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^P � EDMUND G. BROWN JR. <br /> ooYc <br /> nNon <br /> 0001 00 <br /> C AL 1 P O N N I• MATTHEW <br /> Rp DRIOUEZ <br /> SECRET <br /> WaterBoards ENVIRUNMENTNL PROTECTION <br /> Central Valley Regional Water Quality Control Board � E0\1ISER <br /> 6 December 2012 <br /> Belinda May, LTC <br /> Environmental Compliance Officer <br /> 10620 Mather Road <br /> Mather, CA 95655-4176 <br /> WORK PLAN FOR GROUNDWATER INVESTIGATION AND GROUNDWATER <br /> MONITORING WELL INSTALLATION, FIELD MAINTENANCE SHOP #24, <br /> STOCKTON CALIFORNIA ARMY NATIONAL GUARD COMPLEX, SAN JOAQUIN <br /> COUNTY <br /> Central Valley Regional Water Quality Control Board staff (Central Valley Water Board <br /> staff has reviewed the Work Plan for Groundwater Investigation and Groundwater <br /> Monitoring Well Installation (Work Plan) received on 7 November 2012. The Work Plan <br /> provides the rationale and procedures to investigate the Field Maintenance Shop <br /> groundwater plume and source area. This investigation is proposed in support of <br /> potential implementation of an in-situ chemical oxidation remedy. Central Valley Water <br /> Board staff comments on the Work Plan are provided below. <br /> COMMENTS <br /> 1. Page 10, Section 3.3, Membrane Interface Probe Borings: It is unclear how the 2,500 <br /> square foot "source area" was selected for investigation. The area is oval in shape <br /> and appears to be oriented along a line between existing monitoring wells FMS-MW2 <br /> and FMS-MW5. The "source area" does not include the entire footprint of the former <br /> underground storage tanks (USTs) nor the location of dual phase extraction well FMS- <br /> DPE2, which is screened in relatively high concentrations of petroleum hydrocarbons. <br /> Revise the Work Plan to explain how the "source area" was selected for investigation <br /> and explain why some areas with significant contamination are not included. <br /> The primary goal of the Work Plan is to collect additional data necessary to support <br /> potential in-situ chemical oxidation. Therefore, Central Valley Water Board staff <br /> recommends including the entire area of known and suspected high residual <br /> petroleum hydrocarbons concentrations in the proposed "source area" investigation. <br /> KARL E. LONGLEY SCD. P.E., CHAIR I PAMELA C. CREEDON P.E., BCEE,EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200, Rancho Cordova,CA 95670 1 www.waterboards.ca.gov/centralvalley <br /> RECYCLED PAPER <br />