Not sure about the state of TN, but many states in the past 10 years, all gas stations had to remove the old metal tanks and go with the new fiberglass leak proof tanks...... again, NEVER had an issue with below grade tanks....
Yup, same here.
When I was selling the stuff tho (owned/operated an FBO) the tanks had been in the ground for 20 years or more and there simply wasn't an issue.
YMMV, even with an above ground tank. It's all about the care taken by the vendor.
Don.