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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.)

Off-Base Areas

Several residential homes in Sunset, Clinton, Roy, Layton, Riverdale, and South Weber sit abovegroundwater plumes that have migrated from Hill AFB source areas (Figure 2). Additionally,one elementary school, Fremont Elementary in Sunset, overlies a groundwater contaminationplume. Indoor air monitoring of potentially affected buildings showed VOC contaminants werepresent in the air inside certain homes, but at levels below standard references doses (such asEPA's reference dose, LOAELs, or NOAELs). ATSDR also confirmed these findings withconservative 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 contaminatedgroundwater plumes. They are grouped as follows:

  • Sunset and Clinton
  • Roy
  • Layton and Clearfield
  • Riverdale
  • South Weber

Communities of Sunset and Clinton

Summary

From our visits, discussions with base personnel, and information review, ATSDR identifiedthree ways people living in Sunset and Clinton can come in contact with environmentalcontaminants originating from Hill AFB: groundwater contamination off-gassing into indoorair, contact with contaminated springs or field drains, and eating crops irrigated withcontaminated groundwater.

  1. Adults and children living above contaminated groundwater in the off-base towns ofSunset and Clinton may have breathed VOC vapors from contaminants migrating into theair inside homes from shallow groundwater beneath the homes.

    • USAF conducted indoor air sampling in 1993, 1994, 2000, 2001, and early 2002in the communities of Sunset. ATSDR evaluated the results of the indoor airsampling and determined that because levels of VOCs were low, the exposureposed no apparent public health hazard from living in homes in thesecommunities in the past, current, or future.

  2. Adults and children living in Sunset and Clinton may have touched surface watercontaminants or accidentally ingested VOC contaminated surface water in springs inthese communities during outdoor activities.

    • USAF sampling in the late 1980s and early 1990s showed that contamination ispresent in springs in Sunset and Clinton. ATSDR evaluated the results of thesurface water sampling and determined that because levels are low, the humanexposure that occur at these springs, either through dermal contact or accidentalingestion, poses no apparent public health hazard.

  3. Adults and children may have ingested crops grown in Sunset and Clinton that have beenirrigated with VOC contaminated water.

    • USAF sampling of crops in these communities was performed in late 2001.ATSDR evaluated the results of the crop sampling and determined that becausecontaminant levels are low, past, current, and future exposures likely to occurfrom consuming crops grown in these communities pose no apparent publichealth hazard.

Background

Sunset, with a land area of 1.5 square miles, is west of Hill AFB. Clinton, with a land area of 5.5square miles, is also west of Sunset. During a preliminary assessment in the 1980s, the USAFidentified two areas, the U.S. Army Tooele Army Rail Shop (TARS) and Bamberger Pond, aspotential 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 groundwaterand indoor air in these areas (Radian 1995a). In 2000, investigations at Bamberger Pond werediscontinued because it was concluded that this pond was not a source of contamination for thecommunity of Sunset (Montgomery Watson Harza 2001b).

New information gathered in 1998 and 1999, however, suggested that additional groundwatercontaminant sources are present in Zone 16, which includes a former missile testing facility, tothe east of the TARS area near the communities of Sunset and Clinton (Montgomery WatsonHarza 1998). Since then, a third area of soil and groundwater contamination was identified in2000 in the city of Roy. More investigation in 2001 and 2002 identified an area north and westof Zone 16 that apparently received unknown quantities of waste. This site has been designatedthe Aspen Avenue Disposal Site and appears to be the source of groundwater contamination inRoy. The city of Roy is discussed in further detail in the next section of this Public HealthAssessment (PHA). As of late 2002, the USAF has determined that groundwater plumes fromOperable Units (OU) 5 and 10 are impacting Sunset and Clinton.

In 1997, the USAF implemented two cleanup measures in the TARS plume to cleanup andcontain groundwater contamination. These two measures included installation of an aerationcurtain that is designed to keep additional contamination from entering Sunset city, and theinstallation of a groundwater extraction system designed to remove some of the moreconcentrated portion of the plume (Montgomery Watson Harza 2001b). A third cleanup action isplanned to be installed at the Clinton/Sunsetboundary in Fall 2002. This system is designed tostop the flux of contamination into Clinton city.These measures help to diminish the furthermigration of contamination and to preventdegradation of groundwater quality from theuncontrolled movement of the plumes.

How VOCs were used at Hill AFB: VOCs detected in the groundwater in Sunset, Clinton, and Roy include carbon tetrachloride, trichloroethene (TCE) and its breakdown product 1,2-dichloroethene (1,2-DCE). At Hill AFB, TCE may have been used as a cleaning solvent for degreasing. Additional VOCs found in the groundwater in Sunset, Clinton, and Roy, such as 1,1,1-trichloroethane (1,1,1-TCA), tetrachloroethene (PCE), and 1,1-dichloroethene (1,1-DCE), were used to remove grease or oil from metal parts.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).



Trichloroethene BreakdownContamination in the soil has spread to the shallow groundwater aquifer.Resultsof the groundwater and soil sampling have identified two groundwater contamination plumesresulting from leaks and spills at the base rail shop and a missile testing facility upgradient fromthe communities of Sunset and Clinton (Figure 2). These contaminants have spread into thesewestern 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 ofcontaminants into the communities of Sunset and Clinton.

The most predominant VOCs detected in groundwater in the cities of Sunset and Clinton aretrichloroethene (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 inSunset), 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 inClinton 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 westernportions 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 andchloroform are breakdown products of other VOCs. Chloroform results from the breakdown ofcarbon tetrachloride, and vinyl chloride results from the breakdown of TCE. Chloroform is alsoformed as a result of chlorination of drinking water. In Sunset, there is no residential water andmost irrigation to lawns and gardens is done with chlorinated water. Chloroform, with amaximum detected concentration of 45 ppb, does not appear to be co-located with carbontetrachloride (Montgomery Watson Harza 2001b). As a result, the USAF believes that thechloroform 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 peoplein these communities. It is unlikely that high levels of contamination would reach the deeperaquifer because impermeable clay layers more than 200 to 300 feet thick separate the shallowaquifer from the deeper aquifers, greatly impeding groundwater flow between the two aquifersystems. 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 todetermine whether and to what extent the groundwater plumes had affected air quality of homesand two schools in Sunset and Clinton. Thirty residences, the Sunset Elementary School, and theFremont Elementary School were monitored. The USAF chose these buildings primarily becauseof their location directly above the groundwater plumes. The indoor air quality was monitored atvarious times of the year to assess potential differences in VOC levels due to seasonal weatherand living conditions (open or closed doors/windows, use of air conditioning or heatingsystems). The USAF also sampled the air in basements because they were more likely to containthe highest concentrations of VOCs because of their proximity to the water table and limited airflow (Radian 1995a). ATSDR confirmed the findings with air modeling techniques. The USAFagain conducted indoor air sampling in Sunset and Clinton from 2000-2001 as part of theBaseline 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 from1998 to 2002 (Radian 1995a). The most common contaminants found were VOCs.

Indoor Air Exposures for Residents of Sunset and Clinton

Indoor Air Pathway: VOCs - Soil - Groundwater - Soil Vapor - Indoor Air - Residents of Sunset and Clinton

Sunset

TCE, TCA, Chloroform, and Vinyl Chloride: What are these? How are they used? Why would they be indoors in most US homes?: These chemicals, like the BTEX compounds, are commonly detected in homes throughout the country. TCA is a solvent found in 'whiteout', rug cleaners, glues, and aerosol sprays. Nearly all the chloroform made in the United States today is used to make other chemicals. Chloroform enters the environment from chemical companies and paper mills. It is also found in wastewater from sewage treatment plants and drinking water to which chlorine has been added. Chlorine is added to most drinking water and many wastewaters to destroy bacteria. Small amounts of chloroform are formed as an unwanted product during the process of adding chlorine to water. All vinyl chloride is manufactured or results from the breakdown of other manufactured substances, such as TCE, TCA, and PCE. Most of the vinyl chloride produced in the United States is used to make polyvinyl chloride (PVC). PVC is used to make a variety of plastic products including pipes, wire and cable coatings, and packaging materials. Other uses include furniture and automobile upholstery, wall coverings, housewares, and automotive parts. At one time, vinyl chloride was also used as a coolant, as a propellant in spray cans, and in some cosmetics. Since the mid-1970s, it has not been used for these purposes.There are more than 1,800 homes in Sunset, ofwhich approximately 470 appear to be above thegroundwater plume (Figure 2). Of these, the USAFsampled indoor air at thirty residences and twoelementary schools. As in the Patriot HillsHousing area, the choice of indoor air samplinglocations was based on the location of thegroundwater plumes and the contaminantconcentrations beneath the homes. Indoor airsampling in the TARS plume occurred both beforeand after cleanup measures were put in place. Webelieve that the number and location of homessampled in Sunset are sufficient to berepresentative of the highest levels that may havebeen in homes above the groundwater plume.Sampling data in homes sampled in 1993 and 1994where VOCs were detected and then sampledagain in 2002 indicate that VOC concentrationsdecreased below detection limits betweensampling times. The decreasing indoor airconcentrations indicate that near water tableconcentrations may also be decreasing and may beattributed to remediation efforts conducted in thisarea.

Highest Concentrations Detected

In 1993 and 1994, four chemicals that were in theTARS groundwater contaminant plume weredetected in indoor air samples from homes inSunset and in samples from Sunset Elementaryschool. They included TCE, which was detected inall 11 homes tested and in Sunset Elementary (upto 2.95 ppbv); TCA, which was detected in all 11homes and in Sunset Elementary (up to 7.95 ppbv); chloroform, which was detected in all 11homes and in Sunset Elementary (up to 1.1 ppbv); and vinyl chloride, which was only detectedin one home (up to 1.8 ppbv). Contaminant concentrations were typically greater in these homesduring December and March sampling events and may be attributed to the houses being closedup during the winter months. Three of the homes sampled in 1993 and 1994 were sampled againin 2002 when TCE, TCA, and vinyl chloride were not detected. However, in 2 of 19 additionalhomes sampled in Sunset, TCA was detected at levels up to 7.8 ppb. Samples were also collectedat 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 werefound at Fremont Elementary. BTEX compounds were not detected in the groundwater plumeunderlying the school. Therefore, the source of BTEX in the school is not believed to be relatedto Hill AFB.

The ranges of levels of VOCs detected in the homes (from all sources including the subsurfacevapor intrusion from contaminants in the groundwater) were compared with levels commonlydetected in homes. TCE, which ranged from non-detectable to 2.95 ppbv, slightly exceededcommonly detected levels, although, was far below levels that are known to cause adverse healtheffects. 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 constantlyfor 24 hours a day, 365 days per year over a 30-year period. These assumptions create a veryconservative estimate of exposure, most likely higher than an exposure dose for an averageindividual in the community. Furthermore, ATSDR assumed that residents living in the housingunits were exposed to the most contaminated air; therefore, ATSDR used the highest (ormaximum) measured concentrations of contaminants in indoor air. This also is a conservativeassumption since we would not expect people to be exposed to the highest concentration all thetime. Together, these conservative estimates allow ATSDR to safely evaluate the likelihood, ifany, that indoor air contaminants in the home could cause harm to residents. Indoor air samplingmeasures the level of contaminants in the indoor air in that particular residence. It measures thecontribution of all sources of VOCs in the home (paint, cleaners, glues, etc.). The samplingcannot determine the portion of contamination that is a result of the groundwater contaminationplume 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 inadverse health effects. As a result, ATSDR concludes that no adverse health effects shouldresult 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 morethan 20 times lower than its EPA reference dose (Table 4). The maximum exposure dose oftoluene found in Fremont Elementary is far lower than its reference dose. The maximumconcentration of xylenes detected at the elementary school is several hundred times lower thanthe EPA's RBC. (See definition of health comparison values and discussion on choice of valueson page 20 of the on-base section of this document.) Adverse health effects should not resultfrom exposure to this level of contamination in homes. For a more detailed analysis of theexposure to indoor air in Sunset, please see Table 21 in the Tables section at the end of thisdocument.

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 thegroundwater plumes (Figure 2). During 2000 and 2001 indoor air sampling was performed at 7homes in Clinton.

Highest Concentrations Detected

During 2000 and 2001, two contaminants were detected in indoor air samples from homes inClinton. TCA, which was detected in one of 7 homes tested, was found at a maximum of 1.1ppbv. Chloroform, which was detected in one of 7 homes tested was found at a maximum of 1.5ppbv.

The ranges of VOCs detected in the homes (from all sources including the subsurface vaporintrusion from contaminants in the groundwater) were compared with levels commonly detectedin 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. Thetheoretical estimated lifetime cancer risk for chloroform is below levels likely to result inadverse health effects. As a result, ATSDR concludes that no adverse health effects shouldresult from exposure to chloroform in Clinton. The maximum exposure dose for TCA found inindoor 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 contaminationin 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 groundwatercontamination under the homes was at its worst, ATSDR used a model to estimate whetherintrusion at the highest levels of groundwater contamination would have presented a healthhazard. TCE was the predominant contaminant detected in the groundwater plumes in Sunsetand Clinton. The maximum concentration of TCE detected, 870 ppb (in Sunset) and 120 ppb (inClinton), were entered into the model. The model predicted indoor air concentrations of 59 ppband 43 ppb, respectively. An exposure dose was calculated using these concentrations and theassumptions listed above. The resulting exposure doses were more than a hundred times lowerthan the LOAEL (ATSDR 1997b).

The maximum concentration of chloroform detected, 45 ppb (in Sunset), was entered into themodel. The model predicted an indoor air concentration of 33 ppb, which is several thousandtimes lower than the NOAEL for chloroform (ATSDR 1997d). The maximum concentration ofPCE detected, 1,190 ppb (in Clinton), was entered into the model. PCE was not detected inSunset. The model predicted an indoor air concentration of 59 ppb, which is several times lowerthan 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 modelpredicted an indoor air concentration of 3 ppb, which is several thousand times lower than theNOAEL for 1,1-DCE (ATSDR 1994b). The maximum concentration of carbon tetrachloridedetected, 16 ppb (in Sunset) and 50 ppb (in Clinton), were entered into the model. The modelpredicted indoor air concentrations of 1 ppb and 3 ppb, respectively, both several thousand timeslower than the NOAEL for carbon tetrachloride (ATSDR 1994c). The maximum concentrationof vinyl chloride detected, 56 ppb (in Sunset), was entered into the model. Vinyl chloride wasnot detected in Clinton. The model predicted an indoor air concentration of 6 ppb, which isseveral 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 areknown 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: throughaccidental 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 anddermal contact.

Dermal Contact

Surface Water Pathway: VOCs - Soil - Groundwater - Surface Water - Sunset and Clinton residents touching water from springs during outdoor activities

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

Surface Water Pathway: VOCs - Soil - Groundwater - Surface Water - Sunset and Clinton Residents accidentally ingesting water from springs

Table 7 below presents the concentration, ingestion exposure dose, and ingestion comparisonvaluefor the VOCs detected in surface water in Sunset and Clinton. The maximum oral exposure dosesfor accidental water ingestion for TCA, PCE, and chloroform were more than ten times lowerthan their EPA reference doses. The maximum exposure doses for TCE is over 1,000 timeslower than the highest levels at which adverse health effects have been seen for TCE (ATSDR1997b). Using this information, ATSDR concluded that the maximum value of VOCs detected insprings in Sunset and Clinton is much lower than the level at which adverse health effects havebeen seen. No adverse health effects are expected for humans exposed to these levels of VOCsthrough 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

Crop Pathway: VOCs - Soil - Groundwater - Sunset and Clinton residents ingesting crops irrigated with contaminated water

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.

Are garden-grown plants safe to eat if they have been irrigated with private well water?: Yes. ATSDR believes people may safely eat locally-grown fruits and vegetables. Research data suggest that the crops, such as those grown in local communities, do not take in or accumulate harmful amounts of contaminants detected in the groundwater used to irrigate these crops.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 referencedose. Adverse health effects should not result from exposure to this level of contamination in crops in these communities.

Community of Roy

Summary

From our visits, discussions with base personnel, and information reviews, ATSDR identifiedone way people living in Roy can come in contact with environmental contaminants from HillAFB: groundwater contamination off-gassing into indoor air.

  1. Adults and children living above contaminated groundwater in the off-base town of Roymay have breathed VOC vapors from contaminants migrating into the air inside homesfrom shallow groundwater beneath the homes.

    • The USAF conducted indoor air sampling in 2002 in the community of Roy.ATSDR evaluated the results of the indoor air sampling and determined thatbecause VOC levels were low, the exposure poses no apparent public healthhazard from living in homes in these communities in the past, current, or future.

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 fromthe Sunset and Clinton RIs suggested that additional groundwater contaminant sources arepresent in the Zone 16 Area. Since then, in 2000, a third area of soil and groundwatercontamination was identified in 2000 in the city of Roy. More investigation in 2001 and 2002identified an area north and west of Zone 16 that apparently received unknown quantities ofwaste. This site has been designated the Aspen Avenue Disposal Site and appears to be thesource of groundwater contamination in Roy. As of late 2002, the USAF has determined thatgroundwater plumes from Operable Unit (OU) 12 are impacting Roy.

In 2002, the USAF installed vapor extraction systems in homes in Roy with higher detectedlevels of TCE. In 2003, the USAF is planning to install a remedial action to cut off the source ofcontaminated 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 wholived in a home above the groundwater contamination plume requested the indoor air of thehome be sampled, the USAF sampled the home.

The most predominant VOC detected in the city of Roy is trichloroethene (TCE) (up to 1,300ppb). Contamination in the soil has spread to the shallow groundwater aquifer. Results of groundwater and soil sampling have identified one groundwater contamination plume resultingfrom leaking barrels at the Aspen Avenue Disposal Site. These contaminants have spread intothese 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 topeople in these communities. It is unlikely that high levels of contamination would reach thedeeper aquifer because impermeable clay layers separate the shallow aquifer from the deeperaquifers, preventing groundwater from flowing between the two aquifer systems. Both Weberand Davis Counties routinely monitor drinking water for contaminants under the Safe DrinkingWater Act.

Indoor Air Exposures for Residents of Roy

Indoor Air Pathway: VOCs - Soil - Groundwater - Soil Vapor - Indoor Air - Residents of Roy

Roy

Roy has more than 11,000 homes, of which approximately 320 appear to be above thegroundwater plume (Figure 2). In 2002, the USAF sampled one home and took confirmationsamples 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 inthis area. TCE was detected in 7 of these homes. Groundwater has not yet been remediated inRoy, but inplementing a remedial action to cut off the source is planned to be completed andoperational 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. Twomonths later TCE was detected at a lower level (2 to 3 ppb). Subsequent sampling has detectedTCE at a maximum of 16 ppb.

Exposure Evaluation

TCE is a suspected carcinogen. The estimated excess lifetime cancer risk for exposure to thislevel of TCE in homes is below levels likely to result in adverse health effects. However, toreduce the levels in the home, the USAF is working with the homeowner to immediately remedythe problem. For a more detailed analysis of the exposure evaluation process, please see Table22 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 mayhave chemical vapors in their air as well. USAF is currently planning to sample air at 30 homesin the immediate area. ATSDR will review these data to determine whether VOCs exist in homesin 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 groundwatercontamination under the homes was at its worst, ATSDR used a model to estimate whetherintrusion at the highest levels of groundwater contamination would have presented a healthhazard. TCE was the predominant contaminant detected in the groundwater plume in Roy. Themaximum concentration of TCE detected, 1,300 ppb, was entered into the model. The modelpredicted an indoor air concentration of 87 ppb, respectively. An exposure dose was calculatedusing these concentrations and the assumptions listed above. The resulting exposure doses wereover a hundred times lower than the LOAEL (ATSDR 1997b). Once again, ATSDR concludesthat all of the chemicals detected were at levels far below those that are known to cause adversehealth effects.

Surface Water Exposures for Roy

The only surface waters in the community of Roy are several field drains. No springs or seepsdischarge into Roy. Field drains have been installed by farmers through Roy in order to removeexcess 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 identifiedtwo ways people living in Layton or Clearfield can come in contact with environmentalcontaminants originating from Hill AFB: groundwater contamination off-gassing into indoor air and contact with contaminated springs or field drains.

  1. Adults and children living above contaminated groundwater in Layton or Clearfield mayhave been exposed to VOC vapors inside their homes. The air contaminants would havemigrated from shallow contaminated groundwater plumes beneath their homes, throughthe soil, and into their homes.

    • Indoor air sampling was performed in 1993, 1994, 2001, and early 2002 in thecommunity of Layton. ATSDR evaluated the results of the indoor air sampling anddetermined that because VOC levels are below reference values, the exposure fromliving in homes in these communities posed no apparent public health hazard in thepast, current, or future human. Based on indoor air modeling that used groundwaterconcentrations found in Clearfield, ATSDR determined that residents of Clearfieldhave not come in contact with harmful levels of indoor air contaminants, nor are theylikely to in the future.

  2. Adults and children living in Layton or Clearfield dermally contact surface watercontaminants or may have accidentally ingested VOC contaminated surface water insprings in these communities during outdoor activities.

    • Sampling from 1986-1991 determined that contamination is present in springs andopen field drains in Layton. ATSDR evaluated the results of the surface watersampling and determined that because VOC levels are low, the exposure, eitherthrough dermal contact or accidental ingestion, that occurs at these springs posed noapparent public health hazards in the past, current, or future.

Background

Layton, with a land area of 20.7 square miles, is directly south of Hill AFB. Clearfield, with aland area of 7.7 square miles, is southwest of Hill AFB, adjacent to Layton. Contamination fromformer base operations and waste disposal practices has affected soil and groundwater in Laytonand Clearfield. Areas that contributed to this contamination include Berman Pond, the SodiumHydroxide Tank Site, the Refueling Vehicle Maintenance Facility (RVMF), and the IndustrialWaste 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 HillAFB.

Several remedial measures instituted by the USAF have helped reduce further spread ofcontamination to Layton and Clearfield. These measures include covering both the SodiumHydroxide Tank Site and Berman Pond with asphalt caps in the late 1990s to preventcontaminants from leaching into the underlying groundwater. The USAF has installed twogroundwater extraction systems. One is located along the base boundary to stop additionalcontaminants from leaving the base, and the second, located off-base, is extracting groundwaterunder artesian conditions. Perched groundwater has also been removed from under the cappedarea 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 spreadto the shallow groundwater aquifer beneath the base. This groundwater contamination hasmigrated further south to the communities of Layton and Clearfield. The USAF beganenvironmental sampling at Layton and Clearfield in 1983 to determine the type and extent of thecontamination. Results of the groundwater and soil sampling have helped identify twogroundwater contamination plumes in Layton and Clearfield (Figure 2) (HAFB 1997b). Nocontamination has been detected in the deeper aquifer, which is a source of drinking water forresidents of Layton and Clearfield.

VOCs are the primary contaminants detected in the groundwater plumes beneath Layton andClearfield. 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 to9.8 ppb) (Montgomery Watson Harza 2001b). Because the VOC plumes had migrated to areas ofresidential homes, the USAF conducted air sampling in 1997, 2000, and 2001 to determine ifindoor 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 beneathhomes in Layton and the extreme eastern part of Clearfield. This plume is approximately 350acres 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 pocketsof groundwater contamination, the USAF performed indoor air monitoring in 1997, 2000, and2001 to measure indoor air quality in select homes above the plumes in Layton. No indoor airsampling was conducted in Clearfield because there are no homes above groundwatercontamination in that city.

Prior to indoor air sampling, the USAF conducted a survey of residences in the Layton area fromJuly to November 1996 (Dan Jones and Associates, Inc. 1996) to identify homes affected by thegroundwater 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 theprocess of identifying existing wells and determining the need for sampling and analysis of theseprivate wells (ATSDR 2002a). Findings of the Layton survey identified nine residences withinthe bounds of the groundwater plume that had groundwater entering the basements. Groundwatersamples were collected from six of the nine locations in June 1997 and analyzed for VOCs. Themaximum 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 0.11ppb, respectively. Following groundwater analysis, the two homes with levels of TCE above thefederal drinking water standard (known as maximum contaminants level) were determined to beat risk for potential indoor air contamination.

In 1997, the USAF performed air sampling using evacuated stainless steel (SUMMA) canistersin the basements of these homes. SUMMA canisters were generally placed in areas where wateris more likely to enter the home or in the largest room in the basement. The vacuum pressurecanisters are set 3-5 feet off the floor and are empty of everything, including air, at thebeginning of the test. When the canister valve is opened the negative pressure created by thevacuum 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. Additionalresidential air sampling was performed as part of the remedial investigation in May of 2000 andMay to July 2001.

Indoor Air Exposure for Residents of Layton and Clearfield

Indoor Air Pathway: VOCs - Soil - Groundwater - Soil Vapor - Indoor Air - Residents of Layton and Clearfield

Layton

Layton has more than 19,000 homes within its city limits, of which less than 200 appear to besituated above the contaminated groundwater plume (Figure 2). Indoor air sampling locationswere chosen based on the location of the groundwater plumes. The concentrations of VOCsdetected in the 2000-2001 sampling are lower than the levels found in 1997, likely a result ofremedial 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 yearsbefore 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) forresidents of these communities. Based on available base information, ATSDR believes that thisdecrease in groundwater concentrations will continue.

Highest Concentrations Detected

In 1997, the two homes determined to be at risk for potential indoor air contamination weresampled. Five VOCs (trichlorofluoromethane, acetone, benzene, toluene, and xylenes) weredetected 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. Themaximum 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 samplingperformed as part of the remedial investigation reported lower concentrations of contaminantsthan 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 0.12ppb, respectively.

The maximum concentrations of TCE, benzene, toluene, and xylenes were slightly abovecommonly detected levels, though far below levels that are known to cause adverse healtheffects. The maximum concentration of chloroform detected was below commonly detectedlevels. We did not find a commonly detected level of acetone, 4-ethyltoluene, methylenechloride, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, trichlorofluoromethane, vinylchloride, or 1,2-DCE for comparison purposes.

Exposure Evaluation

ATSDR conservatively assumed that an adult was exposed to the highest detected concentrationof indoor air contaminants constantly for 24 hours a day, 365 days per year. These assumptionscreate a very conservative estimate of exposure, most likely higher than an exposure dose for anaverage individual in the community.

TCE, methylene chloride, benzene, 1,2-DCA, vinyl chloride, and chloroform were the onlycarcinogens detected in the indoor air in Layton. The theoretical estimated excess lifetime cancerrisk for TCE, methylene chloride, benzene, 1,2-DCA, chloroform, and vinyl chloride are belowlevels likely to result in adverse health effects.

The maximum exposure dose for toluene found in indoor air in Layton homes in 1997 was halfits EPA reference dose (Table 9). The maximum exposure dose for 4-ethyltoluene found inindoor air in Layton homes in 2000-2001 was ten times lower than its EPA reference doses. Themaximum concentration of trichlorofluoromethane was more than 200 times lower than its EPAreference dose. The maximum concentrations of acetone and xylenes were compared to EPARegion III's RBCs. The RBC for acetone is more than14 times higher than its maximumdetected concentration in 1997. The RBC for total xylenes is more than 100 times higher than itsmaximum detected concentration in 1997. 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzenewere both detected at levels below the testing reporting limits (i.e., safe levels). Adverse healtheffects are not expected for humans exposed to these levels of VOCs in their homes. A moredetailed 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 takenfrom the residences. Therefore, it is reasonable to conclude that they originated from sourcesother than the groundwater (Montgomery Watson Harza 2001b). Trichlorofluoromethane iscommonly 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 iscommonly 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 petroleumproducts. The groundwater concentrations of the compounds that were detected in the air werevery 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 thegroundwater 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-10investigation of the 1200 area of Hill AFB has discovered off-base contamination beneath homesin Clearfield. The extent of the contamination has not yet been determined. To evaluate thequality of indoor air in this community, ATSDR used an indoor air model (see discussionbelow). This indoor air model only considers the groundwater beneath the home. It does notconsider 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 groundwatercontamination under the homes was at its worst. Furthermore, indoor air sampling was notconducted in Clearfield. Therefore, ATSDR used a model to estimate whether intrusion ofgroundwater 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 thegroundwater plumes beneath Layton that had corresponding information available for use in themodel. 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 predictedcorresponding 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 concentrationand the assumptions listed above. The resulting exposure dose for TCE was more than 1,500times lower than the lowest level of TCE determined to cause adverse health effects inlaboratory animals (ATSDR 1997b). The resulting exposure dose for 1,2-DCA was more than2,000 times lower than the highest level found not result in an adverse health effect in laboratoryanimals (ATSDR 1999). The resulting exposure dose for 1,1-DCE was hundreds of times lowerthan the highest level found not result in an adverse health effect in laboratory animals (ATSDR1994b). The resulting exposure dose for vinyl chloride was thousands of times lower than thehighest 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 foundthat did not result in adverse health effects in laboratory animals (ATSDR 1997e). ATSDRconcluded that none of the estimated indoor air concentrations from groundwater off-gassingwould 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 inorder to remove and recirculate excess shallow groundwater. Unused water is channeled intostorm 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 theeastern lobe of the groundwater plume. The maximum concentrations of benzene (3.5 ppb) and1,2-DCA (3.6 ppb) were found in a Layton field drain west of the western lobe of the largergroundwater plume (James M. Montgomery 1991).

No contamination was found in the Davis-Weber Canal. There is a pond near 350 South 500East 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 ingestionof water from springs and through dermal contact of the surface water in the springs. Exposuredoses were calculated for each of these chemicals for both accidental ingestion and dermalcontact.

Dermal Contact

Surface Water Pathway: VOCs - Soil - Groundwater - Surface Water - Layton Residents touching water from springs during outdoor activities

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

Surface Water Pathway: VOCs - Soil - Groundwater - Surface Water - Layton Residents accidentally ingesting water from springs

The maximum exposure doses for water ingestion for TCE, 1,2-DCA, and benzene were tentimes lower than their EPA oral reference doses (Table 11). No adverse health effects areexpected 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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