If septic tanks are compartmentalized, items A to E apply.
When septic tanks are divided into compartments, the volume of the first compartment must be equal to or larger than any succeeding compartments. Each compartment must contain at least 25 percent of the total required liquid capacity and have an inside horizontal dimension of at least 24 inches.
Flow between compartments can be achieved by an unbaffled transfer hole with a minimum size of 50 square inches located in the clarified liquid zone or a minimum 12-square-inch transfer hole located above the clarified liquid zone that is baffled according to part 7080.1960. The final compartment of a tank that employs a transfer hole in the clarified zone shall not be used as a pump tank.
Septic tanks must have at least a two-inch drop between the invert of the inlet to the invert of the outlet. No liquid level drop is required between the compartments.
Adequate venting must be provided between compartments by baffles or by an opening of at least 12 square inches near the top of the compartment wall.
All compartmental walls must be designed to withstand the weight of the effluent against an empty compartment.
32 SR 1347
October 10, 2013