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Former Columbo/I oscana BF' y - 3 - 29 April 2009 1444 S. Lincoln St., Stockton Nevertheless, the May 2008 San Francisco Bay Regional Board (Region 2) Environmental Screening Levels (ESLs), using Region 2 Soil to Indoor Air Attenuation Factor for commercial or industrial land use, were not exceeded by the SG-4 results. The VIS Report concludes there is no risk of soil vapor intrusion to the workers inside of the building. Comments: Staff concur with the VIS Report conclusion that does not indicate a threat from vapor intrusion inside the building. The Evaluation, while not fulfilling the requirement to submit a workplan for a pilot study, does provide an outline for the work necessary to conduct a pilot study. However, the additional soil and groundwater data proposed for evaluating.the remedy feasibility was previously collected for the 2008 TS biosparging pilot study, and that data is available in electronic format by downloading the reports from GeoTracker. That pilot study data, which the Evaluation states was reviewed for your Site, should suffice to write the biosparging pilot study workplan, as staff concur that the two sites, located less than 350' apart, share a similar subsurface geology. Since no schedule for submittal of the biosparging pilot study and its associated workplan was included in the Evaluation, please include a detailed schedule for all pilot study tasks (permitting, mobilization for field work, and turn-around times for receipt of laboratory data) in the Biosparging Pilot Study Workplan Staff concur that sharing co-collected data from nearby sites monitoring wells for the purpose of determining delineation of the inferred commingled plume is appropriate and cost effective. Please continue to do so, and also continue to provide updates in the monitoring reports or by email for the time schedule of the commingled plume application submittal by the group, as well as a copy of the commingled plume application and the final version of the group agreement for our review. The new wells Workplan is approved with the, following changes — either agree to remove the additional sampling used to reevaluate biosparging prior to workplan submittal, for the reasons stated above; or provide additional justification why the existing TS biosparging data are inadequate to write the pilot study workplan, via an email response to me by 11 May 2009. Also include a detailed schedule (permitting, mobilization, and receipt of laboratory data) with specific dates for the new wells Workplan. -The approved well installation work is necessary and appropriate to delineate the vertical and lateral extent of the groundwater plume at your Site. Acquire the necessary drilling permits, and provide the San Joaquin County Environmental Health Department and myself at least three working days notice prior to commencing fieldwork. The wells installation report is due 1 August 2009.. If you have any questions, please call me at (916)464-4615 or I can be reached by email me at jbarton@waterboards.ca.gov. Z James L. L. Barton, P.G. Engineering Geologist cc: Ms. Jennifer Jordan, State Water Resources Control Board, Sacramento Ms. Margaret Lagorio, San Joaquin County Environmental Health Department, Stockton Mr. Edward Overton, P.O. Box 417, French Camp 95231 Mr. Paul Anderson and Mr. John Carrow, PSC Environmental Services, 210 W. Sand Bank Rd., Columbia, IL 62236