Alabama Administrative Code
Title 420 - ALABAMA STATE BOARD OF HEALTH
Chapter 420-3-1 - ONSITE SEWAGE TREATMENT AND DISPOSAL
Site Evaluation
Section 420-3-1-.45 - Percolation Test Procedure

(1) The percolation test hole shall be dug or bored to the appropriate testing depth according to 420-3-1-.40 Soil Testing Depth Requirements, but not less than 12 inches deep. The diameter of the hole shall be 4 to 8 inches (except when a permeameter is used).

(2) In order to remove any glazed or burnished spots on the walls of the test hole, the walls shall be scratched or made rough so as to provide a natural soil interface for absorption. All loose materials shall be removed from the hole. It is recommended that a 2-inch layer of coarse sand or gravel be added to the hole to protect the bottom from scouring.

(3) A percolation test hole shall be filled with clear water to a minimum depth of 12 inches over the bottom of the hole. Water shall be added to the test hole to maintain the 12-inch depth as often as necessary over a minimum period of 4 hours and preferably overnight, in order to saturate the surrounding soil.

(4) Percolation test measurements shall be made no later than 8 hours following the saturation process. The drop in the water surface shall be measured from a stable reference point at or above the surface, not inside the test hole, at 30-minute intervals until the completion of the test.

(5) After the saturation process, the testing professional shall adjust the water level to a depth of 6 inches over the bottom of the hole. From a stable reference point outside the test hole, the depth to the water surface shall be measured at 30-minute intervals for a period of 4 hours, or until a minimum of three readings have essentially the same drop. The total variation in drop between three readings shall be no more than one-eighth inch.

(6) Water shall be added as necessary to maintain the 6 inches of water above the bottom. The drop in the water elevation occurring in the last 30-minute interval shall determine the percolation rate, provided that the absorption rate has stabilized. If there is more than one- eighth inch variation in drop between the last three readings, the test shall continue to be made at additional 30-minute intervals until the rate has stabilized. The rate shall be considered stabilized when the last three readings are the same (not exceeding one-eighth inch) after the minimum 4 hours saturation period.

(7) Soils that are rated higher than moderate shrink-swell potential (plasticity index above 20 percent and a liquid limit greater than 50 percent) shall require a minimum of 24 hours of constant saturation prior to testing. See 420-3-1-.46 Extended Saturation Procedure.

(8) Additional saturation time may be required if sufficient swelling has not occurred as indicated by non-representative test results.

(9) For soils that absorb the first 6 inches of water in less than 30 minutes following saturation, measurements on the water surface shall be made at 10-minute intervals over a period of 1 hour. The drop of water surface that occurs in the final 10 minutes shall be used to compute the percolation rate. Generally, these are coarse textured soils. If this situation occurs in other soils, the test should be relocated.

(10) The percolation rate shall be reported as the number of minutes required for the water surface to drop 1 inch in the test hole after the rate is stabilized (min/inch or MPI).

(11) A copy of all field notes for each percolation test attempted shall be provided to the LHD upon request.