A.
No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of a BMP operations
and maintenance plan which describes how the permanent (e.g., post-construction)
stormwater BMPs will be properly operated and maintained.
B.
The following items shall be included in the BMP operations and maintenance
plan:
(1)
Map(s) of the project area, in a form that meets the requirements
for recording at the offices of the Recorder of Deeds of Montgomery
County, and shall be submitted on twenty-four-inch by thirty-six-inch
or thirty-inch by forty-two-inch sheets. The contents of the maps(s)
shall include, but not be limited to:
(a)
Clear identification of the location and nature of permanent
stormwater BMPs;
(b)
The location of the project site relative to highways, municipal
boundaries or other identifiable landmarks;
(c)
Existing and final contours at intervals of two feet, or others
as appropriate;
(d)
Existing streams, lakes, ponds, or other bodies of water within
the project site area;
(e)
Other physical features, including flood hazard boundaries,
sinkholes, streams, existing drainagecourses, and areas of natural
vegetation to be preserved;
(f)
The locations of all existing and proposed utilities, sanitary
sewers, and water lines within 50 feet of property lines of the project
site;
(g)
Proposed final changes to the land surface and vegetative cover,
including the type and amount of impervious area that would be added;
(h)
Proposed final structures, roads, paved areas, and buildings;
and
(i)
A fifteen-foot-wide access easement around all stormwater BMPs
that would provide ingress to and egress from a public right-of-way.
(2)
A description of how each permanent stormwater BMP will be operated
and maintained, and the identity of the person(s) responsible for
operations and maintenance;
(3)
The name of the project site, the name and address of the owner of
the property, and the name of the individual or firm preparing the
plan; and
(4)
A statement, signed by the landowner and/or responsible party, acknowledging
that the stormwater BMPs are fixtures that can be altered or removed
only after approval by the municipality.
C.
Additional stormwater detention/retention facilities design requirements.
(1)
The following setbacks are required for stormwater management facilities:
(a)
Stormwater retention or detention basins shall be located at
least 50 feet from any structure, whether existing or proposed.
(b)
Whenever possible, stormwater retention or detention basins
shall be located at least 50 feet from any property boundary or right-of-way.
(c)
Recharge systems greater than three feet deep shall be located
at least 15 feet from any basement wall and 25 feet from wastewater
treatment areas.
(d)
Any recharge system designed to handle runoff from any commercial
or industrial impervious parking or outside storage area shall be
a minimum of 50 feet from any water supply well or any wastewater
treatment area.
(2)
Riser. A riser or other acceptable outfall shall be provided at the
outlet of all detention basins. The riser shall be constructed of
precast or poured-in-place concrete with controlled orifices. The
riser shall extend to an elevation one foot below the crest elevation
of the emergency spillway. The riser shall be designed so that the
rate of outflow is controlled by the pipe barrel through the basin
berm when the depth of water within the basin exceeds the height of
the riser. A trash rack or similar appurtenance shall be provided
to prevent debris from entering the riser. All risers shall have a
concrete base attached with a watertight connection. The base shall
be of sufficient weight to prevent flotation of the riser.
(3)
Landscaping. All stormwater control systems, whether existing or
proposed, shall be planted to effectively naturalize areas so as to
become an integral and harmonious element in the local landscape.
No trees shall be planted in dams more than 15 feet high.
(4)
Emergency spillway. Whenever possible, the emergency spillway for
detention basins shall be constructed on undisturbed ground. Emergency
spillways shall be designed according to the Soil Conservation Service
Engineering Field Manual. All emergency spillways shall be constructed
so that the detention basin berm is protected against erosion. The
minimum capacity of all emergency spillways shall be such that, should
the principal spillway become clogged or ineffective, the emergency
spillway can safely convey the one-hundred-year storm event with one
foot of available freeboard. The emergency spillway shall not discharge
over earthen fill and/or easily erodible material.
(5)
Anti-seep collars. Where appropriate, anti-seep collars shall be
installed around the principal pipe barrel within the normal saturation
zone of the detention basin berms. The anti-seep collars and their
connections to the pipe barrel shall be watertight. The anti-seep
collars shall extend a minimum of two feet beyond the outside of the
principal pipe barrel. The maximum spacing between collars shall be
14 times the minimum projection of the collar measured perpendicular
to the pipe.
(6)
Freeboard. Freeboard is the difference between the design flow elevations
in the emergency spillway and the top of the settled detention basin
embankment. The minimum freeboard shall be one foot.
(7)
Slope of detention basin embankment. The maximum slope of earthen
detention basin embankments shall meet the requirements contained
in this subsection. Whenever possible, the side slopes and basin shape
shall be amenable to the natural topography. Straight side slopes
and rectangular basins shall be avoided whenever possible.
(8)
Width of berm. The minimum top width of detention basin berms shall
be 10 feet.
(9)
Slope of basin bottom. In order to ensure proper drainage of the
detention basin, a minimum grade of 2% shall be maintained for all
sheet flow. A minimum grade of 1% shall be maintained for all channel
flow.
(10)
Energy dissipaters. Energy-dissipating devices (riprap, end
sills, etc.) shall be placed at all basin outlets. Any pipe or other
component which discharges directly into the basin shall be equipped
with energy-dissipating devices and shall outlet into the bottom of
the basin.
(11)
Landscaping and grading of detention basin. All landscaping
and grading standards shall be as follows:
(a)
Cuts. No excavation shall be made with a cut face steeper than
two horizontal to one vertical, except under the condition that the
material in which the excavation is made is sufficiently stable to
sustain a slope of steeper than two horizontal to one vertical. A
written statement to that effect is required from an engineer and
must be submitted and approved by the Municipal Engineer. The statement
shall affirm that the site has been inspected and that the deviation
from the slope should not result in injury to persons or damage to
property. Retaining walls shall be required if a stable slope cannot
be maintained. Any retaining wall design must be approved by the Municipal
Engineer. The toe of the slope or headwall of any cut must be located
a minimum of five feet from property lines.
(b)
Fills. No fill shall be made which creates any exposed surfaces
steeper in slope than two horizontal to one vertical, except where
the fill is located so that settlement, sliding, or erosion will not
result in property damage or be a hazard to adjoining property, streets,
or buildings. A written statement is required from an engineer certifying
that s/he has inspected the site and that any proposed deviation from
the slope specified above should not endanger any property or result
in property damage, and must be submitted to and approved by the Municipal
Engineer.
[1]
A concrete or stone masonry wall designed and constructed in
accordance with these specifications and standards may be required
to support the face of the fill where the above-specified slopes are
exceeded.
[2]
The top of any fill or toe of the slope of any fill shall be
located 25 feet from any property line, with the exception of a downstream
property line, where the toe of the embankment shall be placed a sufficient
distance to allow for energy-dissipating devices, but in no case less
than 40 feet, unless approved otherwise by the municipality.
(c)
Planting requirements. All areas proposed for recreational use,
whether active or passive, shall be planted to effectively naturalize
the areas to become an integral and harmonious element in the natural
landscape.
(d)
Drainage channels and retention areas. All storm drainage channels
and retention areas, whether existing or proposed, shall be graded
and planted to effectively naturalize areas so as to become an integral
and harmonious part of the landscape by contour and type of plant
material employed.
(e)
Screening. A suitable vegetation screen shall be provided around
all detention basins as required by the Municipal Engineer. All vegetative
screening shall be at least 3 1/2 feet in height and shall be
composed of the following shrubs: barberry (barberis species), eleagnus
(eleagnus species), (pyracantha species), rose (rose species), or
alternates as approved by the Municipal Engineer.
(f)
Easements for all basins and storm pipes not located with the
public street right-of-way shall be provided.
D.
Stormwater drainage system design requirements.
(1)
Design flow rate. The storm drain system shall be designed to carry
a twenty-five-year peak flow rate. The system must adequately convey
the one-hundred-year storm to detention facilities. The design twenty-five-year
peak flow rate into each inlet shall be indicated on the stormwater
management plan. The twenty-five-year flow rate shall be determined
by the rational formula, Q=CIA.
|
Where:
| ||||
|
Q
|
=
|
Peak runoff rate, in cubic feet per second (cfs).
| ||
|
C
|
=
|
Runoff coefficient equal to the ratio of the runoff rate to
the average rate of rainfall over a time period equal to the time
of concentration.
| ||
|
I
|
=
|
Average rainfall intensity in inches per hour for a time equivalent
to the time of concentration.
| ||
|
A
|
=
|
Drainage area in acres.
| ||
|
Approximate values for the runoff coefficient and runoff intensity
are found in the following sources:
|
|
Commonwealth of Pennsylvania
| |
|---|---|
|
Department of Transportation
| |
|
Design Manual, Part 2
| |
|
Chapter 12
|
(2)
Overflow system. An overflow system shall be provided to carry flow
to the detention basin when the capacity of the storm drain pipe system
is exceeded. The overflow system shall be of sufficient capacity to
carry the difference between the one-hundred-year and the twenty-five-year
peak flow rates.
(3)
Inlet capacity. All inlets must be designed to accommodate the twenty-five-year
peak flow rate. The capacity of each inlet shall be indicated on the
stormwater plan. The capacity of all C-, M-, or S-type inlets shall
be determined from the following source:
Commonwealth of Pennsylvania
Department of Transportation
Design Manual, Part 2
Highway Design
(4)
Straight pipe selections. Wherever possible, all storm drain pipes
shall be designed to follow straight courses. No angular deflections
of storm sewer pipe shall be permitted without the approval of the
Municipal Engineer. No vertical curves shall be permitted in the storm
drain pipe system.
(5)
Minimum grade and size. All storm drain pipes shall be designed to
maintain a minimum grade of 1/2%. All storm pipes shall have a minimum
inside diameter of 18 inches, except that pipes under a twenty-five-foot
or greater fill shall be designed in accordance with PennDOT DMII.
(6)
Pipe material and thickness. All storm sewers shall be a material
which meets the one-hundred-year life expectancy criteria contained
in PennDOT DMII, most recent edition.
(7)
Pipe capacity. The capacity of all pipe culverts shall, as a minimum,
provide the required carrying capacity as determined by the following
source:
United States Department of Commerce
Bureau of Public Roads
Hydraulic Engineering Circular No. 5
Hydraulic Charts for the Selection of Highway Culverts
(8)
Pipe arches. Where headroom is restricted, equivalent pipe arches
may be used in lieu of circular pipes.
(9)
Allowable headwater depth. At all inlets or manholes, the maximum
allowable headwater depth shall be one foot below the top of the inlet
grate of the manhole cover.
(10)
Horizontal pipe deflections. A manhole or inlet shall be provided
at all horizontal deflections in the storm pipe system.
(11)
Minimum and maximum cover. In a roadway or paved area, a minimum
of 18 inches of cover shall be maintained over all storm drain pipes.
The top of storm drain pipes shall be at least 1/2 foot below subgrade
elevation. The cover requirement can be reduced to 12 inches for other
areas as directed by the Municipal Engineer.
(12)
Diversion or runoff. All storm drain pipes shall be designed
to carry the runoff into a detention basin or similar facility utilized
to control the rate of runoff. No discharge at the top or side of
basin embankments shall be permitted.
(13)
Culverts and drainage channels.
(a)
Design flow standards. All culverts and drainage channels shall
be designed to carry a flow rate equal to a fifty-year storm event.
In certain circumstances, the carrying capacity of a channel can be
reduced upon approval of the Municipal Engineer.
(b)
Erosion prevention. All drainage channels shall be designed
to prevent the erosion of the bed and bank areas. The flow velocity
in all vegetated drainage channels shall not exceed three feet per
second to prevent erosion, unless special provisions are made to protect
banks and channel bottoms against erosion. Suitable bank stabilization
shall be provided where required to prevent erosion of the drainage
channels. Where storm sewers discharge into existing drainage channels
at an angle greater than 30° from parallel with the downstream
channel flow, the far side bank shall be properly stabilized. The
stabilization shall be designed to prevent erosion and frost heave
under and behind the stabilizing media.
(c)
Maximum side slope. Any vegetated drainage channel requiring
mowing of the vegetation shall have a maximum grade of three horizontal
to one vertical of those areas to be mowed.
(d)
Design standard. Because of the critical nature of the vegetated
drainage channels, the design of all vegetated channels shall, as
a minimum, conform to the design procedures outlined in the PADEP
manuals. Several acceptable sources outline procedures for nonvegetated
drainage channels, including the following:
Bureau of Public Roads
Hydraulic Engineering Circular No. 5
Hydraulic Charts for the Selection of Highway Culverts
Federal Highway Administration
Hydraulic Engineering Circular No. 13
Hydraulic Design of Improved Inlets for Culverts
(e)
Reference to publications and source documents in this section
shall be deemed to include any amendments and revisions thereof.
A.
The BMP operations and maintenance plan for the project site shall
establish responsibilities for the continuing operation and maintenance
of all permanent stormwater BMPs, as follows:
(1)
If a plan includes structures or lots which are to be separately
owned and in which streets, sewers and other public improvements are
to be dedicated to the municipality, stormwater BMPs may also be dedicated
to and maintained by the municipality.
(2)
If a plan includes operations and maintenance by a single ownership,
or if sewers and other public improvements are to be privately owned
and maintained, then the operation and maintenance of stormwater BMPs
shall be the responsibility of the owner or private management entity.
B.
The municipality shall make the final determination on the continuing
operations and maintenance responsibilities. The municipality reserves
the right to accept or reject the operations and maintenance responsibility
for any or all of the stormwater BMPs.
C.
Specific infiltration system design criteria.
(1)
Infiltration devices shall be selected based on suitability of soils
and site conditions. Measures may include porous pavement with underground
infiltration bed, vegetated infiltration beds, swales, and trenches
or other seepage structures similar to these proposed in the Pennsylvania
Handbook of Best Management Practices for Developing Areas (1998)
and related references or other guidance documents.
(2)
Soil infiltration tests shall be performed for all proposed infiltration
areas; these tests shall include evaluation of selected soil horizons
by deep pits and percolation measurements. Testing shall be reviewed
and approved by the Municipal Engineer. The soil infiltration rate
of discharge from the infiltration area being used in the proposed
design shall be based on these measurements.
(3)
Where possible, the lower elevation of the infiltration area shall
be at least two feet above the seasonal high-water table (SHWT) and
bedrock.
(4)
All infiltration systems shall have appropriate positive overflow
controls to prevent storage within one foot of the finished surface
or grade.
(5)
All infiltration systems shall have a minimum setback of 15 feet
from all residential structures. Care should be taken to prevent any
seepage into subgrade structures.
(6)
All surface inflows shall be treated to prevent the direct discharge
of sediment into the infiltration system; accumulated sediment reduces
stormwater storage capacity and ultimately clogs the infiltration
mechanism. No sand or other particular matter may be applied to a
previous surface for winter ice conditions.
A.
The municipality shall review the BMP operations and maintenance
plan for consistency with the purposes and requirements of this Part
and any permits issued by the DEP.
B.
The municipality shall notify the applicant in writing whether the
BMP operations and maintenance plan is approved.
C.
The municipality may require an as-built survey of all stormwater
BMPs and an explanation of any discrepancies with the operations and
maintenance plan.
It shall be unlawful to alter or remove any permanent stormwater
BMP required by an approved BMP operations and maintenance plan, or
to allow the property to remain in a condition which does not conform
to an approved BMP operations and maintenance plan, unless an exception
is granted in writing by the municipality.
A.
The property owner shall sign an operations and maintenance agreement
with the municipality covering all stormwater BMPs that are to be
privately owned. The agreement shall be substantially the same as
the agreement in Appendix B of this Part.[1]
[1]
Editor's Note: Appendix B is included as an attachment to this chapter.
B.
Other items may be included in the agreement where determined necessary
to guarantee the satisfactory operation and maintenance of all permanent
stormwater BMPs. The agreement shall be subject to the review and
approval of the municipality.
A.
Stormwater management easements are required for all areas used for
off-site stormwater control, unless a waiver is granted by the Board
of Commissioners of the municipality.
B.
Stormwater management easements shall be provided by the property owner if necessary for: (1) access for inspections and maintenance; or (2) preservation of stormwater runoff conveyance, infiltration, and detention areas and other BMPs, by persons other than the property owner. The purpose of the easement shall be specified in any agreement under § 203-19.
A.
The owner of any land upon which permanent BMPs will be placed, constructed
or implemented, as described in the BMP operations and maintenance
plan, shall record the following documents in the office of the Recorder
of Deeds for Montgomery County, within 15 days of approval of the
BMP operations plan by the municipality:
B.
The municipality may suspend or revoke any approvals granted for
the project site upon discovery of the failure of the owner to comply
with this section.
A.
If stormwater BMPs are accepted by the municipality for dedication,
the municipality may require persons installing stormwater BMPs to
pay a specified amount to the Municipal Stormwater BMP Operation and
Maintenance Fund to help defray costs of operations and maintenance
activities. The amount may be determined as follows:
B.
If a BMP is proposed that also serves as a recreation facility (e.g.,
ballfield, lake), the municipality may adjust the amount due accordingly.
