|
Fate and Transport of PCBs in the Subsurface
Since 1988, SSP&A
staff members have participated on an expert panel assembled by the
Texas Eastern Transmission Corporation to develop feasible remedial
alternatives for sites contaminated with polychlorinated biphenyl (PCB)
compounds in soil and groundwater. The Texas Eastern Groundwater Panel,
directed by Dr. Charles Andrews, President of SSP&A,
conducts investigations on the behavior of PCBs in the subsurface
environment and the chemical properties of PCBs and their degradation
products. These investigations include laboratory and field studies in
biodegradation, surfactant chemistry and transport, PCB transport and
sorption, and the behavior of DNAPL in the subsurface, and field testing
methods for PCB solubilization and recovery in fractured and porous
media.
PDF
Figure
Research Efforts
at the University of Alabama
Dr. Chunmiao Zheng, developer of the MT3D code and liaison of SSP&A,
is currently leading an interdisciplinary research team at the
University of Alabama to develop a comprehensive framework for designing
pump-and-treat groundwater remediation systems. The project integrates
groundwater simulation, optimization, and parameter estimation
techniques to design groundwater pump-and-treat systems which meet
various physical, environmental, and budgetary constraints. The key
components of the framework are Modflow and MT3D, two of the most
popular flow and transport simulation models used in groundwater
remediation designs. These simulation models are being coupled with an
optimization model to automatically determine optimal well locations and
pumping/injection rates under realistic field conditions. In addition,
the optimization model is capable of optimizing flow and transport
parameters required by the simulation models. This makes it possible to
automatically update flow and transport parameters, and accordingly, the
well locations and pumping/injection rates, based on the monitoring
results after the remedial operation has begun.
Several additional research projects are underway as part of the
comprehensive simulation-optimization framework. Alternative
optimization approaches, including differential dynamic programming,
simulated annealing, and generic algorithms, are being investigated for
their efficiency and flexibility in developing optimal remediation
designs and parameter estimation under realistic field conditions. New
and improved numerical algorithms are being incorporated into the MT3D
code to significantly increase the computational efficiency that is
essential to a simulation-optimization approach. The feasibility of
linking MT3D with a multi-species geochemical code is also being
studied. This linkage could dramatically enhance the ability of the MT3D
code to simulate more sophisticated chemical reactions and
bioremediation.
Parameterization
and Predictive Analysis in Environmental Modeling
Watermark Numerical Computing (creator of PEST), SSP&A,
and the Department of Environmental Engineering, University of
Queensland are undertaking collaborative research to improve
environmental data processing through the use of numerical models,
pooling resources and expertise to improve the use of computer
simulation in environmental management.. The theme of much of this
research is parameter estimation and predictive uncertainty analysis.
More details here.
Assessment of
Performance Limitations of Soil-Vapor Extraction
SSP&A
participated in a comprehensive assessment of soil-vapor extraction as a
remedial technology for volatile organic compounds. The study was
initiated as part of an evaluation of the effectiveness of a soil-vapor
extraction system in operation at a Superfund site. Although the
extraction system had removed a significant quantity of volatile organic
compounds from the soil, clean-up levels had not been met and the mass
of contaminant remaining was found to be several thousand times greater
than that predicted by the initial studies on the performance of the
extraction system. Site conditions such as variability in the physical
and chemical characteristics of the soils were found to have a profound
influence on the performance of the soil-vapor extraction system. The
work summarized the fundamental chemical and physical phenomena which
can influence the effectiveness of soil-vapor extraction systems on a
practical field-scale, and described the scientific basis upon which the
performance of the systems can be evaluated and predicted. |
