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discussed later in this Proposed Plan. The purpose of the IRM is to capture and treat the <br /> volatile organic "hot spot" contamination in the aquifer and prevent it from migrating off site. <br /> The IRM currently operates under Waste Discharge Requirement No. 90-275X Issued by+ne KWQ <br /> SUMMARY OF SITE RISKS <br /> Environmental studies at DDRW-Tracy have indicated that groundwater contaminated <br /> principally by TCE and PCE flows from the northeast section of the site to off-site private <br /> land. Other potential chemicals of concern detected in DDRW-Tracy off-site groundwater, <br /> including boron, nitrate, dieldrin, carbon tetrachloride, and chloroform, may be naturally <br /> occurring or have off-site sources. There are additional chemicals of concern detected in <br /> monitoring wells located on the depot. These and other potential chemicals will be addressed <br /> in the site-wide RI/FS. <br /> A risk assessment was performed to define the risk posed to public health and the <br /> environment due to the presence of TCE, PCE, and the other chemicals of concern present <br /> in the groundwater. The assessment estimated the risk an off-site resident would face-from <br /> being exposed to contaminated groundwater. Several potential ways of being exposed (called <br /> "exposure pathways") that were evaluated included: the resident drinks from a domestic well <br /> placed within the off-site contamination plume; the resident inhales vapor while showering <br /> with such water, the resident absorbs such water through the skin while showering or <br /> washing; and the resident eats vegetables and crops irrigated with the water. <br /> The groundwater risk assessment concluded that the cancer risks and other health threats <br /> associated with groundwater at the depot exceed recommended protective levels for the <br /> "exposure pathways" described in the above paragraph. Using a hypothetical future scenario <br /> in which a well may be installed into any one of the off-site aquifers, the risk to an off-site <br /> resident again will be greater than the minimum protective levels recommended by the U.S. <br /> Environmental Protection Agency (EPA) in the National Oil and Hazardous Substances <br /> Pollution Contingency Plan (NCP). <br /> Plants and animals in and around DDRW-Tracy include terrestrial vegetation; soil <br /> invertebrates; small mammals; birds;reptiles; and aquatic plants,invertebrates,and vertebrates <br /> associated with the stormwater runoff pond and flood-irrigated fields downgradient of the site. <br /> Q19W003.1(90380CM 8 _ M10079M39 <br />