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RESPONSE TO COMMENTS (December 2010) <br /> DRAFT WORK PLAN FOR GROUNDWATER MONITORING WELL INSTALLATION, SOIL GAS AND GROUNDWATER INVESTIGATION,AND <br /> GROUNDWATER MONITORING, October 2010 <br /> Army Aviation Support Facility, 2000 Stimson Road, Stockton, CA <br /> OTIE Contract Number:W91238-09-D-0017, DO 0004,Amendment 01 <br /> # Doc. Source Section/Page Comment Response(Contractor) <br /> 6 WP CVRWQCB — The Draft Work Plan implies that CANG intends to install Per CVRWQCB recommendation the number of <br /> two permanent groundwater monitoring wells prior to investigative borings has been reduced to <br /> advancement of the 40 investigative borings where both approximately 30. Seven(7)of the 30 borings will be <br /> soil vapor and groundwater grab samples are proposed located in and around the area of the former wash rack <br /> for collection. Central Valley Water Board staff and its associated clarifier. <br /> recommends installing these permanent monitoring points <br /> after advancement of the 40 borings. Data collected from Further, two additional monitoring wells,downgradient <br /> the 40 borings should be used to optimize placement of to the areas of concern are now proposed to be <br /> the permanent monitoring wells. installed. <br /> Additionally, CANG should consider installing additional Prior to the installation of all site wells, investigative <br /> monitoring well(s)downgradient of the former USTs and borings(including the collection of grab groundwater <br /> suspected solvent release areas. Currently, the Draft and soil vapor samples)will be performed to provide <br /> Work Plan proposes installation of two groundwater input regarding each wells specific location and design <br /> monitoring wells in or upgradient of the former USTs and (e.g. screening interval). <br /> fueling areas. Based on the site conceptual model, <br /> releases from the UST and wash racks would have In summary, a total of four monitoring wells(two <br /> occurred many years ago and only investigation the upgradient, one approximately mid-plume, and one <br /> potential release areas may not fully characterize upgradient)and approximately 30 investigative borings <br /> potential groundwater contamination nor provide an for groundwater grab and soil vapor samples are now <br /> adequate monitoring network for the future. Central proposed in the Work Plan <br /> Valley Water Board staff understands that securing funds <br /> for investigations at this site has always been <br /> problematic, so funding for additional wells may not be <br /> available. However, the proposed density of investigation <br /> borings appears to be more than what is necessary to <br /> meet project objectives, so the additional wells may not <br /> actually require additional funding.CANG could <br /> potentially reduce the number of investigation borings <br /> near the existing wash rack and along the surficial <br /> drainage system on the southern site boundary without <br /> losing any key information and replace these borings with <br /> the additional groundwater monitoring well(s). <br /> Specific Comments on Draft Work Plan from Marcus Pierce,CVRWQCB <br /> 1 WP CVRWQCB Page 3, Section This section indicates there is an existing 15,000 gallon Figure 2 of the Work Plan has been updated with the <br /> 1.3 UST in the proposed investigation area, but it is not location of the 15,000-gallon UST. <br /> shown on the referenced figure. Add this UST to Figure <br /> 2. <br /> 3 <br />