Geophysical techniques were employed in this investigation to determine refuse character<br>and thickness, to identify shallow buried metal objects, and to distinguish between leachate and<br>shallow buried metal objects within the 800 Area landfill at Argonne National Laboratory.<br>Resistivity soundings, electromagnetic (EM) and magnetic profiles were completed across the<br>northern portion of the landfill between 1990 and 1993 to achieve these goals.<br>Resistivity soundings were inverted for layered earth models consisting of three or four<br>layers. Simple layered models were applied to obtain one-dimensional structure at each sounding<br>position. A low-resistivity layer (5 10 ohm-m), approximately 8-35 ft (3- 12 m) thick, was<br>consistently seen in the soundings over the landfill and probably represents leachate-saturated fill.<br>Layers of significantly higher resistivity (30-90 ohm-m) were seen below the low-resistivity layers<br>and represent the underlying glacial till. The modeled depth to the base of refuse closely matched<br>depth to the refuse-till interface as determined by borings made through the landfill.<br>EM and magnetic profiles identified areas of high conductivity caused by metal debris or<br>accumulations of leachate across the northern portion of the landfill. A particularly large anomaly<br>represents a French drain pipe (used for disposal of liquid waste) which was abandoned in place.<br>EM anomalies near known leachate seeps on the landfill (with no corresponding magnetic<br>anomaly) probably represent elevated leachate levels.<br>Each of these assessed characteristics is useful. Refuse thickness estimates aid in<br>monitoring well screen placement. Determining the location of buried metal was important in<br>locating a French drain buried in the landfill, which was used for liquid waste disposal. Finally,<br>leachate levels must be monitored to properly manage the landfill’s water balance. Geophysics<br>provides a quick, noninvasive method of assessing these hydrologic and waste characteristics.


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