PUBLIC HEALTH ASSESSMENT
TRACY DEFENSE DEPOT
(a/k/a DEFENSE DISTRIBUTION REGION WEST TRACY ARMY)
TRACY, SAN JOAQUIN COUNTY, CALIFORNIA
An exposure pathway is the process by which an individual is exposed to contaminants that originate from a source. To determine whether people were or continue to be exposed to contaminants originating from the DDJC Tracy site, ATSDR evaluated the factors that might lead to human exposure. These factors, or elements, include a source of contamination, an environmental medium in which contaminants may be present, a point of human exposure, a route of human exposure (such as ingestion, inhalation, or skin contact), and a receptor population (e.g., nearby residences). Figure 4 explains the exposure evaluation process in more detail and Appendix A contains a glossary of environmental and health terms used in this document.
ATSDR identifies exposure pathways as completed or potential. A completed exposure pathway exists in the past, present, or future if all elements of human exposure link the contaminant source to a receptor population. Potential pathways, however, are defined as situations in which at least one of the elements is missing, but could exist. The potential for adverse health effects from an exposure is also considered in relation to contaminant concentration, exposure variables (e.g., duration and frequency), and the toxicology of the contaminant.
ATSDR uses comparison values in selecting contaminants for further evaluation within an exposure pathway. Comparison values are contaminant concentrations in a specific environmental medium to which a person might be exposed that are not expected to produce health effects. Because comparison values do not represent thresholds of toxicity, exposure to concentrations greater than the comparison values does not necessarily produce health effects. Comparison values used in this document include EPA's maximum contaminant levels (MCLs) and ATSDR's environmental media evaluation guides (EMEGs), reference dose media evaluation guides (RMEGs), and cancer risk evaluation guides (CREGs). These values are further described in Appendix B.
ATSDR evaluated environmental data and exposure information to determine if completed or potential pathways of human exposure to contaminants existed in the past or if they exist now or potentially in the future. ATSDR identified several exposure pathways that required further evaluation, including the following:
- Consumption of groundwater
- Dermal contact with surface soil
- Inhalation of soil gas
- Ingestion of locally grown crops
- Ingestion of recreationally caught fish from the on-site stormwater lagoon
In this section, ATSDR evaluates these exposure pathways in more detail, considering data gathered and remedial activities conducted since ATSDR's 1991 site visit, to determine whether these pathways represent, under site-related conditions, a threat to human health. The results of the pathways investigation are summarized in Table 2.
Groundwater use poses the primary exposure pathway of concern. VOCs, predominantly TCE and PCE, are widely present in the on-site shallow aquifer (Upper Tulare Aquifer) located north-northeast of the site. Contamination in this aquifer has been associated with several on-site former waste disposal areas and locations of accidental spills.
The highest concentrations for TCE and PCE (TCE at 560 ppb and PCE at 760 ppb), detected on site in 1986, greatly exceed the MCLs and the California Department of Toxic Substance Control's MCLs of 5 ppb for both contaminants (Woodward-Clyde Consultants, 1992a; Montgomery Watson, 1995). The highest concentrations of these contaminants occur in the Above Upper Horizon of the Upper Tulare Aquifer below the depot's former open drum storage areas located along the northeast boundary of the site and in the maintenance areas (see Figure 2), where soil contaminants from waste disposal practices and accidental spills leached into the groundwater. The greatest lateral extent of contamination, however, is in the Upper Horizon, and contamination has also migrated into the deeper Middle and Lower Horizons carried by a strong gradient that was created by past operation of a nearby agricultural well (AG-2).
TCE and PCE have also migrated off site to the north and northeast in three groundwater horizons of the Upper Tulare Aquifer. A TCE plume (defined by a 5 ppb contour) extends approximately 2,500 feet from the depot boundary, while a PCE plume (also defined by a 5 ppb contour) extends 1,600 feet (see Figure 5).
Of the other VOCs detected at concentrations exceeding comparison values, none is distributed as widely as TCE or PCE, or at such high concentrations. For example, DCE was detected in a limited number of groundwater samples at a maximum on-site concentration of 11.9 ppb--above the ATSDR CREG, but only slightly above the CA MCL of 6 ppb. Similarly, pesticides, primarily dieldrin, were detected at levels greater than comparison values in the north-northeast corner of the site near the VOC plume, but not with the same frequency or high concentration as TCE and PCE (Woodward-Clyde Consultants, 1992b). Waste management practices and accidental spills have contributed to pesticide contamination in the soil, which subsequently leached into the Above Upper and Upper Horizons groundwater (Montgomery Watson, 1995). A dieldrin plume appears to emanate from the sanitary sewage lagoons and is entirely contained within the 5 ppb contour of the VOC plume associated with OU 1, whereas other pesticides show no discernable pattern. Dieldrin has been detected off site in groundwater at levels above ATSDR's CREG of 0.002 ppb, but below the EMEG and RMEG of 0.5 ppb.
Metals and other inorganic compounds were also found in groundwater below the site. Sampling in 1991 found arsenic, chromium, and lead widely distributed in the groundwater below the site. However, these metals had not migrated off site at levels greater than their respective comparison values.
Because of their frequency, high on-site and off-site concentrations, mobility, and potential health concerns, TCE and PCE are the principal compounds of concern in the groundwater.
- DDJC Tracy Water Supply Wells
DDJC Tracy drinking water comes from on-site water supply wells that draw water from the Lower Tulare Aquifer. During the late 1980s and early 1990s (when contamination was first detected on site), drinking water was supplied by water supply well (WSW) 4, located in the path of the VOC plume, and WSW 7, located approximately 2,000 feet upgradient and away from the plume. DDJC Tracy used WSW 4 until 1992, when they took it out of service because of low water yield and signs of rusting (Woodward-Clyde Consultants, 1992b). In 1992, DDJC Tracy installed two additional upgradient wells--WSW 8 and 9. These two newer wells, however, have only been used since 1994 to supplement water obtained from WSW 7. (WSWs 1, 2, 3, 5, and 6 had been abandoned.) Water from the operating on-site wells was pumped into a 250,000-gallon elevated water storage tank, blended, and chlorinated prior to use by the depot (ASCW-BE, 1998b).
DDJC Tracy sampled operating wells and analyzed the samples for metals and selected pesticides every three years, but only water samples collected between 1987 and 1991 from WSW 7 were analyzed for VOCs. Although WSWs 8 and 9 have not been sampled for VOCs since they went on line in 1994, these wells are located approximately 2,000 feet upgradient from known areas of groundwater contamination and, therefore, were probably not affected by site-related contaminants.
Table 3 summarizes the water quality monitoring results of the DDJC Tracy water supply wells. As the table indicates, no pesticides were detected in any well, nor were TCE, PCE, or carbon tetrachloride detected in WSW 7. Additionally, the metals arsenic, lead, and mercury were detected, but only sporadically at levels above comparison values (Woodward-Clyde Consultants, 1992b; DDJC Tracy 1998). Manganese levels (up to 180 ppb) frequently exceeded EPA's secondary MCL (50 ppb) for aesthetic quality and ATSDR's RMEG for a child (50 ppb) in WSW 8; however, the levels were below the 200 ppb RMEG for an adult. (The secondary MCL is intended to provide a guideline for aesthetic aspects such as taste, odor, and color that do not present a health hazard.) While this naturally occurring metal may impart undesirable taste, odor or color, it is unlikely to pose undue health hazards at the detected levels.
Because WSW 4 was located in the path of the plume, ATSDR evaluated the likelihood of exposure to contaminants in this well. In the absence of monitoring data for WSW 4, ATSDR reviewed data gathered from a nearby monitoring well (LM43) (see Figure 5). No TCE or PCE were detected in the monitoring well up to 1991 when WSW 4 was closed (Woodward-Clyde Consultants, 1992b ). Assuming similar conditions exist for both wells, WSW 4 was unlikely to have been affected by TCE and PCE at levels exceeding the MCLs.
- Current and Future Exposures
In January 1998, DDJC Tracy placed WSW 7 on standby status (meaning that it will be used for emergency or maintenance purposes only) because of low level TCE contamination sporadically detected in a Middle Horizon of the Upper Tulare Aquifer groundwater monitoring well located near WSW 7. Although WSW 7 is not screened in the Upper Tulare Aquifer, it could draw a small amount of TCE-contaminated groundwater through its potentially damaged casing (ASCW-BE, 1998a). Because of the absence of upgradient on-site buildings or on-site source areas, the contamination is most likely unrelated to DDJC Tracy. DDJC Tracy continues to investigate potential TCE sources, including an off-site machine shop.
Currently, WSWs 8 and 9 supply drinking water for DDJC Tracy. As stated previously, these wells are not likely to be affected by site-related contaminants because they are located approximately 2,000 feet upgradient from known areas of groundwater contamination. As a precautionary measure, DDJC Tracy is conducting quarterly VOC monitoring in the WSW 7 and the other water supply wells for approximately one year. Since the quarterly monitoring began, no TCE has been detected. DDJC Tracy will continue to monitor the wells, and they will take immediate action to correct any threat to the drinking water supply (ASCW-BE, 1998a). ATSDR will review these data and determine whether any additional measures protective of public health are necessary.
- Off-Site Wells
Municipal Water Supply: Past, Current, and Future Exposures
The city of Tracy municipal water is unlikely to be affected by site-related contaminants. The city supplies municipal water to area residents from 10 municipal supply wells that draw water from the Lower Tulare Aquifer. The nearest municipal well to DDJC Tracy is situated approximately 1.5 miles crossgradient and away from the predominant direction of groundwater flow from the DDJC Tracy site. The city of Tracy monitors the drinking water regularly for chemicals, including TCE and PCE, to ensure that chemical concentrations do not exceed their respective MCLs. (MCLs are enforceable drinking water standards developed to protect public health, but they also consider economic and technological factors.) To date, the drinking water has met these safe drinking water standards (Tracy Water Department, 1997).
- Private Wells: Past Exposures
Contaminated groundwater has migrated off site in a north-northeasterly direction where private wells are located. Through a 1991 survey, the California Department of Health Services identified 18 private, domestic-use wells serving private residences within a 1-mile radius of the site. Of these 18 wells, 11 wells are located upgradient or crossgradient to the site, while seven wells are located downgradient of the site and in or near the VOC plume. DDJC Tracy sampled 12 of the 18 wells for VOCs and metals in February 1987, and two of these wells were sampled again in September or November 1991. (Six additional upgradient private wells were sampled in 1991 for dissolved and total metals to provide a one-time estimate of background levels in groundwater, rather than to characterize potential contamination associated with the plume.)
Contaminant concentrations in the crossgradient and upgradient wells from the site were below the MCLs (and CREGs) for all VOCs and metals except chromium, which was detected in one well at a concentration of 56 ppb--above the CA MCL of 50 ppb but below the EPA MCL of 100 ppb for chromium. TCE, but no PCE, was detected in two downgradient wells at concentrations greater than ATSDR's CREG and the EPA and CA MCL. The highest TCE concentration (6.7 ppb) was detected in a well that draws water from the Upper to Middle Horizons of the Upper Tulare Aquifer in relatively close proximity to the northern boundary of the site. Carbon tetrachloride was also detected in the two downgradient wells at levels (0.6 to 1.8 ppb) above ATSDR's CREG of 0.3 ppb, but below the EPA MCL of 5 ppb. Historically, carbon tetrachloride has been infrequently found at isolated monitoring wells on and off site, but at levels below the MCL. Although the source of the carbon tetrachloride has not been determined and may be unrelated to the DDJC Tracy, the contamination does not appear to be widespread (Montgomery Watson, 1995).
When evaluating the health significance of an exposure pathway, ATSDR estimates exposure doses and compares the values to standard health guidelines, such as ATSDR's minimal risk levels (MRLs) or EPA's reference doses (RfDs). These health guidelines provide a conservative estimate of daily exposure to noncarcinogens that are not likely to result in noncancer adverse health effects. A long-term or chronic exposure (365 days or more) MRL or RfD has not been established for TCE. Therefore, when evaluating chronic exposure to TCE in the private wells, ATSDR focused on cancer. In evaluating cancer risk for either TCE or carbon tetrachloride, ATSDR used EPA's cancer potency factors (CPFs) to define the relationship between the exposure dose and the potential for cancer to occur.
In deriving human exposure doses, ATSDR incorporated information about the frequency and duration of exposure. Because ATSDR does not know with certainty when migrating contaminants first reached the private wells or how much was present during the exposure period, ATSDR made several conservative assumptions. Although one of the two wells was installed as recently as 1988 and residents now use an alternate water supply, ATSDR conservatively assumed exposure occurred over a 30-year period for an adult (EPA's national upper bound limit at one residence) and over 6 years for a child. ATSDR assumed that these individuals drank only water containing the maximum detected level of TCE over the exposure period. ATSDR believes that these assumptions overestimate actual exposure because no one is thought to have been consistently using water with the highest TCE level over a 30-year period. Although it is most likely unrelated to the DDJC Tracy site, ATSDR evaluated exposure to carbon tetrachloride in the private wells (DDJC Tracy, 1997b). ATSDR also evaluated potential health hazards from dermal contact or from inhalation of vapors that might occur during domestic use. The methods used and assumptions applied in deriving the estimated exposure doses and cancer risk are described in greater detail in Appendix C.
The estimated exposure doses and excess cancer risk for ingestion of private well water are provided in Appendix C, Tables C-1 and C-2. The estimated exposure doses for an adult and a child exposed to carbon tetrachloride in private well water are less than the RfD. In addition, the estimated exposure levels for TCE or carbon tetrachloride are not expected to cause excess cancer in the population. Therefore, drinking private well water in the past, or using it in the home (such as for bathing or washing), did not cause harmful noncancer effects for residents or increase their risk of cancer.
- Private Wells: Current and Future Exposures
DDJC Tracy provides alternative water sources to residents of the two affected wells located north-northeast and downgradient of the site, although the carbon tetrachloride present in one well appears to be unrelated to the site. Subsequently, DDJC Tracy has provided a carbon filtration system for residents of the TCE-affected well. The carbon filtration system has effectively removed VOCs to levels below MCLs (Montgomery Watson, 1996b; DDJC Tracy, 1997b). No new private wells are likely to be installed in an area of known groundwater contamination because the California Department of Health Services oversees the installation of wells within 2,000 feet of a hazardous waste site (ATSDR, 1991). Continued monitoring of private wells in the area has not detected VOCs or other site-related contaminants, including chromium, at levels associated with health hazards. DDJC Tracy constructed a groundwater treatment system to control TCE and PCE (and perhaps other VOCs) from migrating off site and to clean up TCE, PCE, and DCE to EPA or CA MCLs.
- Agricultural Wells: Past Exposures
Three former agricultural wells (AGs)--AG-1, AG-2, and AG-3--were situated north and downgradient of the depot on the property currently referred to as the Tracy Annex. In the past, these agricultural wells were extensively used for flood irrigation of commercial (e.g., walnuts, alfalfa, beans) and homegrown row crops during spring and summer months, but not as a drinking water source (Woodward-Clyde Consultants, 1992a). Because AG-2 and AG-3 were situated within the plume, they may have pumped VOC-contaminated groundwater to these crops. AG-2, which is located slightly to the north of the site, also may have changed the plume migration pattern to a more northerly direction (rather than the northeasterly flow of the regional groundwater). Furthermore, pumping of AG-2 also appears to have contributed significantly to vertical migration of the VOC plume to the Middle and Lower Horizons of the Upper Tulare Aquifer. Agricultural well operations were discontinued in 1993, shortly after DDJC Tracy acquired the Tracy Annex (Montgomery Watson, 1995).
DDJC Tracy analyzed water samples collected from the agricultural wells for VOCs, and the results are presented in Table 5. TCE (3.5 to 12 ppb) and PCE (1.5 to 4.3 ppb) were consistently detected at levels above ATSDR's comparison values, although no other chemicals were detected.
In the Consumption of Locally Grown Foods section that follows, ATSDR evaluates potential health hazards posed by the use of contaminated agricultural well water as an irrigation source for locally grown foods.
- Agricultural Wells: Current and Future Exposures
The three agricultural wells are no longer used for irrigation, and therefore, pose no current or potential future public health hazards. The wells have been abandoned to minimize possible contaminant transport to the Lower Tulare Aquifer through well casings or gravel packs. AG-1, AG-2, and AG-3 were sealed in September 1994, December 1994, and June 1995, respectively. In the area of the AG-2 pump, the groundwater flow subsequently returned to north-northeast (Montgomery Watson, 1995). No new agricultural wells are likely to be installed in the vulnerable areas because California Department of Health Services oversees the drilling of new wells within 2,000 feet of a hazardous waste site boundary.
No public health hazards are associated with exposure to contaminated groundwater located beneath DDJC Tracy or in off-site areas. Site-related contaminants at levels that might result in adverse health effects have not been detected in on-site water supply wells, the Tracy municipal water supply, or nearby private wells.
- Day Care Center Play Yard
Approximately 90 children attend the day care center located in the northwest corner of the site. Children play in the center's 0.5 to 1 acre yard that is mostly covered with grass; however, there are areas of exposed soil. A former underground storage tank (UST), which contained No. 2 fuel oil, was partially located within the play yard. The tank and surrounding soil were removed in 1988 (DDJC Tracy, 1997a).
In 1994, DDJC Tracy collected five surface soil samples from within the play yard. The sample locations were selected to represent exposed soil areas commonly used by children. The soil samples were analyzed for semivolatile organic compounds (SVOCs), metals, and pesticides and the results are presented in Table 6. Although several contaminant concentrations (i.e., arsenic, chromium, vanadium, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene [DDE], 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane [DDT], and dieldrin) exceed ATSDR's very conservative comparison values for pica behavior (frequent hand-to-mouth activity), most values are typical of regional background soil concentrations (Montgomery Watson, 1995). Lead was also detected in three of five surface soil samples at a maximum concentration of 20.3 parts per million (ppm). Although a comparison value has not been established for lead, ATSDR determined that the soil lead concentrations are much lower than levels that have been shown to contribute to elevated blood lead level in young children who might incidentally ingest soil (CDC, 1991). DDJC Tracy has since removed the top 1 foot of soil from the entire play yard and play box material and replaced the excavated material with soil that has been certified as clean. The clean soil has been capped with a layer of sod (DDJC Tracy 1995; 1997a).
ATSDR evaluated whether children who attend the day care center are potentially exposed to the contaminants via incidental ingestion of the play yard surface soil at levels known to cause health effects. In evaluating exposure to soil contaminants via incidental ingestion, ATSDR assumes that uptake via ingestion is greater than through skin absorption. The methods used and assumptions applied are presented in Appendix C. ATSDR believes that the assumptions used to estimate exposure doses are very conservative and overestimate the level of actual exposure for a child playing in the day care center yard. The estimated exposure doses for a child are provided in Appendix C, Table C-3. Even using very conservative assumptions about exposure, the estimated exposure doses are lower than corresponding MRLs or RfDs. Therefore, incidental ingestion of surface soil is not expected to result in adverse health effects for young children playing in the day care center yard. Even if one assumes the highly conservative assumption that contaminant concentrations entering the body through dermal contact are approximately equal to ingestion, dermal contact with surface soil likewise is unlikely to lead to adverse health effects.
- Areas Under Investigation
A total of 69 areas have been investigated at DDJC Tracy: 31 SWMUs, 28 USTs, and 10 areas of soil contamination. For a majority of these areas, no public health hazard exists because the levels of contamination in soil are lower than levels associated with health hazards, exposure has been prevented by access restrictions (i.e., site security), and/or contaminated areas will be remediated. DDJC Tracy has designated certain areas of soil contamination for remediation (i.e., SWMUs 8 and 24) because they pose a potential threat to the underlying groundwater.
After considering the limited access to the site and reviewing the pertinent environmental monitoring data, ATSDR determined that workers and visitors at the site are not likely to have frequent or long-term contact with contaminated soil in these areas. Exposure, if any, is not expected to result in adverse health effects.
- Areas of Exposed Surface Soil
Most of the areas are paved or contain buildings. Few areas of exposed soil exist along the boundaries. DDJC Tracy analyzed samples from the exposed soil areas in 1993 and 1994, and Table 7 shows the results of these analyses. As the table indicates, the metals arsenic and beryllium have frequently been detected at levels above the comparison values, whereas the pesticides DDE, DDT, chlordane, and dieldrin have been much less frequently detected near comparison values. Though these contaminant concentrations exceed the very conservative comparison values used for screening, these concentrations are typical of background concentrations in soil for the vicinity. ATSDR determined that infrequent contact with these levels of contamination in this surface soil is not likely to result in an increased risk of adverse health effects for on-site workers or visitors.
No public health hazards are associated with exposure to contaminants in on-site soil for either children playing in the day care center play yard or workers and visitors who may infrequently contact exposed surface soil.
Exposure to soil gas becomes a concern when high levels of VOCs migrate via soil gas into basements through cracks in the foundation walls of buildings. Soil gas accumulates in the small spaces between soil particles when chemicals volatilize from contaminated soil or groundwater. Generally, VOCs in the upper layers of soils gradually diffuse to the surface through soil gas. Under certain circumstances, however, such as when a low-permeability layer in the unsaturated subsurface zone inhibits the upward diffusion of gas, horizontal spreading of soil gas may occur (EPA, 1992a). When this happens, contaminants may migrate with soil gas through foundation walls into a building's basement.
As part of its RI activities, DDJC Tracy sampled soil gas to characterize the presence of VOCs in soil and groundwater. Depot structures (including those overlying the plume and most likely to accumulate vapors) and the residential structures located downgradient of the site do not have basements. As a conservative measure, however, ATSDR reviewed data to determine whether soil gas could potentially contribute to the indoor air environment of on-site buildings.
Of the VOCs measured in soil gas, PCE (0.004 to 950 ppb) and TCE (0.007 and 220 ppb) were the most frequently detected (Montgomery Watson, 1996b). Although the amount of TCE or PCE that may enter a building varies as a function of several properties (e.g., soil characteristics), EPA predicts that indoor air contaminant concentrations typically do not exceed 5% of the surrounding soil gas concentrations (EPA, 1992a). Applying this estimate to PCE and TCE concentrations measured in on-site soil gas, ATSDR predicts indoor air concentrations between 0.0002 and 47.5 ppb for PCE and 0.00035 and 11 ppb for TCE. These estimated ranges include values that are less than or just above ATSDR's comparison values for airborne PCE and TCE (40 ppb and 100 ppb, respectively). Therefore, ATSDR estimates that even if soil gas migrates into indoor environments, VOCs are not likely to accumulate to concentrations that may pose health hazards.
No public health hazards are likely to occur from exposure to VOCs in soil gas. VOCs are not expected to accumulate in on-site buildings or nearby residences at concentrations that contribute to adverse human health effects.
Walnuts, fruits, and vegetables were grown for commercial and private use on the Tracy Annex. Until 1995, three agricultural wells located in the Tracy Annex were used for flood irrigation of commercial or homegrown crops. Two of the wells were located in the VOC plume and contained TCE and PCE at levels above comparison values for drinking water. These wells have since been abandoned and properly sealed, and they no longer provide irrigation water.
ATSDR evaluated whether VOCs in irrigation water accumulated in crops to levels, if any, associated with health effects. The most accurate method for determining concentrations of these contaminants in crops is through laboratory analysis. Samples of walnuts, alfalfa, and beans were collected from the property in September 1991 for use in assessing potential contamination by PCE or TCE, or other VOCs. Although no TCE or PCE were detected in the samples, the quality of the data is in question (Woodward-Clyde Consultants, 1992b).
Even if crops were irrigated with water containing the maximum detected concentration of TCE (12 ppb) or PCE (4.3 ppb), it is unlikely that plants took up significant contaminant concentrations into their edible portions. Nonpolar chemicals such as TCE tend to adsorb to root surfaces rather than pass through the outer layer of the root to the plant tissue (EPA, 1992b). Where TCE does pass through to the tissue, it most likely will transpire through the leaves, rather than accumulate in the edible portion of the plant. Therefore, trees and crops irrigated with water containing TCE and PCE levels slightly above the MCLs would not be expected to accumulate and store these chemicals in nuts, fruits, or vegetables.
No public health hazards are expected to occur from consumption of locally grown fruits, nuts, and vegetables. Locally grown foods most likely have not accumulated site-related contaminants, if any, to harmful levels.
A stormwater lagoon located in the northwest corner of the site (see Figure 2) was built in 1972 to collect stormwater runoff from the depot. Through a network of underground stormwater sewers and open-surface drainage ditches, runoff and rinse water from paint stripping, degreasing, and steam-cleaning operations collected in the lagoon. Sediment samples collected from the lagoon during its RI activities were analyzed for SVOCs, metals, pesticides, and polychlorinated biphenyls (PCBs). With the exception of polycyclic aromatic hydrocarbon (PAH) and dieldrin concentrations, which slightly exceeded ATSDR's CREGs, contaminant concentrations were below ATSDR comparison values for soil.
Although detailed information on the use of the lagoon is not available, the lagoon was probably not widely used for recreational fishing. The lagoon was, however, the site of a one-time fishing derby and was stocked with carp, catfish, perch, and bass for very limited recreational fishing activity until 1992, when DDJC Tracy drained the lagoon (Montgomery Watson, 1996b; DDJC Tracy, 1997a).
Fish can accumulate high levels of contaminants, even when only low levels are present in sediment. ATSDR was interested, therefore, in whether the few anglers using the lagoon could have been indirectly exposed to site-related contaminants when they ate fish from the lagoon. Unfortunately, no fish sampling had been conducted prior to emptying the lagoon of fish. Without these data it is difficult state with certainty whether fish contained harmful levels of contaminants.
In the absence of fish data, ATSDR evaluated the lagoon sediment data along with bioaccumulation parameters (e.g., translocation factors) to estimate contaminant concentrations in lagoon fish. Using the estimated fish tissue concentration, ATSDR predicted exposure doses to determine potential health hazards from eating the lagoon fish. Appendix C describes the method and assumptions used by ATSDR to estimate exposure doses and health risks. ATSDR believes that the assumptions used to predict contaminant concentrations in fish and estimate exposure doses are very conservative and, therefore, greatly overestimate the level of actual exposure for anyone eating fish from the lagoon.
The estimated exposure doses and health risk estimates are provided in Appendix C, Table C-4. As the table indicates, the conservatively derived exposure doses are lower than corresponding MRLs/RfDs. ATSDR therefore believes that consumption of fish in the past poses no noncancer health concerns. ATSDR also estimated cancer risk for consumption of fish from the stormwater lagoon assuming a 30-year exposure period. The resulting excess cancer risk estimates are below levels likely to contribute to excess cancer in the population.
No public health hazards occurred from consumption of lagoon fish in the past. Contaminants, if
any, most likely did not accumulate in fish to levels associated with adverse human health
DDJC Tracy has a community relations plan (CRP) that provides guidance for involving the
community and other interested parties in the remediation decision-making process and for
distributing information to these parties (DDJC Tracy, 1995). As part of its community relations
activities, DDJC Tracy meets periodically with community members to monitor community
concerns. No specific health concerns have been brought to ATSDR's attention, although general
concerns about potential health hazards associated with the site and the off-site migration of
contaminants have been identified in the DDJC Tracy CRP. ATSDR has addressed these concerns
in the Evaluation of Environmental Contamination and Potential Exposure Pathways section of
ATSDR recognizes that infants and children may be more sensitive to environmental exposure than adults in communities faced with contamination of their water, soil, air, or food. This sensitivity is a result of the following factors: 1) children are more likely to be exposed to certain media (e.g., soil or surface water) because they play and eat outdoors; 2) children are shorter than adults, which means that they can breathe dust, soil, and vapors close to the ground; and 3) children are smaller, therefore, childhood exposure results in higher doses of chemical exposure per body weight. Children can sustain permanent damage if these factors lead to toxic exposure during critical growth stages. ATSDR is committed to evaluating their special interests at sites such as DDJC Tracy, as part of the ATSDR Child Health Initiative.
ATSDR evaluated the likelihood that children living near the DDJC Tracy site may have been or may be exposed to contaminants at levels of health concern. ATSDR did not identify any situations in which children were likely to be or have been exposed to harmful levels of chemical contaminants attributed to the DDJC Tracy site.
ATSDR based this conclusion on several factors, including:
- Children have not contacted harmful levels of contaminants when playing at the day care center play yard. ATSDR determined that contaminant concentrations in the day care center play yard soil are too low to pose a health hazard to children playing there. Fences prevent children from wandering to other areas of the site where soil contamination may exist.
- Children have not been exposed to harmful contaminants when drinking water. Both municipal water supplies and private wells provide drinking water that should be safe for children to drink. The municipal water supplier routinely tests the drinking water to ensure that the drinking water meets safe drinking water standards. Two downgradient private wells contained low level site contamination. Drinking this water would not have harmed children because the concentrations in these wells were considerably lower than levels associated with adverse health effects. All other private wells appear to be away from the area of groundwater contamination.