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Effective April 28, 2015 Chapter Four Subsurface Sewage Treatment System Regulations <br />SECTION 13 SEWAGE TANKS <br />13.1 Sewage Tanks, General. <br />Sewage tanks serving SSTS must meet or exceed the applicable requirements of this Section unless otherwise <br />approved by a Minnesota licensed professional engineer and approved by the Department. <br />13.2 Tank Strength Requirements. <br />Tanks, fittings, risers, and apertures must: <br />(1) Be capable of supporting long-term vertical loads for the conditions in which the tank will be <br />placed. These loads include, but are not limited to, saturated soil load, based on 130 pounds per <br />cubic foot. <br />(2) Be capable of withstanding a lateral load for the conditions the tank will be placed. <br />(3) With proper maintenance and venting, not be subject to failure due to corrosion and degradation <br />from sewage or sewage gases, including risers and maintenance hole covers. <br />(4) Be structurally capable of withstanding exposure and stresses from freezing conditions. <br />13.3 Poured -in -place concrete Tanks. <br />Poured -in -place concrete tanks must be designed to meet each requirement in Section 13.2, and be designed by a <br />Minnesota licensed professional engineer. <br />13.4 Septic Tank Design. <br />Septic tanks must: <br />(1) Have a liquid depth of at least 30 inches. Any liquid depth that is greater than 84 inches must not <br />be used when calculating the septic tank liquid capacity. <br />(2) Have a minimum of six feet between the inlet and outlet of the tank, rather than between <br />compartments, or have a minimum of six feet from the inlet of the first tank to the outlet of the last <br />tank in series. <br />(3) If site conditions warrant, the inlet and outlet are allowed to be located on walls that are not <br />opposite each other along axis of the maximum dimension; however, the requirements of Section <br />13.4 (2) must be met. <br />(4) Have an inlet invert at least two inches above the outlet invert. <br />(5) Have a space between the liquid surface and the top of the inlet and outlet baffles of not less than <br />six inches or 100 gallons, whichever is greater, for all liquid depths with an effluent screen and <br />alarm or for liquid depth of less than 39 inches without an effluent screen and alarm. The space <br />between the liquid surface and the top of the inlet and outlet baffles must not be less than eight <br />inches for the liquid depths of 39 inches or more without an effluent screen and alarm. In addition, <br />there must be at least one inch between the underside of the top of the tank and the highest point of <br />the inlet and outlet baffles. <br />13.5 Minimum Tank Capacity. <br />For dwellings, there shall be two (2) septic tanks in series with the liquid capacity based on the number of bedrooms <br />in the dwelling; such tanks shall be as large as the capacities in Table III. The only exception to this requirement is <br />for the upgrade of an existing compliant system if the primary tank capacity is met and there is no garbage disposal <br />or sewage pump. System replacement shall require two (2) tanks in series. <br />48 Washington County Development Code <br />