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groundwater or soil It is possible that these compounds may be related <br /> to regional pesticide usage <br /> The groundwater flow direction in the first zone (shallower than 19-feet <br /> bgs), 1s to the northwest at a gradient of between 0 008 to 0 01 -feet/foot <br /> Only two wells have been installed in deeper zones beneath the site which <br /> does not allow for the calculation of the groundwater flow direction at <br /> these depths from potentiometric surfaces (since three non-linear points <br /> are needed) However, it should be noted that the potentiometric surface <br /> in monitoring well MW-8 is higher than that in monitoring well MW-10 <br /> (both wells screened below 100-feet bgs) and the potentiometric surface <br /> of monitoring well MW-7 is higher than the potentiometric surface in <br /> monitoring well MW-9 (both wells screened between 55-feet bgs and 70- <br /> feet bgs) Based on (a) these potentiometric surface relationships, (b) the <br /> presence of benzene upgradient of the source area in the 55 to 70-foot <br /> zone, and (c) the presence of VOCs at higher concentrations at 70-feet <br /> bgs than at 40-feet bgs in both of the CPT borings drilled for this <br /> assessment, it appears that there is significant pumping influence from <br /> the drinking water well that could be drawing hydrocarbons downward <br /> and upgradient from the source area <br /> 12 . 0 RECOMMENDATIONS <br /> ASE recommends the following <br /> 1 ) The extent of contamination downgradient of the site should be <br /> assessed using Geoprobe borings as well as possible future <br /> monitoring wells <br /> 2 ) Future groundwater samplings for the site should include a silica gel <br /> cleanup as preparation to the TPH-D analysis In addition, EPA <br /> Method 8270 should be added to the analytical suite during the next <br /> groundwater sampling <br /> 3 ) ASE recommends that the site be placed on a quarterly groundwater <br /> sampling schedule However, due to the significance of the benzene <br /> concentrations in the groundwater samples collected from <br /> monitoring wells MW-9 and MW-10, ASE recommends that these <br /> wells be resampled immediately <br /> 4 ) If the resampling of monitoring wells MW-9 and MW-10 again show <br /> significant hydrocarbon concentrations, ASE will recommend an <br /> interim method of remediation for this area such as a wall of oxygen <br /> Franks One Stop Report - June 1999 <br /> -13- <br />