Wyoming Administrative Code
Agency 020 - Environmental Quality, Dept. of
Sub-Agency 0011 - Water Quality
Chapter 25 - SEPTIC TANKS, SOIL ABSORPTION SYSTEMS, AND OTHER SMALL WASTEWATER SYSTEMS
Appendix A - Percolation Test Procedure
Section 1.Purpose
(a) Percolation tests are used to determine absorption system site suitability and to size the absorption system.
Section 2.Procedure
(a) General Requirements:
(i) Percolation tests shall not be conducted in test holes that extend into groundwater, bedrock, or frozen ground.
(ii) The percolation test shall be conducted only after the soil exploration pit has been dug and examined.
(iii) A minimum of three (3) percolation test holes are required.
(iv) The percolation test holes shall be spaced uniformly over the proposed soil absorption system site.
(b) Preparation
(i) A twelve (12) inch diameter hole shall be dug or bored to the proposed depth of the soil absorption system.
(ii) The walls shall be vertical, with the natural soil surface exposed without smearing.
(iii) The sides and bottom shall be scarified with a sharp pointed instrument and the loose material shall be removed from the hole.
(iv) Two (2) inches of gravel or coarse sand shall be placed in the bottom of the hole to prevent it from scouring and sealing during water addition.
(c) Presoaking
(i) The purpose of presoaking is to have the water conditions in the soil reach a stable condition similar to that which exists during continual wastewater application. The minimum time of presoaking varies with soil conditions but must be sufficiently long so that the water seeps away at a constant rate. The following presoaking instructions are usually sufficient to obtain a constant rate.
(A) Fill each hole with clear water to a level at least eighteen (18) inches above the gravel or coarse sand. If the eighteen (18) inches of water seeps away in eighteen (18) minutes or less, add eighteen (18) inches of water a second time. If the second filling of eighteen (18) inches of water seeps away in eighteen (18) minutes or less, this indicates the soil is sandy and is excessively permeable. The soil absorption system shall meet the requirements of Section 8(c).
(B) If either the first or second fillings of eighteen (18) inches of water does not seep away in ninety (90) minutes, eighteen (18) inches of water must be maintained in the hole for at least four (4) hours to presoak the test hole. After the four (4) hours of water contact time, wait at least twelve (12) hours before starting the percolation rate measurement.
(d) Percolation Rate Measurement
(i) Fill each test hole with twelve (12) inches of water and allow the soil to rehydrate for fifteen (15) minutes prior to any measurements.
(ii) Establish a fixed reference point to measure the incremental water level drop at constant time intervals. The water level drop should be measured to the nearest ? of an inch and the minimum time interval is ten (10) minutes.
(iii) Refill the test hole to twelve (12) inches above the gravel before starting the measurements. Continue to measure the incremental water level drop at a constant time interval until a consistent incremental water level drop is achieved. A consistent water level drop is achieved when three (3) consecutive water level drops are within ? inches of each other.
(iv) Before the water level drops below one (1) inch above the gravel, refill the test hole to twelve (12) inches and continue to measure the incremental water level drop.
(v) The percolation rate is calculated for each hole using the following formula:
(vi) If only three to five percolation tests are performed, the design percolation rate for the absorption system is the largest rate from all the holes tested. If six or more percolation tests are performed, the design percolation rate for the absorption system is the average of all the holes tested as determined by the above formula.
(e) The following information shall be recorded:
(i) Date(s) of test(s);
(ii) Location, diameter, and depth of each test hole;
(iii) Duration of presoak;
(iv) Time of day for beginning and end of each water-level drop interval;
(v) Each water-level drop measurement;
(vi) Calculated percolation rate;
(vii) Name and signature of person performing test;
(viii) Name of owner or project name; and
(ix) Certification that the percolation test was done in accordance with Wyoming Water Quality Rules and Regulations Chapter 25 Appendix A.
