The annual rate of capital cost amortization for all improvements necessary to increase the degree of treatment of the wastewater at the city wastewater treatment facilities, where such improvements are required to meet standards of effluent quality and purity established by the State Pollution Control Agency, will be apportioned in accordance with the principles hereof and extend for a period not to exceed the amortization period of such improvements.
(1992 Code, § 276:57)