All septic tanks and holding tanks regardless of material or method of construction shall conform to the following criteria.
001 The depth from the invert of the outlet to the floor of the tank (liquid depth) of any septic tank or compartment thereof shall not be less than 36 inches and a liquid depth greater than 78 inches shall not be considered in determining tank capacity. The diameter of a septic tank shall not be less than 60 inches and the length shall be approximately two to three times the width.
002 No septic tank or compartment thereof shall have an inside horizontal dimension less than 24 inches.
003 Inlet and outlet connections of the septic tank shall be provided with baffles.
004 The space in the septic tank between the liquid surface and the top of the inlet and outlet baffles shall be not less than 20 percent of the total required liquid capacity, except that in horizontal cylindrical tanks and tanks with other irregular, non-rectangular cross-sectional shapes this space shall be not less than 15 percent of the total required liquid capacity.
005 Inlet and outlet baffles shall be constructed of acid resistant concrete, acid resistant fiberglass, or plastic.
006 Sanitary tees shall be affixed to the inlet or outlet pipes with a permanent waterproof adhesive. Baffles shall be integrally cast with the septic tank, affixed with a permanent waterproof adhesive, or affixed with stainless steel connectors top and bottom.
007 The septic tank inlet baffle shall extend at least six inches but not more than 20 percent of the total liquid depth below the liquid surface and at least one inch above the crown of the inlet sewer.
008 The septic tank outlet baffle and the baffles between compartments shall extend below the liquid surface a distance equal to approximately 40 percent of the liquid depth, except that the penetration of the indicated baffles or sanitary tees for horizontal cylindrical tanks and tanks with other irregular, non-rectangular cross-sectional shapes shall be approximately 35 percent of the total liquid depth. The baffles shall also extend above the liquid surface as required in item 004. In no case shall the baffles or tees extend less than six inches above the liquid surface.
009 There shall be at least one inch between the underside of the top of the septic tank and the highest point of the inlet and outlet devices.
010 The septic tank inlet invert shall be not less than one inch above the outlet invert.
011 The septic tank inlet and outlet shall be located opposite each other along the axis of maximum dimension and shall be constructed of non-corrosive materials. The horizontal distance between the nearest points of the inlet and outlet devices shall be at least four feet. A septic tank with two or more compartments may have the inlet and outlet located along the end of the tank or within 12 inches of the end of the tank as long as the inlet and outlet baffle requirements identified in this chapter are met.
012 Sanitary tees shall be at least four inches in diameter. Inlet baffles shall be located no less than six inches or no more than 12 inches measured from the end of the inlet pipe to the nearest point on the baffle. Outlet baffles shall be located six inches measured from beginning of the outlet pipe to the nearest point on the baffle.
013 Septic Tank or Holding Tank Access
013.01 There shall be one or more access manholes at least 12 inches in diameter and located within six feet of all walls of the tank. Each access manhole shall have a properly secured cover.
013.02 Each septic tank shall have an inspection pipe at least six inches in diameter over both the inlet and outlet devices. The inspection pipe shall extend to or above the ground surface and be capped flush or above finished grade. The inspection pipe cap shall be properly secured to prevent unwarranted access. A manhole access riser that meets the requirements of this Title may be used over both the inlet and outlet devices to satisfy the inspection pipe requirement.
013.01A The manhole shall extend through the top of the tank to a point within 12 inches but at least six inches below grade for a tank with no manhole riser. The manhole cover shall be covered with at least six inches of soil unless otherwise properly secured to prevent unwarranted access.
013.01B For a tank with a manhole riser, the riser shall be sufficiently large to allow for access and removal of the manhole cover. The manhole riser may extend to or above the ground surface. The manhole riser shall have a properly secured cover to prevent unwarranted access.
014 Single Tank
014.01 Where a septic system has a single septic tank larger than 3,000 gallons that is fabricated as a single unit, the tank shall be divided into two or more compartments.
014.02 When a septic tank is divided into two compartments, the volume in the first compartment in the direction of flow shall not be less than one-half or more than two-thirds of the total volume of the tank.
014.03 When a septic tank is divided into three or more compartments, one-half of the total volume shall be in the first compartment and the other half equally divided in the other compartments.
014.04 Connections between compartments shall be baffled so as to obtain effective retention of scum and sludge. The submergence of the inlet and outlet baffles of each compartment shall be as specified in 007 and 008.
014.05 Adequate venting shall be provided between compartments by baffles or by an opening of at least 50 square inches near the top of the compartment wall.
014.06 Adequate access to each compartment shall be provided by one or more manholes.
015 Multiple Tanks
015.01 Where more than one septic tank is used to obtain the required liquid volume, the tanks shall be connected in series.
015.02 No more than four septic tanks in series shall be used to obtain the required liquid volume.
015.03 The first septic tank shall be no smaller than any subsequent tanks in series.
016 A holding tank shall be equipped with an alarm or visible float that indicates when the tank is 90 percent or more full, except that an alarm or visible float is not required for an outdoor style toilet facility holding tank where no water supply is used.
017 Septic tanks and holding tanks shall be bedded with at least six inches of sand or fine gravel where rock or other undesirable conditions are encountered. The tank shall be placed level. Backfilling the excavation for the tank shall be done in layers with sufficient compaction to avoid settling. Backfill material shall be free of large stones and debris.
018 A tank subject to flotation, such as one located in an area where the seasonal high water table may be higher than the bottom of the tank, shall be properly secured or ballasted to prevent flotation.
Enabling Legislation: Neb. Rev. Stat. §81-1505(8).
Legal Citation: Title 124, Ch. 8, Nebraska Department of Environmental Quality.