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Moore Petroleum Page 2 of 3 <br /> 5491 F Street 02 July 2009 <br /> Banta, California <br /> collection of soil samples to minimize the potential for problems with heaving <br /> sands while setting the well. <br /> By letter dated 30 April 2009, AEI recommended reducing the analytical regimen <br /> for groundwater samples collected during monitoring events to total petroleum <br /> hydrocarbons quantified as gasoline (TPHg), as diesel (TPHd), as motor oil <br /> (TPHmo) and as kerosene (TPHk) since benzene, toluene, ethylbenzene and <br /> total xylenes (BTEX), fuel oxygenates and lead scavengers have not been <br /> detected at quantifiable concentrations or at concentrations exceeding <br /> Groundwater Screening Levels. Only ethylbenzene has been detected in <br /> samples collected from two wells (MW-8 and RW-2). The EHD concurs with the <br /> recommendation and approves the reduced analytical regimen for monitoring <br /> well samples. <br /> Operation of the soil vapor extraction (SVE) system has yielded very low <br /> concentrations of petroleum hydrocarbons; the EHD recommends ceasing SVE <br /> operations for an extended period for rebound testing of impacted groundwater; <br /> you may want to recommend selected monitoring wells for quarterly monitoring to <br /> document rebound effects or lack thereof. <br /> In the monitoring report for the fourth quarter 2008, AEI recommended <br /> conducting a confirmation soil vapor survey to evaluate the effect of the <br /> additional SVE system operation on the hydrocarbon concentrations detected <br /> during the soil vapor assessment of 31 October 2008. Thirteen vapor sampling <br /> probe points were advanced to collect soil gas samples; all thirteen samples <br /> contained quantifiable concentrations of TPHg and BTEX, the benzene <br /> concentration in one sample exceeding the environmental screening level (ESL) <br /> established by the San Francisco Bay Regional Water Quality Control Board <br /> (SFBRWQCB), indicating a potential risk to human health through vapor <br /> intrusion. The EHD notes that the fourth quarter 2008 monitoring report states <br /> that the soil vapor extraction (SVE) system was operational for most of the fourth <br /> quarter, except when turned off from 10 November to 17 December 2008; <br /> therefore the SVE system was apparently in operation during the soil vapor <br /> assessment of 31 October 2008, and the investigation results may have been <br /> skewed. As the results of the 31 October 2008 investigation appear to be in <br /> doubt, the EHD approves `confirmation' soil vapor sampling as part of the <br /> rebound testing after cessation of the SVE system to be sure there is minimal <br /> vapor intrusion risk. Please submit a work plan for the `confirmation' soil vapor <br /> survey and rebound testing. <br /> The SWRCB 5-year review of your site and has recommended site closure and <br /> the EHD believes that your site is nearing closure consideration; but due to the <br /> high groundwater usage in the immediate area, the EHD also believes that <br /> rebound testing and characterization of the TPHmo hits in the CPT1 and CPT2 <br /> Work Plan and Monitoring Frequency Reduction Approval Letter 0709 <br />