PUBLIC HEALTH ASSESSMENT
HOMESTEAD AIR FORCE BASE
HOMESTEAD, DADE COUNTY, FLORIDA
ENVIRONMENTAL CONTAMINATION AND POTENTIAL PATHWAYS OF EXPOSURE
The Agency for Toxic Substances and Disease Registry (ATSDR) performed an Initial Site Scoping visit at Homestead AFB in January 1991 (ATSDR, 1991). At that time, ATSDR toured the base, reviewed documents, and met with representatives from the base, the Florida Department of Health and Rehabilitative Services, the Dade County Department of Public Health, and the Dade County Department of Environmental Resources Management. During the Initial Site Scoping visit, no completed pathways of human exposure were identified and ATSDR concluded that the potential for human exposure was low.
During the January 1991 visit, ATSDR identified potential public health concerns regarding contaminated groundwater, soil contamination at several of the IRP sites, and contact with contaminated surface water in the Outfall Canal (ATSDR, 1991). Groundwater at Homestead AFB is contaminated with generally very low quantities of volatile organic compounds (VOCs), base/neutral and acid extractable compounds (BNAs), pesticides, and metals, but is not currently used as drinking water. Throughout Homestead AFB, there are areas of soil contaminated with polycyclic aromatic hydrocarbons (PAHs), VOCs, metals (including arsenic), and pesticides. Metals have been detected in the Outfall Canal, which is used for fishing about one mile downstream from the base. PAHs, pesticides, polychlorinated biphenyls (PCBs), and metals were also detected in sediment and fish samples from the canal system.
ATSDR again visited Homestead AFB in July 1997 (ATSDR, 1997a). During the 1997 visit, ATSDR toured the base, reviewed documents and maps, met with Homestead AFB's Community Relations Coordinator to discuss community health concerns, and met with representatives from the base and Dade County Department of Environmental Resources Management. The Dade County Department of Environmental Resources Management expressed concerns regarding levels of PAHs and arsenic detected in the soil at Homestead AFB.
ATSDR has gathered and reviewed IRP data for all sites at Homestead AFB (see Table 1). The following sections discuss ATSDR's findings regarding the potential pathways of exposure to contaminated groundwater and soil at Homestead AFB. The potential pathway of exposure to contaminated surface water in the canal system is evaluated in the Community Concerns section, along with an evaluation of sediment and fish contamination.
Tables and figures are provided at the end of this document. Table 1 summarizes site history, investigation results, current status, and evaluation of public health hazards for all sites evaluated during the IRP. Table 2 provides an evaluation of potential and completed exposure pathways. Figure 1 is a location map of Homestead AFB, Figure 2 is a base site plan, Figure 3 is a map showing land parcels and future use, and Figure 4 provides detail on ATSDR's exposure evaluation process.
Appendix A provides a glossary of environmental and health terms presented in the discussion. In evaluating environmental contamination, ATSDR uses several media-specific comparison values to select environmental contaminants for further evaluation, including environmental media evaluation guides, reference dose media evaluation guides, cancer risk evaluation guides, and EPA's maximum contaminant levels. Appendix B describes the comparison values used in this evaluation. Appendix C provides the estimates of human exposure dose and determination of health effects from potential exposure to contaminated soil at one of the IRP sites, which was formerly located next to a residential and recreational area, and to ingestion of fish from the Boundary and Outfall Canals. Appendix D provides ATSDR's response to comments made during the public comment period for this public health assessment.
Potential Pathway: Groundwater
Conclusions
In evaluating groundwater, ATSDR takes into consideration ingestion, inhalation, and dermal contact pathways. After detailed review of available data, ATSDR has drawn the following conclusions regarding past, present, and future exposures to contaminated groundwater at Homestead AFB:
Discussion
During the IRP investigation, contaminants, including arsenic, lead, beryllium, BNAs, VOCs, and other metals, were detected sporadically and slightly above comparison values in groundwater throughout Homestead AFB (see Table 1).
The Biscayne Aquifer system, comprised of the Miami Oolite and Fort Thompson Formations, covers all of Dade County and is the surficial aquifer in the Homestead AFB area. While it is the sole source of potable water in Dade County, naturally occurring high concentrations of dissolved iron, which commonly exceed the Florida Secondary Drinking Water regulations standard, exist in the Biscayne Aquifer (Geraghty & Miller, 1994a). Within a three-mile radius of Homestead AFB, over 4,000 area residents obtain drinking water from the Biscayne Aquifer and 18,000 acres of farmland are irrigated from aquifer wells (Montgomery Watson, 1996a).
Under natural conditions, groundwater flows southeast toward the Biscayne Bay, following a hydraulic gradient of 0.3 feet per mile (Geraghty & Miller, 1994a). The water table is generally encountered within five or six feet below the ground's surface but may occur at or near land surface during the rainy season from May to October. All groundwater recharge is derived from local rainfall, which averages approximately 58 inches a year, 70 percent of which occurs during the rainy season (Geraghty & Miller, 1994a). Saline groundwater is present in an area paralleling the coast and extends beneath the southeastern half of the base. Salt-water intrusion apparently occurred as a result of pumping water supply wells in the early 1970s (Geraghty & Miller, 1994a).
A drinking water well field was located in the central portion of the base but was dismantled and abandoned in 1978 due to salt water intrusion (Air Force, 1993). To replace these wells, a water supply well field located along the western border of the facility was used to supply drinking water to the base. This well field is not currently used and will be abandoned and dismantled (Versar Inc., 1997a; ATSDR, 1997b). Since 1992, the base has been supplied with water from a well field maintained by Dade County and located approximately 1.5 miles west of the base. In the near future, water will be supplied from another off-base well field maintained by the city of Homestead (ATSDR, 1997b). There are no plans for the installation of drinking water supply wells on base in the future. Due to salt water intrusion, it is also unlikely that a municipal well field would be located downgradient of the base (Geraghty & Miller, 1994a).
Because groundwater movement under Homestead AFB is slow, contaminated groundwater at IRP sites throughout Homestead AFB is not expected to affect off-base drinking water wells or to have affected the drinking water wells located on base in the past. However, the Environmental Baseline Survey indicates that the drinking water wells used until 1978 were located between Elmendorf Street and St. Lo Boulevard in the east central portion of the base (Air Force, 1993). These drinking water wells were at a depth of 72-feet. This area is also the location for OU-12. Investigation of groundwater at OU-12 during the RI detected levels of tetrachloroethane, pesticides, arsenic, beryllium, and thallium above comparison values for drinking water. The January 1998 Extended Site Investigations (ESI) and Preliminary Risk Evaluation (PRE) show that no contaminants were detected above the comparison values in the groundwater (Air Force, 1998).
OU-4, an oil leak behind the motor pool, is located along the western border of the facility near the water supply wells that were used from 1978 to 1992. These wells were at a depth of 70-feet. However, no contaminants above comparison values were detected in groundwater samples in this area during the 1993 RI.
Because the groundwater under Homestead AFB is no longer used and will not be used in the future as a drinking water source, no current or future exposure pathway to contaminants in groundwater exists.
Conclusions:
Discussion
Soil at sites at Homestead AFB contains contaminants above comparison values but most contaminants are detected sporadically or at levels within an order of magnitude of the comparison values (see Table 1). PAHs, such as benzo(a)pyrene, arsenic, and lead were detected at most sites.
Previous to Hurricane Andrew, Homestead AFB was residential as well as industrial. After Hurricane Andrew destroyed most of the base, the mission was changed and there are no longer any residential sections of Homestead AFB. Approximately one-third of the installation is being retained by the Air Force while the remainder of the base is being parceled off for various other uses. All of the contaminated sites identified through the IRP and after Hurricane Andrew are located on parcels that were historically industrial areas or areas of open space near the flightline. All of these sites will either remain with the Air Force or will be parcelled to the Dade County Aviation Department and will continue to have industrial use (see Table 1 and Figure 3).
Several sites have already been remediated since the investigations referred to in Table 1. Through the IRP program, contaminated soil has been removed or capped at several of the sites. As part of the Base Realignment and Closure plan, the Dade County Department of Environmental Resource Management requires that Homestead AFB remediate arsenic-contaminated soil to a cleanup level of 10 parts per million (ppm) in industrial areas that will be parcelled to other entities, and 15 ppm for industrial areas remaining with the Air Force (ATSDR, 1997d). For sites where arsenic levels exceed these requirements, the Air Force must perform either soil removal or containment. Containment may include soil capping, paving, or construction of buildings over the contaminated soil. This work is currently ongoing.
Cleanup goals for PAH-contaminated soils are currently under negotiation by the Base Realignment and Closure cleanup team. Once cleanup goals have been determined, soil remediation will occur at sites with PAH contamination. However, since many of the sites that have arsenic contamination also have PAH contamination, it is expected that soil removal or containment to reach arsenic cleanup goals has already reduced PAH levels in soil.
Lead was detected in soil samples in several industrial sites throughout Homestead AFB (see Table 1). Because none of these sites were located in or near residential areas, exposure to lead in soil, if any, would be limited in nature.
Because one IRP site was located near residential and recreational areas before Hurricane Andrew, there is the potential that juveniles may have trespassed this site in the past. The Contractor Storage Area/Former Construction Debris Landfill, OU-18, was used since 1980 for the disposal of crushed asphalt that resulted from the occasional resurfacing of runways. While OU-18 was a restricted area, no fence or other barrier physically restricted access to the site. PAHs, arsenic, aldrin, and heptachlor epoxide were detected above comparison values in surface soil at OU-18. ATSDR evaluated possible noncancer and cancer effects from exposure to the contaminants in soil at OU-18 using very conservative estimates of exposure duration and contaminant levels for a juvenile trespasser scenario (see Appendix C). Based on the results of that evaluation, ATSDR concludes that exposure to contaminated soil at OU-18 at the concentrations detected is not likely to be associated with adverse health effects.
ATSDR performed a detailed, independent review of soil data for each IRP site at Homestead
AFB. Because these sites have been and will continue to be used for industrial purposes,
exposures to contaminated soils were and will continue to be limited. Furthermore, it is unlikely
that sensitive populations, such as children and the elderly, had long-term or frequent access to
these industrial sites. Limited exposures to the contaminants at levels detected in soils in the past,
present, or future are not expected to be associated with adverse health effects for any of the IRP
sites at Homestead AFB. Furthermore, soil at sites with high levels of arsenic or PAHs have been
or are being remediated, therefore further decreasing exposure potential for the present and future.
The 1991 Community Relations Plan states that concerns related to Homestead AFB include surface water runoff carrying contaminants to Biscayne Bay, radon in base housing, aircraft noise, and the occasional jettison of aircraft fuel onto property surrounding the base (Geraghty & Miller, 1991). During the IRP process, environmental and health issues were evaluated. ATSDR has gathered and reviewed IRP data for all sites at Homestead AFB. Table 1 summarizes site history, investigation results, current status, and evaluation of public health hazards for all sites evaluated during the IRP.
No specific public health concerns were voiced to ATSDR during either the January 1991 or the July 1997 visits. During both visits, community members did express concerns about the possible ecological effects of contamination in the Outfall Canal and, in 1991, community members also expressed concern about high noise levels associated with jet aircraft and about Air Force waste management procedures.
The EPA and the Florida Department of Environmental Protection evaluate ecological risks associated with Homestead AFB. The Air Force has a noise control program which is used to evaluate risks and identify flight patterns. The city and state also determine acceptable environmental and residential noise levels.
In order to evaluate potential public health hazards at Homestead AFB, ATSDR gathered and reviewed data for the Boundary Canal and the Outfall Canal. The following section discusses ATSDR's findings regarding surface water, sediment, and fish contamination in the canal system at Homestead AFB from a public health perspective.
Concern: Boundary and Outfall Canals
Conclusions
After detailed review of available data, ATSDR has drawn the following conclusions regarding potential past, present, and future exposures to contaminants in surface water, sediment, and fish of the Boundary and Outfall Canals:
Discussion
Surface Water and Sediment
Surface water samples were collected during the RI from 30 locations and analyzed for VOCs, BNAs, pesticides, PCBs, metals, and cyanide. Surface water samples in the Boundary and Outfall Canals detected antimony, arsenic, beryllium, and lead above comparison values for drinking water, which was used as a conservative screening value (see Table 1). No PCBs were detected; pesticides were detected below comparison values. The surface water in the canals, however, is not used as drinking water.
Sediment samples were collected at 27 locations along the Boundary and Outfall Canals and analyzed for VOCs, BNAs, pesticides, PCBs, metals, and cyanide. Five of the sediment samples were taken in canals or drainage ditches adjacent to IRP sites. Carcinogenic PAHs, PCBs, antimony, arsenic, beryllium, lead, and thallium were detected in sediment samples slightly and sporadically above comparison values (see Table 1). During the RI, problems were encountered collecting sufficient sediment samples. A supplemental investigation of surface water and sediment samples for the Outfall Canal was performed to substantiate findings during the RI. Sediment samples collected during the supplemental investigation were similar to those taken during the RI (see Table 1).
While fishing occurs along much of the canal system, swimming and wading are possible but probably limited. Some areas of the canals on base are inaccessible because of dense overgrowth of trees, weeds, and grass. Accessibility to the Outfall Canal is limited due to the presence of privately owned agricultural land along much of the canal. The sides of the canals are vertical, making access difficult. Furthermore, alligators and snakes inhabit most of the canal system (Woodward-Clyde, 1995).
Dermal contact with contaminants in surface water in the canals may occur during recreational activities such as fishing, but exposure would be limited. Furthermore, the metals detected in the canals do not easily absorb into the skin. Using drinking water standards for comparison is extremely conservative for evaluating dermal absorption. Contact with contaminants at the levels detected in the surface water of the canals during recreational activities is not expected to be associated with adverse health effects.
Dermal contact with contaminants in sediment may occur during recreational activities such as fishing in the canals. Detections of contaminants in sediment were sporadic and at low levels. Dermal contact with contaminants in sediment at the levels detected are not expected be associated with adverse health effects.
Fish
Largemouth bass were collected from eight locations throughout the Boundary and Outfall Canals and analyzed for VOCs, BNAs, pesticides, PCBs, metals, and cyanide. PCBs, pesticides, and arsenic were detected in fish samples (see Table 1 and Appendix C). A representative bottom feeding fish (the freshwater catfish) was not caught at any of the eight sampling locations. Each fish that was caught was divided into a fillet section and a "remains" section and analyzed both for contaminants in the fillet section and in the whole body. In order to determine background levels, sampling was also performed in Mowry Canal, which is upgradient of Homestead AFB. Findings from all eight locations, including Mowry Canal, were comparable (Woodward-Clyde, 1995).
Because much of the land surrounding Homestead AFB and the Outfall Canal is agricultural, some pesticide contamination in sediment and fish samples in the canal system, especially the Outfall Canal, may be due to agricultural processes, as opposed to activities at Homestead AFB. The Outfall Canal is not owned by the Air Force and access is controlled by the South Florida Water Management District. During the RI, a detailed analysis of the potential for sediment transport through the canals showed that significant movement of sediment either out of the Boundary Canal or out of the stormwater reservoir is unlikely (Woodward-Clyde, 1995). This indicates that contamination in sediments is not migrating off base to the Outfall Canal. Sampling results from the Outfall Canal, therefore, may be due to sources other than or in addition to Homestead AFB. Sampling results from Mowry Canal may suggest that contamination in fish throughout the region exists, unrelated to Homestead AFB.
With the exception of mercury, the Florida Department of Health does not have advisory levels for contaminants in fish. For mercury, the Department of Health issues a limited ingestion advisory for fish containing 0.5 to 1.5 ppm of mercury (ATSDR, 1997f). The highest mercury level detected in fish was 0.46 ppm, which is below the Florida Department of Health's limited ingestion advisory level.
ATSDR performed a review of exposure to contaminants detected in edible fish fillets (with skin removed) collected from the canals (see Appendix C). The occasional ingestion of contaminants in fish is unlikely to be associated with any increased cancer or noncancer health effects. Based on extremely conservative assumptions, however, adverse health effects may be associated with eating several fish meals per month from the canals, for instance, from subsistence fishing. Detected levels of all contaminants in fish varied. Because the analysis was based on ingesting the highest detected quantity of contaminants for every fish meal, the estimated exposure doses are extremely conservative and highly unlikely for an individual actually catching and ingesting fish from the canal.
Some of the contaminants detected in the largemouth bass samples from the Boundary and Outfall
Canals (e.g., PCBs and pesticides) may accumulate more readily in bottom feeding fish such as
catfish. If it is indicated that people might be regularly exposed to this type of fish, ATSDR
recommends that sampling be performed for a representative bottom feeding fish (e.g., catfish) in
order to more fully characterize contaminant levels and potential health effects.
ATSDR'S CHILD HEALTH INITIATIVE
ATSDR recognizes that infants and children may be more sensitive to environmental exposure than adults in communities faced with contamination of their water, soil, air, or food. This sensitivity is a result of the following factors: (1) children are more likely to be exposed to certain media (e.g., soil or surface water) because they play outdoors; (2) children are shorter than adults, which means that they can breathe dust, soil, and vapors close to the ground; and (3) children are smaller, therefore childhood exposures result in higher doses of chemicals per body weight. Children can sustain permanent damage if these factors lead to toxic exposure during critical growth stages. ATSDR is committed to evaluating their special interests at sites such as Homestead AFB as part of ATSDR's Child Health Initiative.
ATSDR evaluated the likelihood that children living at or near Homestead AFB may have been or may be exposed to contaminants at levels of health concern. ATSDR did not identify any situations where children were likely to be or to have been exposed to contaminants at levels which pose a health concern. After reviewing the available data, ATSDR based this conclusion on several factors, including:
No exposure pathway currently exists or will exist in the future to contaminants in groundwater because groundwater is not and will not be used for drinking water.
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