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Petition for Closure of Ar„oF - 2 - 6 December 2012 <br /> Stockton CA ARNG <br /> monitoring data. the groundwater contamination appears to be limited to a small area <br /> beneath and slightly north (downgradient) of the former washrack. <br /> Based on CA ARNG's findings to date, Central Valley Water Board staff agrees that <br /> remediation does not appear warranted. However, we cannot concur with closure at this <br /> time without further evidence the groundwater contamination has been adequately <br /> characterized and the small plume around monitoring well MW-4 is stable or <br /> decreasing. This demonstration cannot be made with only four quarters of groundwater <br /> monitoring data. Furthermore, contaminant concentrations in MW-4 showed a <br /> significant increase in the last quarter, which could potentially indicate the groundwater <br /> plume is not stable. <br /> CA ARNG needs to continue monitoring the on-site wells. Well MW-4 should be <br /> sampled at least quarterly and the other wells should be sampled at least semi-annually <br /> in 2013. The results of this monitoring effort should be reported in two semi-annual <br /> reports. The first semi-annual report can be limited to a simple letter with tabulation of <br /> the analytical results. The second semi-annual report should provide analysis of the <br /> entire year of monitoring and recommendations for future actions at the AASF. <br /> If CA ARNG can demonstrate the groundwater plume is adequately characterized and <br /> the plume is stable or decreasing, Central Valley Water Board staff will consider a future <br /> petition for site closure. However, one of the conditions for closure may include <br /> institutional controls to prevent potential exposure of future site occupants to <br /> contaminated soils and groundwater in the washrack area. Additional investigation and <br /> possibly remedial actions may be necessary to eliminate the need for institutional <br /> controls. <br /> If you have any questions, please contact me at (916) 464-4733 or email me at <br /> mpierce(aDwaterboards.ca. ov. <br /> Marcus Pierce <br /> Associate Engineering Geologist <br /> Federal Facilities Unit <br /> cc: Mr. Mike Quillin, Oneida Total Integrated Enterprises, Walnut Creek <br /> Mr. Nuel Henderson, San Joaquin County EHD, Stockton <br />