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. June 21, 1993 Working To Restore Nature r ARCO Service Station No 2130 pressure to the extent that groundwater mounding occurs, literature indicates that ground- water mounding is the more typical response during sparging i Pressure Vadose zone pressure increases were observed at all sparge monitoring points while 1 sparging, with pressure responses directly related to the sparge flow rate In general, pressures increased at higher sparge flow rates and decreased at further distance from the sparge well In all cases, the pressure responses in crossgradient well MS-1 were an order of magnitude less than responses in downgradient well MS-2 even though both monitoring 1 points are the same distance (9 5 feet) from well AS-1 Pressure responses observed in well MS-3 during 10 to 12 acfm sparge only testing ranged from 0 3 to 12 inches of water column, well MS-3 is located approximately 19 5 feet downgradient from well AS-1 e � During the combined sparge/vent test, the pressure values recorded were lower than those observed during the sparge only test portions A vacuum was achieved in well MS-1 while pressure reductions as high as 58 percent and 46 percent were achieved in wells MS-2 and 1 MS-3, respectively Since vapor was being extracted at a measured flow rate of 190 to 192 acfm, while sparging was occurring at 20 to 27 acfm, continued vapor extraction would likely have resulted in continued pressure reductions and a transition from pressure to vacuum within the sparge and monitoring zones Ground-Water Quality 1 Ground-water samples were collected at selected intervals during all phases of testing for analysis of TPHg, BTEX, and DO Analytical results indicated a reduction in dissolved concentrations of TPHg in wells MS-1 and MS-2 TPHg reductions of 38, 52, and 67 1 percent were identified in wells MS-1 during each test phase, while TPHg removal 30003-8 10 1