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March 9, 1993 Mr Harlin Knoll San Joaquin County, Public Health Services Environmental Health Division P O Box 2009 Stockton, CA 95201 RE Addendum to the Workplan for Soil Excavation, PG&E's Stockton Service Center, 4040 West Lane, Stockton, CA Dear Mr Knoll This letter will serve as an addendum to the Workplan for soil excavation to be conducted at the above referenced site (Figure 1) The additional scope of work is based on findings from previous excavation/sample collection performed on January 12, January 22, and February 10, 1993 SITE BACKGROUND The site was the location of one 10,000 gallon underground product storage tank which contained transformer oil for use at the facility (Figure 2) The tank and ancillary buried product lines were removed in January, 1987 On January 16, 1987, Twining Laboratories Inc collected four soil samples, from varying depths, in the vicinity of the former storage tank and product lines The samples were laboratory analyzed for oil and grease, total volatile organic hydrocarbons, and PCBs All samples contained oil and grease above method detection limits Only samples S-2 and S-4 contained total volatile organic hydrocarbons above method detection limits, and only sample S-2 contained 1 0 ppm PCB On January 12 and 27, 1993 excavation was conducted at the site and confirmation samples were collected from the bottom and sidewalls Additionally, on February 10, 1993 a soil sample was collected with a shovel, two feet below excavation grade, to estimate the extent of transformer oil impact the sump area Results of laboratory analyses are summarized in Table 1 SCOPE OF WORK The following scope of work is based upon the information outlined above Prior to further excavation, the former tank pit will be backfilled with self-compacting fill material Previously collected soil samples (January 12, 1993 and January 27, 1993) have confirmed the removal of transformer oil impacted soils from the former tank pit (Table 1) Subsequent to backfilling the tank excavation will be conducted Excavation is designed to remove impacted soil in the vicinity of the line sump which was located at the northeast corner of the former tank pit (Figure 2, near PL-SS6-7' sample) Analysis of the soil sample collected on February 10, 1993, indicate transformer oil is present in the soils of the sump area (Attachment 1) All field work will be performed under supervision of RESNA personnel in accordance with the Site Safety Plan (Attachment 2, Workplan for Soil Excavation, November 4, 1992) L.EMM[WPA 0393 FNL M\