I have a GE 1/2" format 150mp. main breaker panel. What appears to be the main grounding conductor is a #2 alum. conductor to a water pipe connection, There is also a #6 connection to a single driven rod outside.
The problem is the water service tubing is plastic, which in my opinion makes the water pipe connection merely a bonding connection for the water piping. You can see the outline of a hose clamp in one photo, which tells me the main is plastic. Is the #6 to the rod a sufficient grounding conductor by itself? My first inclination is no. The driven rod looks like a 1/2" copper plated rod also.
I also did mention the double tapped neutrals.