"Class A certificate." Wastewater systems of unlimited permitted discharge flow.
"Class B certificate." Wastewater systems with a permitted average daily discharge flow equal to or less than five million gallons.
"Class C certificate." Wastewater systems with a permitted average daily discharge flow equal to or less than one million gallons.
"Class D certificate." Wastewater systems with a permitted average daily discharge flow equal to or less than one hundred thousand gallons.
"Class E certificate." Wastewater systems consisting only of collection facilities with pumping stations which discharge untreated wastewater into another system.
63 P.S. § 1005