Coffee Break Training: Hazardous Materials: Securing or Removing Unused Underground Tanks [open pdf - 517KB]
"When an underground flammable or combustible liquid storage tank has outlived its usefulness or is otherwise no longer needed, the model fire codes prescribe methods to secure or remove the tank to minimize the chances of leaks, fires or tank collapse. If a tank is being taken out of service temporarily, the fill line, gauge opening, vapor return and pump connection must be secured against tampering. Vent lines must remain open. It is up to the code official to determine what constitutes temporary closure. In addition to the requirement listed above, tanks not used for 90 days must have their contents removed. Tanks that are out of service for one year must be removed from the ground or abandoned in place."
Coffee Break Training - Fire Protection Series No. FP-2013-19
United States Fire Administration: http://www.usfa.fema.gov/