Nevada Administrative Code › Chapter 444 - Sanitation › SEWAGE DISPOSAL › Absorption and Treatment of Effluent › Section 444.8354 - Absorption trench system: Design criteria

Current through June 11, 2024
1. The bottom
				of an absorption trench that is used in an individual sewage disposal system
				must be level and not less than 1 foot or more than 3 feet in width.
2. Excavations for absorption trenches must
				be spaced apart at a distance that is equal to or greater than 4 feet plus 2
				feet for each foot of depth which the trench is below the bottom of the
				distribution piping, as measured from the centerline of the trenches.
3. An individual lateral may not be more than
				110 feet long.
4. An absorption
				trench must not be excavated if the soil is extremely wet. Surfaces in an
				absorption trench which are smeared or compacted must be scarified to the depth
				to which the soils are smeared or compacted, and all loose material must be
				removed.
5. Distribution lines must
				be perforated drain pipe made of polyvinylchloride, unless otherwise approved
				by the administrative authority. The bottom of the distribution lines must be
				laid not less than 12 inches or more than 48 inches below the ground surface in
				continuous straight or curved lines with a slope of not less than 2 inches or
				more than 4 inches per 100 feet of pipe. Distribution lines must be equipped
				with end caps or vented to the surface at the end of the lines.
6. At least 12 inches of clean, graded
				aggregate ranging in size from 3/4 to 2 1/2 inches must be placed in the trench
				below the distribution line, and the aggregate must extend at least 2 inches
				over the top of the distribution line.
7. If an absorption trench is more than 6
				feet in depth below the finished grade, the aggregate must extend to not less
				than 12 inches below the ground surface to avoid an anaerobic condition in the
				trench.
8. The aggregate in an
				absorption trench must be covered with untreated building paper, straw,
				geotextile fabric, or a similar covering approved by the administrative
				authority, and the top of the trench must be overfilled with not less than 4
				inches or more than 6 inches of soil.
9. The percolation rate of the soil must be
				used to determine the design application rate in accordance with the following
				table:
Percolation Rate (minutes/inch)
Design Application Rate (gallons/square foot)
0-10
1.6
11-15
1.3
16-20
1.1
21-25
1.0
26-30
0.9
31-40
0.8
41-50
0.7
51-60
0.6
If the percolation rate of the soil is greater than 60
				  minutes per inch, the system must be designed by an engineer.
10. The required capacity of the septic tank
				must be divided by the design application rate to calculate the minimum
				absorption area required.
11. The
				area of the absorption trench must be determined by calculating the size of the
				effective area of the sidewall needed beneath the distribution line. Not more
				than 4 feet of aggregate below the distribution line may be used to calculate
				the effective area of the sidewall, except that aggregate which is in excess of
				4 feet below the distribution line may be used to calculate the effective area
				of the sidewall with the approval of the administrative authority. The required
				length of distribution line must be determined as follows:
The minimum size required for the absorption area (in square
				  feet) divided by [2 times the depth of the aggregate below the distribution
				  line (in feet)] = required length of distribution line (in feet)
12. The following is a diagram of
				an absorption trench:
Click here
				  to view image.
Added to NAC by Bd. of
				  Health by R129-98, eff. 3-25-99
NRS
					 439.200,
					 444.650