An owner and an operator of a UST system with a field-constructed tank greater than 50,000 gallons or an airport hydrant system may use single-walled piping when installing or replacing piping associated with the UST system. An owner and an operator of a UST system with a field-constructed tank less than or equal to 50,000 gallons that is not part of an airport hydrant system shall meet the piping performance standards and secondary containment requirements of COMAR 26.10.03.02 when installing or replacing piping.