No alteration of a building served by an onsite wastewater system, which will result in an increase in flow or change in type of wastewater discharged, shall be approved in a sensitive regional area, unless after such improvements to the building on the lot satisfies, to the maximum extent possible, all design and siting requirements of the regulations in effect at the time of an onsite wastewater system construction permit application. If the lot does not satisfy all current requirements, the alteration may only be approved if the onsite wastewater system is brought into complete compliance with all local ordinances.