ETPI Progress Report - March 1997

Experimental Progress (PI - Jardine)

We have obtained 10 undisturbed columns of weathered fractured shale from the Oak Ridge Reservation. Numerous experiments are underway that investigate the fate and transport of ⁵⁷Co(II)EDTA, ⁵⁸Co(III)EDTA, ¹⁰⁹CdEDTA, ⁹⁰Sr, and ⁵¹Cr(VI). The experiments are conducted using single and multicomponent mixtures of the toxic metals and radionuclides.

Results to date show that:

1. Co(II)EDTA is oxidized to Co(III)EDTA during transport through the soil. Subsurface Mn- and Fe-oxides catalyze this redox reaction. The environmental implications of this reaction are pronounced, since Co(III)EDTA is extremely stable and this enhances its mobility and persistence in subsurface environments. Incorporating metal-reducing bacteria into these systems should enhance the reduction of Co(III)EDTA to less stable Co(II)EDTA, with this latter species being more readily dissociated by geochemical reactions. The bioreduction experiments are currently being designed.

2. Cr(III) and Cr(VI) are both strongly sorbed to the soil during transport in the soil, with retardation factors near 450 and 20, respectively. Cr(III) is partially oxidized to Cr(VI) during transport, and this fact coupled with the lower retardation factor of Cr(VI) enhances its mobility in subsurface environments. The environmental implications of these reactions are pronounced since Cr(VI) is a potent carcinogen and is quite toxic. Incorporating metal-reducing bacteria into these systems should enhance the reduction of Cr(VI) to the less soluble, more highly reactive Cr(III) species. The bioreduction experiments are being planned.

3. Transport of CdEDTA in these soils is affected by geochemical solid phase dissociation reactions. It appears that solid phase Fe- and Al-oxides dissociate the Cd-EDTA complex and free Cd²⁺ and Fe(III)EDTA and Al(III)EDTA form. This is advantageous from a remedial prospective, since Cd will be significantly reduced due to electrostatic adsorption on the soil.

These experimental results are being used to provide mechanisms and rates of key geochemical and microbial processes for future field scale experiments. They will be modeled using the numerical codes described below.

We have also filed a rather lengthy application with the State of Tennessee to perform our groundwater radiotracer experiment. A favorable decision should be made soon.

Numerical Modeling Progress (PI - Gwo)

A hydrogeochemical computer model has been developed and tested for field-scale computer simulations of coupled solute transport and chemical kinetic and equilibrium reactions. The computer model was shown to be mathematically robust and is currently being merged with a microbiological module so that the model can be used to study the coupled chemical and biological processes. The model will soon be used to simulate the multispieces contaminant transport experimental data described above.

A high-performance multiregion groundwater flow code was developed to utilize the nation's developing supercomputing infrastructure. This computer code was tested using a pumping well problem and the result will be presented in a supercomputing conference in Atlanta, April, 1997. Manuscript of the presentation can be found at http://www.csm.ornl.gov/~g4p/hpc97_2/hpc97_2.html. This computer model will provide important groundwater flow information to the hydrogeochemical model so that the entire spectrum of coupled physical, chemical and biological processes in the groundwater can be studied on the basis of our state-of-the-art understanding of these processes. We encourage you to peruse the website.

Visualization Progress (PI - Hoffman/Gwo)

Using both modeled and measured data from the Melton Branch Watershed (a field facility where the soil columns were taken and the pedon is located), scientific data visualization components were built to display 3-dimensional data. These visualization methods include a 3-dimensional display of soil types/materials, 3-dimensional isosurfaces of concentration (i.e., plumes), 2-dimensional slices through the 3-dimensional data, and cutting planes through the 3-dimensional block. Additional visualization networks are being developed to display 2-dimensional graphs of concentration through time at specific sampling locations (in order to compare modeled data with measurements), to display other data variables (including hydraulic conductivity and flow velocity), and to display field measurements with or without invoking the model.

Routines were developed which will allow any user to read (Groundwater Modeling System) GMS data directly into AVS. This code will be incorporated into an AVS module for use by this project and will be contributed to the International AVS Center which serves as a clearinghouse for publicly-developed AVS modules.

A graphical user interface is being developed inside AVS to provide the scientist or user with easy access to the model and the data analysis and visualization tools. Menus are presently being developed with input from the modeling team and from scientists.

Data editing modules are presently being designed. These modules will allow the scientist or user to modify input data (i.e., node location, cell shape, hydraulic conductivity, etc.) via a graphical user interface prior to modeling and analysis.

A Web page is being developed and will be available at close of business on March 21 which presents further project descriptions and visualization examples. This information will be available at http://research.esd.ornl.gov/programs/ETPI. We encourage you to peruse the website.