Section 62-03.1-03-07 - Septic tanks1.Liquid capacity. The liquid capacity of all septic tanks shall conform to the tables contained in subsection 7 of section 62-03.1-03-03 and this subsection as determined by the number of bedrooms or apartment units in dwelling occupancies and the occupant load or the number of plumbing fixture units as determined from table 7-3 of the Uniform Plumbing Code, whichever is greater, in other building occupancies. CAPACITY OF SEPTIC TANKS *
| Single-Family Dwellings - Number of Bedrooms | Multiple Dwelling Units or Apartments - One Bedroom Each | Other Uses -Maximum Fixture Units Served | Minimum Septic Tank Working Capacity in Gallons |
| 1-3 | 20 | 1000 |
| 4 | 2 | 25 | 1200 |
| 5 or 6 | 3 | 33 | 1500 |
| 7 or 8 | 4 | 45 | 2000 |
| 5 | 55 | 2250 |
| 6 | 60 | 2500 |
| 7 | 70 | 2750 |
| 8 | 80 | 3000 |
| 9 | 90 | 3250 |
| 10 | 100 | 3500 |
| Extra bedroom, 150 gallons each. |
| Extra dwelling units over 10, 250 gallons each. |
| Extra fixture units over 100, 25 gallons per fixture unit. |
* NOTE: Septic tank sizes in this table include sludge storage capacity and the connection of domestic food waste disposal units without further volume increase.
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2.Septic tank construction. Septic tanks must be constructed of sound durable materials not subject to excessive corrosion or decay and must be watertight. Each such tank must be structurally designed to withstand all anticipated earth or other loads and must be installed level and on a solid bed. All tanks regardless of material or method of construction must conform to the following criteria: a. The liquid depth of any septic tank or compartment shall be not less than thirty inches [76.20 centimeters], nor more than six and one-half feet [1.97 meters]. No tank may have an inside horizontal dimension less than twenty-four inches [60.96 centimeters]. b. The space in the tank between the liquid surface and the top of the inlet and outlet baffles must be not less than twenty percent of the total required liquid capacity, except that in horizontal cylindrical tanks this space must be not less than fifteen percent of the total required liquid capacity. c. There must be at least one inch [2.54 centimeters] between the underside of the top of the tank and the highest point of the inlet and outlet devices. The inlet invert must be not less than three inches [7.62 centimeters] above the outlet invert. d. Baffles must be integrally cast with the tank, affixed with a permanent waterproof adhesive or affixed with stainless steel connectors, top and bottom, and be constructed of acid-resistant concrete, acid-resistant fiberglass or plastic. e. The inlet baffle must extend at least six inches [15.24 centimeters], but not more than twenty percent of the total liquid depth below, the liquid surface and at least one inch [2.54 centimeters] above the crown of the inlet sewer. f. The outlet baffle and the baffles between compartments must extend below the liquid surface a distance equal to forty percent of the liquid depth, except that the penetration of the indicated baffles or sanitary tees for horizontal cylindrical tanks must be thirty-five percent of the total liquid depth. They also must extend above the liquid surface. In no case may they extend less than six inches [15.24 centimeters] above the liquid surface. g. Inlet baffles must be no less than six inches [15.24 centimeters] or no more than twelve inches [30.48 centimeters] measured from the end of the inlet pipe to the nearest point on the baffle. Outlet baffles must be six inches [15.24 centimeters] measured from beginning of the outlet pipe to the nearest point on the baffle. Sanitary tees used as baffles must be at least four inches [10.16 centimeters] in diameter. h. The inlet and outlet must be located opposite each other along the axis of maximum dimension. The horizontal distance between the nearest points of the inlet and outlet devices must be at least four feet [1.22 meters]. i. There may be one or more manholes. Manholes must be at least eighteen inches [45.72 centimeters] in diameter, and located within six feet [1.83 meters] of all walls of the tank. The manhole must extend through the cover to a point within twelve inches [30.48 centimeters] but no closer than six inches [15.24 centimeters] below finished grade. The manhole cover must be corrosion resistant, rated three hundred-pound [136.07-kilogram] load bearing, and covered with at least six inches [15.24 centimeters] of earth. When in the opinion of the administrative authority the manhole is permitted above finish grade, it must be safely secured. j. There must be an inspection pipe of at least four inches [10.16 centimeters] in diameter or a manhole over both the inlet and outlet devices. The inspection pipe must extend through the cover and be capped flush or above finished grade. A downward projection of the centerline of the inspection pipe must be directly in line with the centerline of the inlet or outlet device. 3.Multiple tanks.a. When more than one tank is used to obtain the required liquid volume, the tanks must be connected in series. b. No more than four tanks in series can be used to obtain the required liquid volume. c. The first tank must be no smaller than any subsequent tanks in series. 4.Septic tank materials. See table 14-1 of the Uniform Plumbing Code. 5.Depth of septic tank. Where septic tanks are installed above frostline, precautions must be taken to prevent the septic tank from freezing. 6.Service limited. No septic tank shall serve more than one property unless authorized by the administrative authority. 7.Disposal of effluent. The effluent from all septic tanks shall be disposed of underground by subsurface absorption trench, seepage beds, or approved alternative systems. N.D. Admin Code 62-03.1-03-07
General Authority: NDCC 43-18-09
Law Implemented: NDCC 43-18-09