TECHNOLOGY: Old Materials Help Solve Modern Cleanup Problems

William D. Siuru Jr.

Scientists have turned to old materials to solve modern environmental cleanup problems.

Montan wax, a fossil-plant wax derived from coal deposits created more than 250 million years ago, is currently being tested as a barrier to inhibit the flow of toxic contaminants through soils. Developed in Germany, montan wax's applications range from highway construction projects to shoe and furniture polishes.

The wax can be injected into the soil to create an in situ barrier that prevents contaminants from migrating and eventually reaching the water table. The injection process (see chart), which does not require the soil to be removed, is one advantage of this barrier technique.

Although montan wax cannot permanently solve toxic waste problems, it can serve as a temporary barrier around holding tanks, landfills or contaminated soils until technical difficulties, fiscal constraints and scheduling problems are overcome.

An in situ barrier can reduce exposure to workers or, if leaks are detected during cleanup, it can stop the toxic materials from migrating into the groundwater. For example, the Hanford site, a former World War II plutonium production site in southeast Washington generated nearly 60 million gallons of highly toxic materials over 50 years. Large amounts of liquid, salted with smaller amounts of cesium, strontium and other radioactive isotopes are stored in 177 aging underground storage tanks. During waste retrieval, montan wax could be injected below the radioactive waste storage tanks to catch materials that leak.

The wax has been successfully injected into coarser-grained soils at the Sandia National Laboratory in New Mexico. Current tests at a site adjacent to the landfill in Richland, Wash., where the geological characteristics are suited for permeation of the montan wax, will determine if the technique can be used to clean up U.S. Department of Energy (DOE) sites. Mary Peterson, the program's coordinator, believes that the technology has the potential for broad application at DOE and other hazwastes sites.

Because the technology is still under development, tests will be conducted to determine whether the wax is acting as a barrier to clean water filtering into an area. Uncontaminated soil will be excavated and examined to determine the distribution of the montan wax. Soil permeability measurements will be made and, if the wax barrier significantly inhibits the movement of water, the test will be considered successful.

Researchers at Pacific Northwest Laboratory's Environmental Molecular Sciences Laboratory also are investigating cost-effective techniques to safely empty and store the contents of Hanford's tanks.

Crown ethers molecules have proven useful for binding highly radioactive pollutants such as cesium and strontium. Scientists believe that once the crown ethers attach themselves to the radioactive isotopes, the molecules can separate the highly radioactive contaminants from the liquid waste. After the separation, the small amounts of cesium and strontium could be disposed in a long-term repository for high-level waste while the remaining water, now considered low-level waste, could be economically treated and disposed.

While the theory appears to be sound, crown ethers with an affinity for cesium or strontium have yet to be found. Computer modeling based on quantum and classical mechanical methods are being used to narrow down the thousands of possibilities. Although the fastest Cray supercomputers and high-speed workstations are being used, a single calculation can take as long as a month. The next generation of supercomputers will reduce calculation times to one day and will analyze more complicated molecular processes.

Under the DOE's In Situ Remediation Integrated Program, montan wax, as well as several other grout materials, are being evaluated for in situ barriers. The testing has been funded by the DOE's Office of Technology Development under a cooperative effort between PNL, Sandia National Laboratories, the City of Richland and Golder Federal Services, which originally identified montan wax as a promising barrier material.