SITE INFORMATION AND CORRESPONDENCE FILE 2

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Mr. John Parker 23 March 2009 2151 Country Club Blvd. Page 2 of 3 Stockton, California MW-11 (west) is a Continuous Multichannel Tubing (CMT) well with five channels, "A" thru "E" eacA screened in a different hydrological unit (HU-1, HU-2, HU-4, HU-5 and HU-6); the ground water samples from all but the shallowest interval (HU-1) are highly contaminated. MW-13 is a single-screened HU-2 monitoring well located west of MW-11. At the time of the last ground water sampling event, August 2008, only benzene was detected in the MW-13 ground water sample; previously, on May 12, 2008, MW-13 ground water samples contained 16,000 micrograms per Liter (Ng/L) TPHg and varying concentrations of BTEX, TAME and 1,2-DCA. MW-14 (west) is a single-screened HU-4 well located west of MW-13; ground water samples from the August 2008 sampling event contained elevated dissolved petroleum hydrocarbons concentrations. With a potential change of ground water flow direction toward the west/northwest, a lack of adequate monitoring wells in this direction, and the elevated concentrations of dissolved contaminants in the ground water plume potentially migrating in this direction, the EHD considers the plume unstable, undefined, and not adequately monitored. Additional assessment of impacted groundwater is needed toward the northwest between MW-7 and MW-8 well cluster areas. For better cost effectiveness, the EHD recommends that grab ground water samples be collected from HU-2 through HU-6 during the next phase of investigation [H&S Code 25299.10(c)(3)]. Please submit a revised work plan that addresses these concerns by April 3, 2009. The plume of groundwater impacted by the COC covers a large area, contains high concentrations of the COC, and is believed to be migrating offsite, therefore the EHD required you to submit a feasibility study (FS) that includes an evaluation of interim remedial actions potentially both feasible and cost-effective for reducing the plume size, controlling plume offsite migration, and reducing the concentrations of dissolved petroleum hydrocarbons in the ground water. The FS was submitted to address these concerns. Your consultant has evaluated multiple remedial alternatives potentially capable of cleaning up the site and concluded that dual phase extraction (DPE) would be the most cost-effective and most feasible alternative. DPE combines ground water extraction to lower the ground water and remove dissolved petroleum mass with soil vapor extraction in the areas of the depressed ground water. The FS contains a proposal to pilot test DPE, which will require the onsite installation of one remediation well, "DPE-1" and one observation well, "DPE-2". The pilot test will utilize data collected from the newly installed remediation test wells and existing MW-2 during a 5-day pumping test. The performance of the extraction well will be evaluated and the area of influence of the extraction well will be determined. Soil samples will be collected during the well installations and analyzed for TPH-g, BTEX, the fuel oxygenates, and lead scavengers. In addition to the two work plans, a letter was also submitted to the EHD to request a reduction of groundwater monitoring for all the site wells to only once a year (annually). Included in the request was a reference to the delay in reimbursement of corrective action costs from the State Water Resources Control Board Cleanup Fund (CUF) as the reason for the request. The EHD is aware of the current economic situation with the CUF and the difficulties it imposes for responsible parties continuing to investigate their sites and will approve a reduction of the 2151 Country Club FS DPE M&R redc CML 3-23-09