Section R. 325.2143a - Overflow system open tanks and surge capacityRule 43a.
(1) A swimming pool owner shall equip a swimming pool equipped with a perimeter overflow system with an open tank for containing the free discharge of water from the perimeter overflow system for treatment and reuse.(2) A swimming pool owner shall ensure that an open tank meets all of the following requirements: (a) Has a capacity from the design operating level of the surge tank to the tank overflow elevation of not less than 2 minutes of flow from the filtration pump.(b) Has an automatic means to supply potable water to the pool or to the open tank that is activated based on the water level in the pool or in the open tank.(c) Has tank overflow piping that meets both of the following requirements: (i) Is sufficiently lower than the perimeter overflow system lip to assure continuous flow at the design flow rate.(ii) Is designed to prevent flooding of the equipment room or other areas in case of mechanical failure.(d) Has a means to automatically regulate the main outlet system flow rate based on the variation of water level in the open tank or perimeter overflow system.(e) Has a means to completely drain the open tank when necessary.(3) A swimming pool owner shall ensure that a pool which has a perimeter overflow system has surge capacity of not less than 1 gallon per square foot of pool water surface area. A swimming pool owner shall ensure that total surge capacity is the sum of the open tank capacity and either of the following if capacity is available: (a) Capacity in the perimeter overflow system.(b) Capacity in the pool of not more than 50% of the required surge capacity if the perimeter overflow system is equipped with surge weirs.Mich. Admin. Code R. 325.2143a