Lots of B.S. in that email.
All gas is not stored in underground tanks at the stations. In fact, lots of stations have gone to above ground tanks to avoid the liability of leaking buried tanks.
The biggest point I would like to make is that all the gas is delivered through a shared pipeline. Here in SE Missouri there is a big terminal. Trucks from all the different stations fill up from the same tap. I guess Conoco, for instance, puts a million gallons of fuel into the pipeline at one end and takes a million out at the other. But it is all mixed in the process. Buying at one particular retailer gives no guarantee that you are buying US vs Iranian crude based gasoline.
Joe