[Ord. No. 2425, 12/3/2018]
1.
In order to protect the health, safety, and general welfare of the
residents of the Township, as well as to protect, sustain, and enhance
the surface water and groundwater resources of the Township, drainage
and stormwater management practices shall be utilized as directed
herein to achieve the following goals and objectives:
A.
Accommodate site development and redevelopment in a manner that protects
public safety and that is consistent with (or re-establishes) the
natural hydrologic characteristics of each watershed and sustains
groundwater recharge, stream baseflows, stable stream channel (geomorphology)
conditions, the carrying capacity of streams and their floodplains,
groundwater and surface water quality, and aquatic living resources
and their habitats.
B.
Reduce and minimize the volume of stormwater generated.
C.
Protect natural infiltration and groundwater recharge rates in order
to sustain groundwater supplies and stream baseflows.
D.
Maintain runoff characteristics of the site after completion of development
that are consistent with the carrying capacity and stable channel
conditions of the receiving streams.
E.
Protect water quality by removing and/or treating pollutants prior
to discharge to groundwater and surface waters throughout the Township,
and protect, restore, and maintain the chemical, physical, and biological
quality of groundwater and surface waters.
F.
Protect in-stream channels and geomorphology conditions of the receiving
streams; protect their flood-carrying capacity and aquatic habitats
and reduce in-stream erosion and sedimentation.
G.
Reduce flooding impacts and prevent a significant increase in surface
runoff rates and volumes, pre-development to post-development, which
could worsen flooding downstream in the watershed, enlarge floodplains,
erode stream banks and create other flood-related health-welfare-property
losses; in general, to preserve and restore the natural flood-carrying
capacity of streams and their floodplains.
H.
Protect adjacent lands from adverse impacts of direct stormwater
discharges.
I.
Ensure effective long-term operation and maintenance of all permanent
stormwater management facilities.
J.
Maintain natural drainage patterns and encourage the use of natural
drainage systems.
K.
Treat and release stormwater as close to the source of runoff as
possible using a minimum of structures and maximizing reliance on
natural processes.
L.
Maintain the existing water balance in all watersheds, subwatersheds,
and streams in the Township, and protect and/or restore natural hydrologic
characteristics and habitats wherever possible throughout the watershed
systems.
M.
Address certain requirements of the Township Separate Storm Sewer
System (MS4) National Pollution Discharge Elimination System (NPDES)
Phase II Stormwater Regulations.
N.
Reduce the impacts of runoff from existing developed sites undergoing
redevelopment while encouraging development and redevelopment in urban
areas and areas designated for growth.
O.
Prevent scour and erosion of stream banks and streambeds.
P.
Meet legal water quality requirements under state law, including
regulations at 25 Pa. Code § 93.4a, to protect and maintain
existing uses and maintain the level of water quality to support those
uses in all streams, and to protect and maintain water quality in
"special protection" streams.
[Ord. No. 2425, 12/3/2018]
1.
Statutory Authority.
A.
Primary Authority. The Township is empowered to regulate these activities
by the authority of the Act of October 4, 1978, P.L. 864, No. 167,
32 P.S. § 680.1 et seq., as amended, the Storm Water Management
Act, and the First Class Township Code, 53 P.S. § 55101
et seq.
B.
Secondary Authority. The Township also is empowered to regulate land
use activities that affect runoff by the authority of the Act of July
31, 1968, P.L. 805, No. 247, the Pennsylvania Municipalities Planning
Code, as amended, 53 P.S. § 10101 et seq.
2.
Applicability. The standards contained herein shall apply to all
regulated activities within the Township. In addition, all local,
county and state erosion and sedimentation control approvals must
be in place to proceed with any regulated activity.
A.
Activities regulated by this Part include, but are not limited to,
the following:
(1)
Land development and redevelopment.
(2)
Subdivision.
(3)
Construction of new or additional impervious or semi-pervious
surfaces (driveways, parking lots, etc.).
(4)
Construction of new buildings or additions to existing buildings.
(5)
Diversion or piping of any natural or man-made stream channel.
(6)
Installation of stormwater management facilities or appurtenances
thereto.
(7)
Any earth disturbances or any activities that involve the alteration
or development of land or removal of trees and vegetation in a manner
that may affect post-construction stormwater runoff.
B.
Redevelopments shall conform to the requirements contained in § 23-104, Subsection 1C(3), when an area of more than 2,000 square feet of an existing facility is reconstructed following the demolition or partial demolition of the existing facility. The area determination shall be made using the footprint of the area being reconstructed, including all impervious surfaces proposed in the reconstructed area and the area of the parking lot required to support the reconstructed facility. The area of the parking lot required to support the reconstructed facility shall be determined using the Township Zoning Ordinance [Chapter 27] requirements for parking.
3.
Exemptions.
A.
With the approval of Township's Board of Commissioners, the
following activities may be exempted from on-site stormwater runoff
control. An exemption shall apply only to the requirement for on-site
stormwater facilities and the preparation of a stormwater management
plan. All other stormwater management design elements, such as a storm
sewer system, road culverts, erosion and sedimentation control, and
runoff quality, shall be required. All exemption requests must be
filed with the Township Zoning Officer and approved by the Township
Engineer.
(1)
Regulated activities smaller than 400 square feet are exempt
from the requirements of this Part to implement SWM BMPs, unless the
activity is found to be a significant contributor to pollution of
the waters of this commonwealth.
(2)
Small Project Exemption. Activities having a disturbed area of less than 5,000 square feet are exempt from the peak rate control requirements of this Part. These projects shall comply with the water quality volume standards contained in § 23-104, Subsection 1C(1), and the extended detention requirement contained in § 23-104, Subsection 3A(1). The "Small Project Standardized SWM Planning Guidance" document provided in Appendix 23-F was prepared to assist applicants in meeting this requirement for individual lots only. The reduced site plan requirements contained in the "Small Project Standardized SWM Planning Guidance" document shall apply. These projects shall be accompanied by an E&S plan that has been reviewed and approved by the Township.
(3)
Emergency Exemption. Emergency maintenance work performed for
the protection of public health, safety and welfare may be exempted
from the requirements in this Part to obtain approval for a stormwater
management plan before commencement of the activity; however, a written
description of the scope and extent of any emergency work performed
shall be submitted to the Township within two calendar days of the
commencement of the activity. If the Township finds that the work
is not an emergency, then the work shall cease immediately and may
not resume until a written stormwater management plan is submitted
and approved.
(4)
Maintenance Exemption. Any maintenance to an existing stormwater
management system shall be made in accordance with plans and specifications
approved by the Township Engineer or Township.
(5)
Gardening: use of land for gardening for home consumption.
(6)
Agricultural Activities: agriculture when operated in accordance
with a conservation plan, nutrient management plan or erosion and
sedimentation control plan approved by the Allegheny County Conservation
District, including activities such as growing crops, rotating crops,
tilling of soil and grazing animals. Installation of new or expansion
of existing farmsteads, animal housing, waste storage and production
areas having impervious surfaces that result in a net increase in
impervious surface of less than 1,000 square feet are exempt from
the requirement to submit a written stormwater management plan.
(7)
Forest Management: forest management operations which are consistent
with a sound forest management plan as filed with the Township Zoning
Officer and which follow the Pennsylvania Department of Environmental
Protection's management practices contained in its publication
"Soil Erosion and Sedimentation Control Guidelines for Forestry."
Such operations are required to have an erosion and sedimentation
control plan.
B.
Waivers.
(1)
The provisions of this Part are the minimum standards for the
protection of the public health, safety, property, and welfare.
(2)
If an applicant demonstrates to the satisfaction of the county or its designee that any mandatory provision of this Part is unreasonable or causes unique or undue unreasonableness or hardship as it applies to the proposed project, or that an alternate design may result in a superior result within the context of §§ 23-101 and 23-104, Subsection 1A and B, of this Part, the county or its designee, upon obtaining the comments and recommendations of the Township and the Allegheny County Conservation District, may grant a waiver or relief so that substantial justice may be done and the public interest is secured, provided that such waiver will not have the effect of nullifying the intent and purpose of this Part.
(3)
Applicants shall refer to the Pennsylvania Stormwater Best Management Practices Manual, Pennsylvania Department of Environmental Protection (DEP), No. 363-0300-002 (2006), as amended and updated, or the Erosion and Sediment Pollution Control Program Manual, Pennsylvania Department of Environmental Protection (DEP), 363-2134-008 (2000), as amended and updated, or other appropriate references for guidance in the design of stormwater management facilities most appropriate to individual site conditions. References to the Maryland Manual, if not deleted, should be to specific sections of Maryland's manual in order to minimize NPDES permitting conflicts with the guidance provided by the Pennsylvania Stormwater BMP Manual. The applicant shall state in full the facts of unreasonableness or hardship on which the request is based, the provision or provisions of the Part that are involved, and the minimum waiver or relief that is necessary. The applicant shall state how the requested waiver and how the applicant's proposal shall result in an equal or better means of complying with the intent of § 23-101, Purpose, § 23-104, Subsection 1A, Design Goals, and § 23-104, Subsection 1B, General Principles, of this Part.
(4)
The applicant shall submit all waiver requests to Allegheny
County or its designee for review and approval. Copies of the waiver
request shall also be submitted to the Township.
(5)
The Board of Commissioners shall keep a written record of all
actions on waiver requests.
(6)
The Board of Commissioners may charge a fee for each waiver
request, which shall be used to offset the administrative costs of
reviewing the waiver request. The applicant shall also agree to reimburse
the Township, the county and the Allegheny County Conservation District
for reasonable and necessary fees that may be incurred in any review
of a waiver request.
(7)
In granting waivers, the county or its designee may impose reasonable
conditions that will, in its judgment, secure substantially the objectives
of the standards or requirements that are to be modified.
(8)
The county or its designee may grant applications for waivers
when the following findings are made:
(b)
That the waiver is the minimum necessary to provide relief.
(c)
That the applicant is not requesting a waiver based solely on
cost considerations.
(d)
That existing off-site stormwater problems will not be exacerbated.
(e)
That runoff is not being diverted to a different drainage area.
(f)
That increased flooding or ponding on off-site properties or
roadways will not occur.
(g)
That potential icing conditions will not occur.
(h)
That increase of post-development peak flow from the site will
not occur and will, in fact, be reduced by the appropriate amount
if the site is in a subbasin having a release rate of less than 100%.
(i)
There will be no increase in the post-development total runoff
volume for all storms equal to or less than the two-year, twenty-four-hour
storm event.
(j)
That adverse impacts to water quality will not result.
(k)
That increased 100-year floodplain levels will not result.
(l)
That increased or unusual Township maintenance expenses will
not result from the waiver.
(m)
That the amount of stormwater generated has been minimized to
the greatest extent allowed.
(n)
That infiltration of runoff throughout the proposed site has
been provided where practicable and pre-development groundwater recharge
protected at a minimum.
(o)
That peak flow attenuation of runoff has been provided.
(p)
That long-term operation and maintenance activities are established.
(q)
That no receiving streams and/or water bodies within 2,000 feet
downstream will be adversely impacted in flood-carrying capacity,
aquatic habitat, channel stability or erosion and sedimentation.
(9)
Waivers.
(a)
Waivers or modifications of the requirements of this Part may
be approved by the Township if enforcement will exact undue hardship
because of unique physical circumstances or conditions peculiar to
the land in question, provided that the modifications will not be
contrary or detrimental to the public interest and will achieve the
intended outcome, and that the purpose of the Part is preserved. Hardship
must be due to such unique physical circumstances or conditions and
not to circumstances or conditions generally created by the provisions
of the Stormwater Management Ordinance. Cost or financial burden shall
not be considered a hardship. Modifications shall not substantially
or permanently impair the appropriate use or development of adjacent
property. A request for modifications shall be in writing and accompany
the stormwater management site plan submission.
(b)
No waiver or modification of any regulated stormwater activity
involving earth disturbance greater than or equal to one acre may
be granted by the Township. Townships are responsible for reviewing
proposed waivers or modifications. The waiver must come from the landowner
and be presented in writing along with a stormwater management site
plan. The designated plan reviewer shall determine if the plan meets
the requirement of this Part. If the proposed disturbance is one acre
or greater, it must be approved by the Department of Environmental
Protection (DEP) or the delegated County Conservation District.
4.
General Requirements.
A.
The management of stormwater on site, both during and upon completion of the disturbances associated with activities permitted under § 23-102, Subsection 2, shall be accomplished in accordance with the standards and criteria of this Part. The design of any temporary or permanent facilities and structures and the utilization of any natural drainage systems shall be in full compliance with this Part. The intent of these design standards is to encourage environmentally sound stormwater management practices that provide necessary drainage facilities while protecting the hydrologic characteristics and water quality of the site and watershed. Developments shall be required to incorporate stormwater management controls. Stormwater management design shall blend into the natural environment and be aesthetically integrated into the site design.
B.
Applicants shall refer to the Pennsylvania Stormwater Best Management
Practices Manual, as amended, Pennsylvania Handbook of Best Management
Practices for Developing Areas (PACD, 1998), the 2000 Maryland Stormwater
Design Manual (MDE, 2000) or other appropriate references for guidance
in the design of stormwater management facilities most appropriate
to individual site conditions. Objectives for design are to reduce
the volume of stormwater generated, infiltrate runoff at its source
to the maximum extent possible, achieve water quality improvement
at the source or during conveyance, and provide for peak flow attenuation.
Applicants shall examine design alternatives by viewing them in a
series. In addition, applicants are strongly encouraged to use structural
and nonstructural stormwater management practices that reduce or eliminate
the need for detention basins.
C.
All SWM design work must be completed by a qualified design professional.
All designs proposing the use of an SWM retention or detention facility
with outlet structures shall be completed by a professional engineer
licensed in the State of Pennsylvania.
D.
All development activity within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with the Floodplain Ordinance [Chapter 8], the Zoning Ordinance [Chapter 27] and this subsection. All development shall be designed to maintain the flood-carrying capacity of the floodway such that the base flood elevations are not increased, either upstream or downstream, unless an approval is received from the PA DEP. The natural conveyance characteristics of the site and the receiving floodplain shall be incorporated into the stormwater management practices proposed for the site.
E.
The stormwater management system shall not create an adverse impact
on stormwater quantity or quality in either upstream or downstream
areas. Off-site areas which discharge to or across a site proposed
for development shall be addressed in the stormwater management plan
prepared for the development. No stormwater management plan shall
be approved until it is demonstrated that the runoff from the project
shall not adversely impact downstream areas.
F.
Wetlands shall not be used to meet the minimum design requirements
for stormwater management or stormwater runoff quality treatment,
except when used as part of a treatment train that incorporates a
portion of the outer zone (filter strip) of the wetland's riparian
buffer as a stormwater outfall.
G.
All proposed stormwater management systems shall be designed to prevent
the pollution of groundwater resources by stormwater, promote safety,
minimize health hazards, preserve natural features and provide infiltration
and groundwater recharge where appropriate. Neither submission of
a plan under the provisions herein nor compliance with the provisions
of these regulations shall relieve any person from responsibility
for damage to any person or property otherwise imposed by law.
H.
Where deemed necessary by the Township Engineer, or as addressed
in an approved Act 167 stormwater management plan, the applicant shall
construct storm drains to handle on-site runoff; to the maximum extent
permitted under the Municipalities Planning Code, 53 P.S. § 10101
et seq., and Act 167, 32 P.S. § 680.1 et seq., or any amendments
thereto, provide on-site/off-site drainage easements; and provide
for the conveyance of off-site runoff to an acceptable outlet in the
same watershed.
I.
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, except as needed for roadways, driveways and walkways,
or any alterations that may adversely affect the flow of stormwater
within any portions of the easement and require the establishment
and protection of riparian buffers.
J.
For all regulated activities, stormwater management BMPs shall be
designed, implemented, operated, and maintained to meet the purposes
and requirements of this Part and to meet all requirements under Pennsylvania
Code Title 25, the Clean Streams Law, 35 P.S. § 691.1 et
seq., and the Storm Water Management Act, 32 P.S. § 680.1
et seq.
K.
Any regulated activity that may affect the stormwater flows toward
or onto a state or county highway right-of-way or facility shall be
designed, implemented, operated, and maintained in accordance with
the regulations of the Pennsylvania Department of Transportation (PennDOT)
or Allegheny County, as the case may be.
L.
At the time of application for a building permit for any approved
lot created by a subdivision and/or improved as a land development
project, issuance of the permit shall be conditioned upon adherence
to the terms of this Part.
M.
Stormwater discharges to critical areas with sensitive resources
(e.g., special protection waters, cold water fisheries, recharge areas,
water supply reservoirs, etc.) may be subject to additional performance
criteria or may need to utilize or restrict certain stormwater management
practices.
N.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this Part and to meet all
requirements under Pennsylvania Code, Title 25 and the Clean Streams
Law, 35 P.S. § 691.1 et seq. Various BMPs and their design
standards are listed in the Erosion and Sediment Pollution Control
Program Manual (E&S Manual), Commonwealth of Pennsylvania, Department
of Environmental Protection, No. 363-2134-008, as amended and updated.
O.
No regulated earth disturbance activities within the Township shall
commence until the requirements of this Part are met.
P.
Post-construction water quality protection shall be addressed as
required by the stormwater management requirements contained in this
Part.
Q.
Operations and maintenance of permanent stormwater BMPs shall be addressed as required by § 23-105.
R.
All best management practices (BMPs) used to meet the requirements
of this Part shall conform to the state water quality requirements,
and any more stringent requirements as required by the Township.
S.
Techniques described in Appendix 23-B (Nonstructural Stormwater Management
Practices) of this Part are encouraged, because they reduce the costs
of complying with the requirements of this Part and the state water
quality requirements.
T.
In selecting the appropriate BMPs or combinations thereof, the applicant
shall consider the following:
(1)
Total contributing area.
(2)
Permeability and infiltration rate of the site soils.
(3)
Slope and depth to bedrock.
(4)
Seasonal high water table.
(5)
Proximity to building foundations and wellheads.
(6)
Erodibility of soils.
(7)
Land availability and configuration of the topography.
(8)
Peak discharge and required volume control.
(9)
Stream bank erosion.
(10)
Efficiency of the BMPs to mitigate potential water quality problems.
(11)
The volume of runoff that will be effectively treated.
(12)
The nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife habitat.
U.
Transference of runoff from one DEP-designated Act 167 watershed
to another shall be prohibited unless approved by the Township.
V.
SWM site plans approved by the Township shall be on site throughout
the duration of the regulated activity.
5.
Repealer. Any ordinance or ordinance provision of the Township inconsistent
with any of the provisions of this Part is hereby repealed to the
extent of the inconsistency only; provided, however, that this repeal
shall in no manner be construed as a waiver, release or relinquishment
of the right to initiate, pursue or prosecute, as the case may be,
any proceeding at law or in equity pertaining to any act done which
would have constituted a violation of such prior ordinance or ordinance
provision. All of said ordinance or ordinance provisions shall remain
in full force and effect and are not repealed hereby as they pertain
to such acts and to the processing of such plans filed prior to the
effective date of this Part, which are protected from the effect of
intervening ordinances by Section 508(4) of the Pennsylvania
Municipalities Planning Code, 53 P.S. § 10508(4).
6.
Severability. Should any section or provision of this Part be declared
invalid by a court of competent jurisdiction, such determination of
invalidity shall not affect the validity of the remaining provisions
of this Part.
7.
Compatibility with Other Ordinance Requirements. Permits and approvals
issued pursuant to this Part shall not relieve the applicant of the
responsibility to comply with or to secure other required permits
or approvals for activities regulated by any other applicable code,
rule, act, statute or ordinance. This Part shall not preclude the
inclusion in such other permit of more stringent requirements concerning
regulation of stormwater and erosion. Where a conflict exists between
a provision within this Part and that of the PA DEP Phase II NPDES
regulations, as amended, or any other ordinance of the Township, the
more stringent requirements shall govern.
8.
Permit Requirements by Other Government Entities.
A.
All regulated earth disturbance activities subject to permit requirements
by DEP under regulations at 25 Pa. Code Chapter 102.
B.
Work within natural drainageways subject to permit by DEP under 25
Pa. Code, Chapter 105.
C.
Any stormwater management facility that would be located in or adjacent
to surface waters of the commonwealth, including wetlands, subject
to permit by DEP under 25 Pa. Code Chapter 105.
D.
Any stormwater management facility that would be located on a state
highway right-of-way, or require access from a state highway, shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
E.
Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area and any facility which
may constitute a dam subject to permit by DEP under 25 Pa. Code Chapter
105.
9.
Erosion and Sediment Control During Regulated Earth Disturbance Activities.
A.
No regulated earth disturbance activities within the Township shall
commence until the Township receives a copy of any required approvals
from the Conservation District or DEP for an erosion and sediment
control plan.
B.
DEP has regulations that require an erosion and sediment control
plan for any earth disturbance activity of 5,000 square feet or more,
under 25 Pa. Code § 102.4(b).
C.
In addition, under 25 Pa. Code Chapter 92a, a DEP NPDES construction
activities permit is required for regulated earth disturbance activities.
D.
Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate DEP regional office or County Conservation
District must be provided to the Township.
E.
A copy of the erosion and sediment control plan and any required
permits, as required by DEP regulations, shall be available at the
project site at all times.
F.
Additional erosion and sediment control design standards and criteria
are recommended to be applied where infiltration BMPs are proposed
and shall include the following.
(1)
Areas proposed for infiltration BMPs shall be protected from
sedimentation and compaction during the construction phase to maintain
maximum infiltration capacity.
(2)
Infiltration BMPs shall not be constructed nor receive runoff
until the entire contributory drainage area to the infiltration BMP
has achieved final stabilization.
10.
Erroneous Permit. Any permit or authorization issued or approved
based on false, misleading or erroneous information provided by an
applicant is void without the necessity of any proceedings for revocation.
Any work undertaken or use established pursuant to such permit or
other authorization is unlawful. No action may be taken by a board,
agency or employee of the Township purporting to validate such a violation.
11.
Prohibited Discharges and Connections.
A.
No person in the Township shall allow, or cause to allow, stormwater discharges into the Township's separate storm sewer system and/or waters of this commonwealth which are not composed entirely of stormwater, except 1) as provided in Subsection 11B below, and 2) discharges allowed under a state or federal permit.
B.
The following discharges are authorized unless they are determined
to be significant contributors to pollution to the waters of this
commonwealth:
(1)
Discharges from firefighting activities.
(2)
Discharges from potable water sources, including water line
flushing and fire hydrant flushing, if such discharges do not contain
detectable concentrations of total residual chlorine (TRC).
(3)
Noncontaminated irrigation water, water from lawn maintenance,
landscape drainage and flows from riparian habitats and wetlands;
irrigation drainage.
(4)
Diverted stream flows and springs.
(5)
Routine external building washdown (which does not use detergents
or other compounds).
(6)
Noncontaminated HVAC condensation and water from geothermal
systems.
(7)
Water from individual residential car washing.
(8)
Noncontaminated pumped groundwater from foundation and footing
drains and crawl space pumps.
(9)
Pavement wash waters where spills or leaks of toxic or hazardous
materials have not occurred (unless all spill material has been removed)
and where detergents are not used.
(10)
Dechlorinated swimming pool and hot tub discharges, as long
as the PA DEP guidelines for swimming pool water discharge are followed.
C.
In the event that the Township determines that any of the discharges identified in Subsection 11B significantly contribute to pollution of waters of the commonwealth, or is so notified by DEP, the Township or PA DEP will notify the responsible person to cease the discharge.
D.
Nothing in this section shall affect a discharger's responsibilities
under state law.
E.
Existing roof drain, underdrain and sump pump discharge should be
directed to lawn area or other pervious areas. If required by the
Township, the discharge shall be directed to a stone sump or infiltration
BMP. If approved by the Township, the discharge may also be directly
connected to the storm sewer system.
12.
Enforcement and Penalties.
A.
Right of Entry. Upon presentation of proper credentials, the Township
may enter at reasonable times upon any property within the Township
to inspect the condition of the stormwater structures and facilities
in regard to any aspect regulated by this Part.
B.
Inspection. SWM BMPs should be inspected by the landowner/developer
(including the Township for dedicated facilities) according to the
following list of frequencies:
C.
Enforcement.
(1)
It shall be unlawful for a person to undertake any regulated
activity except as provided in an approved SWM site plan.
(2)
It shall be unlawful to alter or remove any control structure
required by the SWM site plan.
(3)
Inspections regarding compliance with the SWM site plan are
a responsibility of the Township.
D.
Suspension and Revocation.
(1)
Any approval for a regulated activity issued may be suspended
or revoked, in whole or in part, by the Township for:
(a)
Noncompliance with or failure to implement any provision of
the approval.
(b)
A violation of any provision of this Part or any other applicable
law, ordinance, rule or regulation relating to the regulated activity.
(c)
The creation of any condition or the commission of any act during
the regulated activity which constitutes or creates a hazard or nuisance,
pollution, or which endangers the life or property of others.
(3)
An approval that has been revoked by the Township cannot be
reinstated. The applicant may apply for a new approval under the provisions
of this Part.
(4)
Prior to revocation or suspension of a permit, if there is no
immediate danger to life, public health, or property, the Township
may notify the landowner/developer to discuss the noncompliance.
(5)
Penalties.
(a)
Any person, firm or corporation who shall violate any provision
of this Part, upon conviction thereof, shall be sentenced to pay a
fine of not more than $1,000 plus costs and, in default of payment
of said fine and costs, to a term of imprisonment not to exceed 30
days. Each day that a violation of this Part continues shall constitute
a separate offense.
(b)
In addition, the Township may institute injunctive, mandamus
or any other appropriate action or proceeding at law or in equity
for the enforcement of this Part. Any court of competent jurisdiction
shall have the right to issue restraining orders, temporary or permanent
injunctions, mandamus or other appropriate forms of remedy or relief.
[Ord. No. 2425, 12/3/2018]
1.
For all regulated activities not eligible for exemptions pursuant to § 23-102, Subsection 3, of this Part, the applicant shall submit a stormwater management plan and report prepared by a professional engineer licensed in the Commonwealth of Pennsylvania, which shall contain, but not be limited to, the following. Final copies of all plans, specifications and reports shall also be submitted to the Township in Adobe PDF format.
A.
A suitable map of the watershed for any and all named streams within
which the project is proposed (A United States Geological Survey quadrangle
map is usually sufficient.) with existing and proposed development
areas presented on the map.
B.
Suitable maps and drawings showing all existing natural and constructed
drainage facilities affecting the subject property.
C.
Hydrologic (watershed) and water feature boundaries, including all
areas flowing to the proposed project, existing streams (including
first order and intermittent streams), springs, lakes, ponds, or other
bodies of water within the project area.
D.
Sufficient topographical information with elevations to verify the
location of all ridges, streams, etc. (two-foot contour intervals
within the project's boundaries and for proposed off-site improvements;
for slopes greater than 15%, five-foot contours are acceptable).
E.
Notes pertaining to and locations of existing standing water, areas
of heavy seepage, springs, wetlands, streams, and hydrologically sensitive
areas. The Chapter 93 water quality standards use designation must
also be provided on the plan.
F.
General type of soils with hydrologic soil group noted, estimated
permeabilities in inches per hour, and location and results of all
soil tests and borings (if needed).
G.
One-hundred-year flood elevations for any special flood hazard areas
on or within 100 feet of the property. For redevelopment sites, also
show the ten- and twenty-five-year flood elevations for any special
flood hazard areas on or within 100 feet of the property. The source
of these elevations shall also be shown on the plans.
H.
Description of current and proposed ground cover and land use. The
total area and percent impervious cover shall be noted.
I.
A wetland delineation report for the project site with a location
map identifying wetland areas if any were found.
J.
A plan of the proposed stormwater drainage system attributable to
the activity proposed, including runoff calculations, stormwater management
practices to be applied both during and after development, and the
expected project time schedule.
K.
The design computations for all proposed stormwater drainage systems,
including storm drain pipes, inlets, runoff control measures and culverts,
drainage channels, and other features, facilities, and stormwater
management practices.
L.
A grading plan, including all areas of disturbance of the subject
activity. The total area of disturbance shall be noted in square feet
and acres; topographic contours showing the existing and proposed
final contours at an interval of two feet; in areas having slope of
greater than 15% a five-foot contour interval may be used.
M.
A plan of the erosion and sedimentation procedures to be utilized
as required by local ordinances and state regulations.
N.
The effect of the project (in terms of runoff volumes and peak flows)
on adjacent properties and on any other stormwater collection system
that may receive runoff from the project site, and specifics of how
erosion and flooding impacts to adjacent properties will be avoided
or otherwise mitigated.
O.
An operation and maintenance plan consistent with the requirements of § 23-105. Such a plan should clearly explain how the proposed facilities operate and the functions they serve.
P.
The name of the development, the name and address of the property
owner and applicant, and the name and address of the individual or
firm preparing the plan.
Q.
A North arrow, submission date, graphic scale and revision dates,
as applicable, shall be included on each page of all plans submitted.
R.
Complete delineation of the flow paths used for calculating the time
of concentration for the pre-developed and post-developed conditions.
S.
Construction details sufficient to completely express the intended
stormwater design components consistent with this Part.
T.
A listing of all permits required for the site providing the status
of the permit application(s) and approval(s).
U.
The following signature block for the Township.
|
"(Township official or Township Engineer) on this date (Signature
date), has reviewed and hereby certifies that the SWM Site Plan meets
all design standards and criteria of the Township Ordinance No. (number
assigned to ordinance), except where waivers have been granted as
noted on the Plan. The review is based on a survey and plan prepared
by others and assumes that all information is correct and valid as
submitted."
|
V.
The SWM site plan shall provide a justification, acceptable to the
designated plan reviewer, must be included in the SWM site plan if
BMPs other than green infrastructure methods and LID practices are
proposed to achieve the volume, rate and water quality controls under
this Part.
[Ord. No. 2425, 12/3/2018]
1.
Design Goals, Principles and Standards.
A.
Design Goals. Applicants shall adhere to a holistic design process incorporating the goals listed below. The objective is to achieve post-development hydrologic conditions that are consistent with the pre-development ground cover assumption for new development (refer to Subsection 2B) and improve the runoff conditions for redevelopment (refer to Subsection 3C). The design goals are:
(1)
Minimize the volume of runoff that must be collected, conveyed,
treated and released by stormwater management facilities.
(2)
Maintain the natural infiltration process and rate, and infiltrate
runoff at its source when appropriate.
(3)
Remove and/or treat pollutants at the source or during conveyance.
(4)
Provide for peak flow attenuation, as needed.
(5)
Attenuate runoff to protect the in-stream channel of the receiving
stream.
B.
General Principles. The following general principles apply to all applicable activities pursuant to § 23-102, Subsection 2:
(1)
Incorporate conservation design practices to minimize the amount
of stormwater generated on a site, encourage the disconnection of
impervious land cover, and maximize the use of pervious areas for
stormwater treatment and on-site rainfall infiltration.
(2)
Infiltration of surface water runoff at its source is to be a mechanism for stormwater management based on hydrologic soil group (or infiltration testing). Infiltration practices include, but are not limited to, those referenced in Subsection 3B(1) and as outlined in the publications listed in Subsection 3 of this section. Infiltration practices shall adhere to the following criteria:
(a)
In choosing methods of infiltration, preference shall be given
to a combination of surface and subsurface infiltration methods.
(b)
Applicants shall first consider minimum disturbance/minimum
maintenance techniques combined with site grading that distributes
runoff to reduce concentration. Next, applicants shall consider depression
areas combined with subsurface infiltration practices followed by
other subsurface measures, including, but not limited to, porous paving
and perforated pipe storage.
(d)
Where high water tables, subsurface contamination, slope stability concerns, or other site constraints preclude achieving the required infiltration volume, additional conservation design practices and alternative stormwater management practices should be implemented to reduce to the maximum extent practicable the total volume of stormwater released to streams. The applicant shall follow the stormwater runoff hierarchy of Subsection 3A(1).
(e)
Infiltration areas should be designed to maintain any broad
and even infiltration pattern which existed prior to development.
Such facilities should use the natural topography and vegetation in
order to blend in with the site. Infiltration designs which do not
provide this may be used if the applicant demonstrates to the Township's
satisfaction that alternative approaches would be more effective,
more harmonious with their existing environment and as easily maintained.
(f)
Aboveground stormwater infiltration facilities should be as
shallow as possible while still achieving the requirements of this
Part.
(3)
Water quality improvement shall be achieved in conjunction with
or as part of infiltration practices. Water quality improvements shall
also be provided for drainage areas not otherwise addressed by infiltration
practices either at the source of runoff and/or during conveyance
away from the source of runoff.
(4)
To reduce the need for large retention and/or detention basins
designed to satisfy the peak flow attenuation and extended detention
requirements, other innovative stormwater management practices located
close to the source of runoff generation shall be considered, including
a combination of practices (e.g., rooftop storage, open vegetated
channels, bioretention, pervious pavement systems and infiltration
trenches).
(5)
When designing stormwater management facilities to satisfy the peak flow attenuation and extended detention requirements [Refer to Subsection 1C(2)(b).], the effect of structural and nonstructural stormwater management practices implemented as part of the overall site design may be taken into consideration when calculating total storage volume and release rates.
(6)
Site hydrology and natural infiltration patterns shall guide
site design, construction and vegetation decisions. All channels,
drainageways, swales, natural streams and other surface water concentrations
shall be considered and, where possible, incorporated into design
decisions.
(7)
A justification, acceptable to the Township official or Township
Engineer, must be included in the SWM Site Plan if BMPs other than
green infrastructure methods and LID practices are proposed to achieve
the volume rate and water quality controls under this Part.
C.
Minimum Performance Criteria.
(1)
The following minimum performance standards shall apply to all applicable activities, whether they are new development or redevelopment, pursuant to § 23-102, Subsection 2A.
(a)
Water quality treatment of stormwater runoff shall be provided
for all discharges prior to release to a receiving water body. If
a stormwater management practice does not provide water quality treatment,
then water quality best management practices shall be utilized prior
to the runoff entering the stormwater management practice.
(b)
Water quality management shall be provided through the use of
structural and/or nonstructural stormwater management practices. Water
quality stormwater management practices shall be designed to reduce
or eliminate solids, sediment, nutrients, and other potential pollutants
from the site. It is presumed that a stormwater management practice
complies with this requirement if it is:
(c)
Stormwater discharges from land uses or activities with higher potential for pollutant loadings (hot spots) may require the use of specific structural stormwater management practices and pollution prevention practices. In addition, stormwater from a hot spot land use shall be provided with proper pretreatment prior to infiltration. For the purpose of this Part, the sites/facilities listed in Subsection 1C(1)(d), below, are considered hot spots.
(d)
Certain industrial sites may be required to prepare and implement
a stormwater pollution prevention plan and file notice of intent as
required under the provisions of the EPA industrial stormwater NPDES
permit requirements. Other industrial sites storing significant quantities
of chemicals/wastes should also prepare a prevention plan. Sites that
are required by EPA to prepare a plan include, but are not limited
to:
(e)
Conveyance structures/channels shall be designed and adequately
sized so as to protect the properties receiving runoff from impacts
of flooding and erosion. Where necessary, and to the maximum extent
permitted under the Municipalities Planning Code, 53 P.S. § 10101
et seq., and Act 167, 32 P.S. § 680.1 et seq., or any amendments
thereto, drainage easements from adjoining properties shall be obtained
to ensure the drainageway and the property and shall also establish
the operation and maintenance requirements for the drainageway.
(f)
All stormwater management practices shall have an operation and maintenance plan pursuant to § 23-105, Subsection 3, of this Part, and if to be privately owned, an enforceable operation and maintenance agreement per § 23-105, Subsection 4, of this Part to ensure the system functions as designed and to provide remedies for system failure.
(g)
Stormwater runoff generated from development and discharged
directly into a jurisdictional wetland or waters of the United States
and their adjacent wetlands shall be treated by an approved stormwater
management practice prior to release into a natural wetlands and shall
not be used to meet the minimum design requirements for stormwater
management or stormwater runoff quality treatment, except when used
as part of a treatment train that incorporates a portion of the outer
zone (filter strip) of the wetland's riparian buffer as a stormwater
outfall. In such instances, the discharge velocity from the terminal
end of a pipe or associated energy dissipation practice shall not
exceed two feet per second for the two-year frequency storm event.
Where such a management strategy is used, all feasible methods shall
be used to convert concentrated flow to uniform, shallow sheet flow
before entering the outer zone of the wetland's riparian buffer.
In addition, it shall be demonstrated that such an approach will not
cause erosion.
(2)
The following minimum performance standards shall apply to all applicable new development activities, pursuant to § 23-102, Subsection 2A.
(a)
Water quality improvement shall be achieved in conjunction with or as part of infiltration practices (if used). Water quality improvements shall also be provided for drainage areas not otherwise addressed by infiltration practices either at the source of runoff and/or during conveyance away from the source of runoff. Stormwater quality management practices shall be designed to capture and treat stormwater runoff generated by the one-inch rainfall event. Refer to Subsection 3A(2) for water quality volume design standards and assumptions. Stormwater quality management practice selection, design and implementation shall be based upon appropriate reference materials, as provided in § 23-102, Subsection 4D.
(b)
The post-development peak discharge rate shall not exceed the pre-development peak discharge rate multiplied by the subbasin release rate percentage (where determined in Act 167 watersheds) for the two-, ten-, twenty-five-, and 100-year, twenty-four-hour storm events pursuant to the pre-development cover assumption described in Subsection 2B. Refer to Appendix 23-A for release rate percentages information.
(c)
Facilities capable of attenuating rainfall runoff shall be provided
and be designed to attenuate the runoff volume from the one-year,
twenty-four-hour storm event for at least 24 hours.
(d)
Stormwater shall be infiltrated and/or discharged within the
same drainage area of the stream receiving the runoff from the development
site prior to development.
(e)
Structural and nonstructural stormwater management practices
that make best possible use of infiltration on site shall be considered
in all site designs, when appropriate.
(3)
The following minimum performance standards shall apply to all applicable redevelopment activities, pursuant to § 23-102, Subsection 2B.
(a)
One of the following minimum performance standards shall be
accomplished. Selection of the performance standard shall be whichever
is most appropriate for the given site conditions:
1)
Reduce the total impervious cover on the site (e.g., by using
pervious pavement, replacement of pavement with pervious planting
areas or green roof systems) by at least 25%, based on a comparison
of existing impervious cover to proposed impervious cover.
2)
Provide facilities designed to attenuate the runoff volume from
the one-year, twenty-four-hour post-development storm event for at
least 24 hours.
3)
Provide facilities to ensure that the post-development peak
discharge rate shall not exceed the pre-development peak discharge
rate multiplied by the subbasin release rate percentage (where determined
in Act 167 watersheds) for the two- and ten-year, twenty-four-hour
storm events. A pre-development cover CN of 71 shall be assumed.
(b)
In addition to the minimum performance standards for redevelopment areas in Subsection 1C(3) above, water quality improvements shall be provided for drainage areas not otherwise addressed by infiltration practices either at the source of runoff and/or during conveyance away from the source of runoff. Stormwater quality management facilities shall be designed to capture and treat 1/4 of one inch of runoff from all pavement areas (i.e., parking lots, pavements and noncovered sidewalks). Roof area may be excluded from this calculation.
2.
Stormwater Runoff Calculation Criteria. In addition to the infiltration
and water quality requirements of this Part, peak flow from those
activities resulting in increases in impervious surface and/or regrading
and compaction shall be attenuated consistent with the following stormwater
calculation methods:
A.
The following design storms shall be used for analysis of the pre-
and post-development conditions. These values are applicable to the
Soil Cover Complex Method:
|
Return Period
(years)
|
24-Hour Storm
(inches)
|
|---|---|
|
1
|
2.00
|
|
2
|
2.35
|
|
5
|
2.88
|
|
10
|
3.30
|
|
25
|
3.91
|
|
50
|
4.40
|
|
100
|
4.92
|
|
The precipitation values for each frequency storm listed above
were abstracted from the precipitation frequency estimates developed
by the National Oceanic and Atmospheric Administration as set forth
in NOAA Atlas 14, Volume 2 (NOAA June 2004). The NOAA data are available
from the Hydrometeorological Design Studies Center of the National
Weather Service.
| |
|
The NOAA Atlas 14, Volume 2 report can be accessed from the
NOAA website at http://hdsc.nws.noaa.gov/hdsc/pfds/.
| |
B.
The following assumptions shall be used for runoff calculations:
(1)
For new development sites, the ground cover used as the predevelopment
assumption for runoff calculations shall be as follows:
(a)
Wooded sites shall use a ground cover of woodland in good condition.
Portions of a site having more than one viable tree of a dbh [Diameter
at breast height (dbh) is the diameter of the tree stem 4 1/2
feet above the ground.] of six inches or greater per 1,500 square
feet shall be considered wooded where such trees existed within 10
years of application. If there is evidence of logging within the ten-year
period, logged area shall be considered as woodland in good condition.
(b)
Agricultural sites shall use a ground cover of pasture in good
condition.
(c)
All other portions of a site shall use a ground cover of meadow
in good condition.
(d)
All watershed areas contributing to the point of interest, including
off-site areas, shall be considered.
(2)
The runoff curve numbers listed in the table below shall be used in developing the runoff calculations for the ground covers noted in Subsection 2B(1). These values are referenced from the Urban Hydrology for Small Watersheds, Technical Release No. 55 (USDA, 1986). Coefficients for equivalent ground cover conditions shall be used if a runoff method other than the Soil Cover Complex Method is used.
|
Ground Cover
|
Hydrologic Soil Group Curve Numbers
| |||
|---|---|---|---|---|
|
A
|
B
|
C
|
D
| |
|
Woodland
|
30
|
55
|
70
|
77
|
|
Meadow
|
30
|
58
|
71
|
78
|
|
Grass
|
39
|
61
|
74
|
80
|
(3)
Impervious cover shall have a curve number of 98.
(4)
Gravel pavement shall have a curve number of 89.
(5)
Average antecedent moisture conditions, or AMC II, shall be
used (for the Soil Cover Complex Method only, for example, TR-55,
TR-20).
(6)
A Type II distribution storm (for the Soil Cover Complex Method
only, for example, TR-55, TR-20).
(7)
For time of concentration calculations, sheet flow lengths shall
not exceed 100 feet and shallow concentrated flow lengths shall not
exceed 1,000 feet.
C.
In all plans and designs for stormwater management systems and facilities
submitted to the Township Engineer for approval, stormwater peak discharge
and runoff shall be determined through the use of the NRCS Soil Cover
Complex Method as set forth in Urban Hydrology for Small Watersheds,
Technical Release No. 55 (USDA, 1986), with specific attention given
to antecedent moisture conditions, flood routing, time of concentration,
and peak discharge specifications included therein and in Hydrology
National Engineering Handbook, § 4, (USDA, 1985) both by
the United States Department of Agriculture, Natural Resources Conservation
Service. Note that when TR-55 is used for natural system-based approaches
and practices encouraged herein, calculations must be performed on
a detailed small subarea basis. Use of Technical Release No. 20 and
other methods listed in Table 23-1 are also acceptable. The design
professional's selection of a specific method shall be based
on the suitability of the method for the given project site conditions
with due consideration to the limitations of the method chosen. Table
23-1 herein summarizes the computational methods available.
|
Table 23-1
| ||
|---|---|---|
|
Acceptable Computation Methodologies for Stormwater Management
Plans
| ||
|
Method
|
Source
|
Applicability
|
|
TR-20 or commercial package based on TR-20
|
USDA — NRCS
|
When use of full model is desirable or necessary
|
|
TR-55 or commercial package based on TR-55
|
USDA — NRCS
|
Applicable for plans within the model's limitations
|
|
HEC - HMS
|
U.S. Army Corps of Engineers
|
When full model is desirable or necessary
|
|
PSRM
|
Penn State University
|
When full model is desirable or necessary
|
|
VT/PSUHM
|
Virginia Polytechnic Institute and Penn State University
|
When full model is desirable or necessary
|
|
Modified Rational Method or commercial package based on this
method
|
Emil Kuiching (1889)
|
For sites less than 20 acres
|
|
SWMM or commercial package based on SWMM
|
U.S. EPA
|
Most applicable in urban areas
|
|
Small Storm Hydrology Method (as included in SLAMM)
|
PV and Associates, or the website www.winslamm.com
|
Calculation of runoff volume from urban and suburban areas
|
D.
A modified Rational Method analysis may be used for drainage areas
smaller than two acres when permitted by the Township Engineer. The
term "modified Rational Method" used herein refers to a procedure
for manipulation of the basic Rational Method techniques to reflect
the fact that storms with a duration greater than the normal time
of concentration for a basin will result in a larger volume of runoff
even though the peak discharge is reduced. The methodology and model
chosen for use shall be well documented as being appropriate for use
in this region, and all relevant assumptions, methodologies, calculations
and data used shall be provided to the Township Engineer for review.
Information on the modified Rational Method is presented in the Recommended
Hydrologic Procedures for Computing Urban Runoff from Small Watersheds
in Pennsylvania (PA DEP, 1982).
E.
Rainfall intensities used for the modified Rational Method shall
be based on the precipitation frequency estimates developed by the
National Oceanic and Atmospheric Administration as set forth in NOAA
Atlas 14.
F.
The Rational Method (that is, Q = CIA) shall be used for calculations
of the peak rate of runoff for the design of storm sewers and drainage
swales but not for the design of stormwater management facilities
where a full hydrograph is needed. The equation representing the Rational
Method is comprised of the following (in English units):
|
Q
|
=
|
Peak flow rate, cubic feet per second (cfs)
|
|
C
|
=
|
Runoff coefficient, dependent on land use/cover
|
|
I
|
=
|
Design rainfall intensity, inches per hour
|
|
A
|
=
|
Drainage area, acres
|
G.
Runoff characteristics of off-site areas that drain through a proposed
development shall be considered and be based on the existing conditions
in the off-site area.
3.
Standards for Stormwater Management Practices. The Pennsylvania Stormwater
Best Management Practices Manual shall serve as a guide for the design
of stormwater management practices. Additional design guidance may
also be obtained from other related sources, including the 2000 Maryland
Stormwater Design Manual, Volumes I and II (MDE, 2000), Design of
Stormwater Filtering Systems (CWP, 1996), and the American Society
of Civil Engineers Manual and Report on Engineering Practice, No.
87, Urban Runoff Quality Management (ASCE, 1998) for the design of
stormwater runoff quality control features for site development. A
list of references is provided with this Part. The water quality volume
design measures used herein are partially based on the methodology
expressed in the Maryland manual referenced above. Pursuant to the
design options recommended in the above documents, the following standards
shall be adhered to:
A.
Extended Detention, Water Quality Volume, Infiltration and Nonstructural
BMP Credits Criteria. The following sizing criteria shall be followed
at all sites required to meet the standards of this Part:
(1)
Extended Detention.
(a)
Detain the one-year, twenty-four-hour design storm using the
SCS Type II distribution. Provisions shall be made so that the one-year
storm takes a minimum of 24 hours to drain from the facility from
a point where the maximum volume of water from the one-year storm
is captured (i.e., the maximum water surface elevation is achieved
in the facility). Release of water can begin at the start of the storm
(i.e., the invert of the water quality orifice is at the invert of
the facility). The design of the facility shall consider and minimize
the chances of clogging and sedimentation potential.
(b)
Detention ponds shall detain the one-year storm event and allow
it to naturally infiltrate and recharge the groundwater table. All
subsequent orifices for the two-, ten-, twenty-five- and 100-year
storm events shall be placed above the maximum water surface elevation
of the one-year storm.
(c)
Normally dry, open-top storage facilities should completely
drain both the volume control and rate control capacities over a period
of time not less than 24 and not more than 72 hours from the end of
the design storm.
(d)
Flow from off-site areas must be considered as pass-through
flow if it is conveyed through the BMP and should be modeled as "present
condition" for the one-year storm event.
(e)
The length of overland flow used in time of concentration (tc)
calculations is limited to no more than 100 feet for post-development
conditions.
(f)
The models TR-55 and TR-20 (or approved equivalent) can be used
for determining peak discharge rates.
(2)
Water Quality Volume.
(a)
Treatment of the water quality volume (WQv) of stormwater prior
to its release to receiving waters or water bodies shall be provided
at all developments where stormwater management is required. The WQv
equals the storage volume needed to capture and treat the runoff from
storms of one inch or less. Runoff from the first one inch of rainfall
transports most of the total pollutant load.
|
The WQv is based on the following equation:
|
|
WQv = [(P)(Rv)(A)]/12 (acre-feet)
|
|
Where:
| ||
|
P
|
=
|
Rainfall depth in inches (set to one inch)
|
|
Rv
|
=
|
Volumetric runoff coefficient, 0.05 + 0.009(I) where I is percent
impervious cover
|
|
A
|
=
|
Site area (acres)
|
(b)
The formula assumes approximately 5% runoff from pervious surfaces,
and 90% runoff from impervious surfaces. A minimum of 0.2 inch per
acre of runoff volume shall be met at sites or in drainage areas that
have less than 15% impervious cover.
(c)
Drainage areas having no impervious cover and no proposed disturbance
during development may be excluded from the WQv calculations. However,
designers are encouraged to incorporate water quality treatment practices
for these areas.
(d)
Stormwater Quality Treatment. The final WQv shall be treated
by an acceptable stormwater management practice(s) from those described
in this section or as approved by the Township.
(e)
For new developments and redevelopments, infiltration is considered
an acceptable method of satisfying part or all of the water quality
volume.
(f)
For new developments, the WQv requirements of this section shall be sized and designed in conjunction with the standards under Subsection 3A(1).
(g)
As a basis for design, the following assumptions may be made:
1)
Multiple Drainage Areas. When a project contains or is divided
by multiple drainage areas, the WQv volume shall be addressed for
each drainage area.
2)
Off-site Drainage Areas. The WQv shall be based on the impervious
cover of the proposed site. Off-site existing impervious areas may
be excluded from the calculation of the water quality volume requirements.
(3)
Infiltration Volume. Where possible, all of the water quality
volume should be treated using infiltration BMPs. The following calculation
shall be used to determine the minimum recharge goal for the site.
|
Recharge Volume (Rev), (acre-feet)
|
|
Fraction of WQv, depending on soil hydrologic group.
|
|
Rev = (S)(Ai)
|
|
Where:
| ||
|
S
|
=
|
Soil-specific recharge factor in inches
|
|
Ai
|
=
|
The measured impervious cover
|
|
Hydrologic Soil Group
|
Soil Specific Recharge Factor (S)
|
|
A
|
0.40 inch
|
|
B
|
0.25 inch of runoff
|
|
C
|
0.10 inch of runoff
|
|
D
|
0.05 inch of runoff
|
(a)
Infiltrated volume may be subtracted from the total site WQv.
(b)
Infiltration should not be considered for sites or areas of
sites that have activities that may allow pollution to be infiltrated.
For example, the use of infiltration for the runoff of a service station's
paved lot would not be appropriate, although roof water from the service
station may be infiltrated.
(c)
Infiltration should only be used when in the opinion of a professional
engineer it will not contribute to slope instability or cause seepage
problems into basements or developed downgradient areas.
(d)
If more than one hydrologic soil group is present at a site,
a composite recharge volume shall be computed based upon the proportion
of total site area within each hydrologic soil group.
(e)
All infiltration facilities shall be set back at least 15 feet
from all structures with subgrade elements (e.g., basements, foundation
walls).
(4)
Credits for Use of Nonstructural BMPs. The developer may obtain
credits for the use of nonstructural BMPs using the procedures outlined
below. Examples of nonstructural credit calculations are provided
in Appendix 23-E.
|
Volume Reduction Method # 1: Natural Area Conservation.
|
|
A water quality volume reduction can be taken when undisturbed
natural areas are conserved on a site, thereby retaining their pre-development
hydrologic and water quality characteristics. Under this method, a
designer would be able to subtract the conservation areas from the
total site area when computing the water quality protection volume.
An added benefit is that the post-development peak discharges will
be smaller, and hence, water quantity control volumes will be reduced
due to lower post-development curve numbers or rational formula "C"
values.
|
|
Rule: Subtract conservation areas from total site area when
computing water quality protection volume requirements.
|
|
Criteria:
|
|
• Conservation area cannot be disturbed during
project construction and must be protected from sediment deposition.
The conservation area shall be protected with a safety fence until
construction has been completed. After construction the area shall
be posted with signage indicating that it is a conservation area.
|
|
• Shall be protected by limits of disturbance
clearly shown on all construction drawings.
|
|
• Shall be located within an acceptable conservation
easement instrument that ensures perpetual protection of the proposed
area. The easement must clearly specify how the natural area vegetation
shall be managed, and boundaries will be marked. [Note: managed turf
(e.g., playgrounds, regularly maintained open areas) is not an acceptable
form of vegetation management.]
|
|
• Shall have a minimum contiguous area requirement
of 10,000 square feet.
|
|
• Rv is kept constant when calculating WQv.
|
|
• Must be forested or have a stable, natural
ground cover.
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Volume Reduction Method #2: Stream Buffers.
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This reduction can be taken when a stream buffer effectively
treats stormwater runoff. Effective treatment constitutes treating
runoff through overland flow in a naturally vegetated or forested
buffer. Under the proposed method, a designer would be able to subtract
areas draining via overland flow to the buffer from total site area
when computing water quality protection volume requirements. The design
of the stream buffer treatment system must use appropriate methods
for conveying flows above the annual recurrence (one-year storm) event.
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Rule: Subtract areas draining via overland flow to the buffer
from total site area when computing water quality protection volume
requirements.
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Criteria:
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• The minimum undisturbed buffer width shall
be 50 feet from top of bank.
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• The maximum contributing length shall be
150 feet for pervious surfaces and 75 feet for impervious surfaces.
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• The average contributing slope shall be 3%
maximum unless a flow spreader is used. In no case shall the average
contributing slope be greater than 10%.
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• Runoff shall enter the buffer as overland
sheet flow. A flow spreader can be installed to ensure this.
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• Buffers shall remain as naturally vegetated
or forested areas and will require only routine debris removal or
erosion repairs.
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• Rv is kept constant when calculating WQv.
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• Not applicable if overland flow filtration/groundwater
recharge reduction is already being taken.
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Volume Reduction Method #3: Enhanced Swales.
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This reduction may be taken when enhanced swales are used for
water quality protection. Under the proposed method, a designer would
be able to subtract the areas draining to an enhanced swale from total
site area when computing water quality protection volume requirements.
An enhanced swale can fully meet the water quality protection volume
requirements for certain kinds of low-density residential development
(see Volume Reduction Method #5). An added benefit is the post-development
peak discharges will likely be lower due to a longer time of concentration
for the site.
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Rule: Subtract the areas draining to an enhanced swale from
total site area when computing water quality protection volume requirements.
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Criteria:
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• This method is typically only applicable
to moderate- or low-density residential land uses (three dwelling
units per acre maximum).
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• The maximum flow velocity for water quality
design storm shall be less than or equal to 1.0 foot per second.
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• The minimum residence time for the water
quality storm shall be five minutes.
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• The bottom width shall be a maximum of six
feet. If a larger channel is needed, use of a compound cross-section
is required.
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• The side slopes shall be 3:1 (horizontal:
vertical) or flatter.
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• The channel slope shall be 3% or less.
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• Rv is kept constant when calculating WQv.
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Volume Reduction Method # 4: Overland Flow Filtration/Groundwater
Recharge Zones.
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This reduction can be taken when overland flow filtration/infiltration
zones are incorporated into the site design to receive runoff from
rooftops or other small impervious areas (e.g., driveways, small parking
lots, etc.). This can be achieved by grading the site to promote overland
vegetative filtering or by providing infiltration or rain garden areas.
If impervious areas are adequately disconnected, they can be deducted
from total site area when computing the water quality protection volume
requirements. An added benefit will be that the post-development peak
discharges will likely be lower due to a longer time of concentration
for the site.
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Rule: If impervious areas are adequately disconnected, they
can be deducted from total site area when computing the water quality
protection volume requirements.
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Criteria:
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• Relatively permeable soils (hydrologic soil
groups A and B) should be present.
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• Runoff shall not come from a designated hot
spot.
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• The maximum contributing impervious flow
path length shall be 75 feet.
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• Downspouts shall be at least 10 feet away
from the nearest impervious surface to discourage reconnections.
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• The disconnection shall drain continuously
through a vegetated channel, swale, or filter strip to the property
line or structural stormwater control.
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• The length of the disconnection shall be
equal to or greater than the contributing length.
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• The entire vegetative disconnection shall
be on a slope less than or equal to 3%.
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• The surface impervious area tributary to
any one discharge location shall not exceed 5,000 square feet.
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• For those areas draining directly to a buffer,
reduction can be obtained from either overland flow filtration or
stream buffers (See Method #2).
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• Rv is kept constant when calculating WQv.
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Volume Reduction Method #5: Environmentally Sensitive Large
Lot Subdivisions.
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This reduction can be taken when a group of environmental site
design techniques are applied to low- and very-low-density residential
development [e.g., one dwelling unit per two acres (du/ac) or lower].
The use of this method can eliminate the need for structural stormwater
controls to treat water quality protection volume requirements. This
method is targeted towards large lot subdivisions and will likely
have limited application.
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Rule: Targeted towards large lot subdivisions (e.g., two-acre
lots and greater). The requirement for structural facilities to treat
the water quality protection volume may be waived.
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Criteria:
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For single lot development:
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• Total site impervious cover is less than
15%.
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• Lot size shall be at least two acres.
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• Rooftop runoff is disconnected in accordance
with the criteria in Method #4.
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• Grass channels are used to convey runoff
versus curb and gutter. For multiple lots:
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• Total impervious cover footprint shall be
less than 15% of the area.
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• Lot areas should be at least two acres, unless
clustering is implemented. Open space developments should have a minimum
of 25% of the site protected as natural conservation areas and shall
be at least a half-acre average individual lot size.
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• Grass channels should be used to convey runoff
versus curb and gutter (see Method #3).
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• Overland flow filtration/infiltration zones
should be established (see Method #4).
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B.
Stormwater Infiltration Practices.
(1)
In selecting the appropriate infiltration BMPs, the applicant
shall consider the following:
(a)
Permeability and infiltration rate of the site soils.
(b)
Slope and depth to bedrock.
(c)
Seasonal high water table.
(d)
Proximity to building foundations and wellheads.
(e)
Erodibility of soils.
(f)
Land availability and topography.
(g)
Slope stability.
(h)
Effects on nearby properties and structures.
(2)
A detailed soils evaluation of the project site shall be performed
to determine the suitability of infiltration BMPs. The evaluation
shall be performed by a qualified professional, and, at a minimum,
shall address soil permeability, depth to bedrock and slope stability.
The general process for designing the infiltration BMP shall be:
(a)
Analyze hydrologic soil groups as well as natural and man-made
features within the watershed to determine general areas of suitability
for infiltration BMPs.
(b)
Provide field testing data to determine appropriate percolation
rate and/or hydraulic connectivity.
(c)
Design infiltration BMPs for required stormwater volume based
on field determined capacity at the level of the proposed infiltration
surface.
(3)
Soil characteristics, as subject to the specific considerations
below:
(a)
Infiltration BMPs are particularly appropriate in hydrologic
soil groups A and B, as described in the Natural Resources Conservation
Manual TR-55.
(b)
Low-erodibility factors ("K" factors) are preferred for the
construction of basins.
(c)
There must be a minimum depth of 48 inches between the bottom
of any facility and the seasonal high water table and/or bedrock (limiting
zones), except for infiltration BMPs receiving only roof runoff, which
shall be placed in soils having a minimum depth of 24 inches between
the bottom of the facility and the limiting zone.
(d)
There must be an infiltration and/or percolation rate sufficient
to accept the additional stormwater load, and to drain completely
as determined by field tests.
(e)
The infiltration system shall have positive overflow controls
to prevent storage within one foot of the finished surface or grade.
(f)
Infiltration rates shall not be used the computing the storage
volume of the infiltration system.
(g)
Surface inflows shall be designed to prevent direct discharge
of sediment into the infiltration system.
(4)
The recharge volume provided at the site shall be directed to
the most permeable hydrologic soil group available, except where other
considerations apply, such as in limestone geology.
(5)
Any infiltration BMP shall be capable of completely infiltrating
the impounded water within 48 hours. The forty-eight-hour period is
to be measured from the end of the twenty-four-hour design storm.
(7)
During the period of land disturbance, runoff shall be controlled
prior to entering any proposed infiltration area. Areas proposed for
infiltration BMPs shall be protected from sedimentation and compaction
during the construction phase, so as to maintain their maximum infiltration
capacity.
(8)
Infiltration BMPs shall not be constructed nor receive runoff
until the entire contributory drainage area to the infiltration BMP
has received final stabilization.
(9)
Infiltration facilities shall be selected based on suitability
of soils and site conditions. Acceptable infiltration facilities include,
but are not limited to: filter strips or stormwater filtering systems
(for example bioretention facilities, sand filters), open vegetated
channels (that is, dry swales and wet swales), infiltration trenches,
dry wells, infiltration basins, porous paving systems, retention basins,
wet extended detention ponds, riparian corridor management, riparian
forested buffers, rooftop runoff management systems, and sand filters
(closed or open).
(10)
Where sediment transport in the stormwater runoff is anticipated
to reach the infiltration system, appropriate permanent measures to
prevent or collect sediment shall be installed prior to discharge
to the infiltration system.
(11)
All infiltration facilities shall be set back at least 15 feet
from all structures with subgrade elements (e.g., basements, foundation
walls).
(12)
All infiltration facilities that serve more than one lot and
are considered a common facility shall have a drainage easement. The
easement shall provide to the Township the right of access.
(13)
If detailed infiltration study is required, the following guidance
shall be followed:
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Soil evaluations shall be performed to determine the feasibility
and extent to which infiltration systems can be used. The evaluation
shall be performed by a qualified, licensed geologist, geotechnical/civil
engineer or soil scientist and, at a minimum, address soil types,
soil permeability, depth to bedrock, limitations of soils, presence/absence
of carbonate geology susceptibility to subsidence and/or sinkhole
formation and subgrade stability. The testing and evaluation should
be completed at the preliminary design stage.
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Infiltration requirements shall be based on the portions of
the site that are permeable prior to disturbance and the degree to
which development will reduce the permeability of the site. Permeability
of the site shall be determined based on the detailed evaluations
described herein. Use of stormwater management facilities to retain
stormwater for infiltration should be applied to all areas where the
soils evaluation indicates favorable conditions. Areas generally not
favorable for infiltration shall still be provided with an appropriate
water quality practice.
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Soil infiltration tests shall be performed to an equivalent
depth or elevation of the bottom of the proposed infiltration areas.
These tests shall follow the procedures of percolation test holes
as established by the Allegheny County Health Department (ACHD) for
on-lot septic systems. The testing shall include a test pit and percolation
test holes. The test hole shall be excavated to a depth so that the
presence or absence of bedrock and/or seasonal high water table can
be determined. A soil log describing the soils present in each test
pit shall be performed. All test holes used for evaluating the percolation
rate shall be pre-soaked in accordance with the procedures established
by the ACHD. The location and number of test pits and percolation
holes shall be determined based on the type(s) of stormwater management
facilities being designed. Acceptability of infiltration rates shall
be based on sound engineering judgment and recommended design considerations
described in the design manuals listed in the references or other
source material acceptable to the Township Engineer.
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(14)
The following design and construction standards shall be followed
when planning and constructing infiltration BMPs:
(a)
The lowest elevation of the infiltration area shall be at least
two feet above the seasonal high water table and bedrock.
(b)
Where roof drains are designed to discharge to infiltration
facilities, they shall have appropriate measures to prevent clogging
by unwanted debris (for example, silt, leaves and vegetation). Such
measures shall include, but are not limited to, leaf traps, gutter
guards and cleanouts.
(c)
All infiltration facilities shall have appropriate positive
overflow controls to prevent storage within one foot of the finished
surface or grade, unless a specific amount of surface storage away
from pedestrian and vehicular traffic is provided and such areas infiltrate
the stored volume within 48 hours after the end of the twenty-four-hour
design storm.
(d)
All infiltration facilities shall be designed to infiltrate
the stored volume within 48 hours after the end of the twenty-four-hour
design storm.
(e)
All surface inflows shall be treated to prevent the direct discharge
of sediment into the infiltration practice; accumulated sediment reduces
stormwater storage capacity and ultimately clogs the infiltration
mechanism. No sand, salt or other particulate matter may be applied
to a porous (pervious) surface for winter ice conditions.
(f)
During site construction, all infiltration practice components
shall be protected from compaction due to heavy equipment operation
or storage of fill or construction material. Infiltration areas shall
also be protected from sedimentation. Areas that are accidentally
compacted or graded shall be remediated to restore soil composition
and porosity. Adequate documentation to this effect shall be submitted
for review by the Township Engineer. All areas designated for infiltration
shall not receive runoff until the contributory drainage area has
achieved final stabilization.
(g)
The following procedures and materials shall be required during
the construction of all subsurface facilities:
1)
Excavation for the infiltration facility shall be performed
with equipment that will not compact the bottom of the seepage bed/trench
or like facility.
2)
The bottom of the bed and/or trench shall be scarified prior
to the placement of aggregate.
3)
Only clean aggregate with documented porosity, free of fines,
shall be allowed.
4)
The tops and sides of all seepage beds, trenches, or like facilities
shall be covered with drainage fabric. Fabric shall meet the specifications
of PennDOT Publication 408, § 735, Construction Class 1.
5)
Perforated distribution pipes connected to centralized catch
basins and/or manholes with the provision for the collection of debris
shall be provided in all facilities. Where perforated pipes are used
to distribute stormwater to the infiltration practice, stormwater
shall be distributed uniformly throughout the entire seepage bed/trench
or like facility.
C.
Open Vegetated Channels.
(1)
Open vegetated channels are conveyance systems that are engineered
to also perform as water quality and infiltration facilities. Such
systems can be used for the conveyance, retention, infiltration and
filtration of stormwater runoff.
(2)
Open vegetated channels primarily serve a water quality function
(WQv); they also have the potential to augment infiltration. Examples
of such systems include, but are not limited to: dry swales, wet swales,
grass channels, and biofilters. Open vegetated channels are primarily
applicable for land uses such as roads, highways, residential developments
(dry swales only) and pervious areas.
(3)
Open vegetated channels shall be designed to meet the following
minimum standards:
(a)
The channel shall be designed to safely convey the ten-year
frequency storm event with a freeboard of at least 12 inches. Freeboard
is the difference between the elevation of the design flow in the
channel and the top elevation of the channel.
(b)
The peak velocity of the runoff from the ten-year storm shall
be nonerosive for the soil and ground cover provided in the channel.
(c)
The longitudinal slope shall be no greater than 4%.
(d)
Channels shall be trapezoidal in cross-section.
(e)
Channels shall be designed with moderate side slopes of four
horizontal to one vertical. Flatter side slopes may be necessary under
certain circumstances.
(f)
The maximum allowable ponding time in the channel shall be less
than 48 hours.
(g)
Channels (for example, dry swales) may require an underdrain
in order to function and dewater.
(h)
Channels shall be designed to temporarily store the WQv within
the system for a maximum period of 48 hours and a minimum period of
one hour.
(i)
Landscape specifications shall address the grass species, wetland
plantings (if applicable), soil amendment and hydric conditions present
along the channel.
(j)
Accumulated sediment within the channel bottom shall be removed
when 25% of the original WQv volume has been exceeded. The channel
shall be provided with a permanent concrete cleanout marker that indicates
the 25% loss level.
(k)
Check dams along the channel length may be warranted.
(l)
The bottom of dry swales shall be situated at least two feet
above the seasonal high water table.
(4)
Additional design information for open vegetated channels is
available in Design of Roadside Channels with Flexible Linings, HEC
15, FHWA, September 2005.
D.
Retention Basins.
(1)
Retention basins shall be designed to create a healthy ecological community with sufficient circulation of water to prevent the growth of unwanted vegetation and mosquitoes or other vectors. If circulation cannot be provided via natural means, then artificial aeration and circulation shall be provided. Care shall be taken to landscape retention basins in accordance with Subsection 4.
(2)
The retention basin shall be of sufficient size to allow the
appropriate aquatic community needed to maintain healthy pond ecology
and avoid mosquitoes capable of carrying West Nile virus and other
diseases. The Allegheny County Health Department, Pennsylvania Fish
and Boat Commission, the Natural Resource Conservation Service, the
Pennsylvania Extension Service, or other qualified professional consultant
shall be consulted during the design of these facilities in order
to ensure the health of aquatic communities and minimize the risk
of creating mosquito breeding areas.
(3)
An outlet structure shall be designed to allow complete drainage
of the pond for maintenance.
(4)
The design of a retention basin shall include the determination
of the proposed site's ability to support a viable permanent
pool. The design shall take into account such factors as the available
and required rate and quality of dry weather inflow, the stormwater
inflow, seasonal and longer-term variations in groundwater table,
and impacts of potential pollutant loadings.
(5)
Sediment storage volume equal to at least 20% of the volume
of the permanent pool shall be provided.
(6)
A sediment forebay with a hardened bottom shall be provided
at each inlet into the retention basin. The forebay storage capacity
shall at minimum be 10% of the permanent pool storage. The forebay
shall be designed to allow for access by maintenance equipment for
periodic cleaning. A permanent concrete cleanout maker shall be installed
in the forebay to indicate the level where 25% for the forebay storage
has been used.
(7)
Emergency spillways shall be sized and located to permit the
safe passage of stormwater flows from an unattenuated 100-year post-development
storm with one foot of freeboard. The maximum velocities in vegetated
spillways excavated in otherwise undisturbed soil shall be analyzed
based upon the velocity of peak flow in the emergency spillway during
an assumed clogged primary outlet condition. Where maximum velocities
exceed design standards contained in the Engineering Field Manual
for Conservation Practices (USDA, SCS, July 1984) suitable lining
shall be provided. All emergency spillways placed on fill materials
shall be lined. Lining for emergency spillways shall incorporate native
colors and materials where possible, including mono slab revetments,
grass pavers, riprap and native stone.
(8)
Basin and pond embankments must be designed by a professional
engineer registered in the State of Pennsylvania. The design must
include an investigation of the subsurface conditions at the proposed
embankment location to evaluate settlement potential, groundwater
impacts, and the need for seepage controls. The submittal of a geotechnical
report from a geotechnical engineer for any embankment over 10 feet
in effective height or posing a significant hazard to downstream property
or life is required. The selection of fill materials must be subject
to approval of the design engineer. Fill must be free of frozen soil,
rocks over six inches, sod, brush, stumps, tree roots, wood, or other
perishable materials. Embankment fills less than 10 feet in fill height
must be compacted using compaction methods that would reasonably guarantee
that the fill density is at least 90% of the maximum density as determined
by standard proctor (ASTM-698). All embankment fills more than 10
feet in fill height must be compacted to at least 90% of the maximum
density as determined by standard proctor (ASTM-698) and must have
their density verified by field density testing. A PA DEP dam permit
is required for embankments having a maximum depth of water, measured
from the upstream toe of the dam to the top of the dam at maximum
storage elevation, of greater than 15 feet; and/or for ponds having
contributory drainage area of greater than 100 acres; and/or for impoundments
of greater than 50 acre-feet.
(9)
The embankment's interior slope may not be steeper than
three horizontal to one vertical. The exterior slope of the embankment
may not exceed two horizontal to one vertical.
(10)
The minimum embankment width shall be four feet for embankments
less than six feet in height, six feet if the embankment is between
6.1 feet and 9.9 feet in height and eight feet if the embankment is
between 10 feet and 15 feet in height.
(11)
Existing ponds or permanent pool basins can be used for stormwater
management, provided that it can be demonstrated that the ponds are
structurally sound and meet the design requirements herein.
(12)
Inlet structures and outlet structures shall be separated to
the greatest extent possible in order to maximize the flow path through
the retention basin.
(13)
Retention basins shall be designed to provide a length-to-width
ratio of at least 3L:1W as measured in plan view (for example, a ratio
of 4L:1W is too narrow).
(14)
The retention basin depth shall average three feet to six feet.
(15)
Fencing of the facility is not required if the interior slope
of the pond is 4H:1V or flatter and the design also includes a five-foot-wide
bench around the pond perimeter at an elevation one foot below the
permanent water surface elevation.
(16)
Any side slopes below the permanent water surface level shall
not exceed 3H:1V. Interior side slopes above the permanent water surface
level shall not exceed 3H:1V.
(17)
Stabilization. Proper stabilization structures, including stilling
basins, energy dissipators, and channel lining, shall be constructed
at the outlets of all retention basins and emergency spillways. The
stabilization structures shall control water to: avoid erosion; reduce
velocities of released water; and direct water so that it does not
interfere with downstream activities.
(18)
Energy dissipators and/or level spreaders shall be installed
to prevent erosion and/or initiate sheet flow at points where pipes
or drainageways discharge to or from basins. Level spreaders shall
be used only where the maximum slope between the discharge point and
the waterway does not exceed 5%. Energy dissipators shall comply with
criteria in Hydraulic Design of Energy Dissipators for Culverts and
Channels, HEC 14, FHWA, July, 2006. Such facilities shall be both
functional and harmonious with the surrounding environment; for example,
native rock shall be used in constructing dissipators where practical.
(19)
Discharge Points. The minimum distance between a proposed basin
discharge point (including the energy dissipator, etc.) and a downstream
property boundary shall in no case be less than 15 feet. Where there
is discharge onto or through adjacent properties prior to release
to a stream, designers shall demonstrate how downstream properties
are to be protected. The Township Engineer may require that the setback
distance be increased based upon factors such as topography, soil
conditions, the size of structures, the location of structures, and
discharge rates. A drainage easement may also be required.
(20)
Outlet Structures. Outlet structures shall meet the following
specifications:
(a)
To minimize clogging and to facilitate cleaning and inspecting,
outlet pipes shall have an internal diameter of at least 15 inches
and a minimum grade of 1%.
(b)
Bentonite plugs shall be provided on all outlet pipes within
a constructed berm.
(c)
All principal outlet structures shall be built using reinforced
concrete with watertight construction joints.
(d)
The use of architecturally treated concrete, stucco, painted
surface or stone facade treatment shall be considered for enhancing
the outlet structure. Such facilities shall be both functional and
harmonious in design with the surrounding environment.
(e)
Outlet pipes shall be constructed of reinforced concrete with
rubber gaskets in conformance with AASHTO M170, M198 and M207, or
smooth interior HDPE pipe in conformance with AASHTO M252 or M294.
(f)
Basin outlet structures shall have childproof nonclogging trash
racks over all design openings exceeding 12 inches in diameter except
those openings designed to carry perennial stream flows. Periodic
cleaning of debris from trash racks shall be included in the operation
and maintenance plan.
(g)
Anti-vortex devices, consisting of a thin vertical plate normal
to the basin berm, shall be provided at the top of all circular risers
or standpipes.
E.
Detention Basins.
(2)
The maximum inside side slopes shall not exceed three horizontal to one vertical (3H:1V). The minimum required slope for the basin bottom is 2%. A level bottom is acceptable, provided the designer demonstrates to the Township's satisfaction that the basin bottom will be landscaped with appropriate wetland vegetation pursuant to Subsection 3D. In addition, detention basins of sufficient size and slope may serve other functions as well, including recreational uses which do not hinder or conflict with the function of the detention basin.
(3)
Inlet Structures. The inlet pipe invert into a basin shall be
six inches above the basin floor or lining so that the pipe can adequately
drain after rainstorms. Inlets shall discharge into areas of the basin
that slope toward the outlet structure.
(4)
Inlet structures and outlet structures shall be separated to
the greatest extent possible in order to maximize the flow path through
the retention basin.
(5)
Low Flow Channels. Low flow channels constructed of concrete
or asphalt are not permitted. Where low flow channels are necessary,
they shall be composed of a natural or bioengineered material. Low
flow channels shall be designed to promote water quality and slow
the rate of flow through the basin. Low flow channels may also be
designed to infiltrate where practical.
(6)
Outlet Structures. Outlet structures shall meet the following
specifications:
(a)
To minimize clogging and to facilitate cleaning and inspection,
outlet pipes shall have an internal diameter of at least 15 inches
and a minimum grade of 1%.
(b)
Bentonite plugs shall be provided on all outlet pipes within
a constructed berm.
(c)
All principal outlet structures shall be built using reinforced
concrete with watertight construction joints.
(d)
The use of architecturally treated concrete, stucco, painted
surface or stone facade treatment shall be considered for enhancing
the outlet structure. Such facilities shall be both functional and
harmonious in design with the surrounding environment.
(e)
Outlet pipes shall be constructed of reinforced concrete with
rubber gaskets in conformance with AASHTO M170, M198 and M207, or
smooth interior HDPE pipe in conformance with AASHTO M252 or M294.
(f)
Energy dissipation facilities that convert concentrated flow
to uniform shallow sheet flow shall be used where appropriate.
(g)
Basin outlet structures shall have childproof nonclogging trash
racks over all design openings exceeding 12 inches in diameter except
those openings designed to carry perennial stream flows.
(h)
Anti-vortex devices, consisting of a thin vertical plate normal
to the basin berm, shall be provided at the top of all circular risers
or standpipes.
(7)
Emergency spillways shall be sized and located to permit the
safe passage of stormwater flows from an unattenuated 100-year post-development
storm with one foot of freeboard. The maximum velocities in vegetated
spillways excavated in otherwise undisturbed soil shall be analyzed
based upon the velocity of peak flow in the emergency spillway during
an assumed clogged primary outlet condition. Where maximum velocities
exceed design standards contained in the Engineering Field Manual
for Conservation Practices (USDA, SCS, July 1984), suitable lining
shall be provided. In general, emergency spillways should not be located
in fill areas; all such facilities placed on fill materials shall
be lined. Lining for emergency spillways shall incorporate native
colors and materials where possible, including mono slab revetments,
grass pavers, riprap and native stone.
(8)
Basin and pond embankments must be designed by a professional
engineer registered in the State of Pennsylvania. The design must
include an investigation of the subsurface conditions at the proposed
embankment location to evaluate settlement potential, groundwater
impacts, and the need for seepage controls. The submittal of a geotechnical
report from a geotechnical engineer for any embankment over 10 feet
in effective height or posing a significant hazard to downstream property
or life is required. The selection of fill materials must be subject
to approval of the design engineer. Fill must be free of frozen soil,
rocks over six inches, sod, brush, stumps, tree roots, wood, or other
perishable materials. Embankment fills less than 10 feet in fill height
must be compacted using compaction methods that would reasonably guarantee
that the fill density is at least 90% of the maximum density as determined
by standard proctor (ASTM-698). All embankment fills more than 10
feet in fill height must be compacted to at least 90% of the maximum
density as determined by standard proctor (ASTM-698) and must have
their density verified by field density testing. A PA DEP dam permit
is required for embankments having a maximum depth of water, measured
from the upstream toe of the dam to the top of the dam at maximum
storage elevation, of greater than 15 feet; and/or for ponds having
contributory drainage area of greater than 100 acres; and/or for impoundments
of greater than 50 acre-feet.
(9)
The embankment's interior slope may not be steeper than
3:1 (three horizontal to one vertical). The exterior slope of the
embankment may not exceed 2:1 (two horizontal to one vertical).
(10)
The minimum embankment width shall be four feet for embankments
less than six feet in height, six feet if the embankment is between
6.1 feet and 9.9 feet in height and eight feet if the embankment is
between 10 feet and 15 feet in height.
(11)
Fencing of the facility is not required if the interior slope
of the pond is 4:1 or flatter.
(12)
Freeboard. Freeboard is the difference between the elevation
of the design flow in the emergency spillway (usually the 100-year
peak elevation) and the top elevation of the settled basin embankment
(that is, top of berm). The minimum freeboard shall be one foot.
(13)
Energy dissipators and/or level spreaders shall be installed
to prevent erosion and/or initiate sheet flow at points where pipes
or drainageways discharge to or from basins. Level spreaders shall
be used only where the maximum slope between the discharge point and
the waterway does not exceed 5%. Energy dissipators shall comply with
criteria in Hydraulic Design of Energy Dissipators for Culverts and
Channels, HEC 14, FHWA, July, 2006. Such facilities shall be both
functional and attractive; for example, native rock shall be used
in constructing dissipators where practical.
(14)
Stabilization. Proper stabilization structures, including stilling
basins, energy dissipators, and channel lining, shall be constructed
at the outlets of all basins and emergency spillways. The stabilization
structures shall control water to avoid erosion, reduce velocities
of released water and direct water so that it does not interfere with
downstream activities.
(15)
Discharge Points. The minimum distance between a proposed basin
discharge point (including the energy dissipator, etc.) and a downstream
property boundary shall in no case be less than 15 feet. Where there
is discharge onto or through adjacent properties prior to release
to a stream, designers shall demonstrate how downstream properties
are to be protected. The Township Engineer may require that the setback
distance be increased based upon factors such as topography, soil
conditions, the size of structures, the location of structures, and
discharge rates. A drainage easement may also be required.
(16)
A sediment forebay with a hardened bottom shall be provided
at each inlet into the detention basin. The forebay storage capacity
shall at minimum be 10% of the permanent pool storage. The forebay
shall be designed to allow for access by maintenance equipment for
periodic cleaning.
F.
Conveyance Systems (Open Channels, Drainageways, and Storm Sewers).
(1)
Applicants are encouraged to design conveyance systems that
encourage infiltration and improve water quality wherever practicable.
(2)
Wherever conveyance channels are necessary, drainage shall be
maintained by an open channel with landscaped banks designed to carry
the ten-year, twenty-four-hour stormwater runoff from upstream contributory
areas. The Township Engineer may increase the design storm, as conditions
require. All open channels shall be designed with one foot of freeboard
above the design water surface elevation of the design runoff condition.
(3)
Flood relief channels shall be provided and designed to convey
the runoff from the 100-year, twenty-four-hour storm, such that a
positive discharge of this runoff to an adequate receiving stream
or conveyance system occurs without allowing this runoff to encroach
upon other properties.
(4)
Manholes and/or inlets shall not be spaced more than 300 feet
apart for pipe sizes up to 24 inches in diameter and not more than
450 feet apart for larger pipe sizes.
(5)
Where drainage swales are used in lieu of or in addition to storm sewers, they shall be designed to carry the required runoff without erosion and in a manner not detrimental to the properties they cross. Drainage swales shall provide a minimum grade of 2% but shall not exceed a grade of 9%. Drainage swales used strictly for conveyance are not the same as open vegetated channels. Design standards for open vegetated channels are provided under Subsection 3C(3) of this section.
(6)
Street curbing for the purpose of stormwater conveyance is discouraged.
On streets that must contain curbing, storm sewers shall be placed
in front of the curbing. To the greatest extent possible, storm sewers
shall not be placed directly under curbing. At curbed street intersections,
storm inlets shall be placed in the tangent section of the road.
(7)
Use of grassed swales or open vegetated swales in lieu of curbing
to convey, infiltrate and/or treat stormwater runoff from roadways
is encouraged. Inlets shall be placed at the center of the shoulder
swale draining the street and shall be located no closer than four
feet from the edge of the cartway.
(8)
When requested by the Township, the developers shall obtain
or grant a minimum twenty-foot-wide drainage easement over all storm
sewers, drainage swales, channels, etc., that are a component of the
stormwater management system when located within undedicated land.
All permanent detention basins and/or other stormwater management
facilities providing stormwater control for other than a single residential
lot shall be located within a defined drainage easement that allows
proper legal access and maintenance vehicle access.
(9)
No property owner shall obstruct or alter the flow, location
or carrying capacity of a stream, channel or drainage swale to the
detriment of any other property owner, whether upstream or downstream.
All subdivision and/or land development plans containing streams,
channels, drainage swales, storm sewers or other conveyance systems
that cross property boundaries, existing or proposed, or whose discharge
crosses such boundaries shall contain a note stating the above.
(10)
Water Quality Inlets. Storm drainage systems that collect runoff
from parking areas and/or loading areas exceeding 10,000 square feet
of impervious coverage and discharge to stormwater management systems,
including surface or subsurface infiltration systems, shall have a
minimum of one water quality inlet per each acre of drainage area.
The purpose of water quality inlets is to remove oil, grease, and
heavy particulates or total suspended solids, hydrocarbons and other
floating substances from stormwater runoff. Methods other than water
quality inlets may be permitted if the applicant demonstrates to the
Township's satisfaction that any such alternative will be as
effective and as easily maintained. Periodic cleaning of these systems
shall be addressed in the operation and maintenance plan submitted
to the Township.
4.
Landscaping of Stormwater Management Facilities. Stormwater management
facilities shall be landscaped in accordance with the following standards:
A.
Landscaping shall be required in and around all constructed stormwater
management facilities with a minimum surface area of 1,000 square
feet for the purposes of:
B.
A planting plan and planting schedule shall be submitted in accordance
with the following:
(1)
Wet Meadows, Including Floors of Stormwater Management Facilities.
(a)
Wet meadows and floors of stormwater management facilities shall
be planted with noninvasive plants native to western Pennsylvania,
such as wildflowers and noninvasive grasses, the intent being to create
a mixed meadow of such plantings, where appropriate. Selection of
plantings shall be based on whether the area in question is usually
well drained or permanently wet and whether the area will be used
for recreation purposes. No woody plants shall be planted within the
saturated zone (phreatic line) of a stormwater management practice
or on a berm constructed for impounded water.
(b)
Seeding by drills, corrugated rollers, cyclone or drop seeders
or hand seeding of such areas is preferred; however, hydroseeding
followed by hydromulching can be used on wet ground and steep slopes.
(c)
Fertilizers, as a nutrient supplement, shall not be used unless
it is documented that soil conditions warrant such use and nutrient
applied does not exceed plant uptake. Soil for planting of wildflowers
shall contain not less than 3% or more than 10% organic matter, as
determined by an agricultural chemist, with certification of the test
before planting.
(d)
Seeding shall take place either between April 1 and May 15 or
between September 1 and October 15. Planting areas shall be soaked
to maintain a consistent level of moisture for at least four to six
weeks after planting. For seeding recommendations, reference the DEP's
E&S Pollution Control Program Manual.
(e)
Once established, a single annual mowing when plants are dormant
should be sufficient to maintain a wet meadow and/or floor of a stormwater
management practice.
(2)
Wet edges that remain wet all or most of the year shall be planted
with wildflowers, grasses and shrubs. Plants to be located on rims
or banks, which remain dry most of the year, shall be planted with
species tolerant of dry soil conditions.
(3)
Wooded Areas.
(a)
Where stormwater management facilities adjoin wooded areas,
trees and shrubs shall be selected and planted outside the practice
so as to blend with existing surroundings.
(b)
Plantings in such areas shall be of sufficient density to eliminate
the need for mowing.
(c)
It is recommended that clusters of trees and shrubs be planted
around stormwater management facilities but well away from outfalls
and any constructed berms, where applicable, to provide for wildlife
habitat, wind control and buffering and screening.
(d)
Vegetation shall be planted during appropriate times of the
year, predominantly between late March and mid-May or from early October
until evidence of ground freezing, depending upon the species selected.
Most deciduous trees and shrubs can be planted in either spring or
fall. Evergreens are best planted in late summer or early fall.
(4)
Slopes.
(a)
Where slopes are gentle, a mixture of meadow grasses and wildflowers
(for wet meadows) shall be planted.
(b)
On steep slopes as defined by the Township's Code of Ordinances,
dense spreading shrubs (shrubs tolerant of dry soils) shall be planted.
Heavy mat mulch shall be used during the period of establishment.
(c)
No woody plant materials or trees shall be located on a constructed
or natural berm acting as the impoundment structure of a stormwater
management practice. Trees shall be located downstream of an impoundment
berm a sufficient distance from the toe of the constructed slope to
assure that the toe of the slope is outside the dripline of the species
planted at maturity but in no case less than 15 feet.
(5)
In cases where stormwater management facilities are to be located
in proximity to wetlands or waterways, the applicant's planting
plan and schedule shall consider the sensitive conditions existing
therein and be modified accordingly to reflect existing flora.
(6)
Stormwater management facilities shall be screened in a manner
which complements the existing landscape and provides sufficient access
for maintenance.
5.
Stream Buffer Requirements. Stream buffers shall be provided for
new development sites as per the following requirements:
A.
In order to protect and improve water quality, a riparian buffer
easement shall be created and recorded as part of any subdivision
or land development that encompasses a riparian buffer. The intent
of this Part in establishing a riparian buffer is to protect and improve
stream water quality. The riparian buffer is intended to slow overland
flow to the stream through the presence of native grasses, trees and
shrubs, following infiltration groundwater recharge, causing deposition
of sediment, nutrients, pesticides, and other pollutants in the buffer
rather than in the stream and reducing erosion by providing stream
bank stabilization. The trees provide shade for streams, keeping waters
cooler and reducing evaporation. Except as required by Pa. Code Title
25, Chapter 102, the riparian buffer easement shall be required for
all stream (as defined in Article II) with a contributing watershed
area of greater than 10 acres. The riparian buffer easement shall
be measured to be a minimum of 35 feet from the top of the stream
bank (on each side).
B.
Minimum Management Requirements for Riparian Buffers.
C.
No use or construction within the riparian buffer shall be permitted that is inconsistent with the intent of the riparian buffer as described in Subsection 5A.
D.
Existing native vegetation shall be protected and maintained within
the riparian buffer easement.
E.
Whenever practicable, invasive vegetation shall be actively removed
and the riparian buffer easement shall be planted with native trees,
shrubs and other vegetation to create a diverse native plant community
appropriate to the intended ecological context of the site.
F.
The riparian buffer easement shall be enforceable by the Township
and shall be recorded in the appropriate County Recorder of Deeds
office, so that it shall run with the land and shall limit the use
of the property located therein. The easement shall allow for the
continued private ownership and shall count toward the minimum lot
area required by zoning, unless otherwise specified in the Township
Zoning Ordinance.[1]
G.
Any permitted use within the riparian buffer easement shall be conducted
in a manner that will maintain the extent of the existing 100-year
floodplain, improve or maintain the stream stability, and preserve
and protect the ecological function of the floodplain.
H.
Stormwater drainage pipes shall be permitted within the riparian
buffer easement, but they shall cross the easement in the shortest
practical distance. Other structural stormwater management facilities
are not permitted within the riparian buffer easement.
I.
The following conditions shall apply when public and/or private recreation
trails are permitted by the Township within riparian buffers.
(1)
It is preferred that trails be designed to be permeable and
for nonmotorized use only; however, impermeable trails are permitted,
provided they have adequate drainage.
J.
Septic drainfields and sewage disposal systems shall not be permitted
within the riparian buffer easement and shall comply with setback
requirements established under 25 Pa. Code Chapter 73.
K.
Underground utilities shall be permitted within the riparian buffer
easement; however, work shall be performed to minimize disturbance
area and removal of trees. Restoration within the riparian buffer
easement shall be with native species of trees, grasses, and other
plantings. One tree shall be planted for each tree removed, and the
restoration shall be designed by a registered professional with the
requisite experience. Aboveground utilities shall only be permitted
to cross the easement perpendicular to the easement or in the shortest
practical distance. Existing utilities may remain and be maintained
as required.
[Ord. No. 2425, 12/3/2018]
1.
General Responsibilities.
A.
The owner of stormwater management facilities shall be responsible for the proper operation and maintenance of those facilities during and after construction. An operation and maintenance plan consistent with the requirements of Subsection 3 shall be prepared for review and approval by the Township Engineer and shall be executed and signed by the Township Engineer and applicant.
B.
The owner of the stormwater management facilities for a tract shall
be responsible for the proper installation and function of those facilities
in accordance with the approved stormwater management plan. All temporary
soil erosion and sedimentation control measures shall be removed or
converted to their permanent configuration in accordance with an approved
erosion control plan. This requirement in no way precludes the authority
of the Allegheny County Conservation District to determine when sufficient
stabilization has occurred on a site in order to convert to the permanent
stormwater management facilities.
C.
Dedication and Acceptance of Stormwater Management Facilities.
(1)
Upon completion of construction of stormwater management facilities
shown on an approved subdivision or land development plan and within
90 days after approval of such construction, the applicant shall submit
a written offer of such stormwater management facilities for dedication
to the Township. Said offer shall include a deed of dedication covering
said facilities together with satisfactory proof establishing an applicant's
clear title to said property. Such documents are to be filed with
the Township Secretary for review by the Township Solicitor. Deeds
of dedication for stormwater management facilities may be accepted
by resolution of the Township at a regular meeting thereof.
(2)
The Township may require that stormwater management facilities
remain undedicated, with operation and maintenance the responsibility
of individual lot owners or a homeowners' association or similar entity,
or an organization capable of carrying out maintenance responsibilities.
(3)
Regardless of ownership, the applicant shall submit a written offer deeding an access and/or drainage easement to the Township pursuant to Subsection 2. Such easement shall cover the stormwater management facilities and any drainage to and from such facilities, and shall clearly permit the Township entry for inspection and/or maintenance purposes.
(4)
Regardless of ownership, the applicant shall submit an actual
as-built plan to the Township for the stormwater management facilities
required per the approved stormwater management plan. The as-built
plan shall show all final design specifications for all permanent
stormwater management facilities, including, but not limited to, pipe
material and diameter, inlet, outlet and overflow elevations, two-foot
contours for all detention/retention basins and drainage swales and
a comparison of as-built capacities compared to the capacities of
the approved design facilities and shall be prepared and certified
by a licensed professional engineer. The as-built plan shall be based
on an actual field survey performed by a licensed professional land
surveyor. The surveyor shall certify as to the accuracy of the plan.
The as-built plan shall be submitted to the Township for review by
the Township Engineer. Any performance and/or financial securities
established for the project shall include requirements for submittal
of as-built plans.
(5)
The as-built plan(s) shall be submitted to the Township in a
digital format or formats approved by the Township.
2.
Ownership and Maintenance. All stormwater management facilities identified
within an approved stormwater management plan shall be owned and maintained
by one, or a combination of, the following entities:
A.
Private Ownership.
(1)
Where individual on-lot stormwater management facilities are
proposed, the subdivision and/or land development plan shall contain
a note in a form satisfactory to the Township Solicitor designating
the entity responsible for operation and maintenance of the on-lot
facilities consistent with an approved operation and maintenance plan
and, in the event that the responsible person or entity fails to do
so, granting to the Township the right but not the duty to enter upon
the premises to repair or restore said facilities, to charge and assess
the costs thereof to the owner, including a reasonable allowance for
overhead, and to enforce said charges and assessments by lien upon
the property. In addition, the deed for each lot shall contain a perpetual
covenant binding the grantee and all successors in interest, designating
the responsibility for operation and maintenance of the on-lot facilities
essentially in the following form:
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"Under and subject, nevertheless, to the following conditions
and restrictions: Prior to any Earth Disturbance for which stormwater
management facilities are required by the Township, Grantee shall
construct the permanent stormwater management facilities as shown
on the stormwater management plan (the "Plan") prepared by <NAME>,
P.E., dated <DATE> and last revised <DATE> and approved by Township;
thereafter, the Grantee, his heirs, executors, administrators, successors
and assigns ("Owner"), at his sole cost and expense, shall operate,
maintain and repair said stormwater management facilities on the lot
in accordance with said plan, so that the facilities shall at all
times continue to operate and function in the same manner and capacity
as they were designed. In the event of the failure of the owner to
comply with these conditions and restrictions, Township shall have
said stormwater management facilities repaired or restored as required,
and the costs thereof plus a reasonable allowance for overhead shall
be assessed to the owner; said assessment shall be a charge and a
continuing lien upon the property herein. The Township, before it
may exercise this right, shall notify the owner by certified mail
of its intention to take the aforesaid action. The notice shall set
forth in what manner the owner has neglected the operation and maintenance
of or repair to the stormwater management facilities, and if the owner
fails, within a period of 90 calendar days, to correct or repair the
items listed in the notice from the Township, then and only then,
may the Township exercise this right."
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(2)
In addition to the above, developers of parcels with more than
one dwelling unit shall record in the office of Recorder of Deeds
for Allegheny County a declaration of covenants and restrictions in
a form satisfactory to the Township Solicitor describing the responsibility
for operation and maintenance of the on-lot facilities, consistent
with an approved operation and maintenance plan, prior to the sale
of any individual lots. The terms of this covenant and restriction
shall run with the land and be binding upon the initial grantees of
each lot within the subdivision, his, her or their heirs, administrators,
successors or assigns.
B.
Homeowners' or Condominium Association Ownership. Where a homeowners'
association is created to own and manage common facilities, the subdivision
and/or land development plan shall contain a note in a form satisfactory
to the Township Solicitor designating the entity responsible for construction
and/or maintenance of the stormwater management facilities consistent
with an approved operation and maintenance plan and, in the event
that the responsible entity fails to do so, granting to the Township
the right but not the duty to enter upon the premises to repair or
restore said facilities, to charge and assess the costs thereof plus
a reasonable allowance for overhead to each owner of property within
the development and to enforce said charges and assessments by lien
upon each property within the development. In addition, the developer
shall record in the office of Recorder of Deeds for Allegheny County
a declaration of covenants in a form satisfactory to the Township
Solicitor setting forth the rights and responsibilities of the homeowners'
association for operation and maintenance of the stormwater management
facilities, prior to the sale of individual lots. The terms of this
covenant and restriction shall run with the land and be binding upon
the initial grantees of each lot within the subdivision, his, her
or their heirs, administrators, successors and assigns.
C.
Township Ownership. Where the Township has accepted an offer of dedication
of the permanent stormwater management facilities, the Township shall
be responsible for operation and maintenance. Township ownership notwithstanding,
the applicant is required to prepare a stormwater management plan
and an operation and maintenance plan, as defined herein. Upon approval
of the stormwater management facilities by the Township, the applicant
shall provide a lump sum long-term maintenance payment to the Township,
to be reserved and used at all times by the Township only for costs
of operation and maintenance of the dedicated facilities, as follows:
(1)
Long-Term Maintenance Payment. The long-term maintenance payment
shall be in an amount equal to the present value of operation and
maintenance costs for the facilities for a ten-year period. The long-term
maintenance payment shall be based on a ten-year cost estimate prepared
by the applicant's engineer and reviewed and approved by the
Township Engineer. The amount of the payment shall include all costs
of operation and maintenance, which shall include, but not be limited
to, typical operation and maintenance costs as well as costs such
as landscaping and planting, tax payments required and construction
of any kind associated with the use, benefit and enjoyment of the
facilities by the owners. In particular, a description of routine
facility operation and day-to-day management requirements and a description
of projected maintenance actions and schedules necessary to ensure
proper operation of stormwater management facilities shall be submitted
for review and approval to the Township Engineer.
(2)
Documentation. The terms of the long-term maintenance payment
shall be documented as part of the stormwater management plan and
the operation and maintenance plan.
3.
Operation and Maintenance Plan. An operation and maintenance plan
shall be prepared by an engineer licensed to practice in the Commonwealth
of Pennsylvania that identifies the ownership, operation and maintenance
responsibilities and as-built conditions for all stormwater management
facilities. At a minimum, the operation and maintenance plan shall
include the following:
A.
Any obligations concerning perpetuation and/or maintenance of natural
drainage or infiltration facilities, and other facilities identified
within the stormwater management plan. Ownership of and responsibility
for operation and maintenance of stormwater management facilities,
including names and contact information, shall be required.
B.
A description of the permanent stormwater management facilities on
the site, explaining how each facility is intended to function and
operate over time. All drainage and access easements shall be depicted,
and any site restrictions to be recorded against the property shall
be identified on the recorded plan. All such easements and restrictions
shall be perfected to run with the land and be binding upon the landowner
and any successors in interest.
C.
A description of the actions, budget and schedule for operating and
maintaining the stormwater management facilities. This description
should be written in a clear manner, consistent with the knowledge
and understanding of the intended user.
D.
A general description of operation and maintenance activities and
responsibilities for facilities held in common or on lot, including,
but not limited to, lawn care, vegetation maintenance, cleanout of
accumulated debris and sediment (including from grates, trash racks,
inlets, etc.), liability insurance, maintenance and repair of stormwater
management facilities, landscaping and planting, payment of taxes
and construction of any kind associated with the use, benefit and
enjoyment of the facilities by the owners. In particular, a description
of routine facility operation and day-to-day management requirements
(as needed) and a description of routine maintenance actions and schedules
necessary to ensure proper operation of stormwater management facilities
shall be submitted.
E.
Assurances that no action will be taken by any lot owner to disrupt
or in any way impair the effectiveness of any stormwater management
system, setting forth in deed restrictions the ability of the Township
to take corrective measures if it is determined at any time that stipulated
permanent stormwater management facilities have been eliminated, altered,
or improperly maintained, including the ability of the Township to
cause the work to be done, and lien all costs plus a reasonable overhead
allowance against the property should the required corrective measures
not be taken by the lot owner, following written notification, within
a period of time set by Township Engineer.
F.
Parties responsible for the long-term operation and maintenance of
stormwater management facilities shall make records of the installation
and of all maintenance and repairs, and shall retain the records for
at least 10 years. These records shall be submitted to the Township
as established by the operation and maintenance plan or if otherwise
required by the Township.
4.
Operations and Maintenance Agreement.
A.
The owner of any land upon which permanent stormwater management
facilities and/or BMPs will be placed, constructed or implemented,
as described in an approved stormwater management plan and the operations
and maintenance plan, shall record the following documents in the
office of the Recorder of Deeds for Allegheny County within 15 days
of approval of the operations and maintenance plan by the Township:
B.
The operations and maintenance agreement shall be substantially the
same as the sample agreement in Appendix 23-C of this Part.
C.
Other items or conditions may be included in the operation and maintenance
agreement where determined necessary to guarantee the satisfactory
operation and maintenance of all permanent stormwater facilities and
BMPs. The agreement shall be subject to the review and approval of
the Township.
D.
The Township may suspend or revoke any approvals granted for the
project site upon discovery of the failure of the owner to comply
with this section of this Part.
[Ord. No. 2425, 12/3/2018]
1.
Plan Submission. The Township shall require receipt of a complete
plan, as specified in this Part.
A.
Five copies of the stormwater management plan shall distributed as
follows:
2.
Review.
A.
The Township Engineer or his agent shall review the stormwater management
plan for consistency with this Part. Any stormwater management plan
found incomplete shall not be accepted for review and shall be returned
to the applicant.
B.
The Township Engineer or his agent shall review the stormwater management plan for any subdivision or land development against the Township Subdivision and Land Development Ordinance [Chapter 22] provisions not superseded by this Part.
C.
When required by regulation, the County Conservation District shall
review and approve the erosion and sedimentation control plan for
consistency with PA DEP's 25 Pa. Code, Chapter 102, regulations.
D.
For activities regulated by this Part, the Township Engineer or his
agent shall notify the applicant and the Township whether the stormwater
management plan is consistent with this Part.
(1)
Should the stormwater management plan be determined to be consistent
with this Part, the Township shall notify the applicant.
(2)
Should the stormwater management plan be determined to be inconsistent
with this Part, the applicant shall be notified. The disapproval letter
shall cite the reason(s) and specific ordinance sections for the disapproval.
Disapproval may be due to inadequate information to make a reasonable
judgment as to compliance with the stormwater management plan. Any
disapproved stormwater management plans may be revised by the applicant
and resubmitted consistent with this Part.
E.
For regulated activities specified in § 23-102 of this Part which require a building permit, the Township Engineer shall notify the Township Building Permit Officer, within a time frame consistent with the Township Building Code [Chapter 5, Part 1] and/or Township Subdivision Ordinance [Chapter 22], whether the stormwater management plan is consistent with this Part. Any disapproved stormwater management plan may be revised by the applicant and resubmitted consistent with this Part.
F.
For regulated activities under this Part that require an NPDES permit
application, the applicant shall forward a copy of the Township Engineer's
letter stating that the stormwater management plan is consistent with
this Part to the County Conservation District. PA DEP and the County
Conservation District may consider the Township Engineer's review
comments in determining whether to issue a permit.
G.
The Township shall not grant preliminary or final approval to any subdivision or land development for regulated activities specified in § 23-102 of this Part if the stormwater management plan has been found to be inconsistent with this Part, as determined by the Township Engineer. All required permits from PA DEP must be obtained prior to final approval of any subdivision or land development.
H.
No building permits shall be issued for any regulated activity specified in § 23-102 of this Part if the stormwater management plan has been found to be inconsistent with this Part, as determined by the Township Engineer, or without considering the comments of the Township Engineer. All required permits from PA DEP must be obtained prior to issuance of a building permit.
I.
The applicant shall be responsible for completing record drawings
of all stormwater management facilities included in the approved stormwater
management plan. The record drawings and an explanation of any discrepancies
with the design plans shall be submitted to the Township Engineer
for final approval. In no case shall the Township approve the record
drawings until the Township receives a copy of an approved highway
occupancy permit from the PennDOT district office, NPDES permit, and
any other applicable permits or approvals, from PA DEP or the County
Conservation District. The above permits and approvals must be based
on the record drawings. The record drawings must include copies of
all applicable permits and approvals.
J.
The Township's approval of a stormwater management plan shall be valid for a period not to exceed five years commencing on the date that the Township approves the stormwater management plan. The Township may specify a term of validity shorter than five years in the approval for any specific SWM plan. If stormwater management facilities included in the approved stormwater management plan have not been constructed, or if constructed and record drawings of these facilities have not been approved within this time period, then the Township may consider the stormwater management plan disapproved and may revoke any and all permits. Stormwater management plans that are considered disapproved by the Township shall be resubmitted in accordance with Subsection 4 of this section.
3.
Modification of Plans.
A.
A modification to a stormwater management plan under review by the
Township for a development site that involves a change in stormwater
management facilities or techniques, or that involves the relocation
or redesign of stormwater management facilities, or that is necessary
because soil or other conditions are not as stated on the stormwater
management plan as determined by the Township Engineer, shall require
a resubmission of a modified stormwater management plan consistent
with this Part and shall be subject to review as specified in this
section of this Part.
4.
Resubmission of Disapproved Stormwater Plans.
A.
A disapproved stormwater management plan may be resubmitted, with
the revisions addressing the Township Engineer's concerns documented
in writing, and addressed to the Township in accordance with this
section of this Part and distributed accordingly, and shall be subject
to review as specified in this section of this Part. Any applicable
Township review and inspection fee must accompany a resubmission of
a disapproved stormwater management plan.
5.
Township Stormwater Plan Review and Inspection Fees.
A.
The Township shall be reimbursed by the applicant for the cost of
plan review and inspection related to this chapter. If requested,
the costs of inspection may be estimated by the Township Engineer
and paid by the applicant into an inspection escrow fund to be held
by the Township or as invoiced to the applicant. All excess funds
not used for inspection shall be returned to the applicant when the
project has been completed.
B.
Any fees established pursuant to this Part may include, but not necessarily
be limited to, any of the following:
(1)
Administrative costs.
(2)
The review of the stormwater management plan by the Township,
county (if applicable), Allegheny County Conservation District (if
applicable) and the Township Engineer.
(3)
The site inspections.
(4)
The inspection of stormwater management facilities and stormwater
management improvements during construction.
(5)
The final inspection upon completion of the stormwater management
facilities.
(6)
Any additional work required to enforce any permit provisions
regulated by this Part, correct violations, and assure proper completion
of stipulated remedial actions.
[Ord. No. 2425, 12/3/2018]
1.
AASHTO
ACCD
ACHD
ACT 167
ACT 167 PLAN (or WATERSHED PLAN)
AGRICULTURAL ACTIVITY
APPLICANT
AQUIFER
ATTENUATE
BASEFLOW
BEST MANAGEMENT PRACTICE (BMP)
CFS
CHANNEL
CONCENTRATED STORM RUNOFF
CONSERVATION DESIGN
CONSERVATION DISTRICT
DEP
DESIGN STORM
DETENTION BASIN
DETENTION OR TO DETAIN
DEVELOPMENT SITE (SITE)
DISCHARGE
DISTURBED AREA
DITCH
DRAINAGE AREA
DRAINAGE SYSTEM
EARTH DISTURBANCE
EASEMENT
ENGINEER
EPA
EROSION
EXISTING CONDITION
FEMA
FIRST-ORDER STREAM
FLOODPLAIN
FLOODWAY
FOREST MANAGEMENT/TIMBER OPERATIONS
FREEBOARD
GROUNDWATER
HOT SPOTS
HYDROGRAPH
HYDROLOGIC SOIL GROUP (HSG)
HYDROLOGY
IMPERVIOUS COVER
IMPERVIOUS SURFACE
INFILTRATION
INTENSITY
INTERMITTENT STREAM
KARST
LAND DEVELOPMENT (DEVELOPMENT)
LEVEL SPREADER
LOADING
LOW-IMPACT DEVELOPMENT (LID)
MAINTENANCE
MEADOW CONDITION
MS4
NATIONAL POLLUTION DISCHARGE ELIMINATION SYSTEM (NPDES)
NEW DEVELOPMENT
NOAA
NONSTRUCTURAL STORMWATER MANAGEMENT PRACTICES
NRCS
OPEN CHANNEL
OPEN VEGETATED CHANNEL
PA DEP
PACD
PASTURE CONDITION
PEAK DISCHARGE
PENNDOT
PERCOLATION RATE
PERVIOUS AREA
PRE-DEVELOPMENT ASSUMPTION
PROJECT SITE
QUALIFIED PROFESSIONAL
RAINFALL INTENSITY
RATE
RECEIVING WATERS
RECHARGE
REDEVELOPMENT
REGULATED ACTIVITIES
REGULATED EARTH DISTURBANCE ACTIVITY
RELEASE RATE PERCENTAGE
RETENTION BASIN
RETENTION or TO RETAIN
RETURN PERIOD
RIPARIAN
RIPARIAN BUFFER
RUNOFF
SCS
SEDIMENT
SEDIMENTATION
SHEET FLOW
SLAMM
SPECIAL FLOOD HAZARD AREA
STATE WATER QUALITY REQUIREMENTS
STORM EVENT
STORMWATER MANAGEMENT BMPs
STORMWATER MANAGEMENT PLAN
STORMWATER MANAGEMENT PRACTICES
STORMWATER or RUNOFF
STRUCTURAL STORMWATER MANAGEMENT PRACTICES
STRUCTURE
SUBAREA (SUBBASIN)
SUBDIVISION
SUBGRADE
SWALE
SWMM
TOTAL SITE AREA (SITE AREA)
TOWNSHIP
USDA
USDOT FHWA
WATER BODY
WATER TABLE
WATERCOURSE
WATERS OF THE COMMONWEALTH
WATERSHED
WETLAND
WETLANDS
WOODLAND CONDITION
As used in this Part, the following terms shall have the meanings
indicated:
American Association of State Highway and Transportation
Officials. The web site home page for AASHTO is http://transportation
1.org/aashtonew/.
Allegheny County Conservation District.
Allegheny County Health Department.
The Storm Water Management Act, Act of October 4, 1978, P.L.
864, No. 167; 32 P.S. § 680.1 et seq., as amended.
The plan for managing stormwater runoff throughout a designated
watershed adopted by Allegheny County as required by the Pennsylvania
Storm Water Management Act, 32 P.S. § 680.1 et seq.
The work of producing crops, including tillage, land clearing,
plowing, disking, harrowing, planting, harvesting crops, or pasturing
and raising of livestock and installation of conservation measures.
Construction of new buildings or impervious area is not considered
an agricultural activity.
A landowner, developer or other person who has filed an application
for approval to engage in any regulated earth disturbance activity
at a project site in the Township.
A geologic formation, group of formations, or part of a formation
that contains sufficient saturated, permeable material to yield useful
quantities of groundwater to wells and springs.
To reduce the magnitude of the flow rate by increasing the
time it takes to release a specified volume of runoff (for example
the one-year, twenty-four-hour storm event). Attenuation is a method
of reducing the peak flow rates for post-development compared to the
peak flow rates in pre-development.
Portion of stream discharge derived from groundwater; the
sustained discharge that does not result from direct runoff or from
water diversions, reservoir releases, piped discharges, or other human
activities.
Activities, facilities, designs, measures, or procedures
used to manage stormwater impacts from regulated activities, to meet
state water quality requirements, to promote groundwater recharge,
and to otherwise meet the purposes of this Part. Stormwater BMPs are
commonly grouped into one of two broad categories or measures: "structural"
or "nonstructural." In this Part, nonstructural BMPs or measures refer
to operational and/or behavior-related practices that attempt to minimize
the contact of pollutants with stormwater runoff, whereas structural
BMPs or measures are those that consist of a physical device or practice
that is installed to capture and treat stormwater runoff. Structural
BMPs include but are not limited to a wide variety of practices and
devices from large-scale retention ponds and constructed wetlands
to small-scale underground treatment systems, infiltration facilities,
filter strips, low-impact design, bioretention, wet ponds, permeable
paving, grassed swales, riparian or forested buffers, sand filters,
detention basins, and manufactured devices. Structural stormwater
BMPs are permanent appurtenances to the project site.
Cubic feet per second.
A natural or artificial watercourse that conveys, continuously
or periodically, flowing water.
Surface runoff from rainfall events, which converges and
flows primarily through water conveyance features such as swales,
gullies, waterways, channels or storm sewers, and which exceeds the
maximum specified flow rates of filters or perimeter controls intended
to control sheet flow.
A series of holistic land development design practices that
maximize protection of key land and environmental resources, preserve
significant concentrations of open space and greenways, evaluate and
maintain site hydrology, and ensure flexibility in development design
to meet community needs for complementary and aesthetically pleasing
development. Conservation design encompasses the following objectives:
conservation/enhancement of natural resources, wildlife habitat, biodiversity
corridors and greenways (interconnected open space); minimization
of environmental impact resulting from a change in land use (minimum
disturbance, minimum maintenance); maintenance of a balanced water
budget by making use of site characteristics and infiltration; incorporation
of unique natural, scenic and historic site features into the configuration
of the development; preservation of the integral characteristics of
the site as viewed from adjoining roads; and reduction in maintenance
required for stormwater management practices. Such objectives can
be met on a site through an integrated development process that respects
natural site conditions and attempts, to the maximum extent possible,
to replicate or improve the natural hydrology of a site.
A conservation district, as defined in Section 3(c) of the
Conservation District Law [3 P.S. § 851(c)] that has the
authority under a delegation agreement executed with DEP to administer
and enforce all or a portion of the regulations promulgated under
25 Pa. Code Chapter 102.
The Pennsylvania Department of Environmental Protection.
The magnitude and temporal distribution of precipitation
from a storm event measured in probability of occurrence (e.g., a
five-year storm) and duration (e.g., 24 hours), used in the design
and evaluation of stormwater management systems.
An impoundment designed to collect and retard stormwater
runoff by temporarily storing the runoff and releasing it at a predetermined
rate. Detention basins are designed to drain completely shortly after
any given rainfall event and are dry until the next rainfall event.
The prevention of, or to prevent, the discharge, directly
or indirectly, of a given volume of stormwater runoff into surface
waters by temporary storage.
See "project site."
To release of water from a project, site, aquifer, drainage
basin or other point of interest (verb); the rate and volume of flow
of water such as in a stream, generally expressed in cubic feet per
second (volume per unit of time) (noun).
An unstabilized land area where an earth disturbance is occurring
or has occurred.
An artificial waterway for irrigation or stormwater conveyance.
That land area contributing runoff to a single point and
that is enclosed by a ridge line.
All facilities and natural features used for the movement
of stormwater through and from a drainage area, including, but not
limited to, any and all of the following; conduits, pipes and appurtenant
features: channels, ditches, flumes, culverts, streets, swales, and
gutters, as well as all watercourses, water bodies and wetlands.
A construction or other human activity which disturbs the
surface of the land, including, but not limited to, clearing and grubbing;
grading; excavations; embankments; road maintenance; building construction;
and the moving, depositing, stockpiling, or storing of soil, rock
or earth materials.
A right of use of a specified portion of land of another
for a specified purpose.
A professional engineer duly appointed as the engineer for
the Township.
Environmental Protection Agency.
The wearing away of land surface by water or wind which occurs
naturally from weather or runoff, but is often intensified by human
activity.
The dominant land cover during the five-year period immediately
preceding a proposed regulated activity.
Federal Emergency Management Agency.
Uppermost perennial tributary in a watershed that has not
yet confluenced with another perennial stream. The confluence of two
first-order streams forms a "second-order" stream.
Any land area susceptible to inundation by water from any
natural source or delineated by applicable Federal Emergency Management
Agency (FEMA) maps and studies as being a special flood hazard area.
The channel of the watercourse and those portions of the
adjoining floodplains that are reasonably required to carry and discharge
the 100-year flood. Unless otherwise specified, the boundary of the
floodway is as indicated on maps and flood insurance studies provided
by FEMA. In an area where no FEMA maps or studies have defined the
boundary of the 100-year floodway, it is assumed absent evidence to
the contrary that the floodway extends from the stream to 50 feet
from the top of the bank of the stream.
Planning and activities necessary for the management of forestland.
These include timber inventory and preparation of forest management
plans, silvicultural treatment, cutting budgets, logging road design
and construction, timber harvesting, site preparation and reforestation.
Freeboard is the difference between the elevation of the
design flow in the emergency spillway (usually the 100-year peak elevation)
and the top elevation of the settled basin embankment (that is, top
of berm). The minimum freeboard shall be one foot.
Water that occurs in the subsurface and fills or saturates
the porous openings, fractures and fissures of underground soils and
rock units.
An area where land use or activities generate highly contaminated
runoff, with concentrations of pollutants in excess of those typically
found in stormwater.
A graph of discharge versus time for a selected point in
the drainage system.
Infiltration rates of soils vary widely and are affected
by subsurface permeability as well as surface intake rates. Soils
are classified into four HSGs (A, B, C, and D) according to their
minimum infiltration rate, which is obtained for bare soil after prolonged
wetting. The Natural Resources Conservation Service (NRCS) of the
United States Department of Agriculture defines the four groups and
provides a list of most of the soils in the United States and their
group classification. The soils in the area of the development site
may be identified from a soil survey report that can be obtained from
local NRCS offices or Conservation District offices. Soils become
less pervious as the HSG varies from A to D.
The study of the properties, distribution, circulation and
effects of water on the earth's surface, soil and atmosphere.
See "impervious surface."
A surface (area) which has been compacted or covered with
a layer of material so that it is resistant to infiltration by water.
It includes semi-pervious surfaces such as compacted clayey soils,
as well as most conventionally surfaced streets, roofs, sidewalks,
parking lots, and other similar surfaces. "Net increase of impervious
surface" refers to the difference between the existing impervious
coverage and the total impervious surface proposed.
Movement of surface water into the soil, where it is absorbed
by plant roots, evaporated into the atmosphere, or percolates downward
to recharge groundwater.
The depth of accumulated rainfall per unit of time.
A defined channel in which surface water is absent during
a portion of the year, as groundwater levels drop below the channel
bottom.
A type of topography that is formed over limestone or other
carbonate rock formations by dissolving or solution of the rock by
water, and that is characterized by closed depressions, sinkholes,
caves, a subsurface network of solution conduits and fissures through
which groundwater moves, and no perennial surface drainage features.
Inclusive of any or all of the following meanings:
A low earthen berm constructed perpendicular to the direction
of slope and extending across the width of the slope for the purpose
of intercepting surface runoff and spreading it behind the berm to
enhance infiltration and reduce erosion and runoff from the slope.
The purpose of a level spreader is to prevent concentrated, erosive
flows from occurring and to spread out stormwater runoff uniformly
over the ground as sheet flow.
The total amount (generally measured in pounds or kilograms
per acre per year) of material (sediment, nutrients, oxygen-demanding
material, or other chemicals or compounds) brought into a lake, stream
or water body by in-flowing streams, runoff, direct discharge through
pipes, groundwater, the air (aerial or atmospheric deposition) and
other sources over a specific period of time (often annually).
Site design approaches and small-scale stormwater management
practices that promote the use of natural systems for infiltration,
evapotransportation, and reuse of rainwater. LID can be applied to
new development, urban retrofits, and revitalization projects. LID
utility design techniques that infiltrate, filter, evaporate, and
store runoff close to its source. Rather than rely on costly large-scale
conveyance and treatment systems, LID addresses stormwater through
a variety of small, cost-effective landscape features located on site.
The action taken to restore or preserve the as-built functional
design of any facility or system.
A natural ground cover with less than one viable tree of
a dbh of six inches or greater per 1,500 square feet within 10 years
of application; a cover condition for which SCS curve numbers have
been assigned or to which equivalent Rational Method runoff coefficients
have been assigned.
Township separate storm sewer system.
Created in 1972, under the Clean Water Act, to authorize
discharges to local receiving waters only pursuant to governmental
permits, in an effort to reduce point source and nonpoint source pollutants.
Any activity regulated by this Part that is not considered
a redevelopment as defined in this Part.
National Oceanic and Atmospheric Administration.
Passive site design approaches or regulatory approaches that
positively impact water quality and reduce or minimize the generation
of stormwater runoff without requiring the construction of specific
or discrete stormwater management control structures.
Natural Resources Conservation Service.
Any natural or man-made watercourse or conduit in which water
flows with a free surface.
Also known as "swales," "grass channels," and "biofilters."
These systems are used for the conveyance, retention, infiltration
and filtration of stormwater runoff.
Pennsylvania Department of Environmental Protection.
Pennsylvania Association of Conservation Districts.
A ground cover of grassland or range with continuous forage
for grazing and greater than 75% ground cover and lightly or only
occasionally grazed; a cover condition for which the Soil Conservation
Service curve numbers have been assigned or to which equivalent Rational
Method runoff coefficients have been assigned.
The maximum rate of stormwater runoff from a specific storm
event.
Pennsylvania Department of Transportation.
The rate of movement of water under hydrostatic pressure
through interstices of rock or soil. For stormwater analysis, it is
typically measured as a distance per unit of time (e.g., inches per
hour).
Any area not defined as impervious.
The ground cover assumption used when analyzing the stormwater
runoff characteristics of a drainage area prior to the proposed development.
The specific area of land where any regulated activities
in the Township are planned, conducted or maintained.
Any person licensed by the Pennsylvania Department of State
or otherwise qualified by law to perform the work required by this
Part.
The depth of accumulated rainfall per unit of time.
Volume per unit of time.
Any water bodies, watercourses or wetlands into which surface
waters flow.
The replenishment of groundwater through the infiltration
of rainfall, other surface waters, or land application of water or
treated wastewater.
An existing, developed property and/or a graded, altered
and compacted site (as of or after the date of adoption of this Part)
that is proposed for reconstruction involving the demolition or partial
demolition of the property.
Any earth disturbances or any activities that involve the
alteration or development of land in a manner that may affect post-construction
stormwater runoff.
Activity involving earth disturbance subject to regulation
under 25 Pa. Code Chapter 92a or Chapter 102, or the Clean Streams
Law, 35 P.S. § 691.1 et seq.
The percentage of pre-development peak rate of runoff from
a watershed subarea (as delineated in the Act 167 watershed plan),
which defines the allowable post-development peak discharge from any
development site in that subarea.
An impoundment designed to collect and retard stormwater
runoff by temporarily storing the runoff and releasing it at a predetermined
rate. Retention basins may also be designed to permanently retain
additional stormwater runoff. Retention basins are designed to retain
a permanent pool of water during dry weather.
The prevention of direct discharge of stormwater runoff into
receiving waters or water bodies by temporary or permanent containment
in a pond or depression; examples include systems which discharge
by percolation to groundwater, exfiltration, and/or evaporation processes,
and which generally have residence times of less than three days.
The average interval, in years, within which a storm event
of a given magnitude can be expected to occur one time. For example,
the twenty-five-year return period rainfall would be expected to occur
on average once every 25 years.
Pertaining to anything connected with or immediately adjacent
to the banks of a stream or other body of water.
An area of land adjacent to a body of water and managed to
maintain the integrity of stream channels and shorelines to:
See "stormwater or runoff."
Soil Conservation Service.
Fragmented material that originated from weathering rocks
and decomposing organic material that is transported by, suspended
in, and eventually deposited in the streambed.
Occurs when sediment particles that have been suspended within
flowing water are deposited on the stream bottom or floodplain.
A flow process associated with broad, shallow water movement
on sloping ground surfaces that is not channelized or concentrated.
Source loading and management model. This model is based
on small storm hydrology and pollutant runoff from urban land uses.
Pollutant sources are identified and both structural and nonstructural
stormwater practices can be accounted for in the model.
Those areas identified by the Federal Emergency Management
Agency (FEMA) and Federal Insurance Administration (FIA) as floodway
area (FW), flood-fringe area (FF), and general floodplain area (FA);
where determined by the Township, identified alluvial soils may be
included as well.
The regulatory requirements to protect, maintain, reclaim,
and restore water quality under Pennsylvania Code Title 25 and the
Clean Streams Law, 35 P.S. § 691.1 et seq.
The storm of a specific duration, intensity, and frequency.
Is abbreviated as "SWM BMPs" or "BMPs" throughout this Part.
The approved detailed analysis, design, and drawings of the
stormwater management system required for all construction.
The designed and/or constructed features which infiltrate,
treat, collect, convey, channel, store, inhibit, or divert the movement
of stormwater; such practices include structural and nonstructural
practices.
The flow of water over land and/or in water bodies that results
from and occurs during and immediately following a rainfall event.
Any measures that require the design and construction of
a facility to help reduce or eliminate a nonpoint source of pollution
and control stormwater.
Anything constructed or installed with a fixed location on
the ground, or attached to something having a fixed location on the
ground.
A portion of the watershed (basin) that has similar hydrological
characteristics and drains to a common point.
As defined in the Pennsylvania Municipalities Planning Code,
Act of July 31, 1968, P.L. 805, No. 247, 53 P.S. § 10101
et seq.
The top elevation of graded and compacted earth underlying
roadway pavement.
An artificial or natural waterway which may contain contiguous
areas of standing or flowing water only following a rainfall event,
or is planted with or has stabilized vegetation suitable for soil
stabilization, stormwater treatment, and nutrient uptake, or is designed
to take into account the soil erodibility, soil percolation, slope,
slope length, and contributing drainage area so as to prevent erosion
and reduce the pollutant concentration of any discharge.
Stormwater management model. EPA developed this model for
analyzing stormwater quantity and quality associated with runoff from
urban areas. Both single event and continuous simulation can be performed
on catchments having storm sewers, or combined sewers and natural
drainage, for prediction of flows, stages and pollutant concentrations.
Information on SWMM is available at http://www.epa.gov/ceampubl/swater/swmm/index.htm.
Total area of the parcel(s) being developed.
The local government that adopted the subject ordinance.
United States Department of Agriculture.
United States Department of Transportation Federal Highway
Administration.
Any natural or artificial pond, lake, reservoir, or other
area which ordinarily or intermittently contains water and which has
a discernible shoreline and receives surface water flow.
The uppermost level of saturation of pore space or fractures
by subsurface water in an aquifer. "Seasonal high water table" refers
to a water table that rises and falls with the seasons due either
to natural or man-made causes.
A permanent or intermittent stream or other body of water,
whether natural or man-made, which gathers or carries surface water.
Any and all rivers, streams, creeks, rivulets, impoundments,
ditches, watercourses, storm sewers, lakes, dammed water, wetlands,
ponds, springs, and all other bodies or channels of conveyance of
surface and underground water, or parts thereof, whether natural or
artificial, within or on the boundaries of this commonwealth.
Region or land area drained by a river, watercourse, or other
surface water of this commonwealth.
Those areas that are inundated or saturated by surface water
or groundwater at a frequency and duration sufficient to support,
and that under normal circumstances do support, a prevalence of vegetation
typically adapted for life in saturated soil conditions, including
swamps, marshes, bogs, fens, and similar areas.
Land areas that are inundated or saturated by surface water
or groundwater with a frequency and duration sufficient to support,
and that under normal circumstances do support, a prevalence of vegetation
typically adapted for life in saturated soil conditions (Wetlands
generally include swamps, marshes, bogs, and similar areas.); or areas
that are defined and delineated in accordance with the Federal Manual
for Identifying and Delineating Jurisdictional Wetlands, dated January
10, 1989, and as may be amended from time to time; or as further defined
and delineated by the United States Army Corps of Engineers, the United
States Environmental Protection Agency, or the Pennsylvania Department
of Environmental Protection.
A natural ground cover with more than one viable tree of
a dbh (diameter at breast height) of six inches or greater per 1,500
square feet which existed within 10 years of application; a cover
condition for which SCS curve numbers have been assigned or to which
equivalent Rational Method runoff coefficients have been assigned.
