Comparison of borehole geophysics, CPT, resistivity, GPR, and high-resolution seismic data across a shallow structure in unconsolidated sediments

The geological characterization of the shallow subsurface in the unconsolidated sediments of the Atlantic Coastal Plain, and other unconsolidated sediment regimes, may involve faulting and channeling not readily detectable by conventional drilling and mapping. A knowledge of these features is required in environmental and geotechnical studies in areas that may have critical impact to groundwater flow and contaminant transport. In many cases, shallow structural influences are missed during site characterization. A case study is presented using ground penetrating radar (GPR) and high resolution seismic data, compared with a geological interpretation from borehole logs and core data, with Wenner and dipole-dipole resistivity data and with cone penetrometer (CPT) data in an area where shallow structure is probable and contamination exists. This study suggests that a correlation may be made for structures imaged by ground penetrating radar and high resolution seismic data. The additional information provided by Wenner and dipole-dipole resistivity surveys, when viewed separately from the other data sources, does not allow for an adequate picture of the shallow faulting. The data from the cone penetrometer (CPT) investigation, when compared to existing well data, did not define the nature of the shallow structures. A comparison of all of the techniques allows for the small scale shallow structures, imaged by the continuous techniques (GPR, seismic) to be compared with the non-continuous techniques (borings, CPT) used to define lithology. Since the various techniques have differing depths of investigation, an effective depth of influence of the shallow structures may be estimated.