N.J. Admin. Code § 7:9A-6.4

Current through Register Vol. 56, No. 21, November 4, 2024

Section 7:9A-6.4 - Percolation test

(a) The following equipment is required for the percolation test:

1. A soil auger, post-hole digger or other means of preparing a test hole as prescribed in (b) below;

2. A knife or trowel for removing smeared or compacted surfaces from the walls of the test hole;

3. Fine (from two to 10 millimeter in diameter) gravel (optional);

4. A water supply (50 gallons is generally adequate);

5. A straight board (to serve as fixed reference point for water level measurements);

6. A clock and a ruler (12 inches or longer, engineering scale);

7. An automatic siphon or float valve (optional); and

8. A hole liner consisting of a 14 inch section of slotted pipe or well screen, or a 14 inch length of one-quarter inch hardware cloth or other similar material rolled into a tube (optional). The hole liner shall be no smaller than two inches in diameter less than the test hole.

(b) Percolation tests shall not be conducted in frozen ground or in holes which have been allowed to remain open to the atmosphere for periods greater than three days. The required configuration of the test hole is illustrated in Figure 7 of Appendix A. The following procedure shall be used in preparation of the test hole.

1. Step One: Excavate a test hole having horizontal dimensions of eight to 12 inches at a depth such that the lower six inches of the test hole are contained entirely within the soil horizon or layer of fill material being tested. In order to facilitate access to the lower portion of the hole, the test hole may be excavated from the bottom of a shallow pit provided that the vertical axis of the test hole is a minimum of 14 inches measured from the bottom of the pit to the bottom of the test hole.

2. Step Two: In soil textures other than sands or loamy sands, remove smeared or compacted soil from the sides and bottom of the test hole by inserting the tip of a knife or trowel into the soil surface and gently prying upward and outward. Remove loose soil from the test hole.

3. Step Three: At this point, a one-half inch layer of fine gravel may be placed in the bottom of the hole to protect the soil surface from disturbance or siltation when water is added to the hole. If additional protection is desired, a hole liner as described in (a)8 above may be placed in the hole and the space between the liner and the sides of the hole may be filled with fine gravel.

4. Step Four: Place and secure a straight board horizontally across the top of the test hole, as shown in Figure 7 of Appendix A, to serve as a fixed point for depth of water measurements to be made at appointed time intervals throughout the test.

(c) All soils, except for sandy textured soils which meet the requirements of (d) below, shall be pre-soaked using the following procedure. Any soil which exhibits cracks or fissures between soil aggregates shall be pre-soaked regardless of the texture. Pre-soak as follows:

1. Fill the test hole with water and maintain a minimum depth of 12 inches for a period of four hours by refilling as necessary or by means of an automatic siphon or float valve.

2. At the end of four hours, cease adding water to the hole and allow the hole to drain for a period of from 16 to 24 hours.

(d) In sandy textured soils, including sands, loamy sands and sandy loams, where a rapid percolation rate is anticipated, fill the test hole to a depth of 12 inches and allow to drain completely. Refill the hole to a depth of 12 inches and record the time required for the hole to drain completely. If this time is less than 60 minutes, the test procedure may begin as prescribed in (e) below without further pre-soaking. If water remains in the test hole after 60 minutes, the hole must be pre-soaked as prescribed in (c) above before proceeding with the test.

(e) Immediately following the pre-soak procedure (no more than 28 hours after the start of the pre-soak procedure), the percolation rate shall be determined using the following procedure:

1. Step One: If water remains in the test hole after the completion of the pre-soak period, the test shall be terminated and the percolation rate shall be reported as greater than 60 minutes per inch. If no water remains in the test hole, fill to a depth of seven inches. At a five to 30 minute time interval, depending upon the rate of fall, record the drop in water level to the nearest one-tenth of an inch. Refill the hole at the end of each time interval and repeat this procedure using the same time interval until a constant rate of fall is attained. A constant rate of fall is attained when the difference between the highest and lowest of three consecutive measurements is no greater than two-tenths of an inch.

2. Step Two: Immediately after the completion of Step One, refill the test hole to a depth of seven inches and record the time required for exactly six inches of water to seep away. This time divided by six will be the percolation rate in minutes per inch.

(f) The results of the percolation test shall be interpreted as follows:

1. When the purpose of the test is to determine the design permeability at the level of infiltration, the slowest percolation rate determined within the proposed disposal field shall be used for design purposes. If any of the measured percolation rates are slower than 60 minutes per inch or faster than three minutes per inch the application shall not be approved. A percolation rate may be the result of a single percolation test or the average of several replicate tests, as allowed in 7:9A-6.1(e)2.

2. When the result of the test(s) is an average percolation rate slower than 60 minutes per inch, the horizon or substratum in question shall be considered hydraulically restrictive.

3. When the result of the test(s) is an average percolation rate faster than three minutes per inch, the horizon or substratum in question shall be considered excessively coarse.

4. When a seepage pit is proposed, the design percolation rate shall be calculated by adding the products of the percolation rate and the thickness of each individual horizon tested and dividing the result by the total thickness of all the horizons tested. Any horizon with a percolation rate slower than 40 minutes per inch shall be excluded from this computation.

N.J. Admin. Code § 7:9A-6.4