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OU #1 is not believed to presently pose an unacceptable environmental risk to plants and <br /> animals. <br /> CLEANUP ALTERNATIVES WILL PROTECT PUBLIC HEALTH <br /> The presently preferred cleanup alternative for groundwater at DDRW-Tracy will reduce any <br /> health risks of exposure (based on the scenarios presented above) posed by the site <br /> contaminants to "acceptable" levels after an operating period estimated to exceed 30 years. <br /> A 45-year period is estimated based on engineering calculations of the amount of <br /> groundwater necessary to be treated and the limits of the treatment system. A 30-year period <br /> is used by EPA as the maximum length of time for estimating the costs of cleanups. EPA <br /> considers an acceptable risk range to be between one in 10,000 and one in 1,000,000 excess <br /> cancers. Once the groundwater cleanup is complete, a person's risk of developing cancer as <br /> a result of exposure to groundwater would fall within or below that range. With the <br /> exception of the no-action and institutional controls alternatives, all alternatives are designed <br /> to reduce risks of the contaminant plume to acceptable levels. Actual or threatened releases <br /> of hazardous substances from the groundwater in OU #1, if not addressed by the preferred <br /> alternative or one of the other active measures considered, may present a current or potential <br /> future threat to public health, welfare, or the environment. <br /> INTERIM REMEDIAL MEASURE <br /> Phase I of the Interim Remedial Measure (IRM) has been constructed at the northeastern <br /> boundary of DDRW-Tracy. The objective of the IRM is to reduce additional contamination <br /> from migrating off depot. The IRM is a groundwater extraction and treatment system <br /> designed to collect groundwater from the upper horizon of the contaminated aquifer (about <br /> 50-foot depth), treat the water by air stripping, treat volatile organic air emissions using a <br /> vapor-phase granular activated carbon control unit, and dispose of the treated groundwater <br /> by shallow well injection. <br /> At present, in the first phase of operation, the air stripping system operates at about 120 <br /> gallons per minute (gpm) using an air stripper designed to treat 500 gpm, six extraction wells, <br /> three injection wells, and ten monitoring wells. Excess effluent is discharged to the <br /> stormwater holding pond which has been linked as a backup containment system. <br /> Q'W9043.1(90380C)\9 9 M1007922139 <br />