Existing Class I, II (except enhanced recovery and hydrocarbon storage) and III wells authorized by rule.

Maximum injection pressure. The owner or operator shall limit injection pressure to the lesser of: (a) A value which will not exceed the operating requirements of § 144.28(f)(3) (i) or (ii) as applicable; or (b) A value for well head pressure calculated by using the formula: Pm = (0.733-0.433 Sg)d where: Pm = injection pressure at the wellhead in pounds per square inch Sg = specific gravity of injected fluid (unitless) d = injection depth in feet.