Geophysical Investigation Of An Abandoned Landfill

We have investigated the structure of an abandoned landfill in Lancaster, PA, with<br>near-surface geophysical techniques, including magnetics, conductivity and magnetic<br>susceptibility. Our previous study used a wide range of data, including field observations,<br>historical aerial photographs and magnetic and conductivity measurements along 10<br>transects across the site to delineate the general boundaries of two landfills (de Wet et al., in<br>press). That low resolution data suggested that one of the landfills was heterogeneous. In<br>this study we investigated the compositional variations in this landfill by 1) collecting<br>higher resolution magnetic and susceptibility data along several of the transects, and 2)<br>completing several high resolution grids over selected areas of the landfill.<br>The total field magnetic intensity data and the magnetic susceptibility data showed<br>large anomalies over the landfill compared to background areas and clearly defined the<br>boundaries of the landfill. The magnetic susceptibility data for the landfill (collected using a<br>Bartington MS2D instrument) indicated numerous anomalies in the upper 10 to 15 cm of<br>the landfill. Specific magnetic susceptibility anomalies were unrelated to the large magnetic<br>intensity anomalies measured in this study, or the anomalies in the quadrature or in-phase<br>conductivity data collected in the earlier study. Data collected at different sampling intervals<br>along widely spaced transects were successful in delineating the landfill and identifying the<br>general heterogeneity of the landfill itself. Detailed grid maps provided additional<br>information about the subsurface that was not evident from the transect data. Sampling<br>scale is an important consideration in geophysical investigations of this type. High<br>resolution grid maps showing a variety of geophysical results provide maximum<br>information about subsurface conditions.