This section does not apply to: A publicly or privately owned sewage treatment plant; or The discharge of any chlorine or chlorine products that are present due to their occurrence as a natural constituent of saline water. A person who has a discharge permit may not discharge chlorine or chlorine products into the Chesapeake Bay or its tributaries during April and May of any year at a level that is greater than the chlorine discharge level that is applicable to a publicly or privately owned sewage treatment plant under § 9-329 of this subtitle.