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.� groundwater samples from wells MW-3 and MW-7 be analyzed for the full scan of analytes by Environmental Protection Agency (EPA) Method 8260B. According to the SJCEHD, other degradation constituents are likely present if MTBE metabolism is occurring in the areas of wells MW-3 and MW-7. GRI began sampling MW-3 and MW-7 for the full scan of analytes by EPA Method 8260B during the first quarter 2003. In December 2002, GRI oversaw the installation of groundwater monitoring wells MW-12 and MW-13, the installation of ten ozone sparge (OS) points (SP-A through SP-H, SP-J, and SP-K) completed at a depth of 30 ft bgs, and drilled two additional CPT probes (CPT-2 and CPT-3) to a maximum depth of 140 ft bgs. The CPT rig was equipped with an on-board computer system that provided a real-time analysis of the subsurface conditions. The CPT device created a `_J stratigraphic log of the boring by comparing the CPT tip resistance to sleeve friction on the CPT cone. TPHg and BTEX constituents were not detected above the laboratory MRLs in the CPT groundwater samples. MTBE and methanol were detected in the 75-foot groundwater sample from CPT-2 at concentrations of 2.0 and 2,700 ppb, respectively. MTBE was detected in the 100-foot groundwater sample from CPT-3 at a concentration of 6.8 ppb. MTBE and TBA were detected in the 125-foot sample from CPT-3 at concentrations of 290 and 88 ppb, respectively (GRI, Groundwater Monitoring Well, CPT, and Ozone Microsparge System Installation Report, dated May 2003). An OS system was installed, connected to the sparge wells, and was brought on-line on December 20, 2002 by GRI. The OS system currently operating at the site consists of a K-V Associates (KVA) "C-Sparge" ozone microsparging system that cycles a mixture of ozone and air into each sparge point for five to 15 minute periods, approximately 16 times per day (GRI, `-' Groundwater Monitoring Well, CPT, and Ozone Microsparge System Installation Report dated May 2003). `-' In September 2011, ATC (now Cardno ATC) oversaw the advancement of CPT probes CPT-4, CPT-5, CPT-7, and CPT-8, as proposed in Stantec Consulting's (Stantec's) CPT Investigation Work Plan, dated March 10, 2011. The CPT assessment activities suggest the majority of the -► remaining dissolved-phase petroleum hydrocarbon impact at the site consists of TPHg, MTBE, and TBA off-site to the northeast (CPT-5) at depths of approximately 31 to 35 feet bgs, and TBA on-site (CPT-7) at depths of approximately 53 to 74 feet bgs. A full discussion regarding the findings of the September 2011 CPT assessment is presented in ATC's Site Assessment and Human Health Risk Assessment Report and Site Conceptual Model Update, dated November 22, 2011. The SJCEHD in a letter dated May 8, 2012 rescinded its previous directive (in a letter dated February 28, 2012) to advance a CPT boring in the down gradient direction. That letter cited the opinion of the State Water Quality Control Board, Clean Up Fund that additional plume definition of TBA in the "C" groundwater bearing zone was not necessary. In the May 8, 2012 letter the SJCEHD also directed that the rebound test continue, which was begun after the SJCEHD approved the ozone remediation system shutdown in their previous letter dated February 28, 2012. U 4 76 Service Station No.11192 Cardno ATC Project Number 52.75118.2390 Stockton,California May 1,2014 u