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` Mr. Denis Brown Page 3 of 3 <br /> 2320 N. EI Dorado St, Stockton, CA 10 December 2009 <br /> preparation of a site closure summary report (CSR) would be appropriate at this time. Please <br /> prepare and submit the report to the EHD by 01 February 2010. The CSR should address all the <br /> information requirements of Appendix A — Reports Tri-Regional Board Staff Recommendations <br /> for Preliminary Investigation and Evaluation of Underground Storage Tank Sites. In addition, <br /> please provide: <br /> • Estimates of the residual contaminant mass in soil and in groundwater, both before and <br /> after corrective action; <br /> • An estimate of the time required for the site to achieve background conditions based on <br /> the concentration trends for each significant COC; <br /> • A comparison of residual COC concentrations to the environmental screening levels <br /> (ESLs) established by the San Francisco Bay Regional Water Quality Control Board <br /> (SFBRWQCB), with Tier 2 risk assessment for any concentrations that exceed the ESLs, <br /> should there be any; <br /> • A comparison of residual contaminant concentrations to the California Human Health <br /> Screening Levels (CHHSLs), with a rational justifying closure in view of any <br /> concentrations that exceed the CHHSLs, should there be any; <br /> • A vapor intrusion evaluation with a justification for site closure if a significant potential for <br /> vapor intrusion is found to exist, but human health and the environment will not be at <br /> risk; <br /> • A discussion of the waste oil tank reportedly removed in 1984, with any documentation <br /> of its removal, disposal and its location during use on the site. The Central Valley <br /> Regional Water Quality Control Board has expressed concern regarding this issue and <br /> its possible relationship to the PCE and TCE occurrences on your site; and <br /> • A thorough discussion of the origins of PCE and TCE in soil and groundwater. <br /> The occurrence of PCE and/or TCE in soil samples collected from the saturated zone suggests <br /> release of the compounds as a separate phase material and their occurrence in the four shallow <br /> soil samples from the dispenser area suggests release of the compounds on site. The <br /> widespread occurrences of these COCs in groundwater samples from wells associated with <br /> both the up-gradient 2315 N. EI Dorado Street site and the subject site suggests there may be <br /> more than one source of these COCs. Whether or not these particular COCs are part of the <br /> UST system release is not clear; therefore you may discontinue laboratory analysis of <br /> groundwater samples for PCE and TCE pending review of the portion of the CSR related to the <br /> former waste oil UST. <br /> If you have any questions, please contact Frank Girardi at (209) 953-7868 or by electronic mail <br /> at fgirardinsicehd.ccorn. <br /> Frank V. Girardi, REHS Nuel Henderson, PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> C: James Barton, RWQCB, 11020 Sun Center Dr., #200, Rancho Cordova, CA 95670 <br /> Tom Sparrowe, CRA, 19449 Riverside Drive, Suite 230, Sonoma, CA 95476 <br /> SCM, QM, NFAR Comment Letter 1210 <br />