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Reniedlai>on Plan Cleanup and Abatement Order No -00-707 EAI Project No 1232 event (MW-l0A at 1 2 µg/L and MW-18 at 4 2 µg/L) The highest deep zone benzene ' concentration was in monitoring well MW-25D at 2,500 4g/L (see Figure 12) 35 Fuel Oxygenates ' Fuel oxygenates, e g , MTBE, TBA, DIPE, ETBE, TAME, EDB, ethanol or methanol (based on EPA Method 8260B) are not chemicals of concern ' 3.6 Findings Based on the results of the latest soil and ground water quality assessments, the following are inferred • Historical operation of the RIW drew fuel hydrocarbons present beneath the Unocal and Wards sites to the RIW, impacting ground water beneath Pacific Avenue and Robinhood Drive 0 Ground water flow direction for the area (when the RIW is not in operation) is easterly • The highest concentrations of dissolved hydrocarbons are present in Unocal well MW- 25D, which is screened from 61 to 66 feet bgs No dissolved hydrocarbons above the laboratory reporting hi-nit were detected in well MW-25S, which is screened from 25 to 45 feet bgs and located immediately next to well MW-25D • Unocal well MW-23S/D is the most downgradient well (when the RIW was formerly in operation) and the deepest well located on the Unocal site Well MW-23 S/D is slotted between 86 and 91 feet bgs, and from 97 5 to 102 5 feet bgs TPH-G at 1,510 tig/L and ' 242 dig/L was detected in MW-23S in March and May 2001 and at 1,420 µg/L and 138 4g/L in MW-23D, respectively Benzene at 59 4 and 11 8 ltg/L was detected in MW- 23S in March 2001 and May 2001 and at 60 9 and 12 3 pg/L in MW-23D, respectively ' These data indicate the vertical extent of contamination has not been defined in this area of the project Further, since well MW-23S/D is located in the downgradient access of the plume (when the RIW was formerly in operation) from well MW-25D, it is probable that the vertical extent of ground water contamination in the area between these two wells extends to depths of 100 feet bgs i Well MW-22S/D is located in the vicinity of the RIW and screened from 30 to 50 feet bgs, and from 61 to 66 feet bgs No dissolved hydrocarbons above the laboratory reporting limit were detected in well MW-22S in March and May monitoring events TAH-G (1,800 µg/L and 890 µg/L) and benzene (140 µg/L and 93 9 pg/L) were detected in well MW-22D • Well M W-24S/D is the well located ciosest to the RIW ana screenea from 85 to 90 feet bgs, and from 98 to 103 feet bgs This is the deepest screened well associated with this ' project TPH-G (2,660 µg/L and 6,710 µg/L) and benzene (538 ltg/L and 1,220 µg/L) were detected in well MW-24S in March and May 2001 monitoring events, respectively In March 2001, no dissolved hydrocarbons above the laboratory reporting limits were detected in well MW-24D In May 2001, TPH-G (111 �tg/L) and benzene (41 9 �tg/L) were detected in this well 65 1232P RAP ADD -5- ' ENVIRONMENTAL AUDIT,INC®