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t <br /> ASSESSMENT OF IMPACTS AND FEASIBILITY STUDY <br /> As required by California law, an assessment of potential impacts is required in formulating a <br /> Corrective Action Plan This assessment includes reviewing the contaminant type and hydrogeologic <br /> setting (discussed above) in evaluating the plan for remediation An analysis of options considered for <br /> remediation is also required to demonstrate the rationale for selecting the treatment option Finally, <br /> target cleanup levels are to be specified <br /> The first impact requiring assessment is the physical and chemical characteristics of the contaminant <br /> The contaminant is gasoline, a volatile liquid substance composed of over 100 separate orgaruc <br /> compounds Many of these individual compounds are volatile (vapor pressure greater than 5 mm Hg <br /> at STP), aromatic hydrocarbons Aromatic hydrocarbons that are typically found in gasoline (such as <br /> benzene) are of concern because many are carcinogenic or suspected of being carcinogenic <br /> Fortunately, these compounds typically are not readily soluble in groundwater (generally solubilities <br /> range from 100 to 200 ppb @ 20°C), and therefore do not mobilize in groundwater as quickly or <br /> • completely as more soluble contaminants These organic compounds are also affected by adsorption <br /> within the unsaturated soil and aquifer which further retards movement The primary impact of <br /> contaminants such as gasoline on the local groundwater is the migration of toxic compounds such as <br /> benzene in the aquifer These compounds may spread downgradient, driven by advection and <br /> hydrodynamic dispersion, to previously pristine areas If there are users of this groundwater, it could <br /> impact their ability to safely utilize the resource <br /> The local hydrogeologic setting of the site and surrounding area is discussed above Groundwater <br /> occurs in an unconfined condition and the elevation is subject to significant fluctuation over time The <br /> primary aquifer unit in the stratified section appears to be the thin saturated sand layer located at about <br /> 65-70 feet below grade This unit is an alluvial deposit composed mostly of fine to medium grained, <br /> poorly sorted sand with minor fractions of silt and clay Based on the drilling logs the unit is <br /> Page 5 <br />