Integrated Geophysical Characterization at a Contaminated Site

A multidisciplinary geophysical study was performed at Naval Air Station, Brunswick, Maine. The goal of the study was to provide a better understanding of the possible migration pathways of the contaminants in bedrock fractures and deeper stratigraphic zones whose geometries might be controlled by bedrock morphology. The scope of work consisted of mapping the bedrock surface, identifying and locating fracture zones, and mapping the continuity and extent of key stratigraphic horizons. Seismic refraction and reflection, GPR, and resistivity were used to meet the study goals. Geophysical data were combined with existing borehole and cone penetrometer information to produce an integrated database that was used to create models of the bedrock and key stratigraphic surfaces. Both raw data and model-slice profiles were prepared to illustrate the morphology of the surfaces and identify possible bedrock fractures. The results of the study included delineation of the post-glacial bedrock valley terrain, identification of glacial depositional features, and suggestion of a pattern for fracture corridors in the study area. Low-velocity zones identified in the refraction surveys and fractures interpreted from the resistivity profiles correlated well with some previously identified regional and local lineaments.