N.J. Admin. Code § 7:9A-10.3 - Specific requirements for conventional disposal field installations

(a) A conventional installation shall be made by placing the disposal bed or each individual disposal trench in an excavation made directly within the natural soil.

(b) All rough-grading shall be in accordance with the following requirements:

1. Sites which have been re-graded prior to site evaluation, soil evaluation or permeability testing shall be considered to be disturbed ground and all requirements relating to disturbed ground shall be met.

2. When a site is re-graded after site evaluation, soil evaluation or permeability testing, this re-grading shall be carried out in conformance with an engineering design which has been approved by the administrative authority.

(c) Excavation for the disposal field shall be in accordance with the following procedures:

1. Adequate measures shall be used to insure that the bottom of the disposal bed or each individual disposal trench is level.

2. In soil textures other than sands or loamy sands, excavation which exposes the infiltrative surface of the disposal field shall not be carried out when the soil moisture content is above the lower plastic limit. This means that when a small lump of soil, taken from the depth of the proposed excavation, can be rolled out with the fingers to form a wire or rod, one-eighth of an inch in thickness, and does not crumble when handled, the soil is too wet to proceed with the excavation.

3. Excavation shall be carried out in a manner that will avoid unnecessary compaction of the disposal field bottom and sidewalls. Heavy equipment such as bulldozers or front-end loaders shall not be driven over the exposed infiltrative surface of the disposal field. Excavation should be carried out with a backhoe operating from between disposal trenches or from outside the perimeter of previously excavated portions of the disposal bed. If it becomes necessary to walk on the disposal field bottom, a suitable board shall be laid over the soil to avoid trampling.

4. Any smeared or compacted soil surfaces which have been produced on the bottom or sidewalls of the excavation shall be removed to expose a fresh soil surface which is rough and uneven.

5. Work should be scheduled so that the bottom and sidewalls of the excavation will not be exposed to rainfall or wind-blown silt between the time of excavation and the time of final inspection and backfilling. Any loose soil or debris which is washed into or otherwise deposited within the excavation as a result of the excavation remaining open to the elements shall be carefully removed prior to backfilling.

(d) The construction of the distribution network shall be in accordance with 7:9A-9.5, when gravity flow or gravity dosing is used, or 7:9A-9.6, when pressure dosing is used. Additional requirements for disposal trenches or beds are given in (d)1, and 2 below, respectively.

1. Disposal trenches shall be constructed in accordance with the following requirements:

i. The minimum spacing between trenches (sidewall to sidewall) shall be six feet.

ii. The minimum width of trenches shall be 1.5 feet.

iii. The maximum width of trenches shall be three feet.

iv. There shall be one distribution line per trench.

2. Disposal beds shall be constructed in conformance with the following requirements:

i. There shall be a minimum of two distribution lines per bed.

ii. The maximum distance from edge of bed to nearest distribution line shall be three feet.

iii. The minimum distance from edge of bed to nearest distribution line shall be one foot.

iv. The maximum spacing between distribution lines for gravity distribution shall be three feet.

v. The required spacing between distribution lines for pressure distribution shall be from 3/4 to 5/4 of the hole spacing;

vi. The spacing between all distribution lines shall be equal and uniform; and

vii. Holes in pressure distribution lines shall be aligned so that holes in adjacent laterals shall be off-set by one-half the hole spacing.

(e) Except as provided by 7:9A-9.8, filter material shall meet the following requirements:

1. Filter material shall cover the distribution lines and extend the full width of the trench or bed, shall extend between 12 and 18 inches deep beneath the bottom of the distribution lines and shall extend at least two inches above the top of the lines.

2. The filter material shall be washed gravel or crushed stone, free of fines, dust, ashes or clay. Refer to the New Jersey Department of Transportation standard sizes for coarse aggregates as shown in Figure 26 of Appendix A. The filter material shall conform in size and gradation to size number 24, size number three or size number four.

3. The filter material shall be covered with drainage fabric as the laying of the distribution lines progresses. In addition, the following requirements shall be met:

i. Edges of adjacent sheets shall be overlapped by a minimum of six inches.

ii. Drainage fabric shall be specified in the engineering design and shall have adequate tensile strength to prevent ripping during installation and backfilling, adequate air permeability to allow free passage of gases, and adequate particle retention to prevent downward migration of soil particles into the filter material.

4. The filter material may be laid into the excavation using a backhoe, front-end loader or dump truck provided that this operation is carried out from sides of the system rather than by driving out onto the exposed disposal field infiltrative surface. In the case of large beds, tracked equipment may be operated within the disposal bed provided that the equipment does not exert a ground pressure in excess of eight pounds per square inch and provided that the filter material is pushed out in front of the vehicle while maintaining a minimum thickness of one foot of filter material below the vehicle tracks at all times.

(f) Backfill and final grading shall be carried out in accordance with the following requirements:

1. A minimum of nine inches and no more than 18 inches of backfill shall be placed over the top of the disposal field filter material.

2. Backfill material shall be of earth similar to that found at the site and free of large stones, tree stumps, broken masonry or other waste construction material.

3. In no case shall the backfill material be more permeable than the surrounding soil.

4. Backfill shall completely cover the entire disposal bed or each of the disposal trenches and shall be graded smoothly into the surrounding topography on all sides.

5. The following practices shall be followed:

i. Heavy machinery, rubber-tired vehicles or other vehicles exerting a ground pressure in excess of eight pounds per square inch shall not be permitted to pass over the disposal field after the filter material and distribution network have been installed.

ii. Tracked equipment may be used for the purpose of backfilling and final grading provided that this equipment does not exert a pressure on the underlying soil in excess of eight pounds per square inch.

iii. Final grading shall be completed in accordance with the approved engineering design and in such a manner that surface water will not collect over the disposal field.

iv. After completion of backfilling and final grading, the backfilled area over the disposal field shall be seeded or sodded to establish a vegetative cover or otherwise stabilized against erosion in a manner acceptable to the administrative authority.

Notes

N.J. Admin. Code § 7:9A-10.3

Amended by R.1999 d.314, effective 9/20/1999.
See: 31 N.J.R. 1416(a), 31 N.J.R. 2741(a).
In (b), deleted a former 3.
Amended by R.2012 d.066, effective 4/2/2012.
See: 43 N.J.R. 478(a), 44 N.J.R. 1047(a).
In the introductory paragraph of (e), substituted "Except as provided by N.J.A.C. 7:9A-9.8, filter" for "Filter"; rewrote the introductory paragraph of (e)3; and deleted (e)3iii.