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concentrations, and appears to represent a minor <br /> source, very possibly unrelated to and separate from <br /> the ground-water hydrocarbon contamination observed. <br /> This is consistent with an off-site ground-water <br /> hydrocarbon source as recharge overlying contaminated — <br /> ground water will preclude communication with the <br /> vadose zone soil vapor, typically a significant on- <br /> site source will result in some free product ( at <br /> least a sheen) which floats and retains communication <br /> with the vadose zone. Y <br /> S . No clear explanation for this hydrocarbon - <br /> distribution is apparent, but reasonable scenarios <br /> include the following: — <br /> a. An off-site source to the north or northwest <br /> existed at a time when ground-water flow Y <br /> direction was different. <br /> b. A source located across North Pershing with only <br /> a small part of the lateral portion of the plume <br /> is being observed. <br /> C. Past activities prior to the recently removed <br /> EXXON station on the site resulted in fuel <br /> spillage or leakage on the northern portion of <br /> the site at a time when ground-water flow <br /> direction was different. — <br /> Based on this investigation the following is recommended: <br /> 1 . Construction plans for the site should proceed and future <br /> investigation/cleanup activities be coordinated with <br /> owner/occupants. <br /> 36 <br />