The Application Of Borehole Geophysics To The Delineation Of Leachate Contamination At The Trail Road Landfill Site: Nepean, Ontario

The sanitary landfill site poses many monitoring problems for the environmental scientist. An understanding of<br>the materials and processes controlling the distribution of leachate in the groundwater at a landfill site is an<br>essential component of landfill management. The Trail Road landfill site in Nepean, Ontario, is perched upon a<br>sand and gravel ridge which is part of a lacustrine silty clay plain. The delineation and monitoring of leachate<br>contamination, created by the decomposing municipal solid waste mixing with groundwater, is presently carried<br>out through chemical sampling of monitoring wells. Such monitoring of a complex and hydraulically conductive<br>environment, is expensive and time consuming because water samples must be analyzed in a laboratory.<br>Borehole geophysical logging of eight of these monitoring wells showed that the delineation of leachate plumes<br>could be accomplished through a full suite of borehole geophysical logs. The logs acquired included: natural<br>gamma ray, density, total magnetic field, magnetic susceptibility, electrical conductivity, and temperature. The<br>use of a full suite of logs provided a measure of the in-situ physical properties of all the components of the<br>subsurface, including air, water, and sediments. Chemical sampling provided only an inventory of ions present in<br>the groundwater. The geophysical logs in this study were acquired, processed and interpreted, in a shorter period<br>than the chemical sampling, and provided information allowing for a more refined geological interpretation, than<br>from drilling alone. Anomalous physical properties, interpreted to be the result of the presence of leachate<br>contamination, correlated well with data from chemical sampling which showed elevated levels of leachate<br>indicator ions, such as, calcium, magnesium, chloride, sulphate, potassium, ammonia, dissolved organic carbon<br>(DOC), phenols and iron. It was concluded that an interpretation of borehole geophysical logs produced a more<br>accurate delineation of areas of leachate contamination at the Trail Road landfill site, more directly (i.e. in situ).<br>and with greater efficiency and simplicity than chemical sampling.