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SECOR <br /> 12.0 CONCLUSIONS AND RECOMMENDATIONS <br /> The TPHg plume is adequately evaluated to the northwest and east in zone "A"; to the north, <br /> east, and southeast in zone "B"; to the east and west in zone "C"; and to the north/northwest <br /> and east in zone "D". The TPHd plume is adequately evaluated to the south and northeast in <br /> zone "A", to the northeast and southeast in zone "B", to the west and northeast in zone "C", and <br /> to the north in the "D" zone. The benzene plume is adequately evaluated to the northwest, east <br /> and south in zone "A", to the northwest, east and southeast in zone "B", to the northeast and <br /> west in zone "C", and to the northeast in the "D" zone. MTBE is adequately evaluated to the <br /> east, south-southeast and northwest in zone "A", to the north northeast and southeast in zone <br /> "B", to the east and west in zone "C", and to the north and east in the "D" zone. <br /> Overall hydrocarbon concentration trends in groundwater beneath the site appear relatively <br /> stable, and likely fluctuate seasonally with changes in groundwater elevation. The following is <br /> noteworthy during the first quarter 2006: <br /> • Historically high concentrations of benzene were detected in "A" zone wells TONT-8 <br /> (2,300 Ng/L), TS-1 (13 pg/L), and TS-5 (540 Ng/L). <br /> • Historically high concentrations of MTBE were detected in "B" zone wells AR/MWAB <br /> • (170 pg/L), AR/MW-11B (270 pg/L), AR/MW-14B (1,100 pg/L), and PS/MW-20 (24 pg/L). <br /> • An historical high concentration of TPHg was detected in "A" zone well TS-9 (220 pg/L) <br /> • An historical high concentration of TPHd was detected in "B" zone well AR/MW-14B <br /> (1,300 pg/L). <br /> • Historically low concentrations of benzene were detected in "A" zone well TS/M-2 (5,400 <br /> pg/L) and "C" zone wells TS/MW-1 C (<0.50 pg/L) and AR/MW-8C (10 pg/L). <br /> • An historical low concentration of MTBE was detected in "A" zone well TS/MW-1A (23 <br /> Ng/L). <br /> • An historical low concentration of TPHg was detected in "C" zone well AR/MW-8C (<50 <br /> Ng/L). <br /> The evaluation of concentration trends in the ozone system monitoring program wells indicates <br /> that the ozone sparge systems are reducing dissolved hydrocarbons in groundwater at the site; <br /> therefore, SECOR recommends continued operation of the ozone sparge systems. <br /> • <br /> STTC 1006 Final Report 23 May 1,2006 <br /> 770T.43673.12.0002 <br />