NAC445A.968. Absorption bed.

     1. If the use of an absorption trench is not practical, an absorption bed may be used in lieu of an absorption trench, if justified by the design engineer. The bottom of the absorption bed must serve as the primary absorptive medium.

     2. An absorption bed used in an on-site sewage disposal system must meet the following design and construction criteria:

     (a) The absorption bed must not be placed on a slope with a grade of more than 5 percent.

     (b) The bottom of the absorption bed must be level.

     (c) The percolation rate of the soils at the bottom of the absorption bed must not be more than 60 minutes per inch.

     (d) The area of the sidewall or the depth of the aggregate beneath each distribution pipe must not be less than 12 inches or more than 36 inches.

     (e) An absorption bed must have at least two distribution pipes, which must not be less than 4 feet or more than 6 feet apart and laid with perforations facing down. The distribution pipes must be:

          (1) Level and placed not less than 3 feet or more than 6 feet from the sidewalls of the bed;

          (2) Not longer than 110 feet;

          (3) Placed on at least 12 inches of clean, graded aggregate and covered by at least 2 inches of aggregate; and

          (4) Not less than 4 inches in diameter,

Ê unless a pressure distribution system is used. Distribution pipes used in a pressure distribution system must meet the requirements for a pressure distribution system set forth in NAC 445A.969.

     3. The invert of the piping for the drain field must not be less than 12 inches or more than 48 inches below the finished grade.

     4. The aggregate covering the distribution pipe must be covered with untreated building paper, straw with a minimum thickness of 1 inch, geotextile fabric or a similar covering approved by the Division or other administrative authority.

     5. The top of the absorption bed must be at least 6 inches below the surface of the natural soil.

     6. A capping fill of soil must be placed on top of the absorption bed. The capping fill must:

     (a) Extend at least 10 feet beyond the perimeter of the leaching area of the absorption bed; and

     (b) Be placed at a minimum depth of 12 inches above the finished grade to allow for settling.

     7. If more than 500 linear feet of distribution pipe is used, dosing is required pursuant to NAC 445A.9664.

     8. The owner or operator of an on-site sewage disposal system must take such precautions as are necessary to prevent compacting the bottom of the absorption bed. Any loose or smeared soil must be raked and removed. No vehicles may travel on the area of the absorption bed during excavation or after excavation is completed.

     9. The following is a diagram of an absorption bed:

     (Added to NAC by Environmental Comm’n by R194-07, eff. 8-26-2008)