On or before January 1, 2012, unless a more advanced upgrade or upgrade schedule is required by a State or federal law or regulation, if funding is available from the Bay Restoration Fund, a nonfederal, publicly owned wastewater treatment plant that discharges wastewater into the Patuxent River or any of its tributaries and has a design capacity of at least 500,000 gallons per day shall upgrade to enhanced nutrient removal, as defined under § 9-1601 of this article. On or before January 1, 2016, unless a more advanced upgrade or upgrade schedule is required by a State or federal law or regulation, if funding is available from the Bay Restoration Fund, a nonfederal wastewater treatment plant that discharges wastewater into the Patuxent River or any of its tributaries and has a design capacity of at least 50,000 gallons per day shall upgrade to enhanced nutrient removal, as defined under § 9-1601 of this article. On or before January 1, 2020, unless a more advanced upgrade or upgrade schedule is required by a State or federal law or regulation, if funding is available from the Bay Restoration Fund, a nonfederal wastewater treatment plant that discharges wastewater into the Patuxent River or any of its tributaries and has a design capacity that is less than 50,000 gallons per day shall upgrade to enhanced nutrient removal, as defined under § 9-1601 of this article.