1.
Applicants proposing regulated activities in the municipality which are not exempt under § 19-106 shall submit a stormwater management site plan (SWM site plan) to the municipality for review and approval in accordance with Parts 3 and 4. SWM site plans approved by the municipality shall be on site throughout the duration of the regulated activity.
2.
The stormwater management and runoff control criteria and standards
in this chapter shall apply to the total proposed regulated activity
even if it is to take place in stages. The measurement of impervious
surfaces shall include all of the impervious surfaces in the total
proposed regulated activity even if the development is to take place
in stages.
3.
No regulated activity within the municipality shall commence until:
A.
The municipality issues approval of a SWM site plan which demonstrates
compliance with the requirements of this chapter; and
B.
The applicant has received a letter of adequacy or approval for the
erosion and sediment control plan review by the municipality and the
Conservation District (if required) and has received all other local,
state and federal permit approvals required for the project involving
the regulated activity. Any project with greater than 5,000 square
feet of earth disturbance requires review and approval of and erosion
and sediment control plan from the Conservation District.
4.
Neither submission of a SWM site plan under the provisions herein
nor compliance with the provisions of this chapter shall relieve any
person from responsibility for damage to any person or property otherwise
imposed by law.
5.
The applicant shall design the site to minimize disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall apply the procedures set forth in § 19-304 for the overall site design and for selection, location, and design of features and BMPs to be used to comply with the requirements of this chapter.
6.
To the maximum extent practicable, post-construction stormwater shall
be discharged within the drainage area of the same stream or water
body receiving the runoff prior to construction of the proposed regulated
activity.
7.
For regulated activities with one acre or more of proposed earth
disturbance, existing drainage peak rate discharges, up to and including
the 100-year storm, and the volume of runoff, up to and including
the two-year storm, onto or through adjacent property(ies) or down-gradient
property(ies), including diffuse drainage discharge, shall not be
altered in any manner by regulated activities under this chapter without
written permission from and, where applicable as determined by the
municipality, an easement and agreement with the affected landowner(s)
for conveyance of discharges onto or through their property(ies).
Altered stormwater discharges shall be subject to any applicable discharge
criteria specified in this chapter.
8.
Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to water quality and volume control, infiltration, stream channel protection, or peak flow rate control requirements (as presented in §§ 19-305, 19-306, 19-307, and 19-308). Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.
9.
If site conditions preclude capture of runoff from limited portions
of the disturbed area for achieving water quality volume control standards,
stream channel protection standards, and the two-year, storm event
peak runoff rate reduction standards for new development required
by this chapter, the applicant shall propose alternate methods to
mitigate the bypass of the BMPs, subject to the approval of the Municipal
Engineer. In no case shall resulting peak rate be greater than the
predevelopment peak rate for the equivalent design storm.
10.
For all regulated activities, erosion and sediment control BMPs shall
be designed, implemented, operated, and maintained during the regulated
activities (i.e., during construction) as required to meet the purposes
and requirements of this chapter, to meet the erosion and sediment
control requirements of the municipality, if applicable, and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law.
11.
For all regulated activities, permanent BMPs and conveyances shall
be designed, implemented, operated, and maintained to meet the purposes
and requirements of this chapter and to meet all requirements under
Title 25 of the Pennsylvania Code, the Clean Streams Law, and the
Storm Water Management Act.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq., and
32 P.S. § 680.1 et seq., respectively.
12.
The design of all BMPs and conveyances shall incorporate sound engineering
principles and practices in a manner that does not aggravate existing
stormwater problems as identified by the municipality. The municipality
reserves the right to disapprove any design that would result in construction
in an area affected by existing stormwater problem(s) or continuation
of an existing stormwater problem(s).
13.
Existing wetlands, either on the site or on an adjacent property,
shall not be used to meet the minimum design requirements for stormwater
management or stormwater runoff quality treatment. Stormwater discharges
to existing wetlands shall not degrade the quality or hydrologic integrity
of the wetland.
14.
Hotspots Runoff Controls. Specific structural or pollution prevention
practices may be required, as determined to be necessary by the Municipal
Engineer, to pretreat runoff from hotspots prior to infiltration.
Following is a list of examples of hotspots:
A.
Vehicle salvage yards and recycling facilities;
B.
Vehicle fueling stations;
C.
Vehicle service and maintenance facilities;
D.
Vehicle and equipment cleaning facilities;
E.
Fleet storage areas (bus, truck, etc.);
F.
Industrial sites based on Standard Industrial Classification Codes;
G.
Marinas (service and maintenance areas);
H.
Outdoor liquid container storage;
I.
Outdoor loading/unloading facilities;
J.
Public works storage areas;
K.
Facilities that generate or store hazardous materials;
L.
Commercial container nursery;
M.
Contaminated sites/brownfields;
N.
Other land uses and activities as designated by the municipality.
15.
Contaminated and Brownfield Sites. Where BMPs may contribute to the
migration of contaminants in groundwater, the water quality and runoff
volume, stream channel protection and peak rate control standards
shall be met; however, at the Municipal Engineer's discretion,
the minimum infiltration requirement may be reduced or eliminated
commensurate with the contaminated area and the required water quality
and runoff control measures may be increased to mitigate the reduced
infiltration requirement for the contaminated area.
16.
Additional Water Quality Requirements. The municipality may require
additional stormwater control measures for stormwater discharges to
special management areas including, but not limited to:
A.
Water bodies listed as "impaired" by PADEP.
B.
Any water body or watershed with an approved total maximum daily
load (TMDL).
C.
Areas of known existing flooding problems.
D.
Critical areas with sensitive resources (e.g., state-designated special
protection waters, cold water fisheries, carbonate geology or other
groundwater recharge areas that may be highly vulnerable to contamination,
drainage areas to water supply reservoirs, etc.).
17.
Applicants shall utilize the Pennsylvania Stormwater Best Management
Practices Manual (PA BMP Manual), as amended, or other sources acceptable
to the Municipal Engineer, for testing and design standards for BMPs,
and where there is a conflict with the provisions of this chapter,
the most restrictive applies.
18.
For areas underlain by karst or carbonate geology that may be susceptible
to the formation of sinkholes and other karst features, the location,
type, and design of infiltration BMPs shall be based on a site evaluation
conducted by a qualified licensed professional and based on the PA
BMP Manual (as amended) or other design guidance acceptable to the
Municipal Engineer.
19.
All regulated activities located within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with Chapter 27, Part 13, of the Franklin Township Code, as amended, and shall be designed to maintain the flood-carrying capacity of the floodway such that the base flood elevations are not increased, either upstream or downstream. The natural conveyance characteristics of the site and the receiving floodplain shall be incorporated into the stormwater management practices proposed for the site.
20.
Disturbance of existing ground cover during construction of the proposed
regulated activity is prohibited within 50 feet of top-of-bank of
all perennial and intermittent waterways, water bodies (lakes, ponds,
etc.) and wetlands, except for activities otherwise approved by state
or local agencies (e.g., stream restoration projects, road crossings,
subsurface utility projects, etc.). At the Municipal Engineer's
discretion, and with Conservation District and PADEP approval where
necessary, the nondisturbance buffer may be reduced because of setback
or other site constraints, but never be less than 10 feet.
[Ord. 2023-01, 4/19/2023]
1.
The following permit or other regulatory requirements may apply to
certain regulated activities and shall be met prior to (or as a condition
of) final approval by the municipality of the SWM site plan and prior
to commencement of any regulated activities, as applicable:
A.
All regulated activities subject to permit or regulatory requirements
by PADEP under regulations at 25 Pa. Code Chapter 102, or erosion
and sediment control requirements of the municipality.
B.
Work within natural drainage ways subject to permit by PADEP under
25 Pa. Code Chapter 105.
C.
Any BMP or conveyance that would be located in or adjacent to surface
waters of the commonwealth, including wetlands, subject to permit
by PADEP under 25 Pa. Code Chapter 105.
D.
Any BMP or conveyance that would be located on or discharge to a
state highway right-of-way or require access to or from a state highway
and be subject to approval by PennDOT.
E.
Culverts, bridges, storm sewers, or any other facilities which must
pass or convey flows from the tributary area and any facility which
may constitute a dam subject to permit by PADEP under 25 Pa. Code
Chapter 105.
[Ord. 2023-01, 4/19/2023]
1.
No regulated activity within the municipality shall commence until:
A.
The municipality receives documentation that the applicant has received:
(1)
A letter of adequacy from the Conservation District or other
approval from PADEP in compliance with 25 Pa. Code Chapter 102, of
an erosion and sediment control plan for construction activities for
projects where the area of disturbance is greater than 5,000 square
feet and less than one acre, where pond dredging is involved, or when
the disturbance is associated with activities described under 25 Pa.
Code Chapter 105 permits;
(2)
A PADEP NPDES permit for stormwater discharges associated with
construction activities for projects where the area of disturbance
exceeds one acre, as required under 25 Pa. Code Chapter 92.a, if applicable;
and
(3)
Evidence of any other permit(s) or approvals required for the
regulated activities.
2.
A copy of the erosion and sediment control plan and any required
permit(s), as required by PADEP regulations, shall be available on
the site at all times.
[Ord. 2023-01, 4/19/2023]
1.
The applicant shall design the site to minimize the disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall demonstrate in its SWM site plan (as required in § 19-402, Subsection 2C) that the design sequence, objectives, and techniques described below were applied to the maximum extent practicable in the site design of the regulated activity while complying with all other requirements of this chapter. The site design shall:
B.
Second, provide a prioritized listing of these resources and features
to identify:
(1)
Those to be incorporated into the site design in a manner that
provides protection from any disturbance or impact from the proposed
regulated activity;
(2)
Those to be protected from further disturbance or impact but
for which the proposed regulated activity will provide improvement
to existing conditions;
(3)
Those that can be incorporated into and utilized as components
of the overall site design in a manner that protects or improves their
existing conditions while utilizing their hydrologic function within
the limits of their available capacity (e.g., for infiltration, evapotranspiration,
or reducing pollutant loads, runoff volume or peak discharge rates,
etc.) to reduce the need for or size of constructed BMPs; and
(4)
Those that may be considered for alteration, disturbance, or
removal.
C.
Third, develop the site design to achieve the following:
(2)
Minimize earth disturbance (both surface and subsurface);
(3)
Maximize protection of or improvement to natural resources and
special management areas;
(4)
Minimize the disturbance of natural site hydrology, in particular
natural drainage features and patterns, discharge points and flow
characteristics, natural infiltration patterns and characteristics,
and natural channel and floodplain conveyance capacity;
(6)
Maximize infiltration and the use of natural site infiltration
features, patterns and conditions, and evapotranspiration features;
(7)
Apply selective grading design methods to provide final grading
patterns or preserve existing topography in order to evenly distribute
runoff and minimize concentrated flows;
(8)
Minimize the cumulative area to be covered by impervious surfaces,
and:
(9)
Minimize the volume and peak discharge rates of stormwater generated;
(10)
Avoid or minimize stormwater runoff pollutant loads and receiving
stream channel erosion;
(13)
For flow volumes requiring conveyance from the source of generation
to a BMP for management, give preference to open channel conveyance
techniques that provide infiltration and water quality benefits and
landscaped-based management in common open space areas, where practicable;
and
(14)
Consider additional guidance for incorporating natural hydrology into the site and BMP designs, methods and techniques that support the objectives of § 19-304, Subsection 1B and C. Appendix B presents additional discussion of conservation design and low-impact development.[1]
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
[Ord. 2023-01, 4/19/2023]
1.
To control post-construction stormwater impacts from regulated activities
and meet state water quality requirements, BMPs shall be provided
in the site design that replicate predevelopment stormwater infiltration
and runoff conditions, such that post-construction stormwater discharges
do not degrade the physical, chemical, or biological characteristics
of the receiving waters. The green infrastructure and low-impact development
(LID) practices provided in the PA BMP Manual, as well as the guidance
on green infrastructure, LID and conservation design (CD) provided
in Appendix B,[1] shall be utilized for all regulated activities wherever
possible. The applicant shall comply with the following water quality
and runoff volume requirements for all regulated activities, including
all new development and redevelopment activities:
A.
The post-construction total runoff volume shall not exceed the predevelopment
total runoff volume for all storms equal to or less than the two-year,
twenty-four-hour duration precipitation ("design storm"). The water
quality and runoff volume to be managed shall consist of any runoff
volume generated by the proposed regulated activity over and above
the predevelopment total runoff volume and shall be captured and permanently
retained or infiltrated on the site. Permanent retention options may
include, but are not limited to, reuse, evaporation, transpiration,
and infiltration.
C.
The design of the stormwater management facility outlet shall provide
for protection from clogging and unwanted sedimentation.
D.
BMPs that moderate the temperature of stormwater shall be used to
protect the temperature of receiving waters.
E.
Water quality improvement shall be achieved in conjunction with achieving the infiltration requirements of § 19-306. The infiltration volume required under § 19-306 may be included as a component of the water quality volume. If the calculated water quality and runoff volume is greater than the volume infiltrated, then the difference between the two volumes shall be managed for water quality and runoff volume control through other techniques or practices but shall not be discharged from the site.
F.
Runoff from the disturbed area shall be treated for water quality
prior to entering existing waterways or water bodies. If a stormwater
management practice does not provide water quality treatment, then
water quality BMPs shall be utilized to provide pretreatment prior
to the runoff entering the stormwater management practice.
H.
When the regulated activity contains or is divided by multiple drainage
areas, the water quality and runoff volume shall be separately addressed
for each drainage area.
I.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
J.
Areas located outside of the site (i.e., areas outside of the regulated
activity) may be excluded from the calculation of the water quality
and runoff volume requirements.
L.
Evapotranspiration may be quantified and credited towards meeting
volume requirements according to the PADEP Post-Construction Stormwater
Management (PCSM) Spreadsheet and Instructions (December 2020) or
the most recent guidance from PADEP.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
[Ord. 2023-01, 4/19/2023]
1.
Providing for infiltration consistent with the natural hydrologic
regime is required to compensate for the reduction in the recharge
that occurs when the ground surface is disturbed or impervious surface
is created or expanded. The applicant shall achieve the following
infiltration requirements:
A.
For regulated activities involving both new development and redevelopment, infiltration should be designed to accommodate the entire water quality and runoff volume required in § 19-305. Infiltration BMPs should be consistent with the design and infiltration period guidelines included in the PA BMP Manual or other PADEP design guidance. If the runoff volume required by § 19-305 cannot be infiltrated, then alternative methods consistent with the PA BMP Manual (as amended) or other PADEP guidance, such as the Managed Release Concept, may be used to manage this volume with approval from the Municipal Engineer.
B.
For regulated activities involving both new development and redevelopment,
the volume of a minimum of one inch of runoff from all regulated impervious
surfaces shall be infiltrated.
C.
If the requirements of § 19-306, Subsection 1A or B, cannot be physically accomplished, then the applicant shall be responsible for demonstrating with data or calculations to the satisfaction of the Municipal Engineer why this infiltration volume cannot be physically accomplished on the site (e.g., shallow depth to bedrock or limiting zone, open voids, steep slopes, etc.) and what alternative volume can be infiltrated.
E.
If site conditions preclude capture of runoff from portions of the
impervious surfaces, the infiltration volume for the remaining area
shall be increased an equivalent amount to offset the loss.
F.
When a project contains or is divided by multiple watersheds, the
infiltration volume shall be separately addressed for each watershed.
G.
Existing impervious surfaces located in areas outside of the site
(i.e., outside of the regulated activity) may be excluded from the
calculation of the required infiltration volume.
H.
A detailed soils evaluation of the site shall be conducted by a qualified
professional and at a minimum shall address soil permeability, depth
to bedrock, and subgrade stability. The general process for designing
the infiltration BMP shall be conducted by a qualified licensed professional
and shall be consistent with the PA BMP Manual (as amended) (or other
guidance acceptable to the Municipal Engineer) and, in general, shall:
(1)
Analyze hydrologic soil groups as well as natural and man-made
features within the site to determine general areas of suitability
for infiltration practices. In areas where development on fill material
is under consideration, conduct geotechnical investigations of subgrade
stability; infiltration may not be ruled out without conducting these
tests.
(2)
Provide field tests such as double-ring infiltrometer or other
hydraulic conductivity tests (at the elevation of the proposed infiltration
surface) to determine the appropriate hydraulic conductivity rate.
Standard septic/sewage percolation tests are not acceptable for design
purposes.
(3)
Design the infiltration facility for the required retention
(infiltration) volume based on field-determined infiltration capacity
(and apply safety factor as per applicable design guidelines) at the
elevation of the proposed infiltration surface.
(4)
On-lot infiltration features are encouraged; however, it shall
be demonstrated to the Municipal Engineer that the soils are conducive
to infiltration on the identified lots.
I.
Infiltration BMPs shall be selected based on suitability of soils
and site conditions and shall be constructed on soils that have the
following characteristics:
(2)
An infiltration rate sufficient to accept the additional stormwater
volume and drain completely as determined by field tests conducted
by the applicant.
(3)
The infiltration facility shall completely drain the retention
(infiltration) volume within three days (72 hours) from the end of
the design storm.
J.
All infiltration practices shall:
(2)
Be set back at least 25 feet from all buildings and features
with subgrade elements (e.g., basements, foundation walls, etc.),
unless otherwise approved by the Municipal Engineer;
(3)
For any infiltration practice that collects runoff from shared
or multiple features and that is located within 50 feet of a building
or feature with subgrade elements (e.g., basements, foundation walls,
etc.), the bottom elevation shall be set below the elevation of the
subgrade element.
K.
Infiltration facilities shall, to the maximum extent practicable,
be located to avoid introducing contaminants to groundwater:
(1)
When a hotspot is located in the area draining to a proposed
infiltration facility, an evaluation of the potential of groundwater
contamination from the proposed infiltration facility shall be performed,
including a hydrogeologic investigation (if necessary) by a qualified
licensed professional to determine what, if any, pretreatment or additional
design considerations are needed to protect groundwater quality.
(2)
When located within a wellhead protection area of a public water
supply well, infiltration practices shall be in conformance with the
applicable approved source water protection assessment or source water
protection plan.
(3)
The applicant shall provide appropriate safeguards against groundwater
contamination for land uses that may cause groundwater contamination
should there be a mishap or spill.
L.
During site construction, all infiltration practice components shall
be protected from compaction due to heavy equipment operation or storage
of fill or construction material. Infiltration areas shall also be
protected from sedimentation. Areas that are accidentally compacted
or graded shall be remediated to restore soil composition and porosity.
Adequate documentation to this effect shall be submitted to the Municipal
Engineer for review. All areas designated for infiltration shall not
receive runoff until the contributory drainage area has achieved final
stabilization.
M.
Where sediment transport in the stormwater runoff is anticipated
to reach the infiltration system, appropriate permanent measures to
prevent or collect sediment shall be installed prior to discharge
to the infiltration system.
N.
Where roof drains are designed to discharge to infiltration practices,
they shall have appropriate measures to prevent clogging by unwanted
debris (for example, silt, leaves and vegetation). Such measures shall
include, but are not limited to, leaf traps, gutter guards, and cleanouts.
O.
All infiltration practices shall have appropriate positive overflow
controls.
P.
No sand, salt or other particulate matter may be applied to a porous
surface material for winter ice conditions.
Q.
The following procedures and materials shall be required during the
construction of all subsurface facilities:
(1)
Excavation for the infiltration facility shall be performed
with equipment that will not compact the bottom of the seepage bed/trench
or like facility.
(2)
The bottom of the bed and/or trench shall be scarified prior
to the placement of aggregate.
(3)
Only clean aggregate with documented porosity, free of fines,
shall be allowed.
(4)
The tops, bottoms and sides of all seepage beds, trenches, or
like facilities shall be covered with drainage fabric. Fabric shall
be nonwoven fabric acceptable to the Municipal Engineer.
(5)
Stormwater shall be distributed throughout the entire seepage
bed/trench or like facility and provisions for the collection of debris
shall be provided in all facilities.
[Ord. 2023-01, 4/19/2023]
1.
For regulated activities involving new development with one or more
acres of earth disturbance, the applicant shall comply with the following
stream channel protection requirements to minimize stream channel
erosion and associated water quality impacts to the receiving waters:
A.
The peak flow rate of the post-construction two-year, twenty-four-hour
design storm shall be reduced to the predevelopment peak flow rate
of the one-year, twenty-four-hour duration precipitation, using the
NRCS Type II distribution.
B.
To the maximum extent practicable, and unless otherwise approved
by the Municipal Engineer, the post-construction one-year, twenty-four-hour
storm flow shall be detained for a minimum of 24 hours and a maximum
not to exceed 72 hours from a point in time when the maximum volume
of water from the one-year, twenty-four-hour storm is stored in a
proposed BMP (i.e., when the maximum water surface elevation is achieved
in the facility). Release of water can begin at the start of the storm
(i.e., the invert of the orifice is at the invert of the proposed
BMP).
D.
The minimum orifice size in the outlet structure to the BMP shall
be three inches in diameter unless otherwise approved by the Municipal
Engineer, and a trash rack shall be installed to prevent clogging.
For sites with small drainage areas contributing to the BMP that do
not provide enough runoff volume to allow a twenty-four-hour attenuation
with the three-inch orifice, the calculations shall be submitted showing
this condition.
E.
When the calculated orifice size is below three inches, gravel filters
(or other methods) are recommended to discharge low flow rates subject
to the Municipal Engineer's satisfaction. When filters are utilized,
maintenance provisions shall be provided to ensure filters meet the
design function.
F.
All proposed stormwater management facilities shall make use of measures
to extend the flow path and increase the travel time of flows in the
facility.
G.
When a regulated activity contains or is divided by multiple drainage
areas, the peak flow rate control shall be separately addressed for
each drainage area.
[Ord. 2023-01, 4/19/2023]
1.
The applicant shall comply with the following peak flow rate control
requirements for all regulated activities including those that involve
new development and redevelopment.
A.
Post-construction peak flow rates from any regulated activity shall
not exceed the predevelopment peak flow rates as shown for each of
the design storms specified in Table 308.1.
|
Table 308.1
Peak Rate Control Standards1
| ||
|---|---|---|
|
Post-Construction Design Storm Frequency
(24-hour duration)
|
Predevelopment Design Storm
| |
|
New Development Regulated Activities
|
Redevelopment Regulated Activities
| |
|
2-year
|
1-year
|
2-year
|
|
5-year
|
5-year
|
5-year
|
|
10-year
|
10-year
|
10-year
|
|
25-year
|
25-year
|
25-year
|
|
50-year
|
50-year
|
50-year
|
|
100-year
|
100-year
|
100-year
|
|
NOTE:
| |
|
1.
|
Peak flow rate of the post-construction design storm shall be
reduced to the peak flow rate of the corresponding predevelopment
design storm shown in the Table.
|
C.
For regulated activities involving only redevelopment, no peak flow rate controls are required when and only if the total regulated impervious surface area is at least 20% less than the total existing impervious surface area to be disturbed by the regulated activity. In all cases where this requirement is not met, the redevelopment regulated activity shall achieve the peak flow rate controls presented in Table 308.1, using the redevelopment ground cover assumptions presented in § 19-309, Subsection 4. This design criterion for redevelopment is only permitted with approval of Municipal Engineer. It shall result in no impact on downstream properties.
D.
Only the area of the proposed regulated activity shall be subject
to the peak flow rate control standards of this chapter. Undisturbed
areas for which the discharge point has not changed are not subject
to the peak flow rate control standards.
E.
Areas located outside of the site (i.e., areas outside of the regulated
activity) that drain through a proposed site are not subject to peak
flow rate control requirements. Drainage facilities located on the
site shall be designed to safely convey flows from outside of the
site through the site.
F.
When a regulated activity contains or is divided by multiple drainage
areas, the peak flow rate controls shall be separately addressed for
each drainage area.
G.
The effect of structural and nonstructural stormwater management
practices implemented as part of the overall site design may be taken
into consideration when calculating total storage volume and peak
flow rates.
[Ord. 2023-01, 4/19/2023]
1.
Stormwater runoff from all regulated activity sites with a drainage
area of greater than five acres shall be calculated using a generally
accepted calculation technique(s) that is based on the NRCS Soil Cover
Complex Method. Table 309.1 summarizes acceptable computation methods.
The method selected for use shall be based on the individual limitations
and suitability of each method for a particular site. The use of the
Rational Method to estimate peak discharges for drainage areas greater
than five acres shall be permitted only upon approval by the Municipal
Engineer.
|
Table 309.1
Acceptable Computation Methodologies for SWM Site Plan
| ||
|---|---|---|
|
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 where limitations described
in TR-55 are met
|
|
HEC-1/HEC-HMS
|
US Army Corps of Engineers
|
Applicable where use of a full hydrologic computer model is
desirable or necessary
|
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For sites up to 5 acres, or as approved by the municipality
|
|
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
|
2.
All calculations using the Soil Cover Complex Method shall use the
appropriate design rainfall depths for the various return period storms
consistent with this chapter. Rainfall depths used shall 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 Atlas 14), values consistent with a
partial duration series. When stormwater calculations are performed
for routing procedures or infiltration, water quality and runoff volume
functions, the duration of rainfall shall be 24 hours.
3.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times-of-concentration ("duration") and
storm events with rainfall intensities obtained from NOAA Atlas 14
partial duration series estimates or the latest version of the PennDOT
Drainage Manual (PDM Publication 584). Times of concentration shall
be calculated based on the methodology recommended in the respective
model used. Times of concentration for channel and pipe flow shall
be computed using Manning's Equation.
4.
The applicant shall utilize the following ground cover assumptions
for all predevelopment water quality and runoff volume, infiltration
volume and peak flow rate calculations:
A.
For regulated activities involving new development, the following
ground cover assumptions shall be used:
B.
For regulated activities involving redevelopment, the following ground
cover assumptions shall be used:
(1)
For areas that are woods (as defined in Part 2 of this chapter), predevelopment calculations shall assume ground cover of "woods in good condition."
(2)
For areas that are not woods or not impervious surfaces, predevelopment
calculations shall assume ground cover of "meadow."
(3)
For areas that are impervious surfaces, predevelopment calculations
shall assume at least 20% of the existing impervious surface area
to be disturbed as meadow ground cover.
C.
The applicant shall determine which stormwater standards apply to
the proposed regulated activity as follows:
(1)
Stormwater standards for new development shall apply to all
proposed regulated activities that involve only new development activities
as defined in this chapter.
(2)
Stormwater standards for redevelopment shall apply to all proposed
regulated activities that involve only redevelopment activities as
defined in this chapter.
(3)
At the discretion of the Municipal Engineer, regulated activities
that involve a combination of both new development and redevelopment
activities, as defined in this chapter, may either:
(a)
Apply the stormwater standards (redevelopment or new development)
that are associated with the activity that involves the greatest amount
of land area; or
(b)
Apply the redevelopment and new development stormwater standards
to the corresponding redevelopment and new development portions of
the proposed regulated activity.
5.
Runoff curve numbers (CN) for both predevelopment and proposed (post-construction)
conditions to be used in the Soil Cover Complex Method shall be obtained
from Table C-1 in Appendix C of this chapter.[1]
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
6.
Runoff coefficients (C) for both predevelopment and proposed (post-construction)
conditions for use in the Rational Method shall be obtained from Table
C-2 in Appendix C of this chapter.
7.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
8.
Hydraulic computations to determine the capacity of pipes, culverts,
and storm sewers shall be consistent with methods and computations
contained in the Federal Highway Administration Hydraulic Design Series
Number 5 (Publication No. FHWA-NHI-01-020 HDS No. 5, as amended).
Hydraulic computations to determine the capacity of open channels
shall be consistent with methods and computations contained in the
Federal Highway Administration Hydraulic Engineering Circular Number
15 (Publication No. FHWA-NHI-05-114 HEC 15, as amended). Values for
Manning's roughness coefficient (n) shall be consistent with
Table C-3 in Appendix C of this chapter.
[Ord. 2023-01, 4/19/2023]
1.
Any BMP intended to hold standing water for four days or longer shall
be designed to incorporate biologic controls consistent with the West
Nile Guidance found in Appendix D,[1] PADEP document 363-0300-001 "Design Criteria - Wetlands
Replacement/Monitoring" (as amended), or contact the Pennsylvania
State Cooperative Wetland Center or the Penn State Cooperative Extension
Office for design information.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
2.
Any stormwater basin required or regulated by this chapter designed
to store runoff and requiring a berm or earthen embankment shall be
designed to provide an emergency spillway to safely convey flow up
to and including the 100-year proposed conditions. The height of embankment
shall provide a minimum one foot of freeboard above the maximum pool
elevation computed when the facility functions for the 100-year proposed
conditions inflow. Should any BMP require a dam safety permit under
25 Pa. Code Chapter 105 regulations, the facility shall be designed
in accordance with and meet the regulations of 25 Pa. Code Chapter
105 concerning dam safety. Chapter 105 of Title 25 of the Pennsylvania
Code may require the safe conveyance of storms larger than 100-year
event.
3.
Any drainage conveyance facility and/or channel not governed by 25
Pa. Code Chapter 105 regulations shall be designed to convey, without
damage to the drainage facility or roadway, runoff from the twenty-five-year
storm event. Larger storm events (fifty-year and 100-year storms)
shall also be safely conveyed in the direction of natural flow without
creating additional damage to any drainage facilities, nearby structures,
or roadways.
4.
Conveyance facilities to or exiting from stormwater management facilities
(i.e., detention basins) shall be designed to convey the design flow
to or from the facility.
5.
Roadway crossings or structures located within designated floodplain
areas shall be able to convey runoff from a 100-year design storm
consistent with Federal Emergency Management Agency National Flood
Insurance Program - Floodplain Management Requirements.
6.
Any stormwater management facility located within a PennDOT right-of-way
shall comply with PennDOT minimum design standards and permit submission
and approval requirements.
7.
Adequate erosion protection and energy dissipation shall be provided
along all open channels and at all points of discharge. Design methods
shall be consistent with the Federal Highway Administration Hydraulic
Engineering Circular Number 11 (Publication No. FHWA-IP-89-016, as
amended) and the PADEP Erosion and Sediment Pollution Control Program
Manual (Publication No. 363-2134-008, as amended), or other design
guidance acceptable to the Municipal Engineer.
[Ord. 2023-01, 4/19/2023]
1.
The following provisions shall be followed and incorporated into
the stormwater management design and construction process:
A.
Stormwater management facilities, including but not limited to recharge
facilities, detention facilities, storm sewers, culverts, bridges
and related drainage installations, shall be designed and constructed
to meet the following purposes:
(1)
To permit unimpeded flow of natural watercourses;
(2)
To insure adequate drainage of all low points;
(3)
To intercept stormwater runoff along streets at intervals reasonably
related to the extent and grade of the area drained to prevent flow
of stormwater across intersections;
(4)
To insure adequate and unimpeded flow of stormwater over or
under driveways;
(5)
To prevent excessive flow on or across streets, sidewalks, drives,
parking areas, and any other paved surface or access way; and
(6)
To lead stormwater away from springs.
B.
All natural streams, channels, swales, drainage systems, and/or areas of concentration of surface water shall be maintained in their existing condition except as necessary for those uses that may be permitted by Chapter 27, Zoning, of the Township Code, and as approved by the Township.
C.
Man-made structures shall be kept to a minimum.
D.
Bridges, culverts, or riprap to be placed in or over a stream shall
be chosen and constructed to maintain the natural characteristics
of the stream and shall meet the approval of the Township and must
obtain necessary approvals from PADEP.
E.
The Township may require that a landowner or developer provide reasonable
corrective measures to alleviate any existing off-site drainage problem
that may be affected by the proposed land development or any other
regulated activity.
F.
No person shall deposit or place any debris or any other material
whatsoever, or cause such to be thrown or placed, in any channel or
stormwater facility in such a manner as to obstruct free flow.
G.
No stormwater facility shall create health, safety or sanitation
problems.
H.
No stormwater facility shall impact the ability of on-lot sewage
disposal systems to treat waste or adequately infiltrate treated wastewater
effluent.
I.
Various BMPs, both structural and nonstructural, other than those
listed in the following sections can be utilized in the stormwater
design. Any BMP not addressed in this chapter shall be designed in
accordance with the design parameters found in the PADEP BMP Manual,
latest edition. Any design parameters found in the PA BMP Manual for
the below BMPs shall apply unless otherwise specified herein.
J.
Reference to publications and source documents shall be deemed to
include any amendments and revisions thereof.
K.
Individual on-lot BMPs (serving only one residential lot) shall meet
the design criteria of Appendix A, Simplified Approach for Stormwater
Management for Small Projects,[1] and shall not be subject to §§ 19-312 and 19-313 unless deemed necessary by the Township Engineer based on design parameters, so long as the regulated impervious area and disturbed area meet the threshold criteria.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
[Ord. 2023-01, 4/19/2023]
1.
General requirements for all types of basins.
A.
Basins shall meet the following minimum setbacks measured from the
top and/or toe of slope (whichever is closer):
B.
The use of multiple basin facilities that are smaller and less intrusive
on the site is encouraged.
C.
Privately owned basin facilities and BMPs shall be located entirely
on one parcel unless otherwise permitted by the Township.
D.
Maintenance of a basin facility shall be the responsibility of only
one lot owner or, if the facility is located in a common area, the
responsibility of the applicable homeowners' association. See Part
7.
E.
When PADEP requires basin facilities to have a state permit, the
developer shall submit all information to PADEP and obtain all necessary
approvals and permits.
2.
Design Requirements for All Types of Basins.
A.
For basins that combine rate and volume controls, the infiltration
discharge should not be taken into consideration when routing the
peak discharge amounts, nor shall the infiltration volume be used
in the routing.
B.
It shall be the developer's responsibility to verify if the
site is underlain by karst. Whenever basins will be located in an
area underlain by karst:
(1)
A geological evaluation of the proposed location shall be conducted
to determine susceptibility to sinkhole formations.
(2)
The design of all facilities over limestone formations shall
include measures to prevent groundwater contamination and, where necessary,
sinkhole formation.
(3)
The installation of an impermeable liner may be required.
(4)
A detailed hydrogeologic investigation may be required.
(5)
Uses where a mishap or spill may cause groundwater contamination,
will require the developer to provide safeguards against contamination.
C.
Inlet and outlet structures shall be located at maximum distances
from one another. For aboveground basins, a rock filter berm, rock-filled
gabions, or other baffle may be required between inlet and outlet
areas when the distance is deemed insufficient for water quality purposes.
D.
A reinforced concrete outlet structure/box shall be used to regulate
water flow through all basins and shall incorporate the following
components and criteria:
(1)
A multiple-stage outlet release design is encouraged.
(2)
The minimum circular orifice diameter for controlling discharge
rates from basin facilities shall be three inches. Designs where a
lesser size orifice would be required to fully meet release rates
shall be acceptable with a three-inch orifice, provided that as much
of the site runoff as practical is directed to the basin facilities.
(3)
The elevation of the top of the outlet structure shall be such
that no flow enters the structure for the twenty-five-year frequency
storm event.
(4)
The base of the outlet structure shall extend a minimum of one
foot below the bottom of the basin for aboveground basins.
(5)
Outlet structure connections shall be watertight.
(6)
The outlet structure shall be cast as one piece.
(7)
A concrete wash (flow channel) across the bottom of the structure
shall be provided.
(8)
Basins with a water depth less than or equal to 1.5 feet may
be exempted from the outlet structure requirements as determined by
the Township.
E.
A trash rack shall be provided for all aboveground orifices.
F.
The outlet pipe shall have reinforced concrete pipe with rubber gaskets/O-ring
joints.
G.
Basins shall be designed to accommodate the 100-year, post-development
storm such that the maximum water surface elevation is a minimum of
six inches below a) the emergency spillway elevation for aboveground
basins; or b) the top of facility for underground basins.
H.
When the outfall point of a proposed basin facility is located at
a point subject to tailwater conditions, a tailwater elevation at
the outfall point will need to be assumed when performing the basin
facility routing calculations. The tailwater elevation assumed shall
be based on the same frequency of the storm being routed.
I.
Any pipe or other component that discharges into an aboveground basin
shall discharge at the bottom of the basin and shall be provided with
an appropriate energy dissipater.
J.
Any pipe or other component that discharges out of a basin shall
be provided with an appropriate energy dissipater.
K.
Where appropriate, adequate drainage channels shall be provided and
maintained for discharge(s) from the basin. If the basin will not
discharge to a suitable natural drainage channel, the developer may
be required to provide facilities to safely and efficiently convey
the discharge to a suitable drainage channel. Securing necessary drainage
easements for this purpose shall be the sole responsibility of the
developer.
3.
Basins that are designed with berms/earthen embankments shall incorporate
the following minimum standards:
A.
The height of the berm shall not exceed 15 feet, unless all appropriate
permits are issued by the PADEP.
B.
The minimum top width of berms shall be 10 feet.
C.
Side Slopes of Basins.
(1)
Whenever possible, the side slopes and basin shape shall be
as shallow as possible and blend/conform to the natural topography.
(2)
Side slopes of basins shall not be steeper than three units
horizontally to one unit vertically (3:1).
(3)
Depending upon the location and the intended use of the detention
facilities during nonrain event times, a flatter side slope, for one
or both slopes, may be required.
(4)
When a basin is to be maintained by a residential lot owner,
the slope shall be four units horizontally to one unit vertically
(4:1).
D.
A key trench shall be provided:
(1)
Extending at least two feet deep in undisturbed soil or to stable
subgrade, whichever is deeper;
(2)
Constructed of compacted relatively impervious material (Unified
Soil Classification CL or ML);
(3)
Having a minimum bottom width of four feet; and
(4)
Having maximum side slopes of one horizontal to one vertical.
F.
All pipes and culverts through berms shall have properly spaced antiseep
collars incorporating the following requirements:
G.
Basin bottom grades shall be a minimum of 2%, unless designed in
combination with an infiltration facility or other BMP where bottom
grade is not indicated, or with the approval of the Township Engineer.
H.
All basin embankments shall:
(1)
Be constructed of suitable material;
(2)
Be placed in eight-inch lifts, maximum;
(3)
Compacted to a minimum of 95% of maximum dry density as established
by ASTM D-1557;
(4)
Have compaction operations be observed by the site inspector;
and
(5)
When required by the Township Engineer, the developer shall
obtain, at the cost of the developer, the services of a qualified
laboratory technician to conduct compaction testing. Copies of all
tests shall be accepted by the Township Engineer.
I.
An emergency spillway shall be provided incorporating the following
requirements:
(1)
The emergency spillway shall be placed in undisturbed earth
whenever possible.
(2)
Emergency spillways shall be designed to safely convey the 100-year
post-development basin inflow with a minimum of six-foot of freeboard
above the water surface elevation to the top of berm, assuming blocked
outlet structure conditions. The total minimum depth of emergency
spillways shall be one foot.
(3)
Emergency spillways shall be constructed such that the basin
berm is protected against erosion. When necessary, erosion protection
shall extend along the upstream and downstream berm slopes.
(4)
Basins with a water depth less than or equal to 1.5 feet are
exempt from emergency spillway and freeboard requirements unless otherwise
deemed necessary by the Township Engineer.
J.
When deemed necessary by the Township, stormwater basin facilities
shall be enclosed with a fence of a type acceptable to the Township.
4.
Underground basins shall incorporate the following minimum standards:
A.
Flow through the outlet structure shall be attenuated with a concrete
weir wall with appropriately sized orifices. Other designs will be
considered with approval of the Township.
B.
Underground facilities that propose pipe storage as a means of detention
shall be constructed of reinforced concrete pipe (RCP) or smooth-lined
corrugated plastic pipe (SLCPP). No metal pipe shall be allowed.
5.
Wet basins shall incorporate the following minimum standards:
A.
Water surface area shall not exceed 1/10 of the tributary drainage
area.
B.
Bank protection shall be provided to prevent erosion.
C.
Minimum normal water depth shall be four feet. If fish are to be
used to keep the pond clean, a minimum of 1/4 of the pond area shall
be a minimum of 10 feet deep.
D.
Facilities shall be provided to allow the pond level to be lowered
by gravity flow for cleaning purposes and bank and other maintenance.
E.
Aeration facilities shall be required as necessary to prevent pond
stagnation. Manufacturer's information to substantiate the effectiveness
of such aeration facilities shall be submitted with the site plans.
Agreements for the perpetual operation and maintenance of aeration
facilities shall be prepared and provided for review. See Part 7.
F.
In the event that the water surface of the pond is to be raised for
the purposes of storing water for irrigation or in anticipation of
the evapotranspiration demands of dry weather, the volume remaining
for storage of excess stormwater runoff shall be sufficient to contain
the fifty-year design storm runoff.
G.
All wet basin designs shall incorporate biological minimization controls
consistent with the West Nile Guidance found in Appendix D.[1]
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
6.
The following items shall be submitted for basin review:
A.
Design computations for the sizing of the outlet structure;
B.
Stage-storage curve;
C.
Routed hydrographs for each storm;
D.
Storage requirement calculations;
E.
Plan(s) showing the berm/embankment and outlet structure in plan
and cross-section views as well as details, including but not limited
to:
(1)
Inlet pipe and energy dissipater;
(2)
Top of berm elevations;
(3)
Width of the top of the berm;
(4)
Outlet pipe and energy dissipater;
(5)
Side slopes;
(6)
Emergency spillway elevation;
(7)
Elevations of all features of the outlet structure;
(8)
Clay core;
(9)
Key trench;
(10)
Dimensions and spacing of anti-seep collars;
(11)
Trash rack; and
(12)
Antivortex device (if included in the design).
[Ord. 2023-01, 4/19/2023]
1.
General.
A.
Storm sewers and associated structures shall be required to be constructed
to:
(1)
Intercept runoff at such intervals as necessary along streets
to provide safe vehicular movement;
(2)
Eliminate standing water at the bottom of all grades regardless
of location;
(3)
Eliminate the use of cross gutters at street intersections and
elsewhere including in parking lots; and
(4)
Discharge collected water (from any and all locations, including
but not limited to streets, parking lots and lawn area) to an infiltration
facility, detention basin or other acceptable BMP that discharges
to the nearest practical natural channel.
B.
Manholes, inlets, headwalls and other stormwater structures must
conform to the standards established by PennDOT and be per details
shown in PennDOT Standards for Roadway Construction or as approved
by the Township Engineer. Such structures must be supplied by a PennDOT
Bulletin 15 approved supplier. These requirements shall be noted on
the plan.
C.
All materials, workmanship, and installation shall conform to PennDOT
specifications contained in Chapter 408, current edition.
D.
Whenever practical, storm sewers and associated structures that drain
the street system shall be located within the right-of-way of the
street.
E.
Easements shall be provided for all conveyance and collection systems that are not located within street rights-of-way and shall be a minimum of 20 feet in width. Easements shall meet the applicable requirements in § 19-704.
F.
No stormwater conveyance facility shall be constructed within 50
feet of a special geologic feature unless it is constructed of reinforced
concrete pipe utilizing rubber gasket/O-ring joints, such pipe shall
be a minimum of 25 feet from a special geologic feature.
G.
Collection and conveyance systems shall be installed to prevent concentrated
flow from crossing or following sidewalks. Pipe and inlet size and
materials used for this purpose shall be acceptable to the Township
Engineer.
H.
Collection and conveyance systems shall be provided where runoff
is concentrated in rear, side or front yards as necessary to prevent
erosion.
I.
Collection and conveyance systems shall be provided in order to adequately
drain parking lots.
2.
Sizing Criteria.
A.
Collection and conveyance systems in public streets shall be adequate
for the anticipated runoff when the area draining to the system is
fully developed as permitted by zoning.
B.
Collection and conveyance systems regardless of location shall be
designed to carry the twenty-five-year peak flow rate determined using
the Rational formula and good engineering practice.
C.
The system shall be evaluated for both gravity (Manning's Equation)
and pressure (inlet/outlet control, hydraulic grade line) as appropriate.
D.
Provisions must be made to transport the runoff from a 100-year frequency
storm to an appropriate stormwater management facility in a manner
that does not damage property or flood streets.
3.
Stormwater Pipes.
A.
The minimum inside diameter of all pipe to be installed shall be
not less than 15 inches. When cover is 25 feet or greater, the minimum
inside diameter shall be 24 inches.
B.
All pipes shall be reinforced concrete Class III or better meeting
PennDOT's 100-year life criteria.
C.
Joints shall be provided with rubber gaskets/O-rings.
D.
The minimum pipe slope shall be 1/2%.
E.
The minimum cover of stormwater pipe shall be 24 inches. This minimum
cover shall be provided and maintained during construction in order
to protect pipe from damage.
F.
Where cover is restricted, equivalent elliptical concrete pipe or
concrete arch pipe maybe used in lieu of circular pipe.
G.
When located within a street cartway, pipe shall be bedded on six
inches of PennDOT 2A stone and backfilled with 2A stone placed and
compacted in six-inch lifts.
H.
All pipe shall be laid in a straight line. A manhole or inlet shall
be provided at all horizontal deflections.
I.
Storm pipe shall not be permitted under buildings or structures.
J.
Underdrains and/or pavement base drains shall be:
K.
A water quality/pretreatment structure (or structures as necessary
based on design flow) shall be:
(1)
Provided at or near the terminus of all conveyance systems;
(2)
Capable of capturing floatables, sediment, gravel, leaves and
liquid contaminates (oil, antifreeze, etc.) prior to leaving the right-of-way
and/or entering a channel or stormwater BMP, whether an infiltration
BMP or detention basin, etc.; and
(3)
Located such that they are easily accessible from the street,
along a vehicular path, to facilitate maintenance.
L.
Prior to dedication of public streets and release of the maintenance
bond:
(1)
A video inspection of all collection and conveyance systems
located within the street right-of-way shall be required using methods
acceptable to the Township Engineer.
(2)
A record of the video inspection shall be provided in an electronic
format acceptable to the Township Engineer.
(3)
Depending on the results of the video inspection, all pipes
and inlets shall be cleaned and/or restored to design specifications.
4.
Inlets.
A.
Inlets shall be spaced to limit the gutter spread to no more than
1/2 of the width of the travel lane during the design storm (twenty-five-year).
B.
The capacity of all Type C, M, or S inlets shall be determined using
the Commonwealth of Pennsylvania, Department of Transportation, Design
Manual, Part 2, "Highway Design."
C.
The maximum allowable headwater depth shall be one foot below the
top of the inlet grate.
D.
If double inlets are proposed, they shall be separated by a minimum
of 20 feet.
E.
Inlet capacity calculations shall be provided in the stormwater management
report, including the design twenty-five-year peak flow rate to each
inlet.
F.
In non-sump areas, inlets shall be placed such that flow to any single
inlet shall not exceed four cubic feet per second (cfs) for standard
(two by four) inlets and five cfs for Type 1 standard (two by six)
inlets, whether located in streets, parking lots or lawn areas.
G.
In sump areas, other than within a street, the maximum depth of water
above the inlet top elevation shall be six inches.
H.
Regardless of capacity calculations, inlets shall be located to intercept
runoff prior to handicapped ramps, prior to every street or driveway
(not including those serving single-family dwellings) intersection
radius, and at sag points of vertical curves and any other low points,
whether in streets or in parking lots.
I.
Inlets shall be placed prior to the radius of an intersection not
on the curved portion unless unavoidable in order to be located at
a low point.
J.
No inlet smaller than standard PennDOT inlet Types C, M and S shall
be used within streets.
K.
Inlets with a depth greater than four feet must be provided with
antislip ladder rungs.
L.
A minimum drop of 0.20 feet shall be provided across inlets between
the invert elevations of the incoming and outgoing pipes of the same
diameter. For pipes of different diameters, the elevation of the crowns
of the pipes shall be equal.
M.
Inlets shall contain the statement "no dumping drains to creek,"
either cast or inserted into the tops, to discourage the placement
of anything other than stormwater into the inlet.
N.
Inlets in paved areas shall be equipped with bicycle safe grates.
All inlets shall be designed and located to prevent hazards to vehicles,
bicycles and pedestrians.
O.
Inlet grates shall be depressed one inch in paved areas with inlet
tops flush with the curb. Inlets in landscaped areas shall be sumped
a minimum of 12 inches.
P.
To promote smooth flow and self-cleaning, the bottoms of inlets shall
be provided with concrete washes (flow channels).
Q.
All pipe entering an inlet shall be cut flush with the inside of
the inlet box.
R.
Weep holes shall be provided in inlets per PennDOT RC Standards.
S.
Only a single precast concrete grade adjustment ring, a maximum of
six inches in height, shall be allowed.
T.
The annular space where pipes enter inlet boxes shall be sealed with
nonshrinking grout.
U.
All backfill around inlets shall be compacted PennDOT 2A stone.
5.
Manholes.
A.
Manholes shall not be spaced more than 400 feet apart for pipes of
less than or equal to twenty-four-inch diameter and 500 feet apart
for pipes of greater than twenty-four-inch diameter.
B.
A manhole shall be placed on a continuous storm sewer at all changes
in alignment, grade or pipe size, and at all points of convergence
of two or more influent storm sewer lines.
C.
Inlets may be substituted for manholes where they serve a useful
purpose.
D.
Manhole covers shall have the word "storm" cast on the top of the
cover.
E.
A minimum drop of 0.2 feet shall be provided across manholes between
the invert elevations of the incoming and outgoing pipes of the same
diameter. For pipes of different diameters, the elevation of the crowns
of the pipes shall be equal.
F.
The maximum allowable headwater depth shall be one foot below the
top of the inlet grate or manhole cover.
G.
To promote smooth flow and self-cleaning, the bottoms of manholes
shall be provided with concrete washes (flow channels).
H.
All pipe entering a manhole shall be cut flush with the inside of
the manhole.
I.
The annular space where pipes enter manholes shall be sealed with
nonshrinking grout.
J.
Manholes with a depth greater than four feet must be provided with
antislip ladder rungs.
6.
End Treatments (Headwalls, Endwalls, Flared End Sections, and Similar
Structures).
A.
At-grade pipe outlets shall be provided with one of these structures.
B.
All end treatments shall be concrete, regardless of pipe material.
C.
Safety grates may be required at the Township's discretion.
D.
Acceptable energy dissipation devices shall be installed per PADEP's
Erosion and Sedimentation Pollution Control Program Manual at every
end treatment.
E.
End treatments shall not be located closer than 10 feet from the
edge of a sidewalk, curb or cartway edge.
7.
Man-made Open Channels/Swales.
A.
Properly designed, graded, and lined channels may be permitted in
lieu of storm sewers where it can be demonstrated that the channel
will be stable under permanent conditions.
B.
Channel shall not be less than 2% in grade nor more than 10%.
C.
Underdrains may be required as determined by the Township Engineer.
D.
Channels shall be located on lot lines as necessary to minimize stormwater
from draining across lot lines.
E.
Channel lining must meet the design standards of PADEP's Erosion
and Sedimentation Pollution Control Program Manual.
F.
Channels shall have a maximum side slope grade of three horizontal
to one vertical (3:1).
G.
Channels shall be provided with a minimum six-inch freeboard, measured
from the top of the design storm (twenty-five-year) flow to the top
of bank of the channel.
H.
Channels leading away from emergency spillways, and other channels
in areas where damage to property would result, shall be designed
to convey the runoff from a 100-year storm.
[Ord. 2023-01, 4/19/2023]
1.
Cul-de-sac turnarounds shall be graded to direct all stormwater to
the curb in order to minimize icing from sheet flows in freezing temperatures.
2.
All grading (cut and fill) shall be set back from property lines
a sufficient distance to prevent any adverse effects on adjacent properties,
but in no case less than 10 feet.
3.
Where a grading cut slope creates an abrupt dropoff from the abutting
property line in contrast to a previously existing gradual change,
a fence or other suitable barrier shall be installed.
4.
Grading shall not be done in such a way so as to divert water onto
the property of another landowner.
5.
Sites shall be graded to secure proper drainage away from buildings
(minimum 2%) and to allow for the proper collection and conveyance
of stormwater.
6.
Grading operations shall be kept to a minimum to ensure conformity
with the natural topography, to minimize erosion hazard, and to adequately
handle the surface runoff.
7.
Except as specified elsewhere in this Part, cut and fill slopes shall
not be steeper than 4:1.
8.
During grading operations, necessary measures for dust control shall
be exercised.
[Ord. 2023-01, 4/19/2023]
1.
When subdivision, land developments or other earth disturbances are
submitted to the Township for approval in phases, plans and calculations
shall be submitted for the design of the entire tract, not for a single
phase.
2.
If construction is contemplated for less than the entire project,
the proposed design of the stormwater from the constructed phase(s)
shall be provided. The design shall prevent damage to adjacent properties
and future phases. Any temporary construction required for the phased
design shall be included with the submittal.
3.
In the event that temporary measures cannot insure protection to
adjacent properties or future phases, the permanent BMPs and permanent
collection and conveyance system, as necessary, shall be included
as part of the construction for the currently proposed phase.
[Ord. 2023-01, 4/19/2023]
1.
Construction of a driveway on a lot shall not cause surface runoff
on the lot to be directed or concentrated onto an adjoining lot or
cause an increase in runoff to an adjoining lot. Stormwater runoff
shall be addressed in accordance with the standards herein.
2.
The intersection of all driveways with the street shall be constructed
so that no surface water from the driveway is directed into the street.
This may be accomplished by use of a drainage swale or a pipe culvert
as follows:
A.
The drainage swale side slope across the driveway shall slope down
from the improved edge of the street for a maximum depth of four inches
over a minimum distance of six feet, resulting in a grade of approximately
5 1/2%. Modifications to this requirement may be permitted as
field conditions indicate at the sole discretion of the Township designated
official issuing the driveway permit.
B.
If a pipe is used, it shall be:
(1)
Sized according to stormwater runoff calculations based upon
a twenty-five-year storm frequency, but in no case shall it be less
than a minimum diameter of 15 inches;
(2)
An approved pipe, per PennDOT specifications in Publication
408, as amended, unless approved otherwise by the Township-designated
official issuing the driveway permit;
(3)
Placed with its edge at least 10 feet from the improved edge
of the street (a ten-foot clearance). A greater distance from the
improved edge of street may be required for larger pipes in order
to allow for acceptable grade (maximum 3:1) from the improved edge
of the street to the bottom of the pipe allowing for a shoulder and
rounding of the cross-slope, four feet minimum. Modifications to this
requirement may be permitted as field conditions indicate at the sole
discretion of the Township-designated official issuing the driveway
permit;
(4)
Extended a minimum of two feet in length from each edge of the
driveway; and
(5)
Provided with the appropriate concrete end treatments such as
flared end sections or endwalls. Downstream end treatments may be
waived at the sole discretion of the Township-designated official
issuing the driveway permit.
