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Woodward-Clyde Const ik'Uit of <br /> PROBLEM ASSESSMENT REPORT <br /> CALIFORNIA DEPARTMENT OF TRANSPORTATION SHOP 10 FACILITY <br /> 1603 SOUTH B STREET <br /> STOCKTON, CALSFORNIA <br /> 1.0 INTRODUCTION <br /> This report describes an environmental investigation performed by Woodward-Clyde <br /> Consultants (WCC) of the area surrounding leaking underground storage tanks at the <br /> California Department of Transportation (CalTrans) Shop 10 facility located at 1603 <br /> South B Street in Stockton, Calliornia. The Stale of California authorized WCC under <br /> Office of State Architect (OSA; agreement no. 6378 to conduct a site investigation to <br /> evaluate the extent of soil and groundwater hydrocarbon contamination that resulted <br /> from fuel leakage from underground storage tanks and evaluate remedial alternatives <br /> that are applicable to site cleanup. To complete this task WCC: 1) conducted a soil gas <br /> survey, 2) installed fivef`shallow)groundwaler monitoring wells and one sot! boring, 3) <br /> sampled soil and groundwater for total petroleum hydrocarbons (TPH) and its dissolved <br /> phase constfluenis benzene, toluene, ethylbenzone and total xylenes (BTEX), and 4) ' <br /> prepared this report evaluating the limits of contamination and applicable remedial <br /> alternatives. Described below is the work performed to complete these tasks, and a <br /> summary and discussion of the analytical results obtained to date. <br /> i <br /> 1.1 Background <br /> Caltrans Shop 10 Is located at 1603 South B Streel, in Stockton, California, at the <br /> location shown on Figure 1. Site plan and utility maps are provided as Figures 2 and 3. <br /> As shown, four 5,000 gallon underground fuel storage tanks were once iocated west of <br /> the shop office and south of the shoo 10 building. In 1987, WCC Installed groundwater <br /> monitoring wells MW-1, -2, -3 and -4 to evaluate soil and groundwater quality around <br /> the underground tanks. In their 1987 report, WCC concluded that BTEX compounds were <br /> present in the shallow groundwater at concentrations that exceed 1987 Department of <br /> Health Services (DOHS) action levels for drinking water. <br /> After reviewing WCC's 1987 report, the Regional Water Quality Control Board <br /> (RWQCB) requested that OSA conduct a st(a investigation to de!ineate the extent of soil F <br /> and groundwater contamination and evaluate remedial alternatives. The results were to <br /> be submitted in Preliminary and Problem Assessment Reports. The RWQCB provided <br /> OSA guidelines dated 24 March 1987 to conduct this work, a copy of which is included in <br /> F <br />