Characterization and Evaluation of Vertical Hydraulic Conductivity Variations as They Contribute to Nonideal Transport Behavior at a Superfund SiteEPA Grant Number: U915031
Title: Characterization and Evaluation of Vertical Hydraulic Conductivity Variations as They Contribute to Nonideal Transport Behavior at a Superfund Site
Investigators: Blue, Julie E.
Institution: University of Arizona
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1996 through July 26, 2000
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996) RFA Text | Recipients Lists
Research Category: Fellowship - Geology , Academic Fellowships , Ecological Indicators/Assessment/Restoration
The objective of this research project is to determine possible causes of reduced efficiency of a pump-and-treat operation at a trichloroethene (TCE)-contaminated Superfund site. Influent TCE concentrations in the system have leveled off at approximately 100 ppb, despite significant earlier reductions.
Pump test results and water level data collected during a dual-well, forced-gradient field experiment were used to obtain a vertically averaged hydraulic conductivity. Bromide concentration data were used to calibrate a vertically averaged longitudinal dispersivity in a numerical model. This dispersivity was compared to results from similar sites. Bromide data collected from a multilevel sampling well were then used to construct a perfectly stratified four-layered model. Travel time calculations were performed, and they were used with Darcy's law and an analytical solution to obtain vertically discrete conductivity values for the model. Vertically discrete longitudinal dispersivities then were calibrated.
Two sublayers will be added to the numerical model to obtain a six-layered model that adequately simulates the double-peaked behavior observed in two of the layers modeled previously. The velocities from this model will be used in a TCE transport model. Rate-limited diffusion out of the low conductivity zones, delineated by the tracer modeling, will be incorporated into the model through the use of laboratory-determined parameters for rate-limited desorption and intraparticle mass transfer. The model will be tested by comparison with measured TCE elution data. Recommendations will be formulated regarding alternative remediation strategies based on the processes that contribute most significantly to TCE transport and fate at this site. If the TCE elution data can be accurately matched, it may be appropriate to apply the procedures used here at other, similar sites.