3D seismic reflection surveying is a viable method of rapidly and effectively performing high-resolution site characterization, particularly at fractured bedrock sites and those sites impacted with Dense Non-Aqueous Phase Liquids (DNAPLs).  3D seismic surveys make it possible to more directly remediate source zones, because migration pathways and, in some cases, DNAPL location can be identified, resulting in the ability to design more cost-effective remedial solutions.

As a result of their physical properties, DNAPL sites present unique challenges to characterization and remediation, including high specific gravity and low viscosity, causing preferential downward migration through relatively higher zones of permeability in complex geologic media. Heterogeneities in geology and DNAPL distribution can severely limit the performance of source zone remediation technologies.  Conventional methods can not be used to accurately characterize the heterogeneity.  3D seismic data were first collected at a waste site in 1994 at Naval Air Station North Island (NASNI), in San Diego, California.  A 3D seismic survey, in conjunction with photoanalysis, review of geology and site history, was performed over a topographically low area call the “fiery marsh”, where an estimated 32 million gallons of liquid waste had been disposed.  The 3D seismic imaged the stratigraphy below the site which consisted of faulted unconsolidated marine sediments.  The disposal area was actually a sag pond formed by the juncture of several faults.  The seismic data, which were interpreted using complex seismic attribute analysis, also showed different amplitude anomalies, which are believed to be from known DNAPL and the later discovery of LNAPL.  Since then 50 surveys have been performed, including fractured bedrock sites and many at DNAPL sources.  Imaging has been effective under variable geologic and surface conditions.  The accurate and detailed seismic image of each site in three dimensions has significantly changed the previous site model to one that is accurate.