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6.0 Dlcussion 6.9 Conclusions 6.1.1 MW-4 j MW4 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 MW4, indicating that used oil E contamination has not spread down gradient from MW-2 as far as MW4 Groundwater from MW4 continued to show contamination from TPH-gasoline, oxygenates 1:1i11� A-r� (except MTBE)and BETX The TPH-gasoline contammation continues to decrease throughout j I the years 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 n a r s U V-'-7 ; MW4 has remained free from THP-diesel contamination since June 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 i , , . Analysis of MW-2 sampled on 06/16/04 continued to show contamination from MTBE, DIPE, TPH-diesel, and TPH motor oils BTEX and TPH-gasolme reappeared at concentrations lower a5 0 than previous quarters MW-2 showed contamination from motor oils as reflected in the 1 amount of floating oil 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 `fib 0 remain free of motor oils contamination, indicating that they have not been affected by �p contamination from the former used oil USTs 6.1.3 DIESEL USTs 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 reporting limit in June 2001,peeked at 72000 ppb in S 2001 and has continued to decrease since then 0a=�yLl G y 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 'r�'J'c (southeast of MW-1) in 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 MW-4 has disappeared The contamination in MW-2 remains although it is decreasing overall The presence of diesel contamination in MW-2 indicates that diesel contamination is still affecting groundwater , ' quality(Figure 6) i i 4