Sec. 31.6. "Combined sewer system", for purposes of sections 31.3, 31.5, 43.5, and 120.5 of this chapter and IC 13-18, means a system of combined sewers that:
(1) is designed, constructed, and used to receive and transport combined sewage to a publicly owned wastewater treatment plant; and
(2) may contain one (1) or more overflow points that discharge combined sewage entering the publicly owned wastewater treatment plant when the hydraulic capacity of the system or part of the system is exceeded as a result of a wet weather event.