NAC445A.9684. Capping fill trench.

     1. Except as otherwise provided in subsection 2, a capping fill trench may be used where conditions relating to high groundwater prohibit the installation of an absorption trench pursuant to NAC 445A.9676.

     2. A capping fill trench must not be used if the soil in which the capping fill is to be placed is saturated.

     3. The soil surrounding and beneath the bottom of a capping fill trench must have a percolation rate that is more than 10 minutes per inch but less than or equal to 120 minutes per inch. A capping fill trench must not be installed on a slope that is more than 5 percent with a percolation rate slower than 60 minutes per inch, but may be installed on a slope of not more than 10 percent if the percolation rate is equal to or faster than 60 minutes per inch.

     4. The required absorption area of the capping fill trench must be determined by calculating the size of the effective sidewall pursuant to NAC 445A.9676.

     5. A minimum depth of 4 feet must be maintained between the bottom of the capping fill trench and the level of the seasonal high groundwater or any impermeable barrier or other limiting feature.

     6. The invert of the distribution pipe must be placed less than 12 inches below the existing grade of the native soil. At least 2 inches of aggregate must be placed over 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 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.

     8. Each capping fill trench must be constructed before the capping fill is constructed.

     9. The existing vegetative mat in the fill area must be disrupted by scarification or plowing to remove roots and other organic matter that may slow the percolation rate. The soil to be used as capping fill must be of a texture similar to the native soil. The native soil and the capping fill must be mixed at their point of interface.

     10. The capping fill must:

     (a) Be placed over the aggregate and the cover set forth in subsection 7 to a depth of not less than 12 inches or more than 18 inches.

     (b) Be graded to provide positive drainage away from the absorption trenches and toward the perimeter of the capping fill.

     (c) Be placed in such a manner as to prevent the compaction of the scarified soil at the interface of the native soil and capping fill.

     (d) Extend at least 10 feet beyond the sidewall of the absorption trench.

     11. Plant vegetation must be established on the top of the fill area to reduce the potential for the erosion of the capping fill.

     12. The owner or operator of the on-site sewage disposal system must take such precautions as are necessary to prevent the compaction of the capping fill, including, without limitation, prohibiting vehicle travel on the capping fill.

     13. The following is a diagram of a capping fill trench:

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