Section 62-03.1-03-05 - Percolation tests 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. 5.Calculating the percolation rate. Divide the time interval by the drop in water level to obtain the percolation rate in minutes per inch [2.54 centimeters]. Percolation rates determined for each test hole must be averaged to determine the final soil treatment system design.
A percolation test may not be run where frost exists below the depth of the proposed soil treatment system.
N.D. Admin Code 62-03.1-03-05
General Authority: NDCC 43-18-09
Law Implemented: NDCC 43-18-09