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C20-SAI-TRACY-BYRON-ROAD-01-04705 Soil and Groundwater Investigation Report at Tracy Byron Road Project Tracy, California 1. INTRODUCTION This report presents the results of the soil and groundwater subsurface investigation performed by Science Applications International Corporation(SAIC)at the Tracy Byron Road Project(TBRP) site. SAIC performed this investigation on behalf of ChevronTexaco Environmental Management Company (ChevronTexaco)in order to evaluate the lateral and vertical extent of petroleum-affected soil and groundwater adjacent to West Byron Road between Corral Hollow Road to the east and Von Sosten Road to the west(referred to herein as the Tracy Byron Road Project or TBRP)in Tracy,California (Figure 1). Prior to conducting the subsurface investigation, SAIC performed oversight of the Westside Channel Outfall(WSCO)project and was responsible for designating and segregating highly affected soil excavated during the installation of two 60-inch diameter storm water pipes installed in the West Byron Road corridor. This storm water sewer project was part of the City of Tracy's Master Plan in response to recent residential growth. The main reach of the WSCO excavation was approximately 7,000 feet in length along Byron Road,beginning from Belconte Drive in the east and terminating just west of Interstate 205. The project involved excavating the centerline of Byron Road to a depth between approximately 11 and 16 feet below ground surface(bgs). Since depth to groundwater in the region ranges between 5 and 10 feet bgs, dewatering of the project prior to pipe construction was undertaken. Viking Drillers,Inc., of Sacramento, California,installed 132 dewatering wells to depths between 25 and 39 feet bgs and an additional 27 dewatering wells to depths between 48 and 50 feet bgs on the north side of Byron Road. During the dewatering well installation, ChevronTexaco's consultant, Geomatrix Consultants,Inc. (Geomatrix), observed the well borings and prepared logs of the drill cuttings. Petroleum-affected soil and/or separate phase oil(SPO)was observed in many of the well borings advanced. Borings in several areas covering up to 1,000 feet in length contained SPO. SAIC was requested by ChevronTexaco to staff the WSCO excavation to assist the City of Tracy in identifying soil not suitable for reuse as backfill of the excavation. During the WSCO project, SAIC observed petroleum-affected soil in the trench at depths ranging from 5 to 16 feet bgs. Based on these observations and other findings during the WSCO project,the Regional Water Quality Control Board (RWQCB)issued a letter on April 17, 2003,which requested that ChevronTexaco conduct an additional soil and groundwater investigation addressing data gaps associated with past environmental investigations adjacent to the corridor and addressing other water quality concerns. Prior to conducting the soil and groundwater investigation at the subject site, SAIC prepared an initial Work plan proposing a data review of past environmental investigations and data gaps; a review of properties surrounding Byron Road within a one-half mile radius; and a agency database review(SAIC: Byron Road Characterization Workplan, dated June 16,2003). The initial Workplan was followed by SAIC's site-specific Workplan titled Tracy Byron Road Soil and Groundwater Investigation Workplan, West Byron Road Corridor dated August 18,2003 (referred to herein as Workplan). The Workplan included a regulatory database review; a historical aerial photograph review; a Department of Water Resources(DWR)Water Supply Well Search within 2,000 feet of the project corridor; a San Joaquin County Environmental Health Division(SJCEHD) file review; a review of the nearest surface water bodies and other potential sensitive receptors; a utility survey; and a data summary of past environmental investigations along the Byron Road corridor. SAIC also reviewed and evaluated observations made from the installation of 159 dewatering wells and approximately 7,000 feet 1