The Savannah River Site is using a number of innovative technologies in its environmental restoration operations. Among them are Air Lift Recirculation Wells, Soil Vapor Extraction, Geosynthetic Capping, and the GeoSiphon Cell. According to SRS Assistant Manager for Environmental Quality Tom Heenan, the major driver for using these approaches is cost savings. He points out, "You wouldn't try any of these approaches if you weren't going to get it done better or cheaper and usually both." Here's what these technologies do.

Soil Vapor Extraction
SRS installed six Soil Vapor Extraction units at the A/M Area between 1995 and 1997. These units remove chlorinated volatile organic compounds in the vadose zone before they move downward into the water table. The vacuum units, which are connected to either horizontal or vertical wells placed into contaminated sources, withdraw contaminant vapors from the subsurface. The vapors pulled from the subsurface flow to a thermal treatment unit that destroys the contaminants using catalytic oxidation.

The Soil Vapor Extraction units have increased the removal rate of organic solvent by 500 percent over the existing aboveground air stripper units that can remove contaminants only from ground water. Heenan says the life cycle cost benefit of the units is estimated to be $30 million.

Air Lift Recirculation Wells
Another innovative technology that SRS uses at the A/M Area is Air Lift Recirculation Wells, which are essentially in situ air strippers. This technology uses two concentric well pipes with upper and lower baffles and screens. Air is pumped down the center well, and then it moves up the outer well carrying with it chlorinated volatile organic compounds. The recirculating flow of air brings more ground water into the well to be cleaned. This method is half the cost of aboveground air stripping.

Geosynthetic Closure Cap
SRS installed the first Geosynthetic Cap approved by the state of South Carolina at its Nonradioactive Disposal Facility (also known as the Sanitary Landfill). The technique had been used elsewhere, but through some applications engineering, it was modified for use at SRS. Geosynthetic Caps are an improvement over conventional kaolin clay cap closures because of flexibility and ease of installation, which shorten installation and construction time. A Geosynthetic Closure Cap consists of seven layers: foundation layer, reinforcement layer, gas vent layer, geosynthetic clay liner, flexible membrane layer, geosynthetic drainage layer, and vegetative layer. According to Heenan, SRS estimates it has 500 acres to cap, half of which are suitable for Geosynthetic Capping. Heenan says the estimated cost savings of using Geosynthetic Caps is $100,000 per acre.

GeoSiphon Cell
Heenan calls the GeoSiphon Cell this year's "gee whiz." It is being evaluated for in situ treatment of chlorinated volatile organic compounds in ground water at the TNX Area at the site. It is suitable for sites with shallow contamination. The Geosiphon Cell is a large- diameter well that can be packed with treatment media such as granular cast iron. Hydraulic pressure induced by the natural hydraulic head difference between the cell and the Savannah River draws contaminated ground water through the treatment cell. The solvent contaminants are reduced to ethane, methane, and chloride ions. The treated water, which meets Primary Drinking Water Standards, is discharged into the Savannah River.

For more information about these and other technologies used in cleanup at SRS, view the Web site at http://www.srs.gov. Information is organized under both the "Technology" and the "Environment" areas on the Web site.