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01 September 2005 AGE-NC Project No 95-0173 ' Page 2 of 10 ' 2.0. GROUND WATER MONITORINGISAMPLING PROCEDURES AND RESULTS On 16 May 2005, ground water monitoring was performed at the site on single-level wells MW-1 ' through MW-12,multi-level well MW-13 (A, B, and C), and air sparge wells AW-1 (A and B)and AW-2 (A and B) Ground water monitoring procedures for the site were outlined in Work Plan Addendum, dated 16 May 2000, and conform to ground water monitoring guidelines issued by the ' San Joaquin County Environmental Health Department (EHD) As-built construction details of all -— monitoring wells are summarized in Table 1 ' 21 WELL MONITORING AND EVACUATION PROCEDURES ' On 16 May 2005, the depth to ground water was measured at each well from the tops of the well casings to the nearest 0 01-foot utilizing a Solinst water level meter Ground water elevation at the site was calculated by subtracting the measured depth to ground water from the surveyed well casing elevations (Table 2) • After water levels were measured, approximately 4'/2 to 10'/z gallons of ground water(a minimum of three casing-water volumes per well)were evacuated(purged)from single-level monitoring wells MW-1 through MW-12 and air sparge wells AW-1A and AW-2A utilizing disposable polyethylene ' bailers, only 1 gallon of water was purged from MW-11 before the well was purged `dry' approximately 21/4 to 19'/z gallons of ground water were purged from multi-level monitoring well MW-13 (A-C) and air sparge wells AW-113 and AW-213 by lowering and raising a3/8-inch outer ' diameter, length-discrete polyethylene hose equipped with a ball-valve water tip through the top chambers into the specific water-charged screened section, a Waterra Hydro-Lift lI inertia 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 in each well using an Oakton water analyzer Field data and logs are provided in Appendix A Purged ' ground water was transferred into properly labeled,Department of Transportation(DOT)-approved 55-gallon drums and stored on-site in an area lacking general public access 22 GROUND WATER SAMPLING tFollowing well purging, ground water levels in the wells achieved a minimum 80%recharge prior to sample collection Subsequently, ground water samples were collected from each purged well utilizing new, disposable polyethylene bailers and transferred into three, 40-milliliter (ml) EPA- approved volatile organic analysis (VOA) vials containing 0 5 ml 18% hydrochloric acid solution . as a sample preservative,ground water samples were collected from multi-level well MW-13 (A-C) Advanced GeoEnv►ronmental,Inc