US Patent 7578910 Deep well anodes for electrical grounding

Improved deep well grounding systems of the kind used for cathodic protection of ground installations according to the invention employ a combination of materials for the casing of the central metallic anode and the backfill in the well which exhibit a degree of permeability sufficient to allow by-product gases develop in ordinary use of this system to escape, avoiding unwanted cavitation, while minimizing the migration of ground water and the attendant undesirable environmental pollution.