[Ord. No. 2022-01, 7/12/2022]
A.
All applicants proposing regulated activities within the Township which do not fall under the exemption criteria contained within § 26-105 of this Part shall submit a stormwater management plan consistent with this Part to the Township for review. These criteria shall apply to the total proposed development even if development is to take place in stages.
B.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property;
(2)
Meet the water quality goals of this Part by implementing measures
to:
(a)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(b)
Create, maintain, repair or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces (i.e., disconnected impervious
areas, DIAs) by directing runoff to pervious areas, wherever possible.
(3)
Incorporate methods described in the Pennsylvania Stormwater
Best Management Practices Manual, Pennsylvania Department of Environmental
Protection (PADEP) No. 363-0300-002 (2006). If methods other than
green infrastructure and LID methods are proposed to achieve the volume
and rate controls required under this Part, the SWM site plan must
include a detailed justification demonstrating that the use of LID
and green infrastructure is not practicable.
C.
The Township may, after consultation with the Department of Environmental
Protection (PADEP), approve measures for meeting the state water quality
requirements other than those in this Part, provided that they meet
the minimum requirements of, and do not conflict with, state law,
including, but not limited to, the Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
D.
For all regulated earth disturbance activities, erosion and sediment
(E&S) control best management practices (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 Title 25 of the Pennsylvania
Code and the Clean Streams Law.[2] Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual, No. 363-2134-008
(April 15, 2000), as amended and updated.
[2]
Editor's Note: See 35 P.S. § 691.1 et seq.
E.
No approval of any subdivision or land development plan, or issuance of any building, zoning, erosion and sedimentation control and grading permit, occupancy permit, or the commencement of any earth disturbance at a project site within the Township, shall proceed until the requirements of this Part are met, including approval of a stormwater management plan under § 26-136 and a permit under PADEP regulations, where applicable.
I.
All best management practices (BMPs) shall conform to the design
criteria of this Part and Pennsylvania Stormwater Management Practices
Manual, December 2006, as amended.
J.
Techniques described in Appendix D (Low Impact Development Techniques)[3] of this Part are encouraged because they reduce the costs
of complying with the requirements of this Part and the state water
quality requirements.
[3]
Editor's Note: Appendix D is included as an attachment to this chapter.
K.
Infiltration BMPs should be spread out, made as shallow as practicable,
and located to minimize the use of natural on-site infiltration features
while still meeting the other requirements of this Part.
L.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities designed to encourage infiltration, groundwater
recharge, and improved water quality.
M.
Existing points of concentrated drainage that discharge onto adjacent
property shall not be altered without written approval of the affected
property owner(s) and shall be subject to any applicable discharge
criteria specified in this Part.
N.
Areas of existing sheet flow discharge shall be maintained wherever
possible. If sheet flow is proposed to be concentrated and discharged
onto adjacent property, the developer must document that adequate
downstream conveyance facilities exist to safely transport the concentrated
discharge, or otherwise prove that no erosion, sedimentation, flooding
or other harm will result from the concentrated discharge; and submit
written approval from the affected adjacent property owner(s).
O.
For all subdivision and land development applications, the tributary
area discharging drainage to any location along the site property
boundary shall not increase by more than 25% over the predevelopment
condition without written approval from the adjacent affected property
owner(s).
P.
Where a development site is traversed by watercourses, drainage easements
shall be provided conforming to the line of such watercourses. The
width of the easement shall be adequate to provide for the unimpeded
flow of stormwater runoff from the 100-year storm event. However,
in no case shall the easement be less than 30 feet in width. Terms
of the easement shall prohibit excavation, the placing of fill or
structures, and any alterations that may adversely affect the flow
of stormwater within any portion of the easement. Periodic maintenance
of the easement shall be required by the landowner to ensure proper
runoff conveyance. The developer will retain the easement until such
time as one of the following is accomplished:
(1)
For subdivisions or land developments, the individual lot owner
assumes responsibility for the maintenance of the portion of their
property through which the easement passes. The record plan shall
contain a description of such easement(s) and notation indicating
the maintenance responsibilities.
(2)
A homeowners' association or other legal entity approved
by the Township assumes responsibility for the maintenance of the
development, including the watercourse easement. The record plan shall
contain a description of such easement(s) and notation indicating
the maintenance responsibilities.
Q.
When it can be shown that, due to topographic conditions, natural
drainageways on the site cannot adequately provide for drainage, open
channels may be constructed conforming substantially to the line and
grade of such natural drainageways. Work within natural drainageways
shall be subject to approval by PADEP through the joint permit application
process, or, where deemed appropriate by PADEP, through the general
permit process.
R.
Any stormwater management facilities regulated by this Part that
will be located in or adjacent to waters of the commonwealth, waters
of the United States, or wetlands shall be subject to approval by
PADEP and/or the U.S. Army Corps of Engineers through the joint permit
application process, or, where deemed appropriate by PADEP and/or
the U.S. Army Corps of Engineers, the general permit process. When
there is a question whether wetlands may be involved, it is the responsibility
of the developer or his agent to show that the land in question cannot
be classified as wetlands, otherwise approval to work in the area
must be obtained from PADEP and/or the U.S. Army Corps of Engineers.
S.
Any stormwater management facilities regulated by this Part that
would be located on state highway rights-of-way, or discharge stormwater
to facilities located within a state highway right-of-way, shall be
subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
T.
Site disturbance and impervious surface shall be minimized. Infiltrating
stormwater runoff through seepage beds, infiltration trenches, etc.,
shall be required, where soil conditions permit, to reduce the size
or eliminate the need for retention/detention facilities.
U.
Roof drains and sump pumps shall discharge to an infiltration bed,
natural watercourse, storm sewer system, or drainage swale (within
a stormwater easement). Roof drains and sump pumps shall be connected
to a storm sewer, drainage structure, or other approved stormwater
conveyance facility that is designed as part of a stormwater management
BMP. In no case shall roof drains or sump pumps be connected to a
sanitary sewer or permitted to discharge across a sidewalk, walkway,
or to a street through the curb.
V.
Special requirements for watersheds draining to high quality (HQ) and exceptional value (EV) waters: The temperature and quality of water and streams that have been determined to be exceptional value and high quality are to be maintained as defined in Chapter 93, Water Quality Standards, Title 25, Pennsylvania Department of Environmental Protection Rules and Regulations. Maintaining the multiple values of these special protection waters occurs through maintaining the predevelopment or natural water cycle; not decreasing infiltration and recharge; and not increasing runoff. In so doing, critical temperature considerations are provided (optimal temperature control is achieved through infiltration of precipitation to groundwater which maximizes temperature-moderated stream base flow). In those cases where runoff volume control cannot be achieved as per § 26-126D, temperature-sensitive BMPs and stormwater conveyance systems are to be used and designed with storage pool areas (drawing outflow from the bottom of the pool) and supply outflow channels shall be shaded with trees. This will require modification of berms for permanent ponds and the relaxation of restrictions on planting vegetation within the facilities, provided that capacity for volumes and rate control is maintained. At a minimum, the southern half of pond shorelines shall be planted with shade or canopy trees within 10 feet of the pond shoreline. In conjunction with this requirement, the maximum slope allowed on the berm area to be planted is 10:1. This will lessen the destabilization of berm soils due to root growth. A long-term maintenance schedule and management plan for the thermal control BMPs is to be established and recorded for all development sites.
W.
All stormwater runoff shall be pretreated for water quality prior
to discharge to surface or groundwater.
X.
Completed stormwater management facilities, including detention/retention
basins, shall be surveyed by a professional land surveyor or engineer
licensed in the Commonwealth of Pennsylvania, to verify compliance
with the character of stormwater management facilities as depicted
on the approved final plan (or subsequently approved revision, thereof).
As-constructed plans shall be submitted to Plumstead Township for
review and approval, upon completion of construction of all facilities.
Where stormwater management facilities are constructed as part of
a subdivision or land development application, the as-built plan must
be submitted to, and approved by, Plumstead Township prior to offer
of dedication of any public facilities and/or release of financial
security for the required maintenance period. Public facilities will
not be accepted by Plumstead Township until such time the as-constructed
plans have been reviewed and approved by the Township Engineer.
Y.
The record plan and development agreement for an approved subdivision
or land development shall define the ownership and maintenance responsibilities
as well as access rights for all drainage-related easements. Specifically,
the record plan shall contain a provision permitting access to such
easement(s), at any reasonable time, for inspection and/or emergency
repair/maintenance, by Plumstead Township or its designee, of all
facilities deemed critical to public welfare. In the event the lot
owner or homeowners' association fails to honor their maintenance
responsibilities set forth herein, in any manner, Plumstead Township
shall have the right of entry upon and within the area of the easement
to undertake any required corrective or maintenance effort. The total
cost of such, including administrative, engineering, and legal costs
for enforcement, may be imposed upon the responsible party as determined
by Plumstead Township. Failure to remedy all associated costs described
above may be subject of the imposition of a lien by the Township against
the owner(s) in question, in the same manner as the Township might
otherwise be empowered by law to assess or impose a lien against a
property for municipal improvements.
Z.
[Ord. No. 2022-01, 7/12/2022]
A.
Mapping of Stormwater Runoff Peak Rate Districts. In order to implement
the provisions of this Part, the Tohickon Creek Watershed Stormwater
Management Plan, Neshaminy Creek Watershed Stormwater Management Plan,
and Delaware River (South) Watershed Stormwater Management Plan, Plumstead
Township is divided into Stormwater Runoff Peak Rate Districts consistent
with the plans. The boundaries of the districts are indicated on the
runoff peak rate district map that is available for inspection at
the Township building. A large-scale boundary map is included as Appendix
G for reference.[1]
[1]
Editor's Note: Appendix G is included as an attachment to this chapter.
B.
The exact location of the Stormwater Runoff Peak Rate District boundary as it applies to a given development site shall be determined by mapping the boundaries using the two-foot or five-foot topographic contours provided as part of the stormwater management plan developed for the site in accordance with Chapter 22, Subdivision and Land Development. The district boundaries, as originally drawn, coincide with topographic divides or, in certain instances, are drawn from the intersection of the watercourse or a potential flow obstruction to the topographic divide consistent with topography. The locations determined on the stormwater management plan shall be reviewed and verified by the Township Engineer.
C.
Description of Tohickon Creek Watershed Stormwater Runoff Hydrologic
Peak Rate Districts.
(1)
Conditional No Detention Districts (Direct Discharge). Subareas are identified on the official Sub-Basin Map available for inspection at the Township office. Included in this district are 2, 3, 8-10. These subareas may discharge post-development runoff without detention facilities without adversely affecting the total watershed peak flow, provided a downstream hydraulic capacity analysis as outlined in § 26-122J of this Part is approved by the Township. These areas are located adjacent to the Delaware River. However, where the conveyance capabilities of the local receiving facilities are not adequate to safely transport the increased peak flows from undetained runoff, a 100% release rate control is applied.
(2)
100% Release Rate District. Subareas included in this district
are 4-7, 11, 13, 16, 33-34. These subareas are not expected to incur
a great deal of development growth due to location, topography, soils,
or a combination of all three factors. Also, the location in the watershed
of these subareas is of minor importance in supporting the overall
watershed level runoff control. Therefore, these areas are allowed
to release development runoff at a rate that does not exceed the existing
rates of runoff.
D.
For the purpose of implementing the provisions of the Neshaminy Creek
Watershed Stormwater Management Plan, District "A," and Delaware River
South Watershed Stormwater Management Plan, District "A," design storm
proposed conditions shall be controlled to design storm existing conditions
as follows:
|
Design Storm Proposed Conditions
|
to
|
Design Storm Existing Conditions
|
|---|---|---|
|
2-year
|
1-year
| |
|
5-year
|
5-year
| |
|
10-year
|
10-year
| |
|
25-year
|
25-year
| |
|
50-year
|
50-year
| |
|
100-year
|
100-year
|
E.
Sites Located in More Than One District. For a proposed development
site located within two or more release category subareas, the peak
discharge rate from any subarea shall be the predevelopment peak discharge
for that subarea multiplied by the applicable release rate. The calculated
peak discharges shall apply regardless of whether the grading plan
changes the drainage area by subarea.
F.
Off-Site Areas. Off-site areas that drain through a proposed development
site are not subject to release rate criteria when determining allowable
peak runoff rates or volume reduction. However, on-site drainage facilities
shall be designed to safely convey off-site flows through or around
the development site to existing points of discharge from the property.
G.
Where the area of a site being impacted by a proposed development
activity differs significantly from the total site area, only the
proposed disturbed area utilizing stormwater management measures shall
be subject to the management district criteria. Nonimpacted or undisturbed
areas that do not flow into, or are bypassing, the stormwater management
facilities shall not be subject to the Stormwater Management District
criteria.
H.
Stormwater Conveyance Corridor Protection (Riparian Corridor Preservation
and Vegetation). Runoff from developed areas of the site, including
but not limited to areas of impervious surface, shall be managed through
a series of riparian corridor vegetation facilities whenever possible.
This will be accomplished in a manner satisfactory to the Township,
utilizing the Pennsylvania Stormwater Best Management Practices Manual,
December 30, 2006, as amended. Riparian forested buffer: the priority
goal of the riparian vegetation will be the reduction of thermal impacts
on stormwater runoff associated with impervious areas, with a secondary
goal being the protection of capacity of existing stormwater conveyance
channels. These goals will be achieved through the use of design criteria
within this Part and the Pennsylvania Stormwater Best Management Practices
Manual, and shall be in addition to any other Township ordinance provisions.
I.
Regional Detention Alternatives. For certain areas within the study
area, it may be more cost-effective to provide one control facility
for more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives are the responsibility of
prospective developers. The design of any regional control basins
must incorporate reasonable development of the entire upstream watershed.
The peak outflow of a regional basin would be determined on a case-by-case
basis using the hydrologic model of the watershed consistent with
protection of the downstream watershed areas. "Hydrologic model" refers
to the calibrated model as developed for the stormwater management
plan.
J.
A downstream hydraulic capacity analysis shall be performed to ascertain
whether runoff from a regulated activity could increase the potential
and/or frequency of flooding of existing downstream drainage facilities.
In the event that a downstream hydraulic capacity analysis determines
that the regulated activity will increase the potential and/or frequency
of flooding of existing downstream drainage facilities, runoff from
the regulated activity must be controlled to mitigate the potential
and/or frequency of flooding of existing downstream drainage facilities.
For regulated activities in Conditional No Detention (Direct Discharge)
Districts that seek to discharge stormwater runoff without detention
facilities, the following criteria shall be used for determining adequacy
of downstream drainage facilities for accepting increased peak flow
rates from the regulated activity:
(1)
Natural or man-made channels or swales must be able to convey
the increased runoff associated with a two-year return period event
within their banks at velocities consistent with protection of the
channels from erosion. Acceptable velocities shall be based upon criteria
included in the PADEP Erosion and Sediment Pollution Control Program
Manual.
(2)
Natural or man-made channels or swales must be able to convey
the increased twenty-five-year return period runoff without creating
any hazard to persons, property, or wildlife and aquatic habitat.
Habitat impact should be minimized or avoided.
(3)
Culverts, bridges, storm sewers or any other facilities which
must pass or convey flows from the tributary area must be designed
in accordance with PADEP, Chapter 105 regulations (if applicable)
and, at a minimum, pass the increased twenty-five-year return period
runoff.
[Ord. No. 2022-01, 7/12/2022]
The requirements of this section apply to all watersheds. In the event that individual watershed volume requirements listed in §§ 26-124, 26-126, and 26-127 of this Part result in a required volume that differs from the volume control requirements of this section, BMP design must comply with the greater volume control requirement, as applicable. The green infrastructure and low impact development practices provided in the BMP Manual shall be utilized for all regulated activities wherever possible. Water volume controls shall be implemented using the Design Storm Method in Subsection A or the Simplified Method in Subsection B below. For regulated activity areas of one acre or less that do not require hydrologic routing to design the stormwater facilities, this Part establishes no preference for either methodology; therefore, the applicant may select either methodology on the basis of economic considerations, the intrinsic limitations on applicability of the analytical procedures associated with each methodology and other factors.
A.
The Design Storm Method (CG-1 in the BMP Manual) is applicable to
any size of regulated activity. This method requires detailed modeling
based on site conditions.
(1)
Do not increase the post-development total runoff volume for
all storms equal to or less than the two-year, twenty-four-hour duration
precipitation.
B.
The Simplified Method (CG-2 in the BMP Manual) provided below is
independent of site conditions and shall be used if the Design Storm
Method is not followed. This method is not applicable to regulated
activities of one acre or greater or for projects that require design
of stormwater storage facilities. For new impervious surfaces:
(1)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(2)
At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow, i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options include reuse, evaporation, transpiration, and infiltration.
(3)
Wherever possible, infiltration facilities shall be designed
to accommodate infiltration of the entire permanently removed runoff;
however, in all cases, at least the first 0.5 inch of the permanently
removed runoff must be infiltrated.
[Ord. No. 2022-01, 7/12/2022]
A.
Volume Control. Volume controls will mitigate increased runoff impacts, protect stream channel morphology, maintain groundwater recharge, and contribute to water quality improvements. Stormwater runoff volume control methods are based on the net change in runoff volume for the two-year storm event. Volume controls shall be implemented using the Design Storm Method in Subsection A(1) or the Simplified Method in Subsection A(3) below. For regulated activity areas of one acre or less, this Part establishes no preference for either methodology; therefore, the applicant may select either methodology on the basis of economic considerations, the intrinsic limitations of the procedures associated with each methodology, and other factors. All regulated activities of one acre or greater must use the Design Storm Method.
(1)
Design Storm Method (Any Regulated Activity): This method requires detailed modeling based on site conditions. For modeling assumptions, refer to § 26-130.
(a)
Post-development total runoff shall not be increased from predevelopment
total runoff for all storms equal to or less than the two-year, twenty-four-hour
duration precipitation.
(b)
To estimate the increased volume of runoff (cubic feet) for
the two-year, twenty-four-hour duration precipitation event for existing
site conditions (predevelopment) and for the proposed developed site
conditions (post-development), it is recommended to use the Soil Cover
Complex Method as shown in this section. Appendix A is available to
guide a qualified professional and/or an applicant to calculate the
stormwater runoff volume.[1] The calculated volume shall be either reused, evapotranspired,
or infiltrated through structural or nonstructural means.
Soil Cover Complex Method:
Step 1: Runoff (in) = Q = (P - 0.2S)2/(P + 0.8S)
|
Where:
| ||
|
P
|
=
|
2-year 24-hour Rainfall (3.26 inches per Appendix A)
|
|
S
|
=
|
(1,000/CN) - 10, the potential maximum retention (including
initial abstraction, la)
|
Step 2: Runoff Volume (Cubic Feet) = Q x Area x 1/12
Q = Runoff (in)
Area = SWM Area (sq ft), as calculated per § 26-124A(2)(a).
[1]
Editor's Note: Appendix A is included as an attachment to this chapter.
(2)
Stormwater Control Measures. The applicant must demonstrate
how the required volume is controlled through stormwater best management
practices (BMPs) which shall provide the means necessary to capture,
reuse, evaporate, transpire or infiltrate the total runoff volume.
(a)
If natural resources exist on the site, the applicant is required
to submit an SWM site plan and determine the total acreage of protected
area where no disturbance is proposed. The acreage of the protected
area is subtracted from the total site area and not included in the
stormwater management site area (SWM area) acreage used in determining
the volume controls.
|
Stormwater Management Site Area =
Total Site Area (for both pre- and post-development conditions)
-
Protected Area
|
(b)
Calculate the volume controls provided through nonstructural
BMPs. Table A-5 in Appendix A[2] is recommended as guidance.
[2]
Editor's Note: Appendix A is included as an attachment to this chapter.
(c)
Volume controls provided through nonstructural BMPs are subtracted
from the required volume to determine the necessary structural BMPs.
|
Required
Volume Control (ft3)
|
-
|
Nonstructural
Volume Control (ft3)
|
=
|
Structural Volume
Requirement (ft3)
|
(d)
Calculate the volume controls provided through structural BMPs. Table A-6 in Appendix A is recommended as guidance. Refer to PA BMP Manual Chapter 6 for description of the BMPs.
(e)
Infiltration BMPs intended to receive runoff from developed
areas shall be selected based on the suitability of soils and site
conditions. Infiltration BMPs shall be constructed on soils that have
the following characteristics:
1)
A minimum soil depth of 12 inches between the bottom of the
infiltration BMPs and the top of bedrock or seasonal high-water table.
2)
An infiltration rate sufficient to accept the additional stormwater
load and dewater completely as determined by field tests. A minimum
of 0.2 inch/hour (in/hr) should be utilized and for acceptable rates
a safety factor of 50% should be applied for design purposes (e.g.,
for soil which measured 0.4 in/hr, the BMP design should use 0.2 in/hr
to ensure safe infiltration rates after construction).
3)
All infiltration facilities shall be designed to completely
infiltrate runoff volume within two days (48 hours) from the peak
of the design storm.
(f)
Soils. A soils evaluation of the project site shall be required
to determine the suitability of infiltration facilities. All regulated
activities are required to perform a detailed soils evaluation by
a qualified design professional which at minimum addresses soil permeability,
depth to bedrock, and subgrade stability. The general process for
designing the infiltration BMP shall be:
1)
Analyze hydrologic soil groups as well as natural and man-made
features within the site to determine general areas of suitability
for infiltration practices. In areas where development on fill material
is under consideration, conduct geotechnical investigations of subgrade
stability; infiltration may not be ruled out without conducting these
tests.
2)
Provide field tests such as double ring infiltrometer or hydraulic
conductivity tests (at the level of the proposed infiltration surface)
to determine the appropriate hydraulic conductivity rate. Percolation
tests are not recommended for design purposes.
3)
Design the infiltration structure based on field determined
capacity at the level of the proposed infiltration surface and based
on the safety factor of 50%.
4)
If on-lot infiltration structures are proposed, it must be demonstrated
that the soils are conducive to infiltrate on the lots identified.
5)
An impermeable liner is required in detention/retention basins
where the possibility of groundwater contamination exists. A detailed
hydrogeologic investigation may be required by the Township.
(3)
Simplified Method (Regulated activities less than one acre only).
(a)
Stormwater facilities shall capture the runoff volume from at
least the first two inches of runoff from all new impervious surfaces.
|
Volume (cubic feet) = (2" runoff/12 inches/ft) x impervious
surface area (sq ft)
|
(b)
At least the first one inch of runoff volume from the new impervious
surfaces shall be permanently removed from the runoff flow, i.e.,
it shall not be released into the surface waters of the commonwealth.
The calculated volume shall be either reused, evapotranspired, or
infiltrated through structural or nonstructural means.
|
Volume (cubic feet) = (1" runoff/12 inches/ft) x impervious
surface area (sq ft)
|
(c)
Infiltration facilities shall be designed to accommodate the
first 0.5 inch of the permanently removed runoff.
(d)
No more than one inch of runoff volume from impervious surfaces
shall be released from the site. The release time must be between
24 and 72 hours.
[Ord. No. 2022-01, 7/12/2022]
A.
For design and applicability of nonstructural BMPs refer to Chapter 5 of the Pennsylvania Stormwater Management Practices Manual, December 2006, as amended. For the nonstructural BMPs proposed, the applicant shall utilize and submit appropriate checklists included in Chapter 8, Section 8.8, of the Pennsylvania Stormwater Best Management Practices Manual, December 2006, as amended (refer to Appendix E[1]) to demonstrate that the BMPs are applicable to the project
and to determine the amount of volume or peak rate credit is applicable.
[1]
Editor's Note: Appendix E is included as an attachment to this chapter.
B.
The applicant shall demonstrate that regulated activities are designed
in the following sequence to minimize the increases in stormwater
runoff and impacts to water quality:
(1)
Prepare a Site Analysis and Resource Conservation Plan (SARCP), as required by Chapter 22, Subdivision and Land Development, showing environmentally sensitive areas, including, but not limited to, steep slopes, ponds, lakes, streams, wetlands, hydric soils, vernal pools, floodplains, riparian corridors, hydrologic soil groups A, B, C, and D, prime agricultural soils (prime farmland and farmland of statewide importance as designated in the soil survey of Bucks County), woodlands, surface waters regulated by the state or federal government, any existing recharge areas, and any other requirements outlined in Chapter 22, Subdivision and Land Development.
(2)
Prepare a draft project layout avoiding sensitive areas identified in § 26-125B(1) (as further defined by Part 24 of Chapter 27 of the Plumstead Township Code) and minimizing total site earth disturbance. The ratio of disturbed area to the entire site area and measures taken to minimize earth disturbance shall be included in the SARCP.
(3)
Identify site-specific existing conditions, drainage areas,
discharge points (points of interest), recharge areas, and hydrologic
soil groups A and B.
(8)
Determine the Watershed Management District within which the
site is located (refer to Appendix G[3]) and conduct a predevelopment runoff analysis.
[3]
Editor's Note: Appendix G is included as an attachment to this chapter.
(9)
Prepare final project design to maintain predevelopment drainage
areas and discharge points, to minimize earth disturbance and impervious
surfaces, to reduce runoff to the maximum extent possible, and to
minimize the use of surface or point discharges.
(10)
Conduct a proposed conditions runoff analysis based on the final design to meet the release rate requirements for stream bank erosion (§ 26-128).
(11)
Manage any remaining runoff through treatment prior to discharge,
as part of detention, biorentention, direct discharge or other structural
control.
[Ord. No. 2022-01, 7/12/2022]
A.
The project plan shall specify permanent stormwater BMPs to be implemented,
operated, and maintained to meet water quality requirements. Because
water quality requirements vary depending on the uses of the water
bodies in the watershed, a framework methodology is provided here.
B.
In order to protect and maintain water quality, additional stormwater
runoff created by the development project must be captured, stored,
and treated. In addition, post-construction stormwater infiltration
of runoff must replicate preconstruction infiltration of runoff to
the maximum extent possible. In high quality and exceptional value
watersheds, special requirements may apply.
C.
The volume of additional stormwater runoff to be captured, stored,
and treated is called the Water Quality Volume ("WQv").
(1)
The formula for determining WQv is:
WQv = [(P)(Rv)(A)]/12 (acre-feet)
|
Where:
| ||
|
P
|
=
|
Rainfall depth in inches, using the "90% storm" - the volume
of rainfall for 90% of the storm events which produce runoff in the
watershed annually. For Year 2008, PennDOT Region 5, the P value is
2.04 inches.
|
|
A
|
=
|
Project Area in acres
|
|
Rv
|
=
|
Volume Runoff Coefficient [0.05 + 0.009(1)], where I is the
impervious surface percentage (impervious area ÷ total project
area) X 100%
|
(2)
In special protection watersheds, as described in 25 Pa Code
Chapter 93, this volume is required to remain on-site through infiltration
and other methods, to protect water quality. Guidance can be obtained
from PADEP.
D.
The following factors must be considered when evaluating the suitability
of BMPs used to control water quality at a given development site:
(1)
Total contributing drainage area.
(2)
Permeability and infiltration rate of the site soils.
(3)
Topographic 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)
Volume of runoff that will be effectively treated.
(12)
Nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife habitat.
(15)
Recreational value.
(16)
Enhancement of aesthetic and property value.
(17)
To accomplish the above, the applicant shall submit original
and innovative designs for review. Such designs may achieve the water
quality objectives through a combination of BMPs (best management
practices).
E.
The applicant may, subject to approval of Plumstead Township, use
any of the following nonstructural stormwater credits, generally described
in the following table, in computing the required water quality volume.
Additional innovative design techniques may be utilized where approved
by the Township. The applicant should consult with the Township early
in the design phase when a new approach to nonstructural stormwater
design is proposed.
|
Stormwater Credit
|
Description
|
|---|---|
|
Natural area conservation
|
Conservation of natural areas such as forest, wetlands, or other
sensitive areas in a protected easement thereby retaining their predevelopment
hydrologic and water quality characteristics. Using this credit, a
designer may subtract conservation areas from total site area when
computing the required water quality volume.
|
|
Disconnection of rooftop runoff
|
Credit is given when rooftop runoff is disconnected and then
directed over a pervious area where it is infiltrated. Credit is typically
obtained by grading the site to promote overland flow or by providing
bioretention on single-family residential lots. If a rooftop area
is adequately disconnected, the impervious area may be deducted from
the total impervious cover.
|
|
Disconnection of non-rooftop runoff
|
Credit is given for practices that disconnect surface impervious
cover by directing it to pervious areas where it is infiltrated. As
with rooftop runoff, the impervious area may be deducted from the
total impervious cover thereby reducing the required water quality
volume.
|
|
Stream buffer credit
|
Credit is given when a stream buffer effectively treats stormwater
runoff. Effective treatment constitutes capturing runoff from pervious
and impervious areas adjacent to the buffer and treating the runoff
through overland flow across a grass or forested area. Areas treated
in this manner may be deducted from total site area.
|
|
Grass channel (open section roads)
|
Credit may be given when open grass channels are used to reduce
the volume of runoff and pollutants during smaller storms. If designed
according to appropriate criteria, these channels may meet water quality
criteria for certain types of residential development.
|
|
Environmentally sensitive rural development
|
Credit is given when a group of environmental site design techniques
are applied to low density or rural residential development. This
credit eliminates the need for structural practices to address water
quality volume.
|
F.
The volume and rate of any stormwater discharges allowed under this
Part must be managed to prevent the physical and chemical degradation
of receiving waters. If a detention facility is proposed which is
part of the BMPs approved for the project, the facility(ies) must
be designed to provide for a twenty-four-hour extended detention of
the one-year, twenty-four-hour storm event (i.e., the stormwater runoff
will be released over a minimum 24 hours for the one-year, twenty-four-hour
storm event from the time of peak inflow to zero outflow).
[Ord. No. 2022-01, 7/12/2022]
A.
Prevention of stormwater runoff is the key objective of Chapter 93
of the PADEP regulations, because runoff can change the physical,
chemical, and biological integrity of water bodies, thereby impacting
water quality.
B.
The project plan shall describe how water quality protection requirements will be met. Infiltration BMPs shall be evaluated and utilized to the maximum extent possible to manage the net change in stormwater runoff generated so that post-construction discharges do not degrade the physical, chemical, or biological characteristics of the receiving waters. These BMPs may be used to satisfy all or part of the requirements in § 26-126.
C.
Post-construction stormwater infiltration of runoff shall replicate preconstruction infiltration of runoff to the maximum extent possible. In high quality and exceptional value watersheds, special requirements apply (refer to § 26-126 of this Part).
D.
In calculating the volume of runoff that can be infiltrated at a
site, the following methodology shall be used:
(1)
Methodology:
Rev = [(S)(Rv)(A)]/12 (acre-feet)
|
Where:
| ||
|
Rev
|
=
|
Recharge Volume (acre-feet)
|
|
S
|
=
|
Soil specific recharge factor (inches)
|
|
A
|
=
|
Site area contributing to the recharge facility (acres)
|
|
Rv
|
=
|
Volumetric runoff coefficient, Rv = 0.05
+ 0.009(I), where:
|
|
I = percent impervious area, and
| ||
|
S shall be obtained based upon hydrologic soil group based upon
the table below:
| ||
|
Hydrologic Soil Group
|
Soil Specific Recharge Factor (S)
|
|---|---|
|
A
|
0.38
|
|
B
|
0.25
|
|
C
|
0.13
|
|
D
|
0.06
|
If more than one hydrologic soil group (HSG) is present
at a site, a composite recharge volume shall be computed based upon
the proportion of total site area within each HSG.
(2)
In selecting the appropriate infiltration BMPs, the applicant
shall consider the following:
(a)
Permeability and infiltration rate of the site soils.
(b)
Topographic slope and depth to bedrock.
(c)
Seasonal high-water table.
(d)
Proximity and elevation relative to building foundations, basements,
and wellheads. (Infiltration BMP should be located downgrade of these
structures.)
(e)
Erodibility of soils.
(f)
Land availability, configuration, and topography.
(g)
Peak discharge and required volume control.
(h)
Stream bank erosion.
(i)
Efficiency of the BMPs to mitigate potential water quality problems.
(j)
Volume of runoff that will be effectively treated.
(k)
Nature of the pollutant being removed.
(l)
Maintenance requirements.
(m)
Creation/protection of aquatic and wildlife habitat.
(n)
Recreational value.
(o)
Enhancement of aesthetic and property value.
(3)
A detailed soils evaluation of the project site shall be performed to determine the suitability of infiltration BMPs (refer to § 26-137A). The evaluation shall be performed by a qualified professional, and at a minimum, address soil permeability, depth to bedrock, susceptibility to sinkhole formation, and subgrade stability. The site testing shall include adequate sampling of all portions of the site not limited by 100% protected natural resources to determine areas of the property which are suitable for infiltration BMPs. 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 at the elevation of the proposed
infiltration zone (bottom surface of infiltration facilities) to determine
appropriate percolation rate and/or hydraulic conductivity. Field
testing guidelines are identified in Appendix C.[1]
[1]
Editor's Note: Appendix C is included as an attachment to this chapter.
(c)
Design infiltration BMPs for required stormwater volume based
on field-determined capacity at the level of the proposed infiltration
surface.
(4)
Soil characteristics:
(a)
Infiltration BMPs are particularly appropriate in hydrologic
soil groups A and B, as described in the Natural Resources Conservation
Service Manual TR-55.
(b)
Low-erodibility factors ("K" factors) are preferred for the
construction of basins.
(c)
There must be a minimum depth of 12 inches between the bottom
of any facility and the seasonal high-water table and/or bedrock (limiting
zones). The minimum required separation between the limiting zone
may be increased, if required by the Township, should project-specific
conditions exist (such as anticipated increased contaminants) which
dictate greater prevention of groundwater contamination.
(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)
A minimum of 30 feet of undisturbed fill shall separate the
foundation wall of any building and an infiltration BMP.
(f)
The infiltration system shall have positive overflow controls
to prevent storage within one foot of the finished surface of grade.
(g)
Infiltration rates shall not be used in computing the storage
volume of the infiltration system.
(h)
Surface inflows shall be designed to prevent direct discharge
of sediment into the infiltration system.
(5)
The recharge volume provided at the site shall be directed to
the most permeable HSG (hydrologic soil group) available, except where
other considerations apply such as in limestone geology.
(6)
Any infiltration BMP shall be capable of completely infiltrating
the impounded water within 48 hours from the peak of the storm.
(7)
Special attention shall be paid to proper installation of infiltration-oriented
stormwater management systems during construction, and to careful
avoidance of soil compaction during site development.
(8)
Infiltration is not permitted in geologically susceptible limestone
areas. All stormwater facilities in geologically susceptible limestone
areas must be constructed with an impermeable liner approved by the
Township to prevent seepage of water into the ground. All proposed
channels or swales receiving or conveying concentrated stormwater
runoff must be protected with an impermeable liner approved by the
Township.
(9)
Caution shall be exercised where salt or chloride would be a
pollutant since soils do little to filter this pollutant and it may
contaminate the groundwater. Extreme caution shall be exercised where
infiltration is proposed in source water protection areas. The qualified
design professional shall evaluate the possibility of groundwater
contamination from the proposed infiltration/recharge facility and
perform a hydrogeologic justification study if necessary. The infiltration
requirement in high quality/exceptional value waters shall be subject
to PADEP's Title 25, Chapter 93, Antidegradation Regulations.
The Township may require the installation of an impermeable liner
in BMP and/or detention basins where the possibility of groundwater
contamination exists. A detailed hydrogeologic investigation may be
required by the Township.
(10)
The plan must include safeguards against groundwater contamination
for uses which may cause groundwater contamination, should there be
a mishap or spill.
(11)
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.
(12)
Infiltration BMPs shall not be constructed nor receive runoff
until the entire contributory drainage area to the infiltration BMP
has achieved final stabilization.
(13)
The requirements for volume control and infiltration are applied
to all disturbed areas, even if they are ultimately to be a pervious
or permeable land use such as lawn or other landscaped area, given
the extent to which development-related disturbance leads to compaction
of the soils and reduces their infiltrative capacity.
[Ord. No. 2022-01, 7/12/2022]
A.
To minimize the impact of stormwater runoff on downstream stream
bank erosion, a BMP must be designed to detain the proposed condition's
two-year, twenty-four-hour design storm to the existing condition's
one-year flow using the SCS Type II distribution. Additionally, provisions
shall be made (such as adding a small orifice at the bottom of the
outlet structure) so that the proposed condition's 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
(e.g., the maximum water surface elevation is achieved in the facility).
B.
Release of water may begin at the start of the storm (e.g., the invert
of the water quality orifice is at the invert of the facility). The
design of the facility shall minimize clogging and sedimentation.
Orifices smaller than four inches in diameter are not allowed unless
the design engineer can verify that the smaller orifice is protected
from clogging by use of trash racks, etc. In that case, smaller orifices
may be permitted. Trash racks are required for any primary orifice.
C.
Whenever a watercourse is located within a development site, it shall
remain open in the natural state and location and shall not be piped,
impeded, or altered (except for road crossings). It is the responsibility
of the developer to restore existing eroded stream/channel banks within
a subdivision or land development site and obtain all permits necessary
from PADEP to do so. The developer must submit pictorial documentation
of existing stream/channel banks to determine whether existing banks
must be stabilized.
[Ord. No. 2022-01, 7/12/2022]
A.
Stormwater runoff which may result from regulated activities listed in § 26-104 shall be controlled by permanent stormwater runoff BMPs that will provide the required standards of this Part. The methods of stormwater control or best management practices (BMPs) which may be used to meet the required standards are described in this Part and the Pennsylvania Stormwater Best Management Practice Manual, December 2006, as amended. The choice of BMPs is not limited to the ones appearing in this Part and the manual; however, any selected BMP must meet or exceed the runoff peak rate requirements of this Part for the applicable hydrologic district.
B.
Any stormwater facility located on state highway rights-of-way shall
be subject to approval by the Pennsylvania Department of Transportation.
C.
Collection System Standards.
(1)
Curb Inlets. Curb inlets shall be located at curb tangents on
the uphill side of street intersections, and at intervals along the
curbline to control the maximum amount of encroachment of runoff on
the roadway pavement so that same does not exceed a width of four
feet during the design storm event. Design and location of curb inlets
shall be approved by the Township.
(2)
Pipe Materials. All storm sewer piping for storm sewer collection/conveyance
systems to be owned and maintained by the Township shall be reinforced
concrete pipe. Piping shall be saw-cut at ends, as needed, and not
hammered or broken. All pipe joints and lift holes must be mortared
except where designed for infiltration. For all privately owned and
maintained storm sewer collection/conveyance systems, smooth-lined
high density polyethylene pipe may be used in lieu of reinforced concrete
pipe, provided that the smooth-lined high density polyethylene pipe
is designed and installed per the pipe manufacturer's specifications.
(3)
Minimum Pipe Size. Minimum pipe diameter shall be 18 inches
(or an equivalent flow area of 1.76 square feet).
(4)
Inlet and Manhole Construction. Inlet and manhole castings and
concrete construction shall be equivalent to PennDOT design standards.
Manholes shall be equipped with open grate lids. All inlet grates
shall be "bicycle safe" heavy-duty structural steel. All storm sewer
inlets must be identified with a storm drain marker. Storm drain markers
shall be stainless steel affixed to the inlet hood with adhesive,
rivets or bolts. (Marker may be bolted to the grate in off-road locations).
Markers shall have a minimum diameter of 3 1/2 inches and include
"No Dumping - Drains to Waterway" and a fish symbol. Alternate designs/sizes
may be used if approved by the Township.
(5)
Open-end pipes must be fitted with concrete endwalls or wing
walls in accordance with PennDOT Standards.
(6)
Flow velocity. Stormwater collection systems shall be designed
to produce a minimum velocity of 3.0 feet per second when flowing
full. The maximum permissible velocity shall be 15.0 feet per second.
Pipe slopes shall not be less than 0.50%.
(7)
Inlets and manholes shall be spaced at intervals not exceeding
300 feet, and shall be located wherever branches are connected or
sizes are changed, and wherever there is a change in alignment or
grade. For drainage lines of at least 36 inches diameter, inlets and
manholes may be spaced at intervals not exceeding 400 feet.
(8)
Storm sewer bedding/backfill requirements shall conform to the
construction details in Appendix L.[1]
[1]
Editor's Note: Appendix L is included as an attachment to this chapter.
(9)
Inlets shall be located to intercept concentrated runoff prior
to discharge over public/private rights-of-way, sidewalks, streets,
and driveways.
(10)
The capacity of all Type "C" inlets shall be based on a maximum
surface flow to the inlets of 4.0 cfs, calculated based on the 100-year
frequency design storm event. The maximum flow to Type "C" inlets
located in low points (such as sag vertical curves) shall include
the overland flow directed to the inlet as well as all bypass runoff
from upstream inlets. The bypass flow from upstream inlets shall be
calculated using inlet efficiency curves included in PennDOT Design
Manual Part 2, latest edition. If the surface flow to an inlet exceeds
4.0 cfs, additional inlets shall be provided upstream of the inlet
to intercept the excessive surface flow. A Type "C" inlet at a low
point of a paved area may be designed to accept a maximum of six cubic
feet per second (cfs). Type "M" inlets shall be designed to accept
a maximum surface flow of six cfs based on the 100-year frequency
design storm event, unless otherwise approved by the Township. Double
inlets will not be permitted where additional pipe and inlets can
be placed upstream to intercept excessive surface flow. A maximum
of 12 cfs shall be permitted to be collected by a Type "M" inlet located
in an isolated pervious area, provided the designer can verify that
such an inlet would not cause stormwater to accumulate on any adjacent
public or private property, outside of an associated storm sewer easement,
and that the depth of the accumulated stormwater would not exceed
12 inches.
(11)
A minimum drop of two inches shall be provided between the inlet
and outlet pipe invert elevations within all inlets and manholes.
When varying pipe sizes enter an inlet or manhole, the elevation of
crown of all pipes shall be matched.
(12)
Reinforced concrete pipes shall have a minimum depth of cover
of 12 inches (including over the bell) or as designated by the American
Concrete Pipe Association (whichever is greater), and in no case shall
any part of the pipe project into the road subbase or curb. Where
cover is restricted, equivalent pipe arches may be specified in lieu
of circular pipe. Where smooth-lined high density polyethylene pipe
is approved in lieu of reinforced concrete pipe, minimum depth of
cover for smooth-lined concrete pipe shall be per the pipe manufacturer's
specifications, or 12 inches, whichever is greater.
(13)
The capacity of all stormwater pipes shall be calculated utilizing
the Manning Equation for open channel flow as applied to closed conduit
flow. The Manning's roughness coefficient shall be 0.013 for
all reinforced concrete pipe, and 0.012 for all smooth-lined high
density polyethylene pipe. In cases where pressure flow may occur,
the hydraulic grade line shall be calculated throughout the storm
sewer system to verify that at least one foot of freeboard will be
provided in all inlets and manholes for the design storm event.
(14)
Culverts shall be designed based on procedures contained in
Hydraulic Design of Highway Culverts, HDS No. 5, U.S. Department of
Transportation, Federal Highway Administration. Where pressure flow
is anticipated in storm sewer pipes (non-open channel flow), the applicant's
designer shall be required to calculate the elevation of the hydraulic
grade line through the storm sewer system. Wherever the hydraulic
grade line elevation exceeds the pipe crown elevation for the design
flow, pipes with watertight joints must be specified.
(15)
Storm sewer structures (i.e., endwalls, inlets, and sections,
etc.) may not be located on top of, or within 10 feet of, electric,
communication, water, sanitary sewer, or gas services and/or mains,
unless approval is received from the Township and the Authority or
utility having jurisdiction over same.
(16)
Stormwater pipes must be oriented at right angles to electric,
water, sanitary sewer, and gas utilities when crossing above or beneath
same. Crossing angles of less than 90° will only be permitted
at the discretion of the Township. When skewed crossings are permitted,
interior angles between alignment of the storm sewer pipe and utility
shall not be less than 45°. Vertical and horizontal design of
storm sewers must be linear.
(17)
Roadway underdrain is required along both sides of all proposed
roadways, existing roadways proposed to be widened, and within existing
or proposed roadside swales as directed by the Township.
(18)
Where a public storm sewer system is not located within a right-of-way,
or dedicated public property, a twenty-foot-wide easement shall be
established to encompass the storm sewer system, including energy
dissipators. For multiple pipes or utilities, the width of the easement
shall be a minimum of 30 feet.
(19)
A minimum of one foot of freeboard, between the inlet grate
and the design flow elevation, shall be provided in all storm sewer
systems (inlets and manholes) for the 100-year frequency design storm
event.
D.
Open Swales and Gutters. Open swales shall be designed on the basis
of Manning's Formula as indicated for collection systems with
the following considerations:
(1)
Roughness Coefficient. The roughness coefficient shall be 0.040
for earth swales.
(2)
Bank Slopes. Slopes for swale banks shall not be steeper than
one vertical to four horizontal.
(3)
Flow Velocity. The maximum velocity of flow as determined by
Manning's Equation shall not exceed the allowable velocities
as shown in the following table for the specific type of material,
unless otherwise approved by the Township and the Bucks County Conservation
District.
Note: Source of the following design criteria is the Pennsylvania
Department of Environmental Protection, Bureau of Soil and Water Conservation
publication, Erosion and Sediment Control Program Manual.
|
Allowable Velocity
| |
|---|---|
|
Material
|
Velocity in feet per second (fps)
|
|
Well established grass on good soil
| |
|
Short pliant bladed grass
|
4.0 to 5.0
|
|
Bunch grass -soil exposed
|
2.0 to 3.0
|
|
Stiff stemmed grass
|
3.0 to 4.0
|
|
Earth without vegetation
| |
|
Fine sand or silt
|
1.0
|
|
Ordinary firm loam
|
2.0 to 3.0
|
|
Stiff clay
|
3.0 to 5.0
|
|
Clay and gravel
|
4.0 to 5.0
|
|
Coarse gravel
|
4.0 to 5.0
|
|
Soft shale
|
5.0 to 6.0
|
|
Shoulders
| |
|
Earth
|
(as defined above)
|
|
Stabilized
|
6.0
|
|
Paved
|
10.0 to 15.0
|
(4)
Swales shall be stabilized with biodegradable erosion control
matting to permit establishment of permanent vegetation. Swales shall
be of such shape and size to effectively contain the 100-year, Rational
Method design storm, and to conform to all other specifications of
the Township.
(5)
To minimize sheet flow of stormwater across lots located on
the lower side of roads or streets, and to divert flow away from building
areas, the cross section of the street as constructed shall provide
for parallel ditches or swales or curb on the lower side which shall
discharge only at drainage easements, unless otherwise approved by
the Township.
(6)
Gutters and swales adjacent to road paving shall be permitted
to carry a maximum flow of four cubic feet per second prior to discharge
away from the street surface, unless it is proven to the satisfaction
of the Township by engineering calculations that the road slopes or
other factors would allow higher gutter or swale capacity.
(7)
Flows larger than those permitted in gutters and roadside swales
may be conveyed in swales outside the required road right-of-way in
separate drainage easements, or may be conveyed in pipes or culverts
inside or outside the required road right-of-way.
(8)
Existing and proposed swales shall be provided with underdrains
as deemed necessary by the Township should overland seepage result
in potential maintenance problems. Underdrains must discharge into
a natural drainage channel or stormwater management system.
(9)
Where drainage swales are used to divert surface waters away
from buildings, they shall be sodded, landscaped, or otherwise protected
as required and shall be of a slope, shape, and size conforming with
the requirements of the Township. Concentration of surface water runoff
shall be permitted only in swales, watercourses, retention or detention
basins, bioretention areas, or other areas designed to meet the objectives
of this Part.
E.
Bridge and Culvert Design. Any proposed bridge or culvert to convey
flow within a perennial or intermittent stream shall be designed in
accordance with the following principals:
(1)
Culverts and bridges shall be designed with an open bottom to
maintain natural sediment transport and bed roughness, avoiding acceleration
of water velocity above the natural (preexisting) condition. Rock
(riprap) lining (native material if possible) shall be installed within
the culvert as needed to prevent erosion within the structure. Approximate
top of rock lining must be at the level of the existing stream bottom
so as to maintain normal water level and unimpeded movement of native
animal species.
(2)
Bottom of opening shall be designed to match the bankfull channel
condition in terms of width and depth. The cross-sectional area of
the bankfull channel (measured at a reference location upstream of
the structure) shall be matched with area in the crossing structure.
(3)
Above the bankfull elevation, the width shall increase a minimum
of 30% to disperse the energy of higher flow volumes and avoid undermining
of the supporting structure by secondary currents.
(4)
The total cross-sectional area of the structure opening must
be equal to or greater than the flood-prone area (cross-sectional
stream area at a depth of twice the maximum bankfull depth, measured
at a reference location upstream of the structure). The flood-prone
area is approximately equal to the area flooded by a fifty-year return
flood.
(5)
All bridges, culverts, and drainage channels shall be designed
to convey a flow rate equal to a 100-year, twenty-four-hour storm
(refer to Appendix A, Table A-1[2]). All bridges and culverts shall be designed to convey
the 100-year design storm without increasing the extent and depth
of the 100-year floodplain.
[2]
Editor's Note: Appendix A is included as an attachment to this chapter.
F.
Storm Sewer Design.
(1)
Design flow rate. The storm sewer system shall be designed to
carry the 100-year frequency design storm peak flow rate. The drainage
area and runoff coefficient to each inlet shall be indicated on the
stormwater management plan. The 100-year flow rate shall be determined
by the Rational Method formula:
Q = CIA
|
Where:
| ||
|
Q
|
=
|
Peak runoff rate measured in cubic feet per second (cfs)
|
|
C
|
=
|
Runoff coefficient - The coefficient of stormwater runoff includes
many variables, such as ground slope, ground cover, shape of drainage
area, etc.
|
|
I
|
=
|
Intensity - Average rainfall intensity in inches per hour for
a time equal to the time of concentration (in/hr).
|
|
A
|
=
|
Area — Drainage area in acres (ac).
|
Appropriate values for the rainfall intensity can be
found in Appendix A, Figure A-1.[3]
[3]
Editor's Note: Appendix A is included as an attachment to this chapter.
(2)
Consideration shall be given to future land use changes in the
drainage area in selecting the Rational ("C") coefficient. For drainage
areas containing several different types of ground cover, a weighted
value of "C" shall be used.
(3)
In determining the peak flow rate to individual storm sewer inlets (or other collection structures), the time of concentration method (as referenced in § 26-130) shall be used for inlet drainage areas in excess of one acre, unless otherwise approved by the Township. For inlet drainage areas less than one acre, a five-minute time of concentration shall be used unless otherwise approved by the Township.
(4)
In determining the required design flow rate through a storm
sewer piping system, if a five-minute time of concentration (storm
duration) results in a pipe size exceeding a thirty-inch diameter
pipe (or equivalent flow area of 4.9 square feet), the time of concentration
approach (as defined herein) shall be used in determining storm duration.
(5)
Overflow System. An overflow system shall be provided to carry
all bypass flow, and/or flow in excess of storm sewer design capacity,
to the stormwater BMP (or other approved outlet point) when the capacity
of the storm sewer system is exceeded. Stormwater runoff will not
be permitted to surcharge from storm sewer structures.
G.
Grading and Drainage.
(1)
After completion of rough grading, a minimum of eight inches
of topsoil, or the existing depth of topsoil encountered on the site
(whichever is greater), shall be returned to remaining disturbed areas
prior to final grading and seeding.
(2)
Lots shall be graded to secure proper drainage away from buildings
and to prevent the collection of stormwater in pools. Minimum 2% slopes
shall be maintained away from and around all structures. Separation
between the top of foundation wall (or slab) shall comply with Township
Construction Code requirements.
(3)
Construction. The developer shall construct and/or install such
drainage structures and/or pipe which are necessary to prevent erosion
damage and to satisfactorily carry off such surface waters to the
nearest practical street, storm drain or natural watercourse.
(4)
Excavation. No excavation shall be made with a cut face steeper
in slope than (4:1 = 25%), except under one or more of the following
conditions:
(a)
The fill is located so that settlement, sliding, or erosion
will not result in property damage or be a hazard to adjoining property,
streets, alleys or buildings.
(b)
A written statement from a professional civil engineer, licensed
in the Commonwealth of Pennsylvania and experienced in erosion control,
certifying the site has been inspected and that the proposed deviation
from the slope specified above will not endanger any property or result
in property damage, is submitted to and approved by the Township Engineer.
(5)
Fill. No fill shall be made which creates any exposed surface
steeper in slope than (4:1 = 25%) except under one or more of the
following conditions:
(a)
The fill is located so that settlement, sliding, or erosion
will not result in property damage or be a hazard to adjoining property,
streets, alleys, or buildings.
(b)
A written statement from a professional civil engineer, licensed
in the Commonwealth of Pennsylvania and experienced in erosion control,
certifying the site has been inspected and that the proposed deviation
from the slope specified above will not endanger any property or result
in property damage, is submitted to and approved by the Township.
(c)
A concrete, segmental block, or stone masonry wall, constructed
in accordance with Township requirements, is provided to support the
face of the excavation.
(6)
Slopes and Fences. The top or bottom edge of slopes shall be
a minimum of five feet from property or right-of-way lines of streets
or alleys, in order to permit the normal rounding of the edge without
encroaching on the abutting property. Where walls or slopes (steeper
than two horizontal to one vertical) are approved under the criteria
in this Part, and are five feet or more in height, a protective fence
conforming to Township Construction Codes shall be required at the
top of the wall (or bank).
(7)
Cleanup. All lots must be kept free of any debris or nuisances
whatsoever during construction.
(8)
Design of erosion and sedimentation control facilities (particularly
stormwater/sediment basins) shall incorporate best management practices
as defined herein.
(9)
Cut and fill operations shall be kept to a minimum. Wherever
feasible, natural vegetation shall be retained, protected, and supplemented.
Cut and fills shall not endanger or otherwise adversely impact adjoining
property.
(10)
No grading equipment shall be permitted to be loaded and/or
unloaded on a public street, and no grading equipment shall be permitted
to travel on or across a public street unless licensed for operation
on public thoroughfares.
(11)
Grading equipment shall not be permitted to cross intermittent
and perennial streams. Temporary crossing shall only be permitted
where application is made, and approval is received, from the Pennsylvania
Department of Environmental Protection (where applicable), the Bucks
County Conservation District, and Plumstead Township.
(12)
Design of energy dissipation for high-volume and/or high-velocity
discharge from storm sewer pipes and channels shall be in accordance
with Hydraulic Engineering Circular No. 14, "Hydraulic Design of Energy
Dissipaters for Culverts and Channels," as published by Department
of Transportation, FHA, when deemed necessary by the Township, and
as approved by the Bucks County Conservation District.
(13)
To control the dissemination of mud and dirt onto public roads
and driveways, tire cleaning areas constructed of AASHTO No. 1 stone
(underlain by geotextile structural fabric), at least 50 feet in length
shall be installed at each point of access to the site and individual
lots (upon construction of internal streets in a binder condition).
When deemed necessary by the Township, washing stations shall also
be set up at every construction entrance in order to wash mud and
dirt from exiting vehicles. Appropriate measures must be taken to
control runoff from such locations. The developer shall be responsible
for the placement of appropriate signage identifying construction
entrances and washing stations. Construction entrances shall be maintained
by the developer during construction, as determined by the Township.
(14)
During construction activities, necessary measures for dust
control shall be exercised, including the application of water to
higher traffic areas of the site.
(15)
In the event any mud and/or debris is transported from the site
onto a public roadway, the debris shall be removed immediately, and
the roadway swept and/or washed as deemed necessary by the Township
at the owner's expense.
(16)
Adequate provision shall be made to prevent surface water from
damaging the cut face of excavation and the sloping surfaces of fills.
H.
Stormwater Detention/Retention Basins.
(1)
If permanent ponds (retention basins) are proposed, the developer
shall demonstrate that such ponds are designed to protect the public's
health and safety.
(2)
During construction, duly authorized representatives of Plumstead
Township may enter at any reasonable time upon any property within
the Township to investigate whether construction activity is in compliance
with this Part.
(3)
When basins are provided, they shall be designed to utilize
the natural contours of the land whenever possible. When such design
is not practical, the construction of the basin shall utilize slopes
as flat as possible to blend the structure into the terrain.
(4)
Structural stormwater BMP design shall follow general design guidelines contained in Chapter 6 of the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual), latest edition.
(5)
Landscaping and planting in and around the perimeter of basins shall be provided. It shall be aesthetically pleasing and compatible with surrounding land uses and require minimum maintenance. Proposed landscaping and planting shall also be in accordance with the provisions of this Part, Chapter 22, Subdivision and Land Development, and Chapter 27, Zoning.
(6)
If a stormwater management basin will serve as a temporary sediment
control device, the temporary sediment control measures shall be shown,
including perforated riser pipes or standboxes, filter berms, cleanout
stakes and other measures as may be required by Pennsylvania Department
of Environmental Protection Chapter 102 regulations. Plans for such
facilities shall require Bucks County Conservation District approval
prior to implementation. Sedimentation basins shall be in place prior
to any earthmoving activities within their tributary drainage areas.
A note identifying the above criteria shall be required on the record
plan of subdivisions and land developments as well as in the development
agreement with the Township.
(7)
Stormwater management basins shall be in place before the creation
of any new impervious surfaces on the site.
(8)
Runoff shall not be directed to any infiltration structure until
all tributary drainage areas are stabilized.
(9)
Where permanent retention (wet pond) facilities are proposed,
there shall be a safety ledge, 10 feet wide, no greater than 15 inches
and no less than 12 inches below the permanent water surface level.
(10)
All basins shall have slopes of (4:1 = 25%) or flatter on the
basin's outer berm and three horizontal to one vertical or less
on the basin's inner berm. The top or toe of any slope shall
be located a minimum of five feet from any property line. The maximum
difference between the top of berm elevation and the invert elevation
of the outlet structure shall be seven feet.
(11)
All portions of a dry detention basin bottom (nonwetland) shall
have a minimum slope of 2%.
(12)
All basin embankments shall be placed in lifts not to exceed
one foot in thickness, and each lift shall be compacted to a minimum
of 95% of Modified Proctor Density as established by ASTM D-1557.
Prior to proceeding to the next lift, the compaction shall be verified
by a soils engineer employed by the applicant/developer. Compaction
tests shall be run on the leading and trailing edge of the berm along
with the top of the berm. Verification of required compaction shall
be submitted to the Township prior to utilization of any basin for
stormwater management.
(13)
Emergency overflow facilities/spillways shall be provided within
basins in order to convey basin inflow in excess of design flows,
out of the basin, or in the event the outlet structure becomes blocked
and is unable to convey flow. Emergency spillways discharging over
embankments shall be constructed of reinforced concrete Checker Blocks® to protect the berm against erosion. Checker
Blocks® shall be backfilled with topsoil
and stabilized in lawn cover. The Checker Block® lining shall extend to the toe of the embankment on the outside
of the berm, and shall extend to an elevation of three feet below
the spillway crest on the inside of the berm. Vegetated spillways
may be utilized for spillways constructed entirely on undisturbed
ground (e.g., not discharging over fill material). A dense cover of
vegetation shall be rapidly established in such spillways by sodding
or seeding with a geotextile anchor. The minimum capacity of all emergency
spillways shall be equivalent to the peak flow rate of the 100-year,
post-development design storm (entering to the basin). Spillway elevations
shall be a minimum of one foot above the maximum depth of detained
runoff within the basin for the 100-year post-development design storm.
(14)
In all cases, the discharge end of the basin shall be provided
with a properly designed outlet control structure (headwall, orifice
structure or other approved flow control structure), culvert pipe,
and endwall. Perforated riser pipes alone, without provision for permanent
outlet control structure (as stated above) and culvert pipe, are not
permitted for permanent basins.
(15)
The minimum top of basin berm width (at the design elevation)
shall be 10 feet. A cutoff trench (keyway) of impervious material
shall be provided under all embankments that require fill material.
The cutoff trench shall be a minimum of eight feet wide, three feet
deep and have side slopes of one horizontal to one vertical.
(16)
The minimum freeboard through the emergency spillway shall be
one foot. Freeboard is defined as the difference between the design
flow elevation through the spillway and the elevation of the top of
the settled basin berm.
(17)
Anti-seep collars shall be installed around the pipe barrel
and shall be centered within the normal saturation zone of the berm.
The anti-seep collars and their connections to the pipe barrel shall
be watertight. The anti-seep collars shall be cast in place and extend
a minimum of two feet beyond the outside of the principal pipe barrel.
Precast collars shall be permitted if approved by the Township. A
minimum of two collars shall be installed on each basin outlet pipe,
and be located a minimum of two feet from any pipe joint.
(18)
A perforated sediment control structure, sized in accordance
with Bucks County Conservation District requirements, shall be provided
at each basin outlet structure (if more than one is to be utilized)
for sediment control. Sediment control structures shall not be removed
until the entire area tributary to the basin has been permanently
stabilized and until approved by the Bucks County Conservation District.
(19)
All basin outlet pipes shall be watertight reinforced concrete
having O-ring joints. All joints and lift holes shall be mortared.
Crushed stone bedding/backfill material shall not be utilized through
basin berms.
(20)
A minimum of six inches is required between the top of an outlet
structure box and the emergency spillway elevation. Six inches, minimum,
is also required between the 100-year water surface elevation and
the top of an outlet structure box.
(21)
Energy dissipating devices (rock lining/riprap, or other approved
materials) shall be provided at all basin outlets and shall be sized
in accordance with Pennsylvania Department of Environmental Protection,
Bureau of Soil and Water Conservation publication, Erosion and Sediment
Control Program Manual, latest revision.
(22)
Stone gabion baskets and retaining wall systems shall not be
utilized in construction of detention/retention basins.
(23)
Access easements and stabilized drives to stormwater detention
facilities shall be provided for maintenance and operation. This access
easement shall be cleared and, when possible, be at least 20 feet
in width. Multiple accesses shall be encouraged for major facilities.
The developer shall provide access easements and drives of reinforced
concrete Checker Block® (back-filled
with topsoil and stabilized in lawn cover) or other similar paver
acceptable to the Township Engineer, over a six-inch bed of compacted
PennDOT Type 3A coarse aggregate (or approved equivalent). Accessways
to basins shall be a minimum of 10 feet wide and be no steeper in
slope than 10 feet horizontal to one foot vertical. In addition, depressed
curb and concrete apron shall be provided where the accessway enters
a street/driveway, and the stabilized driveway shall extend from the
bottom of the interior basin berm embankment to the point of access
to the basin. Access easements shall be owned and maintained by the
individual lot owner(s) or homeowners' association, but shall
be established to permit access by Plumstead Township or its designee,
for emergency inspection and/or maintenance, at any reasonable time.
(24)
Split-rail fence with wire mesh backing is required around all
detention or retention basins where directed by Plumstead Township.
Fence shall consist of concrete posts (dual rail), four feet high,
with cedar rails (eight feet to 10 feet long), and epoxy-coated wire
mesh (color to be determined by the Township) installed six inches
above finished grade. Each basin fence installation shall include
two points of access with ten-foot-wide self-closing, self-latching
gates.
I.
General Design Requirements.
(1)
Prior to finish grading of a development site and final overlay
of streets, roads, and driveways, temporary measures, acceptable to
the Township, shall be taken to ensure that all runoff intended to
be intercepted and collected by an inlet or other facility will be
collected. The plan shall include such details, notes, or specifications,
including bituminous "eyebrows" at inlets, diversion berms, etc.
(2)
Water originating from other than natural sources, such as air-conditioning
units, sump pumps, or other dry weather flow, wherever practical and
possible, shall be connected to a storm sewer, or street drainage
structure, or other approved stormwater conveyance facility that is
designed as part of a stormwater management BMP.
(3)
All stormwater runoff and floodplain calculations and stormwater
management facilities design shall be prepared by a professional engineer
licensed in the Commonwealth of Pennsylvania.
(4)
When subdivisions or land developments are submitted to the
Township for approval in sections or phases, a complete storm sewer
design for the proposed subdivision and land development shall be
submitted. The proposed design must include the entire tract and not
a portion.
[Ord. No. 2022-01, 7/12/2022]
A.
Stormwater runoff from all development sites shall be calculated
using either the Rational Method or a Soil Cover Complex methodology.
B.
Any stormwater runoff calculations shall use a generally accepted
calculation technique that is based on the NRCS Soil Cover Complex
Method. Table 26-130-1 summarizes acceptable computation methods.
Method must be selected by the applicant based on the individual limitations
and suitability of each method for a particular site. The Rational
Method may be used to estimate peak discharges from drainage areas
that contain less than 75 acres. The Rational Method is recommended
for drainage areas under 25 acres.
|
Table 26-130-1 Acceptable Computation Methodologies for Stormwater
Management Plans
| ||
|---|---|---|
|
Method
|
Method Developed By
|
Applicability
|
|
TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
|
|
TR-55 (or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
|
|
HEC-1, HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
|
|
PSRM
|
Penn State University
|
Applicable where use of a hydrologic computer model is desirable
of necessary; simpler than TR-20 or HEC-1
|
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
Applicable sites less than 75 acres, or as approved by the Township
Engineer
|
|
Other methods
|
Varies
|
Other computation methodologies approved by the Township Engineer
|
C.
All calculations consistent with this Part using the Soil Cover Complex
Method shall use the appropriate design rainfall depths for the various
return period storms according to the National Oceanic and Atmospheric
Administration (NOAA) Atlas 14 rain data corresponding to the Doylestown
rain gage, as presented in Table A-1 Appendix A of this Part.[1] The SCS Type 11 rainfall curve from NOAA is found on Figure
A-1 in Appendix A of this Part. This data may also be directly retrieved
from the NOAA Atlas 14 website: https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=pa.
If a hydrologic computer model such as PSRM or HEC-1/HEC-HMS is used
for stormwater runoff calculations, then the duration of rainfall
shall be 24 hours.
[1]
Editor's Note: Appendix A is included as an attachment to this chapter.
D.
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate time of concentration for overland flow and return periods from NOAA Atlas 14, Volume 2, Version 2.1. Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's Equation.
E.
Runoff curve numbers (CN) for both existing and proposed conditions
to be used in the Soil Cover Complex Method shall be obtained from
Table A-4 in Appendix A of this Part.[2]
[2]
Editor's Note: Appendix A is included as an attachment to this chapter.
F.
Runoff coefficients (C) for both existing and proposed conditions
for use in the Rational Method are contained in Table A-7 in Appendix
A of this Part.[3]
[3]
Editor's Note: Appendix A is included as an attachment to this chapter.
G.
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from the design storm curves from PA Department of Transportation Design Rainfall Curves (1986) (Figure A-2). Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's Equation.
H.
For the purposes of existing conditions' flow rate determination,
undeveloped land and existing impervious surfaces shall be considered
as "meadow" in good condition, unless the natural ground cover generates
a lower curve number (CN) or Rational "C" value (e.g., forest), as
listed in Table A-4 or A-7 in Appendix A of this Part.[4] Wooded areas shall use a ground cover of "woods in good
condition." An area shall be considered wooded if there is a contiguous
canopy of trees existing over an area of 1/4 acre or more.
[4]
Editor's Note: Appendix A is included as an attachment to this chapter.
I.
Where uniform flow is anticipated, the Manning Equation shall be
used for hydraulic computations, and to determine the capacity of
open channels, pipes, and storm sewers. Values for Manning's
roughness coefficient (n) shall be consistent with Table A-8 in Appendix
A of this Part.[5]
[5]
Editor's Note: Appendix A is included as an attachment to this chapter.
J.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this Part using any hydraulic
analysis technique or method accepted by the Township.
K.
The design of any stormwater management facilities intended to meet
the performance standards of this Part shall be verified by routing
the design storm hydrograph through these facilities using the Storage
Indication Method. The design storm hydrograph shall be computed using
a calculation method that produces a full hydrograph.
L.
The Township has the authority to require that computed existing
runoff rates be reconciled with field observations and conditions.
If the design professional engineer can substantiate through actual
physical calibration that more appropriate runoff and time-of-concentration
values should be utilized at a particular site, then appropriate variations
may be made upon review and recommendations of the Township Engineer.
Calibration shall require detailed gauge and rainfall data for the
particular site in question.
M.
Infrequent Storm. The rational runoff coefficients given in this
Part are applicable for the two-year through ten-year frequency design
storm event. Less frequent, higher intensity storms require modification
of the runoff coefficient because infiltration and other losses have
a proportionally smaller effect on runoff (Wright-McLaughlin 1969).
The adjustment of the Rational Method for use with major storms shall
be made by multiplying the Rational Formula by a frequency factor
Cf. Cf values are as follows: twenty-five-year frequency design storm:
1.1; fifty-year frequency design storm: 1.2; 100-year frequency design
storm: 1.25. The product of Cf and Rational Coefficient C shall not
exceed 1.0.
N.
The time of concentration (Tc) is the time required for water to
flow from the hydraulically most remote point of the drainage area
to the point of interest (design point). Use of the Rational Formula
requires calculation of a Tc for each design point within the drainage
basin. Travel time estimation for the Rational Method shall be based
on NRCS Technical Release No. 55 (2nd Edition). For design purposes,
the time of concentration may not be less than five minutes. Travel
time (Tt) is the time it takes runoff to travel from one location
to another in a watershed (subreach) and is a component of time of
concentration. Tc is computed by summing all the travel times for
consecutive components of the drainage conveyance system.
O.
Water moves through a watershed as sheet flow, shallow concentrated
flow, open channel flow, or some combination of these. Sheet flow
rates shall be calculated using the NRCS TR-55 (1986) variation of
the kinematic wave equation. Sheet flow length may not exceed 50 feet
over paved surfaces and 150 feet over unpaved surfaces. Maximum permitted
sheet flow length shall be 150 feet unless site-specific conditions
exist (that can be demonstrated) that warrant an increase of the sheet
flow length. Under no circumstances shall sheet flow length exceed
300 feet. Shallow concentrated flow time and open channel flow time
shall be calculated using standard engineering methodologies.
P.
The Township reserves the right to require stormwater management
calculations and analyses related to existing downstream drainage
facilities, in order to ascertain whether the stormwater management
design for the regulated activity adversely effects existing downstream
facilities by increasing flooding potential and/or frequency from
the predevelopment condition.
Q.
For all major residential subdivisions (three lots or more), where
the smallest lot is less than two acres in area, stormwater facilities
shall be designed to manage runoff from the maximum permitted site
and individual lot impervious surface. For all other projects, it
is encouraged that stormwater facilities be designed to account for
construction of additional future impervious coverage on the property.
[Ord. No. 2022-01, 7/12/2022]
A.
Whenever vegetation and topography are to be disturbed, such activity must be in conformance with Chapter 102, Title 25, Rules and Regulations, Part 1, Commonwealth of Pennsylvania, Department of Environmental Protection, Subpart C, Protection of Natural Resources, Article II, Water Resources, Chapter 102, "Erosion Control," and in accordance with the Bucks County Conservation District and the standards and specifications of the Township.
B.
All activities or projects involving earth disturbance of 5,000 square
feet or greater require erosion and sediment control plan adequacy
approval from the Bucks County Conservation District. It is the applicant's
responsibility to make submission to Bucks County Conservation District
for review and approval of the erosion and sediment control plan.
A copy of erosion and sediment control plan adequacy approval correspondence
from the Bucks County Conservation District must be received by the
Township prior to commencing earth disturbance activities, and issuance
of building/zoning permits or approvals by the Township.
C.
No regulated earth disturbance activities within the Township shall
commence until approval by the Township of an erosion and sediment
control and grading plan for construction activities.
D.
Pursuant to 25 Pa. Code Chapter 92, a PADEP NPDES construction activities
permit is required for regulated earth disturbance activities.
E.
Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate PADEP regional office or Bucks County
Conservation District must be submitted to the Township.
F.
A copy of the erosion and sediment control plan and any required
permit, as required by PADEP regulations, shall be available at the
project site at all times.
G.
Additional erosion and sedimentation control design standards and
criteria that must be applied where infiltration BMPs are proposed
include the following:
(1)
Areas proposed for infiltration BMPs shall be protected from
sedimentation and compaction during the construction phase, so as
to maintain their maximum infiltration capacity. Thirty-three-inch
Super Filter Fabric Fence (or other approved protection mechanism)
must be installed around proposed infiltration areas to prevent encroachment
and compaction by construction equipment.
(2)
Infiltration BMPs shall not be constructed nor receive runoff
until the entire contributory drainage area to the infiltration BMP
has received final stabilization. If necessary, thirty-three-inch
Super Filter Fabric Fence (or other approved protection mechanism)
must be installed in the vicinity of the infiltration area to prevent
contamination by runoff containing suspended sediment.
H.
Peak discharges from the site shall comply with the appropriate sections
above, with the following additions:
(1)
For purposes of calculating required detention storage during land disturbance, peak discharge rates and volumes shall be calculated based upon the runoff coefficients for bare soils during the maximum extent of disturbance from clearing, grading, and impervious surface installation, shown on the development plan. Controls shall ensure that the difference in volume and rate of peak discharges before disturbance and during construction shall not exceed those peak discharges and volumes required in §§ 26-122 and 26-123 of this Part. Detention storage during the period of land disturbance and prior to establishment of permanent cover may require additional facilities on a temporary basis. Such measures shall be located so as to preserve the natural soil infiltration capacities of the planned infiltration areas. Calculations based on the above parameters must be submitted to verify "during construction" runoff rate does not exceed predevelopment runoff rate for the one-year frequency through 100-year frequency design storm events.
(2)
Wherever soils, topography, cut and fill or grading requirements,
or other conditions, suggest substantial erosion potential during
land disturbance, the Township may require that the entire volume
of all storms up to a two-year storm from the disturbed areas be retained
on-site and that special sediment trapping facilities (such as check
dams, etc.) be installed.
I.
Areas of the site to remain undisturbed shall be protected from encroachment
by construction equipment/vehicles to maintain the existing infiltration
characteristics of the soil. Four-foot-high orange safety fence or
other similar protection fence approved by the Township must be installed
around the entire limit of disturbance/clearing prior to commencement
of earthmoving activities and maintained until completion of all construction
activity.
[Ord. No. 2022-01, 7/12/2022]
A.
No regulated earth disturbance activities within the Township shall
commence until approval by the Township of a plan which demonstrates
compliance with state water quality requirements after construction
is complete.
B.
The BMPs must be designed, implemented, and maintained to meet state
water quality requirements and any other more stringent requirements
as determined by the Township.
C.
To control postconstruction stormwater impacts from regulated earth
disturbance activities, state water quality requirements may be met
by BMPs, including site design, which provide for replication of preconstruction
stormwater infiltration and runoff conditions, so that post-construction
stormwater discharges do not degrade the physical, chemical or biological
characteristics of receiving waters. As described in the PADEP Comprehensive
Stormwater Management Policy (No. 392-0300-002, September 28, 2002),
this may be achieved by the following:
(1)
Infiltration: replication of preconstruction stormwater infiltration
conditions;
(2)
Treatment: use of water quality treatment BMPs to filter out
the chemical and physical pollutants from the stormwater runoff; and
(3)
Stream bank and streambed protection: management of volume and
rate of postconstruction stormwater discharges to prevent physical
degradation of receiving waters (e.g., from scouring).
D.
PADEP has regulations that require townships to ensure design, implementation,
and maintenance of best management practices (BMPs) that control runoff
from new development and redevelopment after regulated earth disturbance
activities are complete. These requirements include the need to implement
post-construction stormwater BMPs with assurance of long-term operations
and maintenance of those BMPs.
E.
Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate PADEP regional office must be submitted
to the Township.
[Ord. No. 2022-01, 7/12/2022]
Development on lands adjacent to the Delaware Canal which propose
to discharge stormwater into the canal must obtain special right-of-way
approval from Pennsylvania Department of Conservation and Natural
Resources (PADCNR). The PADCNR has established a separate policy for
granting right-of-way for stormwater drainage into the Delaware Canal,
which shall be used in conjunction with this Part. Feeder streams
that flow or feed into the Delaware Canal shall be protected against
soil erosion, water quality degradation, and sedimentation.
[Ord. No. 2022-01, 7/12/2022]
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.
B.
Except as required by PADEP Chapter 102 regulations, the riparian
buffer easement shall be measured to be the greater of the limit of
the 100-year floodplain or a minimum of 95 feet from the top-of-bank
of the watercourse (on each side).
C.
Minimum Management Requirements for Riparian Buffers.
(1)
Existing native vegetation shall be protected and maintained
within the riparian buffer easement.
(2)
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.
D.
The riparian buffer easement shall be enforceable by the Township
and shall be recorded at Bucks County Courthouse, 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
of the property.
E.
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.
G.
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.
[Ord. No. 2022-01, 7/12/2022]
A.
Hot Spots.
(1)
Use of infiltration BMPs is prohibited on hot spot land use
areas. Examples of hot spots are listed in Appendix H.[1]
[1]
Editor's Note: Appendix H is included as an attachment to this chapter.
(2)
Stormwater runoff from hot spot land uses shall be pretreated.
In no case may the same BMP be employed consecutively to meet this
requirement. Guidance regarding acceptable methods of pretreatment
is located in Appendix H.
B.
West Nile Guidance Requirements. All wet basin designs shall incorporate
biologic controls consistent with the West Nile Guidance found in
Appendix I.[2]
[2]
Editor's Note: Appendix I is included as an attachment to this chapter.
