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.)
From our visits, discussions with base personnel, and information review, ATSDR identified twoways people living in Riverdale can come in contact with environmental contaminantsoriginating from Hill AFB: groundwater contamination off-gassing into indoor air and contact with contaminated springs.
- Adults and children living in homes above contaminated groundwater in the Craigdalesubdivision may have breathed VOC vapors from contaminants migrating into the indoorair inside homes from shallow groundwater beneath the homes.
- Indoor air sampling was performed by the Air Force from 1992 to 1994 in theCraigdale subdivision. ATSDR evaluated the results of the indoor air sampling anddetermined that because contamination levels are low, the exposure from living inhomes in these communities posed no apparent public health hazard in the past,current, or future.
- Sampling in the late 1990s determined that contamination is present in springs inRiverdale. ATSDR evaluated the results of the surface water sampling anddetermined that because VOC levels are low, the exposure that occurs at thesesprings, either through dermal contact or accidental ingestion, poses no apparentpublic health hazard in the past, current, or future.
Riverdale, which comprises 4.4 square miles, is north of Hill AFB. The section of Riverdale thatis closest to Hill AFB is the Craigdale subdivision. Craigdale consists of approximately 80homes and borders Hill AFB. The Farr subdivision is the next area in proximity to Hill AFB.Contamination from former base operations and waste disposal practices has spread north andaffected groundwater in Riverdale. Sources of contamination that have created the contaminationin Riverdale are listed in Table 2 and described in Table 18 of this document. Two plumes ofgroundwater contamination affect the community of Riverdale, one as part of OU-6 and theother as part of OU-4. The OU-4 plume under lays approximately 50 acres of primarily farmfields and sparsely vegetated hill slopes in Riverdale. The OU-6 plume under lays approximately60 acres of a residential area known as the Craigdale subdivision in Riverdale (ATSDR 2002a).The USAF began initial sampling and analysis for contamination in the Riverdale area in 1988.This sampling identified contamination, primarily VOCs and metals. Contamination in Riverdaleis related to Operable Units 4 and 6 at Hill AFB.
At the request of Hill AFB in March 1994, ATSDR commented on the public health implicationsof contaminants affecting Riverdale and the portion of Hill AFB nearest Riverdale (ATSDR1994). ATSDR presented findings in a health consultation after a review of base-related recordsand reports, interviews with base personnel and off-base residents, and two base visits. At thetime, ATSDR concluded that VOCs were not present in the indoor air in the Riverdale area atlevels that represented a health threat. ATSDR also found that VOCs were not present ingroundwater or surface water at levels representing a health threat for people who occasionallycontact the water or use it for irrigation, nor would the VOCs be expected to bioaccumulate toharmful levels in fruits and vegetables grown in Riverdale.
In March 1998, the USAF prepared a report regarding the public health implications of thecontaminants detected in the Riverdale area. The USAF concluded that TCE was the primarycontaminant in the shallow groundwater aquifer in the area, but that the contamination did notimpact area drinking water supplies. They concluded that no human health risk resulted from thecontamination in Riverdale (HAFB 1998a).
The USAF has taken remedial actions to reduce groundwater contamination in Riverdale and tolimit its further migration. Landfill 1 was capped in May 1996 and a horizontal drain collectionand treatment system upgrade was completed in June 1997. Groundwater and surface waterextraction was done in June 2001 (ATSDR 2002f). Additionally, fences have been placed aroundthe Landfill 1 Cap, restrictions on issuance of future water rights in the area of contaminationhave been imposed, and wording was added to the Air Force Instruction, AFI 32-7020, to restrictconstruction or other activities that will disturb the soil or ground water in the area (HAFB1998a).
To further reduce contamination spread in Riverdale, hybrid poplar trees were planted in August2001 (ATSDR 2002f). The poplar trees use TCE as a carbon source, removing it from thegroundwater. It is anticipated that the poplar trees will provide hydraulic control to limit thecontinuing mass flow of TCE into Riverdale (ATSDR 2002a). Additionally, air strippers havebeen installed near Cooley Pond and the Craigdale subdivision.
The groundwater contamination in Riverdale has spread to the surface water (Radian 1995b).The USAF conducted sampling for surface water from 1988 until the late 1990s. The mostpredominant contaminants found in the groundwater in Riverdale are the VOCs TCE (up to 329ppb), methylene chloride (7 ppb), and benzene (up to 53 ppb) (HAFB 1994; Radian 1997). Thesechemicals move easily through groundwater and evaporate when exposed to air. Thegroundwater aquifer is not far from the ground surface. The VOCs in the groundwater areexposed to air and are able to evaporate, seeping into homes above pockets of VOCcontamination.
Two VOC groundwater plumes resulting from leaks and spills at Hill AFB have migrated northof Hill AFB, toward and beneath homes in Riverdale (Figure 2). The most predominantcontaminant in these plumes is TCE.
Indoor air was sampled in 14 basements in the Craigdale subdivision three times from December1992 through February 1994 (Radian 1995b). Additionally, during the same sampling events,two locations away from the groundwater contamination, representing background locations,were monitored. Nine of the residences where air sampling was conducted were actually withinthe known extent of the TCE groundwater plume (Radian 1997).
Indoor Air Exposure in Riverdale
There are approximately 2,970 homes in Riverdale, with only 80 in the area nearest the base (Craigdale subdivision). A majority of the city of Riverdale has no exposure to the contaminants that have migrated off base into the Craigdale subdivision (Figure 2). Of the 80 homes above the groundwater plume, the USAF sampled indoor air in the basements of 14 residences. TCE, TCA, and chloroform were detected frequently. 1,1-DCE was detected in 15% of the samples at low levels for each sample. Vinyl chloride and 1,1,2,-trichloroethane were not detected.
Remedial actions instituted by the USAF in the area of the groundwater plumes affecting Riverdale were begun after the indoor air sampling was performed (HAFB 1994; Radian 1997). Considering this, the indoor air sampling results from the 1992-1994 time frame in Riverdale likely represent a worst-case situation for residents of these communities. Future indoor air concentrations in Riverdale are expected to decrease.
Highest Concentrations Detected
TCE (up to 4.3 ppb) and 1,1,1-TCA (up to 41 ppb) were detected in indoor air in homes in theCraigdale subdivision. One sampling location, a garage sump enclosure, had a higher detectedTCE measurement of 117.5 ppb. Access to this location is limited, however, to daily visits ofshort duration by a USAF contractor involved with monitoring the performance of the treatmentsystem at this location (Radian 1995b). This concentration is much higher than the other detectedlevels of TCE. The next highest concentration detected was 4.3 ppb.
Chloroform (up to 5 ppb) was also detected in the indoor air. Chloroform, however, was notdetected in soil or groundwater in Riverdale, nor has it been associated with past operations atthe Hill AFB source areas affecting Riverdale. Therefore, the potential source of chloroform isunknown. Chloroform is a degradation product of carbon tetrachloride, but the use of carbontetrachloride was reported in only one building on base. Furthermore, carbon tetrachloride hasnot been detected in any other media in the area. These data indicate that the occurrences of arechloroform in groundwater appear unrelated to the VOC plume and detected concentrations inthe Craigdale subdivision (HAFB 1995).
The garage spring enclosure had a TCE concentration above commonly detected levels (1.3ppb), while the average of the other TCE measurements in the Craigdale subdivision was belowcommonly detected levels. The maximum detected concentrations of TCA and chloroform in theCraigdale subdivision were below commonly detected levels (48.9 ppb and 8.4 ppb,respectively).
Exposure doses were calculated for the maximum detected concentrations for TCE, TCA, andchloroform. The concentration of TCE found in the garage sump enclosure is also included inour analysis. ATSDR conservatively assumed that adults and children were exposed to themaximum and average contaminants constantly for 24 hours a day/365 days per year. Theexposure dose for the maximum concentration of TCA found in indoor air in homes in Riverdalewas more than ten times lower than the EPA inhalation reference doses (Table 12). Adversehealth effects should not result from exposure to this level of contamination in homes. For amore detailed analysis, see Table 23 in the Tables section at the end of this document.
TCE and chloroform, detected in the indoor air in Riverdale, are suspected carcinogens. Theestimated excess lifetime cancer risk for TCE is below levels likely to result in either cancerousor non cancerous health effects. Adverse health effects are not expected for humans exposed tothese levels of TCE and chloroform in their homes. The maximum exposure dose for TCA is farbelow the EPA Reference Dose. As a result, ATSDR concludes that no health hazard exists inRiverdale.
|Compound||Maximum Concentration (ppb)||Common National (ppb)||Rick (unitless)/Dose (mg/kg/day)||Comparison Value (units)||Source|
|TCA||41.35||48.9||90E-05||600E-05 mg/kg/day||EPA Reference Dose|
Indoor Air Modeling for Riverdale-Past Exposures
It was unclear whether the indoor air sampling was conducted when the groundwatercontamination under the homes was at its worst. Therefore, ATSDR used a model to estimatewhether intrusion of the highest levels would have presented a health hazard. TCE, methylenechloride, and benzene were the only detected VOCs in the groundwater beneath Riverdale thathad corresponding information available for use in the model. The maximum concentration ofTCE, 15,000 ppb, was entered in the model. The model indicated an indoor air concentration of998 ppb, which was far lower than the LOAEL (ATSDR 1997b). The maximum groundwaterconcentration, found near the Davis-Weber Canal, was chosen to serve as a worst-case scenario.Indoor air sampling has not detected TCE concentrations near this magnitude. The highestgroundwater concentration of TCE found in the Craigdale subdivision is 187 ppb (Radian 1997).This concentration was entered into the model and resulted in an indoor air concentration of 13ppb, far below levels that may cause adverse health effects.
The maximum concentration of methylene chloride, 7 ppb, was entered in the model. The modelresulted in an indoor air concentration of 0.5 ppb, which was far lower than the NOAEL(ATSDR 2000). The maximum concentration of benzene, 53 ppb, was entered in the model. Themodel resulted in an indoor air concentration of 6 ppb, which was far lower than the LOAEL(ATSDR 1997a). Based on the modeling results, ATSDR would not expect residents of homesabove the plumes to become sick or develop adverse health effects associated with the low levels of indoor air contaminants.
Surface Water Exposures for Residents of Riverdale
The USAF began surface water sampling in Riverdale as early as 1988 and continued samplinguntil the late 1990s. Surface water in Riverdale in the vicinity of Hill AFB includes one spring,two field drains, an off-base pond (Cooley's Pond), and the Davis-Weber Canal. Cooley's Pondis north of the Davis-Weber Canal near the southernmost home on 1200 West. It is a lined,artificial pond that is fed from the contaminated Cooley garage spring (ATSDR 2002a). One ofthe field drains in the northern section of the Farr subdivision, while the other is found near theintersection of 1150 West and 5600 South. Groundwater, springs, and field drains in this area arehydraulically connected; therefore, surface water near the groundwater plume area as well asCooley's Pond contain contaminants, but at a lower levels than found in the groundwater. FourVOCs have been detected in the springs: TCE (up to 180 ppb), chloroform (up to 3 ppb), 1,1,1-TCA (up to 2.5 ppb), and cis-1,2-DCE (up to 2.1 ppb) (Radian 1995b). Samples collected fromthe Davis-Weber Canal did not contain contamination. Samples taken from Cooley's Pond showlow levels of TCE contamination (below MCLs). The pond is currently being treated (ATSDR2002a).
People come into contact with surface water in Riverdale in two ways: through accidentalingestion of water from springs and through dermal contact of the surface water in the springs.Exposure doses were calculated for each of these chemicals for both accidental ingestion anddermal contact.
The maximum dermal exposure doses for TCE, chloroform, 1,1,1-TCA, and cis-1,2-DCE are substantially lower than their EPA adjusted reference doses (Table 13). Adverse health effects should not result from exposure to this level of contamination in surface water in Riverdale.
|Compound||Maximum Concentration (ppm)||Dose (mg/kg/day)||Comparison Value (mg/kg/day)||Source|
|TCE||0.180||80E-05||100E-05||Adjusted EPA Reference Dose|
|Chloroform||0.003||2.61E-05||500E-05||Adjusted EPA Reference Dose|
|TCA||0.0025||30E-05||14000E-05||Adjusted EPA Reference Dose|
|Cis-1,2-DCE||0.0021||0.0399E-07||500E-05||Adjusted EPA Reference Dose|
Ingestion of Surface Water
The maximum exposure doses for water ingestion for TCE, chloroform, TCA, and cis-1,2-DCEwere more than ten thousand times lower than their EPA oral reference doses (Table 14).Adverse health effects are not expected for humans exposed to these levels of TCE, chloroform,TCA, and cis-1,2-DCE through accidental ingestion to contaminated surface water in Riverdale.
|Compound||Maximum Concentration (ppb)||Dose (mg/kg/day)||Comparison Value (mg/kg/day)||Source|
|TCE||180||0.0563E-05||600E-05||EPA Oral Reference Dose|
|Chloroform||3||0.000781E-05||1000E-05||EPA Oral Reference Dose|
|TCA||2.5||0.000938E-05||28000E-05||EPA Oral Reference Dose|
|Cis-1,2-DCE||2.1||0.000656E-05||1000E-05||EPA Oral Reference Dose|
From our visits, discussions with base personnel, and information review, ATSDR identified twoways people living in South Weber can come in contact with environmental contaminantsoriginating from Hill AFB: groundwater contamination off-gassing into indoor air and contact with contaminated springs.
- Adults and children living above contaminated groundwater in South Weber havebreathed VOC vapors from contaminants migrating into the indoor air inside homes fromshallow groundwater beneath the homes
- Indoor air sampling was performed in 1993, 1994, and 1994-1995 in the communityof South Weber. ATSDR evaluated the results of the indoor air sampling anddetermined that because VOC levels are low, the exposure from living in homes inthis community posed no apparent public health hazard in the past, current, or future.
- Sampling in the early 1990s determined that contamination is present in springs inSouth Weber. ATSDR evaluated the results of the surface water sampling anddetermined that because levels are low, the exposure from dermal contact at thesesprings posed no apparent public health hazards in the past, current, or future.
South Weber, which has a land area of 4.6 square miles, is to the east of Hill AFB.Contamination from former base operations and waste disposal practices on Hill AFB hasspread, affecting soil and groundwater in South Weber. The USAF began soil and groundwatersampling in South Weber in the early 1980s to determine the extent of contamination.Contamination in the soil, resulting from former chemical waste disposal activities, has spread tothe shallow groundwater aquifer. Sources of contamination that have created the contaminationin South Weber are listed in Table 2 and described in Table 18 of this document.
As part of remedial activities for South Weber, a Source Recovery System was installed in 1993to remove DNAPL from the area near CDP 3. Landfill 1 (part of OU-4) was capped in May1996. Groundwater extraction trenches were installed in June 2001 to limit contaminantmigration from CDPs 1 and 2 and FTA 1. Additionally, municipal water connections wereprovided to homes known to have been affected by contamination in the area. Also, hybridpoplar trees were planted in August 2001 to contain the plume affecting South Weber andRiverdale (ATSDR 2002e). The trees are used as part of a treatability study being conducted toassess their viability to intercept and contain contaminated groundwater (ATSDR 2002a).
The USAF also identified contaminants in South Weber Well # 2, a drinking water well withinthe groundwater plume in South Weber on the eastern boundary of the base. This well was usedsporadically over the years during peak demand periods. In 1996, the submersible pump motorin the well failed, and customers of the South Weber drinking water system complained of anoily petroleum hydrocarbon odor. The pump and motor were removed for repairs and oil wasobserved floating on top of the water column in the well. Approximately 300 gallons of oil wereremoved from the well in May 1997. The pump and motor were reinstalled in the well, and onJuly 3, 1997, water produced from the well was tested. The water was found to contain VOCs atless than the detection limit (HAFB 1998c).
In August 1997, an oil odor was again noticed emanating from the well. Oil was observed onwater produced from the well during flushing. The submersible pump motor subsequently failed,and VOCs were detected in samples taken from water collected in the discharge piping (CH2MHill 1998). Benzene (15.3 ppb), chloroform (1.7 ppb), ethylbenzene (1.1 ppb), styrene (1.2 ppb),toluene (11.1 ppb), and total xylenes (2.5 ppb) were detected in the discharge pipe at thewellhouse after the pump failed. At this point, the well was taken off line. To determine if thesource of the light non-aqueous phase liquid (LNAPL) in the well could be attributed tocontamination from Hill AFB, additional sampling was performed. The analysis confirmed thatthe LNAPL from the well was significantly different from the contamination that was present inthe Hill AFB plume (Weston Engineering 1997). The well was taken off-line as soon as thepump failed. Any exposure that took place was short in duration, and far below levels that couldpresent adverse health effects.
The chemicals found in the off-base portion of the OU-1 plume where Well #2 is located areprimarily composed of 1,2-DCE. 1,2-DCE was not detected in the analysis of the oil found in thewell. Additionally, the LNAPL associated with OU-1 is restricted to the source area on base. HillAFB concluded that the probable cause of the problem was from contaminated oil used when thewell was serviced. Therefore, the problem was not connected to the contaminated groundwaterassociated with the OU-1 plume (ATSDR 2002a).
South Weber Sampling
Results of the groundwater and soil sampling have helped identify two shallow groundwatercontamination plumes (Figure 2). No contamination has been detected in the deeper aquifer,which is the source of drinking water for residents of South Weber (HAFB 1994, 1998b). Thelargest plume associated with OU-1 consists of cis-1,2-DCE and lower concentrations of TCE.The highest measured concentration of TCE is 2,400 ppb. The highest 1,1,1-TCA concentrationis 26,000 ppb. Higher concentrations of petroleum hydrocarbons have been measured in thesource area.
Several South Weber private residences are above the groundwater contamination plumes. In1990, 1993, and 1994-1995, the USAF sampled the indoor air in South Weber homes locatedover the groundwater plumes to determine whether contaminants had migrated into the homesand affected indoor air quality. The sampling rounds are summarized below.
South Weber (1990) Indoor Air Exposure
The USAF conducted air sampling in May 1990 in one private residence on West SouthWeber Drive in South Weber. Sampling was performed in May and June for three reasons:groundwater elevations are highest at this time of the year; it is one of the two times duringthe year when TCE levels inside the basement could be expected to be highest; and windowswill be closed, creating additional insulation allowing TCE to build up in the house (HAFB1993). In 1990, pumps were placed 2-5 feet in front of the basement wall and 2-3 feet abovethe ground for 1,470 minutes (24.5 hours) to pull in air and collect contaminants on charcoalfilters. No TCE was detected in the 1990 sampling on West South Weber Drive (at adetection limit of 3,700 ppb), while 1,1,1-TCA was detected at 4 ppb (USGS 1992).
South Weber (1993) Indoor Air Exposure
The second round of sampling, performed on the same home as the 1990 sampling, used theSUMMA canister method, with a lower detection limit of about 1 ppb. TCE was detected ontwo of the four sampling days, with a maximum concentration of 0.74 ppb. TCA (up to 144ppb) and chloroform (up to 0.23 ppb) were also detected (North American WeatherConsultants 1993).
South Weber (1994-1995) Indoor Air Exposure
During the 1993 sampling, two homes, thought to represent worst-case conditions of VOCsin indoor air, were selected. One home on South Weber Drive was sampled in May 1994because it is above groundwater containing cis-1,2-DCE and has a sump where basement aircomes into contact with groundwater, increasing the likelihood of volatilization ofgroundwater contaminants into the basement air. Indoor air was also evaluated at a home onSouth 850 East in July 1995 because this home is in close proximity to Hill AFB. Given thatthis home did not have a sump, its exposure potential was considered to be lower than thehome with a sump (Montgomery Watson 1995c). Chloroform and cis-1,2-DCE were foundin these homes at a maximum of 0.08 ppb and 0.29 ppb. 1,1,1-TCA (up to 0.89 ppb) andTCE (up to 0.4 ppb) were detected in indoor air at South Weber Drive and South 850 East.
Indoor Air Exposure in South Weber
South Weber has a little more than 1,100 homes. A majority of the groundwater contamination is on the hillside where no homes are situated. It appears that less than 100 homes are above the groundwater contamination from Hill AFB. Therefore we believe a majority of the homes in South Weber have no potential for exposure to indoor air contamination resulting from Hill AFB.
Remedial actions instituted by the USAF in the area of the groundwater plumes affecting SouthWeber were initiated at the same time the first sampling was performed and completed severalyears after the 1994-1995 indoor air sampling. The concentrations of VOCs detected in theearlier sampling are higher than the levels found in either 1993 or 1994-1995. Considering this,the earlier sampling round represents a worst-case situation for residents of these communities.Indoor air concentrations in South Weber are decreasing. ATSDR has no reason to believe thatthis decrease will not continue.
Highest Concentrations Detected
Chloroform and cis-1,2-DCE were found in these homes at a maximum of 0.23 ppb and 0.29ppb. 1,1,1-TCA (up to 0.89 ppb) and TCE (up to 0.4 ppb) were detected in indoor air at SouthWeber Drive and South 850 East. Although both of these VOCs were detected in groundwater,the concentrations are higher in air than one would expect if they had volatilized fromgroundwater, indicating that there may be an unknown source of these compounds in the home(Montgomery Watson 1995a). Additional air contamination found in the home can be related togasoline and vapor emissions that are widespread in the atmosphere or found in fumigants,solvents, paints, etc. Both TCA and TCE were detected at concentrations below those commonlydetected. There is no commonly detected level of cis-1,2-DCE for comparison purposes.
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 and chloroform were the only suspected carcinogens detected in indoor air in South Weber.The estimated excess lifetime cancer risk for TCE and chloroform are below levels likely tocause adverse health effects. Adverse health effects should not result from exposure to theselevels of contamination in homes in South Weber.
The maximum exposure dose for TCA found in indoor air in homes in South Weber in 1990 wasmore than 100,000 times lower than its EPA reference dose (Table 15). Adverse health effectsshould not result from exposure to this level of contamination in homes. Because the detectionlimit was so high in this sampling round and the samples were collected on only one day,additional sampling was performed in 1993. For a more detailed analysis, please see Table 25.
The maximum exposure dose for TCA found in indoor air in South Weber in 1993 was morethan five times lower than its EPA reference doses (Table 15). Using this information, ATSDRconcluded that the maximum value of VOCs detected in homes in the South Weber area is muchlower than the level known to cause adverse health effects.
The maximum exposure dose for TCA found in indoor air in South Weber in 1994-1995 was tentimes lower than its EPA reference doses (Table 15). Therefore, adverse health effects shouldnot result from exposure to this level of TCA in homes. The risk based concentration (RBC) forcis-1,2-DCE is more than 30 times higher than its maximum detected concentration. ATSDRconcluded that the maximum value of VOCs detected in homes in the South Weber area is muchlower than the level at which adverse health effects are detected.
|Compound||Maximum Concentration (ppb)||Common National (ppb)||Risk (unitless)/Dose (mg/kg/day)||Comparison Value (units)||Source|
|TCA||0.004||48.9||0.624E-05||6300E-05 mg/kg/day||EPA Reference Dose|
|TCA||18||48.9||0.0281||0.063 mg/kg/day||EPA Reference Dose|
|TCA||0.89||48.9||0.0014||0.063 mg/kg/day||EPA Reference Dose|
|Cis-1,2-DCA||0.29||N/A||-||9.33 ppb||EPA RBC|
Indoor Air Modeling for South Weber-Past Exposures
It was unclear whether the indoor air sampling was conducted when the groundwatercontamination under the homes was at its worst. ATSDR used the Johnson and Ettinger model toestimate whether intrusion of the highest levels would have presented a health hazard. TCE andPCE were the most predominant compounds in the groundwater plumes beneath South Weber.The maximum groundwater concentration of TCE, 6,300 ppb, was entered in the model. Themodel projected an indoor air concentration of 410 ppb, which was more than 100 times lowerthan the LOAEL (ATSDR 1997b). Once again, it was concluded that none of the groundwatercontaminants off-gassing into indoor air were at levels that could contribute to adverse healtheffects.
Surface Water Exposures in South Weber
Surface water in South Weber includes springs and seeps on the hillside, as well as the Davis-Weber Canal and the Bambrough Canal, two constructed irrigation canals. The Davis-Webercanal is lined with concrete and contained from groundwater contamination. Surface watersamples were collected in 1990-1992 from springs and seeps on the hillside that adjoins theDavis-Weber Canal and South Weber to evaluate off-base contamination migration and to assesswhether this contamination was affecting surface water in South Weber. Sampling performed aspart of Operable Unit (OU) 1, 2 and 4 investigations found no contamination in the portion of theDavis-Weber Canal that runs through South Weber.
Surface water samples from the Bambrough Canal were also tested. Low levels of ethylbenzene,toluene, xylenes, semivolatile organic compounds (SVOCs) and pesticides were found in thisirrigation canal. DCE was found in seeps on the hillside downgradient of the eastern portion ofOU 1, on the boundary northeast of Landfill 4, on the downgradient of the central portion of OU1, on the hillside downgradient of the western portion of OU 1, and in the Weber River Valleydowngradient of the western portion of OU 1. The maximum concentration of DCE (530 ppb)was detected in the hillside downgradient of the western portion of OU 1. Arsenic was found inseeps on the hillside downgradient of the eastern portion of OU 1, on the boundary northeast ofLandfill 4, on the downgradient of the central portion of OU 1, and on the hillside downgradientof the western portion of OU 1. The maximum concentration of arsenic detected (1,160 ppb) wasnear the base boundary northeast of Landfill 4. No additional contamination was found insurface water in South Weber (HAFB 1994, 1996b,1998b).
People come into contact with surface water in South Weber in two ways: through accidentalingestion of water from springs and through dermal contact of the surface water in the springs.Exposure doses were calculated for each of these chemicals for both accidental ingestion anddermal contact.
The maximum dermal exposure doses for DCE and arsenic are fifteen times lower than their EPA adjusted reference doses (Table 16). Adverse health effects should not result from exposure to this level of contamination in surface water in South Weber.
|Compound||Maximum Concentration (ppm)||Dose (mg/kg/day)||Comparison Value (mg/kg/day)||Source|
|DCE||0.530||0.0002||0.003||Adjusted EPA Reference Dose|
|Arsenic||1.160||0.000022||0.140||Adjusted EPA Reference Dose|
Ingestion of Surface Water
The maximum exposure doses for water ingestion for DCE and arsenic were more than eightytimes lower than their EPA reference doses (Table 17). ATSDR concludes that adverse healtheffects are not expected for humans exposed to these levels of DCE and arsenic throughaccidental ingestion of contaminated surface water in South Weber.
|Compound||Maximum Concentration (ppb)||Dose (mg/kg/day)||Comparison Value (mg/kg/day)||Source|
|DCE||530||0.0017||0.009||EPA Oral Reference Dose|
|Arsenic||1,160||0.008||0.014||EPA Oral Reference Dose|
ATSDR recognizes that infants and children may be more sensitive to environmental exposurethan adults in communities faced with contamination of their water, soil, air, or food. Thissensitivity is a result of three factors. First, children are more likely to be exposed to certainmedia (e.g., soil or surface water) because they play outdoors. Second, children are shorter thanadults, which means that they can breathe dust, soil, and vapors close to the ground. Third,children are smaller; therefore, childhood exposure results in higher doses of chemical exposureper body weight. Children can sustain permanent damage if these factors lead to toxic exposureduring critical growth stages. ATSDR is committed to evaluating children's sensitivities at areassuch as Hill AFB as part of its Child Health Initiative.
ATSDR has attempted to identify (a) populations of children at and in the vicinity of Hill AFBand (b) any public health hazards threatening these children. Approximately 1,700 dependentslive in on-base housing. Two larger day care centers (with after school programs) and 50 smallerprivate day care facilities are in the area of Hill AFB. Together, these facilities serveapproximately 500 children.
ATSDR determined that exposure of children to the highest levels of contaminants is unlikelybecause children who live at the base do not typically access IRP areas or locations ofcontamination at Hill AFB. However, ATSDR also considered the presence of children inunrestricted areas near schools, day cares, and housing areas where they might contactcontaminants leaving the area, and exposure to children in homes above the groundwaterplumes. These potential exposure pathways are discussed in the Environmental Contaminationand Human Exposure Pathways section of this PHA. Based on our evaluation, ATSDR identifiedno situations in which children are likely to be exposed to harmful levels of contaminantsassociated with Hill AFB.
Each of the exposure calculations discussed in the text were also performed for children.ATSDR concluded that no adverse health effects are expected to occur in children who areexposed to the level of contamination present at Hill AFB and in the surrounding communities.
Through the PHA process, ATSDR has gathered information about health concerns voiced bymembers of the community. In gathering this information, ATSDR interviewed base publicaffairs personnel who address community questions and concerns about Hill AFB, met withother base personnel (including the support group commander, civil engineers, the judgeadvocate, and the commander of public health) who also meet with the public, and reviewed theresults of the base's survey of community concerns.
Hill AFB has a community relations plan (CRP) that provides guidance for involving thecommunity and other interested parties in the remediation decision-making process and fordistributing information to these parties (HAFB 1997b). As part of its community relationsactivities, Hill AFB formed a restoration advisory board (RAB). The RAB, which is representedlargely by local community members, meets to periodically review base documents andcomment on actions and proposed actions taken by Hill AFB.
- Community members have expressed concern that the association of cancer may beassociated with exposure to contamination originating from Hill AFB.
- Community members have expressed concern about the occurrence of brain cancerwithin the community.
- Community members have expressed concern about unexploded ordnance at HillAFB.
In evaluating available data from Hill AFB, ATSDR has not found exposures posing apublic health hazard. Some residents, including adults and children, at Hill AFB and thesurrounding communities could be exposed to contaminants via indoor air, surface waterdermal contact, and consumption of surface water and locally-grown crops. Based on thecurrently available scientific literature, and the community specific data available forreview, the level of exposure from each of these situations individually and combined areat very low levels and would not be expected to present adverse health effects in peopleliving in these areas.
ATSDR uses human epidemiologic and occupational studies and also animal studieswhen evaluating the likelihood of cancerous effects or cancer risk. Using cancer riskestimates, ATSDR determined that cancerous health effects are unlikely in people whowere exposed to VOCs at Hill AFB and in the surrounding communities. A fewepidemiologic studies have suggested that exposure to VOCs at levels 50 to 100 timesgreater than the levels found in homes at Hill AFB and in the surrounding communitiesmay be associated with leukemia, non-Hodgkins lymphoma, and bladder and kidneycancer. The exposure doses in these studies were higher than what was estimated here.Tables 20-24 present exposure and cancer risk estimates.
Most of the VOC detected in groundwater and indoor air are common in homes acrossthe country. Automobiles, household paint, and cleaning products are the usual sourcesof VOCs in indoor air. During our review of the indoor air sampling, no contaminantswere detected at levels likely to cause cancerous or noncancerous adverse health effects.
To help investigate community concerns, the Davis County Health Department thatmonitors cancer incidence in Davis County in conjunction with the University of UtahPublic Health Program, performed a study from January 2001 to January 2002 thatinvestigated the occurrence of brain cancer in Davis County. The study was in responseto citizen concerns about dioxin-containing soil surrounding the Wasatch EnergySystems (WES) Energy Recovery Facility (i.e., "Burn Plant") and fumes emanating fromthis plant and their association with the development of brain cancer. The EnergyRecovery Facility is in Layton, Utah, and is adjacent to the southeastern corner of HillAFB. More than 200,000 tons of garbage is delivered to WES every year. WES helpsreduce landfill waste by recycling, composting, and combusting waste.
As part of the combustion process at the Energy Recovery Facility, garbage is burned in acontrolled environment with special air cleaning equipment that catches ash andimpurities. Combustion reduces the bulk of municipal waste and provides energyproduction. Combustion also produces small amounts of dioxin, which may be releasedinto the air. Airborne dioxin settles into the surrounding soil and even smaller amountsmay be carried by the wind and air currents to communities surrounding the EnergyRecovery Facility. People in the community were concerned about the number of braincancer cases, possibly due to the dioxin releases, from WES. However, investigations ofsoil and air by the Utah Division of Air Quality have determined that dioxin emissionsfrom WES do not pose a threat to public health (Wasatch Energy Systems 2002)
Researchers examined whether there was an increase in cancer cases in Davis Countycompared to the rest of the state. The study recorded a rise in brain-cancer rates over athree-year period, but found no link to the increase with any environmental causes(Khashan 2002a). The Davis County Health Department concluded that while there wasan increase in brain cancer rates in these areas from 1997 to 1999, the rise wasattributable to a random variation. Upon receiving year 2000 census data that showedcancer rates in that same area matched state averages, the study's sponsors determinedthat there was no evidence that brain cancer rate increases for the three years prior wererelated to environmental causes. All other cancers examined were found to be consistentwith statewide averages (Khashan 2002b). The health department plans to continuecancer surveillance in the area (ATSDR 2002f).
People with concerns about cancer rates in the area surrounding the Hill AFB shouldcontact the Davis County Health Department at 801-451-3340.
Recent media attention has been focused on unexploded ordnance (UXO) at the UtahTest and Training Range (UTTR). UTTR is 30 - 60 miles west of Hill AFB, on the westside of the Great Salt Lake. The UXO areas are not on or near Hill AFB proper. Theareas in question are outside the current range boundary and fall under the Corps ofEngineers Formerly Used Defense Sites (FUDS) program. UTTR is highly restricted. Assuch, no access by individuals without authorization is expected. Residents of Hill AFBand those who live in one of the communities surrounding Hill AFB are not expected toencounter UXO.
CONCERN ABOUT QUANTITY OF DATA
Although ATSDR stated throughout the text that its main focus was on indoor air, the primaryemphasis in the Hill AFB studies was directed (especially off-base) on potential exposure topolluted groundwater with almost no indoor sampling in some cities. Therefore, how didATSDR reach its conclusions about indoor air from such a thin data set?
We believe the quantity of data augmented with modeling data and data from other sitesprovided a sufficient database to evaluate the possible hazards posed by indoor air migration.ATSDR used the direct evidence of the indoor air samples and mathematical computer models tocheck indoor air levels and to predict indoor levels at areas where no air sampling has occurred. We also used information from other military bases where groundwater contamination migratedinto the indoor air spaces of homes in other parts of the country. These various data sets alongwith information about the source of the contamination, groundwater movement, and length oftime of contaminant release allowed ATSDR to predict what the levels were in the past andwhether levels were likely to increase or decrease in the future. In this way, ATSDR couldevaluate whether people were likely to have gotten sick in the past from their exposure, whetherthey are now likely to be sick, and whether they are likely to sick in the future fromcontaminants that have come from Hill AFB.
From our evaluation, we have concluded that the levels present or likely to be present in indoorair are much lower than levels of the same chemicals that have been shown to cause cancer ornon-cancerous health effects.
CONCERN THAT INFORMATION ON PROXIMITY TO WASTE SITES SHOWS HEALTHRISKS
The commenter quoted the following information.
The California Birth Defect Monitoring Program (Croen et al 1997), determined that womenwho lived within ¼ mile of a Superfund site during the first 3 months of pregnancy had a greaterrisk of having babies with certain birth defects such as heart defects and neural tube defects.
In another set of studies looking at biogas from landfills in Quebec (Goldberg et al 1995a and1995b), compounds such as tetrachloroethane, chloroform, and benzene that are included inbiogases are embryo- or fetotoxic. Excess risks were found for stomach cancer and cancer ofthe cervix uteri for women living closer to the site. The risk of low birth weight was found inthose living nearest to the site.
In a study of the Lipari Landfill in New Jersey where cleaning solvents, phenols, metals, bis (2-chloroethyl) ether and other compounds were disposed, Berry and Bove (1997) concluded thatthe population living immediately adjacent to the site was significantly impacted regarding birthweight.
Miller and McGeehin (1992) analyzed health questionnaires from residents living within 4 milesof two NPL sites near Houston, Texas. They found increases in a number of afflictions. Thesesincluded eczema and other skin problems, ulcers or other non-cancer stomach diseases, hayfever or other non-asthma respiratory allergies.
A 1998 Report on Air Carcinogens published by EPA noted that many chemical may have healtheffects such as reproductive and developmental effects for which the agency has established nobenchmark standards.
Swartz and Clapp (1992) reported that epidemiologic studies have found significantly elevatedcancer rates among the general population at levels hundreds of times lower than work-placelevels. They stated that there are no thresholds for cancer-causing agents and that exposure tolow doses of these substances produces some increased risk of developing cancer.
Other studies by Peterson et al (1979) and Swartz et al (1982) learned that vinyl chloride caninduce tumors over a range of five order of magnitude and that at the lowest dose, the cancerpotency is 30 time that at the highest dose.
The studies mentioned above make no determination of whether the people have contact withany chemicals. ATSDR used studies about actual chemical exposures to make conclusions as towhether the people living in the areas surrounding Hill AFB are likely to get sick from exposureto chemicals that have come from the base. We believe using direct studies conducted of peopleand animals exposed to the actual chemicals at the relevant exposure levels as is present in thecommunities is more appropriate. The studies mentioned above are statistical reviews of twoseparate parameters 1) people living near a hazardous waste sites and 2) illness; they are indirect and coincidental occurrences which may or may not be related.
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. Conclusions about exposures are described below. (Adescription of the public health hazard conclusion categories is included in the glossary.)
- Residents of the Patriot Hills Housing Area, Sunset, Clinton, Layton, Clearfield,Riverdale, and South Weber exposed to VOCs in indoor air are not expected toexperience adverse health effects from their low dose exposures. Therefore, exposure tothe low levels of VOCs in indoor air in the homes in these areas poses no apparentpublic health hazard.
- Residents of the Patriot Hills Housing Area, Sunset, Clinton, Layton, Clearfield,Riverdale, and South Weber exposed to VOCs and metals in surface water, througheither dermal contact or ingestion are not expected to experience adverse health effectsfrom their low dose exposures. Therefore, exposure to the low levels of VOCs andmetals in surface water near these homes poses no apparent public health hazard.
- Residents in Sunset and Clinton exposed to VOCs by way of ingestion of VOC-containing crops are not expected to experience adverse health effects from their lowdose exposures. Therefore, exposure to the low levels of VOCs in crops poses noapparent public health hazard.
- Residents in the Patriot Hills Housing Area, Sunset, Clinton, Roy, Layton, Clearfield,Riverdale, and South Weber exposed to VOCs in groundwater and soil are not expectedto experience adverse health effects. Therefore, exposure to low levels of VOCs ingroundwater and soil poses no apparent public health hazard.
Although exposure occurred in all of the above situations, the levels are too low topresent a public health hazard.
The Public Health Action Plan (PHAP) for Hill AFB contains descriptions of actions taken andthose to be taken by ATSDR, the USAF, EPA, and Utah Department of Environmental QualityEngineering at and in the vicinity of the base after the completion of this public healthassessment. The purpose of the PHAP is to ensure that this public health assessment not onlyidentifies public health hazards, but also provides a plan of action designed to mitigate andprevent adverse human health effects resulting from exposure to hazardous substances in theenvironment.
Hill AFB has an active environmental program that has developed and implemented innovativeways to reduce the groundwater contamination, and in turn, the indoor air contamination. TheUSAF's remedial efforts have focused on preventing the continued migration of contaminatedgroundwater into the communities surrounding the base. Some of their remedial efforts includeconstructing a hydraulic containment system. From fall 1997 through spring 1998, the USAFconstructed a hydraulic containment system consisting of a series of eight vertical groundwaterextraction wells. The system induces a hydraulic gradient that contains contaminatedgroundwater at the southern boundary of Hill AFB. The USAF installed a source recoverysystem in 1993 to remove dense non-aqueous phase liquid (DNAPL) from the eastern boundaryof the base (near South Weber). Landfill 1, on the northeastern boundary of the base was coveredwith asphalt in May 1996.
Groundwater extraction trenches were installed at several locations on the base in order to limitcontaminant migration from an area near South Weber. The USAF covered the SodiumHydroxide Tank Site and Berman Pond with asphalt caps in the late 1990s. Hybrid poplar treeswere planted in August 2001 in an effort to control the plume affecting Riverdale and SouthWeber.
- The Air Force continues to investigate and clean up areas of contamination both on andoff base. They have implemented numerous new technologies to stop or retard the movement ofcontaminants off base. The USAF continues to investigate groundwater contaminationmovement. New information gathered in the late 1990s has shown that additional contaminantsources are in Zone 16 to the east of the TARS area, near the communities of Sunset and Clinton.For this reason, the RI was reopened. Since then, additional contamination has been found in Roy. The former Wastewater Treatment Plant, on base and north of the TARS area, has been identified as a potential source of this contamination. Sampling in Roy is still on-going.
- ATSDR supports continued monitoring of the groundwater plumes, soil, and indoor airsampling in Roy to characterize the extent of groundwater contamination and determine ifindoor air contamination is present.
- ATSDR recommends that the USAF monitor indoor air quality (both flux and in-homemeasurements) in additional homes in Roy. To more fully assess the exposure potential forVOCs in the homes, residences located above the groundwater contamination plumes as well asresidences not located above groundwater contamination plumes should be chosen. Additionally,the flux measurements would provide valuable insight into the cause of the indoor aircontamination in the homes (i.e., whether VOC contamination resulted from the groundwaterplume, non-base related contamination, or a combination of both). Ideally, this monitoringshould occur as soon as possible and last until sufficient characterization of the contamination is known.
- ATSDR recommends that the USAF determine the need to provide environmentaleducation about suspected contaminants for residents of the communities surrounding Hill AFB.
Environmental Health Scientist
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry
Elizabeth C. Mitchell, MSPH
Environmental Health Scientist
Eastern Research Group, Inc.
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