The way I ground the service installation you are describing is to run a common GEC from the metal water pipe electrode to the larger of the 2 service panels ground bar where the service grounded conductor terminates, sized based on the service entrance conductors feeding the 320 meter...then TAP the common GEC (with a burndie) with a tap conductor based on the size of the 2nd panels service entrance conductors feeding that panel and connect the tap in that panels ground bar where the grounded service conductor in that panel terminates. (Bond each panel enclosure)
I have been told that you can run separate grounding electrode conductors sized based on the service entrance conductors feeding each panels service disconnecting means to the metal water pipe electrode.
IMO... this method seems to conflict with the requirement of 250.104(A) which requires the bonding jumper to metal water piping systems to be sized according to table 250.66 (This is a gray area that the code does't specifically address or prohibit.)
Unless you can prove 25ohms or less to that single ground rod, you better add a 2nd...
shortcircuit
[This message has been edited by shortcircuit (edited 04-02-2005).]
