Pyramid Environmental recently performed a geophysical investigation for the National Park Service at Carlsbad Caverns National Park in Carlsbad, NM. The survey used electrical resistivity mapping (ER) to look for potential underground caves or caverns near an area designated for the construction of an underground utility line. Pyramid owns the SuperSting R8 earth resistivity meter manufactured by Advanced Geosciences, Inc.
A 2D resistivity survey was performed along the length of the proposed water line route (about 6,900 feet) to identify suspected underground anomalies that may be associated with caves. Subsurface anomalies were further investigated with a 3D resistivity survey.
The 3D survey identified six specific locations containing possible, probable, or highly probable air filled voids. Two of these locations were at the ground surface; the remaining voids were between 6-13 feet below the ground surface. The voids ranged in size from less than 5 feet in diameter to as much as 15-20 feet in length. As a result, the planning and/or construction of the new underground water line may be impacted. This project illustrates how invaluable geophysical techniques are when used to investigate unknown subsurface conditions.