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33 INDIVIDUAL SUBSURFACE SEWAGE TREATMENT SYSTEMS 7080.1960 7080.1940 MULTIPLE SEPTIC TANKS. A. If more than one septic tank is used to obtain the required liquid capacity as determined in part 7080.1930, septic tanks must be connected in series or employ multiple collection systems. B. When tanks are connected in series, each tank or compartment must contain at least 25 percent of the required total liquid capacity. Statutory Authority: MSS s 115.03; 115.55 History: 32 SR 1347; 35 SR 1353 Published Electronically: October 10, 2013 7080.1950 COMPARTMENTALIZATION OF SINGLE TANKS. If septic tanks are compartmentalized, items A to E apply. A. 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. B. 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. C. 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. D. 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. E. All compartmental walls must be designed to withstand the weight of the effluent against an empty compartment. Statutory Authority: MSS s 115.03; 115.55 History: 32 SR 1347 Published Electronically: October 10, 2013 7080.1960 SEPTIC TANK BAFFLES. All septic tanks must be baffled according to items A to G. Effluent screens are allowed to be substituted for outlet baffles. A. Baffles must be installed at each inlet and outlet of septic tanks. Outlet baffles are required on compartment walls if the transfer hole is at the liquid level. B. Baffles must be resistant to corrosion or decay. Inlet baffles must not restrict the movement of solids. C. Baffles must be integrally cast with the tank or affixed at the top and bottom with connectors that are not subject to corrosion or decay. Baffles for fiberglass -reinforced polyester tanks are allowed to be either resin bonded or secured with suitable structural adhesive. Sanitary tees used as baffles must be affixed to the inlet or outlet pipes with a permanent waterproof adhesive. Copyright ©2014 by the Rev so of Statutes, State of Minnesota. All Rights Reserved.