NAC444.8384. Capping fill trench: Design criteria.

     1. The soil surrounding and beneath the bottom of a capping fill trench must have a percolation rate that is greater than 2 minutes per inch, but less than or equal to 120 minutes per inch. The required area of the absorption trench must be determined by calculating the size of the effective sidewall pursuant to subsection 11 of NAC 444.8354.

     2. 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, any impermeable barrier or any other limiting features.

     3. A capping fill trench must not be installed on a slope that is greater than 10 percent.

     4. The invert of the disposal drain pipe must be placed not more than 12 inches below the existing grade of the native soil. At least 2 inches of aggregate must be placed above the disposal drain pipe. Untreated building paper, straw, geotextile fabric, or any other similar covering approved by the health authority, must be placed above the aggregate before the placement of the capping fill.

     5. The absorption trenches must be constructed before the capping fill is constructed.

     6. The capping fill must extend at least 10 feet beyond the sidewall of the absorption trench. The vegetative mat in the fill area must be disrupted by scarification or plowing. The owner of the system shall take such precautions as are necessary to prevent compaction of the scarified area. No vehicles may travel on the capping fill.

     7. The native soil and the applied fill must be mixed at their point of interface. The soil to be used as fill must be of a texture similar to the native topsoil. The fill must be placed over the aggregate to a depth of not less than 12 inches or more than 18 inches.

     8. The fill must be evenly graded to provide positive drainage away from the absorption trenches and toward the perimeter of the capping fill. The fill material must be placed in such a manner so as to prevent the compaction of the scarified soil at the interface of the native soil and fill. Plant vegetation must be established on the top of the fill to reduce the potential for the erosion of the capping fill.

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

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

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