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6.0 Dicussion 6.9 Conclusions 6 1 1 MW-4 MW-4 was installed down gradient (at the time) from MW-2 to detect possible movement of used motor oil in the groundwater from the contamination source (former waste oil USTs at MW-2) No oil has been detected in the groundwater at MW-4, indicating that used oil contamination has not spread down gradient from MW-2 as far as MW-4 jqt Groundwater from MW-4 continued to show contamination from TPH-gasolme, oxygenates (except MTBE) and BETX The TPH-gasolme contamination decreased significantly this quarter The source of the gasoline contamination remains unknown at this time Figure 10 shows how the groundwater elevation affects the TPH-gasoline concentration As the groundwater elevations rise,the contamination levels also rise 1 j MW-4 has remained free from TPH-diesel contamination since second quarter 2002 6 1 2 WASTE OIL USTs The former waste oil USTs caused significant contamination of the soil and groundwater immediately adjacent to the tanks Substantial quantities of oil have been removed from MW- 2,however,contamination remains The used oil appears to move very slowly through the soil and in relatively close proximity to the former USTs location . Analysis of MW-2 continued to show contamination from TPH-diesel and TPH-motor oils Oxygenates appeared at an increased concentration than previous quarter MW-2 showed contamination from motor oils as reflected in the amount of floating oil removed during the past quarter and the analytical results The level of oil contammnation has dropped continuously from 2001 MW-1, MW-3 and MW-4 continue to remain free of motor oils contamination, indicating that they have not been affected by contamination from the former used oil USTs 6 1 3 DIESEL USTs MW-1 (site of the former diesel USTs) continues tomi how contanation from diesel The TPH-diesel contamination level, as shown in Figure T, dropped below the reporting limit in June 2001, peeked at 72000 ppb in June 2002, decreased through Sept 2003, increased in March 2004,and,after a slight decrease since March 2004,continues to increase r The former diesel USTs caused moderate contamination of the soil and groundwater adjacent to the tanks Diesel contamination was detected in MW-2 (northeast of MW-1) and MW-3 (southeast of MW-1)m April 2000 This was not evident in later samples until December 2001 (MW-1, MW-2 and MW-4) and March 2001 (MW-3)when contamination was detected again Since that time, the diesel contamination in MW-3 and MW4 has disappeared The contamination in MW-2 remains although it is decreasing overall 4 6166