SITE INFORMATION AND CORRESPONDENCE FILE 1

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r..r 7-Eleven #14117 page 2 2725 Country Club Blvd., Stockton. Additionally, EHD is concerned that this proposal to advance into the remedial action phase is based on incomplete data for lateral and vertical extent of impacted groundwater. With existing shallow monitoring wells continuing to detect elevated levels of dissolved petroleum and oxygenates, EHD will require further lateral and vertical investigation to determine the limits of the petroleum impact before approving a remedial action plan. A work plan for the collection of groundwater samples to the east side of the site and at depths beyond the current monitoring well screened intervals should be submitted to EHD for evaluation. The Central Vfalley Regional Water Quality Control Board (CVRWQCB) guidelines require assessment of the vertical extent of groundwater impacted by MtBE prior to closure consideration. The information is also required to adequately address remediation issues for the site. The latest quarterly monitoring report (QMR) submitted to EHD was for the sampling event held on January 8, 2002 and was received on May 7, 2002. This long period from sampling date to receipt at EHD does not allow for comments before the next sampling event is held. Please adjust your sampling and reporting schedule and ensure that EHD receives the most recent QMR before the next sampling event is held. The feasibility of"intrinsic bioremediation" was evaluated by sampling groundwater in MW-2 prior to performing the dual-phase extraction (DPE) test: EHD requires more information to evaluate the results. Was the well purged prior to sampling? If not, the results apply only to stagnant water in the well casing that is in contact with the atmosphere and potentially with materials occasionally entering the well from above; the sample would not be representative of aquifer conditions, where groundwater has very limited contact with the atmosphere and is in intimate contact with soil minerals and organic matter. Please provide this information to EHD. Soil samples should also be analyzed for bioremediation parameters. The transport model assumed a conductivity of 2.5 feet/day. EHD's analysis of the pumping data, while not demonstrably at steady state conditions, yields a conductivity of 97 ft/day. Also a model run of 428 days (1.17 years) may not be adequate to demonstrate stability of a plume. Additionally, 1,2-DCA and EDB were last analyzed for the November 5, 2001 sampling event and were reported as "<1,200 µg/I" (MW-1) and "<5,000 µg/I" (MW-2). Constituents reported as "less than" for an elevated detection level substantially higher than the maximum contaminant level (MCL) or action level cannot be accepted as delineated.