NAC444.8361. Absorption bed: Design criteria.

     1. The absorptive area of an absorption bed must be at least 50 percent larger than the calculated size that would be required for a standard absorption trench.

     2. The percolation rate of the soils at the bottom of the absorption bed must not be less than 60 minutes per inch.

     3. The effective perimeter of the area of the sidewall beneath the distribution lines, or the depth of the aggregate, must not be less than 12 inches or more than 36 inches. The area of the sidewall may be added to the bottom of the bed when calculating the size of the total absorptive area of the individual sewage disposal system.

     4. An absorption bed must not be placed on a slope if the grade of the slope is greater than 8 percent. The bottom of the absorption bed must be level.

     5. The invert of the piping for the drain field must be not less than 12 inches or more than 48 inches below the finished grade. The top of the absorption bed must be at least 6 inches below the surface line of the natural soil, and a capping fill must be placed on top of the absorption bed. The capping fill must extend at least 10 feet beyond the perimeter of the leaching area of the absorption bed and must be placed at a minimum depth of 12 inches above the finished grade to allow for settling.

     6. An absorption bed must have at least two distribution lines which are separated by not less than 4 feet or more than 6 feet. The distribution lines must be level and placed not less than 3 feet or more than 6 feet from the sidewall of the bed. If a gravity discharge system is used, the distribution line must not be less than 4 inches in diameter. If a pressurized distribution line is used, the line must meet the design guidelines for a pressure distribution system as set forth in NAC 444.8394 and 444.8396.

     7. A distribution line must not be longer than 110 feet and must be placed on at least 12 inches of clean, graded aggregate ranging in size from 3/4 to 2 1/2 inches. At least 2 inches of aggregate must cover the top of the distribution line. Untreated building paper, straw, geotextile fabric, or any similar covering approved by the administrative authority, must cover the aggregate, and a backfill of soil must be placed over the covering.

     8. The owner of an individual sewage disposal system shall take such precautions as are necessary to avoid 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 after excavation is completed.

     9. Dosing is required if more than 500 linear feet of distribution lines are required.

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

     (Added to NAC by Bd. of Health by R129-98, eff. 3-25-99)