North Dakota Administrative Code › Title 62 - State Board of Plumbing › Article 62-03.1 - Plumbing Installation Standards › Chapter 62-03.1-03 - Private Sewage Disposal Systems › Section 62-03.1-03-09 - Absorption trenches

Current through Supplement No. 393, July, 2024
1.
Design.
Absorption trenches shall be designed and constructed on the basis of
				the percolation test results or other soil data. Trench bottom area required is
				shown in the table in subsection 4. The bottom of the trench shall be dug so it
				is dead level throughout its length. The maximum depth to the bottom of
				absorption trenches may not exceed forty-eight inches [121.92 centimeters]. The
				trench bottom must be at least twenty-four inches [60.96 centimeters] above the
				mottled soil condition indicating a water table or from standing water in the
				borehole.
2.
Filter
				material.
The filter material shall cover the four-inch
				[10.16-centimeter] diameter pipe to a depth of two inches [3.08 centimeters]
				measured from the crown of the pipe and extend the full width of the trench and
				shall be not less than six inches [15.24 centimeters] deep beneath the bottom
				of the four-inch [10.16-centimeter] diameter pipe. The filter material may be
				washed rock or crushed stone ranging in size from one inch to three inches
				[2.54 centimeters to 7.62 centimeters]. The filter material shall be covered by
				red rosin paper40 , hay, straw, or approved filter fabric40 , as the laying of
				the pipe proceeds. Approved graveless systems may be used in lieu of rockfill
				providing an equivalent surface area of soil is utilized.
3.
Spacing.
Trenches must have a
				minimum spacing of undisturbed earth of six feet [1.83 meters] for
				eighteen-inch to twenty-four-inch [45.72-centimeter to 60.96-centimeter] trench
				widths and nine feet [2.74 meters] for trenches up to thirty-six inches [91.44
				centimeters]wide.
4.
Absorption field.
The size and requirements for absorption fields
				shall conform to those given in the following table:
Table - Recommended absorption trench area.
Depth of Rock
Percolation Rate
Soil
Classification
Below
Distribution
Pipe
Minutes/Inch
6"
12"
18"
24"
-Trench bottom area loading rate,
							 gal/ft2/day
1 to 5
.Sand
1.2
1.5
1.80
2.1
6 to 15
Sandy loam
0.8
1.0
1.20
1.4
16 to 30
Loam
0.6
0.75
0.90
1.05
31 to 45
Silt loam
0.5
0.63
0.76
0.89
46 to 60
Clay loam
0.45
0.57
0.68
0.79
-Square feet of trench
							 bottom/bedroom1
.1 to 5
125
100
85
70
6 to 15
190
150
125
110
16 to 30
250
200
165
145
31 to 45
300
240
200
170
46 to 60
330
265
220
190
1Based on sewage volume of
				  150/GPD/Bedroom
5.
Absorption lines.
a. Gravity
				distribution. Absorption lines shall be constructed of four-inch
				[10.16-centimeter] pipe. For approved plumbing materials, see table 14-1 of
				chapter 14 of the Uniform Plumbing Code.
b. Pressure distribution. Absorption lines
				must be constructed of one and one-half-inch to two-inch [3.81-centimeter to
				5.08-centimeter] rigid plastic pipe with one-fourth-inch [6.35-millimeter]
				holes drilled in the bottom of the pipes. The number ofperforations and spacing
				of perforations for different diameter pipes for pressure distribution laterals
				must not exceed ten percent of the average pressure head on the perforations.
				The pipe and connections must be able to withstand a pressure of at least forty
				pounds per square inch. The perforated laterals should be attached to a
				two-inch [5.08-centimeter] manifold pipe and should have the ends capped. The
				laterals should be spaced no further than forty inches [101.6 centimeters] on
				center and no further than twenty inches [50.80 centimeters] from the edge of
				the rock. Pipe must be installed level and capped at the ends. The manifold
				must be supported and backfilled by hand.