The procedure for conducting the percolation test is as follows.
(A) Dig or bore holes with horizontal dimensions of from four to 12 inches and vertical sides to the estimated depth of the bottom of the proposed absorption trench. In order to save time, labor and volume of water required per test, the holes may be bored with a four-inch auger.
(B) Scratch the bottom and sides of the hole with a knife blade or sharp pointed instrument in order to remove any smeared soil surface and to provide a natural soil interface into which water may percolate. Remove all loose soil from the hole. Place about two inches of clean coarse sand or fine gravel in the bottom of the hole.
(C) Carefully fill the hole with clear water. By refilling if necessary, keep the hole full of water for at least 12 hours. This saturation procedure will give most soils ample time to swell and approach the conditions that prevail during the wetter seasons of the year.
(D) After the 12-hour saturation period, allow the water in the hole to seep away completely. Remove that portion of the sand or gravel which has become coated with soil particles.
(E) Pour about 12 inches of water into the hole and wait until about six inches of this water remains.
(F) With about six inches of water remaining in the hole, establish a reference point by use of a nail stuck in the side of the hole near the top of the hole. From this point, obtain a measurement to the top of the water level. Record the measurement and the exact time.
(G) Continue the measurement to the top of the water surface for a period of at least three hours and time recording at 15-minute intervals until at least three consecutive readings of approximately the same rates of percolation are obtained. It may be necessary to add another six inches of water more than once to obtain the consecutive same-rate readings.
(H) Convert the final time interval obtained in division (G) above to minutes and divide this figure by the number of inches of water which has seeped away in that interval to obtain the time for one inch of water to seep away. The system design should be based on the percolation rate of the slowest hole on the proposed site.
(I) Determine from Table IV the square feet of trench bottom area needed for each bedroom. See Table V for width and spacing of absorption trenches.
Table V | ||
Width of Trench at Bottom (in Inches) | Depth of Trench (in Inches) | Effective Absorption Area in Square Feet (Per Linear Foot) |
18 | 18 to 30 | 1.5 |
24 | 18 to 30 | 2.0 |
30 | 18 to 36 | 2.5 |
36 | 24 to 36 | 3.0 |
(J) Multiply the square feet of trench bottom absorption area needed for each bedroom by the number of bedrooms in the house to get the total trench bottom area needed.
(1982 Code, § 91.09) (Ord. passed 1-13-1967; Ord. passed 1-22-1979; Ord. passed 4-29-1985; Ord. passed 11-17-1986)