Nevada Administrative Code › Chapter 444 - Sanitation › SEWAGE DISPOSAL › Absorption and Treatment of Effluent › Section 444.8352 - Absorption trench system: General requirements; design calculations

Current through June 11, 2024
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.
Added to NAC by Bd. of
				  Health by R129-98, eff. 3-25-99
NRS
					 439.200,
					 444.650