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 62-03.1-03-05 - Percolation tests

Current through Supplement No. 393, July, 2024
When percolation tests are required, they must be made as
				  follows:
1.
Test hole
				dimensions and locations.
Each test hole must be six inches [15.24
				centimeters] in diameter, have vertical sides, and be bored or dug to the depth
				of the bottom of the proposed individual sewage treatment system. Soil texture
				descriptions must be recorded noting depths where texture changes occur.
2.
Preparation of the test
				hole.
The bottom and sides of the hole must be carefully scratched to
				remove any smearing and to provide a natural soil surface into which water may
				penetrate.
All loose material must be removed from the bottom of the
				  test hole and two inches [5.08 centimeters] of one-fourth-inch to
				  three-fourths-inch [.635-centimeter to 1.90-centimeter] gravel must be added to
				  protect the bottom from scouring.
3.
Soil saturation and swelling.
The hole must be carefully filled with clear water to a minimum depth of
				twelve inches [30.48 centimeters] over the soil at the bottom of the test hole
				and maintained for no less than four hours. The soil must then be allowed to
				swell for at least sixteen, but no more than thirty hours. In sandy soils, the
				saturation and swelling procedure is not required and the test may proceed if
				one filling of the hole has seeped away in less than ten minutes.
4.
Percolation rate measurement.
a. In sandy soils. Adjust the water depth to
				eight inches [20.32 centimeters] over the soil at the bottom of the test hole.
				From a fixed reference point, the drop in water level must be measured in
				inches [centimeters] to the nearest one-eighth inch [.34 centimeter] at
				approximately ten-minute intervals. A measurement can also be made by
				determining the time it takes for the water level to drop one inch [2.54
				centimeters] from an eight-inch [20.32-centimeter] reference point. If eight
				inches [20.32 centimeters] of water seeps away in less than ten minutes, a
				shorter interval between measurements must be used, but in no case may the
				water depth exceed eight inches [20.32 centimeters]. The test must continue
				until three consecutive percolation rate measurements vary by a range of no
				more than ten percent.
b. In other
				soils. Adjust the water depth to eight inches [20.32 centimeters] over the soil
				at the bottom of the test hole. From a fixed reference point, the drop in water
				level must be measured in inches [centimeters] to the nearest one-eighth inch
				[.34 centimeter] at approximately thirty-minute intervals, refilling between
				measurements to maintain an eight-inch [20.32-centimeter] starting head. The
				test must continue until three consecutive percolation rate measurements vary
				by a range of no more than ten percent. The percolation rate can also be made
				by observing the time it takes the water level to drop one inch [2.54
				centimeters] from an eight-inch [20.32-centimeter] reference point if a
				constant water depth of at least eight inches [20.32 centimeters] has been
				maintained for at least four hours prior to the measurement.