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Mr. David A. Rosso `W, Page 2 of 2 <br /> California State University Stanislaus 10 February 2009 <br /> 1252 N. Stanislaus Street, Stockton <br /> depth laterally from the former UST area, which the EHD considers to be consistent with cross <br /> contamination of the deeper grab groundwater samples from CPT-8, therefore the EHD believes <br /> the vertical extent of the chemicals of concern (COCs)to be adequately delineated. <br /> The EHD had not approved the shift from quarterly monitoring to the current semi-annual <br /> groundwater monitoring program implemented by Condor, however, the EHD does consider a <br /> semi-annual program adequate at this time with the following modifications: <br /> • Include MW-4 on the semi-annual sampling schedule (wells sampled semiannually will <br /> be MW-3, MW-4, MW7 and MW-8); <br /> • Sample MW-2 and MW-5 annually; and <br /> • Sample MW-1, MW-6 and MW-9 biennially. <br /> The EHD considers the following analytical regime to be adequate and necessary to properly <br /> monitor the plume of impacted groundwater: <br /> • TPH-g — MW-2, MW-3, MW-4 and MW-8; <br /> • TPH-k, TPH-d or TPH-mo— MW-2, MW-3 (an annual analysis), and MW-4; <br /> • BTEX— MW-3, MW-4 and MW-8; <br /> • 1,2-DCA—MW-2, MW-3, MW-4, MW-5, MW-7 and MW-8; and <br /> • The biennially sampled MW-1, MW-6 and MW-9 should be analyzed for TPH-g and <br /> 1,2-DCA. <br /> To move your site toward closure, the EHD directs the following to be submitted to the EHD by <br /> 01 June 2009: <br /> • An estimate of the sorbed and dissolved masses of TPH-g, TPH-k, and 1,2-DCA; <br /> • A fate and transport model for the COCs; <br /> • A trend analysis for the dissolved contaminants; <br /> • An evaluation of the residual COCs in soil above groundwater against the Environmental <br /> Screening Levels established by the San Francisco Bay Regional Water Quality Control <br /> Board; and <br /> • A work plan to evaluate the potential for vapor intrusion into structures on site from the <br /> residual contaminant mass. <br /> Questions or comments may be directed to Nuel Henderson at (209) 468-3436. <br /> Sincerely, <br /> Nuel C. Henderson, Jr., PG Marga�agono, REHS <br /> Engineering Geologist Program Coordinator <br /> Copies: James L.L. Barton —CVRWQCB, 11020 Sun Center Dr. #200, Rancho Cordova, <br /> CA 95670 <br /> Donald F. Kresse—Condor; 188 Frank West Circle, Ste I, Stockton, CA 95206 <br /> Comment and Directive Letter 0209 <br />