SITE INFORMATION AND CORRESPONDENCE

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CPA0057 Sites • • z West Charter Way and Lincoln Street 2 20 May 2014 Stockton, San Joaquin County 1. We concur to continued operation of the SVE/AS treatment system as long as the extraction rate remains above 2 lbs. per day. Once operation of the SVE/AS system reaches an asymptotic removal rate of less than 2 lbs. a day, rebound testing should be conducted for a minimum of two quarterly monitoring events. If rebound occurs after the first sampling event, the SVE/AS treatment system will be restarted and run in pulse mode (i.e. one week on, one week off etc.) and shut down one week prior to the second sampling event. If rebound is not significant (less than an order of magnitude increase) after completion of the two quarterly monitoring events, then the SVE/AS treatment system compound/module may be installed at the Columbo/Toscanna Bakery (Sara Lee) facility. We require that the Sara Lee infrastructure for the SVE/AS system be in place at the time of the module transfer, so that the transfer and startup will occur in a timely and seamless manner. 2. The data presented in the Monitoring Report indicates delineation of the groundwater Plume down-gradient of the Shell site is a concern. We understand several wells were destroyed due to the redevelopment of properties to the east of the Shell property. However, current datar downgradient of Shell indicate pollution in the intermediate and deep zones is not delineated horizontally and vertically. Benzene concentrations in SMW-3-79 is currently at 8,900 micrograms per Liter(ug/L) in SMW-19-81 is 2,600 ug/L and in SMW-10-81 is 14,000 ug/L. 3. In the Monitoring Report, Stantec indicates data for the most downgradient Shell monitoring wells (SMW-17, SMW-20-83.5, and SMW-23) were not incorporated into the figures to close the C-zone concentration contours, which gives the appearance that the Shell groundwater plume is undefined in the downgradient direction. Future figures should contour all relevant data. 4. Other areas of concern include vertical definition to water quality goals of the groundwater pollution on the Chevron property. In addition, submerged A-zone monitoring wells should be replaced. Therefore you are directed to submit a new work plan to install monitoring wells that provide adequate delineation to water quality objectives based on groundwater flow direction in all zones for all sites by 30 July 2014, in the data gap evaluation. 5. The results of the 30 July 2014 data gap evaluation must also provide a recommendation for additional remediation downgradient of the Shell property, if warranted to achieve cleanup in a timely manner. 6. Geologic cross-sections with the groundwater concentrations and well screens indicated should be updated and presented in the data gap determination. 7. Stantec previously included a Gantt chart in Quarterly Reports showing dates to conduct all activities necessary to reach case closure, along with the rationale for any changes.