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9.0 CONCLUSIONS and RECOMMENDATIONS <br /> Based on the reviewed UST records and the UST system inspection and testing it appears that, <br /> with an exception of minor spills due to automobile drive-offs, there have been no significant <br /> releases from the UST system. Each drive-off may have released as much as one pint of gasoline <br /> and may have been a source of the detected concentrations of petroleum hydrocarbons and <br /> MTBE in groundwater. <br /> Based on the results of this investigation, the groundwater beneath the site appears to be only <br /> slightly impacted by petroleum hydrocarbons, with the exception of MTBE. The maximum TPH- <br /> G and BTEX concentrations detected in the soil borings were 1700pg/1 and < 0.5 pgA, <br /> respectively, at a depth of 10 feet bgs in soil boring SB-1, which is located approximately 25 feet <br /> down-gradient of the pump island. MTBE at this location was detected at a concentration of <br /> 1,800 pg/L. It appears that MTBE has migrated a short distance, to the east southeast, generally <br /> down gradient from site, in the vicinity of soil borings SB-1, and to a lesser extent, in the vicinity <br /> of soil borings SB-2, SB-3. The concentrations of MTBE in the upper aquifer decreases to non- <br /> detectable at soil boring SB-3. Relatively low concentrations of MTBE were detected in the <br /> lower aquifer at soil boring SB-3. <br /> Concentrations of petroleum hydrocarbons in groundwater at the site generally appear to be <br /> naturally attenuating. However, in order to monitor the down-gradient extent of MTBE at the <br /> site, ATC Associates recommends installing a well cluster (an upper aquifer well and a lower <br /> taquifer well) to the east of soil boring SB-3 in the parking area near the "Burger King" fast food <br /> restaurant. <br /> J:Un RopessWKSr0F QS 132(9003)WP0RTs12000ti &Mn70 W-dM 15 ATC Associates Inc. <br />