Underground
Aboveground
Scenario 1[*]
A bulk aboveground storage tank (AST) that directly supplies fuel to the hydrant piping, which fuels the aircraft.  
   * The airport hydrant fuel distribution system is the AST and the underground hydrant piping.  This tank is often referred to as a feeder tank.
   * The proposed definition does not regulate any part of this system UNLESS 10% or more of the volume of the tank and associated underground piping is below ground.  
      



	
Aboveground

Underground



Scenario 2[*]
A bulk AST receives fuel from a pipeline (i.e. "receiver" tank), and this AST supplies fuel to an intermediary AST (i.e. "feeder" tank), which then directly supplies fuel to the hydrant piping.
   * The intermediary AST (also commonly referred to as a feeder tank) and the underground hydrant piping is the airport hydrant fuel distribution system.  The AST that receives the fuel and supplies the intermediary tank is not a part of the airport hydrant system. 
   * The proposed definition does not regulate any part of this system UNLESS 10% or more of the volume of the tank and associated underground piping is below ground.  
Aboveground
Underground
Scenario 3[*]
A bulk AST that directly supplies fuel to an intermediary underground storage tank (i.e. "feeder" tank), which directly feeds the hydrant piping to fuel the aircraft.
   * The bulk AST is not considered to be part of the airport hydrant fuel distribution system under this scenario.
   * The proposed definition defines the airport hydrant fuel distribution system as the storage tank directly connected to the underground hydrant piping, the underground hydrant piping, and any other connected underground piping.  This system will be regulated by the proposal. 
      
Aboveground

Underground







Scenario 4[*]
A bulk UST receives fuel, and this UST supplies fuel to an intermediary UST (i.e. "feeder" tank), which then directly supplies fuel to the hydrant piping.
   * The bulk UST is not considered to be part of the airport hydrant fuel distribution system under this scenario.  However, the bulk UST would be regulated as a field constructed UST or as a traditional UST, depending on how it was constructed.
   * The proposed definition defines the airport hydrant fuel distribution system as the intermediary UST directly connected to the hydrant piping and the hydrant piping.  The piping between the bulk UST and the airport hydrant UST will have to meet the bulk piping requirements under the proposal.
Aboveground
Underground
Underground
Aboveground

Scenario 5[*]
This scenario contains two distinct airport hydrant fuel distribution systems and a bulk AST "receiver" tank.  The receiver AST supplies fuel to two different intermediary tanks (i.e. "feeder" tanks), and these intermediary tanks directly supply fuel to hydrant piping.
   * Each set of storage tanks directly connected to hydrant piping that fuels aircraft is a distinct airport hydrant fuel distribution system.
   * The receiver AST is not regulated by the proposed definition.
   * The proposed definition regulates the intermediary UST directly connected to an airport hydrant piping run and this hydrant piping run, as under Scenario 3.
   * The intermediary AST (also commonly referred to as a feeder tank) and the underground hydrant piping are considered by EPA to be an airport hydrant fuel distribution system.  The proposed definition does not regulate any part of this system UNLESS 10% or more of the volume of the tank and associated underground piping is below ground.  
