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Ms. Vera Fischer, P.G., RWQCB April 24, 2017 Work Plan for Additional Site Assessment Project No. 2154-1817-01 1817 South Fresno Avenue, Stockton, CA Page 3 Only low levels of fuel contaminants extend southeast from the Site across Fresno Avenue, near the areas of wells MW-7 and MW-8. Given this observation, most of the petroleum hydrocarbon impact to the subsurface likely remains onsite (see Figures 5 and 6). For approximately five years (beginning in 2004), a previous consultant (Clearwater Group) utilized an in-situ submerged oxygen curtain (iSOC) technology in an attempt to mitigate Site contaminants. Limited remedial progress appears to have resulted from use of the iSOC system, and given this condition, Clearwater Group prepared a Remedial Action Plan (RAP) in July 2010, that proposed to remediate Site contaminants using an alternate approach. The July 2010 document proposed to perform an in-situ chemical oxidation (ISCO) project that included addition of hydrogen peroxide and iron catalyst, with concurrent de-watering using large diameter (8-inch) wells. In August 2010, the previous regulatory agency for the Site (San Joaquin County Environmental Health Department, [SJCEHD]) approved the RAP; however, the remedial work outlined in that document was never implemented. After assuming consulting duties in March 2012, and meeting with SJCEHD personnel to discuss the Site, Stratus prepared and submitted a Modified Remedial Action Plan and Feasibility Study (RAP/FS). The document originally proposed to perform dual phase extraction (DPE) for a period of approximately 6 to 12 weeks; however, during the 2012/2013 UST Cleanup Fund fiscal year, insufficient funds were available to implement DPE for this length of time. Instead, Stratus attempted to evaluate DPE during a shorter period of time (5 days) between April 29 and May 3, 2013. This proved to be an insufficiently short period of time to evaluate DPE as a remedial technology for the Site. Between November 20 and December 31, 2013, a longer duration DPE event was performed, with the equipment operating approximately 579 hours (24 days), using four wells (MW-5B, IW-2, IW-7, and either IW-6 or IW-8) for extraction. During this time, an estimated mass of approximately 83 pounds of GRO was removed from the subsurface in the vapor phase. At the time of test termination, approximately 4 pounds per day of GRO was being removed from the subsurface in the vapor phase. Groundwater was extracted during the test at an average rate of approximately 3.6 gallons per minute (gpm). Stratus previously concluded, based on the results of this pilot test, that a full-scale DPE system capable of remediating the Site for several years would likely be needed in order to manage the Site's environmental case to closure, and that this course of action was not likely to be the most cost effective approach for achieving case closure. K:\Barnes Trucking\Work Plans\barnes trucking work plan 2017.doc STRATUS