New barrier technology to be demonstrated at Savannah River

DOE chooses EnviroWall to support magnetic seperation technology

Barrier Member Containment Corp. of Belle Chasse, Louisiana developed and holds several patents for EnviroWall, a promising barrier alternative to cement grout. This containment system and installation method will be used at Savannah River to facilitate a demonstration of MAG SEP, a magnetic separation technology developed by Selentec of Atlanta, Georgia. (For more information on MAG SEP, see related article in this issue.)

Demonstrations will be conducted under the Office of Technology Development's contaminant plume containment and remediation focus area. EnviroWall's interlocking polyethylene panels form an impermeable subterranean wall for the control of migrating contaminants through groundwater. The system is designed to cut off a plume or to isolate an area for remediation.

Installation begins by digging a 36 to 42-inch wide trench to the ideal maximum depth of 30 feet or until a clay strata is reached. Anchoring or spreader bars are attached to the base of eight-foot by 10-foot interlocking guide box panels that can be stacked vertically. This stack is lowered into the bottom of the trench. To stabilize the guide boxes and keep them exactly vertical, the trench is half backfilled. Impermeable barrier material (high density polyethylene or polypropylene) is inserted into the vertical void created between parallel guide box panels. The joints between interlocking HDPE or HDPP panels or rolled sheets are sealed with special rubberized, or elastomeric gaskets to prevent leakage. Bentonite material is then placed on both sides of the HDPE or HDPP material to a height of 12 to 30 inches along the bottom of the void to seal the base of the wall to the strata. Where there is no clay strata to anchor the wall and stop groundwater flow, a curtain wall is used. To prevent flow under the curtain, hydraulic pressure is removed from the downgradient side of the curtain.

To check the integrity of EnviroWall's installation, a video camera is lowered into the vertical spaces within the guide boxes. A videotaped inspection ensures that the HDPE or HDPP panels are anchored properly and all interlocks are fully engaged.

The next installation step is to complete the backfilling of the interior and exterior of the guide boxes, thereby securing the HDPE or HDPP panels. The guide box anchoring bars are left behind; the guide box panels are pulled out and re-installed at the head of the trench to receive the next section of rolled sheet or panels of HDPE or HDPP. The EnviroWall installation method reuses the same 15 to 20 guide box sections throughout the operation.

For the demonstration at DOE's Savannah River site, Selentec will use EnviroWall to facilitate in-situ groundwater treatment. In a V-shaped arrangement, EnviroWall will funnel groundwater into a patented pass-through section of wall, or gate, controlling the flow and directing it to Selentec's magnetic separation equipment for contaminant removal. Clean water will be allowed to percolate back into the aquifer.