SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Jimco Truck Plaza '"'' - 3 - `�' 5 September 2012 1022 E. Frontage Rd. (Hwy. 99) Ripon, San Joaquin County In June 2002, a 48-hour groundwater pump test was conducted at extraction well EW-1. At a sustained rate of 6 gallons per minute, maximum drawdown in EW-1was 9.76', with a calculated transmissivity of 1,000 ft2 per day and a hydraulic conductivity of 1.75 x 10-' centimeters per second, which is an acceptable value for a groundwater pump and treatment system. The RP changed consultants in 2002, resulting in a new recommendation for corrective action, and in August 2005, air sparge well AS-1 was installed for a soil vapor extraction/air sparging (SVE/AS) pilot test. During pilot testing in September 2005, SVE/AS radius of influent was reported as 75', and influent concentrations were reported as low, with approximately eleven pounds of TPH removed by SVE/AS. Subsequently SVE/AS was not implemented for corrective action. Two groundwater plumes were tentatively identified during an investigation in March 2007. An additional investigation in May 2008 delineated the extent of soil contamination associated with the 2005 AGSTs piping release, and provided confirmation that two groundwater plumes were separated onsite, one associated with the USTs release that extends under the truck wash, and second plume near MW-6, to the east of the truck wash, emanating from the AGTs piping. On 6 February 2009, the SJCEHD transferred the regulatory lead for the Site to the Regional Board, citing the evidence of a new release and requesting that one agency conduct oversight for both releases, the USTs and the AGTs. Regional Board staff opened a new Cleanup Site case for the AGTs release, which was managed concurrently with the USTs case. On 25 March 2009, the Regional Board Executive Officer issued a Water Code Section 13267 Order for Technical Reports, which required quarterly monitoring and a corrective action plan (CAP) for both releases by 1 July 2009. The CAP recommended insitu chemical oxidation injections consisting of either sodium persulfate or hydrogen peroxide, with a bench scale test for each substance prior to full scale remediation. A free product removal (FPR) system was also proposed in the CAP, although free product disappeared within one quarter of monitoring and the FPR recommendation was not implemented. The CAP recommended additional monitoring wells to define the AGTs plume; subsequently, MW-11 through MW-20 were installed in April 2010. In August 2010, the CAP implementation was placed on hold due to significant reductions in groundwater concentrations during July 2010, and also due to unfavorable results from bench scale testing of the two oxidants.. The second quarter 2010 monitoring report also included a comparison study of the standard 3-casing volume purge versus low flow purging with silica gel cleanup for TPHd for select wells. A request to continue low flow purging was approved in August 2010. Monitored natural attenuation was proposed for three subsequent quarters in October 2010, and the December 2010 approval letter required submittal of a closure report by September 2011, contingent upon receipt of favorable groundwater monitoring data after three quarters. Semi-annual monitoring was approved in May 2011. Groundwater monitoring continued until August 2011 and the closure report was received in December 2011 after a three-month extension was granted. Olympian JV has complied with all Regional Board directives and the 13267 Order. Groundwater monitoring has shown a declining trend, with both plumes estimated to reach