There is a possibility that zero rods are required. Or, maybe 1, or maybe 2. In lieu of a rod or rods, you could use 3/4" galvanized rigid conduit.... or a buried metal plate or a ground ring.
The point I am trying to make is that there is no simple answer to your question. If you are not all that familiar with Article 250, I would recommend you take some classes on the subject, simply because grounding and bonding is such an important aspect of safe electrical wiring. If you are an apprentice in the JATC, you should get some grounding classes in the third year. if you are not an apprentice, hopefully your JATC has some JW classes which can help.
Grounding and bonding is actually a totally cool and interesting subject, and I am not joking!
Now, if you provide us with all pertinent details, we can give you a better answer to your question. For example: Is there a metal waterpipe electrode present? Is there a concrete encased electrode present? What are the soil conditions and what do you think the probability of getting less than 25 ohms to ground on a driven rod or pipe are?
