(A) Sewage tanks serving SSTS must meet or exceed the applicable requirements of this section unless otherwise approved by a Minnesota licensed professional engineer and approved by the Department or the local unit of government.
(B) Tanks, fittings, risers, and apertures must:
(1) Be capable of supporting long-term vertical loads for the conditions in which the tank will be placed. These loads include, but are not limited to, saturated soil load, based on 130 pounds per cubic foot.
(2) Be capable of withstanding a lateral load for the conditions the tank will be placed.
(3) With proper maintenance and venting, not be subject to failure due to corrosion and degradation from sewage or sewage gases, including risers and maintenance hole covers.
(4) Be structurally capable of withstanding exposure and stresses from freezing conditions.
(C) Poured in place concrete tanks must be designed to meet each requirement in division (B) of this section and be designed by a Minnesota licensed professional engineer.
(D) Septic tanks must:
(1) Have a liquid depth of at least 30 inches. Any liquid depth that is greater than 84 inches must not be used when calculating the septic tank liquid capacity.
(2) Have a minimum of six feet between the inlet and outlet of the tank, rather than between compartments, or have a minimum of six feet from the inlet of the first tank to the outlet of the last tank in series.
(3) If site conditions warrant, the inlet and outlet are allowed to be located on walls that are not opposite each other along axis of the maximum dimension; however, the requirements of division (D)(2) of this section must be met.
(4) Have an inlet invert at least two inches above the outlet invert.
(5) Have a reserve or storage space between the liquid surface and the top of the inlet and outlet baffles of not less than eight inches or 100 gallons, whichever is greater.
(E) For dwellings, there shall be two septic tanks in series with the liquid capacity based on the number of bedrooms in the dwelling; such tanks shall be as large as the capacities in Table III. The only exception to this requirement is for the upgrade of an existing compliant system if the primary tank capacity is met and there is no garbage disposal or sewage pump. System replacement shall require two tanks in series.
Table III - Minimum Septic Tank Capacity
Number of Bedrooms | Tank 1 | Tank 2 |
Two or less | 1,000 | 500 |
Three | 1,000 | 1,000 |
Four to five | 1,500 | 1,000 |
Six to seven | 2,000 | 1,000 |
Eight to nine | 2,500 | 1,250 |
Ten or more | Septic tank shall be sized as an MSTS with the second tank in series being at least 50% of the capacity of the first tank | |
Multiple family dwelling containing two or more units | Size shall be the sum of the individual dwelling unit requirements. | |
(F) An effluent screen with an alarm must be installed on the outlet of the last tank in series.
(G) Septic tanks must be connected in series. Each tank or compartment must contain at least 25% of the required total liquid capacity. The first tank must be equal to or larger than any subsequent tank in the series.
(H) Septic tank liquid capacity prior to other treatment devices must accord with the manufacturer’s requirements, accepted engineering principles, or as identified in the product registration recommended standards and criteria.
(I) If septic tanks are compartmentalized, divisions (I)(1) to (5) of this section apply:
(1) 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% of the total required liquid capacity and have an inside horizontal dimension of at least 24 inches.
(2) 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 of 12-square inch transfer hole located above the clarified liquid zone that is baffled according to division (K) of this section. The final compartment of a tank that employs a transfer hole in the clarified zone shall not be used as a pump tank.
(3) 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 two compartments.
(4) 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.
(5) All compartmental walls must be designed to withstand the weight of the effluent against an empty compartment.
(J) All septic tanks must be baffled according to divisions (J)(1) to (7) of this section. Effluent screens are allowed to be substituted for outlet baffles.
(1) 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.
(2) Baffles must be resistant to corrosion or decay. Inlet baffles must not restrict the movement of solids.
(3) 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.
(4) The inlet baffle must extend at least six inches, but not more than 20% of the total liquid depth, below the liquid surface and at least six inches above the liquid surface.
(5) The outlet baffle and any baffles between compartments must extend below the liquid surface a distance equal to 40% of the liquid depth, except that the penetration of the indicated baffles or sanitary tees for horizontal cylindrical tanks must be 35% of the total liquid depth. They must also extend above the liquid surface as required in division (J)(4) of this section.
(6) There must be at least one inch between the underside of the top of the tank and the highest point of the inlet and outlet baffles.
(7) The nearest point on the inlet baffles other than sanitary tees must be no less than six inches and no more than 12 inches from the end of the inlet pipe. The nearest point on the outlet baffle, other than sanitary tees, must not be closer than 6 inches and no more than 12 inches from the beginning of the outlet pipe of the baffle. Sanitary tees used as inlet or outlet baffles must be at least four inches in diameter.
(K) Septic tanks shall have a minimum of two maintenance holes with a minimum diameter of 20 inches (least dimension). One maintenance hole must be over the outlet device (baffles or screen). Another maintenance hole must be either above the inlet device, or near the center of the tank, and facilitate pumping without interference. Enough maintenance holes must be provided so access can be gained within six feet of all walls for solids removal of each compartment. Six-inch inspection pipes shall be provided over any baffles that do not have access maintenance holes.
(L) All maintenance hole risers must extend through the tank cover above final grade.
(M) Covers for maintenance holes must:
(1) Be secured by being locked, being bolted or screwed, having a weight of at least 95 pounds, or other methods approved by the Department or local unit of government. Covers shall also be leak resistant; and be designed so the cover cannot be slid or flipped, which could allow unauthorized access to the tank.
(2) Have a written and graphic label warning of the hazardous conditions inside the tank.
(3) Be capable of withstanding a load that the cover is anticipated to receive.
(4) Be made of a material suitable for outdoor use and resistant to ultraviolet degradation.
(N) A secondary method to control unauthorized access must be provided.
(O) All precast reinforced concrete sewage tanks must be constructed to meet the requirements of this chapter. Information on best practices for tank construction is found in the National Precast Concrete Association’s best practices manual, Precast Concrete On-site Wastewater Tanks (2005). This manual is incorporated by reference, is available through the Minitex interlibrary loan system, and is not subject to frequent change. If a conflict exists between the manual and this chapter, this chapter applies.
(P) All fiberglass-reinforced polyester and polyethylene tanks must be constructed to meet the requirements of this chapter. Information on best practices for these tanks is found in the International Association of Plumbing and Mechanical Officials (IAPMO), Material and Property Standard for Prefabricated Septic Tanks, Standard PS 1-2006 (2006). This standard is incorporated by reference, is available through the Minitex interlibrary loan system, and is not subject to frequent change. If conflicts exist between the standard and this chapter, this chapter applies.
(Q) Precast reinforced concrete tanks must:
(1) Have a method to lift the tank for an ultimate load that is four times the working load.
(2) Undergo proper curing to achieve a compressive strength of 4,000 pounds per square inch before transport, placement, or use.
(3) Have no pipe penetration points or openings in the exterior walls or tank bottom below the tank liquid level, unless designed for a specific operational purpose and approved by the Department or local unit of government.
(R) Fiberglass-reinforced polyester or polyethylene tanks must be protected against deterioration during storage.
(S) Location and installation of tanks:
(1) Sewage tanks must not be placed in areas that prohibit the removal of solids and liquids from the tank according to § 52.22.
(2) Sewage tanks must be set back as specified in Table V in § 52.16.
(3) The top of sewage tanks must not be buried deeper than four feet from final grade for new dwellings, or the tank manufacturer’s maximum designed depth for the tank. The minimum depth of soil cover over the insulation on the top of the tank is six inches.
(4) Sewage tanks must not be placed in floodways, drainageways, or swales. Upslope drainage must be diverted away from the location of all tanks. A tank’s final cover must be crowned or sloped to shed surface water.
(5) Sewage tanks must not be placed in areas subject to vehicular traffic unless engineered for the anticipated load.
(6) Sewage tanks must be placed on firm and evenly compacted soil and with the soil level in all directions. The bottom shall be excavated in a manner so the vertical load is borne by the tank walls and not the tank bottom. If the bottom of the tank excavation contains rocks, bedding material must be used according to manufacturer’s instructions. The soil beneath the tank must be capable of bearing the weight of the tank and its contents.
(7) Sewage tanks and risers must be installed according to manufacturer’s requirements and in a structurally sound and watertight fashion.
(8) If the top of a sewage tank is to be less than two feet from final grade, the lid of the tank must be insulated to an R-value of ten. Maintenance hole covers must be insulated to an R-value often. All insulating materials must be resistant to water absorption.
(9) Sewage tanks placed below the level of the periodically saturated soil must employ a method to protect against flotation under periodic saturated soil conditions when the tank is empty.
(10) Connections between the concrete tank and the building sewer or supply pipe must meet the requirements of American Society for Testing and Materials, Standard Specification for Resilient Connectors Between Reinforced Concrete Manhole Structures, Pipes, and Laterals, ASTM C923 (2002), or equivalent. The standard is incorporated by reference, is available through the Minitex interlibrary loan system, and is not subject to frequent change.
(11) Joints of concrete tanks, concrete tank lids, and concrete risers must be sealed using a bonding compound that meets American Society for Testing and Materials, Standard Specification for Joints for Concrete Pipe, Manholes, and Precast Box Sections Using Preformed Flexible Joint Sealants, ASTM C990 (2003). The standard is incorporated by reference, is available through the Minitex interlibrary loan system, and is not subject to frequent change.
(T) All septic tanks must be assessed in accordance with Minn. Rules Chapter 7080.2010.
(U) Tanks must be identified in accordance with the following:
(1) Sewage tanks must be marked near the outlet with:
(a) The manufacturer’s name.
(b) The model number.
(c) The liquid capacity.
(d) The date of manufacture.
(e) The maximum depth of burial.
(2) The tank manufacturer or manufacturer’s agent shall provide the information in division (T) of this section to the installer in writing.
(3) The tank inlet or outlet must be clearly marked.
(4) The installer shall submit the information in division (T) of this section with the as-built drawing.
(V) Sewage tanks must meet the requirements in Minn. Rules §§ 7080.1910 to 7080.20202 by February 4, 2011. Tanks produced and installed prior to February 4,2011 must meet the requirements of Minn. Rules 2005, § 7080.0130.
(W) All holding or treatment tanks or vessels, including lined vessels and grease interceptors serving MSTS, must conform to the applicable requirements of this section, except as modified in division (W) through (AA) of this section, or as designed by a professional engineer and approved by the Department or local unit of government.
(X) Septic tank capacity for MSTS or other establishments shall be determined by:
(1) Total septic tank liquid capacity for a common tank serving multiple dwellings under gravity flow to the common tank is determined by multiplying the design flow by 3.0.
(2) Total septic tank liquid capacity for a common tank serving multiple dwellings under pressure flow to the common tank is determined by multiplying the design flow by 4.0.
(3) Common multiple septic tanks must be connected in series. Individual tanks connected in series or any compartment of a tank must have a capacity of more than one-fourth of the required to total liquid capacity.
(4) For MSTS that have individual septic tanks at each dwelling, the individual tanks must meet the requirements of § 52.13(E).
(5) Total septic tank liquid capacity prior to other treatment devices shall be according to manufacturer’s requirements or accepted standards.
(6) Holding tanks serving other establishments must provide storage of at least five times the design flow.
(7) Effluent screens must be used on the outlet baffle on the final septic tank or pressure filters must be used in the pump tank if common tanks are employed in series. Alarms must be employed on tanks equipped with effluent screens. Lint filters are recommended if the sewage contains laundry waste.
(Y) For common septic tanks, the liquid depth of septic tanks to determine liquid capacity must be no greater than 84 inches. The length-to-width ratio and the length-to-depth ratio must facilitate settling of solids.
(Z) For common septic tanks, the space in the tank between the liquid surface and the top of the inlet and outlet baffles must not be less than 20 percent of the total required liquid capacity.
(AA) All tanks used for MSTS must be tested for watertightness in accordance with Minn. Rules Chapter 7080.2010, Subp. (3). The test shall be conducted to include the watertightness of all connections and risers.
(BB) Liners used as watertight barriers for treatment devices must be designed and constructed according to liner requirements developed by the Commissioner of the Minnesota Pollution Control Agency. If conflicts exist between this chapter and those requirements, this chapter applies. Compacted soil liners must not be used as watertight barriers for treatment devices. Liners must be tested and must hold water without loss for 24 hours after being filled to the top of the liner.
(CC) A commercial or institutional food preparation facility such as, but not limited to, a restaurant, cafeteria, or institutional kitchen, served by a system regulated under this chapter, the system design for which was submitted to the Department or local unit of government after the effective date of this chapter, shall install an external grease interceptor, unless other grease control measures are taken and approved by the Department or local unit of government.
(Ord. 2010-162, passed 5-17-2010)