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i LM LEEOSHILL HERKENHOFF, INC INTRODUCTION i 1.1 Historical Review The following report describes LEEDSHILL-HERKENHOFF, INC. 's (LH) site investigation at a former underground fuel tank facility located at 102 South Wilson Way in Stockton, California (see Figure 1) . The site was formerly occupied by a gasoline service station; all tanks and appurtenances were removed in late 1978. An initial site assessment was conducted by Balbi & Chang Associates, Inc. (BCA) in April of 1988 without contacting or obtaining appropriate permits from the San Joaquin County Public Health Services. Consequently, the initial site assessment had to be repeated and the results were presented in a BCA report dated April 26, 1989. In BCA's studies, four soil borings and three monitoring wells were installed. The April 1989 report indicated some detectable BTX&E (benzene, toluene, xylene and ethylbenzene) and TPH (total petroleum hydrocarbons as gasoline) in the soil and groundwater samples but the final conclusions contained conflicting information (see Section 2.2 Previous Investigations) In June of 1989 LH was contracted by the professional corporation of Neumiller & Beardslee and requested to conduct an additional site investigation to verify the presence or absence of soil and/or groundwater contamination and, if necessary, provide information regarding the vertical and lateral extent of such contamination. LH submitted a preliminary investigation workplan to the Regional Water Quality Control Board (RWQCB) on September 11, 1989. A copy of this workplan, along with a well drilling permit application, was sent to Public Health Services, San Joaquin County. Comments from RWQCB were received on October 16, 1989. Approval was given under the condition that the comments were addressed Permit approval was received on October 18, 1989. On November 16 and 17, 1989, soil samples were collected by LH from five, 6-inch diameter hollow-stem angered boreholes located on the site. On November 21 and November 28, 1989, LH installed two, 4-inch diameter groundwater monitoring wells. Groundwater samples were collected from these two monitoring wells as well as the three existing monitoring wells on December 7, 1989 All samples were sent to a laboratory for analysis. This report presents the findings, conclusions, and recommendations of this site investigation. _g_