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Chevron Products Company I I Former Chevron Service Station #9-5775, 301 West Kodkinan Lane, Lodz, California June 5, 200I • 4.0 SITE CONCEPTUAL MODEL A Site Conceptual Model (SCM) has been developed to illustrate likely sources, pathways, and receptors Results of the SCM are summarized below and graphically presented on Figure 15 4.1 Sensitive Receptor Survey 41 1 Door -to -Door Survey A door-to-door sensitive receptor survey was performed within a 1 -block radius of the Chevron facility on July 12 and 13, 2000 by a SECOR representative to identify domestic wells not listed in agency databases A total of two businesses and runty -five residences were approached during the sensitive receptor survey During the survey, the businesses and forty of the residential participants indicated that there was no domestic well on the property No one was home at fifty-five of the residences At these locations, an envelope was placed in the doorway containing a blank Water Supply Well Location Survey Form, explanation letter, and a self addressed and stamped envelope As of May 10, 2001, four of the residences responded to the survey by mail The survey did not identify domestic water wells within a 1 -block radius of the subject site 412 Department of Water Resources Survey is On March 15, 1999, G -R conducted a DWR (DWR) file review in an attempt to located domestic and municipal wells within a Y2 -mile radius of the Former Chevron (G -R, Monitoring Well Installation Report, dated June 2, 1999) G -R identified one municipal well (Well 12) within the -mile radius A table and figure (provided by G -R) depicting well search results can be found in Attachment L • 4.2 Chemical Concentrations vs. Time and Distance 4 2 1 Chemical Concentrations vs Time Plots of Chemical Concentration vs Time can be found on Figures M-1 through M-22 within Attachment M Concentrations of TPHg and benzene are shown to decrease over tune in both on- site and off-site wells Concentrations of MtBE were found to decrease in on-site wells, however off-site wells appear to exhibit an increasing trend in concentrations. 422 Chemical Concentrations vs Distance Concentrations of MtBE are shown to decrease in A -Zone wells in Figures N-1 through N-4 from the source to the southeast, southwest, west, and south, respectively (Attachment N) 11Chevron1957751ParFrpl9-5775PARFRP2 doc