[Ord. No. 246, 10/11/2023]
1. Applicants proposing regulated activities in the Township which do not fall under the exemption criteria in §
26-232 shall submit a drainage plan consistent with the applicable Act 167 plan and this Part to the Township for review and approval. These exemption criteria shall apply to the total proposed development even if development is to take place in stages.
2. The applicant is required to perform and submit an alternatives analysis
to find practicable alternatives to the surface discharge of stormwater,
the creation of impervious surfaces and the degradation of waters
of the commonwealth, and must maintain as much as possible the natural
hydrologic regime.
3. The applicant shall design the drainage plan through an alternatives analysis consistent with the sequencing provisions of §
26-222 to ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The drainage plan design professional must proceed sequentially in accordance with Subpart 2C of this Part and present evidence demonstrating that he has followed the sequence with the drainage plan.
4. The applicant shall provide stormwater drainage systems in order
to permit unimpeded flow along natural watercourses, except as modified
by stormwater management facilities or open channels consistent with
this Part.
5. No person shall alter existing points of concentrated drainage that
discharge onto adjacent property in any manner which could cause property
damage without permission of the affected property owner. All alteration
of existing points of discharge shall be subject to any applicable
discharge criteria specified in this Part.
6. Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this Part. If diffused
drainage discharge is proposed to be concentrated and discharged onto
adjacent property, the applicant shall document that adequate downstream
conveyance facilities exist to safely transport the concentrated discharge,
or otherwise prove that no erosion, sedimentation, flooding or other
impacts will result from the concentrated discharge.
7. Where a development site is traversed by existing watercourses, drainage easements (for natural and artificial watercourses) shall be provided, conforming to the line of such watercourses. The terms of the easement shall conform to the stream buffer requirements (for natural watercourses) contained in §
26-223, Subsection
1J(7), of this Part.
8. Any stormwater management facilities regulated by this Part that
would be located in or adjacent to waters of the commonwealth or wetlands
shall be subject to approval by DEP through the joint permit application
process, or, where deemed appropriate by DEP, the general permit process.
When there is a question whether wetlands may be involved, it is the
responsibility of the applicant to show that the land in question
cannot be classified as wetlands; otherwise approval to work in the
area must be obtained from DEP.
9. Any stormwater management facilities regulated by this Part that
would be located on state highway rights-of-way shall be subject to
approval by PennDOT.
10. Infiltration of runoff through seepage beds, infiltration trenches, etc., where soil conditions permit, and minimization of impervious surfaces to the extent permitted by the Zoning Ordinance [Chapter
27] are encouraged to reduce the size or eliminate the need for detention facilities or other structural BMPs.
11. Roof drains and sump pumps shall discharge to infiltration or vegetative
BMPs wherever feasible. Roof drains shall not be connected to streets,
sanitary or storm sewers or roadside ditches in order to promote overland
flow and infiltration/percolation of stormwater where advantageous
to do so. Considering potential pollutant loading, roof drain runoff
in most cases will not require pretreatment.
12. All stormwater runoff, other than rooftop runoff discussed in Subsection
11 above, shall be treated for water quality prior to discharge to surface water or groundwater.
[Ord. No. 246, 10/11/2023]
1. The design of all regulated activities shall include the following
steps in sequence to minimize stormwater impacts.
A. The applicant is required to find practicable alternatives to the
surface discharge of stormwater and the creation of impervious surfaces
and the degradation of waters of the commonwealth, and the applicant
shall maintain as much as possible the natural hydrologic regime of
the development site.
B. An alternative is practicable if it is available and capable of being
done after taking into consideration cost, existing technology and
logistics in light of overall project purposes.
C. All practicable alternatives to the discharge of stormwater are presumed
to have less adverse impact on quantity and quality of waters of the
commonwealth unless otherwise demonstrated.
2. The applicant shall demonstrate that it designed the regulated activities
in the following sequence to minimize the increases in stormwater
runoff and impacts to water quality:
A. Prepare an Existing Resource and Site Analysis Map (ERSAM) showing environmentally sensitive areas, including, but not limited to, steep slopes, ponds, lakes, streams, wetlands, hydric soils, vernal ponds, floodplains, buffer areas, hydrologic soil groups A and B (areas conducive to infiltration), any existing recharge areas and any other requirements outlined in the SALDO [Chapter
22].
B. Establish buffers according to §
26-223.
C. Prepare a draft project layout avoiding earth disturbance in sensitive areas identified in §
26-222, Subsection
2A, and minimizing total site earth disturbance as much as possible. The ratio of the disturbed area to the entire parent tract area and measures taken to minimize earth disturbance shall be included on the ERSAM.
D. Identify development-site-specific predevelopment drainage areas,
discharge points, recharge areas to be preserved and hydrologic soil
groups A and B to be utilized for recharge.
E. Evaluate nonstructural stormwater management alternatives.
(1)
Minimize earth disturbance.
(2)
Minimize impervious surfaces.
(3)
Break up large impervious surfaces.
F. Satisfy water quality and stream bank erosion protection objectives (§
26-223).
G. Satisfy groundwater recharge (infiltration) objectives (§
26-225) and provide for stormwater treatment prior to infiltration.
H. Determine what management district the development site falls into
(Appendix D) and conduct a predevelopment runoff analysis.
I. Prepare final project design to maintain predevelopment drainage
areas and discharge points, to minimize earth disturbance and impervious
surfaces, and to reduce runoff to the maximum extent possible.
J. Conduct a post-development runoff analysis based on the final design and to meet the release rate and in turn the overbank flow and extreme event requirements (§
26-226).
K. Manage any remaining stormwater runoff through treatment prior to
discharge, as part of detention, bioretention, direct discharge or
other structural control.
[Ord. No. 246, 10/11/2023]
1. In addition to the performance standards and design criteria requirements
of this Part, the applicant shall comply with the following water
quality requirements of this Subpart 2C.
A. For water quality and stream bank erosion, the applicant shall design
a water quality BMP to detain the proposed conditions two-year, twenty-four-hour
design storm to the existing conditions one-year flow using the SCS
Type II distribution. The applicant shall demonstrate that applicant
has made provisions (such as adding a small orifice at the bottom
of the outlet structure) so that the proposed conditions one-year
storm takes a minimum of 24 hours to drain from the facility from
a point where the maximum volume of water from the one-year storm
is captured (i.e., the maximum water surface elevation is achieved
in the facility). At the same time, the objective is to not attenuate
the larger storms in "no detention" areas (District C) only. This
can be accomplished by configuration of the outlet structure not to
control the larger storms, or by a bypass or channel to divert only
the two-year design storm into the basin or divert flows in excess
of the two-year storm away from the basin.
Where practicable, wet basins shall be utilized for water quality
control and shall meet the requirements found in the Pennsylvania
Stormwater BMP Manual, as revised.
Release of water can begin at the start of the storm (i.e.,
the invert of the water quality orifice is at the invert of the facility).
The design of the facility shall consider and minimize the chances
of clogging and sedimentation. Orifices smaller than three inches
diameter are not recommended. However, if the design professional
can provide proof that the smaller orifices are protected from clogging
by use of trash racks, etc., smaller orifices may be permitted.
B. Where an NPDES permit for stormwater management discharges associated
with construction activities is required, the water quality requirements
of that permit should be used. However, the buffer provisions listed
below should be applied to all applications.
C. In selecting the appropriate BMPs or combinations thereof, the applicant
shall consider the following:
(2)
Permeability and infiltration rate of the development site soils.
(3)
Slope and depth to bedrock.
(4)
Depth to seasonal high water table.
(5)
Proximity to building foundations, wellheads, and wellhead protection
areas.
(7)
Land availability and configuration of the topography.
(8)
Peak discharge and required volume control.
(10)
Efficiency of the BMPs to mitigate potential water quality problems.
(11)
The volume of runoff that will be effectively treated.
(12)
The nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife habitat.
D. For areas within defined special protection subwatersheds, which
includes exceptional value (EV) and high quality (HQ) waters, the
applicant shall maintain the temperature and quality of water and
streams through the use of temperature-sensitive BMPs and stormwater
conveyance systems.
E. The applicant shall demonstrate that the applicant has considered
and has implemented to the maximum extent feasible the guidelines
found in the references specified in Appendix G for constructed wetlands, where proposed.
F. The applicant shall provide pretreatment in accordance with §
26-221, Subsections
11 and
12, prior to infiltration.
G. Stream bank restoration projects shall include the following:
(1)
No restoration or stabilization projects may be undertaken without
examining the fluvial geomorphology of stable reaches above and below
the unstable reach.
(2)
Restoration project design must then consider maintenance of
stability in the adjacent stable reaches of the stream channel.
(3)
An erosion and sediment control plan approved by the Conservation
District must be provided by the applicant.
(4)
All applicable state and federal permits must be obtained.
H. Biology shall be incorporated into the design of all wet basins in
accordance with the West Nile virus guidance found in Appendix E of
the 2003 update.
I. To accomplish the above, the applicant shall submit original and
innovative designs to the Township Engineer for review and approval.
Such designs may achieve the water quality objectives through a combination
of BMPs (best management practices).
J.
Buffers.
(1)
Wetlands and Vernal Ponds.
(a)
Wetland Identification. Wetlands shall be identified in accord
with the 1987 U.S. Army Corps of Engineers Manual for Identifying
and Delineating Wetlands, and properly flagged and surveyed on the
development site to ensure they are protected.
(b)
Wetlands in an Artificial Watercourse. Wetlands contained within
the banks of an artificial watercourse shall not be considered for
buffer delineation purposes.
(c)
Wetlands in a Natural Watercourse. For wetlands contained within
the banks of a natural watercourse, only the stream buffer shall apply.
(d)
Wetland and Vernal Pond Buffer Delineation. A fifty-foot inner
buffer and 100-foot outer buffer, measured perpendicular to and horizontally
from the edge of the delineated wetland or vernal pond for a total
distance of 150 feet, shall be maintained for all wetlands and vernal
ponds.
1)
Inner Buffer. The inner buffer shall be measured perpendicular
to and horizontally from the edge of the delineated wetland or vernal
pond, for a distance of 50 feet.
a) Permitted Activities/Development. Stormwater conveyance
required by the Township, buffer maintenance and restoration, the
correction of hazardous conditions, stream crossings permitted by
DEP and passive unpaved stable trails shall be permitted. No other
earth disturbance, grading, filling, buildings, structures, new construction,
or development shall be permitted.
b) The area of the inner buffer altered by activities permitted in accord with §
26-223, Subsection 1J(1)(d)1), shall be minimized to the greatest extent practicable.
2)
Outer Buffer. The outer buffer shall be measured perpendicular
to and horizontally from the outer edge of the inner buffer for a
distance of 100 feet resulting in a total buffer of 150 feet.
a) Permitted activities/development. Stormwater conveyance required by the Township, buffer maintenance and restoration, the correction of hazardous conditions, stream crossings permitted by DEP, roads constructed to existing grade, unpaved trails, and limited forestry activities that do not clear cut the buffer (e.g., selective regeneration harvest) in accord with a forestry management plan shall be permitted, provided no buildings are involved, and those activities are permitted under §
26-223, Subsection
1J(6) and
(7).
b) No more than 20% of the cumulative outer buffer on the subject parcel shall be altered by the activities permitted in accord with §
26-223, Subsection 1J(1)(d)2).
(2)
Lakes and Ponds.
(a)
There is no outer buffer around lakes and ponds.
(b)
Lake and Pond Buffer Delineation. A fifty-foot buffer, measured
perpendicular to and horizontally from the edge of any water body,
shall be maintained around any water body.
1)
Permitted Activities/Development. Stormwater conveyance required
by the Township, buffer maintenance and restoration, the correction
of hazardous conditions, lakefront views, boat docks and unpaved trails
shall be permitted, provided no buildings are involved.
2)
The area of the buffer impacted by activities permitted in §
26-223, Subsection
1J(2)(b), shall not exceed 35% of the buffer on the parent tract.
(3)
Streams.
(a)
Stream Buffer Delineation. A fifty-foot inner buffer and 100-foot
outer buffer, measured perpendicular to and horizontally from the
top-of-bank on both sides of any stream, for a total distance of 150
feet, shall be maintained on both sides of any stream. See Figure
223.1.
1)
Inner Buffer. The inner buffer shall be measured perpendicular
to and horizontally from the top-of-bank of the stream for a distance
of 50 feet.
a) Permitted Activities/Development. Stormwater conveyance
required by the Township, buffer maintenance and restoration, the
correction of hazardous conditions, stream crossings permitted by
DEP, fish hatcheries, wildlife sanctuaries and boat launch sites constructed
so as not to alter the floodplain cross section, and unpaved trails
shall be permitted, provided no buildings are involved. No other earth
disturbance, grading, filling, buildings, structures, new construction,
or development shall be permitted.
b) The area of the inner buffer altered by activities permitted in accord with §
26-223, Subsection 1J(3)(a)1) shall be minimized to the greatest extent practicable.
c) Outer Buffer. The outer buffer shall be measured
perpendicular to and horizontally from the outer edge of the inner
buffer for a distance of 100 feet resulting in a total buffer of 150
feet.
2)
Permitted Activities/Development. Stormwater conveyance required
by the Township, buffer maintenance and restoration, the correction
of hazardous conditions, agricultural activities, plant nurseries,
parking lots constructed to existing grade, temporary fairs and carnivals,
accessory uses for residential purposes, private sportsmen's
club activities, athletic facilities, orchards, wildlife sanctuaries,
boat launch sites, roads constructed to existing grade, stream crossings
permitted by DEP and unpaved trails and limited forestry activities
that do not clear cut the buffer (e.g., selective regeneration harvest)
in accord with a forestry management plan shall be permitted, provided
no buildings are involved.
3)
In areas of the outer buffer which are not wetlands, vernal
ponds or slopes of more than 15%, stormwater management facilities
which improve water quality of stormwater discharge shall be permitted
unless prohibited by other Township or state requirements. No other
earth disturbance, grading, filling, buildings, structures, new construction,
or development shall be permitted.
4)
No more than 20% of the cumulative outer buffer on the parent tract shall be altered by the activities permitted in accord with §
26-223, Subsection 1J(3)(a)2).
(4)
In addition to the other requirements of §
26-223, buffers shall be provided in accordance with this section.
(5)
Where resource buffers overlap, the more restrictive requirements
shall apply.
(6)
Preexisting Lots or Parcels/Development in Outer Buffers. In
the case of legally preexisting lots (approved prior to the effective
date of this Part) where the usable area of a lot lies within an outer
buffer area, the applicant shall obtain a waiver from the Board of
Supervisors in accordance with Subpart 2I.
(7)
Improvements to Existing Structures in Outer Buffers. The provisions of this §
26-223, Subsection
1J, do not require any changes or improvements to be made to lawfully existing structures in buffers. However, when any substantial improvement to a structure is proposed which results in a horizontal expansion of that structure, the improvement may only be permitted by the granting of the waiver from the requirements of this Part. In considering a waiver application, the Board of Supervisors shall determine whether the applicant has presented evidence of hardship in addition to the standards for waivers set forth in Subpart 2I.
Figure 223.1. Stream Buffer
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[Ord. No. 246, 10/11/2023]
1. 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
1A or the Simplified Method in Subsection
1B below. For regulated activity areas equal or less than one acre 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-five-hour-duration
precipitation.
(2)
For modeling purposes:
(a)
Existing (predevelopment) nonforested pervious areas must be
considered meadow in good condition.
(b)
Twenty percent of existing impervious area, when present, shall
be considered meadow in good condition in the model for existing conditions.
B. The Simplified Method (CG-2 in the BMP Manual) provided below is
independent of site conditions and should be used if the Design Storm
Method is not followed. This method is not applicable to regulated
activities greater than one acre 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 should be designed
to accommodate infiltration of the entire permanently removed runoff;
however, in all cases, at least the final 0.5 inch of the permanently
removed runoff should be infiltrated.
[Ord. No. 246, 10/11/2023]
1. Maximizing the groundwater recharge capacity of the development site being developed is required. The applicant shall demonstrate that the design of the infiltration/recharge stormwater management facilities has provided for, to the maximum extent feasible, groundwater recharge to compensate for the reduction in the percolation that occurs when the ground surface is disturbed or impervious surface is created. It is recommended that roof runoff be directed to infiltration BMPs which may be designed to compensate for the runoff from parking areas. These measures are required to be consistent with §
26-202 and take advantage of utilizing any existing recharge areas.
A. Infiltration BMPs shall meet the following minimum requirements:
(1)
Where an NPDES permit for stormwater discharges associated with
construction activities is required, the volume control requirement
of that permit should be met unless the volume control requirement
in this plan is greater.
(2)
Maximum Infiltration Requirements. The applicant shall demonstrate that all regulated activities shall recharge (infiltrate), where practicable, a portion of the runoff created by the development as part of an overall drainage plan. The volume of runoff to be recharged shall be determined from §
26-225, Subsection
1A(4)(a) or
(b), depending upon demonstrated development site conditions.
(3)
Infiltration BMPs intended to receive runoff from developed
areas shall be selected based on suitability of soils and site conditions
and shall be constructed on soils that have the following characteristics:
(a)
A minimum depth of 24 inches between the bottom of the BMP and
the limiting zone.
(b)
An infiltration and/or percolation rate sufficient to accept
the additional stormwater load and drain completely as determined
by field tests conducted by the applicant's design professional.
(c)
The recharge facility shall be capable of completely infiltrating
the recharge volume within four days.
(d)
Pretreatment in accordance with §
26-221, Subsection
11 and
12, shall be provided prior to infiltration.
(4)
The size of the recharge facility shall be based upon the following
volume criteria:
(a)
NRCS curve number equation.
The NRCS runoff shall be utilized to calculate infiltration
requirements (P) in inches.
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For zero runoff:
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P = I (Infiltration)(in.) = (200/CN)- 2
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Eqn: 224.1
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Where: CN = SCS (NRCS) curve number of existing conditions contributing
to the recharge facility.
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This equation is displayed graphically in, and the infiltration
requirement can be determined from, Figure 224.1.
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The recharge volume required would therefore be computed as:
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Rev (c.f.) = [I (in) * impervious area
(.s.f)]\12
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Eqn: 224.2
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Where: I = infiltration requirements (in.)
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Figure 225.1 Infiltration requirement based upon NRCS
curve number
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(b)
Annual Recharge - Water Budget Approach. It has been determined that infiltrating 0.6 inch of runoff from the post-development impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of §
26-225, Subsection
1A(4)(a), cannot be achieved, then 0.6 inch of rainfall shall be infiltrated from all impervious areas, up to an existing site condition curve number of 77. Above a curve number of 77, Equation 224.1 or the curve in Figure 224.1 should be used to determine the infiltration requirement.
The recharge volume (Rev) required would
therefore be computed as: Rev = [(0.6 or I,
whichever is less) * % impervious area]/12.
B. Soils. The applicant shall submit a detailed soils evaluation of
the development site to determine the suitability of recharge facilities.
The evaluation shall be performed by a design professional, and, at
a minimum, address 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 watershed to determine general areas of suitability
for infiltration practices.
(2)
Provide site-specific infiltration test results (at the level
of the proposed infiltration surface) in accord with ASTM Guide No.
D 5126 to determine the appropriate hydraulic conductivity rate.
(3)
Design the infiltration structure for the required storm volume
based on field-determined capacity at the level of the proposed infiltration
surface.
(4)
If on-lot infiltration structures are proposed by the design
professional, the applicant shall demonstrate to the Township that
the soils are conducive to infiltrate on the lots identified.
C. Stormwater Hotspots. A stormwater hotspot is defined as a land use
activity that generates higher concentrations of hydrocarbons, trace
metals or toxicants than are found in typical stormwater runoff, based
on monitoring studies. Table 225.1 provides samples of designated
hotspots. If a development site is designated as a hotspot, it has
important implications for how stormwater is managed. First and foremost,
untreated stormwater runoff from hotspots shall not be allowed to
infiltrate into groundwater where it may contaminate water supplies.
Therefore, the Rev requirement is not applied
to development sites that fit into the hotspot category (the entire
WQv must still be treated). Second, a greater level of stormwater
treatment may be needed at hotspot sites to prevent pollutant washoff
after construction. EPA's NPDES stormwater program requires some
industrial sites to prepare and implement a stormwater pollution prevention
plan.
Table 225.1 - Classification of Stormwater Hotspots
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The following land uses and activities are samples of stormwater
hotspots:
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•
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Vehicle salvage yards and recycling facilities
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•
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Fleet storage areas (bus, truck, etc.)
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•
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Public works storage areas
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•
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Facilities that generate or store hazardous materials
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The applicant shall exercise extreme caution where salt or chloride
would be a pollutant, since soils do little to filter this pollutant
and it may contaminate the groundwater. The 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 DEP Chapter 93 antidegradation regulations.
The Township may require the installation of an impermeable liner
in detention basins where the possibility of groundwater contamination
exists. The Township may require a detailed hydrogeologic investigation.
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The applicant shall provide safeguards against groundwater contamination
for uses which may cause groundwater contamination, should there be
a mishap or spill. (See Appendix E).
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D. The applicant shall demonstrate that extreme caution has been exercised
where infiltration is proposed in source water protection areas or
that may affect a wellhead or surface water intake.
E. Recharge/infiltration facilities shall be used in conjunction with
other innovative or traditional BMPs, stormwater control facilities,
and nonstructural stormwater management alternatives.
F. Infiltration BMPs should be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this Part.
[Ord. No. 246, 10/11/2023]
1. The Brodhead and McMichaels Creek Watershed has been divided into
stormwater management districts as shown on the Watershed Map in Appendix
D. The Management District Map is also available on the Monroe
County Conservation District's website.
Standards for managing runoff from each subarea in the Brodhead
and McMichaels Creek Watershed for the various design storms are shown
in Table 226.1. Development sites located in each of the A and B Districts
must control proposed conditions peak runoff rates to existing conditions
peak runoff rates for the design storms in accord with Table 226.1.
District C may allow increases in post-development flows where adequate
downstream conveyances exist.
In addition to the requirements specified in Table 226.1 below, the water quality and stream bank erosion (§
26-223), groundwater recharge (§
26-225), and erosion control (§
26-229) requirements shall be implemented.
Table 226.1. Water Quality Requirements
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District
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Proposed Conditions
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(Reduce To)
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Existing Conditions
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A
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2-year
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1-year
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5-year
|
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5-year
|
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10-year
|
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10-year
|
|
25-year
|
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25-year
|
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50-year
|
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50-year
|
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100-year
|
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100-year
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B-1
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2-year
|
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1-year
|
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5-year
|
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2-year
|
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10-year
|
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5-year
|
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25-year
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10-year
|
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50-year
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25-year
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100-year
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100-year
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B-2
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2-year
|
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1-year
|
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5-year
|
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2-year
|
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25-year
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5-year
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50-year
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10-year
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100-year
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50-year
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B-3
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50-year
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10-year
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100-year
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50-year
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C
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Provisional Direct Discharge District. Development sites which can discharge directly to the main channel or major tributaries or indirectly to the main channel through an existing stormwater drainage system (i.e., storm sewer or tributary) which meets the "Downstream Hydraulic Capacity Analysis" in § 26-229, Subsection 9, and is shown by the design professional to not cause a downstream problem, may allow an increase in flow as long as no downstream harm is demonstrated. However, sites in District C shall comply with the criteria for water quality and stream bank erosion (§ 26-223) and groundwater recharge (§ 26-225). If the proposed conditions runoff is intended to be conveyed by an existing stormwater drainage system to the main channel, assurance must be provided that such system has adequate capacity to convey the increased peak flows or will be provided with improvements to furnish the required capacity. When adequate capacity of the downstream system does not exist and will not be provided through improvements, the proposed conditions peak rate of runoff must be controlled to the existing conditions peak rate as required in District A provisions (i.e., ten-year proposed conditions flows to ten-year existing conditions flows) for the specified design storms.
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2. General. Proposed conditions rates of runoff from any regulated activity
shall not exceed the peak release rates of runoff prior to development
for the design storms specified on the Stormwater Management District
Watershed Map (Appendix D) and §
26-222 of this Part.
3. Sites located within the Township, but outside the limits of the
Brodhead and McMichaels Creek Watershed, shall comply with the peak
runoff rate requirements of District A.
4. District Boundaries. The boundaries of the stormwater management
districts are shown on an official map that is available for inspection
at the municipal office. A copy of the official map at a reduced scale
is included in Appendix D. The exact location of the stormwater management
district boundaries as they apply to a given development site shall
be determined by mapping the boundaries using the two-foot topographic
contours (or most accurate data required), provided as part of the
drainage plan.
5. Sites Located in More than One District. If a development site is located within two or more stormwater management districts, the peak discharge rate from any district shall be the existing conditions peak discharge for that district as indicated in §
26-222. The calculated peak discharges shall apply, regardless of whether the grading plan changes the drainage area by district. The Board of Supervisors may grant a waiver if discharges from multiple districts recombine in proximity to the development site. In this case, peak discharge in any direction may be a 100% release rate, provided that the overall site discharge meets the weighted average release rate.
6. Off-Site Areas. Off-site areas that drain through a development site
are not subject to release rate criteria when determining allowable
peak runoff rates. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site.
7. Site Areas. Where the development site area differs significantly
from the total parent tract area, only the proposed impact area utilizing
stormwater management measures shall be subject to the management
district criteria. In other words, unimpacted areas bypassing the
stormwater management facilities would not be subject to the management
district criteria.
8. "No Harm" Option. For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less restrictive runoff control (including no detention) if the applicant can prove that "no harm" would be caused by discharging at a higher runoff rate than that specified by the applicable Act 167 plan. The "no harm" option is used when an applicant can prove that the proposed hydrographs can match existing hydrographs, or if it can be proved that the proposed conditions will not cause increases in peaks at all points downstream. Proof of "no harm" must be shown based upon the following downstream impact evaluation, which shall include a downstream hydraulic capacity analysis consistent with §
26-226, Subsection
9, to determine if adequate hydraulic capacity exists. The applicant shall submit this evaluation of the impacts due to increased downstream stormwater flows in the watershed to the Township.
A. The hydrologic regime of the site must be maintained.
B. The downstream impact evaluation shall include hydrologic and hydraulic
calculations necessary to determine the impact of hydrograph timing
modifications due to the proposed development upon a dam, highway,
structure, natural point of restricted streamflow or any stream channel
section, established with the concurrence of the municipality.
C. The evaluation shall continue downstream until the increase in flow
diminishes due to additional flow from tributaries and/or stream attenuation.
D. The peak flow values to be used for downstream areas for the design
return period storms (two-, five-, ten-, twenty-five-, fifty-, and
100-year) shall be the values from the calibrated model for the applicable
Act 167 plan.
E. Applicant-proposed conditions runoff controls which would generate increased peak flow rates at storm drainage problem areas would, by definition, be precluded from successful attempts to prove "no harm," except in conjunction with proposed capacity improvements for the problem areas consistent with §
26-226, Subsection
9.
F. A financial distress shall not constitute grounds for the Township
to approve the use of the "no-harm" option.
G. Downstream capacity improvements may be provided as necessary to
achieve the "no harm" option.
H. Any "no harm" justifications shall be submitted by the applicant
as part of the drainage plan submission per Subpart 2D.
9. Downstream Hydraulic Capacity Analysis. Any downstream hydraulic
capacity analysis conducted in accordance with this Part shall use
the following criteria for determining adequacy for accepting increased
peak flow rates:
A. Existing 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 DEP Erosion and Sediment Pollution Control Program
Manual.
B. Existing natural or man-made channels or swales must be able to convey
increased twenty-five-year return period runoff without creating any
hazard to persons or property.
C. Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with Chapter 105 (if applicable) and, at minimum, pass the increased
twenty-five-year return period runoff.
10. Hardship Option. The applicable Act 167 plan and its standards and
criteria are designed to maintain existing conditions peak flows and
volumes throughout the watershed as the watershed becomes developed.
There may be certain instances, however, where the standards and criteria
established are too restrictive for a particular applicant. The existing
drainage network in some areas may be capable of safely transporting
slight increases in flows without causing a problem or increasing
flows elsewhere. If an applicant cannot meet the stormwater standards
due to lot conditions or if conformance would become a hardship to
an applicant, the hardship option may be applied. A financial distress
shall not constitute grounds for the Township to approve the use of
the hardship option. The applicant would have to plead his/her case
to the Board of Supervisors with the final determination made by the
Township. Any applicant's pleading the hardship option will assume
all liabilities that may arise due to exercising this option. A financial
distress shall not constitute grounds for the Township to approve
the use of the "no-harm" option.
[Ord. No. 246, 10/11/2023]
1. Stormwater runoff from all development sites shall be calculated
using a generally accepted calculation technique that is based on
the NRCS Soil Cover Complex Method. Table 227.1 summarizes acceptable
computation methods, and the method selected by the design professional
shall be based on the individual limitations and suitability of each
method for a particular development site. The Township may allow the
use of the Modified Rational Method after consultation with the Township
Engineer to estimate peak discharges from drainage areas on a case-by-case
basis.
Table 227.1. Acceptable Computation Methodologies for Stormwater
Management Site 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
or necessary; simpler than TR-20 or HEC-I.
|
Modified Rational Method (or commercial computer package based
on Modified Rational Method)
|
Emil Kuichling (1189)
|
As approved by the Township and/or Township Engineer.
|
Other Methods
|
Varies
|
Other computation methodologies approved by the Township and/or
Township Engineer.
|
2. 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 consistent with current NOAA Atlas 14 Point Precipitation
Frequency Estimates. If a hydrologic computer model such as PSRM or
HEC-1 is used for stormwater runoff calculations, then the duration
of rainfall shall be 24 hours. The SCS "S" curve shown in Figure B-1
of Appendix B shall be used for the rainfall distribution.
3. For the purposes of existing conditions flow rate determination,
undeveloped land shall be considered as meadow in good condition,
unless the natural ground cover generates a lower curve number or
Rational "C" value, as listed in Table B-2 or B-3 in Appendix B.
4. All calculations using the Modified Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from the current NOAA Atlas 14 Point Precipitation Frequency Estimates. 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.
5. Calculations using the Modified Rational Method shall be based on
a common time of concentration for all contributing drainage areas
to a discharge point in both the predevelopment and post-development
runoff conditions.
6. Runoff curve numbers (CN) for both existing and proposed conditions
to be used in the soil cover complex method shall be obtained from
Table B-2 in Appendix B. Due to limitations of the TR-55 methodology,
a minimum weighted curve number of 40 shall be utilized for calculations.
7. Runoff coefficients (c) for both existing and proposed conditions
for use in the Modified Rational Method shall be obtained from Table
B-3 in Appendix B.
8. The design professional shall consider that the runoff from the development
sites graded to the subsoil will not have the same runoff conditions
as the site under existing conditions, even after topsoiling or seeding.
The design professional may increase his proposed condition "CN" or
"c" to better reflect proposed soil conditions.
9. 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 B-4 in Appendix
B.
10. Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this Part using any generally
accepted hydraulic analysis technique or method.
11. The design of any stormwater detention 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 generally
accepted calculation technique that is based on the NRCS Soil Cover
Complex Method. The Township may approve the use of any generally
accepted full hydrograph approximation technique that shall use a
total runoff volume that is consistent with the volume from a method
that produces a full hydrograph.
[Ord. No. 246, 10/11/2023]
1. Any stormwater facility located on state highway rights-of-way shall
be subject to approval by PennDOT.
2. Pretreatment in accordance with §
26-221, Subsections
11 and
12, shall be provided prior to infiltration.
3. Any stormwater management facility (i.e., BMP, detention basin) designed
to store runoff and requiring a berm or earthen embankment required
or regulated by this Part shall be designed to provide an emergency
spillway to handle flow up to and including the 100-year proposed
conditions, considering the primary outlet control structures are
blocked. The height of embankment must provide a minimum 1.0 foot
of freeboard above the maximum pool elevation computed when the facility
functions for the 100-year proposed conditions inflow. Should any
stormwater management facility require a dam safety permit under Chapter
105, the facility shall be designed in accordance with Chapter 105
and meet the regulations of Chapter 105 concerning dam safety which
may be required to pass storms larger than the 100-year event.
4. Any facilities that constitute water obstructions (e.g., culverts,
bridges, outfalls, or stream enclosures), and any work involving wetlands
governed by Chapter 105, shall be designed in accordance with Chapter
105 and will require a permit from DEP.
5. Any other drainage conveyance facility that does not fall under Chapter
105 must be able to convey at a minimum, without damage to the drainage
structure or roadway, runoff from the twenty-five-year design storm
with a minimum 1.0 foot of freeboard measured below the lowest point
along the top of the roadway. Any facility that constitutes a dam
as defined in Chapter 105 may require a permit under dam safety regulations.
Any facility located within a PennDOT right-of-way must meet PennDOT
minimum design standards and permit submission requirements.
6. Any drainage conveyance facility and/or channel not governed by Chapter
105 must be able to convey at a minimum, without damage to the drainage
structure or roadway, runoff from the twenty-five-year design storm.
Conveyance facilities to or exiting from stormwater management facilities
(i.e., detention basins) shall be designed to convey the design flow
to or from that structure. Roadway crossings located within designated
floodplain areas must be able to convey runoff from a 100-year design
storm. Any facility located within a PennDOT right-of-way must meet
PennDOT minimum design standards and permit submission requirements.
7. Storm sewers must be able to convey at a minimum proposed conditions
runoff from a twenty-five-year design storm without surcharging inlets,
where appropriate. Storm sewers and other drainage conveyance systems
may be required to convey larger design storms based on individual
drainage/subdrainage area characteristics. Storm sewers to or exiting
from stormwater management facilities shall be designed to convey
design flow to or from that structure.
8. Adequate erosion protection shall be provided along all open channels,
and at all points of discharge.
9. The design of all stormwater management facilities shall incorporate
sound engineering principles and practices. The Township reserves
the right to disapprove any design that would result in the construction
of or continuation of a stormwater problem area.
[Ord. No. 246, 10/11/2023]
1. Any earth disturbance must be conducted in conformance with Chapter
102.
2. Additional erosion and sediment control design standards and criteria
that must be or are recommended to be applied where infiltration BMPs
are proposed shall include the following:
A. Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity.
B. Infiltration BMPs shall not be constructed nor receive runoff until
the entire contributory drainage area to the infiltration BMP has
achieved final stabilization.
[Ord. No. 246, 10/11/2023]
1. 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.
2. Except as required by Chapter 102, the riparian buffer easement shall
be measured to be the greater of the limit of the 100-year floodplain
or a minimum of 35 feet from the top of the stream bank (on each side).
3. Minimum Management Requirements for riparian buffers.
A. Existing native vegetation shall be protected and maintained within
the riparian buffer easement.
B. 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.
4. The riparian buffer easement shall be enforceable by the municipality
and shall be recorded in the appropriate County Recorder of Deeds
office, so that it shall run with the land and shall limit the use
of the property located therein. The easement shall allow for the
continued private ownership and shall count toward the minimum lot
area as required by zoning, unless otherwise specified in the municipal
Zoning Ordinance.
5. 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.
6. The following conditions shall apply when public and/or private recreation
trails are permitted within riparian buffers:
A. Trails shall be for nonmotorized use only.
B. Trails shall be designed to have the least impact on native plant
species and other sensitive environmental features.
7. 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.