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when analyzed by EPA Method 8260. These compounds are known as lead scavengers and were a common gasoline additive. ( EDB was detected in NP-1-90',NP-1-80',NP-1-70',SVE-North,and SVE-South at concentrations of 230, 1600,210,6.2,and 770[tg/L,respectively. EDB was not detected in MW-DIS-1 or MW-DIS-2. 1,2-DCA was detected in MW-DIS-1 at a concentration of 150 gg/L,and was not detected in other wells. Conclusions Since 1991,groundwater levels have risen approximately 30 feet(from 77 ft bgs to 47 ft bgs), and the direction of groundwater flow has changed directions by almost 180 degrees. Between 1991 and July 1994,the groundwater flow direction was predominantly towards the northwest at an average groundwater flow direction and magnitude of 312° and 0.0006 ft/ft. From October 1995,through today, the groundwater flow direction has been consistently towards the southeast,at an average direction and magnitude of 143°and 0.0008 ft/ft. The groundwater flow direction has been toward the southeast for the past 13 sampling events,indicating a stable flow regime. Due to the switch in flow directions, previous downgradient wells are now upgradient wells. Prior to the switch in groundwater flow directions,the extent of the plume was defined horizontally by monitoring wells MW-DIS-3,MW-DIS-BS,MW-DIS-9,and MW-DIS-10.The vertical extent downgradient of the source area was defined by monitoring well MW-DIS-BD. Currently, the extent of the plume in the southeast direction is unknown. Analytical results from all wells at the site have been extremely consistent,with the exception of monitoring wells MW-DIS-1 and-2,which have had significant reductions in concentrations of petroleum hydrocarbons. There have been no confirmed detections of oxygenates at this site. Tert-butanol(TBA)has been detected a single time in five different wells. TBA was detected in monitoring wells NP-1-70',NP-1-90',and SVE-North on December 23, 1997. TBA has not been detected in any of these wells during the past five consecutive sampling events. TBA was detected in 1 monitoring wells MW-DIS-1,and SVE-South on.May 21, 1998. TBA has not been detected in these wells during the past five consecutive sampling events. The Disco tanks were in operation between 1966 and 1976. MTBE was first used as an octane booster in the mid- 1980's,and widespread use began in the 1990-1992 period in order to meet air quality requirements. Therefore,it is highly unlikely that the gasoline released from the Disco site contains oxygenates. Recommendations Extent of Plume Monitoring points are needed downgradient of the site, and the vertical extent of the plume directly beneath the source area needs to be determined.An additional site characterization investigation is currently scheduled to address these issues. Frequency of sampling The Disco site has accumulated a large data set of groundwater sample results since . r monitoring began in 1991. Monitoring wells containing petroleum hydrocarbons have either 3 i i