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Ms. Stephanie Furgal 'Now *%ad September 7, 2010 <br /> Former Unocal Page 2 <br /> 1665 Pacific Avenue <br /> Stockton, CA <br /> (approximately 20 feet below surface grade) to the shallow sampling points to <br /> bioattenuation. <br /> • GeoTracker cross-plots of COC concentrations in MW-10 and MW-2 verses time <br /> demonstrate distinctly decreasing concentrations with increasing time. <br /> The EHD considers these findings to indicate that further consideration of this site for a low-risk <br /> closure would be appropriate at this time. Please prepare and submit to the EHD a "No Further <br /> Action Request" (NFAR) by November 8, 2010. Include in the NFAR the following items that the <br /> EHD did not find during this review that would be of further assistance evaluating the site for <br /> closure: <br /> • An estimate of the sorbed and dissolved masses of TPHg and benzene. <br /> • An estimate, based on trend analysis, of the time required for currently impacted <br /> groundwater to achieve the water quality objectives (WQOs) established by the Central <br /> Valley Water Quality Control Board (CVRWQCB) in the Basin Plan, and an evaluation, <br /> based on potential use of the groundwater and local sensitive receptors of whether that <br /> time frame is reasonable. <br /> • Further technical discussion of the data that demonstrates bioattenuation of COCs vapor <br /> in the subsurface. <br /> • An evaluation of residual COC concentrations in soil against the ESLs for direct contact <br /> and gross contamination and against the California Human Health Screening Levels <br /> (CHHSLs) established by the California Environmental Protection Agency. <br /> • An evaluation of the site for closure consideration according to the guidelines in Section <br /> 6 of Appendix A of the Tri-Regional Board Staff Recommendations for Preliminary <br /> Investigation and Evaluation of Underground Tank Sites (2004) issued by the <br /> CVRWQCB. <br /> Questions or comments should be addressed to Lori Duncan, (209) 468-0337, or to Nuel <br /> Henderson; (209) 469-3436; both at the San Joaquin County Environmental Health Department, <br /> 600 E. Main Street, Stockton, CA, 95105. <br /> Lori Duncan, REHS Nuel Henderson, PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> cc: Jim Barton, CVRWQCB <br /> The Bank of Stockton, Helen McCrary Trust, PO Box 201014, Stockton, CA, 95201 <br /> David Evans, ARCADIS, 950 Glenn Drive Ste 125, Folsom, CA 95630 <br /> NFAR Directive Letter 0910 <br />