DISCOVERY OF CONCEALED SUBSURFACE STRUCTURES AND CONTAMINATION AT HISTORIC INDUSTRIAL SITES THROUGH INTEGRATION OF GEOPHYSICAL EXPLORATION INTO THE INVESTIGATION PROCESS

Performance of environmental investigations on properties containing historic industrial operations is a common occurrence. Guided by historic documents, the investigator must endeavor to align past features with current site characteristics that often differ from one another. In some situations, subsurface geophysical exploration helps the environmental geoscientist make informed decisions about the placement of soil borings, wells, or test pits, and provides a visceral image of the site.

The purpose of this paper is to illustrate to geoscience professional some of the circumstances for which there may be tangible benefit from the use of geophysical techniques. Most often, the geophysical survey is performed as a series of regularly spaced measurements within a defined area of interest - measurements of electrical conductivity, magnetic field, and metal content are the most widely used reconnaissance mapping techniques. Ground penetrating radar is also frequently employed to provide 2D or 3D imaging of features discovered by reconnaissance mapping. In some cases resistivity or seismic imaging are selected as a means of adding geologic details, particularly when shallow bedrock is present.

The geophysical objectives often include the need for discovery of buried fuel, process chemical, or waste containment vessels. Associated infrastructure often includes pipes for conveyance of fluids to dispensing or treatment areas. Sumps, dry wells, and septic tanks are often the target of interest due to liquid waste disposal into drain systems. Sewers and other utilities often provide mobile contaminants a pathway for spreading away from the source area and entering aquifers or streams. Knowledge of buried foundations provides confirmation of the location of above or below ground storage, processing or treatment facilities from which contamination originated.

The examples provided illustrate a variety of geologic settings, types of historical facilities, contaminants, and site-specific characteristics and objectives. Tangible benefits resulted in each situation shown. Whether to guide additional sampling activities or estimation of remediation costs, the inclusion of geophysical exploration in site investigation activities may be well advised for historic industrial facilities.