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S E C O R Conceptual Site Model Chevron Service Station #9-6171 March 25, 2005 Page 9 Destruction of Monitoring Well OW- 1 I In March 2001, SECOR contracted and supervised GDT to abandon monitoring well OW-1 GDT pressure grouted the well and cemented over the top IGroundwater Monitoring - 1990 to present In July 1990, SES instituted a quarterly groundwater monitoring program that continues to the present Monitoring wells installed after July 1990 are included in the monitoring program Blaine Tech Services (BTS) administered the groundwater sampling program from July 1990 to May 22, 2000 Gettler-Ryan Incorporated (G-R) has monitored these wells from May 22, 2000 to the present In order to address recent comments by the California Regional Water Quality Control Board (RWQCB) to the 4`h Quarter Sampling Event, SECOR is preparing a request to Chevron to assume responsibilities for quarterly Isampling-report preparation The most recent groundwater analytical data is from the 4'h Quarter 2004 Sampling Event, dated October 11, 2004 Tables 1 through 3 summarize the results of the groundwater monitoring program The most recent groundwater monitoring report is included as Appendix C 33 Well Search and Field Survey IIn 1990, SES conducted a survey of the area to identify any potential receptors (Figure 5) The search extended to a one-half mile radius around the Chevron service station The closest surface water is Fivemile Creek, located approximately one-half mile to the northwest Fivemile Creek flows southwest toward Fivemile Slough, which flows into the San Joaquin River Delta The well survey consisted of a Department of Water Resources (DWR) well records review and a door-to-door survey Fifty-eight water wells were identified, excluding the ten active and two abandoned groundwater monitoring wells on the Chevron property (Table 5) The closest wells are located northwest of the Chevron station, they are the 12 groundwater monitoring wells on the Lincoln Center property (Figure 5) The next closest group of wells consists of four municipal wells located on the Lincoln Center property, one monitoring well west of the Lincoln Center property, and two domestic wells located northwest and southwest of the site There are approximately 22 privately owned domestic wells, 10 city owned municipal wells, 1 state owned municipal well, and 6 United States Geologic Survey owned wells located off site The current activity of these offsite wells is unknown I IN 1FdeslProjects1Chevron1Reta,N#9-617115ate conceptual ModewINAL-CSM doe