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PUBLIC HEALTH ASSESSMENT

U.S. AIR FORCE PLANT NO. 4 (GENERAL DYNAMICS)
FORT WORTH, TARRANT COUNTY, TEXAS


ENVIRONMENTAL CONTAMINATION / PATHWAYS ANALYSIS /
PUBLIC HEALTH IMPLICATIONS

A. INTRODUCTION

This section examines the pathways for exposure to contamination at AFP4. We will examineeach of the media (foodchain, sediment, surface water, air, soil, and groundwater) to determinewhether or not contamination is present and if people in the community are exposed to (or incontact with) the contamination. If people are exposed to contamination in any of the media, wewill evaluate whether there is enough contamination to pose a hazard to people in the community. This analysis will systematically evaluate each of the media. Table 1 presents a summary of theexposure situations identified at this site.

To assess the potential health risks associated with contaminants, we compared contaminantconcentrations to health assessment comparison (HAC) values. HAC values are media specificcontaminant concentrations that are used to screen contaminants for further evaluation. Non-cancer HAC values are called environmental media evaluation guides (EMEGs) or reference dosemedia evaluation guides (RMEGS) and are respectively based on ATSDR's minimal risk levels(MRLs) or EPA's references doses (RfDs). MRLs and RfDs are estimates of a daily humanexposure to a contaminant that is unlikely to cause adverse non-cancer health effects. Cancer riskevaluation guides (CREGs) are based on EPA's chemical specific cancer slope factors andestimated excess lifetime cancer risk of one-in-one-million persons exposed for a lifetime. Weused standard assumptions to calculate appropriate HAC values [6]. Exceeding a HAC valuedoes not imply that a contaminant represents a public health threat, but suggests that the contaminant warrants further consideration.

B. INDETERMINATE PUBLIC HEALTH HAZARD

TDH and ATSDR concluded that the following exposure situation is an indeterminate publichealth hazard. In this situation, more information is required to adequately define the potentialhealth hazard.

Evaluation of Possible Foodchain Exposure Pathways

Summary: Concentrations of PCBs (Arochlor 1254, Arochlor 1260), dieldrin, naphthalene, andPAHs (phenanthrene, and benzo(b)fluoranthene) in edible size fish caught in Lake Worth at theconvergence of Meandering Road Creek pose an indeterminate (potential) public health hazardto people eating fish from this area. Even though edible sized and species fish were not sampled,the Mosquito fish, a small non-edible species, contained elevated concentrations of chemicalsknown to bioconcentrate up the foodchain. Chemical concentrations were compared to thoselevels in fish taken from similar areas not impacted by AFP4. To address this issue, werecommend that the Air Force in coordination with TDH Seafood Safety Division, collect ediblefish samples from this area.

Mosquito fish were collected from five locations along Lake Worth and Meandering Road Creek. Two of the sample locations were background locations or locations not influenced bycontaminants from AFP4. Mosquito fish are tiny fish and are not used as a food source byhumans; however, they are abundant, tolerant of chemical contaminants, store contaminants infatty tissue and may be eaten by other fish which are consumed by humans. The mosquito fishwere collected with seines (net), frozen, and prepared as whole fish tissue samples. Ten fishsamples were composited into five samples for analysis. Fish were analyzed for polycyclicaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs [Arochlors]), organochlorines,and metals.

PCBs (Arochlor 1254, Arochlor 1260), dieldrin, naphthalene, and PAHs (phenanthrene, andbenzo(b)fluoranthene) were detected at higher concentrations in tissue samples from fish collectedadjacent to AFP4 than in fish collected from the background locations [1]; however, in general,the reported concentrations are low (DDE, 0.01mg/kg; dieldrin, 0.01 mg/kg; naphthalene, 0.02mg/kg; phenanthrene; 0.03mg/kg; and benzo(b)fluoranthene, 0.01 mg/kg). The maximumconcentration of PCBs (0.32 milligrams-PCBs per kilogram of fish tissue [mg/kg]) in thesesamples was lower than or equal to the average concentrations of PCBs in fish tissue reported nationwide by others [7], and lower than 2.0 mg/kg, the limit for fish and shellfish (edible portion)set by the Food and Drug Administration (FDA).

In the ecological risk assessment prepared for the U.S. Department of the Air Force, contaminantsof potential concern (CoPCs) were selected by screening the lists of contaminants detected inenvironmental media samples. Contaminants were excluded from the CoPC list if the highestconcentration of the contaminant was detected at a background location, if the analyticalparameter was not a specific contaminant, if the analytical parameter was redundant, or if thecontaminant was not related to site processes (radionuclides only). Contaminants also wereincluded if they were detected in the upper two (2) feet of soil from Landfill No. 3 and No. 4.

Using the selected CoPCs, three aquatic exposure pathways (fish tissue to largemouth bass,sediment to largemouth bass, and water to largemouth bass) were considered to determinepotential risks to aquatic organisms. A potential risk to largemouth bass from exposure tocontaminants in the environmental media was identified. The primary contaminants identified thatcould pose a risk to predator species include: 1,2-dichlorobenzene, 1,2-dichloroethene, lead,PCBs (Arochlor 1254), beryllium, and selected PAHs. We could not determine, with any degreeof certainty, if AFP4 was the only source for these contaminants.

It would be reasonable to assume that edible fish species could potentially accumulatecontaminants and be consumed by people. For instance, because of the lipophilic nature of PCBs,higher fat content species such as carp, drum [gaspergou], catfish, and buffalo fish maybioaccumulate these compounds. Long-term exposure to PCBs potentially could pose publichealth threat; however, because of a lack of edible fish tissue data we could not adequatelyevaluate this exposure situation. Based on available data, we conclude that exposure tocontaminants through the ingestion of fish taken from Meandering Creek or Lake Worth isan indeterminate public health hazard.

Table 1.

Exposure Situations - U.S. Air Force Plant 4
Table 1
Exposure Situations - U. S. Air Force Plant 4
PATHWAY
NAME
PRIMARY
CONTAMINANTS OF
CONCERN
Exposure Pathways Elements TIME CONCLUSIONS
SOURCE ENVIRONMENTAL
MEDIA
POINT OF
EXPOSURE
ROUTE OF
EXPOSURE
POTENTIALLY
EXPOSED
POPULATION
Foodchain PCBs1
Semi-VOCs2
Pesticides
AFP4/
Other
Fish* Residences Ingestion People eating fish caught in Lake Worth near confluence with Meandering Road Creek Past
Present
Future
Indeterminate public health hazard because of insufficient data and information presented in the ecological risk assessment
Meandering Road Creek Sediment PAHs3
VOCs4
TPH5
Landfill No. 3 Sediment Meandering Road Creek Ingestion General Public Past
Present
Future
No apparent public health hazard due to limited access and low probability of exposure
Lake Worth Sediment PAHs
VOCs / Semi-VOCs
TPH
Various site activities Sediment North shore of facility along Lake Worth Ingestion General Public Past
Present
Future
No apparent public health hazard due to low probability of exposure and/or intermittent nature of possible exposures
Surface Water VOCs
Metals
AFP4
NAS
Surface Water Meandering
Road Creek
Lake Worth
Farmers Branch Creek
Dermal Contact
Incidental
Ingestion
General Public Past
Present
Future
No apparent public health hazard due to low probability of exposure and/or intermittent nature of possible exposures
Air VOCs AFP4 Operations/
Other
Ambient Air On Site Inhalation Site Workers Past
Present
Future
No apparent public health hazard since contaminants were not found at levels that would be a public health concern
Soil PAHs
Metals
Various site activities Soil Landfills Area below Assembly/
Parts Bldg
Ingestion
Dermal Contact
Site Workers* Past
Present
Future
No public health hazard to public or workers due to limited access and intermittent nature of possible exposures.
Groundwater VOCs AFP4 Operations Groundwater Residential drinking/
showering water
Incidental ingestion, Inhalation, Dermal contact Residents using White Settlement Water Supply* Future No public health hazard since contaminants have not migrated toward public water supply wells and remedial actions to prevent migration toward these wells are being implemented.
* Pathway element is missing. 1 PCBs- Polychlorinated biphenyls. 2 Semi-VOCs - Semi-volatile organic compounds. 3 PAHs - Polycyclic aromatic hydrocarbons. 4 VOCs- Volatile organic compounds. 5 TPH - Total petroleum hydrocarbons.

C. NO APPARENT PUBLIC HEALTH HAZARD

ATSDR concluded that the following identified exposure situations do not represent a publichealth hazard under current conditions either because there is no evidence that people are cominginto contact with contaminated media or it is unlikely that they are coming into contact withcontaminated media often enough to present a threat to public health.

Evaluation of Possible Sediment Exposure Pathways

Summary: Exposures of children and adults who accidentally ingest sediments from Lake Worthand Meandering Road Creek present no apparent public health hazard. Concentrations ofchemicals detected in off base sediments of Lake Worth and Meandering Road Creek are lowand any possible contact would be infrequent due to the landscape/terrain and fence.

    Lake Worth

A total of 25 sediment samples were collected from various locations in Lake Worth to determineif past contaminant spills or releases from AFP4 have reached the lake [1]. Samples werecollected from areas where contamination was likely to be found such as the coves with drainagefrom AFP4, the area adjacent to the former NARF area, the area along the north shore of the site,and the area near where Meandering Road Creek enters the lake.

One background sample was collected from a cove with drainage not originating from AFP4 andone sample was collected from the drainage area above the background sample location. Thebackground sample location was chosen to be close enough to AFP4 to be considered a similarhabitat, but far enough away to be unaffected by potential contamination from the Plant or otherindustrial facilities. Samples were analyzed for volatile organic compounds (VOCs), semi-VOCs,total petroleum hydrocarbon (TPH), oil and grease, PCBs, pesticides, and metals; however, allsamples were not tested for all constituents. A field scan was performed for alpha, beta, andgamma radiation on all samples collected from sediments near the former NARF area; noradiation levels above background were detected.

Sediment from the background location contained acetone (0.230 mg/kg), 2-butanone (0.053mg/kg), trichloroethylene (TCE) (0.16 mg/kg), TPH (169 mg/kg), oil and grease (290 mg/kg),and various metals (chromium, 23.6 mg/kg; lead, 164 mg/kg; and zinc, 74.3 mg/kg). PAHs weredetected in sediment collected from the drainage area above the background location atconcentrations ranging from 0.01 to 0.130 mg/kg. Adjacent to AFP4, the maximumconcentration of PAHs ranged from 1.3 mg/kg (dibenzo[a,h]anthracene) to 7.9 mg/kg(benzo[a]anthracene); benzo[a]pyrene was found at a maximum concentration of 4.9 mg/kg. Acetone (0.085 mg/kg; max.), carbon disulfide (0.024 mg/kg; max.), 2-butanone (0.035 mg/kg;max), TCE (0.044 mg/kg; max), anthracene (1.8 mg/kg; max), bis(2-ethylhexyl)phthalate (1.5mg/kg; max), fluoranthene (15 mg/kg; max), pyrene (9.2 mg/kg; max), fluorene (0.39 mg/kg;max), naphthalene (0.12 mg/kg; max) and lead (444 mg/kg) were detected in sediment from LakeWorth near AFP4. These contaminants were detected at concentrations below their respectiveHAC values (Table 2). TPH (623 mg/kg), and oil and grease (893 mg/kg) also were found insediment from Lake Worth near AFP4. Although HAC values were not available for TPH, oil andgrease, incidental exposure to these contaminants at the reported concentrations would not pose asignificant public health threat.

Since this in not an area where people would be likely to walk without shoes or boots, we do notconsider dermal contact to be an important route of exposure. Several of the PAHs areconsidered to be probable human carcinogens; however, thus far a quantitative cancer potencyfactor only has been developed for benzo[a]pyrene. EPA and others have developed a relativepotency estimate approach for the PAHs which estimates the cancer potency of the othercarcinogenic PAHs relative to benzo[a]pyrene. Based on maximum reported values for PAHs insediment from Lake Worth, the benzo[a]pyrene equivalent concentration for the carcinogenicPAHs is 8.1 mg/kg. Because this value is derived from the maximum reported concentrations theactual exposure point concentrations would be lower; however, we estimate that chronic ingestionof sediment (70 kg adult ingesting 100 milligrams of sediment each day for a lifetime) containing8.1 mg/kg benzo[a]pyrene, a probable human carcinogen, would result in a low to no apparentincreased lifetime risk for cancer. Thus, sediment in Lake Worth poses no apparent publichealth hazard.

Table 2.

Health Assessment Comparison (HAC) Values for Volatile Organic Contaminants in Sediment From Lake Worth
Contaminant HAC Value (mg/kg) Type of HAC Value
Acetone 5,000 RMEGchild
Carbon Disulfide 5,000 RMEGchild
2-Butanone 30,000 RMEGchild
Trichloroethylene 100 intermediateEMEGchild
Anthracene 20,000 RMEGchild
Bis(2-ethylhexyl)phthalate 1,000 RMEGchild
Fluoranthene 2,000 RMEGchild
Pyrene 2,000 RMEGchild
Fluorene 2,000 RMEGchild
Naphthalene 1,000 intermediateEMEGchild
Lead 500 EPA Action Level
EMEG: an environmental media evaluation guides based on ATSDRs minimum risk level
RMEG: an environmental media evaluation guides based on EPAs reference dose
    Meandering Road Creek

Sediment samples were collected from seven locations along Meandering Road Creek todetermine the extent of contamination in the creek and to better define the locations ofcontamination entering the creek [1]. These samples, collected from areas adjacent to outfalls andpreviously identified hazardous waste areas, were analyzed for VOCs, semi-VOCs, TPH, oil andgrease, and metals. Sediment from the creek contained low concentrations of VOCs, Semi-VOCs, TPH, oil and grease, and metals. VOCs and semi-VOCs were detected infrequently and atconcentrations below levels of health concern. TPH and oil and grease were detected in creeksediment at concentrations comparable to those detected in background samples from LakeWorth. Metals were rarely detected above natural background levels.

In addition to the samples collected along the creek, seven sediment samples (from the surface toa depth of two feet [actual depths of individual samples were not provided]) were collected fromsix locations along a transect (a line crossing the creek) originating from the west side of LandfillNo. 3. These samples contained PAHs (benzo[a]pyrene equivalents of 7.6 mg/kg), and variousmetals. The most notable metals detected were lead (range 10.6 to 10,400 mg/kg), cadmium(range 1.5 to 96 mg/kg), and chromium (range 11.6 to 369 mg/kg). Lead and cadmium weredetected in four of the seven transect samples; chromium was detected in two of the sevensamples.

Since this is not an area where people would be likely to walk without shoes or boots, we do notconsider dermal contact to be an important potential route of exposure. Chronic ingestion (100milligrams per day for a lifetime) of sediment containing 7.6 mg/kg benzo[a]pyrene, a probablehuman carcinogen, could result in a low to no increased lifetime risk for cancer. Children who eatsediment containing lead at concentrations as high as 10,400 mg/kg could be at risk for leadpoisoning; however, the probability of a child ingesting sediment from this area is extremely low. Access to the contaminated area is restricted by a fence extending across the creek, along theboundaries of the Landfill No. 3. This is not an area that would be frequented by small children. Sediment in Meandering Road Creek currently poses no apparent public health hazard.

Evaluation of Possible Surface Water Exposure Pathways

Summary: Exposures of children and adults who accidentally ingest or swim in water from LakeWorth, Meandering Road Creek, and Farmers Branch Creek present no apparent public healthhazard. Concentrations of chemicals detected in off base surface water of Lake Worth, Meandering Road Creek, and Farmers Creek are low and any possible contact would beinfrequent.

Contamination of surface water is an issue of potential concern at AFP4 because of possibletransport of contaminants from other contaminated areas to surface water. The surface waterbodies adjacent to AFP4 include Lake Worth, Meandering Road Creek, and Farmers Branch. Water samples were collected from these water bodies to determine if they were contaminatedwith contaminants likely originating from AFP4.

    Lake Worth

Nine surface-water samples were collected from Lake Worth in October 1991 [1]. Seven sampleswere collected along the northern boundary of AFP4; two samples were collected from areasconsidered to be background. Carbon disulfide (200 micrograms per liter of water [µg/L]; max.),oil and grease (2,010 µg/L; max.), arsenic (11.2 µg/L; max), silver (133 µg/L; max.), and zinc(44.2 µg/L; max.) were the only contaminants detected in water from Lake Worth. Carbondisulfide, and zinc were detected at concentrations below their respective health based comparisonvalues (1,000 µg/L and 3,000 µg/L, respectively). Arsenic was detected at a concentration belowthe drinking water standard established by the EPA for this contaminant (50 µg/L). Although themaximum detected concentration of silver was above the Reference Dose (RfD) basedcomparison value for a child (50 µg/L), a 10 kg child would have to ingest approximately 0.5liters of lake water per day, every day to exceed the RfD. Incidental ingestion of raw surfacewater from Lake Worth adjacent to AFP4 is possible; however, if it were to occur it would occurinfrequently and the amount ingested would be very small resulting in limited exposure. LakeWorth water is used as a source of water by the City of Fort Worth; however, according to theTNRCC Water Utilities Division, site contaminants have not been detected in water collectedfrom any of the entry points to the distribution system. Based on the above we do not consideringestion of Lake Worth water to be a significant exposure pathway.

Exposure to contaminated lake water by swimming is possible; however, the exposure durationand frequency of this activity would limit the total exposure. It is not likely that people wouldswim adjacent to AFP4 where contaminant concentration will be highest; contaminants migratingto other areas of the lake will be significantly diluted. For several reasons: 1) low frequency ofexposure, 2) low duration of exposure, and 3) low contaminant concentrations we do notconsider dermal contact to be a significant exposure pathway. Based on available information,water from Lake Worth poses no apparent public health hazard.

Meandering Road Creek

During the 1995 remedial investigation, surface water samples were collected from 11 locationsalong Meandering Road Creek [1]. Forty samples were collected directly from the creek andthree samples were collected from a seep along the creek near Landfill No. 3. Cis-1,2-dichloroethene, TCE, vinyl chloride, and 1,2-dichloroethane all were detected at maximumconcentrations above their respective drinking water standards (Table 3). Concentrations exceeding the screening values were found in samples collected along the central portion ofLandfill No. 3. The EPA has classified vinyl chloride as a human carcinogen and 1,2-dichloroethane as a probable human carcinogen. TCE is under consideration as to itscarcinogenic classification; it will likely be classified either as a possible or probable humancarcinogen. TCE, vinyl chloride, and 1,2-dichloroethane were detected infrequently (Table 3).

Table 3.

Maximum Concentrations of Volatile Organic Compounds Detected in Surface Water From Meandering Road Creek in 1995
CONTAMINANTMAXIMUM
CONCENTRATION
(µg/L)


HAC Values
(µg/L)

FREQUENCY
OF DETECTION
cis-1,2-Dichloroethene
Trichloroethylene
Vinyl Chloride
1,2-Dichloroethane

430
140
120
1,800

70 (MCL)
5 (MCL)
2 (MCL)
5 (MCL)

9/16
7/41
3/43
1/41

We did not consider exposure to site contaminants either through incidental ingestion or dermalcontact to be significant exposure pathways since: 1) access to the contaminated area is restrictedby a fence, 2) the probability of ingesting or contacting water from this area is very low, 3) thefrequency of exposure would be very low, 4) the duration of contact with contaminated waterwould be low, and 5) the surface area of skin that potentially could come into contact withcontaminated water would be small. Based on available information, water from MeanderingRoad Creek poses no apparent public health hazard. Further contamination of the creek shouldbe mitigated by the treatment system installed by the Air Force to prevent Landfill No. 3contaminants from entering Meandering Road Creek. This system became operational in theSpring of 1997.

    Farmers Branch Creek

Five locations along Farmers Branch Creek have been sampled from 1992 until the present [1]. The farthest upstream location is at the mouth of the aqueduct as the creek enters the Naval AirStation. The farthest downstream sample location is in the golf course area east of NAS LandfillsNo. 4 and No. 5. At the farthest upstream location in Farmers Branch Creek, contaminantconcentrations were at or below the detection limit. Downstream, TCE (67 µg/L) and cis-1,2-dichloroethene (29 µg/L) were detected; however, the highest concentrations of thesecontaminants were found in a small unnamed tributary to the creek. In February 1995, the mostrecent sampling event, the concentrations of TCE and cis-DCE detected in water from thisunnamed tributary were 100 µg/L and 380 µg/L, respectively.

We did not consider exposure to site contaminants either through incidental ingestion or dermalcontact to be significant exposure pathways at this location. 1) the area is on the NAS and theprobability of ingesting or contacting water from this area is very low, 2) the frequency ofexposure would be very low, 3) the duration of contact with contaminated water would be low,and 4) the surface area of skin that potentially could come into contact with contaminated mediawould be small. Currently, water from Farmers Branch Creek poses no apparent publichealth hazard.

Evaluation of Possible Air Exposure Pathways

Summary: Exposure of base workers to ambient air at AFP4 presents no apparent public healthhazard. Concentrations of chemicals detected in ambient outside air are below healthcomparison values. Additionally, air released from air stripping operations on-base used totreat contaminated groundwater would be monitored and required to meet clean air standards. Air stripping operations are not expected to increase air contaminants to levels of healthconcern.

Ambient air: The air data for this site are limited to samples obtained from two air monitoringstations [1]. One off-site station was established approximately 0.75 miles west of the site toprovide information on the general air quality for the White Settlement area. The second airmonitoring station was placed on the site, approximately 300 feet north of Building 176, to assessthe contribution of air contaminants from AFP4. Each monitor was equipped to collect samplesfor VOCs, total particulates, and selected metals. Samples were collected in 1992 between mid-February and mid-May once every six days. A total of fifteen samples were collected from eachlocation. Meteorological data (wind speed and direction) were obtained from the meteorologicalstation at NAS. Exact meteorological data for these sampling episodes were not available. Duringmost of the year, the predominant wind direction is from the south; however, during the wintermonths (December through February) the predominant wind direction is from the north [1]. Stainless steel SUMMAR canisters were used to collect samples for VOC analysis. WhatmanEPM-2000 ultrahigh purity glass fiber filters were used for total particulates and metals analyses.

Five of the 23 VOCs detected in the air samples (chlorodifluoromethane, cis-1,2-dichloroethane,chloroform, n-nonane, and Freon 114) were detected only in one sample. Nine of the remaining18 VOCs (chloromethane, carbon tetrachloride, benzene, tetrachloroethene, chlorobenzene,ethylbenzene, m-and/or p-xylene, o-xylene, and styrene) were detected in the on-site samples atthe same frequency and concentrations as in the off-site/background samples. These likely do notrepresent significant site-related contamination. The remaining nine VOCs(dichlorodifluoromethane, freon 113, methylene chloride, 1,1,1-trichloroethane, TCE, toluene,trichlorofluoromethane, 1,3,5-trimethylbenzene, 1,2,4- trimethylbenzene) were detected off andon site at similar frequencies; however, on average these compounds were detected at higherconcentrations in the on-site samples (Table 4). None of the contaminants exceeded theTNRCC's long-term Effects Screening Levels (ESLs). Although ESLs are not ambient airstandards, they are used by the TNRCC to evaluate the potential impact of air pollutants. Since measured levels of airborne contaminants do not exceed ESLs, adverse health effects would notbe expected. Ambient air at AFP4 poses no apparent public health hazard.

Air Stripping Operations: According to the Final Record of Decision (ROD), the selected remedyto treat contaminated groundwater in the East Parking Lot Plume and the Terrace Alluvial FlowSystem involves the removal of the contaminants from the water by air stripping. Air dischargedfrom the air stripper will be treated with an off-gas treatment system that results in near-zeroemissions of contaminants to the atmosphere. We would not expect air released from a properlyoperated and monitored system to pose a public health hazard.

Table 4.

Health Assessment Comparison Values For Organic Air Contaminants - Air Force Plant 4
CONTAMINANT Average Concentration
On Site                  Off Site

TNRCC
Long Term ESL1
ORGANICS (ppbv) (ppbv) (ppbv)
Dichlorodifluoromethane 2.55 0.47 1,000
Chlorodifluoromethane2 0.12 na 500
Chloromethane 0.36 0.36 50
Freon 1132 0.99 0.20 500
Methylene chloride2 0.19 0.15 7.5
cis-1,2-Dichloroethene 0.10 na 200
Chloroform 0.10 0.07 2.0
1,1,1-Trichloroethane2 0.61 0.35 200
Carbon Tetrachloride 0.10 0.10 2.0
Benzene 0.70 0.50 1.0
Trichloroethylene2 0.71 0.18 25
Toluene2 1.92 1.12 50
Tetrachloroethene 0.18 0.18 5
Chlorobenzene 0.11 0.10 10
Ethylbenzene 0.33 0.37 100
m +/or p-Xylene 1.22 1.51 100
n-Nonane 0.14 na 200
o-Xylene 0.43 0.54 100
Styrene 0.10 0.11 20
Freon 114 0.05 na 1,000
Trichlorofluoromethane2 0.70 0.33 1,000
1,3,5-Trimethylbenzene2 0.18 0.11 25
1,2,4-Trimethylbenzene2 0.44 0.27 25
1 Texas Natural Resource Conservation Commission (TNRCC) Effects Screening Levels (ESLs). ESLs are not ambient air standards, but are used bythe TNRCC to evaluate the potential impact of air pollutants. Adverse health effects are not expected at airborne levels below ESLs.
2 Detected off site and on site at similar frequencies but on average were detected at higher concentrations in the on-site samples.

D. NO PUBLIC HEALTH HAZARD

ATSDR has concluded that under current conditions both possible exposure to on-base soil andpossible exposure to groundwater do not pose a public health hazard because no one is currentlybeing exposed. Proposed remedial actions have been chosen to reduce or eliminate the likelihoodthat groundwater at this site would become a public health threat in the future; thus, exposure tocontaminated groundwater in the future is unlikely. All municipal water well systems are requiredto be frequently sampled to meet clean drinking water standards and sampling strategies havebeen designed to assure the early detection of contaminants should they migrate towardsmunicipal supply wells. Any potential future exposure would be of short duration and not likelyto result in any adverse health effects.

Evaluation of Possible Soil Exposure Pathways

Soil contamination has been documented at several areas within AFP4 [1]. The contaminantspresent include VOCs, PAHs, and metals. These areas, which include the landfill areas and thearea beneath the Assembly/Parts Plant Building, are generally fenced or have public accessotherwise restricted. A six-foot chain-link fence, capped with barbed wire, surrounds the facilityand a security guard is posted at the entrance to the plant. As a result of these institutionalcontrols (and as long as such controls are diligently maintained), the contaminated soil atthese locations does not pose a public health hazard.

Evaluation of Possible Groundwater Exposure Pathways

    Hydrogeology

The hydrogeologic system associated with AFP4 consists of three main units: an upper-zonegroundwater system (the Terrace Alluvial Aquifer); an aquitard system (the Goodland-Walnut Confining Unit); and the Paluxy Aquifer. Natural recharge to the Terrace Alluvial Aquifer occurslocally through direct infiltration of precipitation and runoff. Although paved areas and buildingsover much of the NPL site restrict the natural infiltration of precipitation, infiltration does occurthrough several large grassy areas. Additional recharge occurs from leakage of water-supplylines, firefighting pipe systems, cooling-water systems, sanitary sewers, and storm sewers. AtAFP4, groundwater in the Terrace Alluvial Aquifer flows radially outward, from the northern andsouthern portions of the Assembly Building, toward Bomber Road and Meandering Road Creekto the west, NAS and West Fork Trinity River to the east, and Farmers Branch to the south. TheTerrace Alluvial Aquifer is not used for water supply; however, it discharges naturally byseepage to Meandering Road Creek, Farmers Branch, a few small tributaries along FarmersBranch, and Lake Worth which provides drinking water to the City of Fort Worth.

The Terrace Alluvial Aquifer and the Paluxy Aquifer are separated by two rock layers, theGoodland Limestone and the Walnut Formation. In general, these layers are relativelyimpermeable and restrict the vertical flow of groundwater between the Terrace Alluvial Aquiferand the Paluxy Aquifer. At AFP4, the combined thickness of these layers range from 0.5 to 70feet. In some areas, however, erosion has completely removed the Goodland Limestone and allbut a few feet of low permeability rock of the Walnut Formation. The Walnut Formation hasbeen eroded to a thickness of between 0.5 and 2.5 feet in the vicinity of the east parking lot. Inthis area, which has been referred to as the "Window Area" (Figure 5), there is a potential forshallow groundwater from the Terrace Alluvial Aquifer to migrate into the Paluxy Formation.

The Paluxy Aquifer, comprised of the Paluxy Formation, is an unconfined to semi-confinedaquifer comprised mainly of sandstone and mudstone. At AFP4, the Paluxy Aquifer consists ofthree hydraulically isolated zones; the upper zone (top 50-60 feet), the middle zone (40-50 feetthick), and lower zone (25-30 feet thick). A local sand lens called the "Upper Sand" has beenidentified in the uppermost interval of the upper zone beneath AFP4. The "Upper Sand" islocated beneath the east parking lot area, extends west to the west side of the AssemblyBuilding/Parts Plant, east to the flightline area, south to Clifford Avenue, and north past theengineering building. The Paluxy "Upper Sand" is physically part of the upper zone of the PaluxyAquifer and may be hydraulically disconnected from the deeper regionally extensive parts of theaquifer; however, this is uncertain. The "Upper Sand" is unsaturated, except directly below the"Window Area" and it appears to be underlain by a strongly cemented, shaley, fine grainedsandstone. The lateral extent of the "Upper Sand" is not known.

Groundwater in the Paluxy Aquifer flows from west to east-southeast (Figure 5). The middle andlower zones of this aquifer are widely used as a source of water for domestic, municipal, andindustrial water supplies in Tarrant and Dallas Counties. In the vicinity of AFP4, the middle andlower zones provide municipal water to the city of White Settlement; seven municipal watersupply wells obtain water from the Paluxy Aquifer. White Settlement municipal well #2 (WS-2) isapproximately 1,200 feet west of the creek and draws from the middle Paluxy Aquifer (Figure 5);however, this well is no longer in use. White Settlement municipal well #12 (WS-12) isapproximately 1,700 feet south of the plant and also draws from the middle Paluxy Aquifer(Figure 5). Many private residences across Lake Worth use residential wells for potable water;however, these wells are upgradient (northwest) from AFP4. The lake provides municipal waterto the city of Fort Worth and is a recharge source to the underlying Paluxy Aquifer. The AFP4facility receives its potable water from the city of Fort Worth public water supply [8]; this water istested annually and meets federal drinking water standards.

Contaminants from the site have been documented both in the Terrace Alluvial Aquifer and thePaluxy Aquifer. Each of these aquifers is discussed separately below.

    Contamination in the Terrace Alluvial Aquifer/Upper-Zone Groundwater System

Three distinct plumes of contamination have been identified in the Terrace Alluvial Aquifer(Figure 6); the locations of these are partially controlled by the locations of topographical highs inthe buried bedrock surface. These plumes have been referred to as; 1) the East Parking LotPlume, 2) the West Plume, and 3) the North Plume. The East Parking Lot Plume is the largestplume of groundwater contamination. From the south end of the Assembly Building/Parts Plant,the plume extends to the east and northeast past the East Parking Lot toward the NAS. On NASproperty the plume appears to have merged with source areas on NAS property. Releases fromdegreaser tanks located in Building 181 are believed to be the major source of the contaminationfound in the East Parking Lot Plume. During one documented event that occurred in June 1991an unknown volume of TCE was released. The quantity of TCE spilled has been estimated at20,000 gallons; however, this volume has never been substantiated. During our site visit we sawpart of a soil vapor extraction recovery system just outside and west of Building 181. We weretold that TCE has not been used since 1994 as a degreaser and that the degreasing tanks nowcontained a detergent based soap and water solution.

The West Plume is the next largest plume of groundwater contamination in the Terrace AlluvialAquifer. This plume is a broad area of contaminated groundwater that extends westward towardMeandering Road Creek. Although groundwater discharge to Meandering Road Creek is restricted by bedrock along the creek, a channel cuts through the bedrock and provides a pathwayto the creek. Potential sources for the contamination found in this plume include Fire DepartmentTraining Area-2, Landfill No. 1 and Landfill No. 3, and possible leaking fuel lines betweenBuilding 14 and the Parts Plant that have since been removed from service.

The North Plume is the smallest of the groundwater plumes in the Terrace Alluvial Aquifer andoriginates near the north end of the Assembly Building. Potential sources for contaminants in theNorth Plume include leaking fuel supply lines (that have been removed from service) and storagetanks surrounding the Jet Engine Test Facility. For the purposes of this report, the contaminationin these three plumes will collectively be referred to as "Terrace Alluvial Aquifer contamination".

VOCs (TCE, 1,2-dichloroethene, vinyl chloride, 1,1,2-trichloroethane, tetrachloroethene,benzene, toluene, and chloroform), semi-VOCs (naphthalenes, chlorobenzenes, and di-n-butylphthalates), TPH, oil, grease, and various inorganics (arsenic, chromium, lead, and thallium)were detected in the Terrace Alluvial Aquifer. Since the Terrace Alluvial Aquifer is not used forwater supply, direct contact (ingestion and dermal contact) with water from this aquifer is notlikely. There is no potential public health hazard associated with contaminated groundwaterin the Terrace Alluvial Aquifer. Although water from the Terrace Alluvial Aquifer dischargesnaturally into Lake Worth and Lake Worth is used as a drinking water supply, the water is testedannually at various points of entry into the water supply system; test results have not detectedcontaminants associated with the Terrace Alluvial Aquifer in the drinking water.

    Contamination in the Paluxy Aquifer

Samples from the Paluxy Aquifer were collected and analyzed for VOCs, semi-VOCs, and metals. VOCs (TCE, cis-1,2-dichloroethene, vinyl chloride, 1,2-dichloroethane, methylene chloride, andtoluene) were the most common contaminants found in the Paluxy Aquifer. Two distinctcontaminant plumes have been identified in the Paluxy under AFP4: the East Paluxy Plume(Paluxy "Upper Sand") and the West Paluxy Plume (Regional Paluxy).

    East Paluxy Plume (Paluxy "Upper Sand")

Contamination in the East Paluxy Plume occurs primarily in the Paluxy "Upper Sand," below theEast Parking Lot (Figure 7). TCE, the most commonly detected VOC, was found in the "UpperSand" at concentrations up to 11,000 µg/L. Contaminants may have entered the "Upper Sand"by vertical migration from the Terrace Alluvial Aquifer through the window area of theGoodland-Walnut layer. Water from the "Upper Sand" is not used for water supply; thus,currently there is no public health hazard associated with contaminated groundwater in thePaluxy "Upper Sand". Although the Paluxy "Upper Sand" is thought to be hydraulicallyseparated from the deeper parts of the aquifer this is not known for certain. Contaminants fromthe "Upper Sand" could migrate to the deeper Regional Paluxy Aquifer. The future public healthsignificance of contamination in the Regional Paluxy Aquifer is discussed below.

    West Paluxy Plume (Regional Paluxy)

The West Paluxy Plume, occurs northwest of Building 14 and is within the Regional PaluxyAquifer (Figure 8). Low concentrations of TCE and its breakdown products have been identifiedin this plume. Water from one well, screened in the upper portion of the Paluxy, contained up to100 µg/L TCE (a concentration 20 times greater than the drinking water standard for thiscontaminant). Another well, adjacent to the west side of Building 14, also screened in the upperportion of the Paluxy, contained up to 420 µg/L cis-1,2-dichloroethene (a concentration six timesgreater than the drinking water standard for this contaminant). Lower concentrations (<10 µg/L)of these compounds were found in wells screened in the middle Paluxy. Contamination in theWest Paluxy Plume is believed to have entered the aquifer either as recharge from MeanderingRoad Creek or as vertical migration down a monitoring well bore. The suspect monitoring well(P-22M) had no seal between the outer casing and the Terrace Alluvial Aquifer and no sealbetween the well and the outer casing; it could have been a pathway for leakage from the TerraceAlluvial Aquifer to the Paluxy Aquifer. The well bore has been plugged and abandoned toeliminate the potential for additional vertical migration via this route.

Water supplied by White Settlement municipal wells, south and west of AFP4, is pumped fromthe regional Paluxy Aquifer. One municipal well, WS-2, approximately 1,200 feet west of theplume, was taken out of production by the city of White Settlement (contaminants were not foundin the well). Water levels in the regional Paluxy range from about 720 feet above sea level at thewestern edge of Tarrant County to about 520 feet above sea level at the eastern edge of NAS. This is an average gradient of about 25 feet per mile from west to east. Groundwater in thePaluxy Aquifer flows across AFP4 toward WS-12 (Figure 5); thus, WS-12 has the greatestpotential to be affected by contaminants detected in the groundwater beneath AFP4.

The most recent sampling data available for our review to determine the chemical quality of WhiteSettlement Well #12 and other municipal water supply wells was performed in December of 1996. Water from these wells was tested for metals, radioelements, and VOCs (including site-relatedcontaminants of concern); all constituents either were below detection or below concentrations ofhealth concern. In April 1993 and April 1995, the United States Geological Survey (USGS)sampled water from 10 domestic water-supply wells northwest (upgradient) of the facility todetermine if these wells were affected by contaminants from AFP4. These wells draw water fromthe lower Paluxy Aquifer. A portable gas chromatograph was used in the field to test forbenzene, toluene, xylene, TCE, dichloroethene, and tetrachloroethylene. Samples also weretested in the lab for VOCs and metals. TCE or its breakdown products (dichloroethene or vinylchloride) were not detected in either the field or laboratory samples. Chloromethane was detectedat a concentration of 5.7 µg/L in one of the domestic wells in 1993 but was not detected in 1995. Site contaminants have not been found in domestic water wells near AFP4 [9].

Although site contaminants have been detected in the Regional Paluxy Aquifer, they have notbeen detected either in the domestic wells upgradient from the contaminant plume or in themunicipal water supply wells downgradient from the contaminant plume. At present, thecontamination in the Paluxy Aquifer does not pose a public health hazard. Contamination ofthe Paluxy Aquifer could, in the future, pose a public health hazard if contaminants in the "UpperSand" were to penetrate to the deeper aquifer, migrate to municipal water supply wellsdowngradient from the plume, and remain undetected so that long-term exposures could occur. However, that occurrence is unlikely.

Rust Geotech (a contractor for the Air Force) used an analytical groundwater transport model toestimate the potential future public health hazard posed by contaminant migration toward themunicipal water supply wells. They estimated that in thirty years (in the absence of remediation)the concentration of TCE in WS-12 theoretically could reach 980 µg/L. Although a completedescription of the model was not provided in the RI, it is likely that the concentration of TCE inthis well would exceed the MCL (5 µg/L) much sooner. In White Settlement the domestic watersupply is not a mixture from the various production wells; thus, in the absence of remediation,future residents attached to this water supply well could be exposed to this contaminant throughingestion (drinking), dermal contact (washing/showering), and inhalation (washing/showering/cooking). Additionally, exceeding the MCL would trigger a response from the regulatoryagencies. Thus, unless remediated, contaminated groundwater at this site could pose a publichealth hazard in the future. Remedial activities have been chosen to reduce or eliminate thelikelihood that groundwater at this site would become a public health threat. Sampling strategieshave been designed to assure the early detection of contaminants, thus, reducing or eliminating thelikelihood of long-term exposures (see box below).

Remedies Selected to Reduce or Eliminate the Likelihood That Contaminated Groundwater at This SiteWill
Become a Public Health Hazard in The Future

Paluxy Aquifer and Upper Sand Groundwater

  • Groundwater extraction and treatment with near-zero off-gas emissions are the remedy selected to preventfuture human exposure to trichloroethylene. Contaminated Paluxy Aquifer groundwater will be extractedfrom under Landfill No. 3 and from contaminated Paluxy Aquifer groundwater beneath the Window Areaof the East Parking Lot. The contaminated groundwater will be treated with ultraviolet oxidation or anequivalent near-zero gas emission technology, then the treated water will be discharged to surface water ora sewage treatment plant. The groundwater extraction system has been operational since the Spring of1997.
  • East Parking Lot Plume and Terrace Alluvial Flow System:

  • Enhanced Dense Non-Aqueous Phase Liquid (DNAPL)/Groundwater Extraction and Treatment withDestruction of Contaminants is the selected remedy for contamination in the East Parking Lot Plume andthe Terrace Alluvial Flow System. The DNAPL will be removed by enhanced dissolution into thegroundwater and then extraction of the groundwater. The extracted groundwater will be passed through anoil/water separator then treated by air stripping. The treated groundwater will be discharged to surfacewater or to a sewage treatment plant. Air discharged from the air stripper will pass through a catalyticoxidation unit or vapor-phase carbon adsorption unit before being discharged to the atmosphere. According to the Final Record of Decision, the off-gas treatment system will result in near-zero emission ofcontaminants to the atmosphere. Thus, the enhanced dissolution and subsequent air treatment should notpose a threat to public health. The enhanced DNAPL/groundwater extraction treatment system becameoperational in May of 1997.
  • Other Relevant Remedial Actions

  • Monitoring the movement of contamination in the Paluxy Aquifer and Upper Sand groundwater. Monitoring wells located between the White Settlement production well and the site can be used to monitor possible contaminant migration toward the production well; thus, detecting contaminant movement toward the well before it actually occurs.
  • Monitoring to track contaminant movement and levels in the Terrace Alluvial flow system, Meandering Road Creek, Lake Worth, and Farmers Branch Creek.
  • Monitoring the movement of contamination in the Paluxy Aquifer and the Upper Sand groundwater aswell as monitoring to track the movement of contaminants in the Terrace Alluvial Aquifer, MeanderingRoad Creek, Lake Worth, Farmers Branch Creek has been conducted quarterly since 1992. Thismonitoring includes surface water, sediment, and groundwater. Selected White Settlement public watersupply wells are sampled quarterly for volatile organic compounds.



  • COMMUNITY HEALTH CONCERNS/HEALTH OUTCOME DATA

    In an initial effort to obtain community health concerns, we contacted the EPA Region VI office,the TNRCC, the TDH Region 3 office, the Fort Worth-Tarrant County Department of PublicHealth, the ATSDR Region VI office, and the TDH Epidemiology Investigation Index File. TheEpidemiology Index File is maintained by the TDH Bureau of Epidemiology and coversinvestigations conducted from the 1960s to the present time. Staff members also attended anEarth Day exhibit in a local mall during April 1997 where they spoke with citizens about the U. S.Air Force Plant 4 site and the superfund process. During 1997 Carswell/AFP4 RestorationAdvisory Board meetings, TDH staff noted citizen concerns. The primary community healthconcerns are questions related to available health outcome data (tumor registries, birth defectsregistries, and vital statistics). Identified community concerns are addressed below.

    1. In 1992, TDH received a citizen request to examine the occurrence of eight types ofcancer in the city of White Settlement. The cancers of concern included Hodgkin's andnon-Hodgkin's lymphoma, leukemia, breast, brain, colon, lung,and prostate cancer [9].

    In 1992, to determine if there was an excess of cancer in White Settlement, the TDH examinedcancer mortality data for these eight selected types of cancer, for the period between 1981 to1989 [10]. The mortality data were obtained from death certificate information maintained bythe Texas Department of Health Bureau of Vital Statistics. Basically, the TDH compared thenumber of cancer deaths recorded for each specific type of cancer in White Settlement to whatwould be "expected" based on the age-, sex-, and race-specific cancer deaths for the entire stateof Texas for the same time period. For males, brain and lung cancers were higher than expected.

    The causes of brain cancer are not clear; studies have implicated occupational, environmental,viral, and genetic factors. In many instances, these studies have been complicated by the difficultyin determining an accurate diagnosis, particularly with the determination of whether the tumor isprimary (originating in the brain) or metastatic (cancer that has spread from another part of thebody). All seven cases of brain cancer found were diagnosed as glioblastoma, a common type ofbrain cancer in males [11]. The TDH Texas Cancer Registry reviewed the medical records for sixof the seven individuals who died of this type of brain cancer; they were not able to find anyspecific common risk factor shared among these individuals.

    The higher than expected number of lung cancer deaths among White Settlement white males isconsistent with the higher than expected number of lung cancer deaths observed among whitemales in Tarrant County [12]. The single most significant risk factor associated with lung canceris smoking; smoking history information for those who died from lung cancer was not available.

    As a follow-up to the previous cancer findings, we asked the Texas Cancer Registry to examinecurrent cancer data for White Settlement. They examined the cancer mortality data for the eightselected types of cancer for the period between 1986 to 1995. There were no significantelevations observed among males or females in this area during this period for any of the eighttypes of cancer studied [See Appendix A Table 1].

    1. In 1992, a local resident expressed concerns about the number of miscarriages, birthdefects, and cancers associated with people employed at a White Settlement elementary school.

    In 1992, the TDH was not able to obtain the necessary data to address this concern. Miscarriageswere reportable only under certain circumstances and the Birth Defects Monitoring Division didnot exist. Currently, data on birth defects and cancer are collected on relatively large geographicareas; thus, it would be very difficult to obtain these data for one particular school. At present,the occurrence of harmful exposures from AFP4 is unlikely; thus, any findings from acurrent study would not provide information relevant to AFP4.

    1. In 1996, the ATSDR Region VI office in Dallas forwarded a request for information regarding the rates of asthma and cancer in Tarrant County to TDH [13].

    In 1996, the TDH reviewed deaths due to asthma in Tarrant County and found that the observednumber of deaths due to asthma was not different from what would be expected based on thenumber of asthma deaths observed in Texas. Incidence data for asthma are not routinelycollected; thus, were not available for evaluation. For the years 1990-1994 in Tarrant County, thenumber of cancer deaths due to lung cancer was higher than expected for males and females. Thisis consistent with previous findings of elevated lung cancer rates in Tarrant County [13]. However, lung cancer rates for Tarrant County cannot be used to infer any causal relationshipbetween lung cancer and AFP4.

    Comments received during the Public Comment period:

    Comment 1.
    It is unclear why the last two sentences on page 18 have been added to the PHA. Firstly, thecontamination at Farmers Branch Creek is considered to be that of co-mingled contaminants fromsources on both AFP4 and NAS Fort Worth, therefore the Air Force considers it to be an AFP4problem. As such, we have established a Long Term Monitoring (LTM) program thatencompasses the TCE plume at NAS Fort Worth. Secondly the report unnecessarily recommendsan evaluation of the plumes movement as a part of the NAS Fort Worth program. AFP4 hasestablished a LTM Plan as part of the Record of Decision (ROD) that encompasses the TCEplume and allows for actions if contamination is found to be moving anywhere off the AFP 4/NASFort Worth site. In addition, the Air Force Center for Environmental Excellence (AFCEE) hasconducted an extensive investigation of the Airfield Groundwater (AOC2) over the past year andhalf to compliment the existing data at the facilities. Two rounds of comprehensive groundwatermonitoring were also conducted in 1993 and 1995 to better understand change/movement in theTCE plume.

    Response 1.
    The paragraph formerly read: "Currently, water from Farmers Branch Creek poses no apparentpublic health hazard; however, the upstream and downstream sample results suggest thatcontaminants from NAS are entering the creek. Although not related to the AFP4 site, thepotential for contaminants from NAS to migrate toward the West Fork of the Trinity River shouldbe evaluated as a part of the NAS remedial program."

    The paragraph now reads: "Currently, water from Farmers Branch Creek poses no apparentpublic health hazard."

    Comment 2.
    Page 29 and 30, the second conclusion and second recommendation state the groundwatercontamination entering Farmers Branch creek should be evaluated during the NAS remedialactivities. Contaminant migration of the entire TCE plume has been addressed under the LTMPlan as part of the AFP 4 ROD. The ROD addreses potential actions in case of contaminantmovement towards the West Fork of the Trinity River. As the previous paragraph states,investigative type actions have been taken by AFCEE, but additional actions are being taken toboth the Air Force Base Conversion Agency (AFBCA) and ASC/EMR to further quantify the contamination in and around Farmers Branch Creek.

    Response 2.
    Conclusion 2 has been changed from: "Available environmental data suggest that contaminantsfrom NAS are entering Farmers Branch Creek. While not directly related to AFP4, there is apotential for contaminants to migrate from NAS towards the West Fork of the Trinity River."

    To read: "Available environmental data suggest that contaminants are entering Farmers BranchCreek. There is a potential for contaminants entering the creek to migrate towards the West Forkof the Trinity River."

    Recommendation 2 has been removed. We have added the following statement to the ActionsOngoing section of the PUBLIC HEALTH ACTIONS Section:
    "The ROD addresses potential actions in case of contaminant movement towards the West Forkof the Trinity River."

    Comment 3.
    On page 18 the document states that Farmers Branch Creek is on NAS; thus, access is restricted.People can gain access to NAS and the area of Farmers Branch Creek on NAS.

    Response 3.
    We have changed the paragraph to read: "1) the area is on the NAS and the probability ofingesting or contacting water from this area is very low, 2) the frequency of exposure would bevery low, 3) the duration of contact with contaminated water would be low, and 4) the surfacearea of skin that potentially could come into contact with contaminated media would be small.

    We also have changed page 2 "Surface water contamination" section from: " Farmers BranchCreek, the area where contaminants were found is not accessible to the general public."

    To read "At Farmers Branch Creek the likelihood of ingesting or contacting the water is low andany potential contact would be infrequent and of short duration."


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