N.J. Admin. Code § 7:9A-10.4 - Specific requirements for soil replacement disposal field installations

(a) A soil replacement disposal field installation shall be made by installing the disposal bed or each individual disposal trench on top of or within suitable fill material which has been placed in an excavation made below the existing ground surface. In a bottom-lined installation, the fill material shall be placed below the disposal field only, as prescribed in (b) below. In a fill-enclosed installation, the fill shall be placed around the sides as well as below the disposal field, as prescribed in (c) below. The type of soil replacement disposal field installation required depends upon the soil limitations present and the slope across the disposal area as follows:

1. A fill-enclosed installation shall be required when:

i. The limiting zone is a perched zone of saturation underlain by a hydraulically restrictive horizon and the slope across the disposal field is less than five percent;

ii. The limiting zone is an excessively coarse horizon or substratum; or

iii. The limiting zone is a fractured rock substratum.

2. A bottom-lined installation may be permitted where:

i. The limiting zone is a hydraulically restrictive horizon and no perched zone of saturation is present; or

ii. The limiting zone is a perched zone of saturation underlain by a hydraulically restrictive horizon and the slope across the disposal field is five percent or greater.

(b) Bottom-lined soil replacement disposal field installations shall be constructed as follows:

1. An excavation shall be made within the area occupied by the disposal bed or by each individual disposal trench and, where the limiting zone is a hydraulically restrictive horizon, the excavation(s) shall extend a minimum of two feet below the bottom of the hydraulically restrictive horizon.

2. The excavation shall be backfilled to the level of infiltration with suitable fill material.

3. The disposal field shall be constructed on top of the fill material within the excavation(s).

4. An interceptor drain designed and constructed as prescribed in 7:9A-10.7 shall be provided to divert away from the disposal field laterally moving ground water which may be perched above any hydraulically restrictive horizon penetrated by the excavation.

(c) Fill-enclosed soil replacement disposal field installations shall be constructed as follows:

1. An excavation shall be made to the required depth extending throughout the entire area to be occupied by the disposal field and beyond the perimeter of the disposal field a minimum of two feet in all directions. In cases where the limiting zone is a fractured rock substratum and a pit-bailing or basin flooding test has been used to establish adequate permeability, the depth of the disposal field excavation shall be no less than the depth of the test pit.

2. The excavation shall be backfilled with suitable fill material.

3. The disposal field shall be constructed within the fill material so that the entire disposal bed or each individual trench is surrounded by a minimum of two feet of fill material on all sides.

(d) Requirements and restrictions relating to site regrading shall be the same as those prescribed for conventional installations in 7:9A-10.3(b).

(e) Excavation prior to the placement of fill material shall be carried out in accordance with the requirements of 7:9A-10.3(c)2 through 5.

(f) Fill material used in soil replacement disposal field installations shall meet the following requirements:

1. The fill material used below the disposal field shall meet the requirements for texture and permeability which are prescribed in 7:9A-10.1(f).

2. The minimum depth of fill below the disposal field shall be one foot.

3. Compaction of fill material shall be required whenever fill material is used below the disposal field and shall be carried out in accordance with the following requirements:

i. Compaction of fill shall be carried out as directed by a professional engineer and as indicated on the approved engineering design.

ii. Based upon a final inspection, a professional engineer shall certify by signature and seal that compaction of the fill has been performed adequately to prevent failure of any component of the system due to excessive settlement or differential settlement.

iii. Fill material shall be spread and compacted in layers one foot or less in thickness.

iv. Compaction may be accomplished manually or mechanically, by tamping or rolling, or by driving over the filled area in a controlled pattern using tracked or rubber-tired vehicles. Compaction may also be accomplished by puddling.

v. When heavy excavating equipment is operated within the excavation for the purpose of placement of compaction of the fill material, this equipment shall not be driven directly on the exposed bottom of the excavation. A minimum of one foot of fill material shall be maintained below the vehicle tracks or wheels at all times.

(g) Construction of the disposal field and distribution network shall be as prescribed for conventional installations in 7:9A-10.3(d).

(h) Filter material shall be as prescribed for conventional installations, in 7:9A-10.3(e).

(i) Backfill and final grading shall be as required in 7:9A-10.3(f) and shall extend a minimum of five feet, in all directions, beyond the perimeter of the filled area.

Notes

N.J. Admin. Code § 7:9A-10.4