Laserfiche WebLink
`1 <br /> Environmental <br /> Mr.Marcus Pierce Resources <br /> 3 January 2006 <br /> Management <br /> Page 2 <br /> Substantial reductions of VOCs in the ground water and declining mass <br /> removal rates indicate that remedial action within the source area has <br /> removed or destroyed the bulk of the VOCs, and that additional effort is <br /> not warranted to remove the minor residual amounts remaining. <br /> Because of the diminishing effectiveness in removing mass, along with <br /> the improvement in ground water quality, UPRR proposed performing a <br /> rebound evaluation to the RWQCB. Prior to receiving approval for this <br /> evaluation, UPRR submitted the Workplan for VOC Rebound Evaluation, <br /> Former Tracy Maintenance Facility, Union Pacific Railroad Company, Tracy, <br /> California, dated 13 May 2002, and provided other information in <br /> Supplemental Information, VOC Rebound Evaluation, Former Tracy <br /> Maintenance Facility, Union Pacific Railroad Company, Tracy, California, <br /> dated 26 June 2002. <br /> REBOUND EVAL UA TION <br /> Following receipt of approval, UPRR proceeded with the VOC rebound <br /> evaluation. The procedures and results of the rebound evaluation were <br /> presented in the 2003 Evaluation (dated 16 April 2003) and summarized <br /> below. <br /> UPRR proceeded with the VOC rebound evaluation by shutting off the <br /> dual-phase extraction system on 16 July 2002. The rebound evaluation <br /> included review of the following data: <br /> • Organic vapor concentration (using a photoionization detector [PID]) <br /> at the eight dual-phase extraction wells, the three soil vapor <br /> extraction wells and the five vapor monitoring points collected from <br /> sample ports using a PID on 18 July, 14 August, 11 September, <br /> 28 October, and 19 November 2002; <br /> • Vapor data collected from dual-phase extraction wells, the soil vapor <br /> extraction wells and vapor monitoring points in 12 July 2000 (prior to <br /> dual-phase system startup), 14 August 2002, and 19 November 2002; <br /> and <br /> • Ground water samples collected from wells that were sampled during <br /> both the March and November 2003 events: MW-02A, MW-07A, <br /> MW-09A, MW-10A, MW-11A, MW-14A, MW-15A, MW-22A, and <br /> TW-03. <br />