PUBLIC HEALTH ASSESSMENT
HILL AIR FORCE BASE
HILL AIR FORCE BASE, DAVIS AND WEBER COUNTIES, UTAH
ENVIRONMENTAL CONTAMINATION, HUMAN EXPOSURE PATHWAYS, AND PUBLIC HEALTH IMPLICATIONS (CONT.)
Several residential homes in Sunset, Clinton, Roy, Layton, Riverdale, and South Weber sit above groundwater plumes that have migrated from Hill AFB source areas (Figure 2). Additionally, one elementary school, Fremont Elementary in Sunset, overlies a groundwater contamination plume. Indoor air monitoring of potentially affected buildings showed VOC contaminants were present in the air inside certain homes, but at levels below standard references doses (such as EPA's reference dose, LOAELs, or NOAELs). ATSDR also confirmed these findings with conservative air modeling techniques because of the limited air sampling in these communities.
In the following sections, we present our evaluation of those communities by location. Communities that have been categorized together are exposed to the same contaminated groundwater plumes. They are grouped as follows:
Communities of Sunset and Clinton
Summary
From our visits, discussions with base personnel, and information review, ATSDR identified three ways people living in Sunset and Clinton can come in contact with environmental contaminants originating from Hill AFB: groundwater contamination off-gassing into indoor air, contact with contaminated springs or field drains, and eating crops irrigated with contaminated groundwater.
Background
Sunset, with a land area of 1.5 square miles, is west of Hill AFB. Clinton, with a land area of 5.5 square miles, is also west of Sunset. During a preliminary assessment in the 1980s, the USAF identified two areas, the U.S. Army Tooele Army Rail Shop (TARS) and Bamberger Pond, as potential sources of groundwater contamination affecting the communities of Sunset and Clinton (see Tables 2 and 18). From 1986 and lasting until 1994, the USAF investigated groundwater and indoor air in these areas (Radian 1995a). In 2000, investigations at Bamberger Pond were discontinued because it was concluded that this pond was not a source of contamination for the community of Sunset (Montgomery Watson Harza 2001b).
New information gathered in 1998 and 1999, however, suggested that additional groundwater contaminant sources are present in Zone 16, which includes a former missile testing facility, to the east of the TARS area near the communities of Sunset and Clinton (Montgomery Watson Harza 1998). Since then, a third area of soil and groundwater contamination was identified in 2000 in the city of Roy. More investigation in 2001 and 2002 identified an area north and west of Zone 16 that apparently received unknown quantities of waste. This site has been designated the Aspen Avenue Disposal Site and appears to be the source of groundwater contamination in Roy. The city of Roy is discussed in further detail in the next section of this Public Health Assessment (PHA). As of late 2002, the USAF has determined that groundwater plumes from Operable Units (OU) 5 and 10 are impacting Sunset and Clinton.
In 1997, the USAF implemented two cleanup measures in the TARS plume to cleanup and contain groundwater contamination. These two measures included installation of an aeration curtain that is designed to keep additional contamination from entering Sunset city, and the installation of a groundwater extraction system designed to remove some of the more concentrated portion of the plume (Montgomery Watson Harza 2001b). A third cleanup action is planned to be installed at the Clinton/Sunset boundary in Fall 2002. This system is designed to stop the flux of contamination into Clinton city. These measures help to diminish the further migration of contamination and to prevent degradation of groundwater quality from the uncontrolled movement of the plumes.
Sunset
and Clinton Sampling
The USAF began soil and groundwater sampling in Sunset in 1987 to determine the type and extent of contamination. Monitoring well installation for groundwater sampling coincided with the start of the remedial investigation in 1992. These monitoring wells were throughout the western portion of Hill AFB and in numerous locations in Sunset. Groundwater wells were sampled from 1992 until the mid-1990s to determine the size and concentration of the groundwater plumes. Between 1998 and 1999, inspections performed as part of the OU-9 North Area investigation detected VOCs in the groundwater near the Zone 16 area (Montgomery Watson 1998). The Zone 16 area contamination is predominantly in the cities of Sunset and Clinton. This contamination was thought to have also spread into the city of Roy. As a result, the remedial investigation was expanded in 1998. As RI work continued in late 1999, a third groundwater plume was designated as OU12. Monitoring well installation and sampling in Roy is ongoing (Montgomery Watson Harza 2002). (Please see next section in the PHA for more information on contamination and sampling in Roy).
Contamination in the soil has spread to the shallow groundwater aquifer.
Results
of the groundwater and soil sampling have identified two groundwater contamination plumes
resulting from leaks and spills at the base rail shop and a missile testing facility upgradient from
the communities of Sunset and Clinton (Figure 2). These contaminants have spread into these
western communities from the source areas near the western boundary of Hill AFB.
Furthermore, groundwater flow in this area of Hill AFB has allowed the migration of
contaminants into the communities of Sunset and Clinton.
The most predominant VOCs detected in groundwater in the cities of Sunset and Clinton are trichloroethene (TCE) (up to 870 ppb in Sunset and 120 ppb in Clinton), 1,1,1-trichloroethane (TCA) (up to 560 ppb in Sunset), tetrachloroethene (PCE) (up to 1,190 ppb in Clinton, ND in Sunset), cis-1,2-dichloroethene (cis-1,2-DCE) (up to 185 ppb in Sunset, ND in Clinton), 1,1-dichloroethene (1,1-DCE) (up to 27 ppb in Sunset), and carbon tetrachloride (up to 50 ppb in Clinton and 16 ppb in Sunset). The PCE found in Clinton cannot be tracked back to Hill AFB.
In Sunset and Clinton, carbon tetrachloride has only been detected in the northern and western portions of the Zone 16 plume and at the Sunset/Clinton border. Vinyl chloride (up to 56 ppb) and chloroform were detected sporadically and in limited areas. Both vinyl chloride and chloroform are breakdown products of other VOCs. Chloroform results from the breakdown of carbon tetrachloride, and vinyl chloride results from the breakdown of TCE. Chloroform is also formed as a result of chlorination of drinking water. In Sunset, there is no residential water and most irrigation to lawns and gardens is done with chlorinated water. Chloroform, with a maximum detected concentration of 45 ppb, does not appear to be co-located with carbon tetrachloride (Montgomery Watson Harza 2001b). As a result, the USAF believes that the chloroform found in Sunset and Clinton is from the chlorination of drinking water.
No contamination has been detected in the deeper aquifer that supplies drinking water to people in these communities. It is unlikely that high levels of contamination would reach the deeper aquifer because impermeable clay layers more than 200 to 300 feet thick separate the shallow aquifer from the deeper aquifers, greatly impeding groundwater flow between the two aquifer systems. Both Weber and Davis Counties routinely monitor drinking water for compliance with the Safe Drinking Water Act.
Between 1993 and 1994, and again between 2000 and 2002, the USAF sampled indoor air to determine whether and to what extent the groundwater plumes had affected air quality of homes and two schools in Sunset and Clinton. Thirty residences, the Sunset Elementary School, and the Fremont Elementary School were monitored. The USAF chose these buildings primarily because of their location directly above the groundwater plumes. The indoor air quality was monitored at various times of the year to assess potential differences in VOC levels due to seasonal weather and living conditions (open or closed doors/windows, use of air conditioning or heating systems). The USAF also sampled the air in basements because they were more likely to contain the highest concentrations of VOCs because of their proximity to the water table and limited air flow (Radian 1995a). ATSDR confirmed the findings with air modeling techniques. The USAF again conducted indoor air sampling in Sunset and Clinton from 2000-2001 as part of the Baseline Risk Assessment (Montgomery Watson Harza 2001b).
The same contaminants found in groundwater have also been detected in the surface water. Surface water in Sunset and Clinton was sampled by the Air Force from 1987 to 1994 and from 1998 to 2002 (Radian 1995a). The most common contaminants found were VOCs.
Indoor Air Exposures for Residents of Sunset and Clinton
Sunset
There are more than 1,800 homes in Sunset, of
which approximately 470 appear to be above the
groundwater plume (Figure 2). Of these, the USAF
sampled indoor air at thirty residences and two
elementary schools. As in the Patriot Hills
Housing area, the choice of indoor air sampling
locations was based on the location of the
groundwater plumes and the contaminant
concentrations beneath the homes. Indoor air
sampling in the TARS plume occurred both before
and after cleanup measures were put in place. We
believe that the number and location of homes
sampled in Sunset are sufficient to be
representative of the highest levels that may have
been in homes above the groundwater plume.
Sampling data in homes sampled in 1993 and 1994
where VOCs were detected and then sampled
again in 2002 indicate that VOC concentrations
decreased below detection limits between
sampling times. The decreasing indoor air
concentrations indicate that near water table
concentrations may also be decreasing and may be
attributed to remediation efforts conducted in this
area.
Highest Concentrations Detected
In 1993 and 1994, four chemicals that were in the TARS groundwater contaminant plume were detected in indoor air samples from homes in Sunset and in samples from Sunset Elementary school. They included TCE, which was detected in all 11 homes tested and in Sunset Elementary (up to 2.95 ppbv); TCA, which was detected in all 11 homes and in Sunset Elementary (up to 7.95 ppbv); chloroform, which was detected in all 11 homes and in Sunset Elementary (up to 1.1 ppbv); and vinyl chloride, which was only detected in one home (up to 1.8 ppbv). Contaminant concentrations were typically greater in these homes during December and March sampling events and may be attributed to the houses being closed up during the winter months. Three of the homes sampled in 1993 and 1994 were sampled again in 2002 when TCE, TCA, and vinyl chloride were not detected. However, in 2 of 19 additional homes sampled in Sunset, TCA was detected at levels up to 7.8 ppb. Samples were also collected at Fremont Elementary, which overlies the OU5 groundwater plume. TCA, TCE, vinyl chloride, and chloroform were not detected at Fremont Elementary. Low levels of BTEX compounds were found at Fremont Elementary. BTEX compounds were not detected in the groundwater plume underlying the school. Therefore, the source of BTEX in the school is not believed to be related to Hill AFB.
The ranges of levels of VOCs detected in the homes (from all sources including the subsurface vapor intrusion from contaminants in the groundwater) were compared with levels commonly detected in homes. TCE, which ranged from non-detectable to 2.95 ppbv, slightly exceeded commonly detected levels, although, was far below levels that are known to cause adverse health effects. TCA, which ranged from ND to 7.95 ppbv, was far below commonly detected levels. Chloroform, which ranged from ND to 1.1 ppbv, was slightly below commonly detected levels. We did not find a commonly detected level of vinyl chloride for comparison purposes.
Exposure Evaluation
ATSDR conservatively assumed that an adult was exposed to indoor air contaminants constantly for 24 hours a day, 365 days per year over a 30-year period. These assumptions create a very conservative estimate of exposure, most likely higher than an exposure dose for an average individual in the community. Furthermore, ATSDR assumed that residents living in the housing units were exposed to the most contaminated air; therefore, ATSDR used the highest (or maximum) measured concentrations of contaminants in indoor air. This also is a conservative assumption since we would not expect people to be exposed to the highest concentration all the time. Together, these conservative estimates allow ATSDR to safely evaluate the likelihood, if any, that indoor air contaminants in the home could cause harm to residents. Indoor air sampling measures the level of contaminants in the indoor air in that particular residence. It measures the contribution of all sources of VOCs in the home (paint, cleaners, glues, etc.). The sampling cannot determine the portion of contamination that is a result of the groundwater contamination plume underlying the home.
TCE, vinyl chloride, chloroform, and benzene are each classified as carcinogens by the EPA. The estimated excess lifetime cancer risk for these chemicals are below levels likely to result in adverse health effects. As a result, ATSDR concludes that no adverse health effects should result from exposure to these chemicals sampled in indoor air in Sunset.
The maximum exposure dose for TCA found in indoor air in homes sampled in Sunset was more than 20 times lower than its EPA reference dose (Table 4). The maximum exposure dose of toluene found in Fremont Elementary is far lower than its reference dose. The maximum concentration of xylenes detected at the elementary school is several hundred times lower than the EPA's RBC. (See definition of health comparison values and discussion on choice of values on page 20 of the on-base section of this document.) Adverse health effects should not result from exposure to this level of contamination in homes. For a more detailed analysis of the exposure to indoor air in Sunset, please see Table 21 in the Tables section at the end of this document.
Table 4. Sunset In-Home Indoor Air Measurements
| Compound | Maximum Concentration (ppbv) | Common National (ppbv) | Risk (unitless)/Dose (mg/kg/day) | Comparison Value (units) | Source |
| 1993 and 1994 | |||||
| Carcinogens | |||||
| TCE | 2.95 | 1.3 | 1.16E-5 | - | - |
| Chloroform | 1.1 | 8.4 | 5.33E-5 | - | - |
| Vinyl chloride | 1.8 | N/A | 1.69E-5 | - | - |
| Noncarcingen | |||||
| TCA | 7.95 | 48.9 | 0.0124 | 0.63 mg/kg/day | EPA Reference Dose |
| 2002 | |||||
| Carcinogens | |||||
| Benzene | 1.3 | 1.4-4.7 | 5.16E-05 | - | - |
| Noncarcinogen | |||||
| TCA | 7.8 | 48.9 | 0.0122 | 0.63 mg/kg/day | EPA Reference Dose |
| Toluene | 3.3 | 8.4 | 0.0100 | 0.1140 mg/kg/day | EPA Reference Dose |
| Xylenes | 1.3 | 2.07-8.3 | - | 560 ppbv | EPA RBC |
Clinton
There are more than 3,600 homes in Clinton. Approximately 320 appear to be above the groundwater plumes (Figure 2). During 2000 and 2001 indoor air sampling was performed at 7 homes in Clinton.
Highest Concentrations Detected
During 2000 and 2001, two contaminants were detected in indoor air samples from homes in Clinton. TCA, which was detected in one of 7 homes tested, was found at a maximum of 1.1 ppbv. Chloroform, which was detected in one of 7 homes tested was found at a maximum of 1.5 ppbv.
The ranges of VOCs detected in the homes (from all sources including the subsurface vapor intrusion from contaminants in the groundwater) were compared with levels commonly detected in homes. TCA, which ranged from ND to 1.1 ppbv, was far below commonly detected levels. Chloroform, which ranged from ND to 1.5 ppbv, was slightly below commonly detected levels.
Exposure Evaluation
Chloroform is the only carcinogen detected in Clinton during indoor air sampling. The theoretical estimated lifetime cancer risk for chloroform is below levels likely to result in adverse health effects. As a result, ATSDR concludes that no adverse health effects should result from exposure to chloroform in Clinton. The maximum exposure dose for TCA found in indoor air in homes in Clinton was more than 20 times lower than its EPA reference doses (Table 5). Adverse health effects should not result from exposure to this level of contamination in homes. For a more detailed analysis of the exposure to indoor air in Clinton, please see Table 22 in the Tables section at the end of this document.
Table 5. Clinton In-Home Indoor Air Measurements (2000 and 2001)
| Compound | Maximum Concentration (ppb) | Common National (ppb) | Risk (unitless)/Dose (mg/kg/day) | Comparison Value (units) | Source |
| Carcinogen | |||||
| Chloroform | 1.5 | 8.4 | 7.26E-05 | - | - |
| Noncarcinogen | |||||
| TCA | 1.1 | 48.9 | 0.00171 | 0.6300 mg/kg/day | EPA Reference Dose |
Indoor Air Modeling for Sunset and Clinton - Past Exposures
Because it was unclear whether the indoor air sampling was conducted when the groundwater contamination under the homes was at its worst, ATSDR used a model to estimate whether intrusion at the highest levels of groundwater contamination would have presented a health hazard. TCE was the predominant contaminant detected in the groundwater plumes in Sunset and Clinton. The maximum concentration of TCE detected, 870 ppb (in Sunset) and 120 ppb (in Clinton), were entered into the model. The model predicted indoor air concentrations of 59 ppb and 43 ppb, respectively. An exposure dose was calculated using these concentrations and the assumptions listed above. The resulting exposure doses were more than a hundred times lower than the LOAEL (ATSDR 1997b).
The maximum concentration of chloroform detected, 45 ppb (in Sunset), was entered into the model. The model predicted an indoor air concentration of 33 ppb, which is several thousand times lower than the NOAEL for chloroform (ATSDR 1997d). The maximum concentration of PCE detected, 1,190 ppb (in Clinton), was entered into the model. PCE was not detected in Sunset. The model predicted an indoor air concentration of 59 ppb, which is several times lower than the LOAEL for PCE (ATSDR 1997e). The maximum concentration of 1,1-DCE detected, 27 ppb (in Sunset), was entered into the model. 1,1-DCE was not detected in Clinton. The model predicted an indoor air concentration of 3 ppb, which is several thousand times lower than the NOAEL for 1,1-DCE (ATSDR 1994b). The maximum concentration of carbon tetrachloride detected, 16 ppb (in Sunset) and 50 ppb (in Clinton), were entered into the model. The model predicted indoor air concentrations of 1 ppb and 3 ppb, respectively, both several thousand times lower than the NOAEL for carbon tetrachloride (ATSDR 1994c). The maximum concentration of vinyl chloride detected, 56 ppb (in Sunset), was entered into the model. Vinyl chloride was not detected in Clinton. The model predicted an indoor air concentration of 6 ppb, which is several thousand times lower than the LOAEL for vinyl chloride (ATSDR 1997c). Once again, ATSDR concludes that all of the chemicals detected were at levels far below those that are known to cause adverse health effects.
Surface Water Exposures for Sunset and Clinton
The only surface waters in the communities of Sunset and Clinton are the Davis-Weber Canal, a manmade, concrete-lined canal used only for irrigation purposes, and several seeps, springs, and field drains. Field drains have been installed by farmers through Sunset and Clinton in order to remove excess shallow groundwater and on occasion have used this water as an irrigation or stock watering supply. Unused water discharges to storm drains, which discharge to the 2050 North Canal, which flows to the Great Salt Lake. The Air Force sampled surface water from the canal and seeps and springs in Sunset and Clinton from 1990 to 1997 and again in 1999 and 2000 to determine possible contamination (Radian 1995a; Montgomery Watson Harza 2002). No contamination was found in the Davis-Weber Canal. The maximum concentration of TCE (18.5 ppb) and chloroform (5.2 ppb) were found in the Meadows Park Spring on the border of Sunset and Clinton in 1994. Since 1996, TCE concentrations have been less than 5 ppb. The maximum concentration of PCE (0.5 ppb) and TCA (33 ppb) were detected in a spring in Sunset (Radian 1995a).
People can come into contact with surface water in Sunset and Clinton in two ways: through accidental ingestion of water from springs and through dermal contact of the spring water. Exposure doses were calculated for each of these chemicals for both accidental ingestion and dermal contact.
Dermal Contact
Table 6 below presents the concentration, dermal exposure dose, and dermal comparison value for the VOCs detected in surface water in Sunset and Clinton. The maximum dermal exposure dose for TCA is five times lower than its adjusted EPA reference doses. The maximum dermal exposure dose for chloroform was 700 times higher than the lowest level at which adverse health effects are first seen (ATSDR 1997d). To evaluate the potential for adverse health effects of TCE and PCE, ATSDR compared these dermal doses to the NOAELs. The NOAEL for TCE is 1,000 mg/kg/day, over 5,000 times higher than the maximum dermal exposure dose calculated for TCE in the springs in Sunset and Clinton (ATSDR 1997b). The NOAEL for PCE is 14 mg/kg/day, over 2,000 times higher than the maximum dermal exposure dose calculated for PCE in the springs in Sunset and Clinton (ATSDR 1997e). Using this information, ATSDR concluded that the maximum value of VOCs detected in springs in Sunset and Clinton is much lower than the highest concentration at which adverse health effects are first seen. No adverse health effects are expected for humans exposed to these VOC levels through dermal contact.
Table 6. Sunset and Clinton Surface Water Measurements-Dermal Comparison (1990 to 2002)
| Compound | Maximum Concentration (ppm) | Dose (mg/kg/day) | Comparison Value (mg/kg/day) | Source |
| TCE | 0.0184 | 0.082E-05 | 3E-05 | Adjusted EPA Reference Dose |
| TCA | 0.033 | 0.036E-05 | 15000E-05 | Adjusted EPA Reference Dose |
| PCE | 0.0005 | 0.0007E-05 | 2E-05 | Adjusted EPA Reference Dose |
| Chloroform | 0.0052 | 0.60E-05 | 600E-05 | Adjusted EPA Reference Dose |
Ingestion of Surface Water
Table 7 below presents the concentration, ingestion exposure dose, and ingestion comparison value for the VOCs detected in surface water in Sunset and Clinton. The maximum oral exposure doses for accidental water ingestion for TCA, PCE, and chloroform were more than ten times lower than their EPA reference doses. The maximum exposure doses for TCE is over 1,000 times lower than the highest levels at which adverse health effects have been seen for TCE (ATSDR 1997b). Using this information, ATSDR concluded that the maximum value of VOCs detected in springs in Sunset and Clinton is much lower than the level at which adverse health effects have been seen. No adverse health effects are expected for humans exposed to these levels of VOCs through accidental ingestion of contaminated surface water in Sunset or Clinton.
Table 7. Sunset and Clinton Surface Water Measurements-Ingestion (1987 to 1994)
| Compound | Maximum Concentration (ppb) | Dose (mg/kg/day) | Comparison Value (mg/kg/day) | Source |
| TCE | 18.4 | 0.082E-05 | 3E-05 | EPA Oral Reference Dose |
| TCA | 33 | 0.036E-05 | 15000E-05 | EPA Oral Reference Dose |
| PCE | 0.5 | 0.0007E-05 | 2E-05 | EPA Oral Reference Dose |
| Chloroform | 5.2 | 0.60E-05 | 600E-05 | EPA Oral Reference Dose |
Crops
Residents of Sunset and Clinton occasionally use water from private wells and irrigation canals (the Weber-Davis Canal) to irrigate backyard gardens, including fruits and vegetables (Kirk 1994). Because these wells draw from both the shallow groundwater and the surface water (in the form of canals) near or within documented plumes and because these plants have roots tapped into the shallow groundwater, from August-November 2001, the USAF tested fruit in these communities for TCE. Locations were selected primarily based on landowner requests. Other samples of fresh fruit, vegetables, fresh alfalfa, and hay were collected and tested, as was homegrown canned fruit. Hill AFB is continuing to study TCE uptake into plant tissues, both in the laboratory and in the field.
Using newly developed techniques that allow for the detection of chemicals
in crops at much lower levels than what had previously been possible, scientists
at Utah State University have been able to detect TCE in fruit harvested from
trees in and near areas of groundwater contamination in Sunset and Clinton.
TCE was found in a number of the fruit samples at concentrations ranging from
the method detection limit of 1 ppb to 18 ppb (wet weight). The TCE levels are
similar to levels found in other processed foods (Doucette et al. 2002). Some
fruits, such as apples and plums, showed TCE when green, but showed no TCE when
ripe. The sampling also indicated that TCE was not present in canned fruit samples
or in fruit stored for more than a couple of weeks in boxes or baskets. TCE
also was not present in vegetables, possibly due to their shallow root systems
(Doucette et al. 2002).
The exposure doses for TCE found in crops in Sunset and Clinton were half the EPA reference dose. Adverse health effects should not result from exposure to this level of contamination in crops in these communities.
Summary
From our visits, discussions with base personnel, and information reviews, ATSDR identified one way people living in Roy can come in contact with environmental contaminants from Hill AFB: groundwater contamination off-gassing into indoor air.
Background
Roy, with a land area of 7.6 square miles, is west of Hill AFB (see Tables 2 and 18). Contamination in Roy was not detected until 2000. Information gathered in 1998 and 1999 from the Sunset and Clinton RIs suggested that additional groundwater contaminant sources are present in the Zone 16 Area. Since then, in 2000, a third area of soil and groundwater contamination was identified in 2000 in the city of Roy. More investigation in 2001 and 2002 identified an area north and west of Zone 16 that apparently received unknown quantities of waste. This site has been designated the Aspen Avenue Disposal Site and appears to be the source of groundwater contamination in Roy. As of late 2002, the USAF has determined that groundwater plumes from Operable Unit (OU) 12 are impacting Roy.
In 2002, the USAF installed vapor extraction systems in homes in Roy with higher detected levels of TCE. In 2003, the USAF is planning to install a remedial action to cut off the source of contaminated groundwater.
Roy Sampling
Monitoring well installation and sampling in Roy began in 2000 and continued through 2002. Groundwater contamination in Roy was first detected in 2000. In 2002, after a homeowner who lived in a home above the groundwater contamination plume requested the indoor air of the home be sampled, the USAF sampled the home.
The most predominant VOC detected in the city of Roy is trichloroethene (TCE) (up to 1,300 ppb). Contamination in the soil has spread to the shallow groundwater aquifer. Results of groundwater and soil sampling have identified one groundwater contamination plume resulting from leaking barrels at the Aspen Avenue Disposal Site. These contaminants have spread into these western communities because the source areas are near the western boundary of Hill AFB.
No contamination has been detected in the deeper aquifer, which supplies drinking water to people in these communities. It is unlikely that high levels of contamination would reach the deeper aquifer because impermeable clay layers separate the shallow aquifer from the deeper aquifers, preventing groundwater from flowing between the two aquifer systems. Both Weber and Davis Counties routinely monitor drinking water for contaminants under the Safe Drinking Water Act.
Indoor Air Exposures for Residents of Roy
Roy
Roy has more than 11,000 homes, of which approximately 320 appear to be above the groundwater plume (Figure 2). In 2002, the USAF sampled one home and took confirmation samples two months later. The home is within the area of the groundwater contamination plume. Since the first TCE detection in Roy, Hill AFB has consequently sampled more than 80 homes in this area. TCE was detected in 7 of these homes. Groundwater has not yet been remediated in Roy, but inplementing a remedial action to cut off the source is planned to be completed and operational early in 2003 (ATSDR 2002a).
Highest Concentrations Detected
The sample taken in 2002 at the first Roy home detected TCE at a maximum of 13 ppb. Two months later TCE was detected at a lower level (2 to 3 ppb). Subsequent sampling has detected TCE at a maximum of 16 ppb.
Exposure Evaluation
TCE is a suspected carcinogen. The estimated excess lifetime cancer risk for exposure to this level of TCE in homes is below levels likely to result in adverse health effects. However, to reduce the levels in the home, the USAF is working with the homeowner to immediately remedy the problem. For a more detailed analysis of the exposure evaluation process, please see Table 22 in the Tables section, at the end of this document.
Because a number of homes in the Roy area are above the same groundwater plume, they may have chemical vapors in their air as well. USAF is currently planning to sample air at 30 homes in the immediate area. ATSDR will review these data to determine whether VOCs exist in homes in Roy at levels that could be harmful to residents.
Table 8. Roy In-Home Indoor Air Measurements (2002)
| Compound | Maximum Concentration (ppb) | Common National (ppb) | Risk (unitless) |
| TCE | 16 | 1.4 - 4.7 | 6.34E-05 |
Indoor Air Modeling for Roy - Past Exposures
Because it was unclear whether the indoor air sampling was conducted when the groundwater contamination under the homes was at its worst, ATSDR used a model to estimate whether intrusion at the highest levels of groundwater contamination would have presented a health hazard. TCE was the predominant contaminant detected in the groundwater plume in Roy. The maximum concentration of TCE detected, 1,300 ppb, was entered into the model. The model predicted an indoor air concentration of 87 ppb, respectively. An exposure dose was calculated using these concentrations and the assumptions listed above. The resulting exposure doses were over a hundred times lower than the LOAEL (ATSDR 1997b). Once again, ATSDR concludes that all of the chemicals detected were at levels far below those that are known to cause adverse health effects.
Surface Water Exposures for Roy
The only surface waters in the community of Roy are several field drains. No springs or seeps discharge into Roy. Field drains have been installed by farmers through Roy in order to remove excess shallow groundwater and recirculate it. No contamination was found in the field drains in Roy.
Communities of Layton and Clearfield
Summary
From our visits, discussions with base personnel, and information reviews, ATSDR identified two ways people living in Layton or Clearfield can come in contact with environmental contaminants originating from Hill AFB: groundwater contamination off-gassing into indoor air and contact with contaminated springs or field drains.
Background
Layton, with a land area of 20.7 square miles, is directly south of Hill AFB. Clearfield, with a land area of 7.7 square miles, is southwest of Hill AFB, adjacent to Layton. Contamination from former base operations and waste disposal practices has affected soil and groundwater in Layton and Clearfield. Areas that contributed to this contamination include Berman Pond, the Sodium Hydroxide Tank Site, the Refueling Vehicle Maintenance Facility (RVMF), and the Industrial Waste Treatment Plant. The full list of areas are catalogued in Table 2 and described in Table 18 of this document. Contamination in Layton and Clearfield is related to Operable Unit 8 on Hill AFB.
Several remedial measures instituted by the USAF have helped reduce further spread of contamination to Layton and Clearfield. These measures include covering both the Sodium Hydroxide Tank Site and Berman Pond with asphalt caps in the late 1990s to prevent contaminants from leaching into the underlying groundwater. The USAF has installed two groundwater extraction systems. One is located along the base boundary to stop additional contaminants from leaving the base, and the second, located off-base, is extracting groundwater under artesian conditions. Perched groundwater has also been removed from under the capped area at Berman Pond by a small extraction system (Montgomery Watson Harza 2001b).
Layton and Clearfield Sampling
Contamination in the soil at Hill AFB, resulting from use and disposal of chemicals, has spread to the shallow groundwater aquifer beneath the base. This groundwater contamination has migrated further south to the communities of Layton and Clearfield. The USAF began environmental sampling at Layton and Clearfield in 1983 to determine the type and extent of the contamination. Results of the groundwater and soil sampling have helped identify two groundwater contamination plumes in Layton and Clearfield (Figure 2) (HAFB 1997b). No contamination has been detected in the deeper aquifer, which is a source of drinking water for residents of Layton and Clearfield.
VOCs are the primary contaminants detected in the groundwater plumes beneath Layton and Clearfield. The off-base VOCs include TCE (up to 465 ppb), 1,2-DCA (up to 697 ppb), 1,1-DCE (up to 30,000 ppb), vinyl chloride (up to 11 ppb), chlorobenzene (up to 945 ppb), and PCE (up to 9.8 ppb) (Montgomery Watson Harza 2001b). Because the VOC plumes had migrated to areas of residential homes, the USAF conducted air sampling in 1997, 2000, and 2001 to determine if indoor air contamination had occurred because of the contaminated groundwater.
One VOC groundwater plume resulting from leaks and spills from the RVMF, Berman Pond, and Buildings 220 and 225 at Hill AFB has migrated south of Hill AFB, toward and beneath homes in Layton and the extreme eastern part of Clearfield. This plume is approximately 350 acres in Layton and Clearfield (Figure 2). The most toxic contaminants in this plume are TCE, vinyl chloride, 1,1-DCE, and 1,2-DCA. Because VOC vapors can seep into homes above pockets of groundwater contamination, the USAF performed indoor air monitoring in 1997, 2000, and 2001 to measure indoor air quality in select homes above the plumes in Layton. No indoor air sampling was conducted in Clearfield because there are no homes above groundwater contamination in that city.
Prior to indoor air sampling, the USAF conducted a survey of residences in the Layton area from July to November 1996 (Dan Jones and Associates, Inc. 1996) to identify homes affected by the groundwater plumes. Residential water rights' searches were recently performed in Clearfield. This search indicated that numerous private wells exist in this community. The USAF is in the process of identifying existing wells and determining the need for sampling and analysis of these private wells (ATSDR 2002a). Findings of the Layton survey identified nine residences within the bounds of the groundwater plume that had groundwater entering the basements. Groundwater samples were collected from six of the nine locations in June 1997 and analyzed for VOCs. The maximum concentration of TCE, chloroform, methylene chloride, 1,2,4-trimethylbenzene, p-xylenes, and o-xylene detected were 34 ppb, 0.41 ppb, 0.14 ppb, 0.15 ppb, 0.26 ppb, and 0.11 ppb, respectively. Following groundwater analysis, the two homes with levels of TCE above the federal drinking water standard (known as maximum contaminants level) were determined to be at risk for potential indoor air contamination.
In 1997, the USAF performed air sampling using evacuated stainless steel (SUMMA) canisters in the basements of these homes. SUMMA canisters were generally placed in areas where water is more likely to enter the home or in the largest room in the basement. The vacuum pressure canisters are set 3-5 feet off the floor and are empty of everything, including air, at the beginning of the test. When the canister valve is opened the negative pressure created by the vacuum inside sucks in air through the air intake. Canisters used by Hill AFB personnel had 24-hour regulator valves that allowed air to enter throughout a 24-hour period. Additional residential air sampling was performed as part of the remedial investigation in May of 2000 and May to July 2001.
Indoor Air Exposure for Residents of Layton and Clearfield
Layton
Layton has more than 19,000 homes within its city limits, of which less than 200 appear to be situated above the contaminated groundwater plume (Figure 2). Indoor air sampling locations were chosen based on the location of the groundwater plumes. The concentrations of VOCs detected in the 2000-2001 sampling are lower than the levels found in 1997, likely a result of remedial actions instituted by the USAF in the area of the groundwater plumes affecting Layton. These measures were begun at the same time the first sampling was performed and several years before the 2000-2001 indoor air sampling (Montgomery Watson Harza 2001b). Considering this, the earlier sampling round represents the highest detected levels (a worst case situation) for residents of these communities. Based on available base information, ATSDR believes that this decrease in groundwater concentrations will continue.
Highest Concentrations Detected
In 1997, the two homes determined to be at risk for potential indoor air contamination were sampled. Five VOCs (trichlorofluoromethane, acetone, benzene, toluene, and xylenes) were detected in the sample taken from one residence, and ten VOCs (trichlorofluoromethane, acetone, methylene chloride, benzene, TCE, toluene, xylenes, 4-ethyltoluene, 1,3,5-trimethylbenzene, and 1,2,4-trimethylbenzene) were detected at the other residence. The maximum concentrations of acetone, benzene, toluene, xylenes, and TCE detected were 11 ppb, 6 ppb, 14 ppb, 9.5 ppb, and 2.2 ppb, respectively. The 2000-2001 residential air sampling performed as part of the remedial investigation reported lower concentrations of contaminants than in the earlier 1997 sampling. The maximum concentration of TCE, vinyl chloride, chloroform, and 1,2-DCA detected in these residences was 0.32 ppb, 0.45 ppb, 6.3 ppb, and 0.12 ppb, respectively.
The maximum concentrations of TCE, benzene, toluene, and xylenes were slightly above commonly detected levels, though far below levels that are known to cause adverse health effects. The maximum concentration of chloroform detected was below commonly detected levels. We did not find a commonly detected level of acetone, 4-ethyltoluene, methylene chloride, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, trichlorofluoromethane, vinyl chloride, or 1,2-DCE for comparison purposes.
Exposure Evaluation
ATSDR conservatively assumed that an adult was exposed to the highest detected concentration of indoor air contaminants constantly for 24 hours a day, 365 days per year. These assumptions create a very conservative estimate of exposure, most likely higher than an exposure dose for an average individual in the community.
TCE, methylene chloride, benzene, 1,2-DCA, vinyl chloride, and chloroform were the only carcinogens detected in the indoor air in Layton. The theoretical estimated excess lifetime cancer risk for TCE, methylene chloride, benzene, 1,2-DCA, chloroform, and vinyl chloride are below levels likely to result in adverse health effects.
The maximum exposure dose for toluene found in indoor air in Layton homes in 1997 was half its EPA reference dose (Table 9). The maximum exposure dose for 4-ethyltoluene found in indoor air in Layton homes in 2000-2001 was ten times lower than its EPA reference doses. The maximum concentration of trichlorofluoromethane was more than 200 times lower than its EPA reference dose. The maximum concentrations of acetone and xylenes were compared to EPA Region III's RBCs. The RBC for acetone is more than14 times higher than its maximum detected concentration in 1997. The RBC for total xylenes is more than 100 times higher than its maximum detected concentration in 1997. 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene were both detected at levels below the testing reporting limits (i.e., safe levels). Adverse health effects are not expected for humans exposed to these levels of VOCs in their homes. A more detailed analysis can be found in Table 23 in the Tables section at the end of the document.
A majority of the VOCs in the indoor air were not detected in the groundwater samples taken from the residences. Therefore, it is reasonable to conclude that they originated from sources other than the groundwater (Montgomery Watson Harza 2001b). Trichlorofluoromethane is commonly associated with air conditioning systems and is used in some spray containers. Acetone is used in markers, paint thinners, and nail polish removers. Methylene chloride is commonly found in glues, cleaners, and paint strippers. BTEX, 4-ethyltoluene, 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene are commonly found in gasoline and petroleum products. The groundwater concentrations of the compounds that were detected in the air were very low, indicating that the groundwater may not be a source of contamination.
Table 9. Layton Housing Area In-Home Indoor Air Measurements (1997 and 2000-2001)
| Compound | Maximum Concentration (ppb) | Common National (ppb) | Risk (unitless)/Dose (mg/kg/day) | Comparison Value (units) |
Source |
| 1997 | |||||
| Carcinogens | |||||
| Benzene | 6 | 1.4 - 4.7 | 6.81E-05 | - | - |
| Methylene Chloride | 1.4 | N/A | 983E-05 | - | - |
| TCE | 2.2 | 1.3 | 8.69E-05 | - | - |
| Noncarcinogens | |||||
| Acetone | 11 | N/A | - | 155.8 ppb | EPA RBC |
| 4-Ethyltoluene | 2.3 | N/A | 140E-05 | 11400E-05 mg/kg/day | EPA Reference Dose |
| Toluene | 14 | 8.4 | 1510E-05 | 11400E-05 mg/kg/day | EPA Reference Dose |
| Trichlorofluoromethane | 0.44 | N/A | 70E-05 | 20000E-05 mg/kg/day | EPA Reference Dose |
| 1,2,4-Trimethylbenzene | 2.8 | N/A | - | - | Below Reporting Limits |
| 1,3,5-Trimethylbenzene | 0.73 | N/A | - | - | Below Reporting Limits |
| Xylenes | 9.5 | 2.07-8.3 | - | 560.4 ppb | EPA RBC |
| 2000-2001 | |||||
| Carcinogens | |||||
| TCE | 0.32 | 1.3 | 0.126E-05 | - | - |
| Vinyl chloride | 0.45 | N/A | 0.423E-05 | - | - |
| Chloroform | 6.3 | 8.4 | 30.5E-05 | - | - |
| 1,2-DCA | 0.12 | N/A | 0.541E-05 | - | - |
Clearfield
There are more than 8,300 homes in Clearfield. Previously, no homes were above the groundwater plumes (Figure 2). As a result, no indoor air sampling was performed in Clearfield. However, new remedial investigations performed in Clearfield as part of the OU-10 investigation of the 1200 area of Hill AFB has discovered off-base contamination beneath homes in Clearfield. The extent of the contamination has not yet been determined. To evaluate the quality of indoor air in this community, ATSDR used an indoor air model (see discussion below). This indoor air model only considers the groundwater beneath the home. It does not consider other sources of VOCs in the home, such as cleaning products.
Indoor Air Modeling for Layton and Clearfield-Past Exposures
It was unclear whether the indoor air sampling in Layton was conducted when the groundwater contamination under the homes was at its worst. Furthermore, indoor air sampling was not conducted in Clearfield. Therefore, ATSDR used a model to estimate whether intrusion of groundwater plumes in both Layton and Clearfield would have presented a health hazard.
TCE, 1,2-DCA, 1,1-DCE, vinyl chloride, and PCE were the only detected VOCs in the groundwater plumes beneath Layton that had corresponding information available for use in the model. Using the maximum groundwater concentration of TCE (700 ppb), 1,2-DCA (697 ppb), 1,1-DCE (30,000 ppb), vinyl chloride (11 ppb), and PCE (9.8 ppb) the model predicted corresponding indoor air concentrations of 46 ppb, 24 ppb, 3,420 ppb, 2 ppb, and 0.5 ppb, respectively. ATSDR then derived exposure doses using the estimated indoor air concentration and the assumptions listed above. The resulting exposure dose for TCE was more than 1,500 times lower than the lowest level of TCE determined to cause adverse health effects in laboratory animals (ATSDR 1997b). The resulting exposure dose for 1,2-DCA was more than 2,000 times lower than the highest level found not result in an adverse health effect in laboratory animals (ATSDR 1999). The resulting exposure dose for 1,1-DCE was hundreds of times lower than the highest level found not result in an adverse health effect in laboratory animals (ATSDR 1994b). The resulting exposure dose for vinyl chloride was thousands of times lower than the highest level found not result in an adverse health effect in laboratory animals (ATSDR 1997c). The resulting exposure dose for PCE was hundreds of times lower than the highest level found that did not result in adverse health effects in laboratory animals (ATSDR 1997e). ATSDR concluded that none of the estimated indoor air concentrations from groundwater off-gassing would be at levels that could result in adverse health effects for residents.
Surface Water Exposures in Layton and Clearfield
Surface water in the Layton area is comprised of the manmade Davis-Weber Canal, wells, springs, ponds, and field drains. Field drains have been installed by farmers through Layton in order to remove and recirculate excess shallow groundwater. Unused water is channeled into storm drains, which discharge to Kay's Creek, which flows into the Great Salt Lake. Environmental sampling of field drains between 1986 and 1998 detected several VOCs. In 1986, the maximum concentration of TCE (89 ppb) was found in a Layton field drain south of the eastern lobe of the groundwater plume. The maximum concentrations of benzene (3.5 ppb) and 1,2-DCA (3.6 ppb) were found in a Layton field drain west of the western lobe of the larger groundwater plume (James M. Montgomery 1991).
No contamination was found in the Davis-Weber Canal. There is a pond near 350 South 500 East in Clearfield. No sampling of surface water was performed at this pond.
People come into contact with surface water in Layton in two ways: through accidental ingestion of water from springs and through dermal contact of the surface water in the springs. Exposure doses were calculated for each of these chemicals for both accidental ingestion and dermal contact.
Dermal Contact
The maximum dermal exposure doses for TCE, benzene, and 1,2-DCA are three times lower than their EPA adjusted reference doses (Table 10). No adverse health effects should result from exposure to this level of contamination to VOCs in surface water in Layton.
Table 10. Layton Surface Water Measurements-Dermal (1986 to 1998)
| Compound | Maximum Concentration (ppm) | Dose (mg/kg/day) | Comparison Value (mg/kg/day) | Source |
| TCE | 0.0890 | 40E-05 | 100E-05 | Adjusted EPA Reference Dose |
| Benzene | 0.0035 | 0.732E-05 | 14000E-05 | Adjusted EPA Reference Dose |
| 1,2-DCA | 0.0036 | 0.0363E-05 | 500E-05 | Adjusted EPA Reference Dose |
Ingestion of Surface Water
The maximum exposure doses for water ingestion for TCE, 1,2-DCA, and benzene were ten times lower than their EPA oral reference doses (Table 11). No adverse health effects are expected for humans exposed to these levels of VOCs through accidental ingestion of surface water in Layton springs.
Table 11. Layton Surface Water Measurements-Ingestion (1986 to 1998)
| Compound | Maximum Concentration (ppb) | Dose (mg/kg/day) | Comparison Value (mg/kg/day) | Source |
| TCE | 89 | 30E-05 | 600E-05 | EPA Oral Reference Dose |
| Benzene | 3.5 | 1.09E-05 | 300E-05 | EPA Oral Reference Dose |
| 1,2-DCA | 3.6 | 1.12E-05 | 3000E-05 | EPA Oral Reference Dose |
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