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PUBLIC HEALTH ASSESSMENT

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


EVALUATION OF ENVIRONMENTAL CONTAMINATION AND POTENTIAL
EXPOSURE PATHWAYS

In this section, ATSDR evaluated whether community members have been (past), are (current), or will be (future) exposed to harmful levels of chemicals. Figure 3 describes the conservative exposure evaluation process used by ATSDR. As the figure indicates, ATSDR considers how people might come into contact with, or be exposed to, contaminated media. Specifically, ATSDR determines whether an exposure could occur through ingestion, dermal (skin) contact with contaminated media, or inhalation of dust and vapors, and also considered the likely length (duration) and frequency of the exposure.

If exposure was or is possible, ATSDR then considers whether chemicals were or are present at concentrations that might be harmful to people. ATSDR does this by screening the concentrations of contaminants in environmental media (e.g., groundwater or soil) against health-based comparison values (CVs). CVs are chemical concentrations that health scientists have determined are not likely to cause adverse effects, even when assuming very conservative exposure scenarios. Because CVs are not thresholds of toxicity, however, environmental levels that exceed CVs would not necessarily produce adverse health effects. If a chemical is found in the environment at levels exceeding its corresponding CV, ATSDR examines potential exposure variables and the contaminant's toxicology. ATSDR emphasizes that regardless of contaminant concentrations, a public health hazard exists only if people come in contact with, or are otherwise exposed to, harmful levels of contaminated media.

After initial review of potential health hazards at F.E. Warren, ATSDR identified dust blowing from the base into the Western Hills neighborhood (a current community concern), groundwater contamination, and recreational use of Landfills 2 and 3 as potential concerns that required further evaluation. Following the strategy outlined above, ATSDR examined whether human exposures to harmful levels of contaminants via these pathways existed in the past, exist now, or could potentially exist in the future. ATSDR summarized it's evaluation of exposure pathways in Table 3 and described it in more detail in the discussion that follows. To acquaint readers with terminology and methods used in this report, Appendix A provides a list of CVs, Appendix B summarizes the methods and assumptions used to estimate exposures and to support some of the report's conclusions, and Appendix C provides a glossary of terms.

Concern: Exposure to Dust from the Borrow Area

    Could dust blowing from disturbed soil in the borrow area, located immediately upwind of a residential neighborhood, adversely affect the health of area residents?

Conclusions

After detailed review of the available information, ATSDR concluded that contaminants in dust pose no apparent public health hazard. The following information supports ATSDR's conclusion.

  • The active borrow area is located within the ricochet zone of a nearby firing range and may have been affected by ammunition deflected into the area from the firing range. Soil investigations at the active borrow pit found no contaminants at concentrations above CVs. However, the method detection level (the lowest concentration that the laboratory instrument could "see") for two polyaromatic hydrocarbons (PAHs) and arsenic was above CVs. Therefore, these contaminants may be present at concentrations greater than their respective CVs, but not at concentrations greater than the method detection level that was used. PAHs and arsenic, however, are not contaminants commonly associated with firing range activities. In addition, method detection limits for soil investigations of potential future borrow areas were below CVs. No PAHs were found above CVs; only arsenic was found above its CV.
  • ATSDR conducted an exposure evaluation based on conservative assumptions designed to overestimate the amount of contaminants to which people may be exposed. This evaluation did not identify any exposures that might result in adverse health effects.
  • The USAF has implemented a dust control program at the active borrow area to limit dust generation and potential exposures. This program includes wetting the soil, applying a tackifier (a sticky, sugar substance that creates a coating on the soil surface), and ceasing activities in high winds.

Discussion

Land Use

The active borrow area is located in the northeastern portion of F.E. Warren, immediately north of the riding stable. Historically, the northern portion of the base was used for explosive ordnance disposal and small arms and gunnery training. An open burn, open detonation area for ordnance disposal was located in the northwestern corner of the base and is being investigated as OU6. Two firing ranges for arms training were located in this area, one firing range is immediately north of the open burn, open detonation area and the second firing range is located in the central portion of the base immediately north of Central Avenue (Figure 2). These firing ranges are undergoing investigations as part of OU7 (F.E. Warren, 1998d). The active borrow area is located beyond the boundaries of the open burn, open detonation area and the firing ranges, but within the ricochet zone, which surrounds the firing ranges and may contain ammunition that has deflected from the firing ranges (OHM, 1997a).

Most of the land in the northern portion of the base is currently unused. The USAF is conducting investigations at the open burn, open detonation area and the firing ranges to evaluate potential remediation needs. At nine locations throughout the base, including the active borrow area, the USAF has conducted field studies to determine if the soil is suitable for capping on-base landfills (F.E. Warren, 1999b).

The active borrow area is a site encompassing approximately 40 acres. The USAF is excavating soil from this area for use as capping material for Landfill 6, located in the southwestern portion of the base. Excavation activities began in April 1997 and are scheduled to continue until August 1999. After the area is excavated to approximately 10 feet below ground surface (bgs), it will undergo further construction and serve as part of a new storm water detention basin for Cheyenne (F.E. Warren, 1999b; Wright & Woods, 1999).

Less than 0.25 miles east of the borrow area is a residential neighborhood, Western Hills. This neighborhood is composed of single-family homes that were built in the late-1960s and early 1970s. Western Hills is expanding and newer homes are located in the northern sections of this neighborhood. When homes were first built, residents received drinking water from private wells. However, very soon, in the early 1970s, homes were connected to the Cheyenne municipal water supply (F.E. Warren, 1998c and 1999a).

Nature and Extent of Contamination

Due to concerns about explosive and physical hazards, the USAF has conducted activities to clear the northern portion of the base of ordnance. The active borrow area was included in locations cleared of ordnance between October 19 and 21, 1992 (EBASCO, 1993).

The USAF conducted extensive studies of the active borrow area in 1996 and 1997 to characterize the physical and chemical properties of the soil for potential use as a landfill cap. During these investigations, the USAF excavated 40 test pits and collected 50 soil samples. An additional 11 samples were also collected from southeast of the borrow area. Samples were analyzed for volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), pesticides, polychlorinated biphenyls (PCBs), metals, cyanide, and trimethylenetrinitramine and 2,4,6-trinitrotoluene (two common explosives). In reviewing the sampling data from the first group of samples collected in 1996, ATSDR noted concerns regarding method detection limits and data quality and considered these concerns during our data review. Data quality concerns were rectified for the 1997 sampling of the active borrow area. A review of the 1997 data found no contaminants above CVs, however, three contaminants, including two PAHs [benzo(a)pyrene and dibenz(a,h)anthracene] and arsenic, the method detection limits were greater than the associated CVs. Therefore, these contaminants may be present at concentrations below the method detection limits but above their CVs. PAHs and arsenic, however, are not commonly associated with firing range activities or past site uses and are not expected to be present in surface soil (OHM, 1997a; F.E. Warren, 1999b).

The prominent wind direction is northwest to southeast, therefore Western Hills residents have expressed concern about exposure to contaminants in dust from the active borrow area during excavation. To minimize dust, the USAF has implemented a dust suppression program. This includes wetting the soil, applying a tackifier (a sticky, sugar substance that creates a coating on the soil surface), and ceasing activities in high winds (Wright, 1998). In addition, between April 1997 and November 1998, the USAF monitored ambient air for dust levels, VOC concentrations, and explosive levels of gases. No VOCs or explosive levels of gases were detected. Dust was detected to a maximum of 0.69 milligrams per cubic meter (mg/m3). This is a measurement of dust only, and does not mean that there are any contaminants contained in the dust. The WDEQ standard for suspended particles or dust in ambient air is 0.15 mg/m3 averaged over a 24 hour period. Data collected during July and August 1997 excavation activities, when the maximum concentration was found, indicated that the WDEQ standard for dust in air was exceeded on several occasions. Reported concentrations, however, were averaged over an 8-hour period during active excavation. Comparing these results to a 24-hour standards is speculative; it assumes that dust generating activities did not vary over time. Subsequent monitoring data during November and December 1998 found no instances where the WDEQ standard was exceeded; the maximum dust concentration was 0.099 mg/m3 (OHM, 1997b; OHM, 1998; WDEQ, 1999).

The USAF has also begun investigations of eight other locations that may serve as future borrow areas and sources of soil for landfill capping. A total of 48 test pits were excavated and air within the test pits were field tested for VOCs, which were never detected. In addition, one soil sample from each of the eight sites was collected and analyzed for VOCs and SVOCs. Two composite surface soil samples were also collected and analyzed for metals. Method detection limits for VOCs, SVOCs, and metals analyses at these other borrow area locations were below the CVs for all contaminants. Only arsenic, detected at a maximum of 3.4 ppm, was detected above its CV of 0.5 ppm (F.E. Warren, 1999b). Arsenic is a naturally occurring component of soil. The USAF conducted investigations to identify naturally occurring arsenic concentrations versus arsenic that may have been released by base activities. This investigation found that the average arsenic concentration in soil is 2.3 ppm, but can be as high as 5.1 ppm. A regional study of naturally occurring arsenic, conducted for USGS, found that the mean arsenic concentration in soil was 5.5 ppm (USGS, 1996b; Shacklette and Boerngen, 1984). Therefore, arsenic concentrations detected in the potential borrow areas are within the range of naturally occurring arsenic.

Table 4 provides a summary of the PAHs and arsenic method detection limits, the maximum detected concentrations, and CVs for the active borrow area and potential future borrow areas.

Evaluation of Potential Public Health Hazards

Investigations of the active borrow area did not find any contaminants above CVs. However, for two PAHs and arsenic, the method detection limits were set above the associated CVs, so it was not possible to tell if the contaminants were present above their CVs and below the method detection limits. Because these contaminants are not typically associated with past site uses, we would not expect them to be present. There is a possibility, however, for the contaminants to be present at concentrations below the method detection limit but above the CVs. Residents may be exposed to these two PAHs and arsenic through contact with windblown dust. Additional investigations of eight other areas that may serve as future borrow areas used detection limits below CVs for all analyses. Only arsenic was detected above its CVs. If these areas are excavated in the future, residents in the Western Hills neighborhood may potentially be exposed to arsenic in windblown dust.

To evaluate whether past, current, and potential future health hazards may be associated with soil excavation in the northern portion of the base, ATSDR estimated the potential doses for Western Hills residents (adults and children). To estimate doses, ATSDR used very conservative assumptions believed to overestimate the levels of actual exposure. These assumptions, ATSDR's methods, and the estimated doses are further described in Appendix B. Although method detection limits were higher than CVs for several contaminants and arsenic was detected above its CV, in no cases were levels high enough to present a reasonable likelihood for harmful exposures to occur. ATSDR, therefore, concludes that past, current, and potential future exposures to windblown dust pose no apparent public health hazards. This conclusion is based on the following information:

  • Because the method detection limits for two PAHs and arsenic were above CVs for samples collected from the active borrow area, ATSDR assumed that people are exposed to these contaminants at the method detection limits. This is a very conservative estimate of contaminant concentrations in soil; actual concentrations are expected to be much lower because PAHs and arsenic are not commonly associated with past site activities.
  • ATSDR used extremely conservative assumptions about how often and how long a resident is exposed to contaminants in windblown dust. Residents were assumed to inhale and ingest dust containing the maximum detected contaminant concentrations daily over the entire exposure period of three years, the expected duration of active excavation. Actual exposures are expected to be less frequent and over a shorter duration than assumed by ATSDR.
  • ATSDR also conservatively assumed that people were exposed to dust at the maximum concentration detected during air monitoring over the entire exposure period. Actual dust levels, as shown by air monitoring data, are often much lower than assumed.
  • To minimize potential exposures to dust, the USAF has implemented a dust control program. This includes wetting the soil, applying a tackifier (a sticky, sugar substance that creates a coating on the soil surface), and ceasing activities in high winds.

Concern: Exposure to Contaminants in Groundwater

    VOCs and metals have been found in groundwater at F.E. Warren and in private wells along the southern property boundary (in the Nob Hill and Fair Acres neighborhoods). Could past exposure to these contaminants result in adverse health effects?

Conclusions

After detailed review of available information, ATSDR concluded that contaminants in private wells posed no apparent public health hazard. The following information supports ATSDR's conclusion.

  • Investigations found VOCs and metals in private wells in the Nob Hill neighborhood and TCE in several wells in the Fair Acres neighborhood above CVs. Releases from Landfill 3 at F.E. Warren were identified as a potential source of contaminants in Nob Hill wells. Landfill 5 was originally thought to be the source of TCE in the Fair Acres wells. However, site investigations identified an unknown source within the Fair Acres neighborhood as the likely source of TCE in wells in this area.
  • ATSDR conducted an exposure evaluation based on conservative assumptions designed to overestimate the amount of contamination to which people may be exposed. This evaluation did not identify any exposures that might result in adverse health effects. The evaluation of exposures for Nob Hill residents, however, was based on sampling results from a single round of samples collected from private wells in 1994. Additional sampling may further support this conclusion.
  • To prevent current and future exposures, the USAF connected homes in the Nob Hill neighborhood to the Cheyenne municipal water supply. Cheyenne receives water from groundwater wells located several miles regionally upgradient and west of F.E. Warren and from runoff from the Rocky Mountains. These supplies have not been affected by base activities.
  • During investigations, the USAF provided residents in the Fair Acres neighborhood with bottled water for drinking. These investigations revealed that the source of TCE was beyond base boundaries. In addition, recent sampling has found a decline in the TCE concentrations detected in private wells to below EPA's Maximum Contaminant Level (MCL), which is the concentration that any treatment required by EPA or WDEQ would be trying to achieve. WDEQ and local health officials are working with Fair Acres residents to ensure their health is protected. Recommendations have been made to the residents by WDEQ to continue using bottled water, to have their wells tested for TCE annually, and to consider annexation into the city of Cheyenne, which would give them access to municipal water and sewer; permanently preventing exposure to contaminants that may be in their well water.

Discussion

Hyrdrogeology

Surface geology at F.E. Warren consists mostly of unconsolidated deposits that generally do not exceed 25 feet in thickness. These deposits are thickest along streams and consist of clay, silt, sand, gravel, cobbles, and boulders. The surface deposits are underlain by the Ogallala Formation, which ranges in depth from over 300 feet bgs in the northern portion of the base to only 30 feet bgs in the southern portion of the base. The Ogallala Formation consists of a heterogenous mixture of clay, silt, sand, and gravel (USGS, 1995b).

The High Plains Aquifer underlies F.E. Warren and is contained within the surficial deposits and Ogallala formation. Depth to the water table varies throughout the base, at the surface near streams and deeper farther from discharge areas. In the southern portion of F.E. Warren, depth to the water table generally ranges from approximately 10 to 40 feet bgs. In the shallow zone of the aquifer, groundwater flows toward discharge points in Crow Creek, Diamond Creek, and the unnamed tributary to Crow Creek. Deeper groundwater generally flows to the east. Infiltration of precipitation serves as a local source of recharge. Groundwater and subsurface geology deeper than 130 feet bgs has not been characterized (USGS, 1995b).

Groundwater Use

Cheyenne, including F.E. Warren, receives drinking water from a series of groundwater wells located several miles west of the base. Snow melt and runoff from the Rocky Mountains to the west also provide a significant portion of the city's drinking water. Groundwater contamination from F.E. Warren is not expected to affect the Cheyenne water supply based on the well locations being several miles upgradient of F.E. Warren (F.E. Warren, 1998e).

The High Plains Aquifer is the primary source for domestic and stock water supply in the area surrounding F.E. Warren. Residents in the Nob Hill neighborhood, located along the southern base boundary, relied on groundwater from private wells as their drinking water supply until 1994. In 1994, when contaminants were discovered in private wells, the USAF began providing bottled water to Nob Hill residents. In 1997, the USAF connected homes in the Nob Hill neighborhood to the Cheyenne municipal water supply. Nob Hill is a small neighborhood, containing 16 residences. Most residences are mobile homes owned by long-term residents. Residents in the Fair Acres neighborhood, located along the southwestern base boundary, obtain drinking water from active private wells. Fair Acres is a small neighborhood composed of a mixture of standard homes, modular homes, and mobile homes. Residents tend to live in the neighborhood for a long time (F.E. Warren, 1998c; USGS, 1995b).

Nature and Extent of Contamination

The USAF sampled wells within the Nob Hill neighborhood in April 1994. At the owner's request, one of these wells was resampled in September 1994. Samples were analyzed for VOCs, SVOCs, pesticides, PCBs, ethylene glycol, petroleum hydrocarbons, metals, and selected anions. 1,1-Dichloroethene, heptachlor epoxide, arsenic, and cadmium were detected in private wells above CVs. Tetrachloroethylene and thallium were detected above their CVs and EPA's MCLs. MCLs are the maximum permissible contaminant concentration in a drinking water supply, as enforced by EPA. As a result, the USAF began providing Nob Hill residents with bottled water while investigations were ongoing. Additional investigations at F.E. Warren identified Landfill 3, located northwest of Nob Hill, as a potential source of groundwater contamination. A plume of groundwater contamination, as defined by TCE concentrations, has been identified flowing from Landfill 3 easterly toward Nob Hill. The leading edge of this plume has been determined to be at the edge of the Nob Hill neighborhood (USGS, 1995d, F.E. Warren, 1998f).

In 1994 and 1995, three private wells in the Fair Acres neighborhood were sampled. TCE was detected slightly above ATSDR's CV and EPA's MCL, an enforceable water quality standard for drinking water supplies. As a result, the USAF provided homes with bottled water from December 1994 through April 1996 while additional investigations to identify the source of contamination were conducted. Initially, Landfill 5, located to the north, was believed to be the potential source of TCE contamination. The USAF and WDEQ collected groundwater samples from drinking water wells and monitoring wells within the Fair Acres neighborhood and from monitoring wells located along the southwestern base boundary and within Landfill 5. Samples collected in 1997 contained TCE below EPA's MCL. Phthalates were also detected in drinking water wells, however, their presence was attributed to laboratory contamination rather than actual groundwater contamination. These investigations also determined that groundwater in the Fair Acres neighborhood flows northerly from the community onto the base. Therefore, TCE in groundwater is the result of an unidentified source probably located within the neighborhood rather than Landfill 5. The USAF discontinued supplying bottled water to the neighborhood because TCE was detected below its MCL in drinking water wells and the likely source of contamination is located within the Fair Acres neighborhood rather than at F.E. Warren. However, several residents continue to use bottled water as their drinking water supply. WDEQ recommends that home owners conduct annual sampling to ensure the safety of their water supply. WDEQ and local health officials continue to work with Fair Acres residents to identify potential sources and prevent harmful exposures (URS, 1997; USGS, 1997).

Table 5 provides a summary of the contaminants detected above CVs in drinking water wells in the Nob Hill and Fair Acres neighborhoods, the maximum detected concentrations, and the associated CVs and MCLs.

Evaluation of Potential Public Health Hazards

VOCs and metals in the Nob Hill neighborhood and TCE in the Fair Acres neighborhood were detected when the wells were sampled in 1994 and 1995. Residents in Nob Hill were exposed to contaminants in drinking water wells in the past. Residents in Fair Acres continue to use private wells and may be exposed to TCE in groundwater.

To evaluate whether health hazards are associated with exposures to contaminants in drinking water from private wells, ATSDR estimated the potential doses for residents (adults and children). To estimate doses, ATSDR used very conservative assumptions that overestimate the levels of actual exposure. These assumptions, ATSDR's methods, and the estimated doses are further described in Appendix B. Although low levels of contamination were detected in samples from private wells in Nob Hill and Fair Acres, in no case were these levels found to be high enough to present a reasonable likelihood for harmful exposures to have occurred. ATSDR, therefore, concludes that past, current, and potential future exposures to contaminants in drinking water pose no apparent public health hazards. 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 used extremely conservative assumptions about how often and how long a resident is exposed to a chemical. Residents were assumed to obtain all of their drinking water from private wells within Nob Hill or Fair Acres every day over the entire exposure period of 30 years for adults and 6 years for children. Actual exposures are expected to be less frequent and over a shorter duration than assumed by ATSDR.
  • Wells within the Nob Hill neighborhood were only sampled once during 1994. Therefore, it is unknown when the wells were first contaminated and whether there are any trends in contaminant concentrations. As a conservative estimate, ATSDR assumed that residents were exposed to the maximum detected contaminant concentrations. Additional sampling may provide further information about groundwater contaminants.
  • 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 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.
  • To prevent current and future exposures, the USAF provided Nob Hill residents with bottled water beginning in 1994 and connected homes to the Cheyenne municipal water supply in 1997.
  • Wells within the Fair Acres neighborhood were sampled in 1995 and again in 1997. The 1997 sampling results found decreasing TCE concentrations in contaminated wells. However, as a conservative estimate of exposure, ATSDR assumed that residents were exposed to the maximum detected concentration of TCE.
  • Homes in the Fair Acres neighborhood still rely on private wells for their water supply, however, several residents purchase bottled water for drinking. WDEQ and local health officials continue to work with residents in this neighborhood to identify potential contamination sources and ensure that public health is not compromised.

Concern: Exposure to Contaminants in Site Media at Landfills 2 and 3

    Site investigations detected contaminants above CVs in surface soil, surface water, and sediment at Landfills 2 and 3. Children from nearby on-base housing units have been observed playing in these landfills. Could recreational use of these landfills result in adverse health effects?

Conclusions

After detailed review of available information, ATSDR concluded that contaminants in site media at Landfills 2 and 3 pose no apparent public health hazard. The following information supports ATSDR's conclusion.

  • Arsenic was detected above its CV in surface soil samples from Landfills 2 and 3. Surface water samples from the unnamed tributary to Crow Creek, which flows through Landfill 2, contained TCE, arsenic, lead, and manganese above CVs. Sediment samples from this stream contained arsenic and lead above CVs.
  • ATSDR conducted an exposure evaluation based on conservative assumptions designed to overestimate the amount of contamination to which people may be exposed. This evaluation did not identify any exposures that might result in adverse health effects.
  • The USAF completed investigations at Landfills 2 and 3 in 1995. Landfill 2 is composed of three subunits: Landfill 2a, 2b, and 2c. Based on the 1995 investigations, removal actions, which include partial or total excavation of waste, were completed at Landfill 2c and are scheduled to begin at Landfills 2a and 2b in April 2000. At Landfill 3, the USAF is scheduled to conduct additional investigations in 1999 and begin construction of a landfill cap in April 2001.

Discussion

Land Use

Landfills 2 and 3 are located in the southeastern portion of F.E. Warren. Landfill 2 operated from 1918 to 1947 and Landfill 3 operated from the mid-1950s to the mid-1960s. Both of these landfills accepted general base refuse, including domestic and shop wastes. Shop wastes might have included solvents, waste oils, ethylene glycol, batteries, paint, asbestos insulation, and incinerator ash. Both landfills have a thin soil and grass cover. An unnamed stream, which is a tributary to Crow Creek, flows through a portion of Landfill 2. This stream is an interrupted stream, with alternating reaches that are perennial, intermittent, or ephemeral (USGS, 1995c and 1995d; F.E. Warren, 1998d).

An on-base housing unit is located proximate to Landfills 2 and 3. Housing includes four barracks, with a maximum capacity of 424 residents, occupied by single enlisted personnel. Approximately 265 family housing units are also located in this area. Residents have a turnover rate of 3 years or less. Base personnel have observed children from the housing area biking and playing on Landfills 2 and 3 (F.E. Warren, 1998c and 1998e).

Nature and Extent of Contamination

In 1985, the USAF conducted initial site investigations at Landfill 2, which is composed of three subunits: Landfills 2a, 2b, and 2c. Follow-up investigations began in 1994 and are ongoing. Surface soil was most recently sampled in 1995 and analyzed for SVOCs, pesticides, PCBs, metals, and anions. Surface water and sediment from the unnamed stream were also sampled at this time. Surface water and sediment samples were analyzed for VOCs, SVOCs, pesticides, PCBs, dioxins, total metals, and anions. Surface water samples were also analyzed for ethylene glycol. Arsenic in surface soil; TCE, arsenic, lead, and manganese in surface water; and arsenic and lead in sediment were detected above CVs (USGS, 1995c). A TCE plume in groundwater adjacent to the stream has also been identified; TCE concentrations in this plume are as high as 100 ppb (F.E. Warren, 1998f). Although residents are not directly exposed to groundwater, groundwater may be discharging into the stream and contributing to the TCE concentrations detected in surface water. Based on these sampling results, removal actions, which include partial or total excavation of waste, were completed at Landfill 2c and are scheduled to begin at Landfills 2a and 2b in April 2000 (Springer, 1999).

The USAF conducted initial investigations at Landfill 3 in 1987. Surface soil was most recently sampled in 1995 and analyzed for SVOCs, pesticides, PCBs, metals, and anions. Only arsenic (2.3 ppm) was detected above its CV. Additional investigations at Landfill 3 are scheduled to begin in 1999 and construction of a landfill cap is scheduled to begin in April 2001 (USGS, 1995d; F.E. Warren, 1998d). Arsenic is a naturally occurring component of soil. The USAF conducted investigations to identify naturally occurring arsenic concentrations versus arsenic that may have been released by base activities. This investigation found that the average arsenic concentration in soil is 2.3 ppm, but can be as high as 5.1 ppm. A regional study of naturally occurring arsenic, conducted for USGS, found the that mean arsenic concentrations in soil was 5.5 ppm (USGS, 1996b; Shacklette and Boerngen, 1984). Therefore, arsenic concentrations detected in surface soil at Landfills 2 and 3 were within the range of naturally occurring arsenic.

Table 6 provides a summary of the contaminants detected above CVs in surface soil, surface water, and sediment, the maximum detected concentrations, and the associated CVs and MCLs.

Evaluation of Potential Public Health Hazards

Arsenic in surface soil; TCE, arsenic, lead, and manganese in surface water; and arsenic and lead in sediment were detected above CVs during investigations of Landfills 2 and 3. Residents in the nearby on-base housing units may be exposed to these contaminants during recreational use of the landfills.

To evaluate whether health hazards are associated with exposures to contaminants in surface soil, surface water, and sediment at Landfills 2 and 3, ATSDR estimated the potential doses for residents (adults and children). To estimate doses, ATSDR used very conservative assumptions that overestimate the levels of actual exposure. These assumptions, ATSDR's methods, and the estimated doses are further described in Appendix B. Although low levels of contamination were detected in samples collected from Landfills 2 and 3, in no case were these levels found to be high enough to present a reasonable likelihood for harmful exposures to have occurred. ATSDR, therefore, concludes that past, current, and potential future exposures to contaminants in site media at Landfills 2 and 3 pose no apparent public health hazards. This conclusion is based on ATSDR's exposure evaluation and the following information:

  • Sampling detected contaminants above CVs in only a small portion of the total samples collected for each media. However, in evaluating potential health hazards, ATSDR assumed that residents were exposed to the maximum detected contaminant concentration over the entire exposure period, which is unlikely to occur.
  • ATSDR used extremely conservative assumptions about how often and how long a resident is exposed to a chemical. Residents were assumed to use the landfills and unnamed stream for recreation 5 days per week for 26 weeks each year over the entire exposure period of 6 years. The average time military personnel and their families live in on-base housing, however, is only 3 years. Actual exposures are expected to be less frequent and over a shorter duration than assumed by ATSDR.
  • To prevent current and future exposures, removal actions, which include partial or total excavation of waste, were completed at Landfill 2c and are scheduled to begin at Landfills 2a and 2b in April 2000. The USAF is scheduled to conduct additional investigations at Landfill 3 in 1999 and begin construction of a landfill cap in April 2001.

COMMUNITY HEALTH CONCERNS

ATSDR identified the following community health concerns through meetings, contact with officials, and review of site documents, including Records of Decision and the Community Relations Plan prepared by the USAF in April 1998:

  • Residents report a high number of neurological disorders in the Western Hills neighborhood. Could F.E. Warren activities have contributed to these cases?

    The Western Hills neighborhood was constructed in the late 1960s and early 1970s along the northeastern base boundary. Residences in this neighborhood are connected to the Cheyenne municipal water supply, therefore, residents are not exposed to groundwater contamination identified at F.E. Warren. In addition, groundwater contamination at F.E. Warren is located in the southern portion of the base; no groundwater contamination has been identified proximate to Western Hills.

    Arsenic was detected above CVs 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. Investigations at the active borrow area did not detect any contaminants above CVs, however, the method detection limits for two PAHs and arsenic were above associated CVs. PAHs and arsenic are not typically associated with past site uses. Investigations of potential future borrow areas detected only arsenic above its CV in surface soil, but within the range of naturally occurring concentrations found at the base (OHM, 1997a; F.E. Warren, 1999b)

    A security fence and active security patrols prevent trespassers from accessing the base. Therefore, Western Hills residents are not exposed to contaminants in surface soil through direct contact.

    Surface soil contaminants may migrate beyond base boundaries through erosion and transport along Dry Creek, an intermittent stream that flows from the base through Western Hills. However, contaminant transport in stream sediment is expected to be minimal. Contaminants found in the open burn, open detonation area must be transported approximately 0.25 miles overland before entering Dry Creek. Dry Creek then flows approximately 1.5 miles before entering the Western Hills neighborhood. In addition, Cheyenne is located in a semi-arid region and average annual rainfall is only 14 inches (USGS, 1991a). Therefore, the precipitation necessary to transport contaminants in soil is infrequent and not expected to carry significant amounts of soil to Dry Creek from throughout the northern portion of the base. Also, contact with Dry Creek for recreational purposes is expected to occur infrequently and over short durations.

    Soil may also be transported to Western Hills as windblown dust. ATSDR conducted an exposure evaluation for residents contacting dust though inhalation or incidental ingestion. This evaluation is discussed in detail in the Evaluation of Environmental Contamination and Potential Exposure Pathways section and Appendix B of this PHA. This evaluation did not identify any past, current, and future exposures to windblown dust that might result in adverse health effects.

  • F.E. Warren is scheduled to begin investigations in the northern portion of the base in 2002 and begin remedial actions in 2006. Is public health being compromised due to the extended investigation and remediation time frame?

    The first step in the IRP is to identify and prioritize areas of contamination that may pose a threat to public health and the environment. At F.E. Warren, this step was conducted through the base-wide and site-specific RIs. As a result of the RIs, the northern portion of the base was ranked as having the lowest potential for adversely affecting human health or the environment. This ranking was based on historical information about land use; no landfills or disposal areas were located in the northern portion of the base and only a small portion of this area was used for small guns and artillery training. In addition, preliminary investigations detected minimal contamination in soil and groundwater. Therefore, the northern portion of the base was scheduled for detailed investigation and remediation in 2002 and 2006, after areas with greater concern were addressed. In addition, ATSDR evaluated the potential for human exposure to contaminants detected in the northern portion of the base, as discussed above and in Appendix B, and did not identify any exposures that might result in adverse health effects.

  • 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.


ATSDR CHILD HEALTH INITIATIVE

ATSDR recognizes that infants and children may be more sensitive to exposures than adults in communities with contamination in water, soil, air, or food. This sensitivity is a result of a number of factors. They are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. Children are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children are also smaller, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care. Therefore, ATSDR is committed to evaluating their special interests at sites such as F.E. Warren, as part of the ATSDR Child Health Initiative.

ATSDR has attempted to identify populations of children in the vicinity of F.E. Warren. Seven schools are located within 1 mile of F.E. Warren (Wyoming State Home Page, 1999). Roughly 1980 children under the age of 6 years are estimated to live within 1 mile of F.E. Warren.

Like other people living or working at or in the vicinity of F.E. Warren, children may contact contaminated site media. As discussed in the Evaluation of Environmental Contamination and Potential Exposure Pathways and the Community Health Concerns sections of this PHA, past, current, and future exposures for children include contact with contaminants in soil transported from the northern portion of the base into the Western Hills neighborhood or contaminants in drinking water from private wells in the Nob Hill and Fair Acres neighborhoods. In addition, children living in on-base housing in the southern portion of the base may be exposed to contaminants in surface soil, surface water, and sediment during recreational activities at nearby Landfills 2 and 3.

To evaluate whether children may experience adverse health effects through these potential past, current, or future exposures to site contaminants, ATSDR estimated the potential doses for children. To estimate doses, ATSDR used very conservative assumptions that overestimate the levels of actual exposure. These assumptions, ATSDR's methods, and the estimated doses are further described in Appendix B. ATSDR concludes that exposure to site contamination does not pose unique health hazards for children. This conclusion is based on ATSDR's exposure evaluation and the following information:

  • Sampling detected contaminants above CVs in only a small portion of the total samples collected for each media. However, in evaluating potential health hazards, ATSDR assumed that children were exposed to the maximum detected contaminant concentration over the entire exposure period, which is unlikely to occur.
  • ATSDR used extremely conservative assumptions about how often and how long children are exposed to a chemical. Actual exposures are expected to be less frequent and over a shorter duration than assumed by ATSDR.
  • An evaluation of estimated exposure doses to ATSDR's minimal risk levels and the toxicology literature did not identify childhood doses that are likely to result in adverse health effects.
  • The USAF has completed or is conducting actions to prevent current and future exposures. The USAF implemented a dust suppression program to minimize dust migration to Western Hills. Nob Hill residents were connected to the Cheyenne municipal water supply. Fair Acres residents provide their own bottled water as a drinking water supply, however, TCE concentrations have decreased to below EPA's MCLs. WDEQ and local health officials continue to work with Fair Acres residents. The USAF completed a removal action at Landfill 2c, one of the three subunits of Landfill 2. Removal actions, which include partial or total excavation of wastes, are scheduled to be conducted at Landfills 2a and 2b in April 2000. At Landfill 3, the USAF is scheduled to conduct additional investigations in 1999 and begin construction of a landfill cap in April 2001.


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