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18 April 1997 AGE-NC Project No 95-0141 IPage 3 of 5 by subtracting the depth to ground water from the relative casing elevations surveyed from a temporary benchmark assigned an arbitrary elevation (Table I- Relative Gr ound Water Elevations) Relative ground water elevations were plotted and contoured on a scaled site map (Figure 3 - Relative Elevation Ground Water Map) After water levels were measured, approximately 12 to 15 gallons of ground water (minimum of three I well volumes) were removed from wells MW-1 through MW-5 with a Grundfos Redi-Flo II submersible pump Temperature, pH and conductivity were measured at regular intervals from each well using an ICM model 52200 water analyzer, to monitor stabilization of these characteristics Stabilization data and field logs are included with Appendix A Purged ground water was containenzed in 55-gallon drums and stored on-site in an area lacking access for the general public 3 2 GROUND WATER SAMPLING IThe ground water levels in monitoring wells MW-1 through MW-5, were allowed to recover for a minimum of one hour prior to sample collection Water samples were collected utilizing disposable polyethylene bailers and new nylon rope Sufficient ground water sample was collected from each well to fill three 40-m1 EPA vials containing 0 5 ml 18% hydrochloric acid as a preservative for the samples Care was taken to ensure that visible air bubbles were not present in the VOAs after filling I and capping Ground water sample containers were labeled with the well designation, date, time, and sampler's initials 3 3 LABORATORY ANALYSIS OF GROUND WATER SAMPLES I Each ground water sample was logged on a chain-of-custody form, placed in a chilled container and transported to Castle Analytical Laboratories (CAL), a California state-certified laboratory for analysis of hazardous materials Each sample was analyzed for total petroleum hydrocarbons quantified as gasoline (TPH-g), volatile aromatics (benzene, toluene, ethyl benzene and xylene BTE&X) with methyl-tertiary butyl ether (MTBE) in accordance with EPA methods 8015 and 8020, respectively I4.0. FINDINGS 41 RELATIVE GROUNDWATER ELEVATION AND GRADIENT IGround water depths at the site ranged from 22 58 to 23 60 feet Ground water elevation at the site increased approximately 3 26 feet between September 1996 and February 1997 Ground water is approximately 5 40 to 7 42 feet above the screen intervals of all the monitoring wells I