Ground enhancement materials (GEM) are backfill materials that improve the conductivity of soil surrounding grounding rods, bars, grids, and plates. Conditions with high resistance include rocky and sandy soils, as well as dry and moutainous terrains, and frozen ground. Quality grounding systems will provide a low-impedance path for fault and lightning currents to ground. Typically, rods or grids are buried at the perimeter of a structure, and may need additional conductive elements in the surrounding earth to complete a circuit.
GEM materials must be compatible with the electrode, conductor, and connection material. Bentonite clay is a common GEM choice for its conductivity, easy of application, and non-corrosiveness. However, bentonite runs the risk of becoming dry, increasing resistance. Petroleum coke powder is very conductive and is derived from calcinated carbon, but this substance can be washed away. Conductive cements can be used wet and dry, retain their moisture, and are highly versatile, but are permanent in their application. Salts such as copper sulfate, magnesium sulfate, or sodium chloride can be used to temporarily treat soils if combined with moisture, but may corrode conductors and contaminate groundwater.