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Dan Schreiner - 3 - 15 June 2015 unlikely to occur given that the L&M Group does not own the property and the high methane levels are still considered to be a potential threat to the apartment buildings and utility workers, the work plan needs to address reducing methane caused by degradation of petroleum constituents to levels below the 5% LEL. 4. Regarding the request to suspend the quarterly soil vapor monitoring, the quarterly monitoring should continue so that the data are available for use in further assessment of the work to be performed to address the areas with TPH-g and methane, and to make sure that only UPSV-6 and APSV-15 are of concern for benzene and/or naphthalene. As proposed in the report, and by 14 August 2015, please submit a work plan to address the benzene at UPSV-6 and the benzene and naphthalene at APSV-15. The work plan must also address our above concerns about TPH-g in probes that exceed the 295,000 ug/m3 screening level, including APSV-9 and APSV-10. Additionally, the work plan must address reducing methane levels caused by degradation of petroleum hydrocarbons to below the LEL (5% or 50,000 ppmv) given our concerns about remaining potential threat to the apartment buildings and utility workers. Finally, the quarterly monitoring of the soil vapor probes should continue during the period the work plan is being prepared and reviewed. Depending on the work that is proposed and approved, we may consider adjusting or reducing the soil vapor monitoring program if it is warranted. We are also available to meet with you ahead of the due date for the work plan, if desired. Feel free to contact me with any questions of concerns regarding this letter at(916) 464-4622 or Bill.Brattain(a)-waterboards.ca.gov. Original signed by William Brattain, P.E. Water Resource Control Engineer Private Sites Cleanup Unit cc: Timothy Bishop, Chevron Environmental Management Company, San Ramon Ed Ralston, Phillips 66, Sacramento