ThinkGood—as far as I can tell, chemical rods are not intended to be concrete encased, but backfilled with a diatomaceous-earth slurry to a few inches below the top, with the accessible but subsurface upper end is placed in a valve box for venting and testing/inspection.
Sandwiched between the copper tube and “the earth,” conductive, chemically charged “veins” form in the hardened slurry and adjacent soil through the several inches of intermediate conductive slurry, and is a key part of a desirably low-resistance system.
