Peat Mapping Using Resistivity

NDT Corporation participated with the Federal Highway Administration, Massachusetts Highway Department and Geometrics in a demonstration project to evaluate the effectiveness of Geometric’s OhmMapper system to locate and define the lateral and vertical extents of peat deposits along a highway construction right of way. The test area was in Carver, Massachusetts on a section of Route 44 that is currently under construction. Peat was excavated to depths varying from 15 to 30 feet and replaced with sand. Borings indicated peat deposits below the sand fill. A resistivity survey was conducted in an area where borings indicated the presence of peat. After completion of the resistivity survey the area was excavated and the peat deposits mapped for comparison with resistivity survey results. Soil, ground water, and peat samples were obtained from the site materials for laboratory resistivity tests.

The results of the OhmMapper investigation are show as a comparison of the color resistivity cross sections and test pit drag line results (shown above). These results indicate a correlation of the low resistivity areas and locations that peat/muck was excavated. The low resistivity values for the peat, limited penetration and the definition of the bottom of the peat layer. The method did outline the lateral extent of peat material. This contribution is significant since the most expensive part of a boring – trenching program would be to establish the lateral extent of peat.