Influence of Coupled Processes on the Fate and Transport of Industrial Mixed Waste Plumes in Structured Media

v1-3/6/97

Objectives:

The specific objectives of the research are (1) to use laboratory and field scale experiments to quantify the rates and identify the mechanisms controlling the fate and transport of industrial mixed waste in structured media, (2) to develop an integrated high performance biophysicochemical supercomputer model for predicting mixed waste migration that is influenced by coupled processes, (3) to design and develop a network based visualization interface for the supercomputer model, (4) to verify the model with standard example problems in the literature and validate the model with the multi-scale experimental data sets obtained above, (5) develop an economical framework for risk-based cost-benefit analysis and conduct the analysis using the multi-scale experimental data set, and (6) establish the minimum site characterization necessary to adequately predict contaminant migration.

Approach

The objectives are satisfied by four integrated, multidisciplinary tasks. Task 1 is dedicated to providing multiscale experimental investigations on the influence of physical, chemical, and microbial processes on multispecies toxic metal transport. Task 2 is committed to providing a high performance biophysicochemical model that is interfaced with an advance visualization system and may be used for predicting the mobility of industrial mixed waste in complex subsurface environments. Task 3 merges the efforts of Tasks 1 and 2 for the purpose of validating the model for industrial field-scale applications. The validated model will then become the foundation of risk-based cost-benefit analyses for several remediation scenarios designed to stabilize toxic metal plumes in situ. Lastly, Task 4 will use the validated code to quantify the uncertainties inherent to model predictions and to identify minimum parameter requirements for adequately predicting the transport and stabilization of contaminants in subsurface environments.

Task 1 Transport of Toxic Metals and Multiple Scales

Investigations designed to provide an improved understanding of the fate and transport of industrial contaminants influenced by coupled processes (physical/chemical/microbial) in subsurface environments will involve multiscale experimentation using undisturbed columns (0.2 m X 0.5 m), well-characterized field scale pedons (2 m X 2 m X 3 m), and a well-characterized existing field facility (1-2 ha). The toxic metals Cd, Cr, and Co will be used since they have been classified as priority pollutants in soil and groundwater at many industrial waste sites. Historically, industrial processes have co-disposed toxic metal waste with chelating organic ligands such as ethylenediaminetetraacetate (EDTA). Therefore, will use contaminant tracers 109Cd and redox active 57Co(II), 58Co(II), and 51Cr(VI) in the presence of the complexing agent EDTA. The advantage of using radioisotopes as tracers is that their detection limits are extremely low and they decay to stable isotopes on the time scale of days to years. The contaminant tracers will be used to investigate mixed waste fate and transport in structured media, that is influenced by hydrodynamics (preferential flow and matrix diffusion), microbial reduction and biodegradation, and geochemical oxidation and sorption. The specific details of our experimental design are outlined in the FWP ERKP268.

Task 2 Development of a High Performance Biohydrogeochemical Flow and Transport Model with an Integrated Visualization System

A novel high performance biophysicochemical model will be developed that rigorously simulates individual and coupled physical, chemical, and microbial processes during multispecies transport. Code development will be initiated simultaneously with data collection in Task 1. A currently available multicomponent hydrogeochemical code (3DHYDROGEOCHEM) will be modified to incorporate chemical kinetics and microbial reduction and biodegradation processes. It will then be ported onto the ORNL Intel Paragon supercomputers. The computational capabilities of the Intel Paragons is an insurance for the full-spectrum coverage of the multiscale, biophysicochemical heterogeneities that would otherwise be downplayed on less powerful computational platforms. The resulting coupled processes code will be verified to ensure numerical robustness. The code will then be integrated with a remote steering system. An AVS (Application Visualization System) graphical user interface will be built to provide easy-to-use problem formulation capabilities and control of model execution and interpretation of model results. The specific details of our theoretical and numerical design are outlined in FWP ERKP268.

Task 3 Model Validation for Industrial Field-Scale Application and Cost-Benefit Analysis of Remediation Designs

The multiscale experimental efforts of Task 1, combined with previous data collected from these subsurface facilities, will be used to parameterize the high performance biohydrogeochemical transport model developed in Task 2. This is accomplished using scaling factors determined for functional properties at a reference location (column or pedon) and applied to the field facility using a similar media concept. A frequency distribution of scaling factors will be used to account for heterogeneity of soil properties. The validated model will then be employed to conduct risk-based cost-benefit analysis. Three remediation scenarios will be used to demonstrate the applicability of the biophysicochemical model in the assessment of various in situ remedial strategies designed to stabilize toxic metals. The remediation scenarios include (1) monitoring only, (2) geochemical barriers, and (3) microbial biowall barriers. The specific details of this task are outlined in FWP ERKP268.

Task 4 Uncertainty and Minimum Parameterization Requirements

The biophysicochemical model that was validated in Task 3 will be utilized to identify the minimum parameter characterization required to adequately predict subsurface mixed waste transport within defined confidence limits. The transport model will be stochastically applied using knowledge of the spatial correlation properties by applying a Monte Carlo technique with the Latin Hypercube sampling method. The specific details of this task are outlined in FWP ERKP268.

Benefits

This research will significantly improve our understanding and predictive capability of mixed waste fate and transport processes that are influenced by coupled hydrological, geochemical, and microbial processes. Further it will provide an excellent designing tool for facilitating the exploration of solutions for industrial waste management problems and energy sources recovery. Industry has not historically benefited from the development of these complex models because of a lack of computational capabilities and because of the difficulty in using the resulting models. The proposed effort would significantly reduce these barriers because the code will be available to industry at the Computational Center for Industrial Innovation, a DOE national user facility at ORNL, and because the user interface and visualization capabilities would relax the steep learning curve of the software system. The proposed effort provides a paradigm for the streamlining of decision-making processes, for the management of municipal and industrial mixed waste streams, and the design and development of more cost-effective methods to utilize and recover natural resources.

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J.P. Gwo -- email: g4p@ornl.gov