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INITIAL RELEASE DDJC Tracy <br /> ATSDR evaluated environmental data and exposure information to determine if completed or <br /> potential pathways of human exposure to contaminants existed in the past or if they exist now or <br /> potentially in the future. ATSDR identified several exposure pathways that required further <br /> evaluation, including the following: <br /> ■ Consumption of groundwater <br /> ■ Dermal contact with surface soil <br /> ■ Inhalation of soil gas <br /> ■ Ingestion of locally grown crops <br /> ■ Ingestion of recreationally-caught fish from the on-site stormwater lagoon <br /> In this section, ATSDR evaluates these exposure pathways in more detail, considering data <br /> gathered and remedial activities conducted since ATSDR's 1991 site visit, to determine whether <br /> these pathways represent, under site-related conditions, a threat to human health. The results of <br /> the pathways investigation are summarized in Table 2. <br /> Consumption of Groundwater <br /> Groundwater use poses the primary exposure pathway of concern. VOCs, predominantly TCE <br /> and PCE, are widely present in the on-site shallow aquifer (Upper Tulare Aquifer) located north- <br /> northeast of the site. Contamination in this aquifer has been associated with several on-site former <br /> waste disposal areas and locations of accidental spills. <br /> The highest TCE (560 ppb) and PCE (760 ppb) concentrations, detected in 1986, greatly exceed <br /> the MCLS and the California Department of Toxic Substance Control MCLS of 5 ppb for both <br /> contaminants (Woodward-Clyde Consultants, 1992a; Montgomery Watson, 1995). The highest <br /> concentrations of these contaminants occur in the Above Upper Horizon of the Upper Tulare <br /> Aquifer below the depot's former open drum storage areas located along the northeast boundary <br /> of the site and in the maintenance areas (see Figure 2), where soil contaminants from waste <br /> disposal practices and accidental spills leached into the groundwater. The greatest lateral extent of <br /> contamination, however, is in the Upper Horizon, and contamination has also migrated into the <br /> deeper Middle and Lower Horizons carried by a strong gradient that was created by past <br /> operation of a nearby agricultural well (AG-2). <br /> TCE and PCE have also migrated off site to the north and northeast in three groundwater <br /> horizons of the Upper Tulare Aquifer. TCE concentrations of 5 ppb or greater extend <br /> 7 <br />