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_ *low <br /> San Joaquin County Courthouse ' <br /> 222 East Weber Avenue <br /> Page 2 of 2 <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 /> • Well and boring logs <br /> • An estimate, with calculations and narrative description, of the time and mechanisms <br /> required for contaminant concentrations to reach water quality objectives <br /> • Narrative description of the SCM that describes controls on contaminant distribution; <br /> contaminant migration mechanisms, pathways and rates; plume disposition over time; <br /> and sorbed and dissolved contaminant masses. <br /> While not necessarily showing all data in diagrams and drawings, an adequate SCM can be <br /> utilized to account for most of the known data and to illustrate additional assessment needs <br /> thereby providing the justification for all work proposed in future work plans. All analytical data <br /> should be included in tables. Methods and calculations of contaminant masses should be <br /> included in the SCM, and may be submitted as an appendix. The SCM should be updated each <br /> time new data are acquired that cause a change of interpretation or expands the model until model <br /> modifications are not needed to explain subsequently acquired data. As the SCM becomes <br /> complete, it can be utilized to reasonably predict additional investigation results and plume <br /> response to various remedial technologies or to changes in groundwater flow regime. The model <br /> should adequately demonstrate all interpretations and opinions. <br /> EHD has not been receiving surrogate recoveries associated with groundwater samples analyzed <br /> for BTEX and total petroleum hydrocarbons as gasoline (TPH-g) by US Environmental <br /> Protection Agency SW-846 methods 8021/8015B. Please include this information in future <br /> quarterly monitoring reports. <br /> Please submit an SCM by July 30, 2004. If you have any questions regarding this letter, please <br /> contact Vicki McCartney at (209)468-3456 or by electronic mail at vmccaT-tney@Ls1cehd.com.. <br /> Donna Heran,REHS,Director <br /> Environmental Health Department <br /> Vicki McCartney,REHS Nuel C. Henderson,Jr.,RG <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV <br /> cc: Joseph Ramage,Ramage Environmental <br /> James L.L. Barton, CVRWQCB <br />