A generally accepted approach would be to perform “fall-of-potential” or “3-lead” test(s) on the grounding-electrode system(s), with test-rod spacings based on published literature for such tests. Then, [“4-lead”] Kelvin-resistance measurements should be conducted detween various subsurface metallic components {like tanks} and building-electrical gear.
This will give some idea of the magnitude of potential difference that personnel and facilities may be exposed to in fault situations. It would be desirable to have testing conducted {and competently analyzed and upgraded} before some injury/loss incident forced the issue.
