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10 INTRODUCTION <br /> The purpose of this additional site characterization is to further assess the occurrence <br /> of hydrocarbons and volatile organic compounds beneath the former Unocal Station <br /> ' at 3788 Tracy Boulevard, Tracy, California (Figure 1) This investigation is based on <br /> the Workplan for Additional Site Characterization (January 1995) that was prepared <br /> by Mittelhauser Corporation (Mittelhauser) The workplan is attached as Appendix <br /> A <br /> The workplan was prepared in response to a letter from San Joaquin County Public <br /> ' Health Services/Environmental Health Division (SJCPHSIEHD) Technical Review <br /> Committee dated December 28, 1994. This letter, attached as Appendix B, <br /> expressed concerns regarding potential residual contamination at the site The <br /> investigation described in this report fulfilled the requirements of that letter and <br /> determined that no residual contamination remains at the site Therefore, as Unocal <br /> Corporation (Unocal) addressed the concerns of the SJCPHS/EHD, and the <br /> investigation shows no residual contamination, Unocal would now like to obtain site <br /> closure from the County <br /> 2.0 SITE HISTORY <br /> The former Unocal station, shown in Figure 2, was originally constructed in 1972 <br /> ' It operated as a "full-service" station until 1976, when it was converted to a "self- <br /> service" facility In '1991, soil borings were drilled at the site to evaluate hydrocarbon <br />' contamination Four of the borings were converted into monitoring wells to monitor <br />' the groundwater flow direction and potential offsite groundwater contamination. <br /> In 1992, the station was closed to business In January of 1993, the underground <br /> storage tanks (USTs), fuel dispensers, subsurface piping, and the automobile hoist <br /> 21688010 wfAFWxu"1896 1 �'ttel auser <br /> C 0 ■ r 0 2 w r 1 0 N <br />