Site design features identified under § 172-7F above, or alternative designs in accordance with § 172-7G above, to prevent discharge of trash and debris from drainage systems shall comply with the following standard to control passage of solid and floatable materials through storm drain inlets. For purposes of this section, "solid and floatable materials" means sediment, debris, trash, and other floating, suspended, or settleable solids. For exemptions to this standard, see § 172-15B below.
A.
Grates.
(1)
Design engineers shall use one of the following grates whenever they
use a grate in pavement or another ground surface to collect stormwater
from that surface into a storm drain or surface water body under that
grate:
(a)
The New Jersey Department of Transportation (NJDOT) bicycle-safe
grate, which is described in Chapter 2.4 of the NJDOT Bicycle Compatible
Roadways and Bikeways Planning and Design Guidelines; or
(b)
A different grate, if each individual clear space in that grate
has an area of no more than seven square inches or is no greater than
0.5 inch across the smallest dimension.
(2)
Examples of grates subject to this standard include grates in grate
inlets, the grate portion (non-curb-opening portion) of combination
inlets, grates on storm sewer manholes, ditch grates, trench grates,
and grates of spacer bars in slotted drains. Examples of ground surfaces
include surfaces of roads (including bridges), driveways, parking
areas, bikeways, plazas, sidewalks, lawns, fields, open channels,
and stormwater system floors used to collect stormwater from the surface
into a storm drain or surface water body.
(3)
For curb-opening inlets, including curb-opening inlets in combination
inlets, the clear space in that curb opening, or each individual clear
space if the curb opening has two or more clear spaces, shall have
an area of no more than seven square inches or be no greater than
two inches across the smallest dimension.
B.
The standard in Subsection A(1) above does not apply:
(1)
Where each individual clear space in the curb opening in existing
curb-opening inlet does not have an area of more than nine square
inches;
(2)
Where the municipality agrees that the standards would cause inadequate
hydraulic performance that could not practicably be overcome by using
additional or larger storm drain inlets;
(3)
Where flows from the water quality design storm as specified in N.J.A.C.
7:8 are conveyed through any device (e.g., end of pipe netting facility,
manufactured treatment device, or a catch basin hood) that is designed,
at a minimum, to prevent delivery of all solid and floatable materials
that could not pass through one of the following:
(4)
Note that these exemptions do not authorize any infringement of requirements
in the Residential Site Improvement Standards for bicycle-safe grates
in new residential development [N.J.A.C. 5:21-4.18(b)2 and 7.4(b)1];
(5)
Where flows are conveyed through a trash rack that has parallel bars
with one-inch spacing between the bars, to the elevation of the water
quality design storm as specified in N.J.A.C. 7:8; or
(6)
Where the New Jersey Department of Environmental Protection determines,
pursuant to the New Jersey Register of Historic Places Rules at N.J.A.C.
7:4-7.2(c), that action to meet this standard is an undertaking that
constitutes an encroachment or will damage or destroy the New Jersey
Register listed historic property.
A.
This section sets forth requirements to protect public safety through
the proper design and operation of stormwater management BMPs. This
section applies to any new stormwater management BMP.
B.
The provisions of this section are not intended to preempt more stringent municipal or county safety requirements for new or existing stormwater management BMPs. Municipal and county stormwater management plans and ordinances may, pursuant to their authority, require existing stormwater management BMPs to be retrofitted to meet one or more of the safety standards in § 172-16C(1), (2) and (3) for trash racks, overflow grates, and escape provisions at outlet structures.
C.
Requirements for trash racks, overflow grates and escape provisions.
(1)
A trash rack is a device designed to catch trash and debris and prevent
the clogging of outlet structures. Trash racks shall be installed
at the intake to the outlet from the stormwater management BMP to
ensure proper functioning of the BMP outlets in accordance with the
following:
(a)
The trash rack shall have parallel bars, with no greater than
six-inch spacing between the bars;
(b)
The trash rack shall be designed so as not to adversely affect
the hydraulic performance of the outlet pipe or structure;
(c)
The average velocity of flow through a clean trash rack is not
to exceed 2.5 feet per second under the full range of stage and discharge.
Velocity is to be computed on the basis of the net area of opening
through the rack; and
(d)
The trash rack shall be constructed of rigid, durable, and corrosion-resistant
material and designed to withstand a perpendicular live loading of
300 pounds per square foot.
(2)
An overflow grate is designed to prevent obstruction of the overflow
structure. If an outlet structure has an overflow grate, such grate
shall meet the following requirements:
(a)
The overflow grate shall be secured to the outlet structure
but removable for emergencies and maintenance.
(b)
The overflow grate spacing shall be no less than two inches
across the smallest dimension.
(c)
The overflow grate shall be constructed and installed to be
rigid, durable, and corrosion resistant, and shall be designed to
withstand a perpendicular live loading of 300 pounds per square foot.
(3)
Stormwater management BMPs shall include escape provisions as follows:
(a)
If a stormwater management BMP has an outlet structure, escape provisions shall be incorporated in or on the structure. Escape provisions include the installation of permanent ladders, steps, rungs, or other features that provide easily accessible means of egress from stormwater management BMPs. With the prior approval of the municipality pursuant to § 172-16C, a freestanding outlet structure may be exempted from this requirement;
(b)
Safety ledges shall be constructed on the slopes of all new stormwater management BMPs having a permanent pool of water deeper than 2 1/2 feet. Safety ledges shall be comprised of two steps. Each step shall be four feet to six feet in width. One step shall be located approximately 2 1/2 feet below the permanent water surface, and the second step shall be located one to 1 1/2 feet above the permanent water surface. See § 172-16E for an illustration of safety ledges in a stormwater management BMP; and
(c)
In new stormwater management BMPs, the maximum interior slope
for an earthen dam, embankment, or berm shall not be steeper than
three horizontal to one vertical.
D.
Variance or exemption from safety standard. A variance or exemption
from the safety standards for stormwater management BMPs may be granted
only upon a written finding by the municipality that the variance
or exemption will not constitute a threat to public safety.
E.
Safety ledge illustration.
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Elevation View - Basin Safety Ledge Configuration
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