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R10/71-51-1C <br /> 1.0 INVESTIGATIVE SUMMARY <br /> This report describes the Site Investigation (Sl) of the Caltrans Shop 10 located at 1603 <br /> South B Street, Stockton, California, conducted by Environmental Assessors, Inc (EA) <br /> under the Caltrans Statewide Master Contract for Hazardous Waste Site Investigations <br /> and Development of Remedial Action Plans, Contract Number 53U495 and Caltrans T.O <br /> No 10-365101-01 <br /> Upon being contracted by Caltrans EA to conduct a Site Investigation (SI), EA prepared <br /> a Work Plan which provided guidelines and procedures for the field investigation <br /> Procedures for the Sl included sod drilling, installation of groundwater monitoring wells, <br /> soil and groundwater sampling <br /> An SI was conducted to determine the horizontal and vertical extent of hydrocarbon <br /> contamination of the sod and groundwater The sod and groundwater hydrocarbon <br /> contamination was first discovered in 1987 resulting in the removal in 1989 of the four <br /> 1 5,000-gallon underground fuel tanks The SI was designed to arrive at a final evaluation <br /> and characterization of all hazardous waste issues on the site as required by the Caltrans <br /> Potential contaminants are related primarily to petroleum materials and wastes associated <br /> with fueling and servicing of vehicles and equipment used in the highway maintenance <br /> Contaminants of concern are diesel, gasoline, BTX & E and halogenated hydrocarbons, <br /> oil and grease, PCBs, and chromium Corollary to the Caltrans task requirement is the <br />' formulation of a remedial action plan concept that will satisfy the county and state <br /> regulatory requirements for clean-up of the site <br /> 1 The field investigation for Shop 10 SI included sod drilling, installation of groundwater <br /> monitoring wells, and sampling of soil and groundwater based on the SI Work Plan <br /> prepared earlier for Caltrans Field activities involved the following <br />' o Measurement of water levels of twelve existing groundwater monitoring wells <br /> (MW1 to MW12) using an electronic water level meter Table 1 in Appendix <br />' C presents the water level measurements <br /> o Purging and sampling of existing monitoring wells When these were done, <br /> it was discovered that only the following wells were not dry MW7, MW10, <br /> MW11, and MW12 All the rest were dry due to the lowering of <br /> groundwater elevation <br /> 1 <br /> 1 <br /> 1 <br />