A field study was conducted to determine the rapidity and extent of xylene movement after simulated spills on undisturbed soils of diverse texture and structure. To monitor xylene movement, porous ceramic suction cups and newly developed pan samplers were installed at a depth of 61 cm at two locations in each of three soils. A volume equivalent to a depth of 5 cm of dye labeled xylene was spilled on one plot of each soil contained in large lysimeters. Split applications of 1.25 cm depth equivalent were also made 21 days apart on one lysimeter of each of the soils.
Significant quantities of xylene were detected at the 61 cm depth approximately 1 day, 1 hr, and 0.5 hr after the 5 cm application in the loamy sand, silt loam, and clay, respectively. Xylene movement after the first 1.25 em of the split xylene application was almost as rapid as after the 5 cm application. However, with the second 1.25 cm application of xylene, free xylene was collected in the leachate at the 61 cm depth for all three soils. Dye patterns observed upon excavation of the soils indicated that the xylene moved as a relatively uniform front in the sand but moved through isolated macropores between structural units in the silt loam and clay soils.
The free drainage pan samplers were more effective than the porous ceramic suction samplers in monitoring the movement of xylene in all three soils at high soil moisture contents. The porous cup samplers were ineffective in the well structured clay soil, possibly due to being bypassed by the xylene moving through isolated macropores. Xylene concentrations from the porous cup samplers were often lower than those from the pan samplers. The lower concentrations are thought to be partially due to losses of xylene by volatilization when a vacuum was applied to collect the samples. * Contribution of Texas Agricultural Experiment Station.