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Chronology Page 2 <br /> ' 595 E. 11" Street, Tracy � <br /> concentrations of TPHg and BTEX were found in ground water samples <br /> from P138, PB7, and PB4. <br /> 07/21-23/97 Monitoring wells MW4 thru MW9 were installed during this time. <br /> 03/20/98 The date the EHD received Wright Environmental's Additional Problem <br /> Assessment Investigation dated February 24, 1998, that discusses the <br /> work performed in July 1997. Ground water samples from MW6 and <br /> MW9 had elevated levels of TPHg and BTEX. <br /> 06/16/99 The date the EHD received Wright Environmental's Request for Closure <br /> and Quarterly Monitoring Well Sampling Report dated June 14, 1999. <br /> 07/27/99 The date of the EHD letter not concurring with closure because the lateral <br /> and vertical extent of the contamination was undefined, the data was <br /> incomplete and there was no technical justification for not remediating the <br /> contamination at the site. <br /> 11/24/99 The date of the EHD letter responding to Wright Environmental's <br /> Response to PHS/EHD letter of July 27, 1999, dated October 6, 1999. <br /> The EHD accepted that the aged subsurface irrigation pipe made <br /> excavation in the area unfeasible, required additional vertical investigation <br /> in the MW3 and MW9 area and required evaluation of other remedial <br /> alternatives. <br /> 04/25/00 Geoprobe borings PB10 thru PB14 were placed to depths of 20 to 26 feet <br /> below grade at the site on this date. <br /> 06/30/00 The date the EHD received Wright Environmental's Additional Soil and <br /> Ground Water Site Assessment dated June 30, 2000, that covers the April <br /> 2000 work. Data from the deeper soil samples indicate that little to no <br /> petroleum contamination migrated downward. <br /> 04/19/01 On this date Geoprobe borings PB15 thru PB21 were advanced to depths <br /> of 24 to 26 feet below grade. <br /> 07/12/01 The date the EHD received Wright Environmental's Additional Soil and <br /> Ground Water Site Assessment and Proposed Cleanup Approach dated <br /> June 15, 2001, that covers the subsurface investigation in April 2001 and <br /> evaluates three options for cleanup including feasibility and costs. The <br /> conclusions state soil contamination decreases with depth to non-detect <br /> at 26 feet below grade and recommends excavation of soil as the most <br /> timely, feasible and cost-effective alternative. <br />