Case Study: Three-dimensional Computer Images Help Track Potentially Contaminated Soil

Oak Ridge National Laboratory

Three-dimensional Computer Images Help Track Potentially Contaminated Soil

"Visual examination was the most powerful demonstration to make it clear to everyone where potentially con-taminated sediment is concentrated. Without AVS we wouldn't have had a way to examine this very complicated 3D dataset."
Bill Hargrove, Oak Ridge National Laboratory

AVS technology gives researcher powerful tool to show authorities probable location of potentially harmful environmental contaminants

Hidden somewhere in the 15 million pieces of data he had to analyze was the answer to Bill Hargrove's question: Was the sediment in Tennessee's Clinch River contaminated with toxic mercury and cesium 137 from Cold War era nuclear weapons research and production?

Hargrove, a University of Tennessee research associate working out of the Oak Ridge National Laboratory, needed the answer and a way to effectively present it to federal regulators who control the waterway. Prolonged exposure to mercury can cause brain and kidney damage, and radioactive cesium is also harmful to humans and animals. Both can travel through the environment clinging to soil particles. If the Army Corps of Engineers or the Tennessee Valley Authority ever needed to dredge the river to keep barge channels open, potentially contaminated sediments, if present, could be stirred up into a 44,000 acre waterway system that is used as a municipal water supply and for fishing, boating, swimming, and tourism.

An x-ray view was generated along each of the major axes to gain insight into the composition of the volume.

Hargrove and his colleagues examined the Brashear Island stretch of riverbed for layers of the type of sediment most likely to be contaminated. However, it wasn't easy to understand where within the 15 million "voxels," or volumetric cells that comprised the 3-D model of the Brashear bottom sediments the potentially contaminated sediment lay. Hargrove needed a way to visually present and manipulate this huge 3-D volumetric representation, so he used Advanced Visual Systems Inc's three-dimensional imaging technology to turn the data into a series of colorized models that showed where mercury and cesium were most likely to have settled. The three-dimensional models kept Hargrove from having to use two-dimensional charts and graphs to explain the three-dimensional distribution of the Brashear sub-bottom sediments.

"Without AVS we wouldn't have had a way to examine this very complicated 3-D dataset," Hargrove said. "Visual examination was the most important and most powerful demonstration. I could show regulators pages and pages of data tables and it would not have been as clear or apparent to them as it was when I turned the Brashear Island piece on its end and started chopping across its width. Then it became clear to everyone that the potentially contaminated sediment is concentrated in an area where dredging might occur."

Tracing the history of contamination

The federal sites in Oak Ridge, in concert with Oak Ridge National Laboratory, have developed and produced components for atomic weapons over the past 50 years, including those used to end World War II. While these federal sites were careful, and used state-of-the art pollution control procedures available at the time, some by-products from research and production of fissionable materials never-theless escaped into the environment. The cesium and mercury, released primarily during the 1950s, absorbed into certain particles in the red clay that makes up much of the Tennessee Valley's soil, and over the years, was washed away by erosion toward the river.

Hargrove, along with many other scientists working on the Clinch River Environmental Restoration Program, was hired as part of a federal effort to find out where the contaminants ended up, and whether they posed any danger to humans or the environment. They chose the shallow two-mile section of the Clinch River near Brashear Island for volumetric analysis because it seemed the most likely to be dredged, if federal authorities ever chose to do so.

The Army Corps of Engineers acoustically sounded the sediments below the Clinch riverbottom. The soundings gave Hargrove readings for a depth of eight to ten feet into the sediments below the bottom surface. He ended up with 2-3,000 stacks of data in six-inch vertical increments, and from these stacks he generated the 15 million voxels for the two-mile Brashear section of riverbottom he had to interpret.

The soundings were visualized into stacks of colored balls that represented each category of sediment.

Hargrove used Advanced Visual Systems' AVS (Application Visualization System) to separate voxels of water, which he didn't need, from voxels of bottom sediments, and then to convert the data into three-dimensional images. Initially, he used the X-ray tool to get a broad overview of the volume model and the ÒscatbubÓ procedure to visualize the soundings into stacks of colored balls that represented each category of sediment. Then he used the isosurface and orthogonal slicer modules for a more detailed picture. Finally, Hargrove used the cube module to produce animations of the volume data that "dissolved" each sediment category one at a time, then faded them back in.

"That was one of the most effective ways to get people to understand how the sediments are constructed," Hargrove said. "If someone looks at all of the AVS-generated animations enough times, they can really get a good idea about what those sediments look like down there where no one has ever been. This intuitive understanding, which is so critically important, is made possible by AVS, which allows us to turn the volume this way and that, slice through it, make parts of it disappear, and draw density isoshells through it. As far as I am concerned, this is the only way that people can get such an intuitive understanding of such a complex volumetric data set."

All of Hargrove's AVS animations can be seen on the World Wide Web at URL: www.esd.ornl.gov/programs/CRERP/SEDIMENT/BRASHEAR.HTM

"AVS is what I would run to if I ever had to do this again," Hargrove said.

Animation provides a powerful tool to understand where within the 15 million voxels, contaminated sediment lay.

This powerful example demonstrates equally well the skill of the AVS Professional Services team and the flexibility of AVS software development tools.