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This MTBE concentration is a significant decrease in concentration from <br /> the November 1999 results In addition, the TBA concentration of 44 p p b <br /> is a significant decrease in concentration from the November 1999 <br /> concentration of 2,700 ppb <br /> I collected from monitoring wells MW-13 and MW-14 <br /> Groundwater samples g <br /> contained 490 ppb and 38 ppb MTBE, respectively Both of these wells are <br /> downgradient of the site These MTBE concentrations exceeded the DHS <br /> MCL for drinking water The groundwater sample collected from <br /> I monitoring well MW-13 also contained 100 ppb TBA Since these <br /> monitoring wells are the furthest downgradient monitoring wells from the <br /> site, the downgradaent extent of contamination is still undefined <br /> Groundwater samples collected from shallow monitoring wells MW-1, <br /> p g <br /> MW-2 and MW-15 dad not contain concentrations of any compounds <br /> above DHS MCLS for drinking water <br /> I In locations where significant contamination as present and "clustered" <br /> wells are screened an different zones, there is a significant decrease in <br /> concentrations with depth This relationship as present in wells MW-6, <br /> MW-7 and MW-8 between the USTs and the building and an wells MW-5 <br /> and MW-11 downgradient of the USTs <br /> None of the wells screened below 19-feet bgs contained any compound at <br /> concentrations exceeding DHS MCLS However, various compounds were <br /> detected in groundwater samples collected from all of these wells at <br /> concentrations below DHS MCLS including MTBE, TBA, PCE and 1 ,2- <br /> dachloropropane In addition, ethanol was detected in groundwater <br /> samples collected from three of these deeper wells The highest ethanol <br /> concentration was 58,000 ppb an the groundwater sample collected from <br /> monitoring well MW-12 Ethanol was not present an any of the <br /> groundwater samples collected from wells screened above 19-feet bgs <br /> Ethanol as an alcohol used an some fuels as an oxygenate <br /> IGroundwater in the shallow zone (less than 19-feet bgs) appeared to flow <br /> primarily to the northwest beneath the site at a gradient of approximately <br /> 0 012-feet/foot If anomalous water levels are disregarded, the <br /> potentaometric surface shows groundwater flow to the northwest at a very <br /> flat gradient of 0 0007-feet/foot Groundwater an the 55 to 70-feet bgs <br /> Izone flowed to the east at a gradient of 0 002-feet/foot Potentaometric <br /> surface measurements an locations with monitoring wells screened at <br /> multiple depths also suggest a downward vertical groundwater gradient <br /> I Franks One Stop Report — May 2000 <br /> -14- <br />