Many sites or co-locates never test the soil to see how well it may support a low resistance and low impedance grounding system. In part, this may be due to familiar areas within each state that reportedly have good conductive soils. Even within these known areas, however, you may run across a site that has unknown factors, such as a large rock shelf or subsurface sandstone. Generally, it is common knowledge which geographic areas have very rocky soils; thus, making it difficult to achieve results of less than a 10-ohm grounding system.
In the United States, these are known to be Northern Georgia and Alabama, throughout Tennessee, including the Appalachian Mountains, Pennsylvania, and the entire Northeast. Additionally, much of the Western United States, including Oregon and Washington, have locations where it is difficult to use a cookie-cutter grounding system design while still achieving dependable, low resistance goals. “Cookie-cutter” grounding system designs denote the basic concept of circling (counterpoise) the tower, shelter, and sometimes the fence line with a standard #2-solid-tinned wire installed below the local frost line, or at least 30-inches, as prescribed by Motorola R56.