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Preliminary Endangerment Assessment Page 10 <br /> Former Haley's Flying Service <br /> GPE Project 474.2 <br /> 5.0 HUMAN HEALTH SCREENING EVALUATION <br /> 5.1 Exposure Pathways and Media of Concern <br /> Exposure assessment is the process of describing, measuring or estimating the intensity, fre- <br /> quency, and duration of potential human exposure to chemicals of potential concern <br /> (COPCs) in environmental media (e.g., soil, water and air) at a site. A general discussion of <br /> exposure assessment is included in Section 7 of the original PEA. For the purposes of this <br /> addendum, only the exposure pathways associated with the groundwater need be addressed. <br /> Since pesticides are non-volatile, the only possible exposure pathway is by ingestion of <br /> groundwater. The only known water production well in which ground water could <br /> reasonably hold potential to be contaminated is the onsite domestic water well (see Section <br /> 4.3 of the original PEA). The sample from this well did not, however, contain detectable <br /> organo-chlorine pesticides. The driller's log for the well was obtained by DTSC, but is <br /> considered by State law to be confidential and is therefore not attached to this report. The <br /> log indicates the water production interval is below 50 feet, and what appears to be an <br /> effective clay aquitard is present between 25 and 31 feet. A second clay layer is identified <br /> between 62 and 83 feet. Based on the presence of the aquitard and the absence of detectable <br /> COPCs in the well water, it appears unlikely that humans will be exposed to pesticides in the <br /> groundwater. <br /> It is theoretically possible that a new water well could be constructed near the site that could <br /> produce contaminated water, however this part of Tracy has been zoned for industrial <br /> development. The newly constructed industrial facilities will be connected to the municipal <br /> water system and are therefore unlikely to need a domestic water source. <br /> 2937 Veneman Avenue,Suite B240 Geo-Phase Environmental Inc. Phone: (209)569-0293 <br /> Modesto,Ca 95356 Fax: (209)569-0295 <br />