1887

Abstract

Geophysical techniques offer an economical, noninvasive way of<br>determining buried structure and assessing integrity at certain types of<br>closed landfills. Such landfills often are plagued by cover and liner<br>defects and may accumulate dangerous volumes of highly polluted groundwater<br>(leachate) which can leak into surrounding aquifers. Also, as widespread<br>landfill gas production and mining of landfill materials for recycling<br>becomes a reality, geophysical techniques offer a low-cost alternative to<br>borings for mapping refuse thicknesses and variability at sites where<br>inadequate dumping records exist. In this experiment three landfills in<br>the suburban Chicago area were evaluated using electrical resistivity<br>sounding, azimuthal resistivity and seismic refraction techniques. Wenner<br>and Schlumberger array electrical soundings were inverted in a leastsquares<br>procedure to yield multilayer geoelectrical models. Wood, newspaper, cloth, glass, plastic and metal refuse interspersed with soil<br>exhibited resistivities ranging from 9-53 ohm-m (unsaturated) and 2-7 ohm-m<br>(leachate-saturated). Clay-till cover materials exhibited resistivities<br>typically ranging from 10 to 30 ohm-m. Depths of interfaces such as the<br>top of refuse, leachate level and the base of refuse were estimated from<br>soundings with errors averaging about 30%. Larger errors were encountered<br>over fractured or newly emplaced cover materials, areas where resistivity<br>contrasts with underlying refuse were small (< 10 ohm-m) or where refuse<br>resistivities exceed cover resistivities. Seismic refraction measurements<br>could not be used to determine cover thickness and deeper landfill<br>structure due to a velocity inversion and strong scattering and attenuation<br>of seismic energy in the refuse. Average direct P-wave velocity, however,<br>decreased in heavily fractured cover materials. Strong peaks on azimuthal<br>resistivity plots occurred in these same areas which suggests that seismic<br>velocity changes can be combined with azimuthal resistivity to delineate<br>areas of serious cover fracturing.

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/content/papers/10.3997/2214-4609-pdb.212.1990_007
1990-03-12
2024-03-28
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.212.1990_007
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