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1.0 INTRODUCTION San Joaquin County Public Health Services, Environmental Health Division (EHD) has requested a work plan from the General Services Administration (GSA) for a soil and groundwater investigation at the Federal Building, located at 401 North San Joaquin in Stockton, California. Figure 1 is a Site Vicinity Map depicting relative location of the project site. On behalf of the GSA, Cape Environmental Management, Inc. (Cape) has prepared the following Soil and Groundwater Investigation Work Plan. In accordance with required investigation activities, as specified by EHD letter, dated August 31, 1994, Cape has prepared this work plan to investigate the lateral and vertical extent of observed soil and possible groundwater impacts at the site. Guidance documents used in the preparation of this work plan include the Tri-Regional Board Stglff Recommendations for Preliminary Evaluation and Investigation of Underground Tank Sites, dated August 10, 1990, the California State Water Resources Control Board (CWRCB)Leaking Underground Fuel Tank Reld Manual (LUFI), dated October 1989, and the above-referenced EHD letter to the GSA. 1.1 BACKGROUND This Work Plan is a continuation of site investigation work carried out by Cape and others v in 1994 and 1995. It is Cape's understanding that the EHD is in receipt of and has reviewed previous environmental reports pertaining to assessment activities at the site. Cape prepared a report titled Subsurface Investigation Report, Federal Building, 401 San Joaquin Street, Stockton, California, dated August 1994, which described soil conditions prior to the removal of two (2) 5,000 gallon underground storage tanks (USTs). Elevated concentrations of total extractable petroleum hydrocarbons were reported from soil samples collected during this investigation. On or about May 10, 1995 the two (2) 5,000 gallon USTs, previously used for storage of diesel fuel for the emergency generator system, were removed by Clemens Construction. Sierra Environmental Sampling collected soil samples from the excavation. A discussion of the analytical results for these soil samples is presented in a letter report prepared by Cape and dated July 14, 1995. An addenda to the letter report prepared by Cape, dated August 16, 1995, was also submitted to the EHD. Samples collected from soil located beneath the former UST locations were reported to contain elevated levels of total petroleum hydrocarbons (TPH) as diesel, TPH as gasoline, TPH as oil, ethylbenzene, and total xylenes. Results of laboratory analysis for polychlorinated biphenols (PCBs) and •.� volatile organic compounds were below method detection limits. Additional excavation of impacted soil took place. The excavation was extended south to Lindsay Street, west to the transformer vault, east to the wheelchair access ramp, and north to the retaining wall. Soil samples were collected from the limits of the excavation and it was discovered that impacted soil extended both horizontally and vertically outside the excavated area; beyond what could be reached with available excavation equipment. r 2403c.20\.stockton.p1n 1