All stormwater management system designs, plans and/or construction
shall comply with the following:
A.
Be compatible with this Part 1.
B.
Comply with all the requirements of the Township of Tobyhanna ordinances
and/or the Pennsylvania Department of Environmental Protection and
the United States Army Corps of Engineers. Should any stormwater management
facilities qualify as a dam under DEP Chapter 105, the facility shall
be designed in accordance with Chapter 105 and meet the regulations
of Chapter 105 concerning dam safety.
C.
Be conducted in such a way as to minimize accelerated erosion and
resulting sediment pollution. Measures to control erosion and resulting
sediment pollution shall, at a minimum, meet the standards of Chapter
102, Erosion and Sediment Control, of Title 25, Rules and Regulations
of the Pennsylvania Department of Environmental Protection and Erosion
and Sediment Pollution Control, as amended.
D.
Be conducted in such a way as to conserve, minimize and mitigate
impact upon regulated wetlands. Such areas shall not be altered in
any way without obtaining design approval, required certifications
and permits from the Township of Tobyhanna, the Philadelphia District
United States Army Corps of Engineers and the Pennsylvania Department
of Environmental Protection. Wetlands include swamps, marshes, bogs
and similar areas. As significant natural resources, wetlands serve
important functions relating to fish and wildlife food-chain production,
habitat, nesting, spawning, rearing and resting sites for protected
aquatic and land species; protection of other areas from erosion and
sediment pollution, storage areas for storm- and floodwaters; natural
recharge areas where ground- and surface water are interconnected;
and natural water filtration and purification functions.
E.
Be designed so that the construction of basins within the one-hundred-year floodplain should be avoided, where possible, but where unavoidable, the situation shall be examined for its functionality and supporting documentation submitted to the governing body for review and shall be consistent with Chapter 106, Floodplain Management, of Title 25, Rules and Regulations of the DEP, as amended. All zoning, subdivision and floodplain management regulations at the state and municipal level must be complied with, and the more restrictive regulation(s) supersede(s) all other regulations.
F.
Include financial guarantees for all drainage plan controls as specified
herein.
G.
Be designed by a person trained and experienced in stormwater management
and erosion and sediment pollution control. (The design, structure
interim and installation of the control measures are the responsibility
of the developer.)
H.
Be consistent with the stormwater management criteria (Appendix B[1]) and DEP's Erosion and Sediment Pollution Control Program
Manual.
[1]
Editor's Note: Appendix B is included at the end of this chapter.
I.
Additional studies and a higher lever of control than the minimum
provided in the design criteria may be required by the Township of
Tobyhanna to assure adequate drainage to protect life and property.
J.
It is the responsibility of the developer not to adversely affect
water quality of receiving waters. Best management practices are required
by the Township of Tobyhanna to maintain water quality in the watershed.
K.
Control facilities which receive stormwater from areas which are
potential sources of oil and grease contamination shall include a
baffle, skimmer, grease trap or other mechanism suitable for preventing
oil and grease from leaving the facility in concentrations that would
cause or contribute to violations of applicable water quality standards
in the receiving waters.
L.
Applicants proposing regulated activities in the Brodhead and McMichaels
Creek Watershed which do not fall under the exemption criteria shown
in this Part 1 shall submit a drainage plan required by this Part
1 consistent with the Brodhead and 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.
M.
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.
N.
The drainage plan must be designed through an alternatives analysis
consistent with the sequencing provisions of this Part 1 to reasonably
ensure maintenance of the natural hydrologic regime and to promote
groundwater recharge and protect groundwater and surface water quality
and quantity. The drainage plan designer must proceed sequentially
in accordance with this Part 1.
O.
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 Part 1.
P.
The existing points of concentrated drainage that discharge onto
adjacent property shall not be altered in any manner which could cause
property damage. Proposed discharges shall be subject to any applicable
discharge criteria specified in this Part 1. The existing points of
concentrated drainage that discharge onto adjacent property shall
not be altered without written permission from the affected property
owner(s). Drainage easements shall be established and recorded.
Q.
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 1. 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. Any area(s) of
existing diffused drainage that are proposed to be converted to concentrated
discharge(s) onto adjacent property shall be supported by written
permission from the affected property owner(s).
R.
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 this Part 1.
S.
All drainage plans shall include a consumptive use tracking report
as required in this Part 1.
T.
Any stormwater management facility regulated by this Part 1 that
would be located in or adjacent to waters of the commonwealth or wetlands
shall be subject to approval by PaDEP through the joint permit application
process or, where deemed appropriate by PaDEP, 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 PaDEP.
U.
Any stormwater management facility regulated by this Part 1 that
would be located on state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
V.
Infiltration of runoff through seepage beds, infiltration trenches,
or similar facilities, where soil conditions permit, and minimization
of impervious surfaces to the extent permitted by the municipality's
Zoning Ordinance,[2] are encouraged to reduce the size or eliminate the need
for detention facilities or other structural BMPs.
W.
Roof drains shall not be connected to street, 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.
X.
All stormwater runoff, other than rooftop runoff discussed above,
shall be treated for water quality prior to discharge to surface water
or groundwater.
A.
The design of all regulated activities shall include the following
steps in sequence to demonstrate that stormwater runoff and water
quality impacts have been minimized:
(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.
(a)
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.
(b)
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)
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, compliance with the map preparation criteria denoted in § 124-19B and any other plan preparation criteria set forth in the municipality's Subdivision and Land Development Ordinance[1] as may be required by the municipality.
(3)
Establish buffers according to this Part 1.
(4)
Prepare a draft project layout avoiding earth disturbance in sensitive
areas identified in this Part 1 and minimizing total site earth disturbance
as much as is practicable. The ratio of the disturbed area to the
entire site area and measures taken to minimize earth disturbance
shall be included on the ERSAM.
(5)
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.
(8)
Satisfy groundwater recharge (infiltration) objective (§ 124-11) and provide for stormwater treatment prior to infiltration.
(9)
Determine what management district the site falls into (Appendix
D),[2] and conduct a predevelopment runoff analysis.
[2]
Editor's Note: Appendix D is included at the end of this chapter.
(10)
Prepare final project design to maintain predevelopment drainage
areas and discharge points to minimize earth disturbance and impervious
surfaces and to control runoff as required by the Ordinance.
(11)
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 (§ 124-12).
(12)
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 Part 1, the applicant shall comply with the following
water quality requirements:
A.
Requirements.
(1)
For water quality and streambank erosion, the objective is to 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. Additionally, provisions shall be made 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. At the same time, the objective
is not to 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 flood into the basin or divert flows in excess of
the two-year storm away from the basin.
(2)
Where practicable, wet basins may be utilized for water quality control
and shall meet the requirements found in the Pennsylvania Stormwater
BMP Manual, as revised.
(3)
Release of water can begin at the start of the storm. The design
of the facility shall consider and minimize the chances of clogging
and sedimentation. All orifices less than 18 inches in diameter or
as deemed necessary by the Municipal Engineer shall be protected from
clogging by the use of baffles, trash racks, etc. Orifices smaller
than three inches in diameter are not permitted unless the design
professional can provide proof that the smaller orifices are protected
from clogging by the use of baffles, 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 well heads.
(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 include
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 may consider the guidelines for constructed wetlands
as found in the Pennsylvania BMP manual.
E.
Pretreatment in accordance with this Part 1 shall be provided prior
to infiltration.
F.
Streambank 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 found in Appendix E.[1]
[1]
Editor's Note: Appendix E is included at the end of this chapter.
H.
To accomplish the above, the applicant shall submit original and
innovative designs to the municipality's engineer for review and approval.
Such designs may achieve the water quality objectives through a combination
of BMPs (best management practices).
I.
Buffers.
(1)
Where resource buffers overlap, the more restrictive requirements
shall apply.
(2)
Preexisting lots or parcels in inner or outer buffers. In the case of legally preexisting lots or parcels, which were approved by subdivision or land development of record at the Monroe County Recorder of Deeds, prior to the effective date of this Part 1, where the usable area of a lot or parcel lies within an inner or outer buffer area, as set forth in Subsection I(5)(b), (6)(a) and (7)(a) below, rendering the lot or parcel unable to be developed in accordance with the allowable use per municipal zoning, the development within the inner or outer buffer areas may be permitted subject to the approval of the Board of Supervisors.
(3)
Utility uses in inner or outer buffers. Utility uses, including only stormwater, water, sewer, telephone, telecommunication and electric uses, and not including any buildings or other impervious surfaces relating to said uses, may be permitted within the inner or outer buffer areas set forth in Subsection I(5)(b), (6)(a) and (7)(a) below subject to the approval of the Board of Supervisors.
(4)
Improvements to existing structures in buffer areas. The provisions
of this Part 1 do not require any changes or improvements to be made
to lawfully preexisting structures within the buffer areas. However,
when any improvement to a preexisting structure is proposed within
the buffer areas, this Part 1 and all other applicable ordinances
or laws shall govern.
(5)
Wetlands.
(a)
Wetland identification. For purposes of this section of the
chapter, wetlands that are subject to buffers under this section of
the chapter shall be identified in accordance with the 1987 U.S. Army
Corps of Engineers Manual for Identifying and Delineating Wetlands,
by way of a jurisdictional determination, 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. Wetlands contained within
the banks of a natural watercourse shall be considered for buffer
delineation purposes.
(b)
Wetlands. A five-foot inner buffer and a five-foot outer buffer,
measured perpendicular to and horizontally from the edge of the delineated
wetland, for a total distance of 10 feet, shall be maintained in its
natural state or planted with sufficient native species of shrubs
and trees subject to the municipality's engineer review and approval
for all wetlands.
[1]
Inner buffer.
[a]
The inner buffer shall be measured perpendicular
to and horizontally from the edge of the delineated wetland for a
distance of five feet. The following uses are the only uses permitted
within the inner buffer:
[b]
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided within Subsection I(2) and (3) above. The area of the inner buffer altered by activities permitted in accordance with this section shall be minimized to the greatest extent practicable.
[2]
Outer buffer.
[a]
The outer buffer shall be measured perpendicular
to and horizontally from the outer edge of the inner buffer for a
distance of five feet. The following uses are the only uses permitted
within the outer buffer:
[i]
Stormwater conveyance required by the Township;
[ii]
Buffer maintenance and restoration;
[iii]
The correction of hazardous conditions;
[iv]
Stream crossings permitted by DEP;
[v]
Roads constructed to existing grade;
[vi]
Unpaved trails; and
[vii]
Limited forestry activities that do not clear-cut
the buffer (e.g., selective regeneration harvest) in accordance with
a forestry management plan.
[b]
No other earth disturbance, grading, filling, buildings, structures, new construction or development shall be permitted, except as provided within Subsection I(2) and (3) above. No more than 20% of the cumulative outer buffer on the subject parcel shall be altered by the activities permitted in accordance with this section.
(6)
Lakes and ponds.
(a)
Lake and pond buffer delineation. A twenty-five-foot inner buffer
measured perpendicular to and horizontally from the edge of any lake
or pond, and a twenty-five-foot outer buffer measured perpendicular
to and horizontally from the outer edge of the inner buffer, for a
total distance of 50 feet, shall be maintained in its natural state
or planted with sufficient native species of shrubs and trees subject
to the municipality's engineer review and approval around any lake
or pond.
[1]
Inner buffer.
[a]
The inner buffer shall be measured perpendicular
to and horizontally from the top-of-bank of the lake or pond for a
distance of 25 feet. The following uses are the only uses permitted
within the inner buffer:
[b]
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided within Subsection I(2) and (3) above. The area of the inner buffer altered by activities permitted in accordance with this section shall be minimized to the greatest extent practicable.
[2]
Outer buffer.
[a]
The outer buffer shall be measured perpendicular
to and horizontally from the outer edge of the inner buffer for a
distance of 25 feet. The following uses are the only uses permitted
within the outer buffer:
[i]
Stormwater conveyance required by the Township;
[ii]
Buffer maintenance and restoration;
[iii]
The correction of hazardous conditions;
[iv]
Boat docks;
[v]
Unpaved trails; and
[vi]
In areas of the outer buffer which are not wetlands
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.
[b]
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided within Subsection I(2) and (3) above. No more than 20% of the cumulative outer buffer on the subject parcel shall be altered by the activities permitted in accordance with this section.
(7)
Streams and watercourses.
(a)
Stream and watercourse buffer delineation. A twenty-five-foot
inner buffer and twenty-five-foot outer buffer, measured perpendicular
to and horizontally from the top-of-bank on both sides of any stream
or watercourse, for a total distance of 50 feet, shall be maintained
in its natural state or planted with sufficient native species of
shrubs and trees subject to the municipality's engineer review and
approval on both sides of any stream or watercourse. See Figure 124-10.1.
[1]
Inner buffer.
[a]
The inner buffer shall be measured perpendicular
to and horizontally from the top-of-bank of the stream for a distance
of 25 feet. The following uses are the only uses permitted within
the inner buffer:
[i]
Stormwater conveyance required by the Township;
[ii]
Buffer maintenance and restoration;
[iii]
The correction of hazardous conditions;
[iv]
Stream crossings permitted by DEP;
[v]
Fish hatcheries;
[vi]
Wildlife sanctuaries;
[vii]
Boat launch sites constructed so as not to alter
the floodplain cross section; and
[viii]
Unpaved trails.
[b]
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided in Subsection I(2) and (3) above. The area of the inner buffer altered by activities permitted in accordance with this section shall be minimized to the greatest extent practicable.
[2]
Outer buffer.
[a]
The outer buffer shall be measured perpendicular
to and horizontally from the outer edge of the inner buffer for a
distance of 25 feet. The following uses are the only uses permitted
within the outer buffer:
[i]
Stormwater conveyance required by the Township;
[ii]
Buffer maintenance and restoration;
[iii]
The correction of hazardous conditions;
[iv]
Agricultural activities;
[v]
Plant nurseries;
[vi]
Parking lots constructed to existing grade;
[vii]
Temporary fairs and carnivals;
[viii]
Accessory uses for residential purposes;
[ix]
Private sportsmen's club activities;
[x]
Athletic facilities;
[xi]
Orchards;
[xii]
Wildlife sanctuaries;
[xiii]
Boat launch sites;
[xiv]
Roads constructed to existing grade;
[xv]
Stream crossings permitted by DEP;
[xvi]
Unpaved trails;
[xvii]
Limited forestry activities that do not clear-cut
the buffer (e.g., selective regeneration harvest) in accord with a
forestry management plan; and
[xviii]
In areas of the outer buffer which are not
wetlands 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.
[b]
No other earth disturbance, grading, filling, buildings, structures, new construction, or development shall be permitted, except as provided in Subsection I(2) and (3) above. No more than 20% of the cumulative outer buffer on the subject parcel shall be altered by the activities permitted in accordance with this section.
(8)
Buffer averaging for lakes, ponds and streams.
(a)
If an applicant can establish, and the municipality and the municipality's engineer agree, that a situation exists wherein the conditions and physical characteristics of the applicant's lot and the location of the watercourse on or near the applicant's lot creates a unique physical characteristic wherein it would be unreasonable to require the buffer distances as stated in Subsection I(6)(a) and (7)(a), then an applicant can propose the use of buffer averaging in lieu of the specifically required buffer distances set forth in Subsection I(6)(a) and (7)(a), so long as the proposed buffer averaging does not negatively impact the stormwater quantity and quality, the total buffer area remains the same as if the buffer distances in Subsection I(6)(a) and I(7)(a) were adhered to, and the municipality agrees to the proposed buffer averaging.
(b)
Buffer averaging consists of reducing certain buffer distances at one location and increasing other buffer distances at other locations on the applicant's lot, based on the unique physical characteristics of the applicant's lot. The total required buffer area (i.e., square footage), as required by Subsection I(6)(a) and (7)(a), would stay the same, but the buffer distance at one location may be greater or smaller than the buffer distance at another location in order to meet the unique physical characteristics and conditions of the applicant's lot. Any such buffer averaging shall be subject to the approval of the municipality.
(c)
Buffer averaging shall only be permitted along and/or around
lakes, ponds and streams and shall not be permitted along and/or around
wetlands.
(d)
At no time shall the total buffer along or around a pond, lake
or stream, at any given location, be less than 30 feet, measured perpendicular
to and horizontally from the top-of-bank of the pond, lake or stream,
when using buffer averaging.
|
Figure 124-10.1
Stream Buffer
|
|---|
 |
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 this Part 1 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
this section, 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, and where practicable 36 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 this Part 1 shall be provided
prior to infiltration.
(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)-2
|
(Eq. 124-11.1)
| |
|---|---|---|
|
Where
| ||
|
C N = 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 124-11.1.
|
Figure 124-11.1.
Infiltration Requirement Based Upon NRCS Curve Number.
|
|---|
 |
[3]
The recharge volume required would therefore be computed as:
|
Rev = I* impervious area
|
(Eq. 124-11.2)
| |
|---|---|---|
|
Where
| ||
|
I = Infiltration requirements (in.).
| ||
|
Rev (in cubic feet) = [I (inches)] x
[Impervious Area (square feet)]/[12 inches/1 foot]
|
(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 goal of this section 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 124-11.1 or the curve in Figure 124-11.1
should 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,* impervious
area.
|
B.
Soils. A detailed soils evaluation of the project site shall be required
where practicable 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 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 applicant's
design professional, it must be demonstrated to the municipality that
the soils are conducive to infiltration on the lots identified.
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 124-11.1 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 (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 124-11.1
| ||
|---|---|---|
|
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 as defined
in this Part 1
| ||
(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 and McMichaels Creek Watershed has been divided into
stormwater management districts as shown on the Watershed Map in Appendix
D.[1] Standards for managing runoff from each subarea in the
Brodhead and McMichaels Creek Watershed for design storms are shown
in Table 124-12.1. 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 accord with Table
124-12.1. In addition to the requirements specified in Table 124-12.1
below, the water quality and streambank erosion, groundwater recharge
and erosion control requirements set forth herein shall be implemented.
|
Table 124-12.1
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|---|---|---|---|
|
Water Quantity Requirements
| |||
|
(Reduce To)
| |||
|
District
|
Proposed Conditions
|
Existing Conditions
| |
|
A
|
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
|
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
|
2-year
|
1-year
| |
|
5-year
|
2-year
| ||
|
25-year
|
5-year
| ||
|
50-year
|
10-year
| ||
|
100-year
|
50-year
| ||
|
B-3
|
50-year
|
10-year
| |
|
100-year
|
50-year
| ||
|
C
|
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 this Part 1 and is shown by the design
professional not to 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
streambank erosion and groundwater recharge. 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 D is included at the end of this chapter.
B.
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)[2] and within this Part 1.
[2]
Editor's Note: Appendix D is included at the end of this chapter.
C.
District boundaries. The boundaries of the Stormwater Management
Districts are shown on an official map that is available for inspection
at the office of the municipality. A copy of the official map at a
reduced scale is included in this chapter, Appendix D.[3] 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.
[3]
Editor's Note: Appendix D is included at the end of this chapter.
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 this Part
1. 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 one-hundred-percent 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. 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, 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 stormwater management
plan and this Part 1. 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 this Part 1 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.
The applicant must also establish, in a manner acceptable to the municipality,
that there is an undue hardship.
(1)
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.
(2)
The evaluation shall continue downstream until the increase in flow
diminishes due to additional flow from tributaries and/or stream attenuation.
(3)
The peak flow values to be used for downstream areas for the design
return period storms (two-, five-, ten-, twenty-five-, fifty- and
one-hundred-year) shall be the values from the calibrated model for
the Brodhead and McMichaels Creek Watershed. These flow values can
be obtained from the original Act 167 watershed stormwater management
plans.
(4)
Applicant-proposed conditions for runoff controls which would generate
increased peak flow rates at storm drainage problem areas, by definition,
are precluded from successful attempts to prove "no harm," except
in conjunction with proposed capacity improvements for the problem
areas consistent with this Part 1.
(5)
A financial distress shall not constitute grounds for the municipality
to approve the use of the no-harm option.
(6)
Downstream capacity improvements may be provided as necessary to
achieve the no-harm option.
(7)
Any no-harm justifications shall be submitted by the applicant as
part of the drainage plan submission per this Part 1.
H.
Downstream hydraulic capacity analysis. Any downstream hydraulic
capacity analysis conducted in accordance with this Part 1 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 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.
(2)
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.
(3)
Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with DEP Chapter 105 regulations (if applicable) and, at minimum,
pass the increased twenty-five-year return period runoff.
I.
Hardship option. The stormwater management plan and its standards
and criteria are designed to maintain existing conditions peak flows
and volumes throughout the Brodhead/McMichaels 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 an undue hardship to an applicant, the hardship option may
be applied. A financial distress shall not constitute grounds for
the municipality 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 municipality. Any applicant's
pleading the "hardship option" will assume all liabilities that may
arise due to exercising this option.
J.
Regional detention alternatives. For certain areas within the study
area, it may be more cost effective to provide one control facility
for more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives are the responsibility of
prospective developers. The design of any regional control basins
must incorporate future development of the entire upstream watershed.
The peak outflow of a regional basin would be determined on a case-by-case
basis using the hydrologic model of the watershed consistent with
protection of the downstream watershed areas. Hydrologic model refers
to the calibrated version of the Penn State Runoff Model as developed
for the stormwater management plan.
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 124-13.1 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 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 124-13.1
| |||
|---|---|---|---|
|
Acceptable Computation Methodologies for Stormwater Management
Plans
| |||
|
Method
|
Method Developed by
|
Applicability
| |
|
TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
| |
|
TR-55 (or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
| |
|
HEC-1/HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
| |
|
PSRM
|
Pennsylvania 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 Part 1 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 B of this Part 1.[1] 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, Appendix B, of this Part 1 shall be used for the rainfall distribution. For total developed site impacts of less than one acre which do not require an NPDES permit, the Modified Rational Method may be utilized. Hydrographs with storm durations of at least 10 times the time of concentration shall be utilized.
[1]
Editor's Note: Appendix B is included at the end of 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 Table B-3 in Appendix B of this Part 1.
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 B of this Part 1.
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 B of this Part 1.
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
may 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 B of this Part 1.
I.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this Part 1 using any generally
accepted hydraulic analysis technique or method.
J.
The design of any stormwater detention facility intended to meet
the performance standards of this Part 1 shall be verified by routing
the design storm hydrograph through these facilities using the Storage-Indication
Method. For drainage areas greater than 20 acres in size, the design
storm hydrograph shall be computed using a calculation method that
produces a full hydrograph. The municipality may require full hydrographs
for sites less than 20 acres. 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 municipality has the authority to require that computed existing
runoff rates be reconciled with field observations and conditions.
If the designer can substantiate through actual physical calibration
that more appropriate runoff and time of concentration values should
be utilized at a particular site, then appropriate variations may
be made upon review and recommendations of the Municipal Engineer.
Calibration shall require detailed gauge and rainfall data for the
particular site in question. Calibration should not be misrepresented
to mean a best guess as to what might happen based on experience,
as is oftentimes the case.
A.
Any stormwater facility located on state highway rights-of-way shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
B.
Pretreatment in accordance with this Part 1 shall be provided prior
to infiltration.
C.
All wet basin designs shall incorporate biologic controls consistent
with the West Nile Guidance found in Appendix E.[1]
[1]
Editor's Note: Appendix E is included at the end of this chapter.
D.
Any stormwater management facility designed to store runoff and requiring a berm or earthen embankment required or regulated by this Part 1 shall be designed to provide an emergency spillway to handle flow up to and including the one-hundred-year proposed conditions. Emergency spillways shall be constructed on undisturbed ground and shall not be constructed on embankment fill. The height of embankment must provide a minimum one foot of freeboard above the maximum pool elevation computed when the facility functions for the one-hundred-year proposed conditions inflow. Should any stormwater management facility require a dam safety permit under PaDEP 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 one-hundred-year event.
E.
Any facilities that constitute water obstructions (e.g., culverts,
bridges, outfalls, or stream enclosures), and any work involving wetlands
governed by PaDEP Chapter 105 regulations, as amended, shall be designed
in accordance with Chapter 105 and will require a permit from PaDEP.
F.
Any other drainage conveyance facility that does not fall under PaDEP
Chapter 105 regulations must be able to convey, without damage to
the drainage structure or roadway, runoff from the twenty-five-year
design storm with a minimum one foot of freeboard measured below the
lowest point along the top of the roadway. Any facility that constitutes
a dam as defined in PaDEP Chapter 105 regulations may require a permit
under dam safety regulations.
G.
Any drainage conveyance facility and/or channel not governed by PaDEP
Chapter 105 regulations must be able to convey, 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 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 one-hundred-year
design storm with a minimum one foot of freeboard measured below the
lowest point along the top of the roadway.
H.
Storm sewers must be able to convey proposed conditions runoff from
a twenty-five-year design storm without surcharging inlets, where
appropriate, unless otherwise required by this Part 1.
I.
Adequate erosion protection shall be provided along all open channels
and at all points of discharge.
J.
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.
K.
Any drainage conveyance facility located within a PennDOT right-of-way
must meet PennDOT minimum design standards and permit submission requirements.
Any drainage conveyance facility located within a municipality's right-of-way
must meet the municipality's minimum design standards and permit submission
requirements.
A.
Any earth disturbance must be conducted in conformance with Title
25 of the Pennsylvania Code, Chapter 102, Erosion and Sediment Control.
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) if there exists a threshold for consumptive
use by the designated County departments that is based upon sound
scientific data and acceptable to the Township of Tobyhanna at the
time of the applicant's submittal. The consumptive use shall be developed
in accordance with Appendix F[1] as follows:
(1)
Residential subdivisions and/or land developments or redevelopment
and/or planned residential developments. The CUTR shall be submitted
to the municipality for review and comment prior to the applicant's
submittal to the Monroe County Conservation District.
(2)
Commercial/industrial development or redevelopment. The CUTR shall
be submitted to the municipality during the preliminary and/or final
plan approval process, whichever first occurs, for review and comment
prior to being forwarded to the Monroe County Conservation District.
(3)
A CUTR is not required for existing single lots in recorded subdivisions.
[1]
Editor's Note: Appendix F is included at the end of this chapter.
