SITE INFORMATION AND CORRESPONDENCE

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i 17.40 Houston,Stockton Van Buskirk Golf Course,Page 2 borings (except B-4 (MW-4)) were advanced outside of the MTBE and TPH-G iso-concentration contour lines of non-detect, at locations approximately 40 feet or more away from SB-5 of the above-mentioned 1996 soil investigation. While the MTBE concentration level detected in the soil samples of B-4 (MW-4)approached that of the groundwater samples from MW-4 over the last three monitoring quarters, none of the soil borings from the 1999 investigation was placed at the vicinity of SB-5 from the 1996 investigation. Additional site assessment to further evaluate the vertical and lateral extent of the petroleum contamination impact in soil and groundwater was recommended in both Quarterly Ground Water Monitoring Report—August 1999 dated September 2, 1999 and Quarterly Ground Water Monitoring Report—August 1999 dated June 30, 1999 prepared by AGE. In a telephone conversation with AGE on August 9, 1999,PHS/EHD requested submitting this work plan by August 31, 1999. In a telephone conversation on September 1, 1999, AGE expressed that additional investigation of the diesel contamination may not be warranted. PHS/EHD agreed but stated that additional investigation of MTBE contamination was still needed. In a letter dated September 8, 1999, PHS/EHD agreed to extend the deadline to submit this work plan to September 30, 1999, and requested a 2000 feet radius well survey be conducted. PHS/EHD has received neither the work plan nor the report of the well survey to date. In a letter dated January 20, 2000, you requested reducing future quarterly monitoring to sampling MW- 4 only. PHS/EHD requires sampling of MW-3, MW-4, and MW-5 for future quarterly monitoring at this time. Both MW-4 and MW-5 are located downgradient (north) of the former gasoline and diesel underground storage tanks (UST). Since the concentration of MTBE in the groundwater samples from MW-4 has been increasing, the possibility of a migrating groundwater contamination plume cannot be dismissed. MW-3 should continue to be monitored since it is located closest to the former gasoline UST. Analytical results of the 1999 investigation indicated minimal petroleum and MTBE impact in the soil outside the MTBE and TPH-G iso-concentration contour lines of non-detect, but did not address the area near SB-5/MW-3 and former gasoline UST. Additional work is required to delineate the lateral and vertical extent of the petroleum hydrocarbon contamination in both soil and ground water with the shared goals of calculating the mass balance of the contamination constituents. The work plan should also take into consideration the possibility of the MTBE contamination plume migrating. Submit this work plan to PHS/EHD by May 1, 2000. The work plan should also include the survey of wells within a 2000-foot radius of the site. All wells identified in the survey and the location/addresses on a map along with any known construction details of the wells should be provided to PHS/EHD. PHS/EHD recommends including north-south and east-west geological/contamination concentration cross- sections in the report of the work. If you have any questions,please feel free to contact Jeffrey Wong at (209) 468-0335. Donna Heran,RENS,Director Environmental Health Division cc� � Jeffrey ong, REHS MI argaret gorio,REHS LOP/Site Mitigation Unit IV Supervisor c: RWQCB, Central Valley Region—Marty Hartzell c: Advanced GeoEnvironmental,Inc. —Bill Little/Gary A. Dickenson