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,1 Site l.: Automotive Service Station. A C-Sparger unit (Model 3600) was installed at a gasoline service station The unit was equipped with an oxygen generator, allowing ozone concentrations to be adjusted between 100 and 300 ppmv A recirculating well installation was employed to assure adequate ozone mixing in the vicinity of the morutonng well Dissolved oxygen content and redox potential (ORP) were monitored to define the radius of influence (ROI) ' Previous borings on the site showed static groundwater at depths of 3 0 to 6 0 ft (1 to 1 8 m) below grade A brownish-gray silt extended from fill at 2 5 ft ( 8 m) to about 6 ft (1 8 m) below grade Medium sand and gravel extended to depths of 20 ft (6 m) below grade Soil permeability ranged from 10"3 to 10"7 cm/sec The upper soils between 3 5 to 4 0 ft (1 to 12 m) we[e measured at 9 0 x ' 1077 cm/sec with a moisture content of 299 Fine materials (silt and clay) in smaller fractions (5% or less) were found intermixed with the sand and gravel The pH of the groundwater was determined to fall in the range of 7 0 to 8 5 ' Groundwater flow was low, with a hydraulic gradient of 0 0036 ft/ft across the site Specific conductance ranged from 850 to 1,100 µS Total BTEX concentrations ranged from 5000 to 24,000 ppb in groundwater samples The vertical extent of hydrocarbon contamination extended to a maximum depth of 15 ft (4 6 m) sub-grade No fight non-aqueous phase liquid (LNAPL) was observed at the site Dissolved oxygen contents in the groundwater were below 1 ppm in nearby monitonng wells Combined air/ozone flow to the recirculation well was 2 2 cfm The system was set to run 18 minutes for the lower Spargepoint®, 1 l minutes for the ' in-well Spargepoint®, and 5 minutes for the submersible pump The system operated on 14 cycles of 34 minutes each during a 24-hour period Monitoring was performed during a 20-day test period on the site, beginning July 29, 1997 Analytical results from a monitoring well located 18 ft (5 5 m) from the main recirculation well (CS-1) are presented in Figure 3 During ' the period of the 20-day test, total BTEX plus MTBE concentrations dropped from 19,220 ppb to 1004 ppb This represents a reduction of 94 8% during the test period MTBE concentrations dropped from 520 ppb to 6 ppb during the test period, representing in excess of 99% removal during ozone treatment ' Site 2: Upgradient of Water Supply Well. An oxidative curtain, or "bubble fence", was employed to attempt to contain an advancing MTBE plume threatening a water supply well near Lake Tahoe, California The soil consisted ' of silty, clayey sand The static groundwater level at the time of installation was 5 ft (1 5 m) below grade, although levels are known to drop to 10 ft (3 m) below grade A groundwater gradient of 5 ft (1 5 m) per 40 ft (12 2 m), or 0 125 ft/ft, was measured The observed forward advance of the plume was between 3 ft (1 m) to 10 ft (3 m) per month The bottom of the contaminated zone was 20 ft 1