SITE INFORMATION AND CORRESPONDENCE FILE 3

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` N%0_01 `WV Pagel of 2 Mike Infurna [EH] From: Ben Chevlen [ben.chevlen@atcassociates.com) Sent: Thursday, April 21, 2011 2:54 PM To: Mike Infurna [EH] Subject: ATC's comments regarding the status of several sites formerly managed by other consultants Mike–As we have discussed on the phone, ATC has taken over management of several sites (discussed below) which are currently being overseen by yourself. Below, I am presenting a summary of what ATC understands to be the current status of each site,what work has been proposed and is pending, if ATC feels changes to the proposed work are warranted, and what ATC sees as potential obstacles to reaching case closure. Circle K 1205–16470 Cambridge Dr., Lathrop • Current status–An ozone sparge pilot test is currently being performed on-site;the results of which will be documented in a report being prepared by Stantec, which will be submitted to the SJCEHD by 4/22/11. Pending results of the pilot test,ATC will evaluate the appropriateness of expanding the ozone sparge system to address impact off-site to the north. An SVE system was started up at the site during 1Q10 and is currently operating (being operated by Stantec; ATC will assume operation once all necessary permits are in place); influent concentrations have attenuated significantly(recovery rates during 4Q10 averaged 2lb/day). Groundwater sampling currently being performed semi-annually during 1Q/3Q. • Proposed and pending work–Stantec to prepare a report documenting completion of ozone sparge pilot test. Stantec also to prepare 1Q11 remedial system O&M report and 1Q11 groundwater sampling report. • ATC's recommended changes to proposed work– None;ATC feels the work currently under way is appropriate. ATC will review the results of the ozone sparge pilot test to determine if expanded implementation of ozone sparging off-site to the north is appropriate. • Potential obstacles towards closure–Elevated TPHg concentrations in off-site well MW-12, and lack of delineation of MTBE north of MW-16 may represent obstacles to closure. A more detailed review of subsurface conditions and risk drivers is needed to determine the best approach to dealing with these issues. 76(Former BP)Station No. 11192–1403 West Country Club Blvd.,Stockton �� • Current status–GW sampling semi-annual during 1Q/3Q;a KVA ozone sparge system has been operating at the site since 2003. Majority of GW impact on neighboring Shell property cross Pershing Ave.to the east and north of the neighboring Shell property. — bzt'&) °A ,� • Proposed and pending work–Stantec prepared a work plan dated 3/10/11 to advance 2 on-site CPT soil borings and 3-4 off-site CPT borings; ATC is designated to perform the work. / 713 • ATC's recommended changes to proposed work–ATC questions theappropriateness of advancing off- site CPT borings CPT-5, CPT-6 and CPT-9. ATC questions the relevance of proposed boring CPT-5,.due to the relatively low to non-detect groundwater concentrations in adjacent Shell monitoring welirS-S.,ATC is unclear why proposed boring CPT-6 is justified, considering the continued lack of detections in GW9: samples collected from well MW-9. As for proposed boring CPT-9, ATC recommends that the results of CPT boring CPT-4 be fully evaluated before performing any additional assessment further down- gradient of the site. Additionally,ATC would like to clarify that while Stantec's work plan indicates that �Yr monitoring wells will be installed if the results of the CPT assessment indicate additional monitoring A"n _ wells are warranted,ATC will make such a recommendation in the report documenting the CPT assessment(a separate stand-alone well installation work plan would be submitted, pending SJCEHD concurrence). Please note,ATC respects the fact that Stantec's 3/10/11 work plan has been approved 4/22/2011