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Mr.Harlin Knoll %WW Environmental <br /> Resources <br /> 12 July 2000 <br /> Management <br /> Page 2 <br /> these samples indicate that the concentrations of TPH-g and BTEX <br /> decreases significantly with depth (by two orders of magnitude when <br /> comparing the sample results). In addition, the concentrations of BTEX <br /> compounds at 30 to 33 feet bgs are below their respective State of <br /> California Maximum Contaminant Levels (MCLs) (there is no MCL for <br /> TPH-g). <br /> This information was submitted to the County in the Investigation Results <br /> Report(ERM, 13 April 1999). The sampling results were also discussed <br /> with the County and RWQCB in a meeting on 9 February 2000. During <br /> this meeting, it was discussed that the information available could be <br /> compiled into a Closure Report to proceed towards a"No Further <br /> Action" response. In addition, it was agreed upon that a risk assessment <br /> should be provided in the Closure Report to evaluate the risks posed by <br /> chemicals (primarily benzene) remaining in ground water. The need for <br /> additional ground water data with depth was not discussed at any time <br /> during this meeting. <br /> The decreasing concentrations with depth are consistent with the <br /> dispersion expected for a shallow release of gasoline related compounds. <br /> Furthermore, since the chemicals present in the subsurface are gasoline <br /> related, they would be expected to be present at the highest <br /> concentrations at the surface (as demonstrated) and are not expected to <br /> increase with depth (as demonstrated). Therefore, additional <br /> characterization with depth to a "non-detect" point will not change the <br /> conclusions of the Underground Storage Tank Closure Report (ERM, 7 April <br /> 2000) that no further actions are required. <br /> Additional Investigation <br /> As a continued effort of Heinz's willingness to cooperate and to alleviate <br /> the County's concerns, we propose to collect additional HydroPunch <br /> ground water sampling data at each former tank site to the depth of <br /> TPH-g and BTEX impacts. We plan to collect a HydroPunch sample at <br /> two different locations at each former tank site as shown in Figures I and <br /> 2. <br /> One sample will be collected in the area immediately downgradient of <br /> each former tank location (HB-21 and HB-23). This is the area where the <br /> highest concentrations of TPH-g and BTEX have been detected in shallow <br /> ground water samples. Therefore, this is the area where the greatest <br /> depth of dispersion is anticipated. The second set of samples will be <br />