[Ord. No. 1151, 6/20/2023]
1.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 26-122:
2.
SWM site plans approved by the municipality, in accordance with § 26-136, shall be on-site throughout the duration of the regulated activity.
3.
The municipality may, after consultation with DEP, approve measures
for meeting the state water quality requirements other than those
in this Part, provided that they meet the minimum requirements of,
and do not conflict with, state law including, but not limited to,
the Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
4.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this Part and to meet all
requirements under 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
Manual[2]), No. 363-2134-008, as amended and updated.
5.
Impervious Areas.
A.
The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in stages.
B.
For development taking place in stages, the entire development plan
must be used in determining conformance with this Part.
C.
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this Part; except that the volume controls in § 26-123 and the peak rate controls of § 26-124 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
D.
Parent Tracts. Ordinance criteria shall apply to the total development
even if development is to take place in phases. The date of the municipal
ordinance adoption from the original Brodhead and McMichaels Creek
Act 167 Plans shall be the starting date from which to consider tracts
as "parent tracts" in which future subdivisions and respective impervious
area computations shall be cumulatively considered. Impervious areas
existing on the "parent tract" prior to adoption of this Part shall
not be considered in cumulative impervious area calculations for exemption
purposes.
6.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written notification
to the adjacent property owner(s). Such stormwater flows shall be
subject to the requirements of this Part.
7.
All regulated activities shall include such measures as necessary
to:
A.
Protect Health, Safety, and Property. An exemption shall not relieve
the applicant from implementing such measures as are necessary to
protect the public health, safety, and property.
B.
Drainage Problems. If a drainage problem is documented or known to
exist downstream of, or expected from, the proposed activity, then
the municipality may require an SWM site plan submittal.
C.
Meet the water quality goals of this Part by implementing measures
to:
(1)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(2)
Maintain or extend riparian buffers.
(3)
Avoid erosive flow conditions in natural flow pathways.
(4)
Minimize thermal impacts to waters of this commonwealth.
(5)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(6)
As required by the Borough MS4 program:
(a)
Reduce sediment load to the Little Pocono Creek in accordance
with DEP MS4 Guidelines; see references in Appendix E[3] and updates on the DEP website.
[3]
Editor's Note: Appendix E is included as an attachment to this chapter.
(b)
Confirm pathogen loading to the Brodhead and McMichael Creeks
addressed.
D.
Incorporate methods described in the Pennsylvania Stormwater Best
Management Practices Manual (BMP Manual[4]). If methods other than green infrastructure and LID methods
are proposed to achieve the volume and rate controls required under
this Part, the SWM site plan must include a detailed justification
demonstrating that the use of LID and green infrastructure is not
practicable.
8.
The design of all facilities over karst shall include an evaluation
of measures to minimize adverse effects.
9.
Infiltration BMPs should be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this Part.
10.
Normally dry, open top storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not less than 24 (when possible) and not more than 72 hours
from the end of the design storm. The qualified design professional
shall include a statement in the stormwater management calculations
describing attempts to achieve the goal of a minimum twenty-four-hour
drain time.
11.
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 14[5] can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
12.
14.
Applicants proposing regulated activities in the Brodhead and McMichaels Creek watersheds which do not fall under the exemption criteria shown in § 26-122 shall submit an SWM site plan 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.
15.
Where a development site is traversed by existing watercourses, a drainage covenant acceptable in form to the Borough shall be provided conforming to the line of such watercourses and required buffer. The terms of the covenants shall conform to the stream buffer requirements contained in § 26-125 of this Part.
16.
Any stormwater management facilities regulated by this Part that
would be located in or adjacent to waters of the commonwealth or wetlands
shall be subject to approval by 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.
17.
Any stormwater management facilities regulated by this Part that
would be located on state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
Any stormwater facility located on state highway rights-of-way shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT). Any facility located within a PennDOT right-of-way must
meet PennDOT minimum design standards and permit submission requirements.
18.
All stormwater runoff, other than rooftop runoff, shall be treated
for water quality prior to discharge to surface waters or groundwaters.
Pretreatment shall be provided prior to discharge to infiltration
facilities.
19.
Any stormwater management facility (i.e., BMP, detention basin) designed
to store runoff and requiring a berm or earthen embankment required
or regulated by this Part shall be designed to provide an emergency
spillway to handle the discharge of flows up to and including the
inflow to the facility from the 100-year proposed conditions, considering
the primary outlet control structure(s) are blocked. The height of
embankment must provide a minimum one foot of freeboard above the
maximum pool elevation computed when the facility functions for the
100-year proposed conditions inflow for facilities ponding over three
feet deep. 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 100-year event.
20.
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 PaDEP), shall be designed in accordance with
Chapter 105 and will require a permit from PaDEP.
21.
Any other drainage conveyance facility and/or channel that does not
fall under 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 1.0 foot of freeboard measured below the
lowest point along the top of the roadway for connector roads. Local
access roads and private roads may be designed to a ten-year storm.
Both cases will require the professional to document in the narrative
that the overflow path will not negatively affect the safety of the
public.
22.
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.
23.
Storm sewers must be able to convey proposed conditions runoff from
a twenty-five-year storm or as necessary to convey the design storm
to stormwater management facilities.
24.
Adequate erosion protection shall be provided along all open channels,
and at all points of discharge.
25.
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.
26.
Protect the public from stormwater basin ponding by providing fence
for ponding depths over three feet of depth between the bottom of
the basin and the invert of emergency spillway.
[Ord. No. 1151, 6/20/2023]
1.
Regulated activities that meet all the following criteria are exempt from the SWM site plan submission requirements. Projects exempt from SWM site plan submissions shall comply with § 26-122, Subsection 4. The owner shall submit information confirming the exemption requirements have been met for review by the Borough.
A.
Do not exceed 0.5 acres of cumulative earth disturbance activity.
This criterion shall apply to the total development even if development
is to take place in phases.
B.
Do not add more than 2,000 square feet of impervious area. These
criteria shall apply to the total development even if development
is to take place in phases. The date of this Part adoption shall be
the starting point from which to consider tracts as "parent tracts"
in which future subdivisions and respective impervious area computations
shall be cumulatively considered. Impervious areas existing on the
parent tract prior to adoption of this Part shall not be considered
in cumulative, impervious area calculations for exemption purposes.
C.
Are not located in the drainage areas tributary to Church Alley,
which is an area identified as a drainage concern.
D.
Do not change or concentrate flow paths to adjoiners.
2.
Agricultural activity and gardening are exempt from the SWM site
plan preparation requirements of this Part, provided the activities
are performed according to the requirements of 25 Pa. Code Chapter
102.
3.
Forest management and timber operations are exempt from the SWM site
plan preparation requirements of this Part, provided the activities
are performed according to the requirements of 25 Pa. Code Chapter
102.
5.
The municipality may deny or revoke any exemption pursuant to this
section at any time for any project that the municipality believes
may pose a threat to public health and safety or the environment.
6.
High tunnels shall be exempt from the provisions of this Part if:
A.
The high tunnel or its flooring does not result in an impervious
area exceeding 25% of all structures located on the owners' total
contiguous land area; and
B.
The high tunnel meets one of the following:
(1)
The high tunnel is located at least 100 feet from any perennial
stream or watercourse, public road or neighboring property line.
(2)
The high tunnel is located at least 35 feet from any perennial
stream or watercourse, public road or neighboring property line and
located on land with a slope not greater than 7%.
(3)
The high tunnel is supported with a buffer or diversion system
that does not directly drain into a stream or other watercourse managing
stormwater runoff in a manner consistent with requirements of this
Part and the Act of April 18, 2018, P.L. 91, No. 15, and the Act of
October 4, 1978 (P.L. 864, No. 167).[1]
[1]
Editor's Note: See 32 P.S. § 680.1 et seq.
[Ord. No. 1151, 6/20/2023]
1.
The green infrastructure and low-impact development practices provided
in the BMP Manual[1] shall be utilized for all regulated activities wherever possible. Water volume controls shall be implemented using the Design Storm Method in Subsection 1A or the Simplified Method in Subsection 1B below. For regulated activity areas equal or less than one acre that do not require hydrologic routing to design the stormwater facilities, this Part establishes no preference for either methodology; therefore, the applicant may select either methodology on the basis of economic considerations, the intrinsic limitations on applicability of the analytical procedures associated with each methodology and other factors.
A.
The Design Storm Method (CG-1 in the BMP Manual[2]) is applicable to any size of regulated activity. This
method requires detailed modeling based on site conditions.
(1)
Do not increase the post-development total runoff volume for
all storms equal to or less than the two-year, twenty-four-hour duration
precipitation.
B.
The Simplified Method (CG-2 in the BMP Manual[3]) provided below is independent of site conditions and
should be used if the Design Storm Method is not followed. This method
is not applicable to regulated activities greater than one acre or
for projects that require design of stormwater storage facilities.
For new impervious surfaces:
(1)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(2)
At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow, i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options include reuse, evaporation, transpiration, and infiltration.
(3)
Wherever possible, infiltration facilities should be designed
to accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 0.5 inch of the permanently
removed runoff should be infiltrated.
C.
Projects with a limit of earth disturbance greater than one acre
shall be subject to the requirements of the NPDES permit.
[Ord. No. 1151, 6/20/2023]
1.
For the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year,
twenty-four-hour storm events, the post-development peak discharge
rates will follow the applicable approved release rate maps. For any
areas not shown on the release rate maps, the post-development discharge
rates shall not exceed the predevelopment discharge rates.
A.
The Brodhead and McMichaels Creek watershed has been divided into
stormwater management districts. The Management District Map is available
on the Monroe County Conservation District's website. Standards
for managing runoff from each subarea in the Brodhead and McMichaels
Creek watershed for the various design storms are shown in Table 26-124.1.
Development sites located in the A District must control proposed
conditions peak runoff rates to existing conditions peak runoff rates
for the design storms in accordance with the below table. District
C may allow increases in post-development flows where adequate downstream
conveyances exist.
|
Table 26-124.1 - Peak Runoff Rate Requirements
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|---|---|---|---|---|
|
District
|
Proposed Conditions
|
(Reduce to)
|
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
| |||
|
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 § 26-124, Subsection 1F, and is shown by the qualified 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 streambank erosion (§§ 26-126 and 26-129); and volume (§ 26-123). 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.
| |||
B.
General. Proposed conditions peak rates of runoff from any regulated activity shall not exceed the peak release rates of runoff prior to development for the design storms specified for the Stormwater Management District Watershed Map (refer to map on MCCD website) and § 26-124 of this Part.
C.
District Boundaries. The boundaries of the stormwater management
district are shown in an official map that is available from the MCCD
website. 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 SWM site
plan.
D.
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.
E.
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, undisturbed
areas bypassing the stormwater management facilities would not be
subject to the management district criteria.
F.
Downstream Hydraulic Capacity Analysis. Any downstream hydraulic
capacity analysis conducted in accordance with this Part shall use
the following criteria for determining adequacy for accepting increased
peak flow rates:
(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.
G.
Hardship Option. The stormwater management plan and its standards and criteria are designed to maintain existing conditions peak flows and volumes throughout the Brodhead and McMichaels Creek watershed as the watershed becomes developed. There may be certain instances, however, where the standards and criteria established are too restrictive for a particular applicant. The existing drainage network in some areas may be capable of safely transporting slight increases in flows without causing a problem or increasing flows elsewhere. If an applicant cannot meet the stormwater standards due to lot conditions or if conformance would become a hardship to an applicant, the hardship option may be considered (refer to § 26-110, Waivers, above). 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 governing body 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. A financial distress shall not constitute grounds for the municipality to approve the use of the "no-harm" option.
[Ord. No. 1151, 6/20/2023]
1.
In order to protect and improve water quality, a riparian buffer
covenant shall be created and recorded as part of any subdivision
or land development that encompasses a riparian buffer.
2.
Streams. Except as required by Chapter 102, the riparian buffer shall
be measured as a minimum inner buffer of 50 feet from the top of the
streambank and twenty-five-foot outer buffer (on each side).
A.
Inner Buffer. Stormwater conveyance and BMPs required by the municipality
buffer maintenance and restoration of both existing impervious and
restoration to native vegetation, the correction of hazardous conditions,
stream crossings permitted by DEP, fish hatcheries, wildlife sanctuaries
and boat launch sites constructed so as not to alter the floodplain
cross section, and unpaved trails shall be permitted, providing no
buildings are involved. No other earth disturbance, grading, filling,
buildings, structures, new construction, or development shall be permitted.
The area of the inner buffer altered by activities shall be minimized
to the greatest extent practicable except to remove existing impervious
and establish native vegetation.
B.
Outer Buffer. Stormwater conveyance and BMPs required by the municipality,
buffer maintenance and restoration of both existing impervious and
restoration to native vegetation, the correction of hazardous conditions,
agricultural activities, plant nurseries, parking lots constructed
to existing grade, temporary fairs and carnivals, accessory uses for
residential purposes, private sportsmen's club activities, athletic
facilities, orchards, wildlife sanctuaries, boat launch sites, roads
constructed to existing grade, stream crossings permitted by DEP and
unpaved trails and limited forestry activities that do not clear-cut
the buffer (e.g., selective regeneration harvest) in accord with a
forestry management plan shall be permitted, provided no buildings
are involved.
C.
In areas of the outer buffer which are not wetlands, vernal ponds
or slopes of more than 15% stormwater management facilities which
improve water quality of stormwater discharge shall be permitted unless
prohibited by other township/Borough or state requirements. No other
earth disturbance, grading, filling, buildings, structures, new construction,
or development shall be permitted. No more than 20% of the cumulative
outer buffer on the subject parcel shall be altered except to remove
existing impervious and establish native vegetation.
3.
Minimum Management Requirements for riparian buffers.
A.
Existing native vegetation shall be protected and maintained within
the riparian buffer.
B.
Whenever practicable, invasive vegetation shall be actively removed
and the riparian buffer shall be planted with native trees, shrubs
and other vegetation to create a diverse native plant community appropriate
to the intended ecological context of the site.
C.
Existing impervious surfaces may be removed and replaced with stable
grading and native vegetation subject to Chapter 102 and 105 requirements.
Approval from MCCD/DEP will be required.
4.
The riparian buffer covenant shall be enforceable by the municipality
and shall run with the land and shall limit the use of the property
located therein. The covenant shall allow for continued private ownership
and shall count toward the minimum lot area required by zoning, unless
otherwise specified in the municipal Zoning Ordinance.[1]
5.
Any permitted use within the riparian buffer covenant shall be conducted
in a manner that will maintain the extent of the existing 100-year
floodplain, improve or maintain the stream stability, and preserve
and protect the ecological function of the floodplain.
7.
Septic drainfields and sewage disposal systems shall not be permitted
within the riparian buffer covenant and shall comply with setback
requirements established under 25 Pa. Code Chapter 73.
 Riparian Buffer
|
8.
Where resource buffers overlap, the more restrictive requirements
shall apply.
9.
Outer buffers are not required for any portion of the required buffer
area that does not drain to the resource requiring the buffer.
10.
Preexisting Lots or Parcels/Development in Outer Buffers. In the
case of legally preexisting lots or parcels (approved prior to the
effective date of this Part) where the usable area of a lot or parcel
lies within an outer 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 by waiver granted in
accordance with provisions of this Part.
11.
Improvements to Existing Structures in Outer Buffers. The provisions of this § 26-125 do not require any changes or improvements to be made to lawfully existing structures in buffers. However, when any substantial improvement to a structure is proposed which results in a horizontal expansion of that structure, the improvement may only be permitted by waiver granted in accordance with provisions of this Part.
12.
Wetlands.
A.
Wetland Identification. Wetlands shall be identified in accord with
the most current U.S. Army Corps of Engineers Manual for Identifying
and Delineating Wetlands, 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. Where wetlands are contained
within the banks of a natural watercourse, only the stream buffer
shall apply.
B.
Wetland Buffer Delineation. A fifty-foot inner buffer and twenty-five-foot
outer buffer, measured perpendicular to and horizontally from the
edge of the delineated wetland or vernal pond for a total distance
of 75 feet, shall be maintained for all wetlands and vernal ponds.
(1)
Inner Buffer. Stormwater conveyance and BMPs required by the
municipality, buffer maintenance and restoration, the correction of
hazardous conditions, stream crossings permitted by DEP and passive
unpaved stable trails shall be permitted. No other earth disturbance,
grading, filling, buildings, structures, new construction, or development
shall be permitted. The area of the inner buffer altered shall be
minimized to the greatest extent practicable.
(2)
Outer Buffer. Stormwater conveyance and BMPs required by the municipality, buffer maintenance and restoration, the correction of hazardous conditions, stream crossings permitted by DEP, roads constructed to existing grade, unpaved trails, and limited forestry activities that do not clear-cut the buffer (e.g., selective regeneration harvest) in accord with a forestry management plan shall be permitted, provided no buildings are involved, and those activities permitted under § 26-125, Subsections 10 and 11. No more than 20% of the cumulative outer buffer on the subject parcel shall be altered.
13.
Lakes and Ponds.
A.
Lakes and ponds shall have no outer buffer.
B.
Lake and Pond Buffer Delineation. A fifty-foot buffer measured perpendicular
to and horizontally from the edge of any water body shall be maintained
around any water body.
C.
Permitted Activities/Development. Stormwater conveyance and BMPs
required by the municipality, buffer maintenance and restoration,
the correction of hazardous conditions, lake front views, boat docks
and unpaved trails shall be permitted, provided no buildings are involved.
D.
The area of the buffer impacted shall not exceed 35% of the buffer
on the subject parcel.
[Ord. No. 1151, 6/20/2023]
1.
Biology shall be incorporated into the design of all wet basins in
accordance with the West Nile Virus Guidance found in Appendix D.[1]
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
2.
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:
A.
Analyze hydrologic soil groups as well as natural and man-made features
within the watershed to determine general areas of suitability for
infiltration practices.
B.
Provide site-specific infiltration test results (at the level of
the proposed infiltration surface) in accord with ASTM Guide No. D5126
or other method as described in the PA DEP Stormwater BMP Manual as
amended/treat runoff from the 100-year storm to determine the appropriate
hydraulic conductivity rate.
C.
Design the infiltration structure for the required storm volume based
on field determined capacity at the level of the proposed infiltration
surface.
D.
If on-lot infiltration structures are proposed by the applicant's
qualified design professional, it must be demonstrated to the municipality
that the soils are conducive to infiltrate on the lots identified.
3.
Stormwater Hotspots.
A.
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 26-126.1 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, but the requirements of § 26-124, Subsection 1A, should be met. Second, a greater level of stormwater treatment may be needed at hotspot sites to prevent pollutant discharge after construction. EPA's NPDES stormwater program requires some industrial sites to prepare and implement a stormwater pollution prevention plan.
|
Table 26-126.1 - 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
|
B.
Extreme caution shall be exercised where salt or chloride would be
a pollutant since soil does 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.
C.
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.
4.
Extreme caution shall be exercised where infiltration is proposed
in source water protection areas or that may affect a wellhead or
surface water intake.
5.
Water quality calculations shall be submitted using the DEP spreadsheet,
Worksheets 12 and 13 out of the BMP manual, detaining the two-year,
twenty-four-hour design storm to the existing conditions one-year
storm flow using the SCS Type II distribution or other alternate method
upon approval of the Municipal Engineer.
6.
Where an NPDES permit for stormwater discharges associated with construction
activities is required, the water quality requirements of that permit
should be used; however, the minimum buffer provisions listed below
should be applied to all applications.
7.
Where practicable, wet basins shall be utilized for water quality
control and shall meet the requirements found in the PA Stormwater
BMP manual as revised.
8.
The temperature and quality of water and streams shall be maintained
through the use of temperature sensitive BMPs and stormwater conveyance
systems.
9.
In selecting the appropriate BMPs or combinations thereof, the applicant
shall consider the following:
A.
Total contributing area.
B.
Permeability and infiltration rate of the site soils.
C.
Slope and depth to bedrock.
D.
Depth to seasonal high-water table.
E.
Proximity to building foundations and wellheads.
F.
Erodibility of soils.
G.
Land availability and configuration of the topography.
H.
Peak discharge and required volume control.
I.
Stream bank erosion.
J.
Efficiency of the BMPs to mitigate potential water quality problems.
K.
The volume of runoff that will be effectively treated.
L.
The nature of the pollutant being removed.
M.
Maintenance requirements.
N.
Creation/protection of aquatic and wildlife habitat.
O.
Recreational value.
[Ord. No. 1151, 6/20/2023]
1.
The design of any stormwater detention facilities intended to meet
the performance standards of this Part shall be verified by routing
the design storm hydrograph through these facilities using the Storage-Indication
Method for facilities that are not impacted by tailwater conditions.
Facilities with tailwater conditions should be routed using the Dynamic
Storage Indication Method unless the engineer can provide justification
for another method. Facilities with the potential for reverse flow
should be routed using simultaneous routing.
2.
Orifices smaller than three inches' diameter are not recommended.
However, if the qualified design professional can provide proof that
the smaller orifices are protected from clogging by use of trash racks,
etc., smaller orifices may be permitted. Openings in trash racks should
be no larger than 50% of the orifice size.
3.
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 26-127.1 summarizes acceptable computation methods and
the method selected by the qualified 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 Modified
Rational Method to estimate peak discharges from drainage areas that
contain less than one acre. The Soil Cover Complex Method shall be
used for drainage areas greater than one acre.
4.
All calculations consistent with this Part using the Soil Cover Complex
Method shall use the appropriate design rainfall depths for the various
return period storms consistent with current NOAA Atlas 14 Point Precipitation
Frequency Estimates. If a hydrologic computer model such as PSRM or
HEC-1 is used for stormwater runoff calculations, then the duration
of rainfall shall be 24 hours. The SCS Type II Rainfall Distribution
shall be utilized for the rainfall distribution.
5.
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 (CN)
or Rational "C" value, as listed in Tables B-1 or B-2 in Appendix
B of this Part.[1]
[1]
Editor's Note: Appendix B is included as an attachment to this chapter.
6.
All calculations using the Modified Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from the current NOAA Atlas 14 Point Precipitation Frequency Estimates. Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's Equation.
7.
Calculations using the Modified Rational Method shall be based on
a common time of concentration for all contributing areas to a discharge
point in both the predevelopment and post-development runoff conditions.
8.
Hydrograph volumes generated by the Modified Rational Method for
routing through control (detention and infiltration) facilities should
be comparable to hydrograph volumes generated by the TR-55 methodology.
The ascending and descending limbs of the hydrograph generated by
the Modified Rational Method should be adjusted in order to provide
a comparable hydrograph volume.
9.
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-1 in Appendix B of this Part or from DEP references. Due to
limitations of the TR-55 methodology, a minimum weighted curve number
of 40 shall be utilized for the calculations.
10.
Runoff coefficients (C) for both existing and proposed conditions
for use in the Modified Rational Method shall be obtained from Table
B-2 in Appendix B of this Part.
11.
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 placement of topsoil and/or
seeding. The designer may increase his proposed condition "CN" or
"C" to better reflect proposed soil conditions.
12.
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-3 in Appendix
B of this Part.
13.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this Part using any generally
accepted hydraulic analysis technique or method.
14.
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.
|
TABLE 26-127.1
| ||
|---|---|---|
|
Acceptable Computation Methodologies for Stormwater Management
Plans
| ||
|
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
|
US 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
|
|
Modified Rational Method (or commercial computer package based
on Rational Method)
|
Emil Kuichling (1889)
|
For sites less than 1 acre (or as approved by the municipality
and/or Municipal Engineer)
|
|
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
and/or Municipal Engineer
|
[Ord. No. 1151, 6/20/2023]
1.
Any earth disturbance must be conducted in conformance with 25 Pa.
Code Chapter 102, Erosion and Sediment Control.
2.
Additional erosion and sediment control design standards and criteria
that must be or are recommended to be applied where infiltration BMPs
are proposed shall include the following:
A.
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity.
B.
Infiltration BMPs shall not be constructed nor receive runoff until
the entire contributory drainage area to the infiltration BMP has
achieved final stabilization.
[Ord. No. 1151, 6/20/2023]
1.
Streambank restoration projects shall include the following:
A.
No restoration or stabilization projects may be undertaken without
examining the fluvial geomorphology of stable reaches above and below
the unstable reach.
B.
Restoration project design must consider maintenance of stability
in the adjacent stable reaches of the stream channel.
C.
An erosion and sediment control plan approved by the Conservation
District must be provided by the applicant.
D.
All applicable state and federal permits must be obtained.
