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Petition for Closure of A,,,DF - 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 />mpierceawaterboards.ca.00v. <br />Marcus Pierce <br />Associate Engineering Geologist <br />Federal Facilities Unit <br />cc: Mr. Mike QuiIlin, Oneida Total Integrated Enterprises, Walnut Creek <br />Mr. Nuel Henderson, San Joaquin County EHD, Stockton