(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.
Notes
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".