A.
Applicants proposing regulated activities in the Brodhead/McMichael Creek Watershed which do not fall under the exemption criteria shown in § 365-18 shall submit a drainage plan consistent with the Brodhead/McMichaels Creek Watershed Stormwater Management Plan to the municipality for review. These criteria shall apply to the total proposed development even if development is to take place in stages.
B.
The applicant is required to perform 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.
C.
The stormwater management site plan must be designed through an alternatives analysis and a site analysis performed as shown in Chapter 4 of the Pennsylvania Stormwater Best Management Practices Manual, as amended, consistent with the sequencing provisions of § 365-9, to ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The stormwater management site plan designer must proceed sequentially in accordance with Article III of this chapter.
D.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this chapter.
E.
The existing points of concentrated drainage that discharge onto
adjacent property shall not be altered in any manner which could cause
property damage without permission of the affected property owner(s)
and shall be subject to any applicable discharge criteria specified
in this chapter.
F.
Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this chapter. If diffused
drainage discharge is proposed to be concentrated and discharged onto
adjacent property, the applicant must 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.
G.
Where a development site is traversed by existing watercourses, drainage easements shall be provided conforming to the line of such watercourses. The terms of the easement shall conform to the stream buffer requirements contained in § 365-10I(7) of this chapter.
H.
All stormwater management site plans shall include a consumptive
use tracking report.
I.
Any stormwater management facilities regulated by this chapter that
would be located in or adjacent to waters of the commonwealth or wetlands
shall be subject to approval by PA DEP through the joint permit application
process, or, where deemed appropriate by PA DEP, the general permit
process. When there is a question whether wetlands may be involved,
it is the responsibility of the applicant 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 PA DEP.
J.
Any stormwater management facilities regulated by this chapter that
would be located on state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
K.
Infiltration of runoff through seepage beds, infiltration trenches, etc., where soil conditions permit, and minimization of impervious surfaces to the extent permitted by the Chapter 470, Zoning, are encouraged to reduce the size or eliminate the need for detention facilities or other structural BMPs.
L.
Roof drains and sump pumps shall discharge to infiltration or vegetative
BMPs wherever feasible. Roof drains should not be connected to streets,
sanitary or storm sewers or roadside ditches in order to promote overland
flow and infiltration/percolation of stormwater. Considering potential
pollutant loading, roof drain runoff in most cases will not require
pretreatment.
M.
All stormwater runoff, other than rooftop runoff discussed in Subsection L above, shall be treated for water quality prior to discharge to surface or groundwater.
N.
The design of all facilities over karst shall include an evaluation
of measures to minimize adverse effects.
A.
The design of all regulated activities shall include the following
steps, in sequence, to minimize stormwater impacts.
(1)
The applicant is required 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
the natural hydrologic regime of the site.
(2)
An alternative is practicable if it is available and capable of being
done after taking into consideration existing technology and logistics
in light of overall project purposes.
(3)
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.
B.
Applicants shall demonstrate that they designed the regulated activities
in the following sequence to minimize the increases in stormwater
runoff and impacts to water quality.
(1)
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, floodplains,
buffer areas, hydrologic soil groups A and B (areas conducive to infiltration),
any existing recharge areas, existing structures, property boundary
line, areas of impervious surface, soils lines and descriptions from
the most recent Monroe County Soil Survey, existing well locations,
existing septic systems, existing contours, soil testing locations
keyed to testing results, existing drainage structures, photograph
location (if available), and the ratio of disturbed area to the entire
site area and measures taken to minimize earth disturbance.
(3)
Prepare a draft project layout avoiding earth disturbance in sensitive areas identified in § 365-9B(1) and minimizing total site earth disturbance.
(4)
Identify site-specific predevelopment drainage areas, discharge points,
recharge areas to be preserved and hydrologic soil groups A and B
to be utilized for recharge.
(7)
Satisfy groundwater recharge (infiltration) objective (§ 365-11) and provide for stormwater treatment prior to infiltration.
(9)
Prepare final project design to maintain predevelopment drainage
areas and discharge points; minimize earth disturbance and impervious
surfaces; and reduce runoff to the maximum extent possible.
(10)
Conduct a post-development runoff analysis based on the final
design to meet the required release rate and, in turn, the over-bank
flow and extreme event requirements.
(11)
Manage any remaining runoff through treatment prior to discharge,
as part of detention, bioretention, direct discharge or other structural
control.
In addition to the performance standards and design criteria
requirements of this chapter, the applicant shall comply with the
following water quality requirements of this section.
A.
Objective for design; BMPs; release of water.
(1)
For water quality and stream-bank erosion, the objective is to design
a water quality BMP to detain the proposed conditions' two-year,
twenty-four-hour design storm flow to the existing conditions'
one-year, twenty-four-hour design storm flow using the NRCS 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 conditions' one-year, twenty-four-hour design storm
flow takes a minimum of 24 hours to drain from the facility, from
a point where the maximum volume of water from the one-year, twenty-four-hour
design storm is captured (i.e., the maximum water surface elevation
is achieved in the facility).
(2)
Wet basins and other BMPs shall be utilized for water quality control
in accordance with the requirements found in the Pennsylvania Stormwater
BMP Manual, as revised, and incorporated herein by reference.
(3)
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 four inches diameter
shall not be used unless the design professional can provide proof
that the smaller orifices are protected from clogging by use of trash
racks, etc.
B.
In selecting the appropriate BMPs, or combinations thereof, the applicant
shall consider the following:
(1)
Total contributing area.
(2)
Permeability and infiltration rate of the site soils.
(3)
Slope and depth to bedrock.
(4)
Seasonal high water table.
(5)
Proximity to building foundations and wellheads.
(6)
Erodibility of soils.
(7)
Land availability and configuration of the topography.
(8)
Peak discharge and required volume control.
(9)
Stream-bank erosion.
(10)
Efficiency of the BMPs to mitigate potential water quality problems.
(11)
The volume of runoff that will be effectively treated.
(12)
The nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife habitat.
(15)
Recreational value.
C.
For areas within defined special protection subwatersheds which includes
exceptional value (EV) and high quality (HQ) waters, the temperature
and quality of water and streams shall be maintained through the use
of temperature-sensitive BMPs and stormwater conveyance systems.
D.
The applicant shall consider the guidelines found in the references
specified in the Pennsylvania Stormwater BMP Manual, as amended, for
constructed wetlands, where proposed.
F.
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.
G.
Biology shall be incorporated into the design of all wet basins in
accordance with the West Nile Virus Guidance.
H.
To accomplish the above, the applicant shall submit original and
innovative designs to the Municipal Engineer for review and approval.
Such designs may achieve the water quality objectives through a combination
of BMPs (best management practices).
I.
Buffers.
(1)
In addition to the other restrictions of this section, buffers shall be provided in accordance with this Subsection I.
(2)
Where resource buffers overlap, the more restrictive requirements
shall apply.
(3)
Preexisting lots or parcels/development in buffers. In the case of
legally preexisting lots or parcels (approved prior to the effective
date of this chapter) where the usable area of a lot or parcel lies
within a buffer area, rendering the lot or parcel unable to be developed
in accordance with the allowable use per municipal zoning, the development
may only be permitted if a modification is granted by the Board of
Commissioners.
(4)
Improvements to existing structures in buffers. The provisions of this Subsection I do not require any changes or improvements to be made to lawfully existing structures in buffers. However, when any improvement to a structure is proposed which results in a horizontal expansion of that structure within the buffer or which would result in the percentage impervious area to exceed that allowed by this chapter, the improvement will only be permitted if a modification is first granted by the Board of Commissioners.
(6)
Wetlands.
(a)
Wetland identification. Wetlands shall be identified in accord
with the 1987 United States Army Corps of Engineers Manual for Identifying
and Delineating Wetlands, as amended, and properly flagged and surveyed
on site to ensure they are protected.
[1]
Wetlands in an artificial watercourse. Wetlands contained within
the banks of an artificial watercourse shall not be considered for
buffer delineation purposes.
[2]
Wetlands in a natural watercourse. For wetlands contained within
the banks of a natural watercourse, only the stream buffer shall apply.
(b)
Wetland buffer delineation. A fifty-foot buffer, measured perpendicular
to and horizontally from the edge of the delineated wetland, shall
be maintained for all wetlands, with the exception of the Cranberry
Bog, where the buffer shall be 75 feet measured perpendicular to and
horizontally from the edge of the Cranberry Bog. In addition, where
the 300 feet of land adjacent to the edge of a delineated wetland
has an average upland slope greater than 5%, the minimum buffer width
shall be increased by four feet for each percent of slope at or above
5%, subject to a maximum cumulative buffer of 100 feet.
[1]
Permitted activities/development. Stormwater conveyance required
by the municipality or other body or agency having jurisdiction; buffer
maintenance and restoration; the correction of hazardous conditions;
stream crossings permitted by DEP and passive unpaved stable trails
shall be permitted within the wetland buffer. No other earth disturbance,
grading, filling, buildings, structures, new construction, or development
shall be permitted within the wetland buffer.
[2]
The area of the wetland buffer altered by activities permitted in accordance with Subsection I(6)(b)[1] above shall be minimized to the greatest extent practicable, as determined by the municipality. In no case shall more than 20% of the cumulative wetland buffer on the subject parcel be altered by the activities permitted in accordance with Subsection I(6)(b)[1]. This 20% disturbance shall include both the disturbance created by the applicant and any subsequent owner of the parcel or a portion of the parcel developed by the applicant (i.e., lot owner).
(7)
Lakes and ponds.
(a)
Lake and pond buffer delineation. A fifty-foot buffer measured
perpendicular to and horizontally from the edge of any lake or pond,
shall be maintained around any lake or pond. In addition, where the
300 feet of land adjacent to the edge of a lake or pond has an upland
slope greater than 5%, the minimum buffer width shall be increased
by four feet for each percent of slope at or above 5%, subject to
a maximum cumulative buffer of 100 feet.
(b)
Permitted activities/development. Stormwater conveyance required
by the municipality or other body or agency having jurisdiction, buffer
maintenance and restoration, the correction of hazardous conditions,
boat docks and unpaved trails shall be permitted, provided no buildings
are involved.
(c)
The area of the buffer altered by activities permitted in accordance with Subsection I(7)(b) above shall be minimized to the greatest extent practicable, as determined by the municipality. In no case shall more than 35% of the cumulative lake and pond buffer on the subject parcel be altered by the activities permitted in accordance with Subsection I(7)(b). This 30% disturbance shall include both the disturbance created by the applicant and any subsequent owner of the parcel or a portion of the parcel developed by the applicant (i.e., lot owner).
(8)
Streams.
(a)
Stream buffer delineation. A fifty-foot buffer, measured perpendicular
to and horizontally from the top-of-bank on all sides of any stream,
shall be maintained on all sides of any stream, with the exception
of the Pocono Creek, where the buffer shall be 75 feet, measured perpendicular
to and horizontally from the top-of-bank on all sides of the Pocono
Creek. In addition, where the 100 feet of land adjacent to the edge
of a stream has an average upland slope greater than 5%, the minimum
buffer width shall be increased by four feet for each percent of slope
at or above 5%, subject to a maximum cumulative buffer of 100 feet.
See Figure 365-10I below.
(b)
Permitted activities/development. Stormwater conveyance required
by the municipality or other body or agency having jurisdiction, 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 increase the floodplain
elevation, and unpaved trails, shall be permitted, providing no buildings
are involved. No other earth disturbance, grading, filling, buildings,
structures, new construction, or development shall be permitted.
(c)
The area of the buffer altered by activities permitted in accordance with § 365-10I(8)(b) shall be minimized to the greatest extent practicable, as determined by the municipality. In no case shall more than 20% of the cumulative stream buffer on the subject parcel be altered by the activities permitted in accordance with § 365-10I(8)(b). This 20% disturbance shall include both the disturbance created by the applicant and any subsequent owner of the parcel or a portion of the parcel developed by the applicant (i.e., lot owner).
|
Figure 365-10I Stream Buffer
 |
J.
The municipality may, after consultation with DEP, approve measures
for meeting the state water quality requirements other than those
in this chapter, 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.
Maximizing the groundwater recharge capacity of the area being developed is required. Design of the infiltration/recharge stormwater management facilities shall give consideration to providing 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 § 365-2 and take advantage of utilizing any existing recharge areas.
A.
Infiltration BMPs shall meet the following minimum requirements:
(1)
Maximum infiltration requirements.
(a)
Regulated activities will be required to recharge (infiltrate), where practicable, a portion of the runoff created by the development as part of an overall stormwater management plan designed for the site. The volume of runoff to be recharged shall be determined from Subsection A(3)(a) or (b), depending upon demonstrated site conditions.
(2)
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 three days.
(3)
The size of the recharge facility shall be based upon the following
volume criteria:
(a)
NRCS Curve Number Equation.
[1]
The NRCS runoff shall be utilized to calculate infiltration
requirements (P) in inches.
For zero runoff: P = I (Infiltration) (in.) = (200/CN) Equation
365-11.12.
Where: CN=SCS (NRCS) curve number of existing conditions contributing
to the recharge facility.
[2]
This equation is displayed graphically in, and the infiltration
requirement can be determined from Figure 365-11.
[3]
The recharge volume (Rev) required would
therefore be computed as:
|
Rev = I * % impervious area
|
Equation 365-11.2
|
|
Where: I = infiltration requirements (in.)
| |
|
Figure 365-11. Infiltration Requirement Based Upon NRCS
Curve Number.
 |
(b)
Annual recharge. Water budget approach.
[1]
It has been determined that infiltrating 0.6 inch of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of § 365-11A(2) 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 365-11.1 or the curve in Figure 365-11 shall be used to determine the infiltration requirement.
[2]
The recharge volume (Rev) required would
therefore be computed as:
Rev = 0.6 or I, whichever is less, times
the percent impervious area (* % impervious area).
B.
Soils. A detailed soils evaluation of the project site shall be required
to determine the suitability of recharge facilities. The evaluation
shall be performed by a qualified 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 accordance with the BMP Manual
and/or ASTM Guide No. D5126 to determine the appropriate hydraulic
conductivity rate.
(3)
Design the infiltration structure for the required storm volume based
on field- determined capacity with the appropriate safety factors
applied (as noted in the Pennsylvania Stormwater Best Management Practices
Manual) at the level of the proposed infiltration surface.
C.
Stormwater hotspots.
(1)
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 365-11 provides samples of designated hotspots. If a site is
designated as a hotspot, it has important implications for how stormwater
is managed. First and foremost, untreated stormwater runoff from hotspots
cannot 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
(and the entire WQv must still be treated).
Second, a greater level of stormwater treatment may be needed at hotspot
sites to prevent pollutant wash off after construction. EPA's
NPDES stormwater program requires some industrial sites to prepare
and implement a stormwater pollution prevention plan.
|
Table 365-11 - Classification of Stormwater Hotspots
| |
|---|---|
|
The following land uses and activities are samples of stormwater
hotspots:
| |
|
•
|
Vehicle salvage yards and recycling facilities
|
|
•
|
Fleet storage areas (bus, truck, etc.)
|
|
•
|
Public works storage areas
|
|
•
|
Facilities that generate or store hazardous materials
|
(2)
Extreme 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. 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 the Department's
Chapter 93 Antidegradation Regulations. The municipality may require
the installation of an impermeable liner in detention basins where
the possibility of groundwater contamination exists. A detailed hydrogeologic
investigation may be required by the municipality.
(3)
The municipality shall require the applicant to provide safeguards
against groundwater contamination for uses which may cause groundwater
contamination should there be a mishap or spill.
D.
Extreme caution shall be 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.
A.
The Brodhead/McMichael Watershed has been divided into stormwater
management districts as shown on the Watershed Map in Appendix B.[1]
(1)
Standards for managing runoff from each subarea in the Brodhead/McMichael
Watershed for design storms are shown in Table 365-12. Development
sites located in each of the A, B or C Districts must control proposed
conditions runoff rates to existing conditions runoff rates for the
design storms in accordance with Table 365- 12.
(2)
In addition to the requirements specified in Table 365-12 below, the water quality and stream-bank erosion (§ 365-10), groundwater recharge (§ 365-11), and erosion control (§ 365-15) requirements shall be implemented.
|
Table 365-12, Water Quantity Requirements
| ||
|---|---|---|
|
District
|
Proposed Conditions
(reduce to)
|
Existing Conditions
|
|
A
Subareas: 240-243, 19, 23, and 5
|
2-year
|
1-year
|
|
5-year
|
5-year
| |
|
10-year
|
10-year
| |
|
25-year
|
25-year
| |
|
50-year
|
50-year
| |
|
100-year
|
100-year
| |
|
B-1
Subareas: 7-9, and 15
|
2-year
|
1-year
|
|
5-year
|
2-year
| |
|
10-year
|
5-year
| |
|
25-year
|
10-year
| |
|
50-year
|
25-year
| |
|
100-year
|
100-year
| |
|
B-2
Subareas: 4, 10, 11 12, 18, 21, 24, 26, 27, 28, 29, 30, 32,
36, 44, 225, 226, B-3
|
2-year
|
1-year
|
|
5-year
|
2-year
| |
|
25-year
|
5-year
| |
|
50-year
|
10-year
| |
|
100-year
|
50-year
| |
|
50-year
|
10-year
| |
|
No subareas in Pocono Township
|
100-year
|
50-year
|
|
C
Subareas: 39, 55, 57, 56
|
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 § 365-12H 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 (§ 365-10); and groundwater recharge (§ 365-11). 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.
| |
[1]
Editor's Note: Appendix B, the map of the watershed,
is on file in the Township offices.
B.
General. Proposed condition 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 (Ordinance Appendix B) and § 365-12, of this chapter.
C.
District boundaries. The boundaries of the Stormwater Management
Districts, as indicated on maps approved and adopted on June 11, 1991,
by Monroe County as part of the Brodhead Creek Watershed Act 167 Watershed
Pocono Township Stormwater Management Ordinance, and incorporated
herein by reference, are shown on a map that is available for observation
at the municipal office. 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
stormwater management site plan.
D.
Sites located in more than one district. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall be the existing conditions peak discharge for that subarea as indicated in § 365-12. The calculated peak discharges shall apply regardless of whether the grading plan changes the drainage area by subarea. An exception to the above may be granted by the municipality if discharges from multiple subareas recombine in proximity to the 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.
E.
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. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site.
F.
Site areas. Where the site area to be impacted by a proposed development
activity differs significantly from the total site 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.
G.
"No harm" option. For any proposed development site not located in a provisional direct discharge district (District C), 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 this chapter. 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 § 365-12H to determine if adequate hydraulic capacity exists. The applicant shall submit to the municipality this evaluation of the impacts due to increased downstream stormwater flows in the watershed.
(1)
The hydrologic regime of the site must be maintained.
(2)
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.
(3)
The evaluation shall continue downstream until the increase in flow
diminishes due to additional flow from tributaries and/or stream attenuation.
(4)
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 Brodhead/McMichael
Watershed. These flow values can be obtained from the original Act
167 watershed stormwater management plan adopted on June 11, 1991,
by Monroe County and entitled the "Brodhead Creek Watershed Act 167
Watershed Stormwater Management Plan," which flow values are incorporated
herein by reference.
(5)
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 § 365-12H.
(6)
A financial distress shall not constitute grounds for the municipality
to approve the use of the "no-harm" option.
(7)
Downstream capacity improvements may be provided as necessary to
achieve the "no harm" option.
H.
"Downstream hydraulic capacity analysis." Any downstream hydraulic
capacity analysis conducted in accordance with this chapter shall
use the following criteria for determining adequacy for accepting
increased peak flow rates:
(1)
Existing natural or man-made channels or swales must be able to convey
the increased runoff associated with a two-year and a fifty-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, as amended and included herein by reference.
(2)
Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with DEP Chapter 105 regulations (if applicable) and, at minimum,
pass the increased fifty-year return period runoff.
A.
Stormwater runoff from all development sites with a drainage area
of greater than 200 acres shall be calculated using a generally accepted
calculation technique that is based on the NRCS Soil Cover Complex
Method. Table 365-13 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
site. The municipality may allow the use of the Rational Method to
estimate peak discharges from drainage areas that contain less than
200 acres.
|
Table 365-13
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
|
United States 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-1
|
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For sites less than 200 acres, or as approved by the municipality
and/or Municipal Engineer
|
|
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
and/or Municipal Engineer
|
B.
All calculations consistent with this chapter using the Soil Cover
Complex Method shall use the appropriate design rainfall depths for
the various return period storms according to the region in which
they are located as presented in Table B-1 in Appendix A[1] of this chapter. 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 NRCS "S" curve shown in
Figure B-1, Appendix A of this chapter, shall be used for the rainfall
distribution.
[1]
Editor's Note: Appendix A, Stormwater Management Design Criteria, is attached to this chapter.
C.
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 A of
this chapter.
D.
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 Pennsylvania
Department of Transportation Design Rainfall Curves (1986) (Figures
B-2 to B-4). 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 B-2 in Appendix A of this chapter.
F.
Runoff coefficients (c) for both existing and proposed conditions
for use in the Rational Method shall be obtained from Table B-3 in
Appendix A of this chapter.
G.
The designer shall consider that the runoff from proposed sites graded
to the subsoil will not have the same runoff conditions as the site
under existing conditions, even after topsoiling or seeding. The designer
shall increase his proposed condition "CN" or "c" to better reflect
proposed soil conditions.
H.
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
A of this chapter.
I.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this chapter using any generally
accepted hydraulic analysis technique or method.
J.
The design of any stormwater detention facilities intended to meet
the performance standards of this chapter shall be verified by routing
the design storm hydrograph through these facilities using the Storage-Indication
Method. For drainage areas greater than 200 acres in size, the design
storm hydrograph shall be computed using a calculation method that
produces a full hydrograph. The municipality 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.
K.
The design storm volumes to be used in the analysis of peak rates
of discharge should be obtained from the latest version of the Precipitation-Frequency
Atlas of the United States, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland.
NOAA's Atlas 145 can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
L.
Volume control. 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 (1) or the Simplified
Method in Subsection (2) below. For regulated activity areas equal
or less than one acre that do not require hydrologic routing to design
the stormwater facilities, this chapter 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.
(1)
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.
(a)
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.
(2)
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:
(a)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(b)
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.
(c)
Wherever possible, infiltration facilities should 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 should be infiltrated.
A.
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 chapter shall be designed to provide an emergency
spillway to handle flow up to and including the 100-year proposed
conditions. 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 PA
DEP 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.
B.
Any facilities that constitute water obstructions (e.g., culverts,
bridges, outfalls, or stream enclosures), and any work involving wetlands
governed by PA DEP Chapter 105 regulations (as amended or replaced
from time to time by PA DEP), shall be designed in accordance with
Chapter 105 and will require a permit from PA DEP.
C.
Any other stormwater conveyance facility and/or channel that does
not fall under Chapter 105 regulations must be able to convey, without
damage to the stormwater structure or roadway, runoff from the fifty-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 PA DEP Chapter 105 regulations may require a permit
under dam safety regulations. 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.
D.
Storm sewers must be able to convey proposed conditions runoff from a fifty-year design storm without surcharging inlets, where appropriate and as supplemented by Subsection C above.
E.
Adequate erosion protection shall be provided along all open channels,
and at all points of discharge.
F.
The design of all stormwater management facilities shall incorporate
sound engineering principles and practices. The municipality reserves
the right to disapprove any design that would result in the construction
of or continuation of a stormwater problem area.
A.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this chapter and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law. Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual3), No. 363-2134-008, as amended and updated.
B.
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:
(1)
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity.
(2)
Infiltration BMPs shall not be constructed nor receive runoff until
the entire contributory drainage area to the infiltration BMP has
achieved final stabilization.
A.
Submissions. All regulated activities shall submit a "Consumptive
Use Tracking Report" (CUTR), which shall be developed in accordance
with the forms available at the Township and submitted as follows:
(1)
Residential development and/or redevelopment. The CUTR shall be submitted
to the municipality during the preliminary plan approval process or
building permit approval process, whichever occurs first, and the
Monroe County Conservation District along with the erosion and sedimentation
control plan.
(2)
Commercial/industrial development and/or redevelopment. The CUTR
shall be submitted to the municipality during the preliminary plan
approval process or building permit approval process, whichever occurs
first. The CUTR shall also be submitted to the Monroe County Conservation
District along with the erosion and sedimentation control plan.
