In October 2008 Delta Geophysics completed a one day geologic study of depth to bedrock for estimation of bedrock excavation.  A sanitary sewer force main was scheduled to be installed along a roadway in the Allentown, PA area.  The approximate depth of the installation of the force main was 15’-20’ below ground surface and traversed 800 feet down the roadway.  Delta Geophysics personnel opted to conduct the survey using seismic refraction.

Seismic refraction is one of the most commonly used methods to determine bedrock depths,  for depths of less than 100 feet.  The method requires a seismic energy source, usually a sledgehammer for depths of 100 feet or less.  The seismic waves produced by the energy source penetrate the overburden and refract along the bedrock surface.  While they are traveling along this surface, they continually radiate seismic waves back to the ground surface.   These are detected by geophones placed on the ground surface.

Data was collected and processed by Delta Geophysics personnel using sophisticated geophysical equipment and software.  The final data was presented in a CAD file for referencing.  Also visual cross-sections were printed and provided for more detailed information.