PUBLIC HEALTH ASSESSMENT
TRACY DEFENSE DEPOT
(a/k/a DEFENSE DISTRIBUTION REGION WEST TRACY ARMY)
TRACY, SAN JOAQUIN COUNTY, CALIFORNIA
Based on an evaluation of environmental information collected during the site characterization and remedial process, ATSDR reached the following conclusions and assigned a public health hazard conclusion category.
ATSDR determined that DDJC Tracy poses no apparent public health hazard.
- Groundwater beneath the northern area of DDJC Tracy is contaminated with
VOCs--primarily TCE and PCE--related to past activities. VOCs have migrated with the
groundwater to off-site areas beyond the north-northeast boundary of the depot property,
but no exposures to contaminated groundwater have occurred, are occurring, or are
expected to occur at levels likely to pose health hazards.
DDJC Tracy water supply poses no apparent public health hazards. To date contaminants have not been detected in the water supply wells at levels associated with adverse health effects. WSWs 4 and 7 provided water for the DDJC Tracy water supply. WSW 4 was located in the plume's path, but no contaminants were detected in groundwater immediately near WSW 4, nor in WSW 7 water. WSW 4 has been properly abandoned and is no longer used. WSWs 8 and 9, which are upgradient and away from contaminated wells, currently serve the depot's water supply. WSW 7 is currently on standby status as DDJC Tracy investigates the consequence of nearby low-level TCE contamination.
Private (domestic use) wells pose no apparent public health hazards. Two private wells located north-northeast of the depot boundary contained TCE, PCE, and carbon tetrachloride at levels above the ATSDR CREG and above EPA and CA MCLs. Bottled water and/or carbon filtration systems were offered to residents of the affected wells. Continued monitoring of these wells and other private wells in the area has not detected VOCs at levels associated with adverse health effects. DDJC Tracy constructed a groundwater treatment system that is expected to minimize transport off site and clean up the plume to EPA and/or CA MCLs for TCE, PCE, and DCE. Therefore, no exposure is currently occurring via private well water at levels associated with health hazards, and future exposure above the MCLs is not expected to occur.
Municipal water supply is safe to drink. The drinking water for the city of Tracy is supplied by 10 deep-aquifer wells, none of which are located in or near the plume or have been affected by site-related contamination.
- On-site surface soil poses no apparent public health hazards to on-site workers or visitors, or to children playing in the day care center play yard. DDJC Tracy evaluated contaminant concentrations in areas of exposed soil along the boundary of the site where workers or visitors may access them and in the day care center yard where children play. ATSDR determined that soil contaminant concentrations in the exposed areas of the site and in the day care center play yard are too low to pose a health hazard. Although some areas of the site under investigation contain contaminated media, workers and the general public are have limited access to the areas and thus would not be exposed to contaminants with any frequency or extent.
- Ingestion of locally grown commercial produce or home-grown vegetables pose no apparent public health hazards to individuals consuming these foods. Three agricultural wells located in or near the plume were used to irrigate commercial crops in the past. During monitoring between 1987 and 1991, TCE and PCE were detected in two of the wells at levels above ATSDR's CREG and above EPA and CA MCLs. Because VOCs at levels slightly above the MCLs are not expected to appreciably accumulate in nuts, fruits, or vegetables grown in the area, ATSDR does not anticipate this pathway to pose a health hazard. The three agricultural wells in or near the plume were closed by 1995. Therefore, no exposure is currently occurring or is expected to occur in the future through this pathway.
- Past consumption of fish from the on-site stormwater lagoon poses no past health hazards to individuals who consumed the fish. Water from the stormwater system and from DDJC Tracy water supply well 4 (located in the plume) filled the lagoon, which was fished until 1992, when DDJC Tracy removed all fish from the lagoon. In the absence of fish sampling, ATSDR reviewed the sediment data collected for the lagoon and determined that lagoon fish were unlikely to have accumulated contaminants, if any, at levels known to cause health hazards to people who ate the fish in the past. The lagoon does not contain any fish now, and DDJC Tracy has not developed plans to restock the lagoon; therefore, exposure is not occurring and it is not expected to occur in the future.
- Soil gas poses no apparent health hazards to depot users. Most on-site buildings and nearby off-site residences lack a basement through which vapors could. Even if basements were present, TCE and PCE concentrations in soil gas are low, and these low levels would not be expected to migrate and accumulate in the indoor residential air environment at levels associated with human health hazards.
The Public Health Action Plan (PHAP) for DDJC Tracy contains a description of actions taken and those to be taken by ATSDR and DDJC Tracy at and in the area of the site. The purpose of the PHAP is to ensure that this public health assessment not only identifies public health hazards, but provides a plan of action designed to mitigate and prevent adverse public health effects resulting from exposure to hazardous substances in the environment. The public health actions that are completed, being implemented, or planned are as follows.
- In 1992, DDJC Tracy closed water supply well 4, which was in the path of the plume. Operating DDJC Tracy water supply wells (8 and 9) are upgradient and away from the path of the groundwater plume.
- DDJC Tracy has placed WSW 7 on standby status until the well is repaired or groundwater monitoring confirms that the well could not be affected by TCE contamination.
- DDJC Tracy provided alternative water supplies and/or carbon filtration units to the owners of the affected off-site private domestic wells. DDJC Tracy continues to monitors the quality of water in these wells.
- DDJC Tracy abandoned and sealed three agricultural wells located north of the depot (and on the Tracy Annex property) after detecting VOCs in two of the wells at levels greater than ATSDR comparison values and the EPA and CA MCLs.
- DDJC Tracy installed an air stripping and vapor-phase carbon system to minimize off-site migration of contaminated groundwater and to clean up the plume to EPA or CA MCLs for TCE, PCE, and DCE.
- DDJC Tracy, the US Environmental Protection Agency, the California Department of Health Services, and the California Regional Water Quality Control Board work together to ensure that potential public health hazards at the site are throughly investigated and appropriate remedial actions are taken to protect the health and well-being of the public.
- DDJC Tracy continues to regularly monitor groundwater in the vicinity of the site for site-related contaminants to ensure compliance with EPA and CA MCLs.
- DDJC Tracy is monitoring VOCs in WSWs 7, 8, and 9 quarterly for approximately one year. DDJC Tracy will take immediate action to correct any threat to the water supply. ATSDR will review the new data to determine whether any additional measures are necessary to protect public health.
- DDJC Tracy has proposed soil remediation (bioventing) for on-site areas where contaminated soil may be contributing to VOC-contaminated groundwater.
- Although no apparent public health hazards have been associated with day care center play yard soil, DDJC Tracy excavated 1 foot of soil from the yard, replaced the soil and play area material with 1 foot of certified clean soil, and capped the clean soil with a layer of sod. This measure reduces opportunities for exposure to potential contamination in play yard surface soil.
- DDJC Tracy will continue to provide information to the surrounding community and interested parties about results of environmental investigations and remediation status for the site.
- If new data generated by continued site activities indicate that a potential health hazard exists, ATSDR will re-evaluate the conclusions in this PHA.
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Gary Campbell, Ph.D.
Environmental Health Scientist
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation