A.
Structural stormwater management measures shall be designed to meet
the standards established in this section. These standards have been
developed to protect public safety, conserve natural features, create
an aesthetically pleasing site and promote proper on-site stormwater
management.
B.
The following structural stormwater management measures may be utilized
as part of a stormwater management system at a major land development
in the Pinelands, provided that the applicant demonstrates that they
are designed, constructed and maintained so as to meet the standards
and requirements established by this Part 1. If alternative stormwater
management measures are proposed, the applicant shall demonstrate
that the selected measures will achieve the standards established
by this Part 1.
(1)
Bioretention systems;
(2)
Constructed stormwater wetlands;
(3)
Extended detention basins;
(4)
Infiltration basins;
(5)
Vegetated filter strips;
(6)
Infiltration basins and trenches;
(7)
Wet ponds with suitable liners;
(8)
Pervious paving systems; and
(9)
Manufactured treatment devices, provided their pollutant removal
rates are verified by the New Jersey Corporation for Advanced Technology
and certified by the NJDEP.
C.
Structural stormwater management measures shall be designed to take
into account the existing site conditions, including environmentally
critical areas, wetlands, flood-prone areas, slopes, depth to seasonal
high water table, soil type, permeability and texture, and drainage
area and drainage patterns.
D.
Structural stormwater management measures shall be designed and constructed
to be strong, durable, and corrosion-resistant (Measures that are
consistent with the relevant portions of the residential site improvement
standards at N.J.A.C. 5:21-7.3, 5:21-7.4, and 5:21-7.8 shall be deemed
to meet this requirement.); to minimize and facilitate maintenance
and repairs; and to ensure proper functioning.
F.
To the maximum extent practicable, the design engineer shall design
structural stormwater management measures on the development site
in a manner that:
(1)
Limits site disturbance, maximizes stormwater management efficiencies,
and maintains or improves aesthetic conditions;
(2)
Utilizes multiple stormwater management measures, smaller in size
and distributed spatially throughout the land development site, instead
of a single larger structural stormwater management measure;
(3)
Incorporates pretreatment measures. Pretreatment can extend the functional
life and increase the pollutant removal capability of a structural
stormwater management measure. Pretreatment measures may be designed
in accordance with the New Jersey BMP Manual or other sources approved
by the City's designated engineer.
G.
Stormwater management basins shall be designed in a manner that complements
and mimics the existing natural landscape, including but not limited
to the following design strategies:
(1)
Use of natural, nonwetland wooded depressions for stormwater runoff
storage; and
(2)
Establishment of attractive landscaping in and around the basin that
mimics the existing vegetation and incorporates native Pinelands plants,
including, but not limited to, the species listed in N.J.A.C. 7:50-6.25
and 7:50-6.26.
H.
Stormwater management basins shall be designed with gently sloping
sides. The maximum allowable basin side slope shall be three horizontal
to one vertical.
I.
Guidance on the design and construction of structural stormwater
management measures may be found in the New Jersey BMP Manual. Other
guidance sources may also be used upon approval by the City's designated
engineer.
J.
After all construction activities and required field testing have
been completed on the development site, as-built plans depicting design
and as-built elevations of all stormwater management measures shall
be prepared by a licensed land surveyor and submitted to the City's
designated engineer. Based upon the City's designated engineer's review
of the as-built plans, all corrections or remedial actions deemed
by the City's designated engineer to be necessary due to the failure
to comply with the standards established by this Part 1 and/or any
reasons of public health or safety shall be completed by the applicant.
In lieu of review by the City's designated engineer, the City reserves
the right to engage a professional engineer to review the as-built
plans. The applicant shall pay all costs associated with such review.
A.
Stormwater infiltration BMPs, such as bioretention systems with infiltration,
dry wells, infiltration basins, pervious paving systems with storage
beds, and sand filters with infiltration, shall be designed, constructed
and maintained to completely drain the total runoff volume generated
by the basin's maximum design storm within 72 hours after a storm
event. Runoff storage for greater times can render the BMP ineffective
and may result in anaerobic conditions, odor and both water quality
and mosquito breeding problems.
B.
Stormwater infiltration BMPs shall be designed, constructed and maintained
to provide a minimum separation of at least two feet between the elevation
of the lowest point of the bottom of the infiltration BMP and the
seasonal high water table.
C.
A stormwater infiltration BMP shall be sited in suitable soils verified
by field testing to have permeability rates between one and 20 inches
per hour. If such site soils do not exist or if the design engineer
demonstrates that it is not practical for engineering, environmental
or safety reasons to site the stormwater infiltration BMP(s) in such
soils, then the stormwater infiltration BMP(s) may be sited in soils
verified by field testing to have permeability rates in excess of
20 inches per hour, provided that a bioretention system, designed,
installed and maintained in accordance with the New Jersey BMP Manual,
is installed to meet one of the following conditions:
(1)
The bioretention system is constructed as a separate measure designed
to provide pretreatment of stormwater and to convey the pretreated
stormwater into the infiltration BMP; or
(2)
The bioretention system is integrated into and made part of the infiltration
BMP and, as such, does not require an underdrain system. If this option
is selected, the infiltration BMP shall be designed and constructed
so that the maximum water depth in the bioretention system portion
of the BMP during treatment of the stormwater quality design storm
is 12 inches in accordance with the New Jersey BMP Manual.
D.
The minimum design permeability rate for the soil within a BMP that relies on infiltration shall be 0.5 inch per hour. A factor of safety of two shall be applied to the soil's field-tested permeability rate to determine the soil's design permeability rate. For example, if the field-tested permeability rate of the soil is four inches per hour, its design permeability rate would be two inches per hour. The minimum design permeability rate for the soil within a stormwater infiltration basin shall also be sufficient to achieve the minimum seventy-two-hour drain time described in § 330-21A above. The maximum design permeability shall be 10 inches per hour.
E.
A soil's field-tested permeability rate shall be determined in accordance
with the following:
(2)
The results of the required field permeability tests shall demonstrate
a minimum tested infiltration rate of one inch per hour;
(4)
If the results of the post-development field permeability tests fail to achieve the minimum required design permeability rates in § 330-21E above utilizing a factor of safety of two the stormwater infiltration BMP shall be renovated and re-tested until such minimum required design permeability rates are achieved; and
(5)
The results of all field permeability tests shall be certified by
a professional engineer and transmitted to the City's designated engineer.
F.
To help ensure maintenance of the design permeability rate over time,
a six-inch layer of K5 soil shall be placed on the bottom of a stormwater
infiltration BMP. This soil layer shall meet the textural and permeability
specifications of a K5 soil as provided at N.J.A.C. 7:9A, Appendix
A, Figure 6, and be certified to meet these specifications by a professional
engineer licensed in the State of New Jersey. The depth to the seasonal
high water table shall be measured from the bottom of the K5 sand
layer.
G.
The design engineer shall assess the hydraulic impact on the groundwater
table and design the project site and all stormwater infiltration
basins so as to avoid adverse hydraulic impacts. Adverse hydraulic
impacts include, but are not limited to, raising the groundwater table
so as to cause surface ponding; flooding of basements and other subsurface
structures and areas; preventing a stormwater infiltration basin from
completely draining via infiltration within 72 hours of a design storm
event; and interference with the proper operation of subsurface sewage
disposal systems and other surface and subsurface structures in the
vicinity of the stormwater infiltration basin.
H.
The design engineer shall conduct a mounding analysis, as defined in § 330-31, of all stormwater infiltration BMPs. The mounding analysis shall be conducted in accordance with the requirements in § 330-35C(12). Where the mounding analysis identifies adverse impacts, the stormwater infiltration BMP shall be redesigned or relocated, as appropriate.
I.
Stormwater infiltration BMPs shall be constructed in accordance with
the following:
(1)
To avoid sedimentation that may result in clogging and reduce the
basin's permeability rate, stormwater infiltration basins shall be
constructed according to the following:
(a)
Unless the conditions in Subsection I(1)(b) below are met, a stormwater infiltration basin shall not be placed into operation until its drainage area is completely stabilized. Instead, upstream runoff shall be diverted around the basin and into separate, temporary stormwater management facilities and sediment basins. Such temporary facilities and basins shall be installed and utilized for stormwater management and sediment control until stabilization is achieved in accordance with the Standards for Soil Erosion and Sediment Control in New Jersey, which is incorporated herein by reference as amended and supplemented.
(b)
If the design engineer determines that, for engineering, environmental or safety reasons, temporary stormwater management facilities and sediment basins cannot be constructed on the site, the stormwater infiltration basin may be placed into operation prior to the complete stabilization of its drainage area, provided that the basin's bottom during this period is constructed at a depth at least two feet higher than its final design elevation. All other infiltration BMP construction requirements in this section shall be followed. When the drainage area is completely stabilized, all accumulated sediment shall be removed from the infiltration BMP, which shall then be excavated to its final design elevation in accordance with the construction requirements of this section and the performance standards in Article IV.
(2)
To avoid compaction of subgrade soils of BMPs that rely on infiltration, no heavy equipment such as backhoes, dump trucks or bulldozers shall be permitted to operate within the footprint of the BMP. All excavation required to construct a stormwater infiltration BMP shall be performed by equipment placed outside the BMP. If this is not possible, the soils within the excavated area shall be renovated and tilled after construction is completed to reverse the effects of compaction. In addition, post-development soil permeability testing shall be performed in accordance with § 330-21E of this section.
(3)
Earthwork associated with stormwater infiltration BMP construction,
including excavation, grading, cutting or filling, shall not be performed
when soil moisture content is above the lower plastic limit.
A.
If a structural stormwater management measure has an outlet structure,
escape provisions shall be incorporated in or on the structure. "Escape
provisions" means the permanent installation of ladders, steps, rungs,
or other features that provide readily accessible means of ingress
and egress from the outlet structure.
B.
A trash rack is a device intended to intercept runoff-borne trash
and debris that might otherwise block the hydraulic openings in an
outlet structure of a structural stormwater management measure. Trash
racks shall be installed upstream of such outlet structure openings
as necessary to ensure proper functioning of the structural stormwater
management measure in accordance with the following:
(1)
The trash rack should be constructed primarily of bars aligned in
the direction of flow with one-inch spacing between the bars to the
elevation of the water quality design storm. For elevations higher
than the water quality design storm, the bars shall be spaced no greater
than 1/3 the width of the hydraulic opening it is protecting or six
inches, whichever is less. Transverse bars aligned perpendicular to
flow should be sized and spaced as necessary for rack stability and
strength.
(2)
The trash rack shall not adversely affect the hydraulic performance
of either the outlet structure opening it is protecting or the overall
outlet structure.
(3)
The trash rack shall have sufficient net open area under clean conditions
to limit the peak design storm velocity through it to a maximum of
2.5 feet per second.
(4)
The trash rack 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.
C.
An overflow grate is a device intended to protect the opening in
the top of a stormwater management measure outlet structure. If an
outlet structure has an overflow grate, such grate shall meet the
following requirements:
(1)
The overflow grate shall be secured to the outlet structure but removable
for emergencies and maintenance;
(2)
The overflow grate spacing shall be no more than two inches across
the smallest dimension; and
(3)
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.
D.
The maximum side slope for an earthen dam, embankment, or berm shall
not be steeper than three horizontal to one vertical.
E.
Safety ledges shall be constructed on the slopes of all new structural stormwater management measures having a permanent pool of water deeper than 2 1/2 feet. Such 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 foot to 1 1/2 feet above the permanent water surface. See § 330-22E(1) below, for an illustration of safety ledges in a stormwater management basin.
(1)
Illustration of safety ledges.
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