Flow rate effects on the sorption of methylated benzenes in saturated aquifer materials

[摘要] The rate of movement of contaminants in groundwater is a topic of environmental importance and public concern. Early work in contaminant transport showed that the ratio of the velocity of the water to the velocity of the contaminant (v$sb{m w}$/v$sb{m c}$ or retardation, R) in a flowing saturated soil column can be determined using known values of soil density, soil porosity, percent organic carbon in the soil, and the octanol-water partition coefficient of the contaminant. More recent studies indicate that the retardation of the contaminant in a soil may vary due to soil/contaminant isotherm non-linearity and non-equilibrium conditions in the column. In this research, the effect of velocity on the observed retardation of methylated benzenes is evaluated using three different soils (organic carbon range--0.008% to 0.27%) and a wide range of linear velocities (0.2 ft/day to 40 ft/day). Contaminant solutions of 10 mg/l benzene, toluene, p-xylene and mesitylene, 1 mg/l naphthalene, and 50 mg/l ethylbenzene were pumped through a 0.9 cm ID saturated soil column into a UV/Vis flow-through spectrophotometer for detection of contaminant breakthrough. Breakthrough and flush-out curves, in general, were found to be symmetric, regardless of velocity or contaminant used. Below a velocity of 3 ft/day, compounds with K$sb{m ow}$ values of $>$10$sp3$ showed an increase in retardation with decreasing velocity. Data were fitted to both an equilibrium and non-equilibrium model with one variable parameter. Results indicated that the data could not be modeled by the non-equilibrium model but did fit the equilibrium model with variable retardation.

[发布机构] Rice University