BIOBARRIER - TM
As the name implies, BiobarrierTM is an obstruction that inhibits living tissue. Specifically, it is a slow-release herbicide system that studies have proven effective in long-term control of root growth into buried hazardous waste or contaminated soil. The technology was developed at the U.S. Department of Energy-funded Pacific Northwest Laboratory, then tested at the Savannah River Ecology Laboratory and marketed by Reemay Inc. of Old Hickory, Tenn.
THE NEED FOR ROOT CONTROL
Controlling soil erosion over buried hazardous waste is essential, so workers often plant vegetation to stabilize soil. Although vegetation is a viable, long-term means of stabilizing soil, it is critical that plant roots not intrude into buried waste.
If roots are not excluded, they can disrupt the seal of water diversion layers and clay barriers in place over waste containers. If water penetrates these seals and filters into the waste, groundwater contamination may follow.
Also, the roots could absorb some waste and transfer it into the environment, including the food chain. Thus, plant roots that intrude into hazardous waste burial sites can reduce the longevity and effectiveness of these sites.
HOW BIOBARRIER-TM WORKS
BiobarrierTM is placed between the plant root zone and underlying hazardous waste containers. It consists of polyethylene pellets molded to sheets of a polypropylene fabric. The pellets emit a herbicide called trifluralin into the soil. The herbicide creates a root-free zone a short distance from BiobarrierTM. Vegetation can grow in the overlying soil, but not through BiobarrierTM. Limited root mass is the herbicide's only adverse effect on the plant.
Research conducted so far at the Savannah River Ecology Laboratory, located on the Savannah River Site, indicates that BiobarrierTM may be effective for at least 15 years under SRS conditions.
Continued study at SREL will show if BiobarrierTM is effective for its estimated lifespan of 30 years or more. The release of the herbicide is temperature sensitive. The climate and sandy soils of the Upper Coastal Plain make the herbicide conducive to fast release, so BiobarrierTM might not last as long in this region.
USES OF BIOBARRIER-TM
BiobarrierTM is still in an experimental stage for some uses. Though it is used in landscaping to prevent roots from cracking sidewalks, BiobarrierTM is not yet used in the hazardous waste industry. The industry is taking a conservative approach because the product is expensive -- it costs an estimated $60,000 an acre.
The Department of Energy is supporting research of BiobarrierTM because it wants to make sure the product is effective and long lasting before the agency applies it on the 100,000 acres or so where it potentially could use BiobarrierTM.
To test BiobarrierTM, SREL researchers conducted two types of controlled experiments. First, they planted bermuda grass, soybeans and bamboo with an underlying layer of BiobarrierTM in a rhizotron, a facility containing sunken, soil-filled concrete chambers with a glass wall covering the trench side of each chamber. The glass wall allows researchers to observe root growth non-destructively. Researchers collected data from the rhizotron by photographing each glass wall at the end of each growing season. Also, researchers tested soil samples from the rhizotron to assess the release of the herbicide from BiobarrierTM into the surrounding soil.
In addition, the researchers built a small rhizotron in a forest. The growth of roots in this part of the experiment was much slower than the other rhizotron study, and after four years only a few roots have challenged the BiobarrierTM. Researchers do not yet have enough data to confidently judge its effectiveness in the field study.
Overall, the rhizotron study showed that roots of soybeans, bermudagrass and bamboo generally grew no closer than about a half inch from BiobarrierTM.
Researchers also designed an experiment to more rigorously test BiobarrierTM. They tested the effectiveness of the product in outdoor containers that simulated a landfill soil cap using local plant species likely to be used as cover vegetation on waste sites at SRS. Researchers filled 100- and 200-liter plastic containers with layers of soil and gravel to simulate the cap. Within each treated container, researchers placed a single layer of BiobarrierTM material between the topsoil and the gravel. Then they planted bahiagrass, loblolly pine seedlings and mature bamboo plants. Researchers measured root growth following each growing season.
Results from the container study generally agree with rhizotron observations in that most roots of bahiagrass, bamboo and loblolly pine stopped at about one half inch from BiobarrierTM.