SITE INFORMATION AND CORRESPONDENCE

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Ms. Mary Serra August 19,2002 Page 4 Verification Sampling The excavation is designed to remove soil with TPH and BTEX concentrations above the preliminary remedial cleanup goals: TPH-d< 100 mg/kg;TPH-g< 100 mg/kg and;non-detect concentrations for benzene,toluene,ethylbenzene and xylene. Verification samples will be collected from the perimeter side walls (a minimum of one sample from each of the side walls: based on one sample approximately every 20 linear feet)and from the bottom of the excavation. The spacing of samples within the excavation will provide adequate representation of different lithologies and depth points. Sampling locations and numbers of samples will be assessed based on excavation size and the actual field conditions. Soil samples will be analyzed for BTEX(EPA Method 8021) and TPH (EPA Method 8015 Modified)within 24 to 48 hours of sampling. Analytical results for BTEX and TPH in soil will be evaluated prior to backfilling the excavation areas. Excavation limits may be extended based on the analytical data and permissible field conditions. If the confirmation sampling results indicate that the remedial goals have not been met,the analytical data will be evaluated to determine if further excavation is warranted. The proposed action will be discussed with the CVRWQCB. If verification sampling results from further excavation indicate that TPH concentrations are above the preliminary remedial cleanup goals,the results will be evaluated to assess potential risk to human health. Backfilling Backfill operations shall not commence until the verification sampling results have been reviewed by and are acceptable to the CVRWQCB.The excavation will be backfilled with clean imported materials. Fill material will be placed and spread in horizontal loose lifts of uniform thickness not to exceed 12 inches in uncompacted thickness. Each lift will be compacted to the specified compaction prior to placement of the subsequent lift. Tolerance on final grades shall not exceed plus or minus 0.1 foot. Replacement well MW-2R and MW-7R Upon completion of the excavation activities,monitoring wells MW-2 and MW-7 will be replaced with MW-2R and MW-7R within the proposed excavation limits (Figure 2). Monitoring wells MW-5,MW-8 and MW-6 will not be replaced. Based on results from the Groundwater Monitoring Report Gas Gathering Station,Quarter 11,San Joaquin County, California (July 2002),MW-5 exhibited a decreasing trend. Also,MW-5 is located approximately 10 feet to the west of MW-8 and MW-8 was non-detect. Although the base of the excavation will not extend to MW-8,the trimmed slope walls of the excavation will likely expose MW-8 during excavation. Therefore,we propose to remove MW-8. Monitoring wells MW-6 and MW-2 are located approximately 3 feet from each other.It would be redundant to replace both of these wells,as historically,both of these wells had similar results for BTEX, TPH-g,and TPH-d. Though monitoring well MW-7 exhibited a decreasing trend,,TPH-d and TPH-g concentrations remain significantly elevated. This well will be re-installed to determine the effectiveness of the source removal excavation. Applicable permits will be acquired to install the wells consistent with San Joaquin County requirements. These wells will be constructed based on the MW-2 and MW-7 design and will be used for groundwater monitoring. Documentation of groundwater monitoring activities will be submitted as part of the ongoing groundwater monitoring program that is currently being conducted at the site.