NAC445A.9682. Stepped network of trenches using relief lines.

     1. On sloping terrain where a conventional absorption trench or bed system cannot be installed or is not practical, a stepped network of trenches using relief lines between the trenches may be used.

     2. A design engineer who includes a stepped network of trenches using relief lines in the design specifications for an on-site sewage disposal system must expressly justify the use of such a system.

     3. A stepped network of trenches utilizing relief lines must allow the effluent from a completely filled trench to overflow through relief lines into a trench at a lower elevation, as shown in subsection 8.

     4. The size of the absorption area required for a stepped network of trenches using relief lines must be calculated based on the long-term acceptance rates set forth in NAC 445A.9674, and must conform to the requirements for sizing a standard absorption trench pursuant to NAC 445A.9676. Percolation testing or soils analyses conducted pursuant to NAC 445A.9668 or 445A.967 must be performed at the location of each stepped trench. The size of the required absorption area must be calculated based on the slowest percolation rate or the most restrictive soil found.

     5. Trenches for a stepped network of trenches using relief lines must be spaced at least 10 feet apart.

     6. The leaching aggregate must extend at least 4 inches above the top of the distribution pipe. The depth of aggregate beneath the distribution pipe is site-specific and must be determined by the design engineer with approval from the Division or other administrative authority.

     7. The invert of the relief line must be located not less than 1 inch or more than 2 inches above the top of the distribution pipe.

     8. The following is a diagram of a stepped network of trenches utilizing relief lines:

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