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1.0 INTRODUCTION/BACKGROUND This report is being submitted on behalf of Laidlaw Corporation to summarize the results of the subsurface investigation requested by the San Joaquin County Public Health Services, Environmental Health Division (SJCPHS), for potential soil and/or groundwater contamination at 1444 Tillie Lewis Drive, Stockton, California (Figure 1) On June 29, 1990, one 4,000-gallon underground xylene storage tank was removed at the project site (Figure 2) by Semco Corp of Modesto, California Soil samples were collected beneath the tank and analyzed for benzene, toluene, ethylbenzene, xylenes (BTEX), and total petroleum hydrocarbons as gasoline(TPHG), by BC Laboratories, Inc , utilizing appropriate EPA and DHS methodologies These initial analytical results are summarized in Table 1 and corresponding laboratory data sheets are included in Appendix I The presence of elevated concentrations of hydrocarbons in the tank pit soil samples indicated further investigation was necessary to determine the lateral and vertical extent of soil and/or groundwater contamination at the project site A preliminary report/workplan for the additional investigation was submitted to the SJCPHS and copied to the Central Valley Regional Water Quality Control Board (RWQCB) on December 10, 1990 The workplan was approved with no modifications and the project was placed into the Local UST Oversight Program by the SJCPHS on March 11, 1991 To prevent the contaminated material associated with the former xylene tank from presenting a continued threat to groundwater, approximately 750 cubic yards of contaminated soils were excavated from the project site on March 19 and 20, 1991 The location of the excavation is shown on Figure 2 All xylene contaminated soils were excavated except where physical barriers prohibited The excavation was limited on the west side of the tank pit by the warehouse and access ramp Groundwater was encountered at approximately 15 feet below grade during the excavation Soils within the saturated zone were not excavated Verification soil samples were collected from the i,CR492 I JL 1