N.J. Admin. Code § 7:9A-6.6 - Piezometer test

Current through Register Vol. 54, No. 7, April 4, 2022

(a) The following equipment is required for the piezometer test:
1. A screw type soil auger, minimum of one inch in diameter, with extensions;
2. A piezometer tube consisting of a metal pipe beveled on the outside lower edge, with an inside diameter about one-sixteenth of an inch larger than the diameter of the soil auger;
3. A maul or hammer, to drive pipe into the ground;
4. A pump with tubing, to evacuate water from piezometer tube;
5. A stop watch;
6. A means for accurately measuring the water level within the piezometer tube as a function of time, which may consist of one of the following:
i. A light-weight rod with measuring scale mounted on a cylindrical float with a diameter one-quarter inch or more smaller than the inside diameter of the piezometer tube;
ii. An electric probe consisting of a thin wire embedded in and protruding from the tapered end of a wooden rod, graduated in inches, and connected in series to a limiting resistor, a millimeter and a 33-volt hearing-aid battery, the opposite terminal of which is connected to the piezometer tube; or
iii. For depths greater than six feet, an electric sounder or the "wetted tape" method should be used.
(b) The following procedure shall be used for the piezometer test:
1. Step One: Remove any sod, vegetation or leaf litter from the ground surface where the test hole will be excavated. The test hole may be excavated from the ground surface or from the bottom of a larger excavation or soil profile pit.
2. Install the piezometer in accordance with Step Two A and Two B outlined in (b)2i and ii below or Alternate Step Two outlined in (b)2iii below.
i. Step Two A: Using the soil auger, drill the test hole down to a depth of six inches. Remove the auger and drive the piezometer tube into the hole to a depth of five inches. Re-insert the soil auger through the piezometer tube and into the test hole and drill down six inches further. Remove the soil auger, drive the piezometer tube six inches deeper, re-insert the auger and drill six inches deeper, repeating this procedure until the test hole reaches the top of the soil horizon or zone within a soil horizon to be tested.
ii. Step Two B: Using the soil auger, extend the test hole exactly four inches below the bottom of the piezometer tube (see Figure 9 of Appendix A). In coarse-textured soils lacking cohesion, where the unlined cavity at the bottom of the test hole may be unstable, use a piezometer tube with closely spaced perforations in the lower four inches of its length and drive the tube down to the bottom of the test hole.
iii. Alternate Step Two: Power equipment may be used in lieu of the hand auger to drill the test hole and install the piezometer casing provided that the casing fits tightly into the hole or the installation is sealed with bentonite so that leakage does not occur around the outside of the casing and provided that a suitable unlined cavity is provided at the bottom of the bore hole as required in Step Two B above.
3. Step Three: Allow the lower portion of the test hole to fill with ground water and pump the water out one or more times to minimize the effect of soil puddling and to flush the soil pores in the unlined portion of the test hole.
4. Step Four: Allow the water level to rise within the piezometer until the water level becomes relatively stable. Note the approximate rate of rise and record the static water level using the top of the piezometer tube as a reference point.
5. Step Five: Pump most of the water out of the piezometer tube. Record the time and the depth of the water level below the top of the tube. After an appropriate interval of time, record the new depth of the water level. Choose the length of the time interval based upon the rate of rise observed in Step Four so that the difference in water levels at the beginning and end of the time interval will be large enough to permit an accurate measurement, but do not allow the water level to rise to within eight inches of the static level determined in Step Four.
6. Step Six: Repeat Step Five of this subsection, lowering the water level to approximately the same depth and using the same time interval, until consistent results are obtained.
7. Step Seven: Allow the water level in the piezometer tube to rise and, a minimum of 24 hours later, record the depth of the water table for use in the calculation of permeability.
(c) The permeability of the soil horizon tested shall be determined as follows:
1. Step One: Determine the value of the A-parameter from Figure 10 of Appendix A based upon D, the diameter of the soil auger (or drill bit).
2. Step Two: Calculate the permeability, K, in inches per hour, using the following formula:

K = 60 min/hr x (3.14R[LESS THAN]2[GREATER THAN])/At x 1n (d[1]-D[stat]/d[2]-D[stat]) where:

K = the permeability of the soil horizon tested, in inches per hour;

R = the inside radius of the piezometer tube, in inches;

1n = the natural logarithm;

D[stat] = the depth of the static water level below the top of the piezometer tube determined in Step Seven, in inches;

d[1] = depth of the water level below the top of the piezometer tube at the beginning of the last time interval, in inches;

d[2] = depth of the water level below the top of the piezometer tube at the end of the last time interval, in inches;

t = length of time interval, in minutes; and

A = value determined in Step One above, in inches.

(d) When the permeability calculated in (c)2 above is less than 0.2 inch per hour, the horizon or substratum in question shall be considered hydraulically restrictive and shall not be considered an acceptable zone of wastewater disposal.
(e) When piezometers are used for conducting this test, they shall be installed and removed in accordance with the Department's procedures pursuant to 58:4A-4.1 et seq.

Notes

N.J. Admin. Code § 7:9A-6.6
Amended by R.2012 d.066, effective 4/2/2012.
See: 43 N.J.R. 478(a), 44 N.J.R. 1047(a).
In (b)1, deleted "existing" preceding the second occurrence of "ground".

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