N.J. Admin. Code § 7:9A-5.9

Current through Register Vol. 56, No. 17, September 3, 2024

Section 7:9A-5.9 - Hydraulic head test

(a) When a hydraulic head test is required by the administrative authority to determine the presence or absence of a perched or artesian zone of saturation, piezometers shall be installed and monitored by the applicant as follows:

1. Piezometer A shall consist of a steel or plastic casing, a minimum of two inches in diameter, perforated or open at the bottom, and extending from above the ground surface to a point immediately above but not penetrating into the hydraulically restrictive horizon.

2. Piezometer B shall consist of a steel or plastic casing, a minimum of two inches in diameter located two to five feet from Piezometer A and extending from above the ground surface to a minimum of one foot below the bottom of the restrictive horizon. Piezometer B must be:

i. Open at the bottom or perforated only below the bottom of the restrictive horizon and within the underlying permeable horizon or stratum; and

ii. Installed or sealed in such a manner that no ground water may move upward or downward through the hydraulically restrictive horizon by flowing around the outside of the casing. When the hydraulically restrictive horizon is a horizon of high clay content and plastic consistence, this may be accomplished by use of a steel well-point which may be driven through the restrictive horizon and into the permeable soil below. In other cases, the piezometer shall be installed within an over-sized borehole with a bentonite pellet seal, a minimum of one foot thick, placed at the appropriate level.

(b) The piezometers shall be developed by pumping or surging. After a period of 24 hours, the water levels in both piezometers shall be accurately measured and recorded. All piezometer readings shall be taken from the same point in the piezometer. The number of water level readings shall be proposed by the septic system designer to the administrative authority based upon site conditions. Piezometers shall not be installed prior to administrative authority approval of the number of water level readings. Additional readings may be required if variability is observed in the readings or if the administrative authority finds discrepancy in the measurements.

(c) Water level measurements shall be interpreted as follows:

1. An equal water level in both piezometers means that the water level above the hydraulically restrictive horizon is due to the presence of a regional rather than a perched zone of saturation. Interceptor drains shall not be relied on as a means of providing an unsaturated zone below the disposal field.

2. Where water levels are different in piezometers A and B:

i. A water level in piezometer B which is above the bottom of the hydraulically restrictive horizon means an artesian zone of saturation is present below the hydraulically restrictive horizon. Excavation and removal of the hydraulically restrictive horizon in order to install a soil replacement or mounded soil replacement disposal field shall not be allowed.

ii. A water level in piezometer B which is below the bottom of the hydraulically restrictive horizon means that the water level, if observed, in piezometer A is due to the presence of a perched zone of saturation. No artesian zone of saturation is present below the hydraulically restrictive horizon. Interceptor drains may be proposed as a means of providing an unsaturated zone below the disposal field. Excavation and removal of the restrictive horizon in order to install a soil replacement or mounded soil replacement disposal field may be allowed.

(d) When it is required, the hydraulic head test shall be conducted only during the months of January through April inclusive, and shall be witnessed by the administrative authority or its authorized agent in accordance with 7:9A-3.6. Whenever the Department determines that there has been a significant departure from normal climatic conditions, the Department may, with prior written notice to the administrative authority, lengthen or shorten the period allowed for use of this test during any given year.

(e) When piezometers are installed for the purpose of conducting this test, the piezometers shall be removed or filled with cement grout after completion of the test except in those cases where the piezometers will be utilized for monitoring ground water levels or for ground water sampling as required by the administrative authority or by the Department. Piezometers used for monitoring ground water levels over extended periods of time, or for ground water sampling in connection with water quality monitoring, may be considered to be monitoring wells requiring installation by a licensed well driller and a permit issued by the Department pursuant to State law (58:4-1 et seq.). The applicant shall contact the Department for a determination of whether or not a permit is required.

N.J. Admin. Code § 7:9A-5.9

Amended by 50 N.J.R. 171(a), effective 1/2/2018