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1. ATSDR > Public Health Assessments & Consultations

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 examine each of the media (foodchain, sediment, surface water, air, soil, and groundwater) to determine whether or not contamination is present and if people in the community are exposed to (or in contact with) the contamination. If people are exposed to contamination in any of the media, we will 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 the exposure situations identified at this site.

To assess the potential health risks associated with contaminants, we compared contaminant concentrations to health assessment comparison (HAC) values. HAC values are media specific contaminant concentrations that are used to screen contaminants for further evaluation. Non-cancer HAC values are called environmental media evaluation guides (EMEGs) or reference dose media 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 human exposure to a contaminant that is unlikely to cause adverse non-cancer health effects. Cancer risk evaluation guides (CREGs) are based on EPA's chemical specific cancer slope factors and estimated excess lifetime cancer risk of one-in-one-million persons exposed for a lifetime. We used standard assumptions to calculate appropriate HAC values [6]. Exceeding a HAC value does 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 public health hazard. In this situation, more information is required to adequately define the potential health hazard.

Evaluation of Possible Foodchain Exposure Pathways

Summary: Concentrations of PCBs (Arochlor 1254, Arochlor 1260), dieldrin, naphthalene, and PAHs (phenanthrene, and benzo(b)fluoranthene) in edible size fish caught in Lake Worth at the convergence of Meandering Road Creek pose an indeterminate (potential) public health hazard to 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 chemicals known to bioconcentrate up the foodchain. Chemical concentrations were compared to those levels in fish taken from similar areas not impacted by AFP4. To address this issue, we recommend that the Air Force in coordination with TDH Seafood Safety Division, collect edible fish 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 by contaminants from AFP4. Mosquito fish are tiny fish and are not used as a food source by humans; however, they are abundant, tolerant of chemical contaminants, store contaminants in fatty tissue and may be eaten by other fish which are consumed by humans. The mosquito fish were collected with seines (net), frozen, and prepared as whole fish tissue samples. Ten fish samples were composited into five samples for analysis. Fish were analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs [Arochlors]), organochlorines, and metals.

PCBs (Arochlor 1254, Arochlor 1260), dieldrin, naphthalene, and PAHs (phenanthrene, and benzo(b)fluoranthene) were detected at higher concentrations in tissue samples from fish collected adjacent 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, 0.02 mg/kg; phenanthrene; 0.03mg/kg; and benzo(b)fluoranthene, 0.01 mg/kg). The maximum concentration of PCBs (0.32 milligrams-PCBs per kilogram of fish tissue [mg/kg]) in these samples 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, contaminants of potential concern (CoPCs) were selected by screening the lists of contaminants detected in environmental media samples. Contaminants were excluded from the CoPC list if the highest concentration of the contaminant was detected at a background location, if the analytical parameter was not a specific contaminant, if the analytical parameter was redundant, or if the contaminant was not related to site processes (radionuclides only). Contaminants also were included 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 determine potential risks to aquatic organisms. A potential risk to largemouth bass from exposure to contaminants in the environmental media was identified. The primary contaminants identified that could 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 degree of certainty, if AFP4 was the only source for these contaminants.

It would be reasonable to assume that edible fish species could potentially accumulate contaminants 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 may bioaccumulate these compounds. Long-term exposure to PCBs potentially could pose public health threat; however, because of a lack of edible fish tissue data we could not adequately evaluate this exposure situation. Based on available data, we conclude that exposure to contaminants through the ingestion of fish taken from Meandering Creek or Lake Worth is an indeterminate public health hazard.

Table 1 Exposure Situations - U.S. Air Force Plant 4

C. NO APPARENT PUBLIC HEALTH HAZARD

ATSDR concluded that the following identified exposure situations do not represent a public health hazard under current conditions either because there is no evidence that people are coming into contact with contaminated media or it is unlikely that they are coming into contact with contaminated 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 Worth and Meandering Road Creek present no apparent public health hazard. Concentrations of chemicals detected in off base sediments of Lake Worth and Meandering Road Creek are low and 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 determine if past contaminant spills or releases from AFP4 have reached the lake [1]. Samples were collected from areas where contamination was likely to be found such as the coves with drainage from 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 and one sample was collected from the drainage area above the background sample location. The background sample location was chosen to be close enough to AFP4 to be considered a similar habitat, but far enough away to be unaffected by potential contamination from the Plant or other industrial facilities. Samples were analyzed for volatile organic compounds (VOCs), semi-VOCs, total petroleum hydrocarbon (TPH), oil and grease, PCBs, pesticides, and metals; however, all samples were not tested for all constituents. A field scan was performed for alpha, beta, and gamma radiation on all samples collected from sediments near the former NARF area; no radiation levels above background were detected.

Sediment from the background location contained acetone (0.230 mg/kg), 2-butanone (0.053 mg/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 were detected in sediment collected from the drainage area above the background location at concentrations ranging from 0.01 to 0.130 mg/kg. Adjacent to AFP4, the maximum concentration 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 (1.5 mg/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 Lake Worth near AFP4. These contaminants were detected at concentrations below their respective HAC values (Table 2). TPH (623 mg/kg), and oil and grease (893 mg/kg) also were found in sediment from Lake Worth near AFP4. Although HAC values were not available for TPH, oil and grease, incidental exposure to these contaminants at the reported concentrations would not pose a significant public health threat.

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

Table 2 Health Assessment Comparison (HAC) Values for Volatile Organic Contaminants in Sediment From Lake Worth

Meandering Road Creek

Sediment samples were collected from seven locations along Meandering Road Creek to determine the extent of contamination in the creek and to better define the locations of contamination entering the creek [1]. These samples, collected from areas adjacent to outfalls and previously identified hazardous waste areas, were analyzed for VOCs, semi-VOCs, TPH, oil and grease, 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 at concentrations below levels of health concern. TPH and oil and grease were detected in creek sediment at concentrations comparable to those detected in background samples from Lake Worth. Metals were rarely detected above natural background levels.

In addition to the samples collected along the creek, seven sediment samples (from the surface to a depth of two feet [actual depths of individual samples were not provided]) were collected from six locations along a transect (a line crossing the creek) originating from the west side of Landfill No. 3. These samples contained PAHs (benzo[a]pyrene equivalents of 7.6 mg/kg), and various metals. 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 were detected in four of the seven transect samples; chromium was detected in two of the seven samples.

Since this is not an area where people would be likely to walk without shoes or boots, we do not consider dermal contact to be an important potential route of exposure. Chronic ingestion (100 milligrams per day for a lifetime) of sediment containing 7.6 mg/kg benzo[a]pyrene, a probable human carcinogen, could result in a low to no increased lifetime risk for cancer. Children who eat sediment containing lead at concentrations as high as 10,400 mg/kg could be at risk for lead poisoning; 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 the boundaries 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 Lake Worth, Meandering Road Creek, and Farmers Branch Creek present no apparent public health hazard. 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 be infrequent.

Contamination of surface water is an issue of potential concern at AFP4 because of possible transport of contaminants from other contaminated areas to surface water. The surface water bodies 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 contaminated with contaminants likely originating from AFP4.

Lake Worth

Nine surface-water samples were collected from Lake Worth in October 1991 [1]. Seven samples were collected along the northern boundary of AFP4; two samples were collected from areas considered 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. Carbon disulfide, and zinc were detected at concentrations below their respective health based comparison values (1,000 µg/L and 3,000 µg/L, respectively). Arsenic was detected at a concentration below the drinking water standard established by the EPA for this contaminant (50 µg/L). Although the maximum detected concentration of silver was above the Reference Dose (RfD) based comparison value for a child (50 µg/L), a 10 kg child would have to ingest approximately 0.5 liters of lake water per day, every day to exceed the RfD. Incidental ingestion of raw surface water from Lake Worth adjacent to AFP4 is possible; however, if it were to occur it would occur infrequently and the amount ingested would be very small resulting in limited exposure. Lake Worth water is used as a source of water by the City of Fort Worth; however, according to the TNRCC Water Utilities Division, site contaminants have not been detected in water collected from any of the entry points to the distribution system. Based on the above we do not consider ingestion of Lake Worth water to be a significant exposure pathway.

Exposure to contaminated lake water by swimming is possible; however, the exposure duration and frequency of this activity would limit the total exposure. It is not likely that people would swim adjacent to AFP4 where contaminant concentration will be highest; contaminants migrating to other areas of the lake will be significantly diluted. For several reasons: 1) low frequency of exposure, 2) low duration of exposure, and 3) low contaminant concentrations we do not consider 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 locations along Meandering Road Creek [1]. Forty samples were collected directly from the creek and three 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 maximum concentrations above their respective drinking water standards (Table 3). Concentrations exceeding the screening values were found in samples collected along the central portion of Landfill 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 its carcinogenic classification; it will likely be classified either as a possible or probable human carcinogen. 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

TABLE 3 MAXIMUM CONCENTRATIONS OF VOLATILE ORGANIC COMPOUNDS DETECTED IN SURFACE WATER FROM MEANDERING ROAD CREEK IN 1995
CONTAMINANT	MAXIMUM 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 dermal contact to be significant exposure pathways since: 1) access to the contaminated area is restricted by a fence, 2) the probability of ingesting or contacting water from this area is very low, 3) the frequency of exposure would be very low, 4) the duration of contact with contaminated water would be low, and 5) the surface area of skin that potentially could come into contact with contaminated water would be small. Based on available information, water from Meandering Road Creek poses no apparent public health hazard. Further contamination of the creek should be mitigated by the treatment system installed by the Air Force to prevent Landfill No. 3 contaminants from entering Meandering Road Creek. This system became operational in the Spring 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 Air Station. The farthest downstream sample location is in the golf course area east of NAS Landfills No. 4 and No. 5. At the farthest upstream location in Farmers Branch Creek, contaminant concentrations 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 these contaminants were found in a small unnamed tributary to the creek. In February 1995, the most recent sampling event, the concentrations of TCE and cis-DCE detected in water from this unnamed tributary were 100 µg/L and 380 µg/L, respectively.

We did not consider exposure to site contaminants either through incidental ingestion or dermal contact to be significant exposure pathways at this location. 1) the area is on the NAS and the probability of ingesting or contacting water from this area is very low, 2) the frequency of exposure 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 media would be small. Currently, water from Farmers Branch Creek poses no apparent public health hazard.

Evaluation of Possible Air Exposure Pathways

Summary: Exposure of base workers to ambient air at AFP4 presents no apparent public health hazard. Concentrations of chemicals detected in ambient outside air are below health comparison values. Additionally, air released from air stripping operations on-base used to treat 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 health concern.

Ambient air: The air data for this site are limited to samples obtained from two air monitoring stations [1]. One off-site station was established approximately 0.75 miles west of the site to provide information on the general air quality for the White Settlement area. The second air monitoring station was placed on the site, approximately 300 feet north of Building 176, to assess the contribution of air contaminants from AFP4. Each monitor was equipped to collect samples for 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 each location. Meteorological data (wind speed and direction) were obtained from the meteorological station at NAS. Exact meteorological data for these sampling episodes were not available. During most of the year, the predominant wind direction is from the south; however, during the winter months (December through February) the predominant wind direction is from the north [1]. Stainless steel SUMMA^R canisters were used to collect samples for VOC analysis. Whatman EPM-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 remaining 18 VOCs (chloromethane, carbon tetrachloride, benzene, tetrachloroethene, chlorobenzene, ethylbenzene, m-and/or p-xylene, o-xylene, and styrene) were detected in the on-site samples at the same frequency and concentrations as in the off-site/background samples. These likely do not represent 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 and on site at similar frequencies; however, on average these compounds were detected at higher concentrations in the on-site samples (Table 4). None of the contaminants exceeded the TNRCC's long-term Effects Screening Levels (ESLs). Although ESLs are not ambient air standards, 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 not be expected. Ambient air at AFP4 poses no apparent public health hazard.

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

Table 4 Health Assessment Comparison Values For Organic Air Contaminants - Air Force Plant 4

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 by the 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 and possible exposure to groundwater do not pose a public health hazard because no one is currently being exposed. Proposed remedial actions have been chosen to reduce or eliminate the likelihood that groundwater at this site would become a public health threat in the future; thus, exposure to contaminated groundwater in the future is unlikely. All municipal water well systems are required to be frequently sampled to meet clean drinking water standards and sampling strategies have been designed to assure the early detection of contaminants should they migrate towards municipal supply wells. Any potential future exposure would be of short duration and not likely to result in any adverse health effects.

Evaluation of Possible Soil Exposure Pathways

Soil contamination has been documented at several areas within AFP4 [1]. The contaminants present include VOCs, PAHs, and metals. These areas, which include the landfill areas and the area beneath the Assembly/Parts Plant Building, are generally fenced or have public access otherwise restricted. A six-foot chain-link fence, capped with barbed wire, surrounds the facility and a security guard is posted at the entrance to the plant. As a result of these institutional controls (and as long as such controls are diligently maintained), the contaminated soil at these 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-zone groundwater system (the Terrace Alluvial Aquifer); an aquitard system (the Goodland-Walnut Confining Unit); and the Paluxy Aquifer. Natural recharge to the Terrace Alluvial Aquifer occurs locally through direct infiltration of precipitation and runoff. Although paved areas and buildings over much of the NPL site restrict the natural infiltration of precipitation, infiltration does occur through several large grassy areas. Additional recharge occurs from leakage of water-supply lines, firefighting pipe systems, cooling-water systems, sanitary sewers, and storm sewers. At AFP4, groundwater in the Terrace Alluvial Aquifer flows radially outward, from the northern and southern portions of the Assembly Building, toward Bomber Road and Meandering Road Creek to the west, NAS and West Fork Trinity River to the east, and Farmers Branch to the south. The Terrace Alluvial Aquifer is not used for water supply; however, it discharges naturally by seepage to Meandering Road Creek, Farmers Branch, a few small tributaries along Farmers Branch, 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, the Goodland Limestone and the Walnut Formation. In general, these layers are relatively impermeable and restrict the vertical flow of groundwater between the Terrace Alluvial Aquifer and the Paluxy Aquifer. At AFP4, the combined thickness of these layers range from 0.5 to 70 feet. In some areas, however, erosion has completely removed the Goodland Limestone and all but a few feet of low permeability rock of the Walnut Formation. The Walnut Formation has been eroded to a thickness of between 0.5 and 2.5 feet in the vicinity of the east parking lot. In this area, which has been referred to as the "Window Area" (Figure 5), there is a potential for shallow 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-confined aquifer comprised mainly of sandstone and mudstone. At AFP4, the Paluxy Aquifer consists of three hydraulically isolated zones; the upper zone (top 50-60 feet), the middle zone (40-50 feet thick), and lower zone (25-30 feet thick). A local sand lens called the "Upper Sand" has been identified in the uppermost interval of the upper zone beneath AFP4. The "Upper Sand" is located beneath the east parking lot area, extends west to the west side of the Assembly Building/Parts Plant, east to the flightline area, south to Clifford Avenue, and north past the engineering building. The Paluxy "Upper Sand" is physically part of the upper zone of the Paluxy Aquifer and may be hydraulically disconnected from the deeper regionally extensive parts of the aquifer; 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 grained sandstone. 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 and lower zones of this aquifer are widely used as a source of water for domestic, municipal, and industrial water supplies in Tarrant and Dallas Counties. In the vicinity of AFP4, the middle and lower zones provide municipal water to the city of White Settlement; seven municipal water supply wells obtain water from the Paluxy Aquifer. White Settlement municipal well #2 (WS-2) is approximately 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) is approximately 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 water to the city of Fort Worth and is a recharge source to the underlying Paluxy Aquifer. The AFP4 facility receives its potable water from the city of Fort Worth public water supply [8]; this water is tested annually and meets federal drinking water standards.

Contaminants from the site have been documented both in the Terrace Alluvial Aquifer and the Paluxy 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 in the buried bedrock surface. These plumes have been referred to as; 1) the East Parking Lot Plume, 2) the West Plume, and 3) the North Plume. The East Parking Lot Plume is the largest plume 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 NAS property the plume appears to have merged with source areas on NAS property. Releases from degreaser tanks located in Building 181 are believed to be the major source of the contamination found in the East Parking Lot Plume. During one documented event that occurred in June 1991 an unknown volume of TCE was released. The quantity of TCE spilled has been estimated at 20,000 gallons; however, this volume has never been substantiated. During our site visit we saw part of a soil vapor extraction recovery system just outside and west of Building 181. We were told that TCE has not been used since 1994 as a degreaser and that the degreasing tanks now contained a detergent based soap and water solution.

The West Plume is the next largest plume of groundwater contamination in the Terrace Alluvial Aquifer. This plume is a broad area of contaminated groundwater that extends westward toward Meandering 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 pathway to the creek. Potential sources for the contamination found in this plume include Fire Department Training Area-2, Landfill No. 1 and Landfill No. 3, and possible leaking fuel lines between Building 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 and originates near the north end of the Assembly Building. Potential sources for contaminants in the North Plume include leaking fuel supply lines (that have been removed from service) and storage tanks surrounding the Jet Engine Test Facility. For the purposes of this report, the contamination in 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 for water supply, direct contact (ingestion and dermal contact) with water from this aquifer is not likely. There is no potential public health hazard associated with contaminated groundwater in the Terrace Alluvial Aquifer. Although water from the Terrace Alluvial Aquifer discharges naturally into Lake Worth and Lake Worth is used as a drinking water supply, the water is tested annually at various points of entry into the water supply system; test results have not detected contaminants 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, and toluene) were the most common contaminants found in the Paluxy Aquifer. Two distinct contaminant 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 the East Parking Lot (Figure 7). TCE, the most commonly detected VOC, was found in the "Upper Sand" 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 the Goodland-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 the Paluxy "Upper Sand". Although the Paluxy "Upper Sand" is thought to be hydraulically separated from the deeper parts of the aquifer this is not known for certain. Contaminants from the "Upper Sand" could migrate to the deeper Regional Paluxy Aquifer. The future public health significance 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 Paluxy Aquifer (Figure 8). Low concentrations of TCE and its breakdown products have been identified in this plume. Water from one well, screened in the upper portion of the Paluxy, contained up to 100 µg/L TCE (a concentration 20 times greater than the drinking water standard for this contaminant). Another well, adjacent to the west side of Building 14, also screened in the upper portion of the Paluxy, contained up to 420 µg/L cis-1,2-dichloroethene (a concentration six times greater 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 the West Paluxy Plume is believed to have entered the aquifer either as recharge from Meandering Road 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 seal between the well and the outer casing; it could have been a pathway for leakage from the Terrace Alluvial Aquifer to the Paluxy Aquifer. The well bore has been plugged and abandoned to eliminate the potential for additional vertical migration via this route.

Water supplied by White Settlement municipal wells, south and west of AFP4, is pumped from the regional Paluxy Aquifer. One municipal well, WS-2, approximately 1,200 feet west of the plume, was taken out of production by the city of White Settlement (contaminants were not found in the well). Water levels in the regional Paluxy range from about 720 feet above sea level at the western 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 the Paluxy Aquifer flows across AFP4 toward WS-12 (Figure 5); thus, WS-12 has the greatest potential 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 White Settlement 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-related contaminants of concern); all constituents either were below detection or below concentrations of health 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 to determine if these wells were affected by contaminants from AFP4. These wells draw water from the lower Paluxy Aquifer. A portable gas chromatograph was used in the field to test for benzene, toluene, xylene, TCE, dichloroethene, and tetrachloroethylene. Samples also were tested in the lab for VOCs and metals. TCE or its breakdown products (dichloroethene or vinyl chloride) were not detected in either the field or laboratory samples. Chloromethane was detected at 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 not been detected either in the domestic wells upgradient from the contaminant plume or in the municipal water supply wells downgradient from the contaminant plume. At present, the contamination in the Paluxy Aquifer does not pose a public health hazard. Contamination of the Paluxy Aquifer could, in the future, pose a public health hazard if contaminants in the "Upper Sand" were to penetrate to the deeper aquifer, migrate to municipal water supply wells downgradient 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 to estimate the potential future public health hazard posed by contaminant migration toward the municipal 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 complete description of the model was not provided in the RI, it is likely that the concentration of TCE in this well would exceed the MCL (5 µg/L) much sooner. In White Settlement the domestic water supply 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 through ingestion (drinking), dermal contact (washing/showering), and inhalation (washing/showering/ cooking). Additionally, exceeding the MCL would trigger a response from the regulatory agencies. Thus, unless remediated, contaminated groundwater at this site could pose a public health hazard in the future. Remedial activities have been chosen to reduce or eliminate the likelihood that groundwater at this site would become a public health threat. Sampling strategies have been designed to assure the early detection of contaminants, thus, reducing or eliminating the likelihood of long-term exposures (see box below).

Remedies Selected to Reduce or Eliminate the Likelihood That Contaminated Groundwater at This Site Will 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 prevent future human exposure to trichloroethylene. Contaminated Paluxy Aquifer groundwater will be extracted from under Landfill No. 3 and from contaminated Paluxy Aquifer groundwater beneath the Window Area of the East Parking Lot. The contaminated groundwater will be treated with ultraviolet oxidation or an equivalent near-zero gas emission technology, then the treated water will be discharged to surface water or a sewage treatment plant. The groundwater extraction system has been operational since the Spring of 1997.

East Parking Lot Plume and Terrace Alluvial Flow System:

Enhanced Dense Non-Aqueous Phase Liquid (DNAPL)/Groundwater Extraction and Treatment with Destruction of Contaminants is the selected remedy for contamination in the East Parking Lot Plume and the Terrace Alluvial Flow System. The DNAPL will be removed by enhanced dissolution into the groundwater and then extraction of the groundwater. The extracted groundwater will be passed through an oil/water separator then treated by air stripping. The treated groundwater will be discharged to surface water or to a sewage treatment plant. Air discharged from the air stripper will pass through a catalytic oxidation 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 of contaminants to the atmosphere. Thus, the enhanced dissolution and subsequent air treatment should not pose a threat to public health. The enhanced DNAPL/groundwater extraction treatment system became operational 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 as well as monitoring to track the movement of contaminants in the Terrace Alluvial Aquifer, Meandering Road Creek, Lake Worth, Farmers Branch Creek has been conducted quarterly since 1992. This monitoring includes surface water, sediment, and groundwater. Selected White Settlement public water supply 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 Public Health, the ATSDR Region VI office, and the TDH Epidemiology Investigation Index File. The Epidemiology Index File is maintained by the TDH Bureau of Epidemiology and covers investigations conducted from the 1960s to the present time. Staff members also attended an Earth 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 Restoration Advisory Board meetings, TDH staff noted citizen concerns. The primary community health concerns are questions related to available health outcome data (tumor registries, birth defects registries, and vital statistics). Identified community concerns are addressed below.

1. In 1992, TDH received a citizen request to examine the occurrence of eight types of cancer in the city of White Settlement. The cancers of concern included Hodgkin's and non-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 examined cancer mortality data for these eight selected types of cancer, for the period between 1981 to 1989 [10]. The mortality data were obtained from death certificate information maintained by the Texas Department of Health Bureau of Vital Statistics. Basically, the TDH compared the number of cancer deaths recorded for each specific type of cancer in White Settlement to what would be "expected" based on the age-, sex-, and race-specific cancer deaths for the entire state of 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 difficulty in determining an accurate diagnosis, particularly with the determination of whether the tumor is primary (originating in the brain) or metastatic (cancer that has spread from another part of the body). All seven cases of brain cancer found were diagnosed as glioblastoma, a common type of brain cancer in males [11]. The TDH Texas Cancer Registry reviewed the medical records for six of the seven individuals who died of this type of brain cancer; they were not able to find any specific common risk factor shared among these individuals.

The higher than expected number of lung cancer deaths among White Settlement white males is consistent with the higher than expected number of lung cancer deaths observed among white males in Tarrant County [12]. The single most significant risk factor associated with lung cancer is 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 examine current cancer data for White Settlement. They examined the cancer mortality data for the eight selected types of cancer for the period between 1986 to 1995. There were no significant elevations observed among males or females in this area during this period for any of the eight types of cancer studied [See Appendix A Table 1].

2. In 1992, a local resident expressed concerns about the number of miscarriages, birth defects, 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. Miscarriages were reportable only under certain circumstances and the Birth Defects Monitoring Division did not exist. Currently, data on birth defects and cancer are collected on relatively large geographic areas; 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 a current study would not provide information relevant to AFP4.

3. 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 observed number of deaths due to asthma was not different from what would be expected based on the number of asthma deaths observed in Texas. Incidence data for asthma are not routinely collected; thus, were not available for evaluation. For the years 1990-1994 in Tarrant County, the number of cancer deaths due to lung cancer was higher than expected for males and females. This is 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 relationship between 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, the contamination at Farmers Branch Creek is considered to be that of co-mingled contaminants from sources on both AFP4 and NAS Fort Worth, therefore the Air Force considers it to be an AFP4 problem. As such, we have established a Long Term Monitoring (LTM) program that encompasses the TCE plume at NAS Fort Worth. Secondly the report unnecessarily recommends an evaluation of the plumes movement as a part of the NAS Fort Worth program. AFP4 has established a LTM Plan as part of the Record of Decision (ROD) that encompasses the TCE plume and allows for actions if contamination is found to be moving anywhere off the AFP 4/NAS Fort Worth site. In addition, the Air Force Center for Environmental Excellence (AFCEE) has conducted an extensive investigation of the Airfield Groundwater (AOC2) over the past year and half to compliment the existing data at the facilities. Two rounds of comprehensive groundwater monitoring were also conducted in 1993 and 1995 to better understand change/movement in the TCE plume.

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

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

Comment 2.
Page 29 and 30, the second conclusion and second recommendation state the groundwater contamination entering Farmers Branch creek should be evaluated during the NAS remedial activities. Contaminant migration of the entire TCE plume has been addressed under the LTM Plan as part of the AFP 4 ROD. The ROD addreses potential actions in case of contaminant movement 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 to both 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 contaminants from NAS are entering Farmers Branch Creek. While not directly related to AFP4, there is a potential 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 Branch Creek. There is a potential for contaminants entering the creek to migrate towards the West Fork of the Trinity River."

Recommendation 2 has been removed. We have added the following statement to the Actions Ongoing section of the PUBLIC HEALTH ACTIONS Section:
"The ROD addresses potential actions in case of contaminant movement towards the West Fork of 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 of ingesting or contacting water from this area is very low, 2) the frequency of exposure 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 media would be small.

We also have changed page 2 "Surface water contamination" section from: " Farmers Branch Creek, 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 and any potential contact would be infrequent and of short duration."

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