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LETTER REPORT — WASTE OIL TANK SITE ASSESSMENT POSDEF Power Company, 2526 West Washington Street, Stockton October 29, 1998 Page two On or about April 19, 1998, the tank was inspected and tested. The test indicated that the secondary containment had failed; however, the primary containment had not failed. The source of water in the interstitial space resulted from the secondary containment failure and the high groundwater beneath the site. Based on these findings, POSDEF began to formulate a plan to abandon the tank in place. The decision to abandon the tank in place rather than removing the tank is based on the close proximity of a concrete pedestal that structurally supports a large turbine. As such, tank removal would compromise the structural integrity of this power generating source. Scope of Work The objective of this project was to collect soil and possibly groundwater-grab samples in close proximity to the bottom of the tank, at a depth of approximately five (5) feet, to assess the potential for in-place closure. To achieve this objective, two soil borings were advanced with a hand auger as close to each end of the tank as possible. To access the subsurface soil at both soil boring locations, the 16-inch thick concrete surface was first cored by Cal-West Concrete Coring. The first soil boring (SB-1) was positioned approximately one foot south of the southwest corner of the tank. An aboveground clean oil tank and aboveground piping prevented access to the west end of the tank. The second soil boring (SB-2) was positioned approximately two feet east of the eastern end of the tank. Aboveground piping prevented closer access to the end of the tank. The locations of both soil borings are shown on Figure 1. In accordance with the attached PHS/EHD drilling permit, both soil borings were advanced with a hand auger to a total depth of approximately five feet below ground surface (bgs). At the total depth of five feet, a soil sample was collected from both soil borings using a slide hammer lined with a brass sleeve. The sample sleeve was capped with Teflon® sheets and plastic end caps, labeled, and stored in an iced cooler for transport under chain-of-custody documentation to GeoAnalytical Laboratories, Inc. (GeoAnalytical), a state of California certified hazardous waste testing laboratory (Certification #1157). GeoAnalytical analyzed both soil samples for Total Petroleum Hydrocarbons (TPH)-as- gasoline, TPH-as-diesel, TPH-as-kerosene, and TPH-as-motor oil by EPA 8015M, benzene, toluene, ethylbenzene and xylenes (BTEX) by EPA Method 8020M, chlorinated hydrocarbons by EPA Method 8240, metals (Cadmium, Chromium, Lead, Nickel and Zinc) by EPA Methods 6010 and 7420, and PCBs by EPA Method 8080.