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f i 20 October 2003 AGE-NC Project No 95-0185 ' Page 2 of 6 The ozone-sparging system consisted of three ozone spargmg wells (OW-1 through OW-3) individually plumed to a Cnegee Oxidation (C-Sparge) ozone generator via a subsurface network of 318-inch polyethylene tubing The generator produces gaseous ozone which is Infected at 25 psi into the subsurface, via microsparge points at sparge wells OWI through OW3, to extract and decompose dissolved petroleum hydrocarbon constituents The frequency and duration of ozone injection periods were approximately 20 minutes, initiating with the first well and then cycled Into each well Ozone readily degrades to oxygen In order to monitor the effectiveness of ozone sparging,a YSI-50 dissolved oxygen (D O ) meter was utilized in the field to measure dissolved oxygen at each monitoring well during the monitoring events conducted at the site, additional D O measurements were conducted at wells MW-2 through MW-5 on 25 April, and at wells MW-2 and MW-3 on 09 May Data from the monitoring events are included In Table 2 ' 2 2 WELL MONITORING AND EVACUATION The water level in each monitoring well and free-phase petroleum product in wells MW-1 and lie MW-4 was measured relative to the tops of the well casings using a Solinst free-product interface- probe, the ground water elevations and gradient were determined from this data (Table 1) After gauging the depth to ground water, each monitoring well was purged with a dedicated, disposable bailer During the May 2003 monitoring event, between 3 5 and 4 75 gallons of ground 1 water were removed from wells MWA through MW-3, and MW-5 (minimum of three casing- volumes per well) During the June 2003 monitoring event, between 3 5 and 5 gallons of ground water were removed from wells MW-1 through MW-5 and 7 gallons of ground water were removed ' from well MW-4 During purging,free product was observed and measured in well MW-1 and MW-4 During the May 2003 monitoring event, a thin layer of free-phase product was observed in the first bailer of water from wells MW-I and MW-4 During the June monitoring event, 0 5 feet(6 inches)of free product was present In wells MW-I and MW-4 ' Temperature,pH and conductivity were measured at regular intervals during purging at wells MW-1 through MW-5 using an Oakton water analyzer(Appendix B), however, ground water parameters were not measured at well MW-4 during the May sampling due to the presents of free-product - Purged water was stored on-site in 55-gallon Department of Transportation(DOT)-approved drums Advanced GeoE nvi ron mental,Inc 1