Application of 3D GPR plots to interpreting distribution of paint pigment contamination

During 2000, Hager GeoScience, Inc. (HGI) performed a geophysical survey at a former paint factory site outside Boston, Massachusetts at which lead- and chromium-containing paint residue was known to be present in the subsurface. The goal was to determine the applicability of electromagnetic methods to mapping variations in the concentrations of pigment in fill. GPR and EM terrain conductivity techniques were tested in areas of known contamination and then applied to a nearby area under investigation. A GPR survey was performed along traverses at 2-foot spacing, enabling the use of 3D modeling techniques. Survey results were presented as GPR 3D and filled color contour EM plots. Slices at increasing depths through the GPR 3D plots revealed spatially localized high-amplitude zones of pigment concentration and attenuated zones of normal fill. The shallow depth slices showed that the pigment was most concentrated between 10 and 15 feet. Slices through the 3D plots at greater depths showed that in some areas the attenuated zones of normal fill reached depths of over 30 feet, consistent with fill depths in boring logs provided by the client.