portion of the Columbia Aquifer beneath the housing area. Table 8 summarizes TCE, 1,2-DCE, PCE, and vinyl chloride concentrations measured in these wells.
As noted in Table 8, concentrations of TCE between 0.6 ppb and 660 ppb were detected in groundwater beneath the housing area at the time of the 1993 RI. The highest concentrations were detected in two monitoring wells located within the plume (DM354D at 580 ppb and DM353D at 660 ppb), in the vicinity of East Hawthorne Drive and Myrtle and Walnut Streets. During that time, the chlorinated solvents TCE and 1,2-DCE at concentrations above 1,000 ppb were still contained within the West Management Unit north of the U.S. Route 113.
Data from 1995 show that the TCE and 1,2-DCE concentrations greater than 1,000 ppb traveled south across the highway to the Eagle Heights Housing Area, with lower concentrations extending further south. Some of the highest concentrations of TCE (up to 3,700 ppb) and 1,2-DCE (up to 7,500 ppb) were centered around monitoring well DM353D. A statistical analysis of the groundwater trends in individual groundwater monitoring wells shows an increasing trend in TCE concentrations southwest of the highway since 1995. The data also show that TCE concentrations north of the highway and near the source areas were decreasing, likely due to natural attenuation and other mitigation measures (Dames & Moore 2001).
Public Health Implications of Exposures to Estimated Indoor Air Contaminants
Groundwater contamination in the Eagle Heights Housing Area involves the shallow aquifer at depths less than 50 feet. The majority of contaminants in the groundwater are VOCs that can volatilize into vapor. This vapor can, in turn, move from the groundwater through soil, and eventually seep into basements and affect the indoor air.
Indoor air sampling data were not available for units of the Eagle Heights Housing Area that are situated above the VOC plume. ATSDR therefore applied EPA's Johnson and Ettinger (1991) model to estimate indoor air in those areas not sampled. The model is a health protective screening-level model that estimates the transport of contaminated vapors from either subsurface soils or groundwater into the spaces directly above the source of contamination (EPA 2003a).
ATSDR estimated the concentrations of TCE, 1,2-DCE, PCE, and vinyl chloride in indoor air from vapor intrusion to determine whether indoor air contaminants at the Eagle Heights Housing Area could be associated with any unhealthy effects. The maximum concentrations of these VOCs in the groundwater were used for these calculations. ATSDR then compared the estimated concentrations to health guidance levels, such as ATSDR's inhalation MRLs, and to information in the toxicologic literature on these VOCs. The MRL is an amount of a contaminant in the air that is not expected to cause adverse health effects. As such, an estimated indoor air concentration less than the inhalation MRL is not expected to cause adverse health effects. Table D-1 lists the estimated the indoor air concentrations for TCE, 1,2-DCE, PCE, and vinyl chloride and available health-guidance values.
ATSDR estimated TCE, 1,2-DCE, PCE, and vinyl chloride indoor air concentrations at 13.8 ppb 35.1, 1.3, and 12.7 ppb, respectively, based on the highest detected groundwater concentrations. The estimated exposure concentrations are lower than their intermediate inhalation MRLs of 100 ppb for TCE, 200 ppb for 1,2-DCE, and 30 for vinyl chloride and the chronic MRL of 40 for PCE. ATSDR further compared the estimated exposure concentrations to the LOAELs (lowest-observed-adverse-effect levels, i.e., the lowest levels at which health effects have been observed in animal studies) on which ATSDR based its intermediate MRLs for these compounds. The compounds' estimated indoor air concentrations are more than 700 times lower than their LOAELs (ATSDR 1996, 1997b, 1997c, 1997d; EPA 2003b).
No MRLs currently exist for chronic inhalation exposures to TCE, DCE, or vinyl chloride. Current literature provides evidence that laboratory animals exposed to these VOCs for a long time develop adverse effects, such as neurological, kidney, and renal problems. The concentrations at which these effects develop are several orders of magnitude higher than the exposure concentrations estimated for residents of the Eagle Heights Housing Area (ATSDR 1996, 1997c, d; EPA 2003b).
This comparison suggests that the maximum level of VOCs estimated in homes in the Eagle Heights Housing Area is much lower than the level at which we would expect to see adverse health effects. ATSDR used a very health protective model; the highest values found in the groundwater were used to create a worst-case evaluation. In addition, because residents generally stay in base housing for a short period of time rather than over a lifetime, the exposure is minimized. As a result, ATSDR concludes that homes above the plumes should not accumulate indoor air contaminants to levels that could pose harm to Eagle Heights residents.
It should be noted that the groundwater contaminant levels used to estimate indoor air concentrations were collected since 1993. Monitoring during this period indicates that VOC concentrations had increased over time in the portion of the plume beneath the housing area. But groundwater contamination in the housing area is expected to decrease as a result of DAFB's ongoing remedial efforts. If, however, monitoring of groundwater indicates that VOCs are not decreasing, ATSDR recommends that DAFB consider indoor air sampling in buildings above the plume.
Homes built between the late 1950s and the 1970ssuch as some of those at DAFBare likely to have lead-based paint. Lead can be particularly hazardous to young children because they are generally prone to hand-to-mouth activities and, therefore, could eat lead paint chips or lead-contaminated dust. Base residents are informed about the potential hazards of lead in their houses upon their acceptance into base housing. They also are provided with instructions on how to safely clean chipped or peeled lead paint from interior surfaces of their home. In addition, DAFB is remediating or demolishing homes with lead-based paint. Children living at DAFB are screened for lead exposure and lead poisoning at their 12-month check up. To date, no childhood cases of blood lead poisoning associated with base housing have been confirmed at that base.
Lead Health Hazards
Lead can affect most organs and systems in the human body, particularly the central nervous system. Although lead can cause adverse effects to people of all ages, ATSDR is most concerned about the potential for children (6 years of age and under) to come into contact with lead. Children's growing bodies absorb more lead than adults' bodies, and their developing brains and nervous systems tend to be more sensitive to the damaging effects of lead. A child whose body accumulates high amounts of lead might experience behavioral problems, learning disabilities, and delayed growth, among other effects (ATSDR 1999a).
Children can be exposed to lead in a variety of mediafor example, in drinking water from lead pipes or in soil from industrial processes. Public health screening for lead in children, however, indicates that lead-based paint in older homes (e.g., those built before 1978) is the most important risk factor for lead exposure in children. Lead-based paint is considered a potential hazard if it is damaged (i.e., chipping, cracking, chalking, or peeling) or if it is on a surface subject to impact or frictionsuch as stairs, doors, and windowsthereby creating lead-paint dust (ATSDR 1999a, 1999b; EPA 2001). Children can be exposed to lead-based paint by chewing or mouthing painted surfaces, eating sweet-tasting lead-based paint chips, or by accidentally ingesting lead dust or lead-contaminated soil on their hands. Lead is absorbed through ingestion more readily than through inhalation or dermal contact. Preschool-age children are most likely to inadvertently ingest soil through hand-to-mouth activity (ATSDR 1999a). Children who eat nutritious low-fat meals that are high in iron and calcium absorb less lead (CSU 2003).
Historical Use of Lead-Based Paint at DAFB
Lead was used in paint, as well as other commercial and household products, long before its harmful effects were known. About 75% of U.S. homes built before 1978 contain some lead-based paint (CSU 2003). Some of the most heavily leaded paint was used in homes built before the 1950s. Because the Eagle Heights Housing Area was built during the late 1950s to early 1960 and the Eagle Meadows Housing Annex was constructed in the 1960s and 1970s, some homes in these areas contain lead-based paint (DAFB Housing Division 2003). In 1978, the U.S. Consumer Product Safety Commission banned the use of lead-based paint in homes due to the associated health hazards, at which time DAFB stopped using lead-based paints.
Lead-Based Paint Hazards in DAFB Housing
If properly maintained, lead-based paint poses little risk of lead poisoning. Lead-based paint that peels or chips, however, poses an immediate hazard of lead poisoning to young children. In March 2001, the 436th Medical Group Commander outlined a blood lead program for DAFB (DAFB 2001b). Responsibilities and procedures for reducing lead hazards at DAFB are defined by the 436th Medical Group Commander's Blood Lead Program (DAFB 2001b).
As part of the 436th Medical Group Commander's Blood Lead Program, the Division of Bioenvironmental Engineering (in cooperation with Civil Engineering) at DAFB surveyed base-housing units for lead-based paint in 1994. Information collected in the surveys has been used to recommend removal or cleanup measures and assist in investigations of lead exposure (DAFB 2001b). DAFB tested the exterior and some interiors of a 100 base homes for the presence of lead-based paint. The homes were chosen for investigation based on the use of the home as a daycare, any lead toxicity investigations, any work on the housing unit where exposure was possible, and random selection. Less than 10% of the paint samples contained lead, including two interior samples, one from a basement and the other from an attic access panel (DAFB Housing Division undated).
Lead Poisoning Prevention at DAFB
One can prevent lead poisoning by keeping children from coming into contact with lead. DAFB has been demolishing housing units as part of a modernization effort and this serves to reduce or prevent exposure to lead at the base. Demolition was phased in increments of 120 units and was based on geographic location (DAFB 2003). There are plans to demolish additional base housing possibly tainted with lead-based paint and conduct further cleanup efforts. In addition, every time occupants vacate a residence–every 3-4 years on average–the empty house is prepared for the new occupant. This includes repairing any surfaces with deteriorated paint and, in most cases, completely repainting the unit with non-lead-based paint. During occupancy, residents are encouraged to report any significant chipped or peeling paint so that it can be dealt with immediately. Until all affected homes are demolished or remediated, DAFB advises residents to protect their children against unwanted exposure as follows:
- Notification about lead-based paint. A memorandum from the DAFB Housing Division notifies prospective residents about lead-based paint at DAFB before they move into base housing (DAFB Housing Division undated; DAFB 2001c).
- Temporary cleaning/removal measures. Lead painted surfaces generally do not pose a health hazards. The DAFB Housing Division, however, advises residents to report severely chipped or peeled painted surfaces to the Family Maintenance Office (DAFB Housing Division undated) because of possible risk to children. Children should be kept away from surfaces with chipped paint and activities that disturb or damage lead-based paint, such as sanding or scraping painted surfaces, should be avoided. For surfaces that exhibit minor chipping or peeling, residents should:
- Collect small amounts of paint chips with duct tape.
- Clean the chipped surface with a solution high in phosphates. The Housing Division recommends dishwashing detergents, like Cascade. Phosphates, such as those found in dishwater detergents, adhere to lead and keep it from spreading around. The chipped surface should be cleaned weekly and protective gloves should be worn while cleaning.
Special Care for Children
A physician at DAFB screens each young child for possible lead exposure as follows:
- Assess the extent of lead exposure. The Centers for Disease Control and Prevention and the American Academy of Pediatrics have recommended that physicians evaluate the potential for lead exposure to children (9 months to 6 years of age) and, when appropriate, perform blood-lead screening (ATSDR 1999a, 1999b; AAP 1998; CDC 2003). At DAFB, a physician administers a questionnaire to the guardian of a child less than 7 years of age starting at the 12-month well baby checkup. Information gathered from the questionnaire helps the physician determine the child's level of lead exposure and what type of further care is needed (DAFB 2001b).
- Screen blood lead levels. Tests that measure lead levels in blood are typically used to assess lead exposure. Links between blood-lead levels and health effects have been studied extensively to evaluate the potential for lead exposure to cause adverse health effects. Children living at DAFB are tested for blood lead levels at their 12-month well baby visits as required by the state of Delaware.7 DAFB also screens children less than 7 years of age who have not already been tested, who have blood lead levels of 10 µg/dL or higher, or who are at risk for lead exposure (DAFB 2001b). Children might be at risk of lead exposure if they live in or frequent a building built before 1978 that has peeling or chipping paint, or if the adults in the home work with lead. EPA also recommends that children who are at high risk for lead exposure be tested for blood lead levels at 6, 12, 18, and 24 months, and annually between the ages of 2 and 6 years (EPA 1998).
- Provide additional preventative and follow-up measures. During the 12-month well baby checkup, the physician provides information about lead exposure to the child's guardian (DAFB 2001b). DAFB's Public Health group investigates incidents of possible lead exposure, ensuring appropriate follow-up screening, education, and preventative measures for all identified cases of elevated blood lead levels (DAFB 2001b).
Public Health Implications of Exposure to Lead-Based Paint at DAFB
Lead-based paint was used in DAFB housing units built before 1978. A survey of lead hazards at housing units determined that about 10% of tested homes had lead-based paint. In some cases the paint was visibly chipped or peeling. Children living at DAFB are screened for blood lead levels as part of the state of Delaware's 12-month well baby checkup. Since 1995, no children living in base housing at DAFB have tested positive for elevated blood lead levels (i.e., levels above CDC's recommended 10 µg/dL). 8
Current and Future Exposure
Although there are still some homes containing lead-based paint, DAFB is currently remediating or destroying base homes built before 1978. Residents can help prevent childhood lead poisoning by complying with the following measures:
- Be aware of and reduce lead-based paint hazards in the home. Keep children away from chipped surfaces. Contact the Family Maintenance Office with concerns about severely chipped surfaces. Treat minor chipped surfaces with caution as outlined above.
- Have your child assessed for lead exposure at the 12-month well baby visit under Delaware's universal blood lead screening program.
- If your young child resides in or frequently visits a housing unit that has chipping or peeling paint and was built before 1978, he or she be considered as "at risk for lead exposure" EPA recommends that children "at risk for lead exposure" be tested for blood lead levels at 6, 12, 18, and 24 months, and annually between the ages of 2 and 6 years (EPA 1998). Parents who are concerned about their child's exposure to lead should discuss this with their child's physician.
Three ball fields are situated on top of the landfill D11 (LF26), a former construction debris and general refuse landfill. The former landfill is also northwest of the Welch Elementary School and Middle School. Children who visit these areas are not likely to contact landfill material or landfill gases. The landfill is covered with a layer of grassy soil, which limits direct contact with the landfill material. Because of the type of material disposed of and the age of landfill (more than 50 years old), little, if any, gas is expected to be emitted from the landfill at this time.
Use of the Landfill
Landfill D-11 (also known Site LF26) is a 2-acre site located along West Hawthorne Road in the West Management Unit. During the 1950s and 1960s, DAFB used the area for disposal of general refuse and construction debris (USAF 2003). Currently, three ball fields are situated on top of the landfill. Also, the Welch Elementary and Middle Schools are located northwest of the area (see Figure 6).
Environmental Sampling Results
DAFB investigated LF26 in 1991 as part of its site investigation and in 19931994 as part of the West Management Unit RI activities for the base-wide RI. The sampling indicated that surface and subsurface landfill materials have affected isolated areas of soil at LF26. VOCs, total petroleum hydrocarbons, and polycyclic aromatic hydrocarbons were detected in one deep test pit sample. Two buckets filled with black liquid (contents unknown) were discovered near that test pit (Dames & Moore 1997c). Another 4-foot test pit contained elevated concentrations of the pesticides DDD, DDE, DDT, and dieldrin; however, the surface and deeper test pits contain only minor amounts of those pesticides.
Sampling of the groundwater at LF26 showed no evidence of fuel-related compounds that were present in the soil. Trace levels of VOCs were present in one downgradient well pair, but at concentrations below EPA's MCLs and ATSDR's CVs. The results of these field investigations indicated low levels of contaminants warranting no further action. The landfill has since been covered with clean soil and seeded with grass (USAF 2003).
Public Health Implications of Use of the Ball Field and School
Contact with Landfill Material
Waste buried at the landfill in the 1950s and 1960s included general refuse and construction debris. After closure, the landfill was covered with local soil and grass. There is no documentation as to the thickness of the soil cover that was placed over the landfill after closure. Test pit monitoring results collected during the 1993 base-wide RI suggest that the fill, or soil, could have been 1 to 2 feet thick at the surface. Each year, DAFB spreads and grades more clean soil on the ball fields as part of its general grounds maintenance. The soil cover prevents exposure of the public to materials or contaminants within the landfill.
DAFB enforces land use controls at LF26, although the ROD for land use controls has not been signed yet. Land use controls at the former landfill place prohibitions on the use of groundwater from the Columbia Aquifer and on activities that could threaten the integrity of the landfill soil cover, such as on digging into the cover or contents of the landfill. DAFB expects to generate the ROD for base-wide land use controls and schedules for inspections and maintenance of the landfill cover during the fall of 2003. As long as the cover on each landfill is undisturbed, ATSDR does not anticipate any public exposure to the materials in the landfill in the future.
Exposure to Landfill Gases
Landfills can emit gases created from decomposing waste or from other non-methane organic compounds created when liquid or solid waste changes into vapors. By volume, landfill gas is typically 45% to 60% methane and 40% to 60% carbon dioxide, with smaller amounts of non-methane organic vapors (e.g., VOCs) (ATSDR 2002). Sometimes these gases can pose hazards when they travel through the soils and then upward into the indoor air of nearby buildings. People in these buildings can then be exposed when breathing air containing the contaminants. On occasion, these gases can also pose explosive hazards. Several factors greatly influence how much gas a landfill currently releases and whether any gas releases might pose a public health hazard. A review of these factors suggests that the former landfill beneath the ball field and near the school is not likely to release harmful amounts of gases at this time. These factors include:
- Age of the landfill. Gases are usually emitted within 20 years after the waste is disposed of, peaking within 5 to 7 years after disposal. Only small volumes of gases would be expected after 50 or more years. Given this information, older landfills, such as LF26which accepted refuse about 50 years agoare beyond the age at which they should still generate substantial volumes of gases (ATSDR 2002). No soil gas monitoring data, however, are available to confirm whether this is the case.
- Waste composition. The greater the amounts of organic waste present in the landfill, the more landfill gases (e.g., methane and carbon dioxide) are produced through the decay process. LF26 waste probably contained some organic compounds found in solid waste and household waste. Monitoring for the LF26 area indicates that only low levels of VOCs were found in the groundwater. This information suggests that LF26 is not likely to emit landfill gases that are created when VOCs change from liquids into vapors (ATSDR 2002).
- Presence of an impervious cap. Protective impervious landfill caps tend to inhibit upward movement of certain gases. When upward movement is inhibited, these gases, such as methane, can move laterally out from beneath the landfill and build up in surrounding areas with lower gas concentrations. Buildup of high levels of methane can pose an explosive hazard. LF26, however, is covered with soil and grass, not an impervious cap. This soil layer should not inhibit the upward movement and diffusion of any remaining small volumes of landfill gases (ATSDR 2002).
Given the information about the former landfill, ATSDR expects that people either using the ball field or attending the school today will not reasonably come in contact with either landfill waste material or landfill gases.
1 Natural attenuation involves the dilution, dispersion, and degradation of contaminants to lower levels by natural processes at work in the environment.
2 The city of Dover supplements their water supply with water drawn from the Columbia Aquifer. The supplemental water supply wells are northeast of the city of Dover, in a separate drainage basin.
3 The Dover Air Park Trailer Park is located downgradient of DAFB and the former P&F Motorcycles and Paradee Gulf properties. The wells at this trailer park draw from the confined, deep aquifers and have not been contaminated. They are the only known drinking water wells located across U.S. 113 from the base still in use (DAFB 2003).
4 DAFB recently funded a contract with Tidewater Utilities to provide municipal water to the Gooch Trailer Park, the P&F motorcycle business, and a private residence, and disconnect them from the DAFB water supply. This is being done to comply with recent changes in Delaware water utility regulations that preclude DAFB from being able to supply water to off-base properties (DAFB 2003).
5 Although a direct comparison of exposure doses from animals may not be entirely appropriate for a number of reasons (e.g., differences in exposure situations, differences in how animals and humans process the chemical within the body) it can provide a relative sense of the potential for effects to occur.
6 The MCL is not strictly based on health: it also considers economic feasibility and best technology available to achieve the standard.
7 The DOD required DAFB to screen each child at 1 year of age to establish a baseline blood lead level. Testing under this program since 1995 has demonstrated that children at DAFB are not at risk of lead poisoning. Because of this low level of risk, DAFB has been permitted to discontinue the universal blood lead testing of 1-year-old children. Children are, however, still tested for blood lead levels at 1 year of age under the state of Delaware's universal testing requirement at the 12-month well baby checkup (USAF 2001, DAFB 2003).
8 A few children tested by the Dover AFB clinic have had elevated blood-lead levels. These children were military dependents living off base in one of the local communities (DAFB 2003).