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i 15 January 1997 AGE-NC Project No 96-0229 Page 6 of 6 ' dispenser area(P-2 and P-3) Laboratory and field data suggests that impacted ground water beneath the site forms a narrow, elongated dissolved petroleum hydrocarbon plume (Figure 5 -Approximate Extent of Dissol ved Petroleum Hydrocarbons) that extends in a northeastern direction (downgradient) • Concentrations of benzene detected in grab ground water samples from probe borings P-1 through P-4 and P-7 through P-9 were above the State of California Maximum Contaminant ' Levels (MCLs) for drinking water of i 0µg/l * Concentrations of MTBE collected from P-1 through P-4 and P-9 were above the State of ' California Drinking Water Action Level (AL) of 35 ppb The detection of MTBE is suggestive that a leak may have occurred within the last 15 years 5 2 RECOMMENDATIONS ' Based upon data collected from the site, AGE has the following recommendations • Further assessment is warranted northeast of soil probe boring P-8 and west of soil probe boring P-5 to determine the lateral extent of dissolved hydrocarbons ' • A minimum of four ground water monitoring wells is recommended at the site At least one ground water monitoring well should be installed upgradient, one ground water monitoring well crossgradient, and two ground water monitoring wells should be installed downgradient ' of the hydrocarbon source to monitor the possible migration of the dissolved petroleum hydrocarbon plume Proposed ground water monitoring well locations are depicted on Figure 2 ' • Additionally, consideration should be given for the installation of at least two soil vapor extraction/in-situ air sparging (SVE/IAS)wells and the performance of an SVE/IAS feasibility ' test Feasibility testing will help determine eventual remediation alternatives for the site 6.0. LIMITATIONS Our professional services were performed using that degree of care and skill ordinarily exercised by ' environmental consultants practicing in this or similar localities The findings were based mainly upon analytical results provided by an independent laboratory Evaluations of the geologic/ hydrogeologic conditions at the site for the purpose of this investigation are made from a limited number of available data points(i e grab water samples and soil samples) and subsurface conditions may vary away from . these data points No other warranty, expressed or implied, is made as to the professional recommendations contained in this report