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29 December 2004 AGE-NC Project No 95-0130 Page 2 of 10 I2.0. GROUND WATER MONITORING PROCEDURES A quarterly groundwater monitoring event was performed at the site on 30 September 2004 Ground water monitoring procedures for the site were outlined in the Work Plan Addendum -June 2001, dated 11 June 2001 and approved by the San Joaquin County Environmental Health Department (SJCEHD)by letter dated 07 July 2001 Due to a scheduling conflict,the Top Filling Station site ground water monitoring event was delayed, and was subsequently not performed on or near the date of the adjacent Knowles-Roek ground water ' monitoring event(102 South Wilson Way)which was performed 24-25 August 2004,the Knowles- Roek ground water monitoring event analytical results are tabulated and included in Appendix A 2 1 WELL MONITORING AND PURGING On 30 September 2004, depth to ground water was measured in each well from the top of the well casing to the nearest 0 01-foot utilizing a Solmst water level meter Ground water was not • encountered in wells VW-lA, VW-1B, VW-2B and VW-3B and were reported as `dry', ground water could not be recovered from wells MW-6A and MW-7A and the monitoring locations were subsequently reported as `dry', well MW-4 was inaccessible due to a parked car and could not be sampled The ground water elevation at wells MW-1, MW-2, MW-3 and MW-5 through MW-8, VW-1C, VW-2A and VW-3A were calculated by subtracting the measured depth to ground water from the surveyed casing elevation As-built monitoring well construction details are summarized in Table 1 Ground water elevations were plotted and contoured on scaled site maps depicting First Zone and Second Zone ground water elevations (Figures 3 and 4, respectively) After water levels were measured, approximately '/3 to 17'/4 gallons of ground water (a minimum of three casing-water volumes per well) were purged from wells MW-1, MW-2, MW-3, MW-5 through MW-8, VW-1C, VW-2A and VW-3A by lowering and raising a 5/g or %-mch outer diameter,length-discrete polyethylene hose equipped with a ball-valve water tip through the specific water-charged screened section A Watera Hydro-Lift H pump equipped with a mechanical arm was utilized to surge the polyethylene hose Temperature, pH and conductivity were measured for stabilization at regular purge-volume intervals from each well using the Oakton water analyzer Field data and logs are in Appendix B Multi-level well purged ground water was transferred to 55-gallon drums and stored on-site in an area lacking general public access I 1 • Advanced GeoEnvironmental,Inc