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• secured with water tight traffic boxes. <br /> CONCLUSIONS <br /> The results of ground water monitoring, January 12, 1990, indicate <br /> that the ground water has risen approximately one foot since early <br /> December and is flowing to the southeast. Depth to water <br /> measuxementro taken on May 25, 1990 shows a similiar ground water <br /> gradient and a drop in the ground water elevation by as much as <br /> 4.380 in monitor well MW1, see FIGURES 4A, 4B, azid 4C. Chemical <br /> results of the water samples taken from the monitor wells show <br /> minor contAe i..ation to the ground water with gasoline range <br /> hydrocarbons. <br /> A former Chevron site, located northwest of the site, across <br /> Harding and El Dorado, may be contributing to the ground water <br /> contamination. A review of the file on this site has been <br /> inconclusive, ground water has dropped lower than the monitor <br /> wells at this site can test for. <br /> Soil contamination is limited to beneath the eastern half of the <br /> pump island and beneath the southeastern half «f the tank <br /> excavation. This Contamination is of gasoline range hydrocarbons <br /> to the 30 foot depth beneath the excavation and to the 15 foot <br /> depth beneath the pump island. <br /> RECOMMM(DATIONS <br /> • I. Place a temporary onsite ground water monitoring well <br /> near the intersection of Harding and E1 Dorado streets in the <br /> planter. This well will help define the ground water gradient and <br /> may determine if the former Chevron site, across the street, is <br /> influencing the ground water beneath this site. <br /> 2. Clean out and excavate the tank cavity to as deep as <br /> field screening indicates measurable contaminated soil exists. <br /> 3. Field screws the ambient air conditions at the site <br /> during excavation activities with a calibrated Photoionizing <br /> detector. If the ambient air near the excavation exceeds 100 <br /> parts per million TVO, shat down the excavating process and do not <br /> continue until ambient air monitoring shows that conditions are <br /> safe to proceed. <br /> 4. Install a vapor recovery well in the excavation to the <br /> depth of final excavation. <br /> 5. Place a neat cement-bentonite seal from surface to the <br /> 10 foot depth around the vapor recovery well. <br /> 6. Use the clear: aerated soil to backfill the excavation <br /> once the vapor recovery well has been installed. <br /> 7. Continue to locate area and install an offsite monitor <br /> �� 4 <br />