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Andrew Richle - 3 - May 18, 2020 <br /> for PCE at that time. This location is downgradient of the Central Plume Source Area <br /> and evaluation including of possible indoor sources is ongoing. All the remaining PCE <br /> detections were below 1.0 pg/m3. <br /> Based on the results of the passive soil gas sampling and indoor air sampling within the <br /> Central Plume Source Area, the City proposes closing out the existing SVE system, <br /> which has been shut down since February 2019 and the GWET system that has been <br /> shut down since August 2014. To complete the Central Plume Source Area <br /> remediation, the City proposes excavating soil containing the highest soil vapor impacts <br /> along the alley sewer line. The City will also conduct annual indoor and ambient air <br /> monitoring within the Central Plume Source Area. Groundwater monitoring and <br /> sampling of the Central Plume Source Area groundwater monitoring wells will continue <br /> as part of the ongoing groundwater monitoring program. If indoor air monitoring <br /> indicates increased PCE concentrations due to remaining soil or groundwater <br /> contamination, the City will perform additional targeted remediation to address the <br /> area(s) of impacts. The City also proposes to implement institutional and engineering <br /> controls for the Central Plume Source Area. These controls would include the <br /> requirement for additional characterization and installation of vapor mitigation for any <br /> site redevelopment. <br /> Central Valley Water Board staff generally concurs with the proposed path forward. By <br /> July 31, 2020, please submit a schedule that includes the alleyway excavation, indoor <br /> and ambient air testing dates, and implementation of institutional controls. <br /> If you have any questions regarding this letter, please contact us at (916) 464-4678 or <br /> steven.meeks(o)_waterboards.ca.gov. <br /> Nathan Casebeer, P.G. <br /> Engineering Geologist <br /> OFESSI <br /> Private Sites Cleanup Unit tiop W"ITT p"q! <br /> EN�F <br /> y� C 057461 N iy�m <br /> Expires 1213112021 <br /> Steven W. Meeks, P.E. CIVIL <br /> _,�!�' <br /> Senior Water Resources Control Engine kOF /18/2020 <br /> Chief, Private Sites Cleanup Unit <br /> cc: Varinder Oberoi, Civil Hydro Tech, Sunnyvale <br />