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6.0 TDicussion 6.1 Conclusions t61.i MW-4 MW-4 was installed down gradient (at that 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 MW4, indicating that used oil contamination has not spread down gradient from MW-2 as far as MW4 I Groundwater from MW4 continued to show contamination from TPH-gasoline, oxygenates d BETX The TPH-gasoline contamination has decreased significantly from 18500 ppb to I '540 ppb MW-4 has remained free from THP-diesel contamination since June 2002 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 f 6 1 2 WASTE OIL UST The former waste oil UST 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 UST location Analysis of MW-2 sampled on 03/10/04 continued to show contamination from TPH-diesel, ' TPH-motor oils, MTBE, TBA and DIPE BTEX and TPH-gasoline were not detected this quarter MW-2 showed contamination from motor oils as reflected in the amount of floating oil f removed during the past quarter and the analytical results The level of oil contamination has dropped continuously from 2001 MW-1, MW-3 and MW4 continue to remain free of motor oil contamination, indicating that they have not been affected by contamination from the former used oil UST . f 3 6.1 3 DIESEL USTs E MW-1 (site of the former diesel USTs) continues to show contamination from diesel The ' TPH-diesel contamination level, as shown in Figure 5, dropped below the detection limits in I E June 2001,peeked at 72000 ppb in J THI"UrLt - I y d has continued to decrease since then VON /rY ' I 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-3F 91 (southeast of MW-1) in April 2000 This was not evident in lateir amples until December 2001 (MW-1 and MW-4) and March 2002 -2) ,heir contamination as ected again Since that time,the diesel contamination in MW-4 has disappear The contamination in MW-2 remains although it is decre consistent y presen of dies contamination in g g tMW-2 indicates that diesel conta matron is still affecting grou water quality Figure 5)0 i The reversal of trends over/the past 3 years may have resulted from the extreme changes in groundwater elevation,this is illustrated in Figure 9 f i