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INITIAL RELEASE DDJC Tracy of the site has not been used for drinking or irrigation (Woodward-Clyde Consultants, 1992a; Montgomery Watson, 1995). In the vicinity of the site, the Corcoran Clay Layer is estimated to be between 80 to 100 feet thick and is generally encountered at approximately 220 feet below ground surface. The Lower Tulare Aquifer lies below the Corcoran Clay and contains water under confined conditions, flowing generally toward the north and northeast. The total thickness of this layer is not well documented; however, estimates suggest that the layer ranges in thickness from 90 feet to greater than 1,400 feet. The on-site wells draw water the Lower Tulare Aquifer (Woodward-Clyde Consultants, 1992a; Montgomery Watson, 1995). Natural surface water bodies do not exist on site. A storm drain system receives runoff from the entire site and transports it to an unlined on-site stormwater lagoon. In the past, the lagoon was stocked with fish and was used as a recreational fishing spot, but was not used for swimming. Any surplus water that has not percolated downward into the soil is pumped to a local drainage ditch that ultimately drains into the nearest natural surface water body, the San Joaquin River, 4.5 miles northeast of the site. ATSDR Involvement ATSDR conducted a site visit in April 1991. During this visit, ATSDR staff met with DDJC Tracy site representatives and officials from the San Joaquin County Health Services, Council of Governments, and Department of Public Works to gather community concerns and information related to the site, area private wells, and the municipal water distribution system. From the meetings and a review of the data available at the time, ATSDR did not find any completed human exposure pathways that posed a public health hazard, nor did ATSDR identify any community health concerns. However, ATSDR determined that additional DDJC Tracy site data were needed to evaluate more fully any potential exposures that might occur through groundwater (via on-site supply wells or private wells located north-northeast and downgradient from the site) and surface soil pathways, and through consumption of locally grown foods or fish (ATSDR, 1991). Quality Assurance and Quality Control In preparing this Public Health Assessment (PHA), ATSDR relied on environmental data and discussions with DDJC Tracy representatives. The majority of the environmental data presented in this PHA comes from monitoring programs and more detailed studies conducted by DDJC Tracy. These include the November 1992 final operable unit no. 1 remedial investigation (RI)/risk assessment, the August 1993, final operable unit no. 1 record of decision, and the August 1995 5