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Dolly Madison/Langendorf Bakery - 3 - 18 June 2008 1426 S. Lincoln St., Stockton The FS section of the Pilot Test/FS compares two full scale remediation systems: • AS/SVE and • In-Situ Chemical Oxidation (ISCO) using Ozone and Hydrogen Peroxide Injection into groundwater in conjunction with SVE soil remediation. AS/SVE was determined to be the preferred alternative as most cost effective at an estimated total cost of $490,000 versus the ISCO/SVE alternative estimate of $701,000. The FS recommended the design and installation of a full scale AS/SVE system. Workplan The Workplan proposes the installation and surveying (Enclosed Figure 2) of two additional shallow groundwater monitoring wells (MW-15 and MW-16); three mid-depth groundwater monitoring wells (MW-17, MW-18, and MW-19); three additional soil vapor extraction wells (VW-4, VVb'-5, and VW-6); and three additional air sparge wells (AS-2, AS-3, and AS-4). The Workplan also proposes to destroy MW-3, if and when the City of Stockton decides if the well is or is not acceptable in its present location in S. Lincoln St. Comments: 1. The AS/SVE pilot testing results are significant in that the removal rate nearly reached 100 ppd. The results show that the residual source in soil appears to be significant and has not diminished by natural attenuation since the USTs were removed in 1987, and that active soil remediation is necessary to stop contaminant leaching into groundwater. Additionally, the depth of the contamination in soil makes another alternative, soil remediation by over-excavation, impractical. I concur that AS/SVE is the most cost effective and practical method for remediation. The PIER Addend and Pilot Test/FS are accepted and fulfill requirements for CAO Orders #8 and #11. 2. The Workplan did not include a figure showing the ROI around the SVE wells. By superimposing 15 foot ROI circles drawn over the proposed vapor extraction wells in Figure 2 and incorporating the soil petroleum hydrocarbons data from the PIER, the data show that Workplan proposed soil vapor wells VW-5 and VW-6 do not appear to be located where contaminant concentrations are present in soil. Likewise, the ROI for VW-4 and VW-5 do not appear to intersect for maximum efficiency of the SVE system (the distance between the two wells scales out to approximately 20 to 25 feet ROI). I cannot approve VW-5 and VW-6 at this time, since additional justification for installing these soil vapor remediation wells is necessary. Please provide a letter justification for the proposed SVE well locations for VW-5 and VW-6, or modifications for these well locations (if necessary) in a revised Figure 2; by 7 July 2008. 3. The remaining Workplan proposed soil and groundwater remediation wells (VW-4, AS-2, AS-3, and AS-4) and all proposed investigation wells (MW-15 through MW-19) are approved. You may proceed with the installation of those wells. CAO Order#9 requires implementation of the approved Workplan within 30 days of staff concurrence, which will be 18 July 2008 for the investigation wells. Since CAO Order#9 refers to the PIER investigation and does not include the remediation wells that are required under the FRP, you have the option to install the