[Adopted 6-28-2019 by Ord. No. 1311[1]]
[1]
Editor's Note: This ordinance repealed former Art. IV, Stormwater
Systems, adopted 10-28-2014 by Ord. No. 1274.
Unless otherwise noted, the following design standards and requirements
apply to construction plans submitted for review by the City of Roseville
for all types of developments or drain-related construction activities.
A.
With this article, the City adopts the requirements identifying best
management practices for any activity, operation, or facility which
may cause or contribute to pollution or contamination of stormwater,
the storm drain system, or waters of the state. The owner or operator
of a commercial or industrial establishment shall provide, at their
own expense, reasonable protection from accidental discharge of prohibited
materials or other wastes into the municipal separate storm sewer
system (MS4) or watercourses through the use of these structural and
nonstructural BMPs.
B.
Further, any person responsible for a property or premises, which
is, or may be, the source of an illicit discharge, may be required
to implement, at said person's expense, additional structural and
nonstructural BMPs to prevent the further discharge of pollutants
to the municipal separate storm sewer system. Compliance with all
terms and conditions of a valid NPDES permit authorizing the discharge
of stormwater associated with industrial activity, to the extent practicable,
shall be deemed compliance with the provisions of this section. These
BMPs shall be part of a stormwater pollution prevention plan (SWPPP)
as necessary for compliance with requirements of the NPDES permit.
C.
"Reasonable protection" for the purposes of this article shall mean
the installation, operation and maintenance of the required structural
and/or nonstructural BMPs, implementation and documentation of the
BMPs operation and maintenance procedures and practices; and pollution
prevention and good housekeeping (P2/GH) procedures and practices
necessary for the establishment to comply with state and federal stormwater
regulations.
The following general stormwater management requirements apply
to all new developments and redevelopments in the City of Roseville.
A.
The design process shall begin by identifying sensitive areas located
on the site and laying out the site to protect the sensitive areas.
B.
Best management practices. Best management practices (BMPs) that
reduce the amount of stormwater runoff and improve water quality are
required and shall be designed on a site-specific basis. Rate and
volume reduction BMPs shall be used to protect open channel storm
drains. All BMPs shall be included on the plans and will be subject
to review and approval by the City of Roseville, the Macomb County
Public Works Office (MCPWO) and the Michigan Department of Environment,
Great Lakes and Energy (EGLE formerly MDEQ), or the authorized state
regulatory agency, as necessary for permits.
(1)
During construction, all sites that disturb one or more acres of
land, or are located within 500 feet of waters of the state, BMP usage
shall be monitored and recorded in the weekly soil erosion sedimentation
control (SESC) reports. In such cases, weekly SESC reports shall also
be required during construction.
(2)
Land uses with potential for significant pollutant loading ("hot
spots"), including but not limited to gas stations, commercial vehicle
maintenance and repair, auto recyclers, recycling centers, and scrap
yards, will require BMPs which address regulation of the specific
hazard as determined by the MCPWO or the City Engineer. In such cases,
weekly SESC reports shall also be required.
(3)
The developer/owner shall include a long-term operation and maintenance
schedule for all permanent BMPs. A maintenance agreement between the
developer/owner and the City is necessary for permanent BMPs which
shall include but not be limited to: inspection of structural or vegetative
BMPs, performance of maintenance and corrective actions when BMPs
are neglected by the owner, and deed restrictions. All such maintenance
agreements shall be binding on the property and shall remain in effect
in the event the property ownership is transferred or sold.
C.
On-site management of stormwater is required first and foremost,
unless site constraints consistent with the flow chart preclude this
approach.
D.
Stormwater shall be managed using four standards: channel protection,
flood control, water quality, and pretreatment to protect both water
resources and real property.
E.
Channel protection control system shall be provided on all new developments
connecting to an open drain to protect the drain's channel and banks
from erosion due to the increased flow. Direct discharges to the Macomb
County Public Works Office drains are generally governed by MCPWO
design standards. Open drains within the City of Roseville jurisdiction
shall be protected by incorporating a restricted flow of the channel
protection volume. It is required that the postdevelopment project
site runoff volume and peak flow rate must be maintained at or below
predevelopment levels for all storms up to the two-year, twenty-four-hour
event. "Predevelopment level" means the runoff flow volume and rate
for the last land use prior to the planned new development or redevelopment.
Compliance with this requirement is determined by calculating the
existing ("predevelopment") and postdevelopment runoff volume and
rate for the two-year and smaller storm events. The method is described
in the Department of Environmental Quality (DEQ) publication, Computing
Flood Discharges for Small Ungaged Watersheds, dated July 2003 (updated
January 22, 2010).
(1)
If it is demonstrated using the Alternative Approach Flowchart (Exhibit
A[1]) that the development cannot meet the required channel
protection performance standard, the development may propose incorporation
of green infrastructure [i.e., rain gardens, green (vegetated) roofs,
permeable pavement, impervious cover removal, use of trees, etc.]
This includes instances where site conditions (e.g., space limitations
or tight soils that prevent infiltration, or soil or groundwater contamination,
"hot spots") challenge or prohibit feasibility of maintaining the
project site's predevelopment runoff levels for all storms up to the
two-year, twenty-four-hour event. Green infrastructure shall be allowed
under all circumstances consistent with the flowchart. Review of these
proposals will be consistent with the SEMCOG Low Impact Development
Manual for Michigan, 2008 or current standards.
[1]
Editor's Note: Exhibit A is on file in the City offices.
F.
Flood control shall be provided for all sites through retention or
detention. On-site detention or retention of stormwater is required
of all new developments or redevelopments to maintain the peak outflow
to a rate similar to the predevelopment runoff rate. On-site flood
control may be reduced or waived for direct discharges to large lakes
and rivers if the developer demonstrates no negative impacts, or if
provided in a regional facility with adequate upstream infrastructure.
G.
Overland flow routes and the extent of high water levels for the
100-year storm shall be identified for all sites.
H.
Water quality treatment shall be provided for all sites. A minimum
treatment volume equal to one inch of runoff from the project site
is required. A minimum volume of 900 cubic feet per acre is required
for directly connected disturbed pervious areas (i.e., lawns). BMPs
shall be designed to reduce postdevelopment solids loadings by 80%
or to not exceed solids loadings of 80 milligrams per liter. Developments
that disturb less than one acre, and are not part of a larger common
plan of development or sale, may be exempted from the City's water
quality treatment standards as approved by the City Engineer.
I.
Pretreatment is required for infiltration, filtration and detention
BMPs for ease of maintenance and to protect BMP integrity and preserve
longevity.
J.
Stormwater discharges from activities with a high risk for an accidental
spill of pollutants (stormwater hot spots) shall provide spill containment.
K.
The design maximum release rate, volume or concentration of stormwater
discharged from a site shall not exceed the capacity of existing infrastructure
or cause impairment to the off-site receiving area. Evaluation of
the existing outlet must be performed and an adequate outlet must
be provided.
L.
The use of many decentralized low-impact development (LID) BMPs is
not mandated but is encouraged on private sites.
M.
Unless otherwise noted, hydraulic and hydrologic calculations (including
rainfall volumes and distributions) shall be based on current EGLE
standards (i.e., NOAA Atlas 14) and procedures in place at the time
of application.
N.
Construction plans for a phased development shall show the existing
and/or proposed drainage systems for all prior phases of the development,
unless the drainage system for the current phase is entirely independent
of the prior phases. Furthermore, drainage plans for a phase of a
development must not be dependent upon work planned to be performed
in a future phase.
O.
Plans shall include a grading plan showing existing and proposed
topographic contour lines and proposed finish floor and basement floor
elevations.
P.
All existing natural or man-made watercourses shall be shown on the
plans. The proposed changes to the site must not interfere with common
law natural flow rights. Existing watercourses must be preserved or
relocated, or the flow otherwise accommodated by the proposed plans.
Provisions for the maintenance of the watercourse must be included
in the deed restriction or an equivalent legally binding agreement.
EGLE and/or the Army Corps of Engineers may also require permits for
changes made to such watercourses.
Q.
No construction activities shall be allowed without approval of the
City of Roseville Building Official in a 100-year floodplain as determined
by the City of Roseville.
R.
The cover sheet of the plans shall include a "permit status table"
indicating the status of all permits being obtained.
S.
If an established drain is involved, construction plans shall include
a note indicating that "All work performed in the right-of-way of
an established drain shall require a permit from the Drain Commissioner."
T.
The engineer's seal shall be affixed to all sheets of the construction
plans.
U.
Unless the storm sewers are to be owned and maintained by a single
private entity (i.e., municipal or commercial development, manufactured
housing community, etc.), all storm sewers shall be located within
an easement. The minimum easement width for a storm sewer shall be
12 feet centered on the sewer center line. City Engineer may require
a larger easement as necessary for access and to facilitate maintenance
and future repairs. The dedication of the easement shall be required
prior to acceptance of the continuous maintenance and service by the
City.
V.
Privately maintained storm infrastructure, including but not limited
to pipes, stormwater detention facility, water treatment units, bioswales,
etc., will require a maintenance agreement.
W.
All existing and proposed on-site drainage easements shall be clearly
shown.
X.
No public right-of-way runoff shall be routed through private storm
sewer unless approved by City Engineer. All storm sewer intended to
be public (i.e., road drainage), shall be within a public right-of-way
except as may be necessary to outlet said public storm sewer to another
public sewer.
A.
No construction activities shall be allowed without approval from
the Macomb County Public Works Office for any development directly
discharging to an established county drain. All work within the right-of-way
of the established drain is subject to the design standards and requirements
of the Macomb County Public Works Office.
B.
If an established county drain is involved, construction plans shall
include a note indicating that "All work performed in the right-of-way
of an established drain shall require a permit from the Macomb County
Public Works Office."
C.
Where drainage is discharged to an established drain, such outlets
shall be so designed as to enter the drain at an angle of 90°
or less, as determined by the upstream center line.
A.
Plans shall show boundaries and acreages of catchment areas contributing
runoff to each proposed or existing catch basin and/or inlet. Runoff
from off-site tributary areas must be accommodated in design or rerouted.
B.
The required discharge capacity for each reach of sewer shall be
determined by the Rational Method.
(1)
A ten-year design storm shall be used such that rainfall intensity,
I = 175/(T + 25), where T = time of concentration in minutes.
(2)
The runoff coefficient, C, shall be in conformance with normal design
practice. Where a weighted average coefficient is employed, the computations
shall be submitted for review.
(3)
Minimum C-coefficients for various finish surfaces are as follows:
|
Finish Surface
|
Minimum C-coefficient
|
|---|---|
|
Water surface
|
1.00
|
|
Impervious pavement and roofs
|
0.90
|
|
Dense graded stone and pavers
|
0.80
|
|
Open graded stone
|
0.60
|
|
Lawns
|
0.35
|
|
Other surface C-coefficients
|
Subject to approval by City Engineer
|
(4)
The following averaged C-coefficients may be used in lieu of weighted
coefficient for proposed developments:
|
Development
|
Averaged C-coefficients
|
|---|---|
|
Single-family residential
|
0.35
|
|
Multifamily residential
|
0.55
|
|
Commercial
|
0.85
|
|
Industrial
|
0.90
|
C.
A complete set of storm sewer design calculations shall accompany
every set of construction plans submitted for review.
(1)
Sewer capacities shall be based on the Manning Equation for full
flow velocity. With Manning's "n" coefficient as follows:
|
Pipe Material
|
"n" Coefficient
|
|---|---|
|
Smooth lined, metal, PVC or HDPE pipe
|
0.011
|
|
Reinforced concrete pipe
|
0.013
|
|
Corrugated, metal, PVC, or HDPE pipe
|
0.024
|
|
Other pipe material
|
n-coefficients subject to approval by City Engineer
|
(2)
Energy losses from friction shall be based on calculated design storm
peak discharges and velocities, not Manning design (i.e., full-pipe)
capacities.
(3)
Energy losses from friction shall be based on typical Manning "n"
roughness values as approved by the City Engineer.
(4)
Energy losses through manholes and other appurtenances shall be included
in the design calculations or reflected in friction losses through
use of conservative Manning "n" roughness values as approved by the
City Engineer.
D.
The storm sewer pipe shall have a minimum diameter of 12 inches when
constructed in a public right-of-way or easement.
E.
Minimum allowable pipe velocity shall be 2.5 feet per second (except
where the minimum diameter requirement makes this unachievable). Desirable
pipe velocity range shall be four to eight feet per second. Maximum
allowable pipe velocity shall be 10 feet per second.
F.
Hydraulic grade lines for the ten-year storm shall be calculated
and shown as a part of all storm sewer profiles. In no case shall
the elevation of the hydraulic grade line exceed the elevation of
a point lying one foot below the rim elevation of a manhole, catch
basin or inlet. The hydraulic grade line upstream of a detention or
retention storage facility shall be calculated assuming the design
high water elevation (e.g., full detention basin) or 8/10 height of
pipe, whichever is higher.
G.
The storm sewer plan and profile drawing shall show the following
data:
(1)
Proper identification and numbering of manholes, catch basins and
inlets.
(2)
Invert and casting elevations for all structures.
(3)
Pipe length (C/L to C/L to structures).
(4)
Pipe diameter.
(5)
Pipe slope.
(6)
Pipe class or designation.
(7)
Detail of trench construction and type of backfill material.
H.
Generally, manholes shall be placed not more than 400 feet apart
for sewers less than 30 inches diameter and 600 feet apart for larger
sewers.
I.
The minimum inside diameter of all manholes, catch basins and inlets
shall be 48 inches, with the following exception: Inlet structures
from which water will be discharged directly into a catch basin may
be 24 inches inside diameter. The depth of such inlets shall be no
greater 5.0 feet and no less than 3.5 feet from the top of frame and
cover to the invert.
J.
Manholes and inlet structures may be constructed of brick, manhole
block, precast concrete (ASTM C478) or cast-in-place concrete.
K.
All manhole block or brick structures shall be plastered on the outside
with one to 2.5 mix of portland cement mortar, 1/2 inch thick. No
calcium chloride or other chemical shall be added to lower the freezing
point of the mortar, as the strength of the mortar may be lessened.
L.
Inlet structures in the public street right-of-way shall be spaced
a maximum of 400 feet apart (or a maximum of 400 feet on either side
of a high point). The spacing and/or number of inlet structures required
to accommodate the design flows in streets and in private drives and
parking areas shall be based on a maximum of one cubic foot per second
per 90 square inches of opening in an inlet or catch basin cover.
M.
All storm sewer pipe, manholes, catch basins, and inlets shall meet
MDOT specifications.
N.
Generally, drops of over 2.0 feet at manholes, from invert of higher
pipes to lower pipes, shall be avoided.
O.
Joints in concrete pipe having a diameter of 30 inches or larger
shall be pointed up on inside with mortar after backfilling has been
completed.
P.
Where drainage is discharged to an established drain or natural watercourse,
such outlets shall be so designed as to enter the drain or watercourse
at an angle of 90° or less, as determined by the upstream center
line. Preformed end sections, grouted riprap or specially designed
outlet structures will be required.
Q.
Unless the storm sewers are to be owned and maintained by a single
private entity (i.e., municipal or commercial development, manufactured
housing community, etc.), all storm sewers shall be located within
an easement. The minimum easement width for a storm sewer shall be
12 feet centered on the sewer center line.
R.
All existing and proposed on-site drainage easements shall be clearly
shown.
S.
To account for energy losses, at structures a flow change of direction
of greater than 45°, a 0.10 foot drop shall be added from the
upstream to downstream pipes. Approval from City Engineer is required
to waive the requirement for sites where existing conditions do not
provide adequate storm depth to facilitate the drop.
T.
At structure with a change of pipe size, the 8/10th elevation, or
obvert of the pipes shall align. Approval from City Engineer is required
to waive the requirement for sites where existing conditions do not
provide adequate storm depth to facilitate the drop.
U.
Storm sewers shall have a minimum of 3 1/2 feet of cover from
the finished surface to the horizontal center line, where existing
conditions allow. City Engineer may approve less cover where existing
conditions restrict cover.
V.
An end section with prefabricated bar screen shall be installed on
the end of all storm sewers 12 inches in diameter or larger. Openings
of the bar screen shall be no more than six inches on center.
W.
All connections of storm sewers shall be at structure (i.e., manhole,
catch basins etc.) locations. Blind taps or wye connections are not
allowed with the exception of sump pump connections per the City's
Stormwater Detail Sheet. All sump pumps shall be directed, via an
enclosed three-inch diameter minimum pipe, to the storm system.
A.
The peak ten-year flow in each reach of open channel shall remain
within the banks of the channel. Off-site tributary area shall be
included in the design, or the off-site tributary runoff shall be
rerouted around the channel.
B.
The values of Manning's "n" shall be no less than 0.040 except where
the channel is smooth and paved, in which case an "n" value of 0.013
to 0.022 shall be used.
C.
The maximum velocity for grass-lined channels shall not exceed five
feet per second. Where the above velocity is exceeded, the channel
shall be protected by cobble paving or other means to prevent scour.
D.
The minimum acceptable nonsiltation velocity should be 1.5 feet per
second.
E.
Unless the open channels are to be owned and maintained by a single
private entity (i.e., industrial/commercial development, manufactured
housing community, etc.), all open channels shall be located within
an easement. Open channels shall have a minimum right-of-way of 40
feet plus top width of channel centered on the center line. A consistent
right-of-way width shall be maintained along the entire reach of channel
on the proposed site. A minimum width of 20 feet must be maintained
from the top-of-bank to the edge of the right-of-way to allow for
maintenance. The above minimum width shall govern generally; however,
wider rights-of-way may be required at the discretion of the City
Engineer.
F.
Side slopes of open channels shall normally be no steeper than one
vertical to three horizontal. Where conditions dictate steeper side
slopes, consideration should be given to slope paving and fencing.
The final decision in such matters rests with the City Engineer.
G.
All existing and proposed on-site drainage easements shall be clearly
shown on the plans.
A.
All culverts should be labeled on the plans as "existing," "proposed,"
or "to be extended."
B.
Plans shall show boundaries and acreages of tributary areas contributing
runoff to each proposed or existing culvert on the proposed site.
C.
Proposed or extended culverts must be approved by the City Engineer.
Proposed or extended culverts may also require the approval of the
Macomb County Road Commission, the Macomb County Public Works Commission,
the Michigan Department of Environmental Quality and/or the Michigan
Department of Transportation (MDOT).
D.
The Rational Method shall be used to determine the peak design flow
for the culvert, if the tributary area to the culvert is less than
20 acres. For larger tributary areas, the SCS Method shall be used.
The runoff coefficients used should be consistent with those in standard
engineering practice, as approved by the City Engineer, and selected
to reflect the future land use of the tributary area.
E.
All culverts shall be designed with consideration of both inlet and
outlet control conditions. Calculations of the ten-year and 100-year
headwater elevations for all culverts thus designed shall accompany
the final plans.
(1)
The ten-year headwater elevation of each culvert shall not exceed
an elevation one foot below the road or driveway center line elevation.
The backwater shall not extend beyond the limits of the proprietor's
property.
(2)
The 100-year headwater elevation of each culvert may overtop the
road or driveway center-line elevation, but must remain below proposed
finish floor elevations of all nearby existing and proposed structures.
(3)
The tailwater elevation assumed for each culvert should be estimated
as the normal depth of the peak flow in the downstream channel, unless
the tailwater is influenced by the headwater of another downstream
culvert or the confluence of another watercourse.
F.
Wing walls, headwalls, end sections, and all other culvert extremities
shall be designed to ensure the stability of the surrounding soil
and to meet the requirements of other governing agencies (e.g., Macomb
County Road Commission, MCPWO, MDOT, EGLE), if applicable.
G.
Roadways over culverts or bridges may be required to be paved or
designed in such a way as to prevent the erosion of road material
into the established drain or watercourse.
I.
Riprap must be provided for all culverts in established drains or
significant watercourses. The riprap provided for the protection of
culvert ends shall:
(1)
Extend at least one culvert diameter upstream of the culvert inlet
and at least four culvert diameters downstream of the culvert outlet;
(2)
Extend across the bottom of the channel and up the banks of the channel
to at least the elevation of the crown of the culvert;
(3)
Be inlayed such that it does not cause an obstruction in the watercourse;
and
(4)
Have a minimum dimension no smaller than that consistent with HEC-11
Design Guidelines for Rock Riprap and MDOT standards. (A conservative
guideline for water depths less than three feet would be to use eight-inch-diameter
riprap for flow velocities up to six feet per second, and sixteen-inch-diameter
riprap for flow velocities up to 11 feet per second.)
J.
Minimum diameter for a driveway or crossroad culvert shall be 18
inches or equivalent pipe arch.
K.
The pipe used in culverts shall meet MDOT specifications and Macomb
County Road Commission standards.
A.
A bioretention system consists of a soil bed planted with native
vegetation located above an underdrained sand layer. It can be configured
as either a bioretention structure or a bioretention swale. Stormwater
runoff entering the bioretention system is filtered first through
the vegetation and then the sand/soil mixture before being conveyed
downstream by the underdrain system. Runoff storage depths above the
planting bed surface are typically shallow. The adopted TSS removal
rate for bioretention systems is 90%.
B.
Bioretention systems are used to remove a wide range of pollutants,
such as suspended solids, nutrients, metals, hydrocarbons, and bacteria
from stormwater runoff. They can also be used to reduce peak runoff
rates and increase stormwater infiltration when designed as a multistage,
multifunction facility.
(1)
Predesign site evaluation.
(a)
For infiltration trench and structure practices, a minimum field
infiltration rate (fc) of 0.52 inch per hour is required; lower rates
preclude the use of these practices. For surface sand filter and bioretention
practices, no minimum infiltration rate is required if these facilities
are designed with a "day-lighting" underdrain system; otherwise these
facilities require a 0.52 inch per hour rate.
(b)
Feasibility testing is to be conducted to screen unsuitable
sites, and reduce testing costs. A soil boring is not required at
this stage. However, a designer or landowner may opt to engage concept
design borings at his discretion, without feasibility testing.
(c)
Initial testing involves either one field test per facility,
regardless of type or size, or previous testing data, such as the
following:
[1]
On-site septic percolation testing, within 200 feet of the proposed
BMP location, and on the same contour which can establish initial
rate, water table and/or depth to bedrock;
[2]
Geotechnical report on the site prepared by a qualified geotechnical
consultant; or
[3]
Natural Resources Conservation Service (NRCS) County Soil Mapping
showing, an unsuitable soil group such as a hydrologic Group D soil
in a low-lying area.
(d)
If the results of initial feasibility testing as determined
by a qualified professional show that an infiltration rate of greater
than 0.52 inch per hour is probable, then the number of concept design
test pits shall be per the following Table D-1 (Exhibit B[1]). An encased soil boring may be substituted for a test
pit, if desired.
[1]
Editor's Note: Exhibit B is on file in the City offices.
(2)
Design criteria.
(a)
Storage volume, depth, and duration. Bioretention systems shall
be designed to treat the runoff volume generated by the stormwater
quality design storm (two-year). The maximum water depth during treatment
of the stormwater quality design storm shall be 12 inches in a bioretention
structure and 18 inches in a bioretention swale. The minimum diameter
of any outlet or overflow orifice is 2.5 inches. The bottom of a bioretention
system, including any underdrain piping or gravel layer, must be a
minimum of one foot above the seasonal high groundwater table. The
planting soil bed and underdrain system shall be designed to fully
drain the stormwater quality design storm runoff volume within 72
hours.
(b)
Permeability rates. The design permeability rate through the
planting soil bed must be sufficient to fully drain the stormwater
quality design storm runoff volume within 72 hours. This permeability
rate must be determined by field or laboratory testing. Since the
actual permeability rate may vary from test results and may also decrease
over time due to soil bed consolidation or the accumulation of sediments
removed from the treated stormwater, a factor of safety of two shall
be applied to the tested permeability rate to determine the design
permeability rate. Therefore, if the tested permeability rate of the
soil bed material is four inches/hour, the design rate would be two
inches per hour (i.e., four inches per hour/two). This design rate
would then be used to compute the system's stormwater quality design
storm drain time.
(c)
Planting soil bed. The planting soil bed provides the environment
for water and nutrients to be made available to the vegetation. The
soil particles can absorb some additional pollutants through cation
exchange, and voids within the soil particles can store a portion
of the stormwater quality design storm runoff volume. The planting
soil bed material should consist of 10% to 15% clays, a minimum 65%
sands, with the balance as silts. The material's pH should range from
5.5 to 6.5. The material shall be placed in twelve-inch to eighteen-inch
lifts. The total depth or thickness of the planting soil bed should
be a minimum of three feet. As noted above, the design permeability
rate of the soil bed material must be sufficient to drain the stormwater
quality design storm runoff volume within 72 hours. Filter fabric
should be placed along the sides of the planting soil bed to prevent
the migration of soil particles from the adjacent soil into the planting
soil bed.
(d)
Vegetation. The vegetation in a bioretention system removes
some of the nutrients and other pollutants in the stormwater inflow.
The use of native plant material is recommended for bioretention systems
wherever possible. The goal of the planting plan should be to simulate
a forest-shrub community of primarily upland type. In general, trees
should dominate the perimeter zone that is subject to less frequent
inundation. Shrubs and herbaceous species that are adapted to moister
conditions and expected pollutant loads should be selected for the
wetter zones. The number of stems per acre should average 1,000, with
tree spacing of 12 feet and shrub spacing of eight feet.
(e)
Sand layer. The sand layer serves as a transition between the
planting soil bed and the gravel layer and underdrain pipes. It shall
be a minimum thickness of 12 inches and consist of clean medium aggregate
sand (AASSHTO M-6/ASTM C-33 or MDOT Class II). To ensure proper system
operation, the sand layer must have a permeability rate at least twice
as fast as the design permeability rate of the planting soil bed.
(f)
Underdrain. The underdrain piping must be rigid Schedule 40
PVC pipe. The portion of drain piping beneath the planting soil bed
and sand layer must be perforated. All remaining underdrain piping,
including cleanouts, must be nonperforated. All joints must be secure
and watertight. The underdrain piping must connect to a downstream
storm sewer manhole, catch structure, channel, swale, or ground surface
at a location that is not subject to blockage by debris or sediment
and is readily accessible for inspection and maintenance. Blind connections
to downstream storm sewers are prohibited.
(g)
Overflows. All bioretention systems must be able to safely convey
system overflows to downstream drainage systems. The capacity of the
overflow must be consistent with the remainder of the site's drainage
system and sufficient to provide safe, stable discharge of stormwater
in the event of an overflow.
(h)
Tailwater. The hydraulic design of the underdrain and overflow
systems, as well as any stormwater quantity control outlets, must
consider any significant tailwater effects of downstream waterways
or facilities. This includes instances where the lowest invert in
the outlet or overflow structure is below the flood hazard area design
flood elevation of a receiving stream.
(i)
Maintenance. The following requirements must be included in
the system's maintenance plan.
[1]
General maintenance.
[a]
All bioretention system components expected to
receive and/or trap debris and sediment must be inspected for clogging
and excessive debris and sediment accumulation at least four times
annually as well as after every storm exceeding one inch of rainfall.
Such components may include bottoms, trash racks, low-flow channels,
outlet structures, riprap or gabion aprons, and cleanouts.
[b]
Sediment removal should take place when the structure
is thoroughly dry. Disposal of debris, trash, sediment, and other
waste material should be done at suitable disposal/recycling sites
and in compliance with all applicable local, state, and federal waste
regulations.
[2]
Vegetated areas.
[a]
Mowing and/or trimming of vegetation must be performed
on a regular schedule based on specific site conditions. Grass should
be mowed at least once a month during the growing season. Vegetated
areas must be inspected at least annually for erosion and scour. Vegetated
areas should also be inspected at least annually for unwanted growth,
which should be removed with minimum disruption to the planting soil
bed and remaining vegetation.
[b]
When establishing or restoring vegetation, biweekly
inspections of vegetation health should be performed during the first
growing season or until the vegetation is established. Once established,
inspections of vegetation health, density, and diversity should be
performed at least twice annually during both the growing and nongrowing
seasons. The vegetative cover should be maintained at 85%. If vegetation
has greater than 50% damage, the area should be reestablished in accordance
with the original specifications and the inspection requirements presented
above.
[c]
All use of fertilizers, mechanical treatments,
pesticides and other means to assure optimum vegetation health should
not compromise the intended purpose of the bioretention system. All
vegetation deficiencies should be addressed without the use of fertilizers
and pesticides whenever possible.
[3]
Structural components. All structural components must be inspected
for cracking, subsidence, spalling, erosion, and deterioration at
least annually.
A.
An infiltration structure is a facility constructed within highly
permeable soils that provides temporary storage of stormwater runoff.
An infiltration structure does not normally have a structural outlet
to discharge runoff from the stormwater quality design storm. Instead,
outflow from an infiltration structure is through the surrounding
soil. An infiltration structure may also be combined with an extended
detention structure to provide additional runoff storage for both
stormwater quality and quantity management. The adopted TSS removal
rate for infiltration structures is 80%.
B.
Infiltration structures are used to remove pollutants and to infiltrate
stormwater back into the ground. Such infiltration also helps to reduce
increases in both the peak rate and total volume of runoff caused
by land development. Pollutant removal is achieved through filtration
of the runoff through the soil as well as biological and chemical
activity within the soil.
(1)
Predesign site evaluation.
(a)
Infiltration structures can present some practical design problems.
When planning for an infiltration structure that provides stormwater
quality treatment, consideration should be given to soil characteristics,
depth to the groundwater table, sensitivity of the region, and runoff
water quality. Specifically, infiltration structures must not be used
in the following locations:
[1]
Industrial and commercial areas where solvents and/or petroleum
products are loaded, unloaded, stored, or applied or pesticides are
loaded, unloaded, or stored.
[2]
Areas where hazardous materials are expected to be present in
greater than "reportable quantities" as defined by the United States
Environmental Protection Agency in the Code of Federal Regulations
at 40 CFR 302.4.
[3]
Areas where infiltration structure use would be inconsistent
with an NJDEP approved remedial action work plan or landfill closure
plan.
[4]
Areas with high risks for spills of toxic materials such as
gas stations and vehicle maintenance facilities.
[5]
Areas where industrial stormwater runoff is exposed to source
material. "Source material" means any material(s) or machinery, located
at an industrial facility that is directly or indirectly related to
process, manufacturing, or other industrial activities, that could
be a source of pollutants in any industrial stormwater discharge to
groundwater. Source materials include, but are not limited to, raw
materials, intermediate products, final products, waste materials,
by-products, industrial machinery and fuels, and lubricants, solvents,
and detergents that are related to process, manufacturing, or other
industrial activities that are exposed to stormwater.
[6]
Areas where their installation would create a significant risk
for basement seepage or flooding, cause surficial flooding of groundwater,
or interfere with the operation of subsurface sewage disposal systems
and other subsurface structures. Such adverse impacts must be assessed
and avoided by the design engineer.
(b)
Infiltration structures must be configured and located where
their construction will not compact the soils below the structure.
In addition, an infiltration structure must not be placed into operation
until the contributing drainage area is completely stabilized.
[1]
General setback requirements for infiltration structures:
[a]
Soil absorption systems for Title 5 systems: 50
feet.
[b]
Private wells: 100 feet.
[c]
Public wells: 150 feet.
[d]
Public reservoir, surface water sources for public
water systems and their tributaries: 400 feet.
[e]
Other surface waters: 50 feet.
[f]
Property lines: 10 feet.
[g]
Building foundations: greater than 10 feet to 100
feet, depending upon soil types and infiltration structure type.
(c)
Soils are perhaps the most important consideration for site
suitability. In general, county soil surveys can be used to obtain
necessary soil data for the planning and preliminary design of infiltration
structures. For final design and construction, soil tests are required
at the exact location of a proposed structure in order to confirm
its ability to function without failure.
(2)
Design criteria.
(a)
Storage volume, depth, and duration.
[1]
An infiltration structure must be designed to treat the total
runoff volume generated by the structure's maximum design storm. This
may either be the groundwater recharge or stormwater quality design
storm, depending upon the structure's proposed use. An infiltration
structure must also fully drain this runoff volume within 72 hours.
Runoff storage for greater times can render the structure ineffective
and may result in anaerobic conditions, odor, and both water quality
and mosquito breeding problems. The bottom of the infiltration structure
must be at least two feet above seasonal high water table or bedrock.
For surface structures, this distance must be measured from the bottom
of the sand layer. The structure bottom must be as level as possible
to uniformly distribute runoff infiltration over the subgrade soils.
[2]
To enhance safety by minimizing standing water depths, the vertical
distance between the structure bottom and the maximum design stormwater
surface in surface infiltration structures should be no greater than
two feet. Construction of an infiltration structure must be done without
compacting the structure's subgrade soils. Excavation must be performed
by equipment placed outside the structure whenever possible. This
requirement should be considered when designing the dimensions and
total storage volume of an infiltration structure. It is important
to note that the use of infiltration structures is recommended only
for the stormwater quality design storm and smaller storm events.
Use of infiltration structures for larger storm events and the requirements
by which such structures are to be designed, constructed, and maintained
should be reviewed and approved by all applicable reviewing agencies.
(b)
Permeability rates.
[1]
The minimum design permeability rate of the soils below an infiltration
structure will depend upon the structure's location and maximum design
storm. The use of infiltration structures for stormwater quality control
is feasible only where soil is sufficiently permeable to allow a reasonable
rate of infiltration. Therefore, infiltration structures designed
for storms greater than the groundwater recharge storm can be constructed
only in areas with Hydrologic Soil Group A and B soils.
|
Maximum Design Structure Location
|
Minimum Design Permeability Rate
(inches/hour)
|
|---|---|
|
Groundwater recharge subsurface
|
0.2
|
|
Groundwater recharge surface
|
0.5
|
|
Stormwater quality surface and subsurface
|
0.5
|
[2]
In addition to the above, the design permeability rate of the soil must be sufficient to fully drain the infiltration structure's maximum design storm runoff volume within 72 hours. This design permeability rate must be determined by field testing. [See § 256-57B(1), Bioretention, predesign site evaluation.] Since the actual permeability rate may vary from test results and may also decrease over time due to soil bed consolidation or the accumulation of sediments removed from the treated stormwater, a factor of safety of two must be applied to the tested permeability rate to determine the design permeability rate. Therefore, if the tested permeability rate of the soils is four inches per hour, the design rate would be two inches per hour (i.e., four inches per hour/two). This design rate would then be used to compute the structure's maximum design storm drain time.
(c)
Bottom sand layer. To help ensure maintenance of the design
permeability rate over time, a six-inch layer of sand must be placed
on the bottom of an infiltration structure. This sand layer can intercept
silt, sediment, and debris that could otherwise clog the top layer
of the soil below the structure. The sand layer will also facilitate
silt, sediment, and debris removal from the structure and can be readily
restored following removal operations. The sand layer must meet the
specifications of a MDOT Class II sand. This must be certified by
a certified testing lab.
(d)
Overflows. All infiltration structures must be able to convey
overflows to downstream drainage systems in a safe and stable manner.
The capacity of the overflow must be consistent with the remainder
of the site's drainage system and sufficient to provide safe, stable
discharge of stormwater in the event of an overflow.
(e)
Subsurface infiltration structures. A subsurface infiltration
structure is located entirely below the ground surface. It may consist
of a vault, perforated pipe, and/or stone bed. However, due to the
greater difficulty in removing silt, sediment, and debris, all runoff
to a subsurface infiltration structure must be pretreated. This pretreatment
must remove 80% of the TSS in the runoff from the structure's maximum
design storm.
(f)
Basis of design.
[1]
The design of an infiltration basin is based upon Darcy's Law:
|
Q = KIA
|
|
Where:
| ||
|
Q
|
=
|
The rate of infiltration in cubic feet per second (cfs)
|
|
K
|
=
|
The hydraulic conductivity of the soil in feet per second (fps)
|
|
I
|
=
|
The hydraulic gradient
|
|
A
|
=
|
The area of infiltration in square feet (sf)
|
[2]
From the variables shown in the figure below:
|
Average Hydraulic Gradient = Davg/d
|
|
Minimum Hydraulic Gradient = D1/d
|
|
Maximum Hydraulic Gradient = D2/d
|
 |
(g)
Maintenance. The following requirements must be included in
the system's maintenance plan.
[1]
General maintenance. All infiltration structure components expected
to receive and/or trap debris and sediment must be inspected for clogging
and excessive debris and sediment accumulation at least four times
annually as well as after every storm exceeding one inch of rainfall.
Such components may include bottoms, riprap or gabion aprons, and
inflow points. This applies to both surface and subsurface infiltration
structures. Sediment removal should take place when the structure
is thoroughly dry. Disposal of debris, trash, sediment, and other
waste material should be done at suitable disposal/recycling sites
and in compliance with all applicable local, state, and federal waste
regulations.
A.
Detention storage facilities are designed to detain runoff for a
short period of time and then release it to a watercourse where it
returns to the hydrologic cycle. The objective of detention storage
is to regulate the released runoff rate and to reduce the impact on
downstream drainage systems. Detention storage should not be confused
with retention storage (i.e., retention basins), a facility with no
engineered outlet (other than an emergency-type outlet) designed to
hold runoff for a considerable length of time. The water in a retention
basin is not discharged to surface water, although it may infiltrate
into the ground, evaporate, or be consumed by plants.
B.
In keeping with common law natural flow rights and the Michigan Drain
Code,[1] concentrated discharges of stormwater (such as the outflow
from a detention facility) or increased surface water runoff over
property owned by others must be pursuant to a valid right-of-way,
easement, or other written permission from all property owners affected.
The outflow from a detention facility is considered to be such a concentrated
discharge of stormwater.
[1]
Editor's Note: See MCL § 280.1 et seq.
C.
All forms of detention storage shall meet the following criteria:
(1)
On-site detention (or retention, see § 256-60, Retention basins, below) of stormwater is required of all new developments or redevelopments to maintain the peak outflow to a rate similar to the predevelopment runoff rate or to a discharge rate approved by the City Engineer. In no case shall the outflow from a site exceed the capacity of the receiving watercourse to accept the flow. In the case where the alternative of extended detention is approved, the channel protection volume shall be held for 48 hours or released at the one-year/twenty-four-hour discharge rate.
(2)
For development sites greater than five acres, the detention basin
volume shall be determined for the 100-year flood volume from all
tributary area, including off-site area.
(a)
The tributary area shall include all acreage contributing runoff
to the detention storage facility, including any off-site tributary
area in its existing state, whether developed or undeveloped.
(b)
The following equations shall be used to determine the 100-year
detention volume:
|
Qa = Allowable release rate, cfs
|
|
Qo = Qa/(A C)
|
|
Where:
| ||
|
A
|
=
|
Tributary area in acres
|
|
C
|
=
|
Weighted runoff coefficient
|
|
Detention time in minutes, T = -25 + sqrt (10,312.5/Qo)
| ||
|
Storage volume per impervious acre, Vs = 16,500 T/(T + 25) — 40 Qo T
| ||
|
Required detention volume in cubic feet, V = Vs x A x C
| ||
(3)
For development sites five acres and less, the detention basin volume
shall be determined for the ten-year flood volume from all tributary
area, including off-site area.
(a)
The tributary area shall include all acreage contributing runoff
to the detention storage facility, including any off-site tributary
area in its existing state, whether developed or undeveloped.
(b)
The following equations shall be used to determine the ten-year
detention volume:
|
Qa = Allowable release rate, cfs
|
|
Qo = Qa/(A C)
|
|
Where:
| ||
|
A
|
=
|
Tributary area in acres
|
|
C
|
=
|
Weighted runoff coefficient
|
|
Detention time in minutes, T = -25 + sqrt (6,562.5/Qo)
| ||
|
Storage volume per impervious acre, Vs = 10,500T/(T+25) - 40 Qo T
| ||
|
Required detention volume in cubic feet, Vs x A x C
| ||
(4)
If the site is located near the downstream end of a watercourse or drainage district, the City Engineer may require that the proprietor's engineer generate and submit hydrographs of the outflow from the existing site and from the proposed site (i.e., detention facility) and a hydrograph of the flow in the receiving watercourse to verify that the detained outflow would not result in an increase in the peak flow in the receiving watercourse. If the detained outflow would result in an increase in the peak flow in the receiving watercourse, then stormwater detention is not an acceptable stormwater management option. Retention of stormwater or other stormwater management design approved by the City Engineer must be provided. See § 256-60, Retention basins, for design requirements.
(5)
Portions of the developing site may be allowed to drain unrestricted
(i.e., not through a detention facility) if either of the following
conditions are met:
(a)
The areas draining unrestricted are not being disturbed or altered
by the construction, such that they will maintain their existing drainage
characteristics and patterns.
(b)
The areas draining unrestricted are being disturbed or altered
but will be permanently stabilized to prevent erosion and will not
contain any impervious surface postconstruction. In this case, the
unrestricted flow must be draining to a receiving watercourse with
valid rights-of-way, or else written agreement from the affected property
owners would have to be obtained per common law natural flow rights
and the Michigan Drain Code.[2] In addition, the postconstruction peak 100-year flow from
these areas should be calculated and deducted from the total allowable
peak flow from the detention facility (Qa).
The detention outlet(s) should be designed to restrict the basin outflow(s)
to this reduced allowable peak flow rate.
[2]
Editor's Note: See MCL § 280.1 et seq.
(6)
Where the detention facility is to be equipped with a pump discharge,
the proprietor shall be required to furnish design data on pump(s)
and discharge force main so that the capacity of the system can be
verified. These data will include system curve calculations, the pump
performance curves, and a profile of the system piping. The pumping
station should be able to release the first flush volume over approximately
24 hours, the bankfull flood volume over 24 to 48 hours, and the 100-year
flood volume at a rate not to exceed 0.15 cfs/ac of tributary area.
A backup generator will be required to ensure the operation of the
pumping station in the event of power loss. The City discourages the
use of pumped outlets and will not accept responsibility for damages
due to power failure, pump malfunction, or acts of God that result
in storm conditions that exceed the design conditions of the pump
station.
(7)
An agreement for acceptance and maintenance of the detention facility,
if executed by the proprietor, shall be submitted to the City of Roseville
prior to final approval. The agreement both as form and content shall
be subject to the approval of the City.
D.
Detention basins. A detention basin is a form of detention storage where the stormwater is detained aboveground as surface water. In addition to the general requirements indicated above in § 256-58, detention basins shall meet the following requirements:
(1)
Detention volume in a gravity-outlet detention basin must be located:
(a)
Above the invert of the lowest row of orifices in the outlet
standpipe;
(b)
Above the elevation of the dry weather base flow in the receiving
watercourse;
(c)
Above the elevation of the groundwater table. Soil boring data
used to determine the groundwater table elevation shall be submitted
with the plans.
(2)
The detention basin outlet shall consist of a vertical standpipe
with multilevel orifices to control the release of stormwater from
the basin, including the first flush volume, bankfull flood volume,
and 100-year flood volume (or ten-year flood volume for sites less
than five acres).
(a)
The standpipe shall not be less than 36 inches in diameter.
(b)
The standpipe shall contain multiple rows of orifices (i.e.,
holes) to control the release of the first flush runoff volume, the
bankfull flood volume, and the 100-year flood volume (or ten-year
for sites less than five acres).
[1]
First flush orifices shall be located at the elevation of the
basin floor (or permanent pool water level, if a wet basin).
[2]
Additional bankfull flood orifices shall be at the elevation
of the first flush volume in the basin, where the first flush volume
is calculated as the first one-inch of runoff over the site, or Vff
(cf) = 3630 x A(acres) x C, where C is the runoff coefficient.
[3]
Additional 100-year (or ten-year for sites less than five acres)
flood control orifices shall be located at the elevation of the bankfull
flood volume in the basin, where the bankfull flood volume is calculated
as the rainfall from a 1.5-year storm, or Vbf (cf) = 8170 x A (acres)
x C.
(3)
To promote improved filtering of runoff sediment from smaller, more
frequent storm events, the bankfull flood and first flush volumes
shall be based on the developing tributary site area only, and not
include off-site tributary area.
(a)
Orifices should not be less than one-inch in diameter or greater
than four inches in diameter.
(b)
The top of the standpipe shall consist of a grating at or above
the design (high) water level to serve as an overflow mechanism, in
addition to the overflow spillway/berm.
(c)
The standpipe shall be encased in stone extending to the design
(high) water level to allow for filtering of the stormwater prior
to discharge from the basin. The encasement stone size shall be large
enough so as not to plug or pass through the orifices in the standpipe.
(d)
The standpipe shall contain a sediment sump with a depth of
at least one foot.
(e)
Double standpipes (e.g., a thirty-six-inch-diameter inner standpipe
within a forty-eight-inch-diameter outer standpipe) are encouraged.
Double standpipes are believed to be less prone to blockages of the
control orifices, and therefore require less maintenance. The inner
standpipe should contain the appropriate number and configuration
of orifices to provide the controlled release of the first flush volume,
the bankfull flood volume, and the 100-year (or ten-year for sites
less than five acres) flood volume. The outer standpipe should contain
at least several times the orifice area as the inner standpipe over
the entire height of the standpipe, such that the head loss across
the outer standpipe orifices is negligible.
(f)
The outlet pipe extending from the standpipe to the receiving
watercourse shall be sized to convey the calculated 100-year (or ten-year
for sites less than five acres) peak inflow to the detention basin.
(g)
The location of the outlet pipe extending downstream of the
standpipe shall be indicated on a profile drawing of the receiving
watercourse, whether or not the receiving watercourse is an established
drain. The receiving watercourse profile shall extend at least from
the upstream end of the site to the downstream end of the site.
(4)
A sediment sump shall be provided within the basin, below the lowest
orifice elevation but above the groundwater table, to provide for
sediment accumulation.
(5)
All detention basins must have standpipe overflow grates and spillway
berms for emergency overflow at the high water level.
(a)
The standpipe overflow grate and spillway must provide adequate
capacity to overflow the peak 100-year (or ten-year for sites less
than five acres) basin inflow with no more than one-foot of head (i.e.,
water level must not exceed the one-foot of freeboard).
(b)
Downstream of the overflow spillway, the stormwater overflow
must be directed (either by overland flow or via a swale or ditch)
to the receiving watercourse.
(6)
A minimum of one foot freeboard shall be provided above the design
high water elevation.
(7)
The side slopes shall not be steeper than six feet horizontal to
one-foot vertical. Slope protection shall be provided as necessary.
Basin side slope elevation contours shall be shown on the plans.
(8)
Unless the detention basin contains a permanent pool, the bottom
of all detention basins shall be graded in such a manner as to provide
positive flow to the outlet. A minimum bottom slope of 1% shall be
provided.
(9)
A twelve-foot-wide minimum access easement shall be provided for
all detention basins, as measured from the top of bank.
(10)
A twenty-five-foot-wide minimum setback from property lines
shall be provided for all detention basins, as measured from the top-of-bank.
(11)
Detention basin configurations where stormwater must back up
into the basin (i.e., stormwater enters the conveyance system downstream
of the basin) will not be permitted.
(12)
Multiple detention basins serving a single development should
function independently. If the outflow from one basin passes through
another basin before being discharged to the receiving watercourse,
a full hydraulic analysis (i.e., a computer model simulation) will
be required to ensure that the system functions satisfactorily.
(13)
If at any time the detention basin is to function as a sediment
basin (for use during the construction phase), an outlet filter shall
be provided. Such an outlet filter is to be designed in accordance
with criteria established by the Macomb County Public Works office.
Such use of a detention pond shall be considered a temporary measure
only. The proprietor shall be responsible for sediment removal upon
completion of construction.
(14)
Detention basins shall meet all local ordinances and/or requirements
for "ponds."
E.
Underground storage. Underground storage is a form of detention storage where the stormwater is detained in underground pipes. Like a detention basin, the water is released at a controlled rate to a receiving watercourse. In addition to the general requirements indicated above in § 256-59, underground detention facilities shall meet the following requirements:
(1)
Detention volume in an underground detention facility shall be located
above the elevation of the dry weather baseflow in the receiving watercourse
and above the elevation of the groundwater table. Soil boring data
used to determine the groundwater table shall be submitted with the
plans.
(2)
To minimize sedimentation in the downstream drainage district, sediment
shall be removed from the stormwater before water enters the underground
storage facility (e.g., in first flush forebay or within the catch
basins using removable filtration inserts).
(3)
The pipe material used for the underground storage facility shall
have an expected life of at least 50 years.
(4)
Access manholes shall be provided along the underground storage facility
to allow for maintenance.
(5)
A minimum of one foot of freeboard shall be provided between the
design hydraulic grade line in the underground storage facility and
the rim elevations of all access manholes.
(6)
A twenty-five-foot-wide setback from property lines shall be provided
for all underground storage facilities.
(7)
An access easement shall be provided to and above the underground
storage facility.
(8)
No permanent structures shall be constructed above the underground
storage facility.
F.
Parking lot surface storage is a form of detention storage where the stormwater is detained in the parking lot surface creating temporary flooding of the parking lot. Like a detention basin, the water is released at a controlled rate to a receiving drain. In addition to the general requirements indicated above in § 256-59, parking lot surface storage shall meet the following requirements:
A "retention basin" is a facility with no engineered outlet
(other than an emergency-type outlet) designed to hold runoff for
a considerable length of time. The water in a retention basin is not
discharged to a natural watercourse, although it may be consumed by
plants, evaporate, or infiltrate into the ground. A retention basin
should not be confused with a "detention basin," a facility designed
to detain runoff for a short period of time and then release it to
a watercourse.
A.
On-site retention (or detention; see § 256-59, Detention storage facilities) is required of all new developments or redevelopments to prevent an increase in peak flows downstream in the drainage district.
(1)
Retention basins are an acceptable stormwater management practice
on sites where the soil has an infiltration rate of at least 0.52
inch per hour and a clay content of less than 30% (per recommendations
in Guidebook of Best Management Practices for Michigan Watersheds).
The required storage volume of a retention basin is that of the runoff
from a 100-year design storm as determined using the SCS Method. On
sites with soils having a lower infiltration rate and/or higher clay
content, the City Engineer may allow retention basins with storage
volume for the runoff from two consecutive 100-year design storms.
(2)
Retention basins shall accommodate runoff from off-site areas that
drain onto/across the developing site. An exception to this rule would
be if off-site runoff were to be routed around the site to a receiving
watercourse, if done in a manner such that runoff from the developing
site would not contribute to this off-site flow. If the off-site flow
were to be concentrated from overland flow to a point discharge into
a receiving watercourse without valid rights-of-way, written agreement
from the affected property owners would have to be obtained per common
law natural flow rights and the Michigan Drain Code.[1]
[1]
Editor's Note: See MCL § 280.1 et seq.
B.
One foot of freeboard shall be provided above the design high water
elevation.
C.
Retention volume must be provided above the elevation of the groundwater
table. Soil boring data used to determine the groundwater table elevation
shall be submitted with the plans.
D.
All retention basins must have a spillway for emergency overflow
at the high water level.
(1)
The spillway must provide adequate capacity to overflow the peak
100-year basin inflow with no more than two feet of head (i.e., water
level must not exceed the two feet of freeboard).
(2)
The plans must identify where the overflow would be directed to flow
or stored in the event of an overflow.
E.
The side slopes shall not be steeper than six feet horizontal to
one foot vertical unless fenced in accordance with City requirements.
Slope protection shall be provided as necessary. Basin side slope
elevation contours shall be shown on the plans.
F.
A twelve-foot-wide access easement shall be provided to and around
all retention basins.
G.
An agreement for acceptance and maintenance of the retention basin
system, if executed by the proprietor, shall be submitted to the City
of Roseville prior to final approval. The agreement both as form and
content shall be subject to the approval of the City.
H.
If at any time during the construction period the retention basin
is to function as a sediment basin, the proprietor shall be responsible
for sediment removal prior to completion of construction. (See Macomb
County Public Works Office for requirements regarding soil erosion
and sedimentation control during construction.)
A.
In order to help in analyzing site hydrology and the predevelopment
runoff rate, soil types, the normal groundwater table, and an accurate
delineation of wetlands must be provided as part of preliminary plats/plans.
The City Engineer may require confirmation of the absence or presence
of regulated wetlands from EGLE through its wetland assessment program.
Construction activities to be performed within a regulated wetland
may require a permit from the EGLE.
B.
Any regulated wetlands or other wetlands that will be part of the
drainage system shall be designated as a common area and placed within
a conservation easement.
D.
If any disturbed or impervious surfaces will drain into an existing
wetland or low-lying area, calculations may be required to be submitted
indicating that the wetland will accommodate runoff from a 100-year
design storm without exceeding the finished grade elevation of any
adjacent existing or proposed structure.
E.
If a wetland will be used for stormwater storage, a sediment forebay
shall be provided upstream of the wetlands to reduce the stormwater
velocity and encourage sedimentation. Additionally, a permit from
the EGLE may be required.
Oil must be removed from stormwater as appropriate prior to
discharge to a receiving watercourse. The City Engineer will consider
means of oil removal on a case-by-case basis.
When standalone BMPs such as permanent first flush basins and
prefabricated sediment collection units are proposed or required for
a specific site, the following design standards shall apply:
A.
A settling pond (first flush pond) is a means to detain the first
flush volume so that a minimum of 80% of the TSS settle to the bottom
of the pond.
B.
A settling pond may be standalone or adjacent to a detention pond
as a settling forebay.
C.
The bankfull volume is calculated as the rainfall from a 1.5-year
storm while the first flush volume is calculated as the first one
inch of runoff from the on-site impervious tributary area, or
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Vff (cf) = A x C x 3630 cf/ac-impervious
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D.
The outlet of a first flush basin or sediment collection unit shall
be designed to release the first flush volume over 24 to 36 hours.
E.
The outlet of a first flush basin or sediment collection unit shall
not be submerged by the receiving watercourse at a ten-year design
level.
F.
The first flush basin or sediment collection unit shall contain a
bypass structure and/or berm to allow the ten-year peak flow to bypass
without hydraulic interference.
A.
Discharge prohibitions.
(1)
Prohibition of illegal discharges.
(a)
No person shall discharge or cause to be discharged into the
municipal separate storm sewer system (MS4) or watercourses any materials,
including but not limited to pollutants or waters containing any pollutants,
that cause or contribute to a violation of applicable water quality
standards, other than stormwater.
(b)
The commencement, conduct or continuance of any illegal discharge to the storm drain system is prohibited except as described as provided in § 256-64A(2).
(2)
The following discharges if identified as not being a significant
contributor to violations of water quality standards (WQS) are excluded
from discharge prohibitions established by this article:
(a)
Waterline flushing and discharges from potable water sources.
(b)
Landscape irrigation runoff, lawn watering runoff, and irrigation
waters.
(c)
Diverted stream flows and flows from riparian habitats and wetlands.
(d)
Rising groundwaters and springs.
(e)
Uncontaminated groundwater infiltration and seepage.
(f)
Uncontaminated pumped groundwater, except for groundwater cleanups
specifically authorized by NPDES permits.
(g)
Foundation drains, water from crawl space pumps, footing drains,
and basement sump pumps.
(h)
Air-conditioning condensation.
(i)
Waters from noncommercial car washing.
(j)
Street wash water.
(k)
Dechlorinated swimming pool water from single-, two-, or three-family
residences. (A swimming pool operated by the permittee shall not be
discharged to a separate storm sewer or to surface waters of the state
without NPDES permit authorization from the EGLE).
(l)
Discharges or flows from firefighting activities if identified
as not being significant sources of pollutants to waters of the state.
(m)
Discharges specified in writing by the authorized enforcement
agency as being necessary to protect public health and safety.
(n)
Dye testing is an allowable discharge, but requires a "Notice
of Intent to Treat" under the General Rule 97 Certification of Approval
to be obtained from EGLE prior to the commencement of the test.
(o)
The prohibition shall not apply to any nonstormwater discharge
permitted under an NPDES permit, waiver, or waste discharge order
issued to the discharger and administered under the authority of the
Federal Environmental Protection Agency, provided that the discharger
is in full compliance with all requirements of the permit, waiver,
or order and other applicable laws and regulations, and provided that
written approval has been granted for any discharge to the storm drain
system.
B.
Prohibition of illicit connections.
(1)
The construction, use, maintenance or continued existence of illicit
connections to the storm drain system is prohibited.
(2)
This prohibition expressly includes, without limitation, illicit
connections made in the past, regardless of whether the connection
was permissible under law or practices applicable or prevailing at
the time of connection.
(3)
A person is considered to be in violation of this article if the
person connects a line conveying sewage to the MS4, or allows such
a connection to continue.
Monitoring of discharges.
A.
Applicability.
(1)
This section applies to all facilities that have stormwater discharges,
facilities associated with industrial activity, and those having construction
activity.
B.
Access to facilities.
(1)
The City of Roseville shall be permitted to enter and inspect facilities
subject to regulation under this article as often as may be necessary
to determine compliance with this article. If a discharger has security
measures in force which require proper identification and clearance
before entry into its premises, the discharger shall make the necessary
arrangements to allow access to representatives of the City.
(2)
Facility operators shall allow the City ready access to all parts
of the premises for the purposes of inspection, sampling, examination
and copying of records that must be kept under the conditions of an
NPDES permit to discharge stormwater, and the performance of any additional
duties as defined by state and federal law.
(3)
The City shall have the right to set up on any permitted facility
such devices as are necessary and/or required by the MS4 permit to
conduct monitoring and/or sampling of the facility's stormwater discharge.
(4)
The City has the right to require the discharger to install monitoring
equipment as necessary. The facility's sampling and monitoring equipment
shall be maintained at all times in a safe and proper operating condition
by the discharger at its own expense. All devices used to measure
stormwater flow and quality shall be calibrated to ensure their accuracy.
(5)
Any temporary or permanent obstruction to safe and easy access to
the facility to be inspected and/or sampled shall be promptly removed
by the operator at the written or oral request of the City and shall
not be replaced. The costs of clearing such access shall be borne
by the operator.
(6)
Unreasonable delays in allowing the City access to a permitted facility
is a violation of a stormwater discharge permit and of this article.
A person who is the operator of a facility with a NPDES permit to
discharge stormwater associated with industrial activity commits an
offense if the person denies the authorized enforcement agency reasonable
access to the permitted facility for the purpose of conducting any
activity authorized or required by this article.
(7)
If the City has been refused access to any part of the premises from
which stormwater is discharged, and he/she is able to demonstrate
probable cause to believe that there may be a violation of this article,
or that there is a need to inspect and/or sample as part of a routine
inspection and sampling program designed to verify compliance with
this article or any order issued hereunder, or to protect the overall
public health, safety, and welfare of the community, then the City
may seek issuance of a search warrant from any court of competent
jurisdiction.
A.
Notice of violation. Whenever the City of Roseville or other enforcing
agency finds that a person has violated a prohibition or failed to
meet a requirement of this article, the authorized enforcement agency
may order compliance by written notice of violation to the responsible
person. Such notice may require without limitation:
(1)
The performance of monitoring, analyses, and reporting;
(2)
The elimination of illicit connections or discharges;
(3)
That violating discharges, practices, or operations shall cease and
desist;
(4)
The abatement or remediation of stormwater pollution or contamination
hazards and the restoration of any affected property;
(5)
Payment of a fine to cover administrative and remediation costs;
and
(6)
The implementation of source control or treatment BMPs.
B.
If abatement of a violation and/or restoration of affected property
is required, the notice shall set forth a deadline within which such
remediation or restoration must be completed. Said notice shall further
advise that, should the violator fail to remediate or restore within
the established deadline, the work will be done by a designated governmental
agency or a contractor and the expense thereof shall be charged to
the violator.
