A.
Applicants may select runoff control techniques, or a combination
of techniques, which are most suitable to control stormwater runoff
from the development site. All controls shall be subject to approval
of the Township Engineer. The Township Engineer may request specific
information on design and/or operating features of the proposed stormwater
controls in order to determine their suitability and adequacy in terms
of the standards of this chapter.
B.
The applicant should consider the effect of the proposed stormwater
management techniques on any special soil conditions or geological
hazards which may exist on the development site. In the event such
conditions are identified on the site, the Township Engineer, at his
sole and absolute discretion, may require in-depth studies by a competent
geotechnical engineer approved by the Township Engineer. Not all stormwater
control methods may be allowable at a particular development site.
C.
In developing a stormwater management plan for a particular site,
stormwater controls shall be selected according to the following order
of preference:
D.
Infiltration practices shall be used to the extent practicable to
reduce volume increases and promote groundwater recharge. A combination
of successive practices may be used to achieve the applicable minimum
control requirements. The applicant shall provide justification for
rejecting each of the preferred practices based on actual site conditions.
A.
Infiltration systems shall be sized and designed based upon local
soil and ground water conditions.
B.
Infiltration systems greater than three feet deep shall be located
at least 10 feet from basement walls.
C.
Infiltration systems may not receive runoff until the entire drainage
area to the system has received final stabilization.
D.
The stormwater infiltration facility design shall provide an overflow
system with measures to provide a nonerosive velocity of flow along
its length and at the outfall.
E.
All stormwater infiltration systems shall provide a volume of at
least one cubic foot of every two square feet of impervious surface,
and any stormwater infiltration system shall be located to capture
runoff from all impervious surfaces.
[Amended 11-15-2022 by Ord. No. 2022-03]
F.
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase, so as to maintain their
maximum infiltration capacity.
A.
If flow attenuation facilities are employed to assist in the control
of peak rates of discharge, their effects must be quantified using
the NRCS Technical Release (TR) 55 Urban Hydrology for Small Watersheds
or other approved method approved by the Township Engineer. The effects
of the flow attenuation facilities on travel time should be reflected
in the calculations.
B.
Flow attenuation facilities such as swales and natural depressions
should be properly graded to ensure positive drainage and avoid prolonged
ponding of water.
C.
Swales shall be properly vegetatively stabilized or otherwise lined
to prevent erosion.
D.
Swales shall be designed according to the recommendations contained
in the Erosion and Sediment Pollution Control Program Manual (E&S
Manual)2, No. 363-2134-008 (April 15, 2000),
as amended and updated.
A.
If detention/retention facilities are utilized for the development
site, the facilities shall be designed such that postdevelopment peak
runoff rates from the developed site are controlled to those rates
defined by this chapter.
B.
All detention facilities shall be equipped with outlet structures
to provide discharge control for the designated storm frequencies.
Provisions shall also be made to safely pass the postdevelopment one-hundred-year
storm runoff with a minimum of one foot of freeboard without damaging
or impairing the continued function of the facilities. Should any
stormwater management facilities be regulated by Pennsylvania DEP
Chapter 105 regulations, the facility shall be designed in accordance
with those regulations and meet the Pennsylvania DEP regulations concerning
dam safety which may require the passage of storms larger than the
one-hundred-year event.
C.
Shared-storage facilities which provide detention of runoff for more
than one development site within a single subarea are encouraged wherever
feasible and provided such facilities meet the criteria contained
in this chapter. In addition, runoff from the development sites involved
shall be conveyed to the facility in a manner that avoids adverse
impacts (such as flooding or erosion) to channels and properties located
between the development site and the shared-storage facilities.
D.
Where detention facilities will be utilized, multiple use facilities,
such as wetlands, lakes, ball fields or similar recreational/open
space uses are encouraged wherever feasible, subject to the approval
of the Township and compliance with the Pennsylvania DEP's Chapter
105 regulations.
E.
Construction of the detention/retention facilities shall conform
to the construction specifications of the PennDOT, Publication 408,
latest edition, and RC Standards for Roadway Construction, latest
edition.
F.
Design of the detention/retention facilities shall be in accordance
with the standard details included in Appendix B[1] and include the following:
(1)
Inflow and outflow structures shall be designed and installed to
prevent erosion to the side slopes and bottom of the structures shall
be protected from soil erosion.
(2)
Control and removal of debris both in the storage structure and in
all inlet or outlet devices shall be a design consideration.
(3)
Inflow and outflow structures, pumping stations, and other structures
shall be designed and protected to minimize safety hazards.
(4)
The water depth at the perimeter of a storage pond should be limited
to that which is safe for children. Current ordinances call for restriction
of access by way of fencing is required. Further restriction of access
(walls, for example) may be necessary depending on the location of
the facility and the maximum depths of water.
(5)
Side slope of storage ponds shall not exceed a ratio of 2.5:1 horizontal
to vertical dimension.
(6)
Landscaping shall be provided for the facility which harmonizes with
the surrounding area.
(7)
Facilities shall be located to facilitate maintenance, considering
the frequency and type of equipment that will be required. All detention
ponds shall be provided with a suitable access road to be approved
by the Township.
(8)
Bottoms of detention basins should be graded with sufficient slope
to provide positive surface drainage. A subdrainage system may be
required depending on the location of the pond bottom relative to
groundwater levels.
(9)
The perimeter of all stormwater detention/retention basins shall
be completely fenced with a fence having a minimum height of six feet.
Said fence shall be constructed of chain link or similar material
as may be approved by the Township. A double gate having a minimum
width of 12 feet shall be installed to provide access to the stormwater
detention/retention basin. The developer shall furnish a gate lock.
To facilitate maintenance and inspection, all stormwater detention/retention
basins shall be provided with a stabilized access roadway of a type
subject to approval of the Township Engineer and having a minimum
width of 12 feet. The access roadway shall be placed with an easement
not less than 20 feet wide, as approved by the Township Engineer,
who may require additional width of easement as circumstances warrant.
The fence shall be constructed in accordance with PennDOT, Publication
408 Sections 624 and 1110, latest edition, and the standard detail
contained in Appendix B.[2]
[2]
Editor's Note: Said appendix is on file and available for
review in Township offices.
[1]
Editor's Note: Said appendix is on file and available for
review in Township offices.
A.
All stormwater runoff collection or conveyance facilities, whether
storm sewers or other open or closed channels, shall be designed in
accordance with the following criteria:
(1)
Lots shall be laid out and graded to provide positive drainage away
from and around structures. The Township may require a grading and
drainage plan for individual lots indicating the buildable area within
each lot, complying with the setback requirements, for which positive
drainage is assured.
(2)
Springs, surface sump pump discharges and French drains shall extend
to a stormwater collection/conveyance/control system or natural watercourse
in accordance with the approved stormwater management plan for the
development site. The outlets for these facilities shall be equipped
with energy dissipation devices to prevent erosion.
(3)
Collection/conveyance facilities should not be installed parallel
and close to the top or bottom of a major embankment to avoid the
possibility of failing or causing the embankment to fail.
(4)
All collection/conveyance facilities shall be designed to convey
the twenty-five-year storm peak flow rate from the contributing drainage
area and to carry it to the nearest suitable outlet such as a stormwater
control facility, curbed street, storm sewer or natural watercourse
without damage to the drainage structure or roadway, with runoff from
the twenty-five-year design storm at a minimum 1.0 foot of freeboard
measured below the lowest point along the top of the roadway. Roadway
crossings located within designated floodplain areas must be able
to convey runoff from a one-hundred-year design storm with a minimum
of 1.0 foot freeboard measured below the lowest point along the top
of the roadway. When it can be shown that, due to topographic conditions,
natural drainageways on the site cannot adequately provide for drainage,
open channels may be constructed conforming substantially to the line
and grade of such natural drainageways. Work within natural drainageways
shall be subject to approval by Pennsylvania DEP through the joint
permit application process, or, where appropriate by Pennsylvania
DEP, through the general permit process.
(5)
Where drainage swales or open channels are used, they shall be suitably
lined to prevent erosion and designed to avoid excessive velocities.
Rock lining shall conform to Section 850, Rock lining, of PennDOT
Publication 408. The minimum size of rock lining shall be R4.
(6)
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this chapter.
(7)
Existing points of concentrated drainage that discharge onto adjacent
property shall not be altered without permission of the altered property
owner(s) and shall be subject to any applicable discharge criteria
specified in this chapter.
(8)
In those instances where proposed stormwater facilities alter existing
drainage flow patterns, or concentrate discharge flows, flow across
lands of adjoining property owners before entering waters of the commonwealth,
the developer must secure stormwater releases from said adjoining
property owners evidencing their approval of the proposed alteration.
Securance of such releases shall be a precondition of Township subdivision
and land development preliminary plan approval.
(9)
Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this chapter. If diffused
flow is proposed to be concentrated and discharged onto adjacent property,
the developer must document that adequate downstream conveyance facilities
exist to safely transport the concentrated discharge or otherwise
prove that no erosion, sedimentation, flooding, or other harm will
result from the concentrated discharge.
(10)
Where watercourses traverse a development site, drainage easements
shall be provided conforming to the line of such watercourses. The
terms of the easements shall prohibit excavation, the placing of fill
or structures, and any alterations that may adversely affect the flow
of stormwater within any portion of the easement. Also, maintenance,
including mowing of vegetation within the easement shall be required
except as approved by the appropriate governing authority.
(11)
Any stormwater management facilities regulated by this chapter
that would be located in or adjacent to waters of the Commonwealth
of Pennsylvania or wetlands shall be subject to approval by Pennsylvania
DEP through the joint permit application process or, where deemed
appropriate by Pennsylvania DEP, the general permit process. When
there is a question whether wetlands may be involved, it is the responsibility
of the developer or his agent to show that the land in question cannot
be classified as wetlands, otherwise approval to work in the area
must be obtained by Pennsylvania DEP.
(12)
Any stormwater management facilities regulated by this chapter
that would be located on federal, commonwealth or county highway rights-of-way
shall be subject to approval by the appropriate governmental agency
having jurisdiction.
(13)
Stormwater drainage, including roof drains, shall not be connected
to the sanitary sewer system.
B.
Wherever storm sewers are proposed to be utilized, they shall comply
with the following criteria:
(1)
Where practical, storm sewer shall be designed to traverse under
seeded and planted areas. If constructed within 10 feet of road paving,
walks or other surfaced areas, drains shall have a narrow trench and
maximum compaction of backfill to prevent settlement of the superimposed
surface or development. When located in undedicated land, storm sewers
shall be placed within an easement not less than 20 feet wide, as
approved by the Township Engineer, who may require additional width
of easement as circumstances warrant.
(2)
Storm sewers shall be installed after excavating and filling in the
area to be traversed is completed, unless the drain is installed in
the original ground with a minimum of three feet cover and/or adequate
protection during the fill construction.
(3)
Storm sewers shall be designed with cradle when traversing fill areas
of indeterminate stability and with anchors when gradient exceeds
20%.
(4)
Storm sewers shall be backfilled with PennDOT No. 2A coarse aggregate
when traversing under a paved area and shoulder areas.
(5)
Storm sewers shall be designed to adequately handle the anticipated
stormwater flow and be economical to maintain. The minimum pipe size
shall be 15 inches in diameter.
(6)
Storm sewer pipe, trenching, bedding and backfilling requirements
shall conform to the requirements of PennDOT Publication Form 408
specifications.
(7)
Storm sewers shall be constructed of one of the materials specified
in PennDOT Publication Form 408 specifications, Sections 601, 602
and 603. All corrugated polyethylene pipe shall be Type S pipe within
a Township right-of-way shall be reinforced concrete pipe.
(8)
Storm inlets and structures shall be designed to be adequate, safe,
self-cleaning and unobtrusive and consistent with Township standards.
The maximum spacing of inlets shall be 600 feet. Inlets shall be PennDOT
Type C or M with cast-in-place reinforced concrete or precast concrete
tops.
(9)
The appropriate grates shall be provided for all stormwater inlets
and other entrance appurtenances.
(10)
Manholes shall be designed so that the top shall be at finished
grade and sloped to conform to the slope of the finished grade. Top
castings of structures located in roads or parking areas shall be
machined or installed to preclude clanking.
(11)
Where a proposed storm sewer connects with an existing storm
sewer system, the developer shall demonstrate that sufficient capacity
exists in the downstream system to handle the additional flow. The
developer shall furnish a letter from the owner of the existing storm
sewer system approving the connection of the proposed storm sewer
system.
(12)
Storm sewer outfalls and culverts, including driveway cross
pipes, shall be equipped with either reinforced concrete headwalls
or pipe end sections and energy dissipation devices to prevent erosion
and conform with applicable requirements of the Pennsylvania DEP for
stream encroachments (Chapter 105 of Pennsylvania DEP rules and regulations).
