PUBLIC HEALTH ASSESSMENT
WRIGHT-PATTERSON AIR FORCE BASE
FAIRBORN, GREENE COUNTY, OHIO
Figure 4. ATSDR's Exposure Evaluation Process
APPENDIX A: COMPARISON VALUE EVALUATION METHOD
The conclusion that a contaminant exceeds the comparison value does not mean that it will cause adverse health effects. Comparison values represent media-specific contaminant concentrations that are used to select contaminants for further evaluation to determine the possibility of adverse public health effects.
Cancer Risk Evaluation Guides (CREGs)
Estimated contaminant concentrations that would be expected to cause
no more than one excess cancer in a million (10-6) persons exposed
over a 70-year life span. The Agency for Toxic Substances and Disease Registry's
(ATSDR's) CREGs are calculated from the U. S. Environmental Protection Agency's
(EPA's) cancer potency factors (CPFs).
Environmental Media Evaluation Guides (EMEGs)
EMEGs are based on ATSDR minimal risk levels (MRLs) and factors in
body weight and ingestion rates. An EMEG is an estimate of daily human exposure
to a chemical (in mg/kg/day) that is likely to be without noncarcinogenic health
effects over a specified duration of exposure.
Maximum Contaminant Level (MCL)
The MCL is the drinking water standard established by EPA. It is the
maximum permissible level of an individual contaminant in water that is delivered
to a free-flowing water supply. MCLs are derived for individual contaminants
based on toxicity. MCLs are considered protective of public health over a lifetime
(70 years) for people consuming 2 liters of water per day.
Reference Media Evaluation Guides (RMEGs)
ATSDR derives RMEGs from EPA's oral reference doses (RfDs). The RMEG
represents the concentration in water or soil at which daily human exposure
is unlikely to result in adverse noncarcinogenic effects.
Soil Screening Level (SSL)
Generic SSLs were derived by EPA for nation-wide application to sites
used for residential areas. SSLs are estimates of contaminant concentrations
that would be expected to be without noncancer health effects over a specified
duration of exposure or to cause no more than one excess cancer in a million
(10-6) persons exposed over a 70-year life span.
Risk-Based Concentration (RBC)
The RBCs were developed by EPA Region III. RBCs for tap water, air, and soil
were derived using EPA RfDs and cancer potency factors combined with standard
exposure scenarios, such as ingestion of 2 liters of water per day, over a 70-year
life span. RBCs are contaminant concentrations that are not expected to cause
adverse health effects over long-term exposures.
TCDD Toxic Equivalents (TEQs)
Dioxins and furans include over 200 compounds with various numbers of attached chlorine molecules, from 0 to 8. Compounds with the same number of chlorine molecules are referred to as isomers. The location of the chlorine molecule on the dioxin or furan compound can also vary within an isomer group. Dioxins and furans with the same number of chlorine molecules, but at different locations are referred to as congeners. The potency (or relative toxicity) of different isomers and congeners varies with structure. Isomers with four chlorine molecules include the most toxic forms, and congeners with chlorines in the 2,3,7,8 positions are the most toxic forms within each isomer group. Therefore, the most toxic form is the compound with four chlorines in the 2,3,7,8 positions (2,3,7,8-tetrachlorodibenzodioxin or 2,3,7,8-TCDD), while the related furan is only slightly less toxic. Other dioxins and furans can range from slightly less toxic to 1,000 times less toxic. In dealing with mixtures of dioxins and furans, a system has been developed to weigh concentrations of isomers and congeners with factors that relate their toxicity to that of 2,3,7,8-TCDD, generating a "TCDD equivalency factor (TEF)". These factors are then used to assess the health risks of a dioxin/furan mixture.
Throughout this public health assessment (PHA), concentrations of dioxins and furans have been presented as TCDD equivalents (TEQs). The TEQ is a weighed concentration that represents a mixture of isomers and congeners. The TEQ compensates for the differences in toxicity among isomers and congeners. The TEFs used in this evaluation are as follows:
| Compound | TEF (ATSDR, 1997) | |
| 2,3,7,8-Tetrachlorodibenzodioxin (TCDD) | 1 | |
| 2,3,7,8-Tetrachlorodibenzofuran (TCDF) | 0.1 | |
| 2,3,7,8-Hexachlorodibenzodioxin (HxCDD) | 0.1 | |
| 2,3,7,8-Hexachlorodibenzofuran (HxCDF) | 0.1 | |
| 2,3,7,8-Heptachlorodibenzodioxin (HpCDD) | 0.01 | |
| 2,3,7,8-Heptachlorodibenzofuran (HpCDF) | 0.01 | |
| 2,3,7,8-Octachlorodibenzodioxin (OCDD) | 0.001 | |
| 2,3,7,8-Octachlorodibenzofuran (OCDF) | 0.001 | |
The concentration of each isomer and congener detected in a sample is multiplied by the associated TEF and results are summed to calculated the TEQ. The TEQ can than be used to screen dioxin and furan concentrations against comparison values. The TEQ can also be used in the exposure evaluation to calculate the potential dose of dioxins and furans.
APPENDIX C: EXPOSURE EVALUATION
Estimates of Human Exposure Doses and Determination of Health Effects
Deriving Exposure Doses
The Agency for Toxic Substances and Disease Registry (ATSDR) estimated the human exposure doses from ingestion of drinking water from groundwater supplies, incidental ingestion of surface soil, incidental ingestion of surface water and sediment, and inhalation of air. Deriving exposure doses requires evaluating the concentrations of the contaminants to which people may have been exposed and how often and how long exposures to those contaminants occurred. Together, these factors help influence the individual's physiological response to chemical contaminant exposure and potential for noncancer or cancer outcomes. In the absence of exposure-specific information, ATSDR applied several conservative assumptions to define site-specific exposures as accurately as possible for people contacting contaminated media.
Evaluating Potential Health Hazards
The estimated exposure doses are used to evaluate potential noncancer and cancer effects associated with contaminants detected in site media. When evaluating noncancer effects, ATSDR first compares the estimated exposure dose to standard toxicity values, including ATSDR's minimal risk levels (MRLs) and the U.S. Environmental Protection Agency's (EPA) reference doses (RfDs), to evaluate whether adverse effects may occur. The chronic MRLs and RfDs are estimates of daily human exposure to a substance that is likely to be without appreciable risk of adverse noncancer effects over a specified duration. The chronic MRLs and RfDs are conservative values, based on the levels of exposure reported in the literature that represent no-observed-adverse-effects levels (NOAEL) or lowest-observed-adverse-effects-levels (LOAEL) for the most sensitive outcome for a given route of exposure (e.g., dermal contact, ingestion). In addition, uncertainty (safety) factors are applied to NOAELs or LOAELs to account for variation in the human population and uncertainty involved in extrapolating human health effects from animal studies. If estimated exposure doses are greater than the MRL or RfD, ATSDR reviews the toxicological literature to determine the likelihood of adverse effects.
When evaluating the potential for cancer to occur, ATSDR uses cancer potency factors (CPF) that define the relationship between exposure doses and the likelihood of an increased risk of developing cancer over a lifetime. The CPFs are developed using data from animal or human studies and often require extrapolation from high exposure doses administered in animal studies to lower exposure levels typical of human exposure to environmental contaminants. The CPF represents the upper-bound estimate of the probability of developing cancer at a defined level of exposure; therefore, they tend to be very conservative (i.e., overestimate the actual risk) in order to account for a number of uncertainties in the data used in the extrapolation.
ATSDR estimated the potential for cancer to occur using the following equation. The estimated exposure doses and CPF values for the contaminants of concern are incorporated into the equation:
Lifetime Cancer Risk = Estimated exposure dose (milligrams contaminants per kilogram body weight per day [mg/kg/day]) x CPF (mg/kg/day)-1
Although no risk of cancer is considered acceptable, because a zero cancer risk is not possible to achieve, ATSDR often uses a range of 10-4 to 10-6 estimated lifetime cancer risk (or 1 new case in 10,000 to 1,000,000 exposed persons), based on conservative assumptions about exposure, to determine whether there is a concern for cancer effects.
Estimated Exposure Dose for Media at OU1
Investigations at OU1 (Landfills 8 and 10) detected contamination in ambient air, surface soil, surface water, sediment, and private wells. Residents living in the military housing complex (Woodland Hills) that surrounds these landfills might have been exposed to contaminants in ambient air. Between the early 1970s and 1985, the landfills were used as a recreational area and people were exposed to contamination in surface soil, surface water, and sediment. Residents along National, Zink, and Kauffman Roads with private wells were exposed to contamination in their well water. The USAF has completed remedial activities to prevent current and future exposures. To determine whether past exposures to these contaminants may be related to adverse health effects, if any, ATSDR estimated exposure doses for people living in the Woodland Hills housing complex and in nearby private residences. In estimating to what extent people might be exposed to contaminants, ATSDR used "conservative" assumptions about contaminant concentrations, as well as how much and how often people were exposed to contamination. These assumptions allow ATSDR to estimate the highest possible exposure dose and determine the corresponding health effects. Although ATSDR expects that few, if any, residents were exposed to the highest contaminant concentrations, the "conservative" estimates are used to protect public health. ATSDR used the following equation and exposure assumptions to estimate exposure doses:
where:
C = Maximum concentration (parts per million [ppm]) IR = Intake rate:
Soil and sediment: adult=50 milligrams/day; child=100 milligrams/day
Surface water: adults and children=0.15 liters/day
Drinking water: adult=2.35 liters/day; child=1.3 liters/dayEF = Exposure frequency: resident=365 days/year; recreational user=130 days/year ED = Exposure duration or the duration over which exposure occurs:
off-site resident: adult=30 years; child=6 yearsBW = Body weight: adult=70 kg (154 pounds); child=10 kg (22 pounds) AT = Averaging time or the period over which cumulative exposures are averaged
Off-site resident: 6 or 30 years x 365 days/year for noncancer effects and 70 years x 365 days/year for cancer effects
Based on estimated exposure doses and review of toxicology literature, ATSDR concluded that exposures to contaminants in site media at OU1 are unlikely to result in adverse health effects.
Noncancer
ATSDR calculated noncancer doses assuming that people were exposed to the maximum detected concentration over the entire exposure period. ATSDR also used conservative assumptions about how often and how long people were exposed. The calculated doses were then compared to ATSDR's MRLs or EPA's RfDs. MRLs and RfDs are not available for several contaminants, including dimethyl sulfide, polyaromatic hydrocarbons (PAHs), delta-BHC, endrin ketone, and lead. The calculated doses for contaminants in private wells, ambient air, surface soil at both landfills, surface water, and sediment were all below the associated MRLs or RfDs, except for acetone in ambient air, arsenic in surface water, and arsenic in private wells.
The calculated dose for Woodland Hills residents, adults (2.1 mg/kg/day) and children (2.3 mg/kg/day), exposed to acetone in ambient air slightly exceeded the MRL of 2 mg/kg/day. MRLs are developed with uncertainty (safety) factors. These safety factors may result in a derived MRL hundreds of times less than the LOAEL observed in laboratory studies. In addition, ATSDR calculated doses based on the maximum detected concentration of acetone (236,000 micrograms per cubic meter [ug/m3]) and assumed a person was exposed to this concentration over the entire exposure period. However, acetone was detected in only 17 of the 40 ambient air samples collected. The next highest concentration of acetone was only 45,244 ug/m3. The dose was calculated using conservative assumptions about frequency and duration of site use. An actual resident is very unlikely to be in daily contact with the highest level of contamination over the entire exposure period. Actual doses are expected to be much lower than assumed by ATSDR.
The calculated dose for children (0.00038 mg/kg/day) exposed to arsenic in surface water while using the stream located between Landfills 8 and 10 for recreational purposes slightly exceeds the MRL for arsenic (0.0003 mg/kg/day). Exposure considered incidental ingestion only because dermal absorption of arsenic is negligible. In surface water, arsenic was detected in 8 of the 52 samples collected; concentrations did not exceed EPA's Maximum Contaminant Level (MCL).
The calculated dose for adults (0.0017 mg/kg/day) and children (0.0024 mg/kg/day) exposed to arsenic in private wells along National, Zink, and Kauffman Roads exceeded the arsenic MRL of 0.0003 mg/kg/day. Exposure considered incidental ingestion only because dermal absorption of arsenic is negligible. During site investigations, ten private wells along National, Zink, and Kauffman Roads were sampled. Arsenic was detected in 25 of the 31 samples collected over three sampling rounds. In one sample, the arsenic concentration (52 parts per billion [ppb]) slightly exceeded the MCL (50 ppb).
Epidemiologic investigations suggest that noncancer effects from chronic arsenic exposure may lead to skin problems, neurological effects, and gastrointestinal irritations. The lowest observed levels at which these adverse health effects have been reported range from 0.014 to 0.05 mg/kg/day (ATSDR, 1993). The estimated doses for adults and children exposed to arsenic in surface water and drinking water are at least 10 times lower than the lowest arsenic dose reported to cause health effects. In addition, ATSDR calculated doses using conservative assumptions about exposure concentration and frequency and duration of site use. An actual resident is very unlikely to be in contact with the highest level of contamination over the entire exposure period. Actual doses are expected to be much lower than assumed by ATSDR.
Cancer
Not all contaminants in the environment have the potential to cause cancer. ATSDR evaluated contaminants that could potentially cause cancer, including: six volatile organic compounds (VOCs), eight PAHs, bis(2-ethylhexyl)phthalate, five pesticides, Aroclor-1254 (a polychlorinated biphenyl [PCB]), arsenic, beryllium, cadmium, chromium, and dioxins. The derived lifetime cancers risks for exposure to contaminants in surface soil, surface water, and sediment at Landfill 10 and for Woodland Hills residents in contact with ambient air, surface soil, surface water, and sediment are below levels that are likely to result in increased instances of cancer.
ATSDR evaluated the following contaminants detected in private wells that could potentially cause cancer: bromodichloromethane, chloroform, dibromochloromethane, bis(2-ethylhexyl)phthalate, and arsenic. Except for arsenic, the derived lifetime cancer risk for exposure to contaminants are below levels that are likely to result in increased instances of cancer. ATSDR derived a lifetime cancer risk of 2 x 10-4 (or an increased likelihood of 2 in 10,000 of developing cancer) for arsenic. EPA classified arsenic as a carcinogen based on epidemiological studies. However, unlike other carcinogens, arsenic dose not cause cancer in laboratory animals when administered orally. The basis for classifying arsenic as a human carcinogen are results of a Taiwanese study in which the lowest exposure levels associated with the onset of cancer (skin) were observed in people drinking 170 to 800 ppb arsenic for a 45-year exposure period (ATSDR, 1993). Residents using private wells were exposed to a maximum detected concentration of 52 ppb arsenic. Concentrations detected in repeat sampling rounds were even lower. It is unlikely that the level of exposure to off-site residents would lead to cancer.
Estimated Exposure Dose for Contact with Drinking Water from Wright-Patterson AFB
When the U. S. Air Force (USAF) first began sampling its water supply system in the 1980s, they detected several VOCs above their MCLs. Well sampling of untreated water in 1991 detected bromodichloromethane, carbon tetrachloride, dibromochloromethane, tetrachloroethylene (PCE), and trichloroethylene (TCE) above comparison values (CVs). Sampling of water in the distribution system detected bromodichloromethane, chloroform, and dibromochloromethane above CVs. Residents in military housing and civilians working at WPAFB were and are exposed to VOCs in drinking water. In estimating to what extent people might be exposed to contaminants, ATSDR used "conservative" assumptions about contaminant concentrations, as well as how much and how often people were exposed to contamination. These assumptions allow ATSDR to estimate the highest possible exposure dose and determine the corresponding health effects. Although ATSDR expects that few residents and workers were exposed to the highest contaminant concentrations, the "conservative" estimates are used to protect public health. ATSDR used to following equation and exposure assumptions to estimate an exposure dose for contact with drinking water:
where:
| C | = Maximum concentration (ppm) |
| IR | = Intake rate: adult=2.35 liters/day; child=1.3 liters/day |
| EF | = Exposure frequency: resident=365 days/year; worker=250 days/year |
| ED | = Exposure duration or the duration over which exposure occurs: resident (adult and child)=5 years; worker=30 years |
| BW | = Body weight: adult=70 kg (154 pounds); child=10 kg (22 pounds) |
| AT | = Averaging time or the period over which cumulative exposures are averaged:
resident=5 years x 365 days/year for noncancer effects and 70 years [considered
a lifetime] x 365 days/year for cancer effects worker=30 years x 365 days/year for noncancer effects and 70 years x 365 days/year for cancer effects |
Based on estimated exposure doses and review of toxicology literature, ATSDR concluded that past, current, and potential future exposures to contaminants in the WPAFB water supply are unlikely to result in adverse health effects.
Noncancer
Exposures to the maximum detected concentration of VOCs using conservative exposure assumptions resulted in doses for residents (adults and children) and civilian workers less than the MRLs, except for vinyl chloride. Vinyl chloride was detected in supply samples collected between 1985 and 1988. The estimated doses for workers (0.000042 mg/kg/day), adult residents (0.000062 mg/kg/day), and child residents (0.000087 mg/kg/day) slightly exceeded the MRL (0.00002 mg/kg/day). Doses were estimated assuming that workers and residents were drinking the maximum detected concentration over the entire exposure period. Vinyl chloride, however, was only detected in 2 of the 522 samples collected between 1985 and 1988. Actual doses are expected to be much lower than the estimated doses. The USAF currently treats and monitors the water supply system to insure that drinking water safety is not compromised and contaminant concentrations are below MCLs.
Cancer
Each of the VOCs detected in the WPAFB water supply is considered a carcinogen. ATSDR derived lifetime cancer estimates for each contaminant based on assumed resident and worker exposures. Using conservative assumptions about frequency and duration of site use, the derived lifetime cancer risk for each contaminant was within or below the "acceptable" range of 10-4 to 10-6. An actual resident or worker is very unlikely to have been in contact with the highest level of contamination over the entire exposure period (70 years).
Estimated Exposure Dose for Contact with Surface Water and Sediment
The Mad River flows along the northwestern base boundary and receives surface water runoff from the storm water drainage system serving WPAFB. The Mad River is accessed by area residents for recreational activities, including boating, fishing, and swimming. Hebble Creek, Trout Creek, and Lily Creek flow through WPAFB and collect surface water runoff prior to discharging in the Mad River. These streams are located in operations areas of WPAFB and are unlikely to be used for recreation. One unnamed stream that discharges to Hebble Creek was evaluated previously under the OU1 exposure evaluation. In addition to the streams and river, four lakes (Bass, Gravel, East Twin, and West Twin) are located within WPAFB's boundaries and are maintained as recreation areas. The USAF annually stocks each of these lakes with fish. Access to the on-base lakes is limited to military personnel.
Investigations at WPAFB detected semivolatile organic compounds (SVOCs), alpha-BHC, and metals above CVs in surface water and pentachlorophenol, PAHs, pesticides, metals, and dioxins above CVs in sediment. Analysis of fish from the Mad River detected PCBs above CVs. To determine the potential for adverse health effects from exposure to contaminants in surface water, sediment, and fish, ATSDR estimated an exposure dose for recreational users based on conservative assumptions of site use. ATSDR used the following equation and exposure assumptions to estimate an exposure dose for contact with surface water and sediment and ingestion of fish:
where:
| C | = Maximum concentration (ppm) |
| IR | = Intake rate: |
surface water: adult and children = 0.15 liters/day (during swimming) |
|
| EF | = Exposure frequency: recreational user=130 days/year; swimming=6 days/year |
| ED | = Exposure duration or the duration over which exposure occurs: adult=30 years; child=8 years |
| BW | = Body weight: adult=70 kg (154 pounds); child=10 kg (22 pounds) |
| AT | = Averaging time or the period over which cumulative exposures are averaged: (8 or 30 years x 365 days/year for noncancer effects and 70 years [considered a lifetime] x 365 days/year for cancer effects) |
ATSDR evaluated doses for exposure to contaminants using the maximum detected concentrations in surface water and sediment samples from the Mad River, on-base streams, and on-base lakes as military personnel may use any of these water bodies for recreation. Fish samples have only been collected from the Mad River, and ATSDR used these results to estimate doses for consumption of fish. Fish tissue samples have not been collected for the stocked fish supplied for on-base fishing. Due to heavy recreational use and the need for annual restocking, ATSDR believes that fish in Gravel, East Twin, and West Twin Lakes are unlikely to bioaccumulate significant concentrations of contaminants. Based on estimated exposure doses and site conditions, ATSDR concluded that recreational use of water bodies at and near WPAFB is unlikely to result in adverse health effects.
Noncancer
Exposure doses for the maximum detected concentrations of SVOCs, alpha-BHC, and metals, expect thallium, in surface water were below their associated MRLs for both adults and children. In sediment, exposure doses for the maximum detected concentrations of pentachlorophenol, PAHs, pesticides, and metals were below their MRLs. Exposure doses for the maximum detected concentration of PCBs in fish slightly exceeded the MRL for adults and children.
The calculated dose for an adult (0.0001 mg/kg/day) and a child (0.00026 mg/kg/day) exposed to thallium in surface water exceeds the MRL of 0.00007 mg/kg/day. MRLs are developed with uncertainty (safety) factors. These safety factors may result in a derived MRL hundreds of times less than the LOAEL observed in laboratory studies. A review of the literature indicated that the dose associated with the LOAEL in laboratory studies is 0.08 mg/kg/day, approximately 300 times greater than the dose received by recreational users (ATSDR, 1992). In addition, the dose was calculated using conservative assumptions about frequency and duration of site use. A recreational user is very unlikely to be in contact with the highest level of contamination over the entire exposure period.
The calculated dose for an adult (0.000099 mg/kg/day) and a child (0.000027 mg/kg/day) exposed to PCBs in fish tissue slightly exceeds the MRL of 0.00002 mg/kg/day. ATSDR derived the MRL for PCBs based on a study with rhesus monkeys in which the LOAEL was reported at 0.005 mg/kg/day, approximately 50 greater than the dose received by recreational users (ATSDR, 1998). ATSDR calculated doses using the maximum detected concentration found during sampling. PCBs tend to accumulate in a fish's fatty tissue and sampling analyzed whole fish samples, including this fatty tissue. The fillet, or muscular part of the fish, eaten by people may not contain as high a concentration of PCBs as detected in the whole fish sample. ATSDR also calculated dose using conservative assumptions about how often and how much fish was consumed by recreational users. A recreational user is very unlikely to be in contact with the highest level of contamination over the entire exposure period. The Ohio Environmental Protection Agency (OEPA) has placed a restriction on consumption of fish caught in the Mad River. This restriction extends up and downstream of WPAFB.
Cancer
Carcinogens detected in surface water included bis(2-ethylhexyl)phthalate, pentachlorophenol, alpha-BHC, arsenic, beryllium, and cadmium. Carcinogens detected in sediment include: five PAHs, bis(2-ethylhexyl)phthalate, pentachlorophenol, heptachlor epoxide, arsenic, beryllium, and cadmium. PCBs were the only carcinogens detected in fish tissue. ATSDR derived lifetime cancer risks for contaminants in surface water, sediment, and fish tissue were within or below the "acceptable" range.
APPENDIX E: RESPONSES TO PUBLIC COMMENTS
The Agency for Toxic Substances and Disease Registry (ATSDR) received the following comments/questions during the public comment period (August 17 to September 29, 1999) for the Wright-Patterson Air Force Base (WPAFB) Public Health Assessment (PHA) (August 17, 1999). For comments that questioned the validity of statements made in the PHA, ATSDR verified or corrected the statements. The list of comments does not include editorial comments concerning such things as word spelling or sentence syntax.
Reviewers raised questions concerning the adequacy of the data and requested more information about sampling methods used to characterize soil gas at Landfills 8 and 10. One reviewer requested that ATSDR provide more information regarding the sampling regimen methodology to gather the data supporting the conclusions presented in the Summary section. For example, what measurement or analysis equipment was used and was methane specifically sampled for or was a non-specific combustible gas meter employed? ATSDR completed a Health Consultation for Landfills 8 and 10 in 1990. There was concern that no new data were available for the 1999 PHA and that past data were not adequate to draw conclusions regarding public health hazards.
In the 1990 Health Consultation for Landfills 8 an 10, ATSDR identified a potential explosion hazard from collection of methane in housing units located close to Landfills 8 and 10. The 1990 Soil Gas Investigation stated that methane exceeding its lower explosive limit (LEL = 50,000 ppm) was recorded in outdoor soil gas well locations "immediately adjacent" to housing units, in addition to LEL exceedances near the reported disposal trenches and other soil gas wells on the landfills proper. This suggests that an inhalation exposure pathway to a potential simple asphyxiant gas, methane, was occurring to Woodland Hills residents for a period from approximately 1973 through 1990. A reviewer recommended that the wording of the sentence "In 1990, methane was detected in soil gas in the vicinity of the landfills." (page 1, paragraph 3) be changed to "From 1985 though 1990, methane gas concentrations exceeding the lower explosive limit were detected in outdoor soil gas wells located within the landfills proper and also in areas adjacent to Woodland Hills residential homes on the eastern side of Landfill 10 and on the entire border of Landfill 8 within Woodland Hills homes."
Reviewers also noted that cracks in the housing unit foundations that may provide migration pathways for methane, as noted in the 1990 Health Consultation, may also provide a migration pathway for exposure to many contaminants, including such known or probable human carcinogens such as benzene and vinyl chloride. These reviewers suggested that data presented did not seem sufficient to support a conclusion that possible low levels of contamination from OU1 in ambient air have not posed past health hazards. This concern should be addressed in the document.
Response: Since 1985, the U.S. Air Force (USAF) has conducted numerous investigations to characterize soil gas at and migrating from Landfills 8 and 10. To keep the PHA concise and easily accessible to the public, ATSDR has not included a detailed discussion of sampling methodologies and data quality reviews. This information can be found in the sampling summary documents (referenced at the end of Appendix E). To provide a more complete understanding of soil gas characterization activities, however, ATSDR included more information about sampling events conducted from 1985 through 1991 under the discussion of the nature and extent of contamination at OU1 in this PHA. For the 1990 Health Consultation and 1991 follow-up, ATSDR reviewed sampling data collected between 1985 and winter 1991. Additional data, which were not available for ATSDR's 1991 review, were collected in from July through December 1991 (Engineering-Science, 1992 and 1993). These sampling data underwent strict quality assurance and quality control and data validation under EPA guidelines. In drawing conclusions about potential hazards from landfill gas at Landfills 8 and 10, ATSDR relied on the ambient air and indoor air sampling data from the July through December 1991 investigations.
ATSDR agrees that sampling results indicate that past Woodland Hills residents may have been exposed to high levels of methane. Methane is a simple asphyxiant, therefore, no long term health effects from exposure to methane are expected. Of greater concern is methane's potential to accumulate in enclosed spaces and present an explosion hazard. The USAF has conducted remedial actions (installing a gas collection system and capping the landfills) to prevent current and future concerns about inhalation exposures and explosion hazards from methane. Based on the suggested text, ATSDR modified the wording of the sentence "In 1990, methane was detected in soil gas in the vicinity of the landfills." to read "From 1985 though 1991, methane gas concentrations exceeding the lower explosive limit were detected in outdoor soil gas wells located within the landfills proper, areas adjacent to housing units on the eastern side of Landfill 10, and around the perimeter of Landfill 8 within the Woodland Hills housing complex."
ATSDR agrees that cracks in the housing unit foundations could have provided a migration pathway for landfills gases into homes. Indoor air sampling conducted in 1991, before remedial actions were implemented, found no contaminants at concentrations above health-based comparison values (CVs). Analysis of 40 ambient air samples collected over five sampling rounds in 1991 detected several contaminants above CVs. As such, ATSDR evaluated exposures to identify any potential health hazards, as detailed in Appendix C. The 1991 data used for this evaluation were collected and validated according to EPA guidelines and were, therefore, considered acceptable. ATSDR added text to the "Summary" section of this PHA to summarize this concern and the exposure evaluation results. Text was also added to the "ATSDR Involvement" section of this PHA to highlight the concern about potential exposures to contaminants other than methane, as discussed in the 1990 Health Consultation. More information about the 1991 sampling data used to evaluate exposures was also added to the "Nature and Extent of Contamination" section of this PHA.
Response: The sentences referring to the fishing restriction in the Mad River (page 2, paragraph 2, sentences 4 and 5) were changed to read, "The Ohio Department of Health has issued a fish consumption advisory for the Mad River between Dayton and Urbana, Ohio, to reduce intake of contaminated fish tissue. This advisory indicates that people should eat no more than one 8-ounce meal of white sucker or common carp caught from the Mad River per week. This advisory is based on levels of PCBs found in fish tissue samples, however, no on-base sources of PCBs have been found during investigations at WPAFB." The text on pages 20 (bullet 3), 23 (bullet 5), and 29 (conclusion number 3) were also modified accordingly.
Response: The text was changed to read, "Sampling of the treated water in 1998 detected chloroform, bromodichloromethane, and dibromochloromethane at concentrations above CVs, but below EPA's MCLs."
Response: The word "believes" was replaced with "concludes" as suggested.
Response: This recommendation was deleted because the USAF, with oversight by regulatory agencies, is in the final stages of receiving approval of the Groundwater OU ROD. The third bullet under "Ongoing and Planned Actions" (page 30) was modified as follows to reflect the status of the Groundwater OU ROD, "The USAF, with oversight by regulatory agencies, finalized the ROD September 29, 1999."
Response: Only remedial actions associated with soil contamination are discussed under the "Corrective Activities and/or Current Status" entry on page 48 for Site Spill 11. The text under this heading was modified to read "No further action is proposed for soil contamination. Soil contamination at this site was included in the 1998 ROD for 41 No Action Sites. Groundwater remediation is addressed under the BMP."
Remedial actions planned to address groundwater contamination at Site Spill 11 are discussed under the Basewide Monitoring Program (BMP) (page 56). The entry under "Corrective Activities and/or Current Status" for the BMP discusses the proposed long-term monitoring and in situ oxidation activities proposed at Site Spill 11.
References
Engineering-Science, Inc. 1989. Methane Migration Study, Work Plan for Landfills 8 and 10. November 1989.
Engineering-Science, Inc. 1990. Analysis of Soil Gas Survey Results for Landfill 8, the Fire Training Area Adjacent to Landfill 8, Landfill 10, and the Chemical Disposal Trenches at Wright-Patterson Air Force Base, Ohio. May 1990.
Engineering-Science, Inc. 1991. Methane Gas Migration Study Summary Report. June 1991.
Engineering-Science, Inc. 1992. Focused Remedial Investigation Report for Landfills 8 and 10 at Wright-Patterson Air Force Base, Ohio. March 15, 1992.
Engineering-Science, Inc. 1993. Off-Source Remedial Investigation Report for Landfills 8 and 10 at Wright-Patterson Air Force Base, Ohio. August 12, 1993 (Revision No. 2).
