Nev. Admin. Code § 444.8352 - Absorption trench system: General requirements; design calculations

1. An individual sewage disposal system utilizing absorption trenches may be used wherever practical except if limiting conditions such as high groundwater, sloping terrain, impervious soil or bedrock exist at the site where the individual sewage disposal system is to be located.

2. The design for an individual sewage disposal system utilizing absorption trenches must comply with the design criteria set forth in this section and NAC 444.8354 and 444.8356.

3. A homeowner or a licensed contractor may design a residential system that uses absorption trenches for the residence of the homeowner if the percolation rate of the soils in which the residential system will be placed is 60 minutes per inch or less and the site is free of the limiting conditions described in subsection 1.

4. The following is an example of the calculations required to design an individual sewage disposal system utilizing absorption trenches:

A homeowner plans to build a 4-bedroom house. Percolation testing yields percolation rates of 15 minutes per inch in test hole number one and 23 minutes per inch in test hole number two. To determine the required capacity of the wastewater treatment tank, the required number of square feet of disposal area, and the required number of lineal feet of absorption trench:

Step 1 - Pursuant to the table in subsection 1 of NAC 444.8306, a septic or wastewater treatment tank that has a capacity of 1,200 gallons is required for a 4-bedroom house.

Step 2 - The slowest percolation rate, which is 23 minutes per inch, must be used to determine the design application rate. Pursuant to the table in subsection 9 of NAC 444.8354, the design application rate is 1.0 gallon per square foot.

Step 3 - The required absorption area is calculated by dividing the capacity of the septic or wastewater treatment tank by the design application rate as follows:

1,200 gallons / 1.0 gallon/square foot = 1,200 square feet

Step 4 - The effective sidewall area must be calculated by multiplying the number of feet of aggregate beneath the distribution line by 2, to utilize the absorption area on each side of the trench. For the purposes of this example, assume that a maximum of 4 square feet of the area of the sidewall will be utilized on each trench wall per each lineal foot as follows:

2 * 4 square feet = 8 square feet per each lineal foot of trench

Step 5 - The required trench length is now determined by dividing the required absorption area by the effective sidewall area as follows:

1,200 square feet / 8 square feet/lineal foot = 150 lineal feet

Since the maximum length of a distribution line may not exceed 110 feet, a minimum of two trenches of equivalent lengths are required. Therefore, the use of two distribution lines that are 75 feet long with 4 feet of aggregate beneath the distribution lines would be acceptable.

Notes

Nev. Admin. Code § 444.8352

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

NRS 439.200, 444.650