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1. ATSDR > Public Health Assessments & Consultations

PUBLIC HEALTH ASSESSMENT

F.E. WARREN AIR FORCE BASE
CHEYENNE, LARAMIE COUNTY, WYOMING

TABLES

Table 2. Evaluation of Potential Public Health Hazards at F.E. Warren AFB

Site	Site Description/Waste Disposal History	Investigation Results/Environmental Monitoring Results	Corrective Activities and/or Current Status	Evaluation of Public Health Hazard
Zone E/OU1, Spill Site 1	Over a 6 month period in 1973, an estimated 2,000 to 2,500 gallons of gasoline leaked from an underground storage tank (UST) at the service station located in the southeastern portion of the base. Additional spills may have occurred after 1973.	Groundwater: Volatile organic compounds (VOCs), naphthalene, and metals were detected above comparison values (CVs). Surface soil: Arsenic was detected above its CV.	The leaking UST was removed and replaced in 1973. An above ground storage tank and another UST were also removed from the site in 1989 and 1990. Additional Zone E investigations will evaluate groundwater and are scheduled to commence in 2001. F.E. Warren operated a bioventing program from 1992 to 1996 to treat soil contamination. A Record of Decision (ROD) for soil was signed in August 1995 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface Soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration. F.E. Warren conducted remedial actions to reduce contaminant concentrations.
Zone D3/OU1, Spill Site 2	In September 1983, 30 55-gallons drums containing waste with hydraulic fluid and oil residues were dumped on the ground near Building 810. Numerous spills have also occurred at the Building 810 waste accumulation and storage points.	Groundwater: VOCs, manganese, and molybdenum were detected above CVs. Surface soil: Arsenic was detected above its CV.	Most of the spilled liquid was recovered during the September 1983 spill event. Additional Zone D3 investigations will evaluate groundwater and are scheduled to commence in 2002. A ROD for soil was signed in August 1995 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface Soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration.
Zone E/OU1, Spill Site 3	In April, May, and June 1980, a total of 150 gallons of used battery acid were poured in two dry wells west of Building 338.	Groundwater: Arsenic was detected above CVs. Surface soil: Arsenic was detected above its CV.	Additional Zone E investigations will evaluate groundwater and are scheduled to commence in 2001. A ROD for soil was signed in August 1995 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface Soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration.
Zone D1/OU1, Spill Site 4	Pin hole leaks were discovered in a 55-gallon drum containing trichloroethylene (TCE) in October 1982. Approximately 15 to 20 gallons of TCE leaked to the soil adjacent to Building 1250.	Groundwater: VOCs, arsenic, and manganese were detected above CVs. Surface soil: Arsenic was detected above its CV. Surface water runoff: No contamination was detected.	Additional Zone D1 investigations will evaluate groundwater and are scheduled to commence in 2001. Approximately 530 cubic yards of soil were removed in 1984 and disposed of off base under Resource Conservation and Recovery Act (RCRA) regulations. A ROD for soil was signed in August 1995 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface Soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration. F.E. Warren completed a removal action, preventing current and future exposures.
Zone E/OU1, Spill Site 5	A waste oil accumulation point used since 1962 and located east of Building 336 contained visual evidence of oil spills. Two storage tanks, containing used oil and antifreeze, and several 55-gallon drums were stored here.	Groundwater: VOCs, arsenic, and manganese were detected above CVs. Surface soil: Arsenic was detected above its CV.	Additional Zone E investigations will evaluate groundwater and are scheduled to commence in 2001. A ROD was signed in August 1995 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface Soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration.
Zone E/OU1, Spill Site 6	The courtyard of Building 316 was used as a waste accumulation point beginning in 1962. Numerous oil spills were reported in the courtyard. Until 1982, waste battery acid was dumped on the ground.	Groundwater: VOCs, beryllium, lead, and manganese were detected above CVs. Surface soil: Arsenic was detected above its CV.	Additional Zone E investigations will evaluate groundwater and are scheduled to commence in 2001. The courtyard area was covered with topsoil and gravel in the early to mid-1980s. A ROD for soil was signed in August 1995 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface Soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration. The soil cover should prevent current and future exposures.
Zone D1/OU1, Spill Site 7	Between 1960 and 1966, TCE from Building 1294 spilled to a floor drain and leaked to an outside grease trap, which discharges to Diamond Creek.	Groundwater: VOCs, metals, and nitrate were detected above CVs. Surface soil: Arsenic was detected above its CV. Surface water: TCE was detected above its CV. Fish tissue: DDE was detected above its CV.	A treatability study for a groundwater treatment system operated from 1995 to 1996, but proved ineffective. A ROD for groundwater treatment using an iron reaction wall was signed in 1997 and construction will begin in spring 1999. Additional groundwater investigations will be conducted during the Zone D1 RI scheduled to begin in 2001.The grease trap, sludge, and some surrounding soil were excavated in 1989. The excavated soil was delivered to an EPA-approved disposal site. A ROD for soil was signed in August 1995 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration. The soil removal should prevent current and future exposures. Surface water poses no apparent public health hazards. Exposures are likely infrequent and of short duration. Fish tissue is unlikely to pose a public health hazard. DDE was detected above CVs in only one sample collected in an upstream location.
Zone D3/OU9, Landfill 2 and Zone E/OU9, Landfill 4	These landfills encompass a total of 50 acres in the southeastern portion of the base. Landfill 2 operated from 1918 to 1947 and Landfill 4 operated from 1947 to 1959. These landfills accepted base refuse, including waste oils, batteries, pesticides, incinerator ash, solvents, paints, asbestos insulation, ethylene glycol, and battery acid.	Groundwater: VOCs, iron, manganese, dioxins, and nitrate were detected above CVs. Surface soil: Arsenic and iron were detected above CVs. Soil gas: TCE, tetrachloroethylene, vinyl chloride, and methane were detected. Surface water: TCE, heptachlor epoxide, arsenic, lead, and manganese were detected above CVs. Sediment: Arsenic and lead were detected above CVs.	Additional Zone E and D3 investigations will evaluate groundwater and are scheduled to begin in 2001 and 2002, respectively. F.E. Warren is removing debris in Landfill 2 under an Action Memorandum signed in March 1998. Wastes are transported off site for disposal in permitted facilities. Remedial options for Landfill 4 include capping or removal. Remedial actions at these landfills are ongoing.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil, surface water, and sediment pose no apparent public health hazards. Contaminant concentrations were below levels likely to cause adverse health effects. Exposures were likely infrequent and of short duration. Remedial actions should prevent future exposures.
Zone C/OU3, Landfill 3 and Zone A/OU3, Landfill 6	These landfills encompass a total of 50 acres in the southern and western portions of F.E. Warren. Landfill 3 operated from the mid-1950s to the mid-1960s and Landfill 6 operated from 1970 to 1984. These landfills received base refuse, including fly ash, pesticides, asbestos, waste oil, hydraulic fluid, ethylene glycol, silicone oil, waste jet fuel, solvents, paint, battery acid, and batteries.	Groundwater: Alpha-hexachlorocyclohexane, VOCs, arsenic, manganese, and nitrate were detected above CVs. Surface soil: Heptachlor epoxide and arsenic were detected above CVs. Soil gas: VOCs and methane were detected. Surface water: TCE, chromium, and manganese were detected above CVs.	Investigations identified a TCE plume moving toward Crow Creek and off base into the Nob Hill neighborhood. The USAF connected Nob Hill residents to municipal water supplies in 1997. Landfill cap construction should begin at Landfill 3 in April 2001. The USAF plans to install a cap at Landfill 6, based on Dispute Resolution Committee negotiations in 1998. Cap construction began in 1998 and is ongoing. Additional Zone C and A investigations are scheduled to begin in 1999.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil and surface water pose no apparent public health hazards. Contaminants were detected at concentrations below levels likely to result in adverse health effects. Exposures were likely infrequent and of short duration. The landfill caps should prevent future exposures to surface soil.
Zone B/OU8, Landfill 5	From 1960 to 1970, this 24-acre landfill, located in the south-western portion of the base, was used to burn and dispose of wastes generated at the base. Wastes included solvents, waste oils, ethylene glycol, silicone oil, hydraulic fluid, waste jet propulsion fuel, batteries, battery acid, pesticides, paint, asbestos insulation, and incinerator ash.	Groundwater: VOCs, manganese, and nitrate were detected above CVs. Surface soil: Dieldrin and arsenic were detected above CVs. Surface water: Heptachlor epoxide and manganese were detected above CVs. Sediment: Arsenic was detected above its CV.	Additional Zone B investigations, scheduled for 1999, will evaluate groundwater. Under a November 1996 ROD and January 1998 Explanation of Significant Differences, a landfill cover to prevent infiltration was the selected remedial action for a portion of the landfill. Cover construction began in June 1998 and was completed by December 1998. Other remedial actions may include removal. Investigations and remedial actions are ongoing.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil, surface water, and sediment pose no apparent public health hazards. Contaminant concentrations were too low to cause adverse health effects. Landfill 5 is located in a remote portion of the base, far away from on-base housing, therefore, access by base residents is unlikely.
Zone D2/ OU10, Landfill 7	Landfill 7, 15 acres located in the central portion of the site along Crow Creek, was used in the 1930s for disposal of domestic wastes.	Groundwater: VOCs, bis(2-ethylhexyl)phthalate, arsenic, manganese, and nitrate were detected above CVs. Surface soil: Heptachlor epoxide and arsenic were detected above CVs. Soil gas: TCE and methane were detected. Surface water: Bis(2-ethylhexyl)phthalate, heptachlor epoxide, arsenic, and manganese were detected above CVs. Sediment: Arsenic and lead were detected above CVs.	In 1992, the USAF conducted a treatability study for bioventing and TPH removal from soil. A RI for zone D2, scheduled to begin in December 2000, will address remaining contamination. Additional remedial actions are scheduled for 2003. Remedial options include excavation and off site disposal or consolidation in other F.E. Warren landfills.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil, surface water, and sediment pose no apparent public health hazards. Contaminant concentrations were too low to cause adverse health effects, and exposures were likely infrequent and of short duration. Remedial actions should prevent future exposures.
Zone D2/OU4, Acid Dry Wells	Daily from 1962 to 1986, approximately 5 gallons of waste battery acid were drained into this dry well through sink drains in Building 826.After 1977, the acid was neutralized with baking soda or soda ash prior to disposal.	Groundwater: Methylene chloride, TCE, and chloroform were detected above CVs.	Investigations under zone D2, scheduled for 2001, will further evaluate groundwater contamination. In 1986, the dry wells, associated structures, and approximately 500 tons of contaminated soil were removed. Excavated soil was disposed at an off site RCRA facility. Contaminated material was disposed at an approved site in Utah. A ROD was signed in December 1992 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil poses no apparent public health hazard. Contamination was limited to the subsurface and inaccessible. Remedial actions removed contaminated soil from the site.
Zone D2/ OU5 and OU10, Fire Protection Training Area (FPTA) 1	Fire training exercises were conducted in two burn pits in the central portion of the base near Crow Creek. Exercises were conducted three to four times a month from 1950 to 1966. FPTA 1 overlies a portion of Landfill 7.	Groundwater: VOCs, arsenic, manganese, and vanadium were detected above CVs. Surface soil: Arsenic was detected above its CV. Sediment: Arsenic was detected above its CV.	Additional Zone D2 investigations will evaluate groundwater and are scheduled to begin n 2001. F.E. Warren conducted a bioventing treatability study in 1993 and treatment operations from 1995 to 1996. A ROD selecting bioventing as the preferred remedial action for soil contamination was prepared in 1997, but remains unsigned.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil and sediment pose no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were infrequent and of short duration. F.E. Warren is conducting remedial actions to reduce contamination.
Zone D2/OU5, FPTA 2	Semi-monthly fire training exercises were conducted at this site in the south-central portion of the base from 1965 to 1989. Combustible liquids were poured directly on the ground, ignited, and then extinguished as part of these exercises.	Groundwater: VOCs, bis(2-ethylhexyl)phthalate, and manganese were detected above CVs. Surface soil: Arsenic was detected above its CV.	Additional Zone D2 investigations, scheduled to commence in 2001, will evaluate groundwater. A ROD for soil was signed in November 1994 and called for no further action at the site.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface Soil poses no apparent public health hazard. Arsenic concentrations were too low to cause adverse health effects, and exposures were infrequent and of short duration.
Zone E/OU6, Open Burning Pit/ Open Detonation Area	Three pits for burning ordinance material and detonating explosives are located in the northwestern portion of the base. These pits were used from the early 1960s to 1990.	Groundwater: Methylene chloride, semivolatile organic compounds, and metals were detected above CVs. Surface soil: Arsenic and 4-nitrotoluene were detected above CVs.	The USAF determined that additional investigations are necessary to define the nature and extent of contamination at this site. The site will be evaluated under the Zone E RI scheduled for 2001.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil poses no apparent public health hazard. Contaminant concentrations were too low to cause adverse health effects. The site is located in a remote portion of the base away from on-base housing. Base residents are unlikely to access this site.
Zone E/OU7, Firing Range	Small arms, cannons, and anti-tank weapons were tested in the firing range, located in the northern portion of the site.	Groundwater: Analysis for metals did not detect any contaminants above CVs. Surface soil: Analysis for lead did not detected this contaminant above CVs.	Based on the limited sampling data, the USAF concluded that additional investigations are needed in this area. A RI is scheduled to begin in 2001.	Groundwater poses no apparent public health hazard because no one consumes on-site groundwater. Surface soil poses no apparent health hazards as access to the area is restricted. However, if the site use changes, additional soil samples may be needed to assess potential health hazards.
Basewide USTs	A basewide UST assessment was completed in May 1996. Currently there are 12 active USTs at F.E. Warren.	The USAF conducted groundwater and soil sampling under the base UST program as petroleum products are not considered under Comprehensive Environmental Response, Compensation, and Liability Act. Necessary restoration efforts were conducted under the UST program versus the Installation Restoration Program.	Based on the UST assessment, the USAF removed 6 inactive and 6 abandoned-in-place USTs, another 12 active USTs were replaced and/or upgraded. The USAF complete UST activities prior to the December 1998 deadline imposed under federal regulations. The USAF is in the process of formally closing USTs under the IRP program.	Groundwater and soil pose no apparent public health hazards. People received drinking water from off-site sources. Soil contamination was likely limited to the subsurface and was inaccessible. The USAF has completed remedial actions where necessary to prevent contaminant migration and future exposures.
Groundwater Contamination
OU2, Basewide Groundwater	From 1988 to 1990, the United States Geological Survey identified five TCE plumes located throughout F.E. Warren. The exact nature and time of the spills that resulted in these plumes is unknown.	Basewide groundwater investigations focused on shallow groundwater (0 to 30 feet below ground surface [bgs]) and does not consider deep groundwater (30 to 300 feet bgs). Groundwater: VOCs, primarily TCE, arsenic, manganese, and nitrate were detected above CVs. Surface water: VOCs, beryllium, cadmium, manganese, and dioxins, were detected above CVs. Sediment: Dioxins were detected above CVs.	The USAF is planning additional investigations to further characterize groundwater contamination, specifically vertical migration. Groundwater investigations will be conducted under RIs for each designated zone and are scheduled to begin between 1998 and 2002.	Groundwater, surface water, and sediment present no apparent public health hazards. Groundwater underlying the base does not serve as a water supply. Groundwater discharge to surface water may transport contaminants to on-base streams. However, recreational use of streams is expected to be infrequent and of short duration.
Nob Hill Neighborhood Groundwater	Nob Hill is a neighborhood of approximately 16 homes located along the southeastern base boundary. Most homes are mobile homes owned by long-term residents. Historically, private wells were the primary drinking water source; currently homes are connected to the Cheyenne municipal water supply.	Private wells: VOCs, heptachlor epoxide, arsenic, cadmium and vanadium were detected above CVs.	Landfill 3 investigations indicated that a TCE plume was migrating toward private wells in this neighborhood. The USAF connected homes to municipal water in 1997.	Groundwater poses no apparent public health hazard. An evaluation of past exposures found that contaminants were present at concentrations below those likely to result in adverse health effects. Remedial actions prevent current and future exposures.
Fair Acres Neighborhood Groundwater	Fair Acres is a small neighborhood located along the southwestern base boundary. Homes are a mixture of standard homes, modular homes, and mobile homes. Groundwater is the primary drinking water supply.	Private wells: TCE was detected above its CV. Phthalates were detected above CVs, however, their presence was attributed to laboratory contamination.	The USAF provided homes with bottled water during investigations. These investigations detected low levels of TCE in private wells. Generally concentrations were below the U.S. Environmental Protection Agency's (EPA) Maximum Contaminant Level (MCL), therefore, the USAF discontinued the bottled water program. Several residents still use bottled water as a drinking water supply. EPA and the Wyoming Department of Environmental Quality are continuing to work with residents to identify potential sources and prevent exposures to harmful levels of TCE.	Groundwater poses no apparent public health hazard. An evaluation of potential exposures found that TCE was present at concentrations below those found to result in adverse health effects. In addition, sampling between 1995 and 1997 found that TCE concentrations were decreasing and are currently below EPA's MCL.

Sources: EBASCO, 1991a and 1991b; Ensearch Environmental Corporation, 1994; F.E. Warren, 1992, 1994, 1995, 1997a, 1997b, and 1998a-e; USGS, 1991a, 1991b, 1992a, 1992b, 1993a-c, 1994, 1995a-d, 1996a-d, and 1997

Source: OHM, 1997a, F.E. Warren, 1999b.
¹The method detection limit exceeds CVs for this contaminant, therefore, it is uncertain if it is present above or below its CV. This contaminant, however, is not expected to be present at levels of concern based on past site uses.

FIGURES

Figure 1: Site Map

Figure 2: Locations of Areas of Contamination

Figure 3: ATSDR's Exposure Evaluation Process

APPENDICES

APPENDIX A: Comparison Values

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. The following presents a description of the comparison values (CVs). CVs are presented in the order that was used by ATSDR to select the most appropriate CV for an individual contaminant.

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. ATSDR's CREGs are calculated from 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. A MRL is an estimate of daily human exposure to a chemical (in milligrams of contaminant per kilogram of body weight per day [mg/kg/day]) that is likely to be without noncarcinogenic health effects over a specified duration of exposure.

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.

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 CPFs 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.

Soil Screening Level (SSL)
Generic SSLs were derived by EPA (as described in the Soil Screening Guidance: Technical Background Document, EPA document number EPA/540/R-95/128) 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. Direct ingestion SSLs were selected for use in this PHA.

Maximum Contaminant Level (MCL)
The MCL is the drinking water standard established by EPA. It is the maximum permissible level of a contaminant in water that is delivered to the free-flowing outlet. MCLs are considered protective of public health over a lifetime (70 years) for people consuming 2 liters of water per day. MCLs are standards enforceable by EPA.

APPENDIX B: Estimated Exposures and Health Effects

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 inhalation and incidental ingestion of dust; ingestion, inhalation, and dermal (skin) contact with drinking water from groundwater supplies; and incidental ingestion and dermal (skin) contact with surface soil, surface water, and sediment at Landfills 2 and 3. 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 the 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 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 of contaminant 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 Doses for Exposures to Dust

Investigations at the active borrow area in the northeastern portion of F.E. Warren Air Force Base (F.E. Warren) did not detect any contaminants above comparison values (CVs) in soil. However, the method detection limits for two polyaromatic hydrocarbons (PAHs) and arsenic were above the associated CVs. Currently, the U. S. Air Force (USAF) is excavating this soil for use as a landfill cap. During excavation dust is generated and blown toward Western Hills, a residential neighborhood immediately to the east. In addition to the active borrow area, the USAF conducted investigations at eight other areas throughout the base that may serve as future borrow areas. These investigations detected only arsenic above its CV. To determine whether exposures to contaminants may be related to adverse health effects, if any, ATSDR estimated exposure doses for people inhaling and potentially ingesting dust. In estimating to what extent people might be exposed to contaminants, ATSDR used "conservative" assumptions about contaminant concentrations in dust, as well as how much dust is inhaled and ingested. These assumptions allow ATSDR to estimate the highest possible exposure dose and determine the corresponding health effects. Although ATSDR expects that few residents 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 inhalation and incidental ingestion of dust:

Estimated exposure dose=

C x IR x EF x ED BW x AT

where:

C	Maximum concentration (parts per million [ppm])
IR	Intake rate
	Inhalation: adult=11 mg/day; child=7 mg/day (Calculated using the maximum dust monitoring result [0.69 mg dust per cubic meter] multiplied by the volume of air inhaled [15.2 cubic meters per day for adults and 10 cubic meters per day for children]) Incidental ingestion: adult=100 mg/day; child=200 mg/day
EF	Exposure frequency: 365 days/year
ED	Exposure duration or the duration over which exposure occurs: adult and child =3 years (Excavation commenced in April 1997 and is scheduled to be completed by August 1999.)
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 (3 years x 365 days/year for noncancer effects and 70 year [considered a lifetime] x 365 days/year for cancer effects)

The USAF collected 50 soil samples from the borrow area immediately west of the Western Hills neighborhood and an additional 11 soil samples from an area to the southeast. No contaminants were detected above CVs. However, the method detection limits for two PAHs, including benzo(a)pyrene and dibenz(a,h)anthracene, and arsenic were greater than the associated CVs. The USAF also collected soil samples from the eight potential future borrow areas. These samples contained arsenic above its CV. Based on estimated exposure doses and review of toxicology literature, ATSDR concluded that exposure through inhalation or incidental ingestion of dust from the borrow area is unlikely to result in noncancer or cancer health effects.

Noncancer

No MRLs are available for the PAHs; potential cancer effects are considered a greater threat to human health than noncancer effects. Noncancer effects from exposure to arsenic from the active borrow area and potential future borrow areas were evaluated. Because the method detection limit for arsenic in the active borrow area was above the CV, ATSDR conservatively assumed that Western Hills residents have been exposed to arsenic concentrations equal to the method detection limit (10 ppm). For exposure to dust from potential future borrow areas, ATSDR assumed residents would be exposed to the maximum detected concentration of arsenic (3.4 ppm). The estimated exposure doses for adults and children, using conservative exposure assumptions, were below the arsenic MRL of 0.0003 mg/kg/day.

Cancer

ATSDR also evaluated potential cancer effects for the PAHs and arsenic, considered known carcinogens, or cancer-causing substances. Because the method detection limits for the PAHs and arsenic in the active borrow area were above CVs, ATSDR conservatively assumed that Western Hills residents have been exposed to PAHs (0.3 ppm) and arsenic (10 ppm) concentrations equal to the method detection limits. For exposure to dust from potential future borrow areas, ATSDR assumed residents would be exposed to the maximum detected concentration of arsenic (3.4 ppm). The derived lifetime cancer risks for exposure to PAHs or arsenic through either inhalation or ingestion were all below 9 x 10^-7 (or an increased likelihood of 9 in 10,000,000 of developing cancer). This is below the "acceptable" range of 10^-4 to 10^-6.

Estimated Exposure Doses for Groundwater Use

Residents in the Nob Hill and Fair Acres neighborhoods, located along the southern F.E. Warren boundary, have used groundwater as a drinking water supply. Nob Hill homes were connected to the Cheyenne municipal water supply in 1997 because investigations detected contamination in private wells. Fair Acres residents continue to use groundwater as drinking water supply although low levels of trichloroethylene (TCE) contamination have been detected in several wells. To determine whether exposures to contaminants in private wells may be related to adverse health effects, if any, ATSDR estimated exposure doses for people using contaminated well water. In estimating to what extent people might be exposed to contaminants, ATSDR used "conservative" assumptions about contaminant concentrations in well water, as well as how much and how often people drink well water. These assumptions allow ATSDR to estimate the highest possible exposure dose and determine the corresponding health effects. Although ATSDR expects that few residents 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 water:

Estimated exposure dose=

C x IR x EF x ED BW x AT

where:

C	Maximum concentration (ppm)
IR	Intake rate (accounts for ingestion, inhalation, and dermal contact): adult=4 liters/day; child=3 liters/day
EF	Exposure frequency: 365 days/year
ED	Exposure duration or the duration over which exposure occurs: adult=30 years; child=6 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 (6 or 30 years x 365 days/year for noncancer effects and 70 year [considered a lifetime] x 365 days/year for cancer effects)

For each neighborhood, ATSDR selected the maximum detected concentration for each contaminant to represent the concentration to which residents may be exposed. Sampling of private wells in Nob Hill detected 1,1-dichloroethene (1.7 parts per billion [ppb]), tetrachloroethylene (PCE) (130 ppb), heptachlor epoxide (0.15 ppb), arsenic (4.7 ppb), cadmium (3.1 ppb), and thallium (160 ppb) above CVs. Exposures are no longer occurring nor are they expected to occur in the Nob Hill neighborhood because homes have been connected to the Cheyenne municipal water supply. Sampling of private wells in Fair Acres detected only TCE (5.9 ppb) above its CV. Exposures in the Fair Acres neighborhood are ongoing, however, several residents use bottled water for drinking and the most recent sampling data have found decreasing concentrations of TCE in private wells. Evaluation of exposures and doses found that use of drinking water supplies is unlikely to result in noncancer or cancer health effects.

Noncancer

In 1994, the USAF conducted a single sampling round of private wells in the Nob Hill neighborhood. Therefore, it is unknown when the wells were first contaminated and how long Nob Hill residents may have been exposed to these contaminants. As a result, ATSDR estimated doses using conservative estimates of how long and how often a Nob Hill resident would contact the maximum detected contaminant concentrations in private well water. The USAF has identified a groundwater contamination plume, composed mainly of the chlorinated solvents TCE and PCE, extending easterly from Landfill 3, and flowing toward Nob Hill. This plume has been identified as one potential source of contamination found in private wells in the Nob Hill neighborhood. Heptachlor epoxide, cadmium, and thallium, which were each detected in only one of the eleven wells, have not been identified as plume contaminants. The leading edge of this plume has been determined to be at the edge of the Nob Hill neighborhood. Based on the plume location and flow direction, any impacts to private wells in Nob Hill would likely have occurred recently, whereas ATSDR assumed an exposure period of 30 years. ATSDR also assumed that daily exposure would occur; it is unlikely that a resident only drinks water from their well every day over the entire 30-year exposure period. The leading edge of the plume is also defined by the lowest contaminant concentrations with higher concentrations located nearer the source. Therefore, it is likely that past contaminant concentrations were lower than the maximum detected concentration used to assess exposures.

Using these conservative assumptions, doses for adult residents exposed to thallium and child residents exposed to PCE, heptachlor epoxide, arsenic, cadmium, and thallium exceeded their MRLs. However, the MRLs are developed with safety factors. These safety factors may result in a derived MRL hundreds of times less than the LOAEL or NOAEL observed in laboratory studies. In all instances, the calculated doses are at least one order of magnitude below the associated LOAEL or NOAEL. Table B-1 shows the calculated dose, MRL, and the LOAEL or NOAEL for each contaminant detected above CVs.

Table B-1: Nob Hill Exposure Doses and Associated MRLs, LOAELs, and NOAELs

Contaminant	Adult Dose (mg/kg/day)	Child Dose (mg/kg/day)	MRL (mg/kg/day)	LOAEL or NOAEL (mg/kg/day)
1,1-Dichloroethene	0.00002	0.00008	0.009	9
PCE	0.007	0.04	0.01	400
Heptachlor epoxide	0.000009	0.00005	0.000013	0.0125
Arsenic	0.0003	0.001	0.0003	0.014
Cadmium	0.0002	0.0009	0.0002	0.0021
Thallium	0.009	0.05	0.00007	0.2

Source: ATSDR, 1992, 1993, 1994, 1997a, 1997b, 1998; EPA, 1999

Although doses exceeding MRLs were found from past use of private wells in Nob Hill, no apparent public health hazards are likely based on a review of the toxicological literature and the overly conservative assumptions used by ATSDR to assess exposures. The USAF began providing Nob Hill residents with bottled water in 1994 when groundwater contamination was first detected and, in 1997, the USAF connected homes in the Nob Hill neighborhood to the Cheyenne municipal water supply. Therefore, current and future exposures are unlikely.

Exposure to the maximum detected concentration of TCE in private wells in Fair Acres using conservative exposure assumptions resulted in doses less than its MRL of 0.2 mg/kg/day. The estimated exposure dose for adults was 0.0003 mg/kg/day. For children, the estimated exposure dose was 0.002 mg/kg/day. ATSDR conservatively assumed that residents are exposed to the maximum detected concentration of TCE daily over the entire exposure period. However, sampling data from 1997 detected TCE at concentrations lower than previously found. Therefore, actual doses are expected to be lower than those calculated by ATSDR.

Cancer

Not all contaminants in the environment have the potential to cause cancer. ATSDR evaluated contaminants that could potentially cause cancer, including 1,1-dichloroethene, PCE, heptachlor epoxide, and arsenic in Nob Hill wells and TCE in Fair Acres wells. Cadmium is also considered a human carcinogen, but only when inhaled. Based on its chemical properties, cadmium is not expected to volatilize and any exposure through inhalation would be minimal. There are no human studies that have shown an increase in cancer with oral exposure to cadmium (ATSDR, 1997a). Therefore, ATSDR did not evaluate potential cancer effects from exposure to cadmium in drinking water.

Within the Nob Hill neighborhood, ATSDR derived a lifetime cancer risk for 1,1-dichloroethene of 4 x 10^-6 (or an increased likelihood of 4 in 1,000,000 of developing cancer) and a risk for heptachlor epoxide of 3 x 10^-5 (or an increased likelihood of 3 in 100,000 of developing cancer). These estimates are within the "acceptable" range of 10^-4 to 10^-6. The derived lifetime cancer risk for PCE and arsenic were above this range, but below 2 x 10^-4 (or an increased likelihood of 2 in 10,000 of developing cancer).

In a review of the toxicological literature, ATSDR found that the link between PCE exposure and cancer in humans is uncertain. Studies looking at occupational and drinking water exposures have been largely inconclusive, but PCE has been shown to cause cancer in laboratory animals (rodents) at high doses (ATSDR, 1997b). EPA, in an effort to determine a cancer classification, is currently reviewing the scientific literature pertaining to the carcinogenicity of PCE. To provide a conservative evaluation of the potential adverse effects from exposures to PCE in drinking water, ATSDR used a previously derived CPF to estimate the lifetime cancer risk. In addition, adults and children are extremely unlikely to use water at the maximum contaminant concentration over the entire exposure period and at the frequency and duration assumed. PCE was detected in only 4 of the 13 wells sampled, with only 2 wells containing concentrations above the MCL. The USAF has identified a groundwater contamination plume extending easterly from Landfill 3, and flowing toward Nob Hill. The leading edge of this plume has been identified at the edge of the Nob Hill neighborhood. Based on the plume flow direction, any impacts to private wells in Nob Hill would have occurred recently, rather than 30 years ago as assumed by ATSDR. In addition, the leading edge of the plume is defined by the lowest contaminant concentrations with higher concentrations located nearer the source. Therefore, it is likely that past PCE concentrations were lower than the maximum detected concentration used to assess exposures.

Review of toxicological literature for arsenic found that EPA classified arsenic as a carcinogen based on epidemiological studies of people exposed to 170 to 800 ppb of arsenic in drinking water for a 45-year exposure period (ATSDR, 1998). According to sampling data, residents in Nob Hill were exposed to a maximum arsenic concentration of only 4.7 ppb. Unlike other carcinogens, arsenic does not cause cancer in laboratory rats when administered orally. In addition, adults and children are extremely unlikely to use water at the maximum contaminant concentration over the entire exposure period and at the frequency and duration assumed.

Within the Fair Acres neighborhood, ATSDR derived a lifetime cancer risk of 2 x 10^-5 from exposure to TCE (or an increased likelihood of 2 in 100,000 of developing cancer). This estimate is within the "acceptable" range. In addition, a review of the toxicological literature has shown that, although TCE has been shown to produce cancer in experimental animals when administered in large doses, the link between TCE in drinking water and human cancer cases is not well established (ATSDR, 1997c). EPA, in an effort to determine a cancer classification, is currently reviewing the scientific literature pertaining to the carcinogenicity of TCE. For screening purposes, ATSDR used a previously derived CPF for TCE to provide a conservative evaluation of the likelihood of exposures to TCE in drinking water supplies. In addition, adults and children are extremely unlikely to use water at the maximum contaminant concentration over the entire exposure period and at the frequency and duration assumed.

Estimated Exposure Doses for Contact with Media at Landfills 2 and 3

Landfills 2 and 3 are located proximate to on-base family housing units in the southern portion of F.E. Warren. Access to these landfills is unrestricted and children have been observed biking and playing within the Landfill boundaries. An unnamed tributary to Crow Creek also flows through Landfill 2 and may be used for recreation by area residents. The stream does not support a fish population that could serve as a food source nor a stream flow that would allow swimming. ATSDR considered wading as the most likely recreational use. To determine the potential for adverse health effects from exposure to contaminants in surface soil at the landfills and surface water and sediment in the stream, ATSDR estimated oral (incidental ingestion) and dermal (skin) contact exposure doses using conservative assumptions based on past, current, and proposed future land uses. Adult and child exposures were considered.

ATSDR used the following equation and exposure assumptions to estimate an exposure dose for incidental ingestion and dermal contact with soil:

Estimated exposure dose=

C x IR x EF x ED BW x AT

where:

C	Maximum concentration (ppm)
IR	Intake rate:
	incidental ingestion: surface soil and sediment - adult=100 mg/day; child=200 mg/day; surface water - adult and child=0.15 liters/day dermal contact: adult=1,380 mg/day; child=426 mg/day (Dermal contact intake rates are multiplied by chemical-specific absorption factors which account for the skin's protective ability. The absorption factor is 0.2 for TCE and 0.01 for metals.)
EF	Exposure frequency: recreational user=130 days/year
ED	Exposure duration or the duration over which exposure occurs: adult and child=6 years (conservative estimate of average stay in military housing)
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 (6 years [conservative estimate of average stay in military housing] x 365 days/year for noncancer effects and 70 years [considered a lifetime] x 365 days/year for cancer effects)

Investigations at Landfills 2 and 3 have detected arsenic (2.3 ppm) above its CV in surface soil. Surface water samples from the unnamed stream contained TCE (6.9 ppb), arsenic (9 ppb), lead (280 ppb), and manganese (480 ppb) above CVs. Sediment samples contained arsenic (6.5 ppm) and lead (556 ppm) above CVs. Based on an evaluation of exposures and doses and a review of toxicological data, ATSDR concluded that contact with surface soil, surface water, and sediment during recreational use is unlikely to result in noncancer or cancer health effects.

Noncancer

ATSDR calculated doses assuming that recreational users contacted the maximum detected contaminant concentrations over the entire exposure period. Exposure was assumed to occur 5 days per week for 26 weeks each year, based on climate constraints. In addition, military personnel were assumed to reside in on-base housing for 6 years, whereas the average duration in military housing is only 3 years. Using these conservative assumptions, exposure doses for both adults and children contacting contaminants in surface soil, surface water, and sediment were below their associated MRLs. In addition, the USAF is conducting investigations and remedial actions to prevent current and future exposures at these landfills.

Cancer

ATSDR evaluated exposures to TCE and arsenic, known or suspected human carcinogens. The derived lifetime cancer risk for exposure to each of these contaminants was below 9 x 10^-7 (or an increased likelihood of 9 in 10,000,000 of developing cancer). This estimate is below the "acceptable" range of 10^-4 to 10^-6. In addition, cancer estimates were calculated using conservative assumptions about frequency and duration of site use, as discussed under the evaluation of noncancer doses. An actual resident is very unlikely to be in contact with the highest level of contamination at the assumed frequency and duration.

Lead

Lead (280 ppb) was detected above EPA's maximum contaminant level (MCL) of 15 ppb in one of nine surface water samples analyzed for total metals. In sediment, lead (556 ppm) was detected above EPA's soil screening level (SSL) of 400 ppm. The MCL and SSL are drinking water and soil exposure CVs used to screen surface water and sediment, respectively, because media-specific CVs have not been developed. The MCL is derived assuming daily ingestion of 2 liters of water and the SSL is derived assuming daily incidental ingestion of contaminants in soil. Recreational exposure to surface water and sediment are expected to be less frequent and of shorter duration than assumed by the MCL and SSL. The stream is an interrupted stream with alternating reaches that are perennial, intermittent, and ephemeral, therefore, daily exposure to lead in surface water is not possible. At it's closest, this stream is located approximately 600 feet from the residential housing area. Based on the distance from the housing areas and physical hazards associated with streams, ATSDR assumes that pre-school age children, who are most vulnerable to lead poisoning, are unlikely to be biking and playing in the stream. Recreational use of the stream by older children is only likely for short periods a day and for only portions of the year, based on the regional western climate. For these reasons, lead is unlikely to pose any health hazards.

APPENDIX C: Glossary

Background Level

A typical or average level of a chemical in the environment. Background often refers to naturally occurring or uncontaminated levels.

Carcinogen

Any substance that may produce cancer.

CERCLA

The Comprehensive Environmental Response, Compensation, and Liability Act of 1980, also known as Superfund. This is the legislation that created ATSDR.

Comparison values (CVs)

Estimated contaminant concentrations in specific media that are not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight. The comparison values are calculated from the scientific literature available on exposure and health effects.

Concentration

The amount of one substance dissolved or contained in a given amount of another. For example, sea water contains a higher concentration of salt than fresh water.

Contaminant

Any substance or material that enters a system (the environment, human body, food, etc.) where it is not normally found.

Dermal

Referring to the skin. Dermal absorption means absorption through the skin.

Dose

The amount of substance to which a person is exposed. Dose often takes body weight into account.

Environmental contamination

The presence of hazardous substances in the environment. From the public health perspective, environmental contamination is addressed when it potentially affects the health and quality of life of people living and working near the contamination.

Exposure

Contact with a chemical by swallowing, by breathing, or by direct contact (such as through the skin or eyes). Exposure may be short term (acute) or long term (chronic).

Hazard

A source of risk that does not necessarily imply potential for occurrence. A hazard produces risk only if an exposure pathway exists, and if exposures create the possibility of adverse consequences.

Ingestion

Swallowing (such as eating or drinking). Chemicals can get in or on food, drink, utensils, cigarettes, or hands where they can be ingested. After ingestion, chemicals can be absorbed into the blood and distributed throughout the body.

Inhalation

Breathing. Exposure may occur from inhaling contaminants because they can be deposited in the lungs, taken into the blood, or both.

Media

Soil, water, air, plants, animals, or any other parts of the environment that can contain contaminants.

Method Detection Limit

The lowest contaminant concentration that a laboratory instrument can measure in water, soil, or air samples. The method detection limit changes for different contaminants.

National Priority List (NPL)

The U.S. Environmental Protection Agency's (EPA) list of sites where uncontrolled releases of contaminants to the environment has occurred. These sites are considered to have the highest priority for long-term remediation. At the time F.E. Warren was placed on the NPL in 1990, EPA used the NPL as a tool to determine which sites needed further study to evaluate the extent of contamination and potential hazards. EPA also used the NPL to evaluate which funding sources could be used to conduct studies and remediation at a site.

No Apparent Public Health Hazard

An ATSDR defined category: Sites where human exposure to contaminated media is occurring or has occurred in the past, but the exposure is below a level of health hazard. The ATSDR conclusion categories are, in sequence: Urgent Public Health Hazard, Public Health Hazard, Indeterminate Public Health Hazard, No Apparent Public Health Hazard, and No Public Health Hazard.

Plume

An area of chemicals in a particular medium, such as air or groundwater, moving away from its source in a long band or column. A plume can be a column of smoke from a chimney or chemicals moving with groundwater.

Potentially Exposed

The condition where valid information, usually analytical environmental data, indicates the presence of contaminant(s) of a public health concern in one or more environmental media contacting humans (i.e., air, drinking water, soil, food chain, surface water), and there is evidence that some of those persons have an identified route(s) of exposure (i.e., drinking contaminated water, breathing contaminated air, having contact with contaminated soil, or eating contaminated food).

Public Health Assessment

The evaluation of data and information on the release of hazardous substances into the environment to assess any current or future effects on public health, develop health advisories or other recommendations, and identify studies or actions needed to evaluate and mitigate or prevent human health effects; also, the document resulting from that evaluation.

Public health hazard

Sites that pose a public health hazard as the result of long-term exposures to hazardous substances.

Risk

In risk assessment, the probability that something will cause injury, combined with the potential severity of that injury.

Route of exposure

The way in which a person may contact a chemical substance. For example, drinking (ingestion) and bathing (skin contact) are two different routes of exposure to contaminants that may be found in water.

Superfund

Another name for the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), which created ATSDR.

Superfund Amendments and Reauthorization Act (SARA)

The 1986 legislation that broadened ATSDR's responsibilities in the areas of public health assessments, establishment and maintenance of toxicologic databases, information dissemination, and medical education.

Volatile organic compounds (VOCs)

Substances containing carbon and different proportions of other elements such as hydrogen, oxygen, fluorine, chlorine, bromine, sulfur, or nitrogen; these substances easily become vapors or gases. A significant number of the VOCs are commonly used as solvents (paint thinners, lacquer thinner, degreasers, and dry cleaning fluids).

APPENDIX D: Responses to Public Comments

The Agency for Toxic Substances and Disease Registry (ATSDR) received the following comments/questions during the public comment period (August 11 to October 22, 1999) for the F.E. Warren Air Force Base (F.E. Warren) Public Health Assessment (PHA) (August 11, 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.

General Comments

1. Comment: In light of broad public interest in the findings of this assessment, the Wyoming Department of Environmental Quality (WDEQ) requests that a public meeting be held in Cheyenne to address citizen concerns and answer citizen questions related to this PHA.

   Response: To ensure that the needs and concerns of the communities surrounding F.E. Warren were met, ATSDR held public availability sessions in Cheyenne in January 1999 and extended the public comment period for review of the PHA. Before and during ATSDR's site visit in December 1998, the U.S. Air Force (USAF) informed ATSDR about the community interest and concern about F.E. Warren. As a result, ATSDR held day and evening public availability sessions at local meeting rooms in Cheyenne in January 1999. During these sessions, community members spoke with ATSDR to discuss their concerns and ask questions about the base and potential health hazards. ATSDR then developed a public comment draft of the public health assessment and released that draft for a 30-day public comment period ending September 19, 1999. Comments were received from one agency and one individual. To ensure that the community had ample opportunity to review and comment, the comment period was extended to October 22, 1999. During this interval one individual contacted ATSDR and requested clarification on certain points. That inquiry resulted in an effort to clarify several sections of the text of the assessment. At the September 1999 Restoration Advisory Board meeting, a representative of the USAF also announced the extension of the public comment period for review of the PHA. No additional comments were received.

2. Comment: ATSDR has not assessed the public health effects of contaminants found in Crow Creek, which is used by children for recreation both on and downstream of the base. Public parks are located along Crow Creek immediately downstream of the base. A complete assessment of the public health concerns for F.E. Warren should include assessment of exposure pathways associated with recreational use of Crow Creek.

   Response: ATSDR added the following text to the "Community Health Concerns" section of this PHA.

   What potential public health hazards are posed by recreational use of Crow Creek, both on and off base?

   Crow Creek may have been impacted from overland transport of contaminants in surface soil or discharge of contaminants in groundwater to surface water. The family camping area is the only recreational area along Crow Creek within F.E. Warren boundaries. The family camping area is located in the western portion of the base upstream and upgradient of, and therefore away from, potential source areas. Recreational areas are also located along Crow Creek downstream of the base. To assess potential contamination in Crow Creek, the USAF sampled on-base surface water and sediment. Sampling found cadmium (12 ppb) above its drinking water comparison value (CV) in surface water and arsenic (1.2 ppm) above its soil CV in sediment upstream of the family camp. No contaminants above CVs in surface water and only arsenic (2.9 ppm) above its soil CV in sediment were found in samples collected from the base boundary where Crow Creek flows off base (EBASCO, 1991b; USGS, 1996c). The drinking water and soil CVs used to evaluate contamination in surface water and sediment, respectively, are derived using conservative assumptions about exposure, such as daily ingestion of 2 liters of contaminated water and daily contact with contaminated soil. Actual exposures during recreational activities occur much less frequently. In addition, the detected arsenic concentrations are within background concentrations found at F.E. Warren. ATSDR, therefore, found no apparent public health hazards associated with recreational use of Crow Creek.

3. Comment: WDEQ uses 10^-6 estimated lifetime cancer risk level as a threshold value indicating exposure pathways which present an unacceptable cancer risk. Based on this criteria and the assumptions used in ATSDR's PHA, residents of the Fair Acres neighborhood could face an unacceptable risk of cancer via the drinking water pathway should affected residents discontinue use of bottled water. Likewise, based on ATSDR's PHA, residents of the Nob Hill neighborhood could also face an unacceptable risk of cancer via the drinking water pathway should these residents return to using groundwater as a drinking water source. In the case of the Nob Hill neighborhood, this pathway has been eliminated through connection to the municipal water supply.

   Response: In evaluating potential health hazards from exposure to contaminants in drinking water at Fair Acres and Nob Hill, ATSDR derived lifetime cancer risk values above 10^-6 for several contaminants, as described in Appendix B. To further assess the potential for public health hazards, ATSDR considers the assumptions used to derive lifetime cancer risk values and the toxicological data for different contaminants. For evaluating Fair Acres and Nob Hill, ATSDR assumed that residents drank 4 liters of water from a well containing the maximum detected contaminant concentrations every day for 30 years. These assumptions are extremely conservative and resident exposures are expected to be much less frequent and of shorter duration than ATSDR assumed. Using less conservative assumptions would reduce the derived lifetime cancer risks. In addition, the toxicological data used to derive the lifetime cancer risks include "safety" factors that serve to overestimate the potential for adverse health effects in humans. As such, ATSDR concluded that although derived lifetime cancer risks for some contaminants were above 10^-6, no apparent public health hazards exist from consumption of well water from Fair Acres or Nob Hill. Because a groundwater plume has been identified at F.E. Warren migrating toward Nob Hill, residents in this neighborhood were connected to the Cheyenne municipal water supply as a preventative measure.

Specific Comments

4. Comment: Evaluation of Environmental Contamination and Potential Exposure Pathways, Page 21. ATSDR exposure dose estimates for trichloroethylene (TCE) in groundwater is based, in part, on the assumption that Fair Acres residents will consume water from contaminated wells. In this section, one of the assumptions listed is that residents will continue to use bottled water for drinking purposes. This assumption was not used in the calculation of exposure dose and should be deleted here. If it is ATSDR's recommendation that residents continue to use bottled water for drinking, that recommendation should be made in the appropriate section of the PHA.

   Response: To evaluate exposure doses to Fair Acres residents drinking groundwater, ATSDR assumed that residents drank 4 liters of water from a well containing the maximum detected TCE concentration every day for 30 years. The bulleted list of information on pages 20 and 21 of this PHA contains information about the assumptions used to derive the exposure dose. This list also contains further information about expected exposure frequency and duration and remedial actions that also supports ATSDR's conclusion that TCE in Fair Acres wells poses no apparent public health hazards. For clarity, the sentence "This conclusion is based on ATSDR's exposure evaluation and the following information:" was changed to "This conclusion is based on ATSDR's exposure evaluation which uses conservative estimates of exposure frequency and duration. The following information about expected exposures and completed remedial actions also serves to support the conclusion of no apparent public health hazards:"

   ATSDR does not recommend that Fair Acres residents must continue using bottled water for drinking because most recent sampling data have found TCE below EPA's Maximum Contaminant Level. ATSDR does recommend, as listed under "Recommended Actions" on page 31, that residents regularly monitor their well water to ensure that TCE concentrations remain below the MCL.

5. Comment: Community Health Concerns, Page 25. What was the CV used to evaluate 4-nitrotoluene?

   Response: ATSDR used the EPA Region III Risk-Based Concentration (RBC) value for comparison with detected 4-nitrotoluene concentrations. In addressing this comment, ATSDR noted that the PHA incorrectly reports that 4-nitrotoulene was detected above this CV. The maximum detected concentration of 4-nitrotoulene (3.2 ppm) is actually well below the EPA Region III RBC value of 780 ppm. Therefore, the reference to 4-nitrotoulene was deleted from the text and the sentence on page 25 was changed to "Arsenic was detected above its CV in surface soil samples collected from the open burn, open detonation area located in the northern portion of the base, approximately 1.5 miles west of Western Hills." To ensure the accuracy of other data used in this PHA, ATSDR conducted a full data review and found no other errors in evaluating data against CVs.

6. Comment: Appendix C: Glossary, Page C-2. The USAF recommends that ATSDR revise the definition of "National Priority List" (NPL) with a definition that is the same as or similar to the definition provided in the National Oil and Hazardous Substances Pollution Contingency Plan. ATSDR should provide a statement explaining the purpose of the NPL at the time F.E. Warren was listed.

   Response: ATSDR revised the definition of NPL to the following:

   "National Priority List (NPL)
   The U.S. Environmental Protection Agency's (EPA) list of sites where uncontrolled releases of contaminants to the environment has occurred. These sites are considered to have the highest priority for long-term remediation. At the time F.E. Warren was placed on the NPL in 1990, EPA used the NPL as a tool to determine which sites needed further study to evaluate the extent of contamination and potential hazards. EPA also used the NPL to evaluate which funding sources could be used to conduct studies and remediation at a site."

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