Wisconsin's Role in Great Lakes Restoration - American Water ...

Geophysical Survey of an Arsenic Contaminated Site in the Kewaunee Marsh,
Kewaunee, WI
David J. Hart, Wisconsin Geological and Natural History Survey, Madison, WI,
djhart@wisc.edu
Peter M. Chase, Wisconsin Geological and Natural History Survey, Madison, WI,
pmchase@wisc.edu
We used an EM-31 ground conductivity meter to map the extent of arsenic pesticide
contamination in the Kewaunee Marsh. The source of the arsenic is thought to be from a spill
that occurred 60 years ago at a nearby railroad. The survey illustrates a successful use of
geophysics where the method was properly matched to the project needs and setting.
The geophysical investigation was designed around the site and contaminant. Although the
site has undergone remediation by capping the contaminated area, contaminant levels remain
extremely high, greater than 1000 mg/Kg in the peat and silt sediment and greater than
1,000,000 ug/L in groundwater samples. These very high levels caused the electrical
conductivity of the contaminated sediment and water to be much higher than the
uncontaminated areas. The investigation was further constrained by the marsh setting where
well installation and sediment sampling is difficult. Much of the site was either covered in a
thin layer of melting ice with several inches of water above the ice or in very soft sediment.
We chose the EM-31 ground conductivity meter because it could resolve conductivity
differences between contaminated and background locations at the depths of interest. The
survey was conducted in less than two hours and delineated the extent of the arsenic.
The survey results will be used to focus selection of locations for additional groundwater and
sediment sampling. This geophysical survey succeeded because the needs, site, and
methods matched.
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