N.J. Admin. Code § 7:9A-10.1

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

Section 7:9A-10.1 - General design requirements for disposal fields

(a) A disposal field shall be required for all new systems except as allowed in 7:9A-7.6, in which case a seepage pit may be approved in lieu of a disposal field. The disposal field shall consist of one or more disposal trenches or a disposal bed designed, constructed and installed as hereafter prescribed.

(b) No disposal field shall be installed in areas where the depth to any limiting zone below the existing ground surface is less than 24 inches. The disposal field installation shall be such that the disposal field is underlain by a suitable zone of treatment as prescribed in (d) below and a suitable zone of disposal as prescribed in (e) below. Acceptable options for disposal field installation are as follows:

1. Conventional installation: The disposal field shall be installed directly within the native soil and the level of infiltration shall be from one to three feet below the existing ground surface, as shown in Figure 17 of Appendix A.

2. Soil replacement, bottom-lined installation: The excavation for the disposal bed or each individual trench shall be extended below the level of infiltration and back-filled up to the level of infiltration with suitable fill. The disposal bed or trenches shall be installed on top of the fill with the level of infiltration one to three feet below the existing ground surface, as shown in Figure 18 of Appendix A.

3. Soil replacement, fill-enclosed installation: An excavation shall be made below the level of infiltration and extending laterally a minimum of two feet beyond the perimeter of the disposal field on all sides. This excavation shall be back-filled with suitable fill, the disposal bed or trenches installed within the fill, and the level of infiltration shall be at existing ground surface to three feet below the existing ground surface, as shown in Figure 19 of Appendix A.

4. Mounded installation: Fill material shall be placed above the existing ground surface; the disposal field shall be installed within the fill; and the level of infiltration shall be one to four feet above the existing ground surface (measured on the upslope side of the disposal bed or each individual disposal trench), as shown in Figure 20 of Appendix A.

5. Mounded soil replacement installation: An excavation shall be made below the existing ground surface; fill material shall be placed within this excavation and mounded up above the existing ground surface; the disposal field shall be installed within the fill; and the level of infiltration shall be at existing ground surface or up to four feet above the existing ground surface (measured on the upslope side of the disposal bed or each individual disposal trench), as shown in Figure 21 of Appendix A.

(c) The type of disposal field installation permitted shall be determined based upon the soil suitability class as outlined in Table 10.1 below.

TABLE 10.1
TYPE OF DISPOSAL FIELD INSTALLATION
C = Conventional Installation M = Mount Installation
SRB = Soil Replacement, Bottom-lined Installation MSR = Mounded Soil
Replacement Installational<1>
SRE = Soil Replacement, Fill-enclosed Installation
Type of Limiting Zone	Depth,<2>	Suitability	Type of
ft.	Class	Installation
Permitted<3>
Fractured Rock or	>5	I	C, (SRB, SRE, M,
MSR)
Excessively Coarse	0-5	IISc	SRE, M, (MSR)
Substratum
Massive Rock	>9	I	C, (SRB, SRE, M,
Hydraulically	MSR)
Restrictive Substratum	4-9	IISr	M, (MSR)
<4	IIISr	UNSUITABLE
Hydraulically	>9	I	C, (SRB, SRE, M,
Restrictive	MSR)
Horizon, Permeable	4-9	IIHr	SRB, SRE, M,
(MSR)
Substratum	<4	IIIHr	SRB, SRE, (MSR)
Excessively Coarse	>5	I	C, (SRB, SRE, M,
Horizon	MSR)
0-5	IIHc	SRE, M, (MSR)
Zone of Saturation,	>5	I	C, (SRB, SRE, M,
Regional	MSR)
2-5	IIWr	M, (SRE, MSR)
<2	IIIWr	UNSUITABLE
Zone of Saturation,	>5	I	C, (SRB, SRE, M,
Perched	MSR)
2-5	IIWp	C<4>, (SRB<4>,
SRE, M, MSR)
<2	IIIWp	C<4>, (SRB<4>,
SRE, M, MSR)

[LESS THAN]1[GREATER THAN] Mounded soil replacement systems are generally required only in cases where several limiting zones are present as, for example, in compound soil suitability classes such as IIScWr, IIIHr (IISr) or IIIHr (IIWr).

[LESS THAN]2[GREATER THAN] Depth is measured from the ground surface to the top of the limiting zone. In the case of disturbed ground, the depth to the limiting zone shall be measured from the existing ground surface, identified as prescribed in 7:9A-5.10(c), or the ground surface, whichever is lowest.

[LESS THAN]3[GREATER THAN] Installations shown in parentheses are allowed but are generally not the most cost-effective type of installation for the soil suitability class unless other soil limitations are present.

[LESS THAN]4[GREATER THAN] An interceptor drain or other means of removing the perched zone of saturation is required.

Note: In soils with a compound soil suitability class, where more than one limiting zone is present in the soil, a disposal field installation shall not be approved unless the type of installation proposed is listed in Table 10.1 as an acceptable option for each of the soil suitability classes which apply.

(d) A zone of treatment (see Figures 22, 23 and 24 in Appendix A), a minimum of four feet in thickness, shall be present below the disposal field and shall meet all of the following requirements:

1. The zone of treatment shall be composed of suitable soil which meets all of the criteria listed in (d)2 below, suitable fill material which satisfies the requirements of (f) below, or a combination of suitable soil and suitable fill.

2. Suitable soil within the zone of treatment shall meet the following criteria:

i. Coarse fragment content less than 50 percent by volume;

ii. Permeability less than 20 inches per hour and greater than 0.2 inches per hour, or a percolation rate slower than three minutes per inch and faster than 60 minutes per inch.

3. The zone of treatment shall not contain or be interrupted by fractured or massive rock substrata, hydraulically restrictive horizons or substrata, perched zones of saturation or regional zones of saturation. When excessively coarse horizons or substrata are present above, within or below the zone of treatment, these horizons shall not be considered part of the zone of treatment.

4. For design purposes, the top of the zone of treatment shall be considered to be the bottom of the disposal field or the bottom of an excessively coarse horizon when such a horizon is present immediately below the bottom of the disposal field. The bottom of the zone of treatment shall be considered to be whichever of the features listed below occurs at a shallower depth below the disposal field, except that in no case shall the bottom of the zone of treatment extend to a depth greater than eight feet below finished grade.

i. An imaginary horizontal surface at a depth of four feet below the top of the zone of treatment, excluding the thickness of any intervening excessively coarse horizons;

ii. The top of the shallowest limiting zone which is present in the soil below the disposal field; or

iii. The bottom of the shallowest soil profile pit or boring made within the area of the disposal field.

5. The thickness of the zone of treatment may be reduced, at the administrative authority's discretion, to a minimum of 18 inches in thickness when the system design incorporates an advanced wastewater pretreatment device in accordance with 7:9A-8.3.

(e) A zone of disposal (see figures 22, 23 and 24 in Appendix A), a minimum of four feet in thickness, shall be present below the zone of treatment and shall meet all of the following requirements:

1. The zone of disposal shall be composed of native soil or rock material which has a permeability more rapid than 0.2 inch per hour or a percolation rate more rapid than 60 minutes per inch;

2. When the permeability in the zone of disposal has been determined, as prescribed in N.J.A.C. 7:9A-6, to be two inches per hour or faster, the minimum required thickness of the zone of disposal may be reduced to two feet. This determination shall not be made using the percolation test or basin flooding test;

3. When the permeability of the zone of disposal has been determined to be two inches per hour or faster, as prescribed in N.J.A.C. 7:9A-6, or the basin flooding test drains in less than three hours on each and every filling, the minimum required field bottom area of the zone of disposal may be reduced by 25 percent, except in cases where a perched zone of saturation exists and interceptor trenches are not proposed. This determination shall not be made using the percolation test. The permeability test shall be conducted within the zone of disposal at the location of the proposed disposal field. In no case shall the reduction result in drainage from the zone of treatment being inhibited. Accordingly, the unexcavated area of the zone of disposal shall be sloped to promote drainage to the excavated area. The minimum field bottom area of the zone of treatment shall not be reduced.

4. The zone of disposal shall not contain or be interrupted by any hydraulically restrictive horizon unless the entire thickness of this horizon has been removed throughout the entire area of the disposal field and has been replaced with fill material meeting the requirements of (f)5 below. The thickness of any restrictive horizon which has been removed shall not be counted as part of the zone of disposal; and

5. For design purposes, the top of the zone of disposal shall be taken as the bottom of the zone of treatment. The bottom of the zone of disposal shall be considered to be whichever of the following features is present at a shallower depth below the disposal field:

i. The top of any massive rock or hydraulically restrictive substratum;

ii. The top of the shallowest hydraulically restrictive horizon which occurs below the bottom of the disposal field, except when the hydraulically restrictive horizon is to be removed and replaced with suitable fill materials; or

iii. The bottom of the shallowest soil profile pit or boring made below the disposal field.

(f) When fill material is used in disposal field construction, the following requirements shall be met:

1. When a soil replacement installation is proposed, the zone of treatment may consist partly or entirely of fill material provided that the requirements of 7:9A-10.4 are satisfied and the fill material used meets the requirements of (f)4 below. The zone of disposal may contain a layer of fill provided that the fill material used within the zone of disposal meets the requirements of (f)5 below.

2. When a mound installation is proposed, the zone of treatment may consist partly or entirely of fill material provided that the requirements of 7:9A-10.5 are satisfied and the fill material used meets the requirements of (f)4 below.

3. When a mounded soil replacement installation is proposed, the zone of treatment may consist partly or entirely of fill material provided that the requirements of 7:9A-10.6 are satisfied and the fill material used meets the requirements of (f)4 below. The zone of disposal may contain a layer of fill provided that the fill material used within the zone of disposal meets the requirements of (f)5 below.

4. When fill material is utilized within the zone of treatment, the fill shall meet the following requirements:

i. Coarse fragment content (greater than a No. 8 sieve) less than 15 percent by volume or less than 20 percent by weight;

ii. Textural analysis (composition, by weight, of size fraction passing the particular sieve as stated below in this subparagraph) between 80 and 100 percent must pass a No. 8 sieve (2.36 mm); between 50 and 85 percent must pass a No. 16 sieve (1.18 mm); between 25 and 60 percent must pass a No. 30 sieve (0.6 mm); between 10 and 30 percent must pass a No. 50 sieve (0.3 mm); and between two and 10 percent must pass a No. 100 sieve (0.15 mm); and

iii. Permeability for this material is established in this chapter at the range of six to 20 inches per hour for design purposes.

5. When fill material is placed within the zone of disposal, the fill material shall meet the specifications in (f)4 above, or the following requirements:

i. Coarse fragment content less than 15 percent by volume or less than 25 percent by weight;

ii. Textural analysis (composition, by weight, of size fraction passing the two millimeter sieve): 85 percent or more sand; and

iii. Permeability greater than two inches per hour; or percolation rate faster than 30 minutes per inch.

6. Use of the term or specification "bank run," which implies a material of alluvial deposition which is high in coarse fragment content, in system designs shall be prohibited unless a septic system designer includes a specification for that material consistent with (f)4 or 5 above, as applicable.

(g) The following requirements shall be met when installing a disposal field in sloping ground:

1. The interface between filter material and the underlying soil or fill material at the bottom of each individual trench or bed shall be level;

2. On strongly sloping sites the shape of the disposal field shall be elongated with the long axis parallel to the topographic contour;

3. When the slope of the existing ground surface is between 10 and 25 percent, trenches shall be used rather than beds;

4. Mound or mounded soil replacement installations shall be restricted to slopes less than 10 percent; and

5. When disposal trenches are installed at different elevations and gravity flow or gravity dosing are used, the distribution of effluent between trenches shall be accomplished by means of a distribution box.

(h) When a conventional or soil replacement installation is proposed, the bottom of the disposal field shall be at a depth from one to three feet below the existing ground surface. When a mound or mounded soil replacement installation is proposed, the level of infiltration shall be at an elevation no higher than four feet above the existing ground surface, measured on the upslope side of the disposal bed or each individual disposal trench. In no case shall the level of infiltration be greater than three feet below the finished grade.

N.J. Admin. Code § 7:9A-10.1

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), substituted "at existing ground surface" for "one" following "shall be" in the last sentence in 3, and substituted "at existing ground surface to four feet above the existing" for "between one foot and four feet above the" following "shall be" in 5; and in (c), inserted a reference to SRE in Zone of Saturation, Regional in Table 10.1.
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 (b), inserted the first sentence; in (b)4 and (b)5, inserted "existing" preceding the first occurrence of "ground surface"; in (b)5, inserted "or up"; in the second footnote following Table 10.1, deleted "existing" preceding the first and fourth occurrences of "ground", and substituted "existing" for "pre-existing natural" preceding the third occurrence of "ground"; added (d)5 and new (e)3; recodified former (e)3 and (e)4 as (e)4 and (e)5; rewrote (f)4 and (f)5; added (f)6; in (g)3, substituted "of the existing ground surface is between 10 and 25" for "is greater than 10"; and in (h), deleted "of" following "depth".