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Description
Petroleum hydrocarbons differ in their composition and in their potential to contaminate groundwater. The effective solubilities of BTEX from gasoline were found to be 27 mg/l, 54 mg/l, 4 mg/l, 15 mg/l (m+p-xylene) and 8 mg/l (o-xylene), respectively. The effective solubility of gasoline additive, methyl-tertiary-butyl ether (MTBE) was estimated to be higher than 5 mg/l. They were all above the maximum contamination levels (MCLs) set for drinking water. MTBE and benzene were not found in kerosene-saturated water. Toluene, ethylbenzene, m+p-xylene and o-xylene (TEX) were found to be 1.7 mg/l, 3.2 mg/l, 5.3 mg/l (m+p-xylene) and 3.4 mg/l (oxylene), respectively. TEX were above MCLs. In diesel No. 2-saturated water, MTBE was estimated to be higher than 0.150 mg/I. The concentrations of BTEX were 0.159 mg/l, 0.922 mg/l, 0.228 mg/l, 0.844 mg/l (m+p-xylene), and 0.506 mg/l (oxylene), respectively. Of them, MTBE, benzene, toluene were above MCLs but ethylbenzene, xylenes were all below MCLs. Gasoline and kerosene columns were designed to evaluate the order of BTEX elution and their changes in water soluble fraction (WSF) concentration from residual NAPL saturation of gasoline and kerosene. The order of elution was benzene first, toluene second, then ethylbenzene, m+p-xylene, and o-xylene. After 250 pore volumes of water were passed through the column, tailing concentration of BTEX were still found to be 0.063 mg/l, 0.096 mg/l, 1.2 mg/l, 7 mg/l (m+p-xylene), and 1.7 mg/l (oxylene), respectively in the Gasoline Column. MTBE was below the detection limit at the end of the column test. BTEX were still above the MCLs. At the end of the Kerosene Column test, only toluene was found to be higher than MCL. The concentrations of TEX were 0.016 mg/l, 0.059 mg/l, 0.367 mg/l (m+p-xylene), and 0.140 mg/l (o-xylene). The field LNAPL sample was collected from a site where the hydrocarbon fuels released more than ten years ago. MTBE was not found in the field LNAPL-saturated water. However, benzene was still found at 0.384 mg/l, much higher than MCL. Toluene was found in a low concentration of 0.028 mg/l. Ethylbenzene, m+pxylene were 0.386 mg/l, 0.305 mg/l respectively. O-xylene was not found in the field LNAPL-saturated water. We may conclude that the environmental threat from gasoline release is more serious than that from kerosene and diesel No. 2. A mass-balance model was used to predict the order of elution and the concentrations of the contaminants with the same input parameter as Gasoline Column. The predicted order of elution was the same as observed from the column test: benzene, toluene, then ethylbenzene, xylenes. A reduced residual NAPL saturation was require to have a better match in the absolute elution time between model and the Gasoline Column test.
