SITE INFORMATION AND CORRESPONDENCE

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J Pete Graffigna Flame Mini-Mart 1301 W Kettleman Lane, Lodi Page 2 of 3 the on-site MWs near the release have increased. MTBE concentration in the off-site, downgradient MW-5 has also increased. The SCM, which is supported by the data, indicates to EHD that the most likely primary source of soil contamination is the former UST pit/dispenser area. Probe borings P-4 and P-5 in the current, active dispenser area greatly minimize the potential that a significant new dispenser release has occurred.; The minimal impact near MW-6 and CPT-4 does not appear to be directly related to the primary MTBE release from the former UST and dispenser location or to a major inew release from the new dispensers. EHD's interpretation of the current data is that aisignificant portion of the gasoline and MTBE released at or near the former UST and dispensers location, migrated vertically to the sand/fine-grained unit contact at approxiE;nately 42 feet bgs and then traveled easterly on the contact and intensely impacted groundwater near MW-2. AGE has made the determination that soil vapor extraction (SVE) would not be necessary in the former UST and dispenser aIrea. AGE has estimated, based on current soil analytical results, that 10 gallons of absorbed MTBE mass residual is in the -unsaturated (vadose) zone above groundwater. Theoretically, this quantity of MTBE could be migrating and resulting in increasing MTBE concentrations above the California Maximum Contaminant Level (MCL) in hundreds of thousands of gallons of groundwater. The vadose zone MTBE should be addressed as soon and as efficiently as possible. Remediation expenses and time elements increase significantly as the vadose zone MTBE reaches and enters groundwater. In the WP, AGE favors ozone groundwater injection and interim batch groundwater extraction. The Central Valley Regional Water Quality Control Board (CVRWQCB) must be contacted to set the requirements for the proposed ozone injection. If the use of this technology is approved/granted by the! CVRWQCB, EHD recommends the sparger be located more upgradient of MW-2 than is illustrated on AGE's WP figure 2. More than one on-site injection point may be necessary to remediate the entire area of groundwater contamination and additional down-gradient MWs may be needed to meet any monitoring requirements set by CVRWQCB. EHD approves a short-term batch groundwater extraction measure as interim remediation. Ideally, some tests should include use of level loggers to observe drawdown and recovery of groundwater levels to derive hydraulic conductivities. The data may be useful in determining aquifer characteristics and for further development of the SCM. i I