Laserfiche WebLink
3 4 2 Dissolved H carbon Mass in Groundwater <br /> Based on the cumulative groundwater analytical results, groundwater beneath the site appears to <br /> be impacted by TPH-as-gasoline, BTEX compounds and MTBE beneath the south end of the <br /> former gasoline UST The hydrocarbon mass in groundwater is calculated using the following <br /> assumptions <br /> • The concentrations of gasoline compounds detected over the past eight quarters at MW-1 <br /> extend approximately 50 feet away from MW-1 <br /> • The thickness of the impacted groundwater interval is approximately 10 feet <br /> • The estimated porosity of the groundwater-bearing interval is approximately 35 percent <br /> Mass = Volume of impact cu ft x Concentration WWI) x 7 481gallons/cu ft x 8 0 Ibl allon <br /> ix 109 <br /> The average concentrations\(based on the past eight quarters of analytical data from MW-1) <br /> TPH-Gasoline Benzene Toluene Ethylbenzene XylenesMTBE <br /> 19,625 1,324 1,124 -1,353 4,138 15 <br /> The mass (in pounds) in groundwater for each compound is <br /> TPH-Gasoline Benzene Toluene Ethylbenzene Xylenes MTBE <br /> ' 0 805 0 056 0 Q46 Q D56 0 172 0 001 <br /> 3 5 Plume Disposition Over Time <br /> For eight consecutive quarters of groundwater monitoring, the groundwater flow direction has <br /> remained consistent toward the northeast For the first six quarters of groundwater sampling, the <br /> plume of impacted groundwater appeared to be confined to the area around MW-1, and the <br /> concentrations of gasoline compounds in MW-1 appeared to be relatively stable In the last two <br /> quarterly sampling events on March 24, and June 18, 2004, concentrations of MTBE were <br />' detected in the perimeter wells (MW-2 and MW-3) As such, it appears that MTBE has migrated <br /> away from the source area in the downgradient direction , <br /> 10 <br />