The EM39 Borehole Conductivity Probe has been designed for rapid, accurate measurements of groundwater contamination in the earth and rock surrounding monitoring wells. Since clays also impact the electrical measured conductivity, Geonics introduced the GAMMA39 Natural Gamma Ray Probe to resolve this ambiguity. Whereas conductivity highs with coincident gamma ray highs often indicate enhanced clay content, conductivity highs not associated with a gamma ray high can be expected to be due to enhanced TDS in the groundwater.

Like the conductivity probe, the gamma ray probe is unaffected by plastic casing in the well. It requires no special licences, can be used anywhere, is relatively fast to operate and can, of course, also be employed to detect radioactive wastes in the ground.