An "Underground Plan" to Capture Radioactivityby Alan Rose
Dr. Lee, Environmental Research, AECL, is a Hydrologist with the Environmental Research Branch, Chalk River Laboratories, who is currently working on methods for mitigating the discharge of groundwater plumes. Lee obtained his Ph.D from Virginia Polytechnic Institute and State University in 1976 and is an Adjunct Professor with the Dept. of Earth Sciences, University of Waterloo.
Lee's talk dealt with the subject of contamination of groundwater by various pollutants, the manner in which those pollutants move and a new method by which they can be intercepted and eliminated from the environment. Given the current controversy about groundwater contamination by any number of chemical and radioactive pollutants, Lee's message is of great interest to both the producers of contamination and the populace which has to live with it.
Many sources of contamination were cited such as agricultural wastes and landfills which produce mainly biodegradable pollutants which break down in the soil given enough time and space and are therefor only a problem if located too close to residential areas. Many other sources like dry cleaning fluids and chlorinated hydrocarbons that do not break down have to be intercepted and contained.
Groundwater flows at various speeds but in general is very slow. Lee noted that contaminants flow even slower, about three percent of the water speed.
The Chalk River team has developed a Wall-And-Curtain technique for passive collection and treatment of contaminant plumes. Contamination from a point source does not spread in all directions but follows a relatively narrow path in the direction of the groundwater flow.
To test the method, field application this year will treat an existing plume in the CRL area in a 12 metre thick sandy aquifer containing a minute concentration of Strontium 90. An impermeable wall will be placed across the plume and sealed to the bedrock. Against the upstream side of this wall a layer of absorbent material called clinoptilolite (resembles kitty litter) will be put in place. A system of weeping tiles will then divert surface water away from the plume and conduct the contaminated water to flow through the clinoptilolite which will absorb the Strontium 90 and hold it for at least twenty years. A thicker bed would increase the retention time to whatever is desired.
The strength of this system is its passive nature, the ease of monitoring the results and the low cost of application. Although the tests will be conducted on a strontium 90 plume, because of the ease of measurement of this radioisotope at extremely low concentrations, the system has generic applicability, combining three existing technologies; cut-off walls, reactive treatment with agents such as clinoptilolite and passive tile drains, allowing single point monitoring of effluent concentration and flow.
For a more detailed description of this innovation in pollution control, and an opportunity to discuss the subject personally with the author, don't miss Dr. Lee's presentation at Algonquin College in Pembroke tomorrow night at 7:00 pm.