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$\sb{\rm w}$/v$\sb{\rm c}$ 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$\sb{\rm ow}$ 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.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/16332 |
| Date | January 1990 |
| Creators | Clark, Gary Lee |
| Contributors | Tomson, Mason B. |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | 105 p., application/pdf |
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