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Surface-geophysical investigation of the University of Connecticut landfill, Storrs, Connecticut

USGS Water Resources Investigation Report 99-4211

C.J. Powers, Jody Wilson, F.P. Haeni, and Carole D. Johnson

Abstract

A surface-geophysical investigation of the former landfill area at the University of Connecticut in Storrs, Conn. was conducted as part of a preliminary hydrogeologic assessment of the contamination of soil, surface water, and ground water at the site. Geophysical data were used to help determine the dominant direction of fracture strike; subsurface structure of the landfill; locations of possible leachate plumes, fracture zones or conductive lithologic layers; and the location and number of chemical waste-disposal pits. Azimuthal square-array direct-current (dc) resistivity, two-dimensional (2D) dc-resistivity, inductive terrain conductivity, and ground-penetrating radar (GPR) were the methods used to characterize the landfill area.

The dominant strike direction of bedrock fractures interpreted from azimuthal square-array resistivity data is north, ranging from 285 to 30 degrees east of True North. These results complement local geologic maps that identify bedrock foliation and fractures that strike approximately north-south and dip 30 to 40 degrees west.

The subsurface structure of the landfill was imaged with 2D dc-resistivity profiling data, which were used to interpret a landfill thickness of 10 to 15 meters. Orientation of the landfill trash disposal trenches were detected by azimuthal square-array resistivity soundings; the dimension and the orientation of the trenches were verified by aerial photographs.

Inductive terrain conductivity and 2D dc-resistivity profiling detected conductive anomalies that were interpreted as possible leachate plumes near two surface-water discharge areas. The conductive anomaly to the north of the landfill is interpreted to be a shallow leachate plume and dissipates to almost background levels 45 meters north of the landfill. The anomaly to the southwest is interpreted to extend vertically through the overburden and into the shallow bedrock and laterally along the intermittent drainage to Eagleville Brook, terminating 140 meters south of the landfill. Inductive terrain conductivity and 2D dc-resistivity profiling also detected two dipping, sheet-like conductive features that extend vertically into the bedrock. These features were interpreted either as fracture zones filled with conductive fluids or conductive lithologic layers between more resistive layers. One dipping conductive feature was detected south of the landfill, and the other feature was detected to the west of the former chemical waste-disposal pits. Both anomalies strike approximately north-south and dip about 30 degrees to the west.

GPR was used unsuccessfully to locate the former chemical waste-disposal pits. Although the entire overburden and the upper few meters of bedrock were imaged, no anomalous features were detected with GPR that could be correlated with the pits. It is possible that the area surveyed by GPR was entirely backfilled after the soil was removed from the site and that the outline of the former chemical waste-disposal pits no longer exists.

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Citation: Powers, C.J., Wilson, Joanna, Haeni, F.P., and Johnson, C.D., 1999, Surface-geophysical investigation of the University of Connecticut landfill, Storrs, Connecticut: U.S. Geological Survey Water-Resources Investigations Report 99-4211, 34 p.