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' S E C O R <br /> Conceptual Site Model <br /> Chevron Service Station #9-6171 <br /> March 25, 2005 <br /> Page 33 <br /> 9.0 CONCLUSIONS <br /> This section provides a summary of the CSM elements, Including sources, potential <br /> receptors, and routes of exposure The complied data presented within the CSM are <br /> generalized on a site conceptual schematic (Figure 21) An exposure pathway model, <br /> based on the Identified routes of exposure, is presented in Figure 22 <br /> 9.1 Primary Sources <br /> In addition to the Chevron site there are, at a minimum, four potential separate sources for <br /> petroleum hydrocarbon Impacts in the vicinity of Benjamin Holt Drive and Pacific Avenue <br /> These sources include the <br /> • Former Norge Cleaning Village <br /> • Former Regal service station #603/Exxon service station #7-0136 <br /> • Canepa's Carwash <br /> • Shell service station <br /> Two additional former gasoline service stations, the former Unocal #5421 and the Asian <br /> Market, are located within 1,350 feet northwest of the Chevron service station 9-6171 <br /> These service stations are located cross-gradient from the Chevron site and have had <br /> historical groundwater flow directions to the northeast In addition, any reported releases <br /> from these other sources have been remediated and granted closure by the County <br /> Data from quarterly groundwater monitoring reports for the site, indicate that the primary <br /> groundwater flow direction between 1990 and 2004 is to the south/southeast (Figure 6) <br /> However, groundwater flow has also been to the south/southwest Data from surrounding <br /> sites to the south of the Chevron site Indicate that the primary groundwater flow direction <br /> between 1988 and 2004 is to the north/northeast However, data from surrounding sites to <br /> the north of the Chevron site indicates that the primary groundwater flow direction between <br /> 1986 and 2000 has also been to the north/northeast Currently the depth to groundwater <br /> ranges from approximately 38 62 to 42 97 feet bgs The depth to groundwater has varied <br /> since groundwater monitoring and sampling was Initiated in 1990 From 1990 to 1999, <br /> groundwater elevations Increased from approximately -42 to -18 feet MSL From 1999 to <br /> 2004, groundwater elevations decreased from approximately -18 to -26 feet MSL due to <br /> unknown factors <br /> N 1F,Ies,projects\clevronlReta,ll#9-61711site Conceptual ModeI1FINAL—CS M clot <br />