Location And Delineation Of Subsurface Tar Contamination Using Electrical Methods

Electrical resistivity and induced polarization (IP) measurements were made to explore the<br>variability of electrical parameters within tar-contaminated soils at the site of a former shingle<br>manufacturing facility on the floodplain of the Oswego River in Fulton, NY. Degradation of the<br>buried shingles generated diapirs of tar, which extrude onto the surface, creating self-replenishing<br>“tar boils” at the site. Data from offset Wenner electrical resistivity surveys conducted in December<br>of 1997 and 1998 were used to delineate highly resistive areas believed to be associated with the tar.<br>Trenching and drilling after the 1997 effort revealed tar in some of the resistive zones; other<br>resistive zones contained large sandstone boulders believed to be associated with the building of the<br>Oswego River Barge Canal. Known and potential tar-contaminated zones were the focus of IP<br>surveys conducted in May through July of 1999. The field experiments conducted at this site were<br>designed to test the ability of IP parameters to distinguish between types of resistive zones in the<br>subsurface. Both dipole-dipole and gradient data were collected, targeting zones with the highest<br>resistivity and surface tar boils.<br>Results indicate that maps of chargeability at early times on the decay curve indicate the<br>presence of tar. In addition, Cole-Cole parameters calculated from the decay curve for exponent c =<br>0.25 were used to generate amplitude, phase and critical frequency values. Maps of these values<br>also separate zones of tar contamination from sandstone boulders and other resistive zones.