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California gional Water Quality Ca`-ol Board <br /> Central Valley Region <br /> Katherine Hart, Chair <br /> 4 Fa <br /> 11020 Sun Center Drive,#200, Rancho Cordova, California 95670-6114 <br /> Linda S.Adams (916)464-3291 • FAX(916)464-4645 Edmund G.Brown Jr. <br /> Acting Secretary for http://www.waterboards.ca.gov/centraIvaIley Governor <br /> Environmental Protection <br /> RECEIVED <br /> 5 July 2011 <br /> Jl!l_ 1 �' 2011 <br /> Chris Markowski ENVIRONMENTAL HEALTH <br /> PERMIT/SERVICES <br /> Project Manager <br /> 10620 Mather Road <br /> Mather, CA 95655-4176 <br /> PROPOSED SCOPE REVISION FOR SOIL GAS INVESTIGATION, ARMY AVIATION <br /> SUPPORT FACILITY, CALIFORNIA ARMY NATIONAL GUARD, STOCKTON, SAN <br /> JOAQUIN COUNTY <br /> Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff has <br /> reviewed the Proposed Scope Revision for Soil Gas Investigation, California Army National <br /> Guard, Army Aviation Support Facility (Proposed Scope Revision) received via email on 13 <br /> June 2011. The Proposed Scope Revision is based on a meeting between the California <br /> Army National Guard (CA ARNG) and Central Valley Water Board staff on 19 May 2011, <br /> where reductions in the soil vapor sampling proposed in Work Plan for Groundwater <br /> Monitoring, Well installation, Soil Gas and Groundwater Investigation, and Groundwater <br /> Monitoring (December 2010) were discussed. CA ARNG is proposing to reduce the soil vapor <br /> investigation to six locations for two reasons. Relatively low concentrations of volatile organic <br /> compounds were detected in groundwater grab samples collected from 30 site locations in <br /> February 2011. Secondly, soils were screened for vapors with a photoionization detector <br /> (PID) during advancement of the borings for these groundwater grab samples and vapors <br /> were not detected in most of them. <br /> With one exception Central Valley Water Board staff concurs with the changes discussed in <br /> the Proposed Scope Revision. Central Valley Water Board staff recommends collection of an <br /> additional shallow soil vapor sample from one of the two borings proposed for advancement in <br /> the former wash rack area and near recent grab groundwater sample locations AASF-GW-15 <br /> through -18. Even though the soils are predominantly clay from 0 tol5 feet below ground <br /> surface (bgs) at the Army Aviation Support Facility, the PID detected vapors in both shallow (0 <br /> to 15 feet bgs) and deep (> 15 feet bgs) vadose zone soils in this area. If a shallow soil vapor <br /> sample can be collected from a depth of approximately 5 to 10 feet below ground surface <br /> (bgs), then CA ARNG should collect it in addition to the proposed samples from the sandy <br /> zone at 18 to 21 feet bgs. <br /> Although Central Valley Water board staff concurs with the proposed reduction in soil vapor <br /> sampling, we may request additional sampling if significant soil vapor contamination is <br /> encountered in one or more of the six boring locations proposed for sampling. If you have any <br /> questions, please contact me at (916) 464-4733 or email me at mpierce@waterboards.ca.gov. <br /> California Environmental Protection Agency <br /> 0Recycled Paper <br />