Title 124 - NEBRASKA DEPARTMENT OF ENVIRONMENTAL QUALITY
Chapter 8 - SEPTIC TANK DESIGN
All septic tanks regardless of material or method of construction shall conform to the following criteria as shown in Figures 8.1, 8.2, 8.3, and 8.4.
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 42 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 tank or compartment thereof shall have an inside horizontal dimension less than 24 inches.
003 Inlet and outlet connections of the tank shall be provided with baffles. See Figure 8.5.
004 The space in the 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 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 tank, affixed with a permanent waterproof adhesive, or affixed with stainless steel connectors top and bottom.
007 The inlet baffle shall extend at least 6 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 outlet baffle and the baffles between compartments shall extend below the liquid surface a distance equal to 40 percent of the liquid depth except that the penetration of the indicated baffles or sanitary tees for horizontal cylindrical tanks shall be 35 percent of the total liquid depth. They also shall extend above the liquid surface as required in item 004. In no case shall they extend less than six inches above the liquid surface.
009 There shall be at least 1 inch between the underside of the top of the tank and the highest point of the inlet and outlet devices.
010 The inlet invert shall be not less than 2 inches above the outlet invert.
011 The inlet and outlet shall be located opposite each other along the axis of maximum dimension and shall be constructed of noncorrosive materials. The horizontal distance between the nearest points of the inlet and outlet devices shall be at least 4 feet.
012 Sanitary tees shall be at least 4 inches in diameter. Inlet baffles shall be located no less than 6 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 6 inches measured from beginning of the outlet pipe to the nearest point on the baffle.
013 Access to the septic tank shall be as follows:
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. The manhole shall extend through the top of the tank to a point within 12 inches but at least six inches below grade. Each manhole shall have a cover. The manhole cover shall be covered with at least six inches of earth. A riser as described in Chapter 9, Section 003 may also be provided.
013.02 There shall be an inspection pipe at least 6 inches diameter or a manhole over both the inlet and outlet devices.
014 Compartmentation of single tanks.
014.01 Septic tanks larger than 3000 gallons and fabricated as a single unit shall be divided into two or more compartments.
014.02 When a septic tank is divided into two compartments, not less than one-half nor more than two-thirds of the total volume shall be in the first compartment.
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 tank is used to obtain the required liquid volume, the tanks shall be connected in series.
015.02 No more than four tanks in series shall be used to obtain the required liquid volume.
015.03 The first tank shall be no smaller than any subsequent tanks in series.
Figure 8.1 Septic Tank, Profile View
Figure 8.1
Figure 8.2
Figure 8.3
Figure 8.4
Figure 8.5 | 
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Enabling Legislation: Neb. Rev. Stat. §81-1505(8).
Legal Citation: Title 124, Ch. 8, Nebraska Department of Environmental Quality
Nebraska Department of Environmental Quality
1200 "N" Street, Suite 400
P.O. Box 98922
Lincoln, Nebraska 68509
(402) 471-2186