Generally soil resistivity is measured in ohms per cm which is a volume of soil, not just in meters which is linear, placing rods closer then twice their length will cause a low gain over installing just over this, this is because you want each rod to be out of the sphere of influence of the other rods, longer rods over 4.5m or 15 deep will not gain much unless a steady moisture level can be obtained at reaching a greater depth, even a CCE might not reach the desired ohms if the soil's ohms per cm doesn't support it,, removing the high resistance soil and replacing it with a much higher conductive soil can sometime be the best option but not always an available option, chem rods are also not always a good choice because they require constant maintenance of adding chemicals to keep them working.
But as others have said, there is no scientific bases for requirements like this unless it in being used for a single wire earth return electric supply to a remote area, if this is for a lightning protection system then someone needs to learn a little more about lightning because earth electrode resistance plays very little to no part in a lightning protection system, it is more important to have a low impedance path around what ever that is being protected then how good a connection to earth is, the reason for the above is that lightning is an opportunity event, as the clouds move across an area and the charge builds up to the point the air breaks down, then what ever is under that point is going to be hit, you don't attract lightning, its going to take a path to earth that may include what ever low impedance paths that might be in that route, you build paths around what you want to protect, the resistance of the soil plays no part in this, look at aircraft, if it is within the path of the break down of the air the lightning can and will take the path through the metal body of it because it provides a little less impedance in the stroke in the path of it to the earth, the aircraft was just in the wrong place at the wrong time.
If this is for other electrical purposes, keep in mind current does not want to go to earth, it wants to return to source from which it came, most times this is the last transformer it was fed from, except the SWER system mention above that actually uses the earth as one of the conductors of a circuit earth plays no part in the operation of electrical systems, most of these kind of requirements are built around old myths that keep on circling around in the electrical world.