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After conducting a thorough evaluation of available environmental monitoring data and potentialexposures situations, ATSDR concluded that exposure to contaminated groundwater, soil,residential indoor air, surface water, and fruits and vegetables do not pose a health hazard to residents and workers of Hill AFB or the surrounding communities.

Hill Air Force Base (AFB) is in northern Utah, approximately 30 miles north of Salt Lake Cityand 8 miles south of Ogden. Hill AFB stretches across two counties, Davis and Weber, covers6,700 acres, and has more than 1400 buildings. Hill AFB is bordered by the communities ofSunset, Clinton, Clearfield, and Roy on the west, Layton on the south, and South Weber andRiverdale on the north.

Hill AFB has been the location of military activities since 1920 when the War Departmentestablished the Ogden Arsenal Army Reserve Depot in the area now occupied by thenorthwestern portion of Hill AFB. The Ogden Arsenal's principal function was to store unusedordnance from World War I. When World War II (WWII) began, the Ogden Arsenal was rebuiltand its mission was expanded to include manufacturing and loading explosives and stocking anddistributing motorized and related equipment. In 1940 and 1941, four runways were built and theOgden Air Depot was activated.

After WWII and until 1950, the primary activity at the Ogden Air Depot was equipment andaircraft storage and equipment salvage and redistribution. In 1948, the Ogden Air Depot wasrenamed Hill AFB. In 1955, the Ogden Arsenal was transferred from the U.S. Army to the U.S.Air Force (USAF) and the base doubled in size to 6,700 acres. Since 1955, Hill AFB has been amajor center for missile assembly and storage and aircraft maintenance. Today, Hill AFB'smission encompasses supply and repair of aircraft and missile parts, including munitions storageand handling.

As a result of former base operations and waste disposal practices at Hill AFB, various fuels andchemicals have spilled or have been released to the ground, some of which have reachedunderlying groundwater and storm water ponds. The U.S. Environmental Protection Agency(EPA) listed Hill AFB on its National Priorities List in July 1987 based on indications thatcontamination in multiple areas had spread to communities surrounding the base. The primarycontaminants of concern are volatile organic compounds, such as those used in cleaningsolvents. These contaminants, as well as others, have been detected in groundwater and soil.

ATSDR evaluated whether exposures to environmental contaminants are expected to affect thehealth of residents of Hill AFB or surrounding communities. At Hill AFB, the USAF hasconducted an extensive amount of sampling at possible contamination points and at locationswhere people could be exposed to contamination. This has made our evaluation more complete.As part of evaluation process, ATSDR conducted base visits and met with representatives fromHill AFB in 1991, 1994, and 1998. At the time of the visits, ATSDR did not identify anyenvironmental health hazards posing immediate threats to the public. However, ATSDRidentified ways in which people living at or near the base or in surrounding communities mightcome in contact with environmental contamination associated with Hill AFB, including contactwith contaminants in groundwater, surface soil, surface water and/or sediment, locally grownfoods, and indoor air.

The exposure to contaminated indoor air is ATSDR's main focus in this document. Theexposures to contaminated surface water, dermally and through incidental ingestion, and theexposure to contaminated fruit were also evaluated. ATSDR determined that they proved less ofa concern than the indoor air exposure. Contaminated groundwater in the shallow aquifer is notused as a source of drinking water for people at Hill AFB or in the surrounding communities.Additionally, there is no accessibility to contaminated soil at Hill AFB. ATSDR developed thefollowing conclusions about potential exposure hazards to indoor air and surface watercontamination.


Some of the contamination found in the indoor air in sampled homes was not found in thegroundwater contamination plumes located near these homes. For a majority of the communitiesstudied, background samples (sampling performed in homes that are not above groundwaterplumes used to identify typical levels of contaminants in the indoor environment) found thesame level of contamination as in homes directly above the groundwater plumes. From thisinformation, it appears that groundwater off-gassing in most of the communities is not asignificant source of indoor air contamination. We did evaluate the indoor air contaminant levels(from all sources) in this assessment.

Conclusions regarding potential past, current, and future exposure situations on and in thecommunities near Hill AFB are based on a thorough evaluation of base investigation data andobservations made during base visits. Although exposure occurred in indoor air, surface water,crops, groundwater and soil, the levels are much lower than those shown to cause adverse healtheffects.

Hill AFB

Contaminants, primarily volatile organic compounds (VOC), have been detected in indoor air atcertain residential units in the Patriot Hills Housing Area. However, the VOC levels are low andbelow those associated with adverse health effects. Pond 3 is the only surface water body on HillAFB where exposure to contaminants (via dermal contact) is possible. The contaminationdetected is low and far below levels associated with adverse health effects.

Surrounding Communities

Several hundred residential homes and a school in the cities of Sunset, Clinton, Roy, Layton,Riverdale (Craigdale subdivision), and South Weber sit above groundwater plumes that havemigrated from Hill AFB source areas. Indoor air monitoring of potentially affected buildingsshowed VOC contaminants were present in the air inside certain homes, but at levels belowthose known to be associated with adverse health effects. ATSDR also confirmed these findingswith air modeling techniques because of the limited air sampling in the housing area. Airmodeling uses known groundwater contamination values to determine a likely indoor airconcentration.

Past indoor air exposure was most likely higher in some of the communities when thegroundwater contamination was higher. Exposure possibly began sometime in the 1960s.ATSDR used indoor air modeling techniques to determine how high indoor air concentrationscould have been in the past from groundwater off-gassing. The results of the modeling indicatethat past indoor air levels were several times higher than they are today, but at levels far belowthose shown to cause adverse health effects. Future indoor air concentrations are not expected tobe higher due to the remediation efforts that have been initiated or soon will be initiated at HillAFB and in the communities surrounding Hill AFB. In communities that have had indoor airsampled, both before and after remediation efforts were implemented, the indoor airconcentrations are declining, indicating that remediation efforts are working. Additionally, thewaste disposal practices on Hill AFB that led to this groundwater contamination have stoppedand remedial actions have been put in place at most source area locations that have eithercleaned up or controlled contamination from leaving the base.

Several surface water bodies, in the form of springs, field drains, creeks, and ponds, arecontaminated with low levels of VOCs. Adults and children who come into contact with thecontaminated surface water, through either accidental ingestion or touch, are not exposed toharmful levels of contaminants. The VOC levels are low and below those associated withadverse health effects.

Contamination is present in water that some community members may use for irrigation. It isbelieved that adults and children who eat crops grown with contaminated water are not exposedto harmful levels of contaminants from Hill AFB. Preliminary research has found that uptake ofcontaminants from the contaminated groundwater by crops grown in the area is low and belowlevels that are known to cause illness. The USAF is continuing to study the issue.


Base Description and Operating History

Hill Air Force Base (hereafter referred to as Hill AFB) is in northern Utah, approximately 30miles north of Salt Lake City and 8 miles south of Ogden. Hill AFB stretches across twocounties, Davis and Weber, and covers 6,698 acres housing over 1,400 buildings. Hill AFB isbordered by the communities of Sunset, Clearfield, and Roy on the west, Layton on the southand east, and Riverdale and South Weber to the north (Figure 1). The city of Clinton is west ofSunset, but does not border the base. The population of these communities totals about 147,000(Bureau of the Census 2002).

Hill AFB has been the location of military activities since 1920, when the War Departmentestablished the Ogden Arsenal Army Reserve Depot on 3,300 acres in the area now occupied bythe northwestern portion of Hill AFB. The Ogden Arsenal's principal function was to storeunused ordnance from World War I. When World War II (WWII) began, the Ogden Arsenal wasrebuilt and its mission was expanded to include manufacturing and loading explosives andstocking and distributing motorized and related equipment. The U.S. Army Air Corps' RockyMountain Air Depot was established adjacent to the Ogden Arsenal in 1940 (MontgomeryWatson 1995a).

During WWII, the Rocky Mountain Air Depot was the regional aircraft supply and maintenancedepot and air depot training facility. In 1940 and 1941, four runways were built and the RockyMountain Air Depot was activated. After WWII, until 1950, the primary activity at the AirDepot was equipment and aircraft storage and equipment salvage and redistribution. In 1948, theAir Depot was renamed Hill AFB. In 1955, the Ogden Arsenal was transferred from the UnitedStates (U.S.) Army to the U.S. Air Force (USAF), thus doubling the size of Hill AFB to nearly6,700 acres. Since 1955, Hill AFB has been a major center for missile assembly and storage andaircraft maintenance. Through the 1980s, Hill AFB had a lead role in aircraft maintenance andlogistics support, and in the assembly, logistics, and management of Intercontinental BallisticMissiles (Montgomery Watson 1995a). More recently, Hill AFB contributed directly to DesertStorm and Desert Shield by deploying combat forces as well as supplying and repairing F-4, F-16, C-130, and A-10 aircraft, air munitions, landing gear, reconnaissance equipment, andtraining devices.

Today, Hill AFB's mission encompasses supply and repair of aircraft and missile parts,including munitions storage and handling. The base is one of three air logistics centers in theUSAF Materiel Command, serving as home to the Ogden Air Logistics Center (OO-ALC). OO-ALC provides worldwide engineering and logistic management for the F-16, A-10, MinutemanIII, and Peacekeeper intercontinental ballistic missiles (Montgomery Watson 1995a). OO-ALCalso provides maintenance for the C-130 and B-2 composite mission (ATSDR 2002a)

Remedial and Regulatory History

Since it began operation in 1940, one of Hill's functions historically has been aircraft, missile,vehicle, and railroad engine maintenance and repair. To support these functions, many on-baseindustrial processes, such as metal plating, degreasing, paint stripping, and painting, have beenperformed, generating a considerable amount of hazardous waste (Montgomery Watson 1995a).Most of the waste generated for recycling or disposal was solvents, paints, or adhesives. Releases of these materials to the environment occurred as a result of landfilling operations,discharge from the base Industrial Wastewater Treatment Plant (IWTP), fire training exercises,disposal practices, and accidental spills and leaks (HAFB 1997a).

Concern about hazardous waste contamination at Hill AFB began in 1975 when a resident ofSouth Weber complained of an orange colored discharge from a spring on his property adjacentto the base. In response to this concern, the USAF began investigations in 1978 to determine thesource and extent of the contamination. Since that time, groundwater and soil samples taken atthe base and on property adjacent to the base indicated the presence of various contaminants. Aninitial assessment of the potentially contaminated areas began in 1981 as part of the Departmentof Defense (DoD) Installation Restoration Program (IRP). The USAF implemented a two-phaseIRP program to comply with the Comprehensive Environmental Response, Compensation, andLiability Act (CERCLA), also known as the Superfund Act. A Phase I records search, completedin 1982, identified 10 potentially contaminated areas. Subsequently, two base-wideenvironmental investigations have been conducted.

Hill AFB was placed on the U.S. Environmental Protection Agency's (EPA) National PrioritiesList (NPL) in July 1987, requiring the base to determine the nature and extent of contaminationon base, while assessing the risk to human health and the environment. The NPL, or theSuperfund List, is a list of hazardous waste areas scheduled for cleanup. The Agency for ToxicSubstances and Disease Registry (ATSDR) is mandated to conduct a public health assessment ateach area proposed for or listed on the NPL. The USAF, the EPA, and the Utah Department ofEnvironmental Quality signed a Federal Facilities Agreement in April 1991 that outlines theroles and responsibilities of the three agencies in studying and addressing contamination at HillAFB.

As part of the environmental investigations at Hill AFB, the USAF has conducted a RemedialInvestigation/Feasibility Study (RI/FS) at locations throughout the base since 1987. Otherpotential locations are being evaluated and will be added if contamination is confirmed. To date,108 areas have been identified as potentially containing contamination (ATSDR 2002a). Theseareas include landfills, disposal areas, storage areas, spill locations, and training areas and arebeing managed under DoD's IRP and CERCLA. The investigations have also revealed themigration of some contamination beyond the source areas and into surrounding communities. Inaddition to ongoing investigations, removal and interim actions have been undertaken at HillAFB to reduce and control contamination identified as part of these investigations.

As part of the CERCLA RI/FS process, Hill AFB has grouped areas of contamination identifiedthrough investigations into 12 Operable Units (OU). These OUs were originally organized basedon geographical location, but have since been reorganized based upon type of contaminatedmedia. The OUs at Hill AFB, shown in Figure 2, are defined as follows (Montgomery WatsonHarza 2001a):

OU-1 - Landfills 3 and 4, Chemical Disposal Pits 1 and 2, Fire Training Areas 1 and 2, the Waste Phenol/Oil Pit, the Waste Oil Storage Tanks, and contaminated groundwater in the Weber River Valley (South Weber).
OU-2 - Chemical Disposal Pit 3, Perimeter Road, and contaminated groundwater in the Weber River Valley (South Weber).
OU-3 - Sodium Hydroxide Tank Site, Industrial Wastewater Treatment Plant Sludge Drying Beds, Berman Pond, Refueling Vehicle Maintenance Facility (RVMF; Building 510, 511, and 514), Pond 1, and Pond 3 (soil, sediment, and surface water only).
OU-4 - Landfills 1 and 2, Spoils Pit, North Gate Dump Site, Munitions Dump, and contaminated groundwater in the Weber River Valley (South Weber and Riverdale).
OU-5 - U.S. Army Tooele Rail Shop, Zone 16 area, Bamberger Pond (site closed in 2000), and contaminated groundwater underlying the cities of Sunset and Clinton.
OU-6 - Building 1915, the Asphalt Pad Area, Munitions and Missile Storage-2 Area, and contaminated groundwater in the Weber River Valley (Riverdale City).
OU-7 - Buildings 220 and 225 and the Building 225 fill soils placed at Base Supply Well 6 (soils only).
OU-8 - Groundwater beneath the Industrial Complex (OUs 3, 7, and 9) and the cities of Layton and Clearfield (off base).
OU-9 - Ponds 1 and 3, the deferred areas identified in the North and South Area Site Investigations, and all sites not covered under another OU.
OU-10 - Groundwater contamination beneath the series 1100 and 1200 buildings on base (West Gate area) and groundwater contamination near the Defense Reutilization Marketing Office and underneath the cities of Sunset and Clearfield.
OU 11 - Soil and groundwater contamination at former Building 454 and the Base Golf Course near Building 710.
OU 12 - Aspen Avenue Disposal site and former Wastewater Treatment Plant, soil and groundwater along the western boundary of Hill AFB and contaminated groundwater underlying the city of Roy.

ATSDR Involvement

Through the public health assessment process, ATSDR assesses base conditions from a publichealth perspective to determine whether exposures to environmental contaminants exist fromcontact with the groundwater/drinking water, surface water, soil, food chain (biota), or air.

ATSDR conducted a preliminary health assessment for the Hill AFB in January 1989. Relyingon environmental data at the time, ATSDR considered Hill AFB to be of public health concernbecause of the possible risk to human health caused by the likelihood of exposure to hazardoussubstances via ingestion, inhalation, and direct dermal contact with contamination in thegroundwater and soil (ATSDR 1989).

ATSDR conducted an initial visit of the Hill AFB in 1991. The purpose of the visit was toidentify community health concerns and public health issues related to environmentalcontamination at the base and to collect information necessary to address those concerns. Duringthe visit, staff met with USAF personnel and representatives from federal and state agencies aswell as members of the public. From these meetings and a review of the available data, ATSDRdetermined that no immediate threats to public health existed, but that several potential exposurepathways and community health concerns required further evaluation.

In 1992 and 1994, the USAF requested that ATSDR comment on the public health implicationsof contaminants at OU 6. ATSDR visited the base twice, in November 1992 and May 1994 andmet with base personnel who indicated their concern that volatile organic compound (VOC)contaminated groundwater was migrating off base into nearby neighborhoods. Based on theavailable information, ATSDR concluded that VOCs at OU 6 were not present in air or irrigationwater at levels that represented a health hazard. ATSDR also concluded that VOCs would notbioaccumulate in fruits or vegetables grown in OU 6 at levels likely to pose a health hazard(ATSDR 1994a).

As part of its ongoing involvement at Hill AFB, ATSDR visited the base again in March-April1998 and met with representatives from the USAF to obtain updated information onenvironmental studies and community concerns. During this visit, ATSDR did not identify anynew health threats at Hill AFB or any requiring immediate attention. The findings of ATSDR'sevaluation of potential pathways of exposure and public health concerns are addressed in theEvaluation of Environmental Contamination and Human Exposure Pathways and Community Health Concern sections of this public health assessment.

Demographics and Land Use

ATSDR examines demographic data (i.e., population information) to determine the number ofpeople potentially exposed to environmental chemicals and to determine the presence ofsensitive populations, such as women of childbearing age (age 15 - 44), children (age 6 andyounger), and the elderly (age 65 and older). Demographic data also provide details onpopulation mobility, which, in turn, helps ATSDR evaluate how long residents might have beenexposed to environmental chemicals. We also examine land and natural resource use todetermine what activities might put people at risk for exposure. Below, we provide some of thegeneral information we used in our analysis.

When Hill AFB began operation as the Ogden Arsenal in the 1920s, only 790 people workedthere. Over time, Hill AFB has grown substantially. During its peak operation in May 1943,20,480 people worked on base. Today, Hill AFB is the largest employer in Utah withapproximately 20,000 employees (ATSDR 2002a). About 4,300 military personnel and theirfamilies live in one of 1,141 homes in residential areas at Hill AFB. Another 630 dorm roomsoffer single-occupancy accommodations. Hill AFB has no schools, but Hill Field ElementarySchool is just outside the fence adjacent to the Patriot Hills housing area (ATSDR 2002a). HillAFB has several child-care facilities that provide services to young children. The ChildDevelopment Center cares for an average of 195 children per day under the age of 6 years. Thereare also 50 private day care facilities in the base housing area, each caring for 3 to 4 children. Inaddition, a Youth Center provides before and after school care (ATSDR 2002b).

Land at Hill AFB is used primarily in support of its missions to maintain and repair aircraft andaircraft parts. Access to the base is highly restricted by security fencing that surrounds the entireinstallation. All base entrances are gated and guarded 24 hours a day. Outdoor recreationalactivities at Hill AFB include the archery range with the trap shooting range, the base golfcourse, and the footpath around Pond 3. Most outdoor recreational areas are away from areas ofknown contamination, but the base golf course is above groundwater contamination from OU-11(ATSDR 2002a). Additional recreational activities are softball, baseball, and soccer that are allplayed on a series of fields at the southern boundary of the base. Several swimming poolssupplied with water from municipal sources also are present on the base (ATSDR 2002c).

Land use in the area surrounding Hill AFB is predominantly residential with some agriculturaluse and limited commercial and industrial use. The base is bordered by the communities ofSunset, Clinton, Clearfield, and Roy on the west, Layton on the south and east, and Riverdaleand South Weber to the north. Due to substantial growth in the past 10 years, the collectivepopulation of the surrounding communities is about 147,000 people, and continued growth isexpected (See Appendix A for demographic information by community). U.S. Census 2000demographic information for the residential area immediately around the base is presented inFigure 3. As the figure indicates, 1,242 residents live within 1-mile of the base, including 73adults age 65 years or older and 166 children age 6 years or younger.

Hill AFB and, to a lesser extent, the surrounding communities rely on a combination of surfacewater reservoirs and groundwater as the source of their drinking water (ATSDR 2002a).Groundwater beneath Hill AFB flows within three layers of underground water formations,known as aquifers. A shallow, unnamed aquifer is encountered at depths ranging from about10-165 feet below the ground surface (bgs) on base and 4-65 feet bgs off base (ATSDR 2002a).The shallow aquifer consists of thinly to thickly interbedded sequences of mostly sands, silts,and clay. The shallow aquifer has a marginal water quality (total dissolved solids [TDS] 500 toover 1200 milligrams per liter [mg/l]) and typically has a low yield. It is not considered aprincipal aquifer. Hill AFB is set up on a topographic high and is the recharge area for theshallow aquifer. Groundwater flow in the shallow aquifer is predominantly horizontal and flowsradially away from the base in almost every direction (i.e. at the southern base boundary the flowis southerly, on the western side of the base it flows toward the west, and on the east side of thebase it flows off the steep hillside to the east). On the steep hillside on northeast side of the base,there are numerous seeps and springs (ATSDR 2002a).

Beneath the shallow aquifer are the Sunset and Delta Aquifers. These are confined aquifers thatserve as major drinking water aquifers for the area. The Sunset Aquifer is approximately 250 to400 feet bgs and there is approximately 200 to 400 feet of interbedded clay sequences separatingit from the shallow aquifer. Below the Sunset Aquifer is the Delta Aquifer that lies about 500 to750 feet bgs. These two aquifers recharge at the base of the Wasatch Mountains that lie east ofHill AFB and flow generally in a western direction toward the Great Salt Lake.

The drinking water for Hill AFB is obtained from eight wells that draw water from the Sunsetand Delta aquifers on base; the shallow aquifer is not used as a water source. Well 1 is no longerused; Wells 2, 3, 6, and 9 are routinely used; Well 8 has not been used since mid-2001 Old well5 is capped and not used, new Well 5 was drilled to deeper level and being used as drinkingwater source. Well 4 is infrequently because of its historically naturally occurring high iron andmanganese content (ATSDR 2002c). These wells are located throughout the base. When waterdemand increases during the summer, water is purchased from the Weber Basin WaterConservancy District (WCD). The Weber Basin WCD supplies water to all of Davis, Weber andMorgan counties from the Weber River and deep aquifer wells throughout the area. Nonpotablewater also comes from groundwater. The Weber River is approximately 3,000 to 6,000 feet awayfrom the eastern and northern base boundaries and lies in a small valley about 300 below thedelta terraces on which Hill AFB is situated.

Surrounding communities obtain their drinking water from the municipal water supplier, theWeber Basin WCD. Some people in the area of the base also have private wells. According towater use surveys, no one uses the water from their private wells as a drinking water source, butsome do rely on the private wells as a source of irrigation water.

No natural surface water bodies exist at Hill AFB. Several ponds, however, are used to collectstorm water runoff. These include Ponds 1, 3, 4, 5, 7, 8, 9, 10, 12, 13, Bamberger Pond, BermanPond, and the Roy Gate Pond. Ponds 1 and 3 are along the southern base boundary. BambergerPond is near the central western boundary of the base. The Roy Gate Pond is found in thenorthwestern section of Hill AFB near the base boundary and the Hill AFB Museum. BermanPond no longer exists. It is an IRP site that has its final remedy (a cap and extraction system) inplace. Additional stormwater retention ponds (Ponds 4, 5, 7, 8, 9, 10, 12, and 13) are throughoutHill AFB (ATSDR 2002a). Only Pond 3 is used for recreational use (catch and release fishing).It is currently designated as a wildlife habitat area.

There are two privately owned irrigation canals in the Hill AFB area. The Davis-Weber Canal,which flows along the northern, western, and part of the southwestern boundaries of Hill AFB, isused each year from April to October. The canal is concrete lined, but cracks in the concretehave allowed water from the canal to infiltrate the shallow aquifer. Portions of the canal wererelined with concrete in 1997 and 2000. The Canal has been included in the OU6 area and iscurrently being included in the OU1 and OU2 areas. In July 1999, a section of the Davis-WeberCanal collapsed along the northeast corner of the base. This collapse caused extensive floodingin Riverdale. As a consequence, a two-mile long segment of the canal on the northeast side ofthe base was reconstructed and put underground with a leak detection system. The Davis-WeberCanal has also been put underground in corrugated pipe throughout most of Layton (ATSDR2002a).

The Bambrough Canal, east of Hill AFB, also provides irrigation water, but to a lesser extentthan the Davis-Weber Canal. It is only used in the upper reaches near the Weber River (ATSDR2002a). Bambrough Canal and the Davis-Weber Canal receive their water from the Weber River.Several off-base privately owned ponds, storm ponds, holding ponds, and field drains also exist.None of these ponds receive water from the base. Kay's Creek is an enclosed creek thatoriginated from groundwater seeps. It begins immediately south of Hill AFB in Layton and runs 10-15 miles into the Great Salt Lake. It is used as a discharge for stormwater.

Quality Assurance and Quality Control

In preparing this public health assessment, ATSDR reviewed and evaluated informationprovided in the referenced documents. Documents prepared for the CERCLA programs mustmeet specific standards for adequate quality assurance and control measures for chain-of-custodyprocedures, laboratory procedures, and data reporting. The environmental data presented in thisPHA are from base characterization, remedial investigation, and groundwater monitoring reportsprepared by the USAF under CERCLA. After evaluating this information, ATSDR determinedthat the quality of environmental data available in base-related documents is adequate to make public health decisions.


ATSDR analyzed environmental data for Hill AFB to determine if identified exposures couldpresent past, current, or future public health hazards. Table 18 (in the Tables section) provides adescription of each OU and a summary of our evaluation. ATSDR's exposure assessmentprocess is summarized in Appendix B. Our review indicated that most areas within each OU atHill AFB are not associated with known public health hazards because: (1) no base-relatedcontaminants are present, (2) contaminant concentrations detected are too low to pose a healthhazard, and (3) past and current exposure to the general public has been prevented.

From this review, however, ATSDR did identify exposure situations in some areas on and off base that required further evaluation: groundwater, surface soil, surface water/sediment, indoor air, and the food chain. In response to community concern, ATSDR also evaluated cancer and its potential for relation or association to Hill AFB contaminants. Our evaluation is summarized by exposure pathway in Table 19 and addressed in greater detail in the discussion that follows. To acquaint the reader with terminology and methods used in this PHA, Appendix C provides a glossary of environmental and health terms presented in the discussion.

ATSDR found that residents of Hill AFB, Sunset, Clinton, Layton, Clearfield, Riverdale, and South Weber have not come in contact with harmful levels of base-related contamination, nor are they expected to in the future. Certain homes in Roy are situated above groundwater contamination that originated at Hill AFB. Limited indoor air testing to date has shown that the air levels inside these homes are safe and below levels associated with health effects. USAF, however, continues to sample more homes in Roy.Our main focus was migration of contaminants from on basesoil into groundwater into indoor air of homes in specific areason and off base.

Spills and releases of VOCs at Hill AFB have saturated thesoils and seeped into underground water (groundwater). Spillsoccurred in industrial areas, in areas where materials were putinchemical disposal pits, and landfills (ATSDR 2002a). In off-base areas, the water table is generally shallow, approximately2to 15 feet below the ground surface. However, in some off-base areas, the water can be 30 to 60 feet or more below theground surface. In the off-base areas, homes are a few feetabove the water table. As a result, VOC vapors coming fromthecontaminated groundwater off-base may have migrated intothehomes. The groundwater contamination on Hill AFB has alsospread to the surface water. Surface water forms when waterthat is in the groundwater aquifer moves to the earth's surface. This water can be present as springs,seeps, rivers, and lakes. Adults and children who live near or encounter surface water may beexposed through dermal contact with VOCs in the water or by accidental ingestion ofcontaminated surface water. Crops grown in these communities have potentially been irrigatedwith water contaminated with VOCs.

Groundwater and soil were not found to be significant exposure pathways. The USAF hasinstalled many groundwater monitoring wells on and off base to help characterize and define theextent of the groundwater contamination. Using this information, ATSDR determined that thereis no exposure to contaminated groundwater via drinking water for residents of Hill AFB or thesurrounding communities. The contaminated groundwater is not used as a source of drinkingwater nor is it used for any other municipal purpose (bathing, cleaning, etc.). Groundwater wassampled at OU-1, OU-5 (Zone 16) source area, and downgradient of the MAMS II area in thevicinity of OU-12 for explosive compounds that were used or stored at Hill AFB. Severalexplosives have been detected, but all detections are at trace values and below the Safe DrinkingWater Act Standard Maximum Contaminant Levels (MCL) (ATSDR 2002a).

People living on Hill AFB or in these communities have not nor are they likely to contactharmful levels of soil contaminants in their community. Samples that were collected suggest thatthe contamination was either at low levels or were found in areas, such as subsurface soil, thatare inaccessible to the public.

ATSDR has organized the following part of the document by specific community so that peopleliving in those communities can identify themselves and their specific exposure to contaminantsthat may have originated from Hill AFB. The actual number of people that come in contact withbase-related contamination by all the various ways is only a small portion of the wholecommunity. We have included general maps of the areas affected.

The exposure to contaminated indoor air was ATSDR's main focus in this document. Theexposures to contaminated surface water, dermally and through incidental ingestion, and theexposure to contaminated fruit were evaluated. Based on the evaluation (found in the remainingsections of this PHA) ATSDR determined that indoor air exposure was of greater concern.

Indoor air continues to be examined in the Patriot Hills Housing Area and in the communitiessurrounding Hill AFB. Where contamination is detected, remediation systems are beinginstalled. The extent of groundwater contamination, groundwater remediation, and a summary ofthe indoor air contamination are found in Table 1.

Residents of Hill AFB and the surrounding communities could possibly be exposed to base-related contaminants by one or more of the exposure situations listed above. To determine ifcombined exposure to both inhalation of contaminated indoor air and dermal contact withcontaminated surface water could result in adverse health effects, ATSDR typically creates acombined exposure dose by summing the exposure doses for each chemical in each affectedmedia. In each community, the combined exposure dose was far below levels that can causeadverse health effects.

ATSDR considered the exposure to mixtures of contaminants at Hill AFB and the surroundingcommunities. Several types of mixtures are possible and include those that are additive and thosethat are synergistic. When the effect of the mixture can be estimated from the sum of exposurelevels or the effects of the individual components,the mixture is said to be additive (i.e., 2 + 2 =4). When the effect of the mixture is greater than estimated for additivity, the mixture is said tobe synergistic (i.e., 2 + 2 = 6). After analyzing the available data, ATSDR concluded that thelevels of contaminants individually and in the form of chemical mixtures are too low to present adverse health effects.

Table 1.

Indoor Air Summary Information
Community Range of VOCs in the Groundwater (ppb) Groundwater Remediation # of Air Samples/Year Indoor Air Sampling Range (ppb) Number of Homes Located above the Plume
Patriot Hills Housing Area Benzene: 1-550
Toluene: 1-20 Ethylbenzene: 1-800
Xylenes: 1-1,800
1992-1997: Active and passive jet fuel recovery
1992-present: Bioventing
In-home sampling: 13 samples in 1993, 8 in 1994
Flux sampling: 33 samples in 1993 and 1994
Benzene: 0.3-1.67, ND-18*
Toluene: 0.84 - 10.05, ND-43*
Ethylbenzene: ND - 0.68, ND-0.5*
Xylenes: ND - 2.88, ND-2.17*
30 out of 200 homes in the Patriot Hills Housing Area
Sunset TCE: 1-870
TCA: ND - 70
Chloroform: ND - 8
1997: Aeration Curtain and groundwater extraction system
1998: EE/CA phase II groundwater extraction system
1993: 36 samples at 6 locations
1994: 21 samples at 6 locations
2000: 3 samples from Fremont Elementary School
2001: 11 samples from 11 locations
2002: 12 samples from 12 locations
TCE: ND-2.95
TCA: ND-7.95
Chloroform: ND-1.1
471 out of 1,832 homes in Sunset
Roy TCE: 1-1,800 First remedial action at the base boundary will be implemented in late summer 2002 2002: 2 sampling rounds with more than 80 locations
2003: more than 70 locations anticipated
TCE: ND-16 320 out of 11,053 homes in Roy
Clinton TCE: ND - 120 Scheduled for Fall 2002: OU5 EE/CA phase III groundwater extraction trench 2000: 5 samples collected at 5 locations
2001: 2 samples collected at 2 locations
2002: one samples collected at one location
All compounds: ND Approximately 320 homes out of 3,600 homes in Clinton
Layton TCE: 1-700 late 1990s: covering Berman Pond with a cap
1997-1998: groundwater extraction system and soil vapor extraction
1997: 2 samples
2000: 1 sample
2001: 20 samples
TCE: ND-2.2
Chloroform: ND-6.3
Benzene: ND-6
Toluene: ND-14
Xylenes: ND-9.5
< 200 out of 19,145 homes in Layton
Riverdale TCE: 1-15,000 1996: Landfill 1 capped and groundwater extraction and treatment system installed
1998: horizontal drain collection and treatment system
1999: groundwater extraction
1992-1993: 17 samples TCE: 0.03-4.3 (117.5 in the garage sump enclosure)
TCA: 0.95-41.35
Chloroform: ND-5
80 homes out of 2,970 homes in Riverdale
South Weber TCE: 1-6,300 1993: Source Recovery System installed
1996: Landfill 1 capped
1998: horizontal drain collection and treatment system
2001: groundwater extraction trenches
1990-1995: 4 samples TCE: ND-0.74
TCA: 0.004-18
Chloroform: 0.08-0.23
< 100 homes out of 1,110 homes in South Weber

Indoor air levels are not a public health hazard

ND: Not detected
*: flux chamber measurements

TCE: trichloroethene
TCA: 1,1,1-trichloroethane

Hill AFB


After our visits, discussions with base personnel, and information reviews, ATSDR identified twoways non-workers at Hill AFB can come in contact with contaminants in the environment;groundwater contamination off-gassing into indoor air and touching water in Pond 3.

  1. What are VOCs?: Volatile organic compounds (VOCs) are a group of organic chemicals having similar physical properties. VOCs were detected in high concentrations in most of the groundwater plumes moving beneath Hill AFB. VOCs were also detected in the portions of the plumes that have migrated beyond base boundaries. VOCs move easily in groundwater and, under some circumstances, can evaporate into air directly from water or soil.Adults and children living in homes above groundwater contaminated with volatile organic compounds (VOCs) at Patriot's Hill Housing Area may have breathed vapors from contaminants migrating into the indoor air from shallow groundwater.

    • Indoor air sampling wasperformed in 1993 in thePatriot Hills Housing Area.ATSDR evaluated the results ofthe indoor air sampling anddetermined that becausecontaminant levels of VOCs were low, the exposure posed no apparent publichealth hazard in the past, current, and future.

  2. Children fishing in Pond 3 may have touched surface water contaminated with VOCs inthe pond during fishing activities.

    • Sampling in the 1980s determined that minimal contamination is present in thepond. ATSDR evaluated the results of the surface water sampling and determinedthat because contaminant levels were low, the exposure posed no apparent publichealth hazard at Pond 3 in the past, current, and future.


The USAF began soil and groundwater sampling at Hill AFB in the early 1980s to determine thetype and extent of the contamination resulting from former base operations and waste disposalpractices at the base. The investigations indicated that soil in certain areas of the base wascontaminated. Areas that contributed to this contamination are listed in Table 2 and described inTable 18 (in the Tables section at the end of this document).

A groundwater plume resulting from leaks and spills at Underground Storage Tank (UST) Site870 has migrated toward and beneath residences at the on-base Patriot Hills Housing Area(Montgomery Watson 1995b). UST Site 870, which consists of a pumping facility, fuel filters,piping and a 1,000-gallon UST for overflow liquids from the fuel filters, was used to receive,store, and distribute JP-4 (jet fuel) and diesel fuel. The area is north and upslope of the Patriot Hills Housing Area.

Table 2.

Sources of Groundwater Contamination by Community
Community Sources of Contamination Primary Contaminants
Hill AFB Tooele Army Rail Shop (TARS); Zone 16, the former Wastewater Treatment Plant; Fire Training Areas 1 and 2; Landfills 1, 3 and 4; the Waste Phenol/Oil Pit; the Waste Oil Storage Tank Site; Chemical Disposal Pits (CDPs) 1, 2 and 3; Landfill 1, Building 1915; the Asphalt Pad area; the Sodium Hydroxide Tank Site; Buildings 43, 220 and 225, 257, 272 and 454; Berman Pond; IWTP sludge drying beds; the Refueling Vehicle Maintenance Facility (RVMF); Pond 1; the Underground Storage Tank (UST) Sites 260 and 280; Base Supply Well 6; the former Air Force Plant 77; portions of the original Hill Field; the former Ogden Ordnance Depot; the former Ogden Arsenal; the main runway and flightline area north of the 388th Fighter Wing; the Missile Assembly, Maintenance and Storage Area (MAMS); the current administration complex in the west-central portion of the base; the area between the eastern base boundary and the main runway; the Aspen Avenue Disposal area; and UST Site 870 which affects the Patriot Hills Housing Area. Benzene, Toluene, Ethylbenzene, Xylenes, TCE
Sunset and Clinton Operable Unit 10; Groundwater contamination beneath the series 1100 and 1200 buildings on base (West Gate area) and groundwater contamination near the Defense Reutilization Marketing Office. TCE, TCA, cis-1,2-DCE, 1,1-DCE, Carbon Tetrachloride, Chloroform, Methylene Chloride
Roy OU-12: former Wastewater Treatment Plant TCE
Layton and Clearfield OU-8: The Sodium Hydroxide Tank Site, Buildings 43, 220 and 225, 257, 272, and 454, Berman Pond, Industrial Wastewater Treatment Plant (IWTP) sludge drying beds, the Refueling Vehicle Maintenance Facility (RVMF), Pond 1, and the Underground Storage Tank (UST) Sites 260 and 280. TCE, 1,2-DCA, 1,1-DCE, Vinyl Chloride, Benzene, Toluene, Xylenes
Riverdale OU-4: Landfill 1, Building 1915, and a cluster of buildings in the MAMS II area to the south of the asphalt pad TCE, Methylene Chloride, Benzene
South Weber Fire Training Areas 1 and 2, Landfills 1, 3, and 4; the Waste Phenol/Oil Pit, the Waste Oil Storage Tank Site; and the Chemical Disposal Pits 1, 2, and 3 TCE, cis-1,2-DCE, TCA, PCE

In response to the groundwater contamination in this area, the USAF implemented active andpassive jet fuel recovery during1992-1997 (Montgomery Watson Harza 2001a). "Bioventing"has also been ongoing since 1992 to remove VOCs. In addition, long-term groundwatermonitoring, natural attenuation, and residential indoor air sampling are ongoing. The size of thegroundwater plumes is stable, neither increasing nor decreasing in size (ATSDR 2002a). VOCs(soluble in water) flow easily through the shallow aquifer, extending about 1,400 feet from itssource.

Patriot Hills Housing Area Sampling

The plume has extended toward and beneath the Patriots Hill Housing Area. Because VOCs areable to evaporate, they can seep into homes above pockets of VOC groundwater contamination.The USAF conducted indoor air sampling at certain base residential units in 1993 and 1994 todetermine if indoor air contamination had occurred because of the contaminated groundwater.

Why is BTEX in my home?: VOCs that were detected at Hill AFB include benzene, toluene, ethylbenzene, and xylenes (BTEX). Most people are exposed to a small amount of BTEX on a daily basis. The major sources of BTEX exposure are exhaust from motor vehicles, tobacco smoke, automobile service stations, and industrial emissions.In the Patriot Hills Housing Area, the primary contaminants evaluated in the indoor air were benzene, toluene, ethylbenzene, and xylenes (BTEX). Indoor air sampling was performed at 11 homes above the plume and at 2 homes outside the plume area (used for background samples). The number and location of sampling points are sufficient for ATSDR to make a health determination. Groundwater remediation, which began in 1992 and continued throughout the sampling period, has lowered the amount of indoor air contamination detected between 1993 and 1994 in the Patriot Hills Housing Area. Further decreases are expected.

The most toxic contaminants in the plume associated with Site 870 are the BTEX compounds.During July 1993 sampling, total xylenes and ethylbenzene were detected in the groundwater atconcentrations up to 100 parts per billion (ppb) (1) and 25 ppb, respectively. Toluene and benzenewere detected in the groundwater at concentrations between 1 and 5 ppb. Investigations in 1994indicated that the groundwater plume extended approximately 1,400 feet to the southwest of Site870 and was about 400 feet across at its widest point. A layer of light non-aqueous phase liquids(LNAPL) about 1/4 inch thick has also been reported floating on top of the groundwater. TheLNAPL is composed primarily of jet fuel (JP-4). The depth to the LNAPL and groundwaterranged from 10 to 35 feet below ground surface (Montgomery Watson 1995b).

Because the plume had migrated beneath certain homes at the Patriot Hills Housing area, the AirForce monitored air quality inside the homes for VOCs to determine whether contaminantsassociated with the groundwater plume had entered the homes and adversely affected indoor airquality. The USAF conducted two types of air monitoring measurements: in-home and fluxchamber measurements. ATSDR also confirmed the USAF findings using air modelingtechniques.

In-Home Measurements: The USAF tested air quality in 13 homes in the Patriot HillsHousing Area between 1993 and 1994. Most homes were directly over the groundwaterplumes. Homes over uncontaminated groundwater were also chosen to serve as referencehomes, or benchmarks, to identify typical levels of pollutants in the indoor environment.Samples were collected in basements of homes that had basements and collected inhallways or utility rooms in homes without basements. Samples were analyzed for BTEXcompounds and ethylene glycol monomethyl ether (EGME), a jet fuel additive.

BTEX compounds were detected in all homes, but at relatively low concentrations. Benzene wasdetected at concentrations up to 2 ppb. The highest concentration was found in one of thereference homes. Contamination in reference homes is not expected to be affected bycontamination from Hill AFB. Toluene was detected at levels up to 10.1 ppb in one home. Thishome is directly over the plume and has a basement. It is of interest to note that the concentrationis not substantially higher than the maximum concentration found in the reference homes (8.5ppb).

How are flux chamber measurements different from in-home measurements?: The flux chamber measures petroleum and EGME vapors coming from beneath the ground and eliminates the effect of above-ground sources (such as cigarette smoke and automobile emissions). Flux measurements only provide an indirect estimate of exposure concentrations and do not reflect the actual concentrations people are exposed to indoors. In-home measurements sample the indoor air directly and are representative of the actual VOC exposure in the home. They are independent of the source of contamination.Ethylbenzene and m, p-xylenes were detected at a maximum of 0.85 ppb and 3.2 ppb, respectively, with the highest concentrations found in the reference homes. O-xylene was detected at levels up to 1.73 ppb. EGME was not detected in the sampled homes. BTEX is normally present in homes due to emissions from automobiles and other sources, so the presence of these compounds is not by itself an indication that there is environmental exposure due to contamination from Hill AFB. These results suggest that the indoor air quality of homes in the Patriot Hills Housing Area are not affected by contaminates in the underlying plume.

Flux Chamber Measurements: From 1993 to1994, the USAF collected 33 flux chambersamples from 7 homes in the Patriot HillsHousing Area (Montgomery Watson 1995b).The purpose of the flux chamber investigationwas to determine whether VOCs in thegroundwater contamination plume were actually entering space in the soil which couldpotentially enter the homes located above the plume in the Patriot Hills Housing Area.Flux chamber measurements directly sample volatilized compounds from beneath theground surface. The benefit of this type of measurement is that they are unaffected byinterfering sources of petroleum compounds, such as automobile emissions, that may be inor around tested homes. The flux chambers are placed in a shallow well 4 feet belowground. Air in the subsurface passes into the flux chamber and is mixed with pure air.Most of the air is vented to the outside, but a small portion is collected in an evacuatedsampling container known as a SUMMA canister. A pressure regulator allows air to exitthe flux chamber and enter the canister at a specified rate (Montgomery Watson 1995b).

Results of the flux chamber sampling indicated that toluene was detected most frequently(25 out of 33 samples) and at levels up to 43 ppb. Benzene, ethylbenzene, and xyleneswere also detected at concentrations up to 18 ppb (in 10 samples), 0.50 ppb (in 4 samples),and 2.17 ppb (in 14 samples), respectively (Montgomery Watson 1995b). EGME was notdetected in any samples. Note that these concentrations do not represent what is in theindoor air. They are simply a measurement of vapors that emanate from the contaminatedgroundwater plume beneath the home. Using the flux measurement information, it appearsthat BTEX vapors are present in the soil gas and are possibly from the volatilization of the contaminants from the groundwater plume.

Indoor Air Exposure at the Patriot Hills Housing Area

Indoor Air Pathway: VOCs - Soil - Groundwater - Soil Vapor ŞIndoor Air - Hill AFB Patriot Hills Housing Area Residents

Comparison of BTEX in Indoor Air

Concentrations of VOCs Measured in Indoor Air Nationally: Benzene: 1.4 - 4.7 ppb, Toluene: 8.4 ppb, Ethylbenzene: 0.48 - 1.9 ppb, Xylenes: 2.07 - 8.3 ppb, TCE: 1.347 ppb, TCA: 48.9 ppb, Chloroform: 8.4 ppbOf the several hundred housing units in the Patriot Hills Housing Area, less than 30 appear to be above the groundwater plume (Figure 2). The ranges of VOCs detected in the homes were compared with commonly detected levels found in homes nationwide. These national averages are typically not far above the background levels found in the communities surrounding Hill AFB, but provide a good estimation of levels across the country. Benzene, which ranged from 0.3 to 1.67 ppb in the in-home measurements, fell into the range of common levels for benzene. Toluene, which ranged from 0.84 to 10.05 ppb in the in-home measurements, slightly exceeded the commonly detected levels, although the measured levels were far below levels that are known to cause adverse health effects. Ethylbenzene, which ranged from non-detectable to 0.68 ppb in the in-home measurements, was below the range of common levels for ethylbenzene. Xylenes, which ranged from non-detectable to 2.88 ppb in the in-home measurements, was within the range of common levels.

These common levels were based on two studies. Shah and Singh (1988) created a nationaldatabase of VOCs reported in 101 homes. The averages for TCE, TCA, and chloroform weretaken from this study. For benzene, ethylbenzene, and xylenes the best database is from the TotalExposure Assessment Methodology (TEAM) Study (EPA 1997). This study measured indoor airexposure in Bayonne and Elizabeth, NJ on 3 occasions; Los Angeles, CA on 2 occasions; and inDevils Lake, ND, Greensboro, NC, and Contra County, CA, once each. The number of homesinvolved in these studies varied from 23 to 110. Both of these studies included homes of smokersand nonsmokers (cigarette smoke contains benzene).

Can I be exposed to VOCs if I live in an area near the groundwater plumes?: VOCs were detected in the groundwater beneath housing units and in off-base residential areas. Under some conditions, VOCs can travel upward from the groundwater and through the soils, into the air of subsurface spaces. For example, vapors can seep into basements through cracks in the foundation or around the sump pump. Residents living in the housing units could come into contact with the VOCs by breathing air containing these compounds. Due to the possibility of this type of contaminant movement, indoor air was sampled at homes near the groundwater plumes in the Patriot Hills Housing Area. Indoor air was also sampled at select homes in Sunset, Clinton, Roy, Layton, Riverdale, and South Weber.Sources of BTEX

BTEX, found in the groundwater plume underlying most of the sampled homes, was also detected in the indoor air in homes that were not directly above the contaminated groundwater. Most people are exposed to some amount of BTEX every day, regardless of whether they live near BTEX-contaminated groundwater. Benzene is used to make plastics, dyes, drugs, and pesticides. It is a natural part of crude oil, gasolines, and cigarette smoke. Toluene, a component of petroleum, is used in paint, solvents, lacquers, nail polish, and spot removers. Ethylbenzene and xylenes are both components of petroleum compounds.

Because some uncertainty exists regarding how long the contaminants have been in the homes, ATSDR conservatively assumed that an adult was exposed to indoor air contaminants for 30 years. In all likelihood, families stationed at Hill AFB will be there for no more than 5 years (ATSDR 2002a). We also assumed that the exposure is constant (24 hours a day for 365 days over the 30 year period). These assumptions create a very conservative estimate of exposure, most likely higher than the actual exposure dose for an average individual in the community. Further, 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 is another conservative assumption because 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.

What is a slope factor and how are carcinogenic risks calculated?: A slope factor is used to estimate the lifetime cancer risks associated with various levels of lifetime exposure to potential human carcinogens. They are derived from human epidemiology studies and are expressed in units of (mg/kg/day)-1. For carcinogens, the risk of cancer is assumed to be proportional to the dose with the assumption that any exposure results in a nonzero risk probability. Carcinogenic risk probabilities were calculated by multiplying the estimated exposure level by the route-specific cancer slope factor for each carcinogen: R = E x SF -- where: R = estimated individual lifetime cancer risk, E = exposure level for each compound (mg/kg/day), SF = slope factorComparison of Exposure Doses to Adverse Health Effects Levels

ATSDR estimated the toxic effects of chemicals found at Hill AFB by using toxicity assessments published by the U.S. Environmental Protection Agency (EPA). The estimates of potential individual excess carcinogenic risks and noncarcinogenic health effects were developed separately. EPA has developed a list of which chemicals are possible carcinogens and has derived slope factors that define the relationship between exposure and the theoretical possibility of carcinogenic effects. Risk probabilities are compared to a risk range specified by EPA. ATSDR considers carcinogenic risks at a level greater than 1 x 10-4 as possibly requiring action, whereas risks smaller than 1 x 10-6 are considered to be of minimal concern. No action may be necessary in the risk range of 10-6 to 10-4.

What is a reference dose (RfD)?: A reference dose is amount of contaminant taken into the body per unit weight per day that is not likely to cause adverse health effects. Reference doses are derived from the scientific literature available on exposure and health effects. At doses less than the reference dose, no adverse health effects have been noticed.EPA has determined which compounds are noncarcinogenic, but may potentially cause other types of adverse health effects. For noncarcinogens, adverse health effects may not occur until a specific level of exposure occurs. Toxicity values for noncarcinogens are based on a level of exposure, typically demonstrated in laboratory animals, with the incorporation of uncertainty factors to ensure the protection of sensitive human individuals. The resulting chronic reference doses (RfDs) are defined as an estimate of the maximum daily exposure that will not produce an appreciable risk of adverse health effects during a lifetime. If reference doses were unavailable for a contaminant, ATSDR compared the concentration of the contaminant to EPA Region III's risk-based concentration (RBC). The RBC corresponds to a target risk for a particular chemical in a particular media. RBCs are calculated using similar assumptions to those that ATSDR used in calculating exposure doses. The dermal exposure doses were compared to an adjusted EPA oral reference dose. This reference dose is an estimated exposure contaminant concentration that is not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight. It was multiplied by the percent absorbency rate following oral administration to create an adjusted reference dose. At doses less than the reference dose, no adverse health effects have been observed in studies.

What is a LOAEL?: The lowest-observed-adverse effect level (LOAEL) is the lowest dose at which an adverse health effect has been observed.Other health comparison values include LOAELs and NOAELs. The LOAEL, or lowest-observed-adverse-effect level, is the lowest concentration at which an adverse health effect has been observed. It is typically presented in toxicological literature as either a dose or a concentration and is typically based on animal studies. Although human data are preferred, LOAELs often must be based on animal studies because relevant human studies are lacking. In the absence of evidence to the contrary, ATSDR assumes that humans are more sensitive than animals to the effects of hazardous substances and that certain persons may be particularly sensitive.

At levels below the LOAEL, no adverse health effects have beennoticed in studies. The NOAEL, or no observed adverse effectlevel, is the highest dose from a study that did not find any adversehealth effects. At levels below the NOAEL no adverse healtheffects were seen.

What is a NOAEL?: The no-observed-adverse- effect level (NOAEL) is the highest dose from a study that did not find any adverse health effects.In the table below (Table 3), we present the levels of VOCs detected in indoor air and thecomparison value we used to draw a conclusion. For a more detailed analysis, please see Table20 in the Tables section at the end of this document.

Exposure Estimates

Benzene is the only carcinogenic chemical detected in indoor air at the Patriot Hills Housingarea. The lifetime cancer risk we estimated for benzene exposure is below 1 x 10-4. As a result,ATSDR concludes that no adverse health effects should result from exposure to benzene in thePatriot Hills Housing area.

The inhalation exposure doses estimated for ethylbenzene and toluene at the Patriot HillsHousing area are lower than their EPA inhalation reference doses. Adverse health effects shouldnot result from exposure to detected levels of ethylbenzene or toluene in homes. A referencedose does not exist for xylenes. In the absence of a reference dose, ATSDR compared themaximum total concentration to xylenes (calculated by adding the maximum concentration ofm,p-xylenes to the maximum concentration of o-xylene) to EPA Region III's RBC for totalxylenes. The RBC for total xylenes is over 200 times higher than the maximum detectedconcentration at the Patriot Hills Housing Area. Taking this into consideration, ATSDRconcluded that no adverse health effects should result from exposure to the level of xylenes in homes in the Patriot Hills Housing Area.

Table 3.

Patriot Hills Housing area In-Home Indoor Air Measurements (1993 and 1994)
Compound Maximum Concentration (ppb) Common National (ppb) Risk (unitless)/Dose (mg/kg/day) Comparison Value (units) Source
Benzene 2 1.4 - 4.7 2 x 10-5 - -
Toluene 10.05 8.4 0.0108 0.1140 mg/kg/day EPA Reference Dose
Ethylbenzene 0.85 0.48 - 1.9 0.0011 0.2900 mg/kg/day EPA Reference Dose
Xylenes 4.93 2.07 - 8.3 0.0101 560 ppb EPA RBC

Indoor Air Modeling for Hill AFB

ATSDR applied the Johnson and Ettinger model to predict indoor air concentrations of benzenefrom the groundwater plume in those homes not sampled. Of the VOCs detected in thegroundwater plume, benzene was the only VOC that had corresponding information available foruse in the indoor air model. We assumed that each home sat above the highest groundwaterconcentration of benzene--that is, 550 ppb. Using conservative parameters and assumptionsabout exposure, the model estimated an indoor air benzene concentration of 57 ppb from thegroundwater off-gassing. The value of the indoor air concentration predicted by the Johnson andEttinger model is over 13 times smaller than the LOAEL (780 ppb), suggesting that healtheffects are not likely to result from benzene vapor migration from the groundwater plume intohomes in this area (ATSDR 1997a).

The measured concentrations of benzene in the indoor air support the model predictions becausethey too are significantly less than the screening value (over 13 times less). The measuredconcentrations reflect the contribution of benzene from all possible sources.

In addition, the measured benzene concentrations are within the range measured in other homesacross the country. This suggests that the model's predicted indoor benzene concentrations inhomes from this area will not be adversely affected by the groundwater plume.

It should be noted that the 1993-1994 indoor air concentrations likely represent the highestexposure concentrations for residents of the housing area. Remedial actions in the area of thegroundwater plume affecting the Patriot Hills Housing area were initiated in 1993 by the USAFabout the same time the indoor air sampling was performed (Montgomery Watson 1995b).Groundwater contamination in the area surrounding the Patriot Hills Housing area is, therefore,expected to decrease because of the on-going remedial efforts. Likewise, indoor air contaminantconcentrations in homes above the plumes are also expected to decrease with time.

Surface Water Dermal Contact at Hill AFB

Surface Water Pathway: VOCs - Soil - Surface Water - Hill AFB residents touching Pond 3 water during catch and release fishing

Most of the water bodies at Hill AFB are manmade ponds intended for the collection of surfacewater runoff or industrial wastewater releases. These ponds include Ponds 1 and Pond 3,Bamberger Pond, Berman Pond, and the Roy Gate Pond (Montgomery Watson 2000). Pond 3 isalso used for limited catch and release fishing by children (i.e., no fish are supposed to be eaten).Pond 3 is the only surface water body on Hill AFB that is used for a recreational activity(ATSDR 2002d). Considering this, Pond 3 was the only pond considered as a potential point ofexposure for contaminated surface water, and dermal contact with the surface water from thispond was the only pathway studied.

The USAF began sampling at Pond 3 in the 1980s. None of the samples from the pond containedchemical contamination.

1 A part per billion (ppb) means one part of something in a billion parts of something else.

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