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Den's Auto Repair Page 2 <br /> 308 South El Dorado Street June 13,2008 <br /> Stockton, California 95203-3404 <br /> • Cross sections showing subsurface geological features, depth to groundwater, man-made <br /> conduits, monitoring well construction and the interpreted vertical extent of soil and <br /> groundwater contamination; <br /> • Cross-plots of key chemical concentrations verses time for representative wells that <br /> demonstrate significant contaminant concentration trends; <br /> • Summary tables of contaminant concentrations in the different media; <br /> 0 Rose diagram showing directions of dominant groundwater..flow; <br /> • Well and boring logs (including construction/screening); and <br /> • Narrative description of the SCM that describes controls on contaminant distribution; <br /> contaminant migration mechanisms, pathways and rates; plume disposition over time; and <br /> sorbed and dissolved contaminant masses.` <br /> While not necessarily showing all data in diagrams and drawings, an adequate SCM can be utilized to <br /> account for most of the known data and to evaluate the sporadic detection of contaminants in MW-4 <br /> and MW-7; and to evaluate the fate of impacted groundwaterwith an estimate of when background <br /> conditions will be restored. All analytical data should be included in tables. Residual contaminant <br /> concentrations should be compared to Environmental Screening Levels (ESL) and California Human <br /> Health Screening Levels (CHHSLs) established by California Environmental Protection Agency San <br /> Francisco Bay Regional Water. Quality Control Board. Methods and calculations of contaminant <br /> masses.should be included in the SCM,and may be submitted as an appendix. <br /> The SCM should be updated as new data are acquired that cause a change of interpretation or expands <br /> the model until model modifications are not needed to explain subsequently acquired data. As the <br /> SCM becomes complete, it can be utilized to reasonably predict additional investigation results and <br /> plume response to various,remedial technologies or.to changes in groundwater flow regime. The <br /> model should adequately demonstrate all interpretations and opinions. <br /> AGE has recommended the preparation of a Corrective Action Plan that includes an ozone injection <br /> (in-situ chemical oxidation) feasibility study. The EHD concurs with AGE. Please submit an <br /> interim remediation proposal to the EHD by August.29,2008. <br /> If you have any questions, please contact Vicki McCartney, Senior Registered Environmental <br /> Health Specialist, at(209)468-9852 or by email at vmccartnevL},sicehd.com. <br /> Sincerely, <br /> Victoria L. McCartney,REHS Nuel C.Henderson, Jr.,PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> c: Ms. Lauren D. Cardinalli, Advanced GeoEnvironmental, Inc., 837 Shaw Road, Stockton, <br /> California 95215 <br /> Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central Valley <br /> Region, 11020 Sun Center Drive, Suite 200,Rancho Cordova, California 95670 <br />