[Ord. No. 170-2014, 5/14/2014, as amended by Ord. No. 202-2019, 11/13/2019, and by Ord. No. 210-2023, 9/13/2023]
1.
Applicants proposing regulated activities in the Municipality which are not exempt under § 20-106 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.
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 § 20-304 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, postconstruction 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 downgradient
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.
A.
For regulated activities with one acre or less proposed earth disturbance
the applicant shall provide written notification to the affected landowner(s)
describing the proposed regulated activity and proposed discharge(s),
unless otherwise required by the Municipality.
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 §§ 20-305, 20-306, 20-307, and 20-308). 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, five-year and
ten-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 Pa. Code and the Clean Streams
Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
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,[2] and the Storm Water Management Act.[3]
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 Honey Brook Township zoning ordinance (Chapter 27), § 27-802, and the Honey Brook Township Floodplain Ordinance (Chapter 8) 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 non-disturbance buffer may be reduced because of setback
or other site constraints, but never be less than 10 feet.
22.
The grading, regrading, or other alteration of a property in any
manner that alters the existing drainage pattern of the area or increases
the rate, volume or manner in which surface runoff leaves a property
is prohibited.
[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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 Title 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
Title 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 Title 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 Title 25 Pa.
Code Chapter 105.
[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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 Title 25 Chapter 102 of the
Pennsylvania Code of an erosion and sediment control plan for construction
activities for projects where the area of disturbance exceeds one
acre, where pond dredging is involved, or when the disturbance is
associated with activities described under Title 25 Chapter 105 of
the Pa. Code permits;
(2)
A PADEP NPDES Permit for Stormwater Discharges Associated with
Construction Activities as required under Title 25 Pa. Code Chapter
92a, if applicable;
(3)
Evidence of any other permit(s) or approvals required for the
regulated activities; and
B.
An erosion and sediment control plan has been approved by the Municipality,
if required.
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. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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. For regulated activities with 10,000 or more square feet of proposed earth disturbance OR 2,000 or more square feet of regulated impervious surfaces, the applicant shall demonstrate in its SWM site plan (as required in § 20-402, Subsection 1C) 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 § 20-304, Subsection 1B and 1C. Appendix 20-C[1] presents additional discussion of "conservation design"
and "low-impact development."
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
1.
To control postconstruction 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 postconstruction 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 20-C,[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 postconstruction 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 § 20-306. The infiltration volume required under § 20-306 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. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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 § 20-305. 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 § 20-305 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 § 20-306, Subsection 1A or 1B, 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 sub-grade
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, minimum of two 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:
(1)
A minimum depth of 24 inches between the bottom of the BMP and the top of the limiting zone. Additional depth may be required in areas underlain by karst or carbonate geology (see Subsection 1M).
(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 sub-grade 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 25 feet of a building
or feature with sub-grade elements (e.g., basements, foundation walls,
etc.), the bottom elevation shall be set below the elevation of the
sub-grade element.
(4)
Infiltration facilities shall be setback a minimum of 10 feet
from any lot line or right-of-way line.
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 "well head protection area" of a public water supply well, as defined and regulated by the Honey Brook Township zoning ordinance, § 27-803, 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.
Consideration of infiltration BMPs for areas underlain by karst or
carbonate geology is encouraged, but only where the design, supporting
calculations, results of soils or other site investigations or other
documentation are provided to the Municipality demonstrating that
the potential or likelihood of subsidence or sinkholes is minimal.
Evaluation of site conditions and infiltration design shall rely on
guidance in the PA BMP Manual (as amended) or other guidance acceptable
to the Municipal Engineer.
N.
Groundwater quality of the carbonate aquifer shall be protected from
infiltration of pollutants. At a minimum, stormwater runoff from hotspots
(i.e., sources of significant pollutant runoff) shall first be discharged
through a water quality BMP(s) to remove pollutants prior to infiltration.
Where soil characteristics are insufficient to provide removal of
pollutants from sources other than hotspots, stormwater runoff shall
first be discharged through a water quality BMP(s) to remove pollutants
prior to infiltration.
O.
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.
P.
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.
Q.
All infiltration practices shall have appropriate positive overflow
controls.
R.
No sand, salt or other particulate matter may be applied to a porous
surface material for winter ice conditions.
S.
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 top and sides of all seepage beds, trenches, or like facilities
shall be covered with drainage fabric. Fabric shall be non-woven 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. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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 postconstruction 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
SCS Type II distribution.
B.
To the maximum extent practicable, and unless otherwise approved
by the Municipal Engineer, the postconstruction 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. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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 that are not located in the Conestoga
River watershed.
A.
Postconstruction 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 20-308.1.
|
Table 20-308.1
| ||
|---|---|---|
|
Peak Rate Control Standards
| ||
|
(Peak Flow Rate of the Postconstruction Design Storm Shall be
Reduced to the Peak Flow Rate of the Corresponding Predevelopment
Design Storm Shown in the Table)
| ||
|
Postconstruction Design Storm Frequency (24-Hour Duration)
|
Predevelopment Design Storm
| |
|
New development regulated activities
|
Redevelopment regulated activities
| |
|
2-year
|
1-year
|
2-year
|
|
5-year
|
2-year
|
5-year
|
|
10-year
|
2-year
|
10-year
|
|
25-year
|
25-year
|
25-year
|
|
50-year
|
50-year
|
50-year
|
|
100-year
|
100-year
|
100-year
|
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 20-308.1, using the redevelopment ground cover assumptions presented in § 20-309, Subsection 5. 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 non-structural 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.
H.
Any portion of the volume control storage that is designed according to the infiltration standards in § 20-305 and § 20-306 and is available within 24 hours from the end of the design storm based on the stabilized infiltration rate and/or the evapotranspiration rate may be also utilized for rate control storage.
I.
For regulated activities located within the Conestoga River Watershed,
the postdevelopment peak discharge rates shall not exceed a certain
percentage of the predevelopment peak discharge rate for the two-,
ten-, twenty-five-, fifty- and 100-year (twenty-four-hour duration)
storm events as identified on the Conestoga River Watershed Release
Rate Map in Appendix 20-G[1] of this chapter, using the ground cover assumptions presented in § 20-309, Subsection 5.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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 20-309.1 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 20-309.1
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 five 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.
Hydrographs may be obtained from NRCS methods such as TR-55, TR20,
or from use of the "modified" or "unit hydrograph" rational methods.
If "modified" or "unit hydrograph" rational methods are used, the
ascending leg of the hydrograph shall have a length equal to three
times the time of concentration (3xTc) and the descending leg shall
have a length equal to seven times the time of concentration (7xTc)
to approximate an SCS Type II hydrograph.
5.
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.
6.
Runoff curve numbers (CN) for both predevelopment and proposed (postconstruction)
conditions to be used in the Soil Cover Complex Method shall be obtained
from Table D-1 in Appendix 20-D[1] of this chapter.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
7.
Runoff coefficients (C) for both predevelopment and proposed (postconstruction)
conditions for use in the Rational Method shall be obtained from Table
D-2 in Appendix 20-D[2] of this chapter.
[2]
Editor's Note: Said appendix is included as an attachment to this chapter.
8.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
9.
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 D-3 in Appendix 20-D[3] of the chapter.
[3]
Editor's Note: Said appendix is included as an attachment to this chapter.
[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]
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 20-E, PADEP document 363-0300-001
"Design Criteria - Wetlands Replacement/Monitoring" (as amended)[1], (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 six inches 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 PA Chapter 105 regulations, the facility shall be designed in
accordance with and meet the regulations of PA Chapter 105 concerning
dam safety. PA Chapter 105 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. 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. No. 170-2014, 5/14/2014, as amended by Ord. 183-2016, 3/9/2016; by Ord. No. 202-2019, 11/13/2019, and by Ord. No. 210-2023, 9/13/2023]
1.
Aboveground Storage Facilities. Aboveground storage facilities consist
of all stormwater facilities which store, infiltrate/evaporate/transpire,
clean or otherwise affect stormwater runoff and the top of which is
exposed to the natural environment. Aboveground storage facilities
are located above the finished ground elevation. Aboveground storage
facilities do not include stormwater management facilities designed
for conveyance or cisterns.
A.
Design Criteria. Aboveground storage facilities shall comply with
the design criteria in Table 20-311.1:
|
Table 20-311.1
| |||||
|---|---|---|---|---|---|
|
Aboveground Storage Facility Design Criteria
| |||||
|
Facility Depth
| |||||
|
Less than 2 feet
|
2 feet to 8 feet
|
Greater than 8 feet
| |||
|
(a)
|
Embankment geometry
| ||||
|
[1]
|
Top width (minimum)
|
5 feet
|
5 feet
|
8 feet
| |
|
[2]
|
Interior side slope (maximum)
|
3:1
|
3:1
|
3:1
| |
|
[3]
|
Exterior side slope (maximum)
|
3:1
|
3:1
|
3:1
| |
|
(b)
|
Embankment construction
| ||||
|
[1]
|
Key trench
|
Not required
|
Required
|
Required
| |
|
[2]
|
Pipe collar
|
Not required
|
Required
|
Required
| |
|
[3]
|
Compaction density
|
Not required
|
Required
|
Required
| |
|
(c)
|
Internal construction
| ||||
|
[1]
|
Dewatering feature
|
Required
|
Required
|
Required
| |
|
[2]
|
Pretreatment elements
|
Not required*
|
Required
|
Required
| |
|
(d)
|
Outlet structure
| ||||
|
[1]
|
Pipe size (minimum)
|
6 inches
|
15 inches
|
18 inches
| |
|
[2]
|
Pipe material
|
SLHDPE, PVC, RCP
|
RCP
|
RCP
| |
|
[3]
|
Pipe slope
|
0.5%
|
1.0%
|
1.0%
| |
|
[4]
|
Anticlogging devices
|
Required
|
Required
|
Required
| |
|
[5]
|
Antivortex design
|
Not required
|
Required
|
Required
| |
|
[6]
|
Watertight joints in piping?
|
No
|
Yes
|
Yes
| |
|
(e)
|
Spillway requirements
| ||||
|
[1]
|
Spillway freeboard (minimum)
|
Not required
|
6 inches
|
6 inches
| |
|
[2]
|
Width (minimum)
|
Not required
|
10 feet
|
20 feet
| |
|
[3]
|
Width (maximum)
|
Not required
|
50 feet
|
50 feet
| |
|
[4]
|
Spillway channel design
|
Not required
|
Required
|
Required
| |
|
[5]
|
Routing of 100-year storm
|
Permitted
|
Permitted
|
Permitted
| |
|
NOTES:
|
|---|
|
* Pretreatment required for infiltration BMPs unless shown to
be unnecessary.
|
|
N/A = Not applicable
|
|
SLHDPE = Smooth lined high density polyethylene pipe;
|
|
PVC = Polyvinyl chloride;
|
|
RCP = Reinforced concrete pipe
|
B.
Facility Depth.
(1)
For the purposes of the design criteria, the facility depth
is defined to be the depth between the bottom invert of the lowest
orifice and the invert of the spillway. If there is no spillway, the
top of the berm shall be used. For basins with no orifices or outlet
structure, the bottom elevation of the basin shall be used.
(2)
Facilities with a facility depth greater than eight feet shall
not be permitted in residential areas.
(3)
Facilities with a facility depth greater than 15 feet require
a dam permit from DEP.
C.
Embankment Construction.
(1)
Impervious core/key trench. An impervious core/key trench, when
required, shall consist of a cutoff trench (below existing grade)
and a core trench (above existing grade). A key trench may not be
required wherever it can be shown that another design feature, such
as the use of an impermeable liner, accomplishes the same purpose.
(a)
Materials. Materials used for the core shall conform to the
Unified Soil Classification GC, SC, CH, or CL and must have at least
30% passing the No. 200 sieve.
(b)
Dimensions.
1)
The dimensions of the core shall provide a minimum trench depth
of two feet below existing grade, minimum width of four feet and side
slope of 1H:1V or flatter.
2)
The core should extend up both abutments to the ten-year water
surface elevation or six inches below the emergency spillway elevation,
whichever is lower.
3)
The core shall extend four feet below any pipe penetrations
through the impervious core. The core shall be installed along or
parallel to the centerline of the embankment.
(c)
Compaction.
(d)
Pipe Collars. All pipe collars, when required, shall be designed
in accordance with Chapter 7 of the DEP E&S Manual. The material
shall consist of concrete or otherwise non-degradable material around
the outfall barrel and shall be watertight. Design calculations shall
be provided.
(e)
Embankment Fill Material. The embankment fill material shall
be taken from an appropriate borrow area which shall be free of roots,
stumps, wood, rubbish, stones greater than six inches, frozen or other
objectionable materials.
(f)
Embankment Compaction. When required, embankments shall be compacted
by sheepsfoot or pad roller. The loose lift thickness shall be nine
inches or less, depending on roller size, and the maximum particle
size is six inches or less (two-thirds of the lift thickness). Five
passes of the compaction equipment over the entire surface of each
lift are required. Embankment compaction to visible nonmovement is
also required.
D.
Internal Construction.
(1)
Bottom Slope. The minimum bottom slope of facilities not designed
for infiltration shall be 2%. A flatter slope may be used if an equivalent
dewatering mechanism is provided.
(2)
Dewatering Features. When required, dewatering shall be provided
through the use of underdrain, surface device, or alternate approved
by the Municipal Engineer. If the facility is to be used for infiltration,
the dewatering device should be capable of being disconnected and
only be made operational if the basin is not dewatering within the
required timeframe.
(3)
Pretreatment Elements. When required, pretreatment elements
shall consist of forebays, or alternate approved by the Municipal
Engineer, to keep silt to a smaller portion of the facility for ease
of maintenance.
(4)
Infiltration Basins. Within basins designed for infiltration, existing native vegetation shall be preserved, if possible. For existing unvegetated areas or for infiltration basins that require excavation, a planting plan shall be prepared in accordance with the Honey Brook Township subdivision and land development ordinance § 22-629 and the PA BMP Manual, and contain plantings that are water-tolerant and which promote infiltration.
(5)
Inlet Structures. The invert of an inlet pipe into a basin shall
be six inches above the basin floor or lining so that the pipe can
adequately drain after rain storms. Inlet and outlet structures shall
be separated to the greatest extent possible in order to maximize
the flow path through the basin.
E.
Outlet Configuration.
(1)
For facilities with a depth of two feet or greater, a type D-W
endwall or concrete riser box outlet structure shall be provided.
(2)
For facilities with a depth less than two feet, no outlet structure
is required.
(3)
All discharge control devices with appurtenances shall be made
of reinforced concrete and stainless steel. Bolts/fasteners shall
be stainless steel.
(4)
The minimum distance between a proposed basin discharge point
including the energy dissipater and a downstream property boundary
shall be 25 feet. The setback distance may be adjusted at the discretion
of the Municipal Engineer based upon factors such as flow rate, topography,
soil conditions, and location of structures.
F.
Spillway.
(1)
Material. The spillway shall be designed to provide a non-erosive,
stable condition when the project is completed. Linings for emergency
spillways shall be based upon the maximum velocity in the emergency
use condition.
(2)
Non-Emergency Use. Use of the spillway to convey flows greater
than the fifty-year design storm is permitted.
(3)
Emergency Use. The spillway shall be designed to convey the
100-year peak inflow based upon a blocked outlet structure.
(4)
When required, freeboard shall be measured from the top of the
water surface elevation for emergency use.
G.
Breach Analysis. The municipality may require a breach analysis based
on site-specific conditions and concern of threat for downstream property.
When required, the breach analysis shall be conducted in accordance
with the NRCS methodology, the U.S. Army Corps of Engineers methodology
(HEC-1) or other methodologies as approved by the municipality.
2.
Subsurface Storage Facilities. Subsurface storage facilities consist
of all stormwater facilities which store, infiltrate/evaporate/transpire,
clean or otherwise affect stormwater runoff and the top of which is
not exposed to the natural environment. Subsurface facilities are
located below the finished ground elevation. Subsurface facilities
do not include stormwater management facilities designed for conveyance.
A.
Design Criteria. Subsurface storage facilities shall comply with
the design criteria in Table 20-311.2:
|
Table 20-311.2
| ||||
|---|---|---|---|---|
|
Subsurface Storage Facility Design Criteria
| ||||
|
Facility Type
| ||||
|
Infiltration and Storage
|
Storage without Infiltration
| |||
|
(a)
|
Facility geometry
| |||
|
[1]
|
Depth from surface (maximum)
|
2 feet less than limiting zone
|
N/A
| |
|
[2]
|
Loading ratio (maximum)
|
Per BMP Manual*
|
N/A
| |
|
(b)
|
Distribution system requirements
| |||
|
[1]
|
Pipe size (minimum)
|
4 inches
|
4 inches
| |
|
[2]
|
Pretreatment
|
Required
|
Required
| |
|
[3]
|
Loading/balancing
|
Required
|
Not required
| |
|
[4]
|
Observation/access ports
|
Required
|
Required
| |
|
[5]
|
Overflow system
|
Required
|
Required
| |
|
* Unless otherwise determined by professional geologic evaluation.
|
B.
Distribution System Requirements.
(1)
Pretreatment Requirements. The facility shall be designed to
provide a method to eliminate solids, sediment, and other debris from
entering the subsurface facility.
(2)
Loading/Balancing. The facility shall be designed to provide
a means of evenly balancing the flow across the surface of the facility
to be used for infiltration.
(3)
Observation/Access Ports.
(a)
For facilities with the bottom less than five feet below the
average grade of the ground surface, a clean-out shall be an acceptable
observation port.
(b)
For facilities with the bottom five feet or more below the average
grade of the ground surface, a manhole or other means acceptable to
the municipality shall be provided for access to and monitoring of
the facility.
(c)
The number of access points shall be sufficient to flush or
otherwise clean out the system.
C.
Materials.
(1)
Pipe Material. Distribution system piping may be PVC, SLHDPE,
or RCP.
(2)
Stone for Infiltration Beds. The stone used for infiltration
beds shall be clean washed, uniformly graded coarse aggregate (AASHTO
No. 3 or equivalent approved by the municipality). The void ratio
for design shall be assumed to be 0.4.
(4)
Lining Material. Non-woven geotextile shall be placed on the
tops and sides of subsurface infiltration facilities.
D.
Cover.
(1)
When located under pavement, the top of the subsurface facility
shall be a minimum of three inches below the bottom of pavement subbase.
(2)
Where located under vegetative cover, the top of the subsurface
facility shall be a minimum of 12 inches below the surface elevation
or as required to establish vegetation.
E.
In all cases, subsurface facilities shall be designed to safely convey
and/or bypass flows from storms exceeding the design storm. An overflow
system shall be provided to accommodate flows in excess of design
criteria and divert flows to appropriate areas of discharge without
damage to property. Design of the overflow system shall be approved
by the Municipal Engineer.
3.
Conveyance Facilities. Conveyance facilities consist of all stormwater
facilities which carry flow, which may be located either above or
below the finished grade. conveyance facilities do not include stormwater
management facilities which store, infiltrate/evaporate/transpire,
or clean stormwater runoff.
A.
Design Criteria. Conveyance facilities shall comply with the design criteria in Table 20-311.3 and be sized in accordance with the criteria of § 20-310, Subsection 2:
|
Table 20-311.3
| |||||
|---|---|---|---|---|---|
|
Conveyance Facility Design Criteria
| |||||
|
Location
|
Within Public Street Right-of-Way
|
Outside Public Street Right-of-Way
| |||
|
Loading
|
All
|
Vehicular loading
|
Non-Vehicular Loading
| ||
|
(a)
|
Pipe design
| ||||
|
[1]
|
Material
|
RCP
|
SLHDPE, RCP
|
SLHDPE, RCP
| |
|
[2]
|
Slope (minimum)
|
0.5%
|
0.5%
|
0.5%
| |
|
[3]
|
Cover
|
1 foot to stone subgrade
|
1 foot to stone subgrade
|
1 foot to surface
| |
|
[4]
|
Diameter (minimum)
|
15 inches
|
15 inches
|
12 inches
| |
|
[5]
|
Street crossing angle
|
75° to 90°
|
N/A
|
N/A
| |
|
[6]
|
Access/maintenance port frequency (maximum)
|
400 feet
|
400 feet
|
400 feet
| |
|
(b)
|
Inlet design
| ||||
|
[1]
|
Material
|
Concrete
|
Concrete
|
N/A
| |
|
[2]
|
Grate depression
|
2 inches
|
2 inches
|
1 inch minimum
| |
|
(c)
|
Manhole design
| ||||
|
[1]
|
Material
|
Concrete
|
Concrete
|
Concrete
| |
|
(d)
|
Swale design
| ||||
|
[1]
|
Freeboard (minimum)
|
1 foot
|
N/A
|
1 foot
| |
|
[2]
|
Velocity (maximum)
|
Stability check
|
N/A
|
Stability check
| |
|
[3]
|
Slope (minimum/maximum)
|
2%/9%
|
N/A
|
2%/9%
| |
|
[4]
|
Side slopes (residential area)
|
4:1 max
|
N/A
|
4:1 max
| |
|
[5]
|
Side slopes (non-residential area)
|
4:1 max
|
N/A
|
3:1 max
| |
|
[6]
|
Bottom width to flow depth ratio
|
12:1
|
N/A
|
12:1
| |
|
(e)
|
Outlet design
| ||||
|
[1]
|
End treatment
|
Headwall/endwall
|
N/A
|
Headwall/endwall or flared end section
| |
|
[2]
|
Energy dissipater
|
Required
|
N/A
|
Required
| |
|
NOTES:
|
|---|
|
N/A = Not applicable or no criteria specified
SLHDPE = Smooth lined high density polyethylene pipe
PVC = Polyvinyl chloride
RCP = Reinforced concrete pipe
|
B.
Conveyance pipes, culverts, manholes, inlets and endwalls within
the public street right-of-way or proposed for dedication shall conform
to the requirements of PennDOT Standards for Roadway Construction,
Publication No. 72M. conveyance pipes, culverts, manholes, inlets
and endwalls which are otherwise subject to vehicular loading shall
be designed for the HS-25 loading condition.
C.
Conveyance Pipes.
(1)
Backfill Requirements. For all storm sewer pipes, the trench
shall be backfilled as follows unless otherwise approved by the Township
Engineer.
(a)
With PennDOT 2A stone a minimum six inches below and to each
side of the pipe and one foot above the pipe crown.
(b)
In street right-of-way areas, the remainder of the trench shall
be backfilled with select backfill compacted in six-inch lifts.
(c)
Outside of street right-of-way areas, the remainder of the trench
shall be backfilled with clean fill compacted in eight-inch lifts.
(d)
Backfill shall be free of large (not exceeding four inches in
any dimension) objectionable or detritus material.
(2)
Inlets or manholes shall be placed at all points of changes
in the horizontal or vertical directions of conveyance pipes. Curved
pipe sections are prohibited.
(3)
Access/maintenance ports. An access/maintenance port is required
may either be an inlet or manhole.
(4)
Watertight joints shall be provided where pipe sections are
joined, except for perforated pipe installed as pavement base drain.
(5)
The street crossing angle shall be measured between the pipe
centerline and the street centerline.
(6)
Elliptical pipe of an equivalent cross-sectional area may be
substituted in lieu of circular pipe where cover or utility conflict
conditions exist.
(7)
The roughness coefficient (Manning "n" values) used for conveyance
pipe capacity calculations should be determined in accordance with
PennDOT Publication 584, PennDOT Drainage Manual, or per the manufacturer's
specifications.
(8)
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.
D.
Inlets.
(1)
All pipes must enter inlets completely through one of the sides.
No corner entry of pipes is permitted. Inlet box sizes shall be determined
based upon the size of entering/exiting pipes and noted in the storm
sewer profiles.
(2)
When there is a change in pipe size through an inlet, the top
inside elevation of the outlet shall be at or below the top inside
elevations of all incoming pipes (i.e., match crowns).
(3)
Storm sewer design shall be based upon PennDOT design methods.
Inlet efficiency and bypass flow for the 100-year storm shall be determined
for all inlets and the gutter flow spread shall not exceed 1/2 the
travel lane width, or to a maximum of eight feet where parking is
permitted. Honey Brook Township may require that a hydraulic grade
line analysis be performed on storm sewer systems.
(4)
Flow Depth within Intersections. Within intersections of streets,
the maximum depth of flow shall be 1 1/2 inches based on the
100-year storm.
(5)
Curbed Streets.
(a)
Inlets in streets shall be located along the curbline.
(b)
At street intersections, every attempt should be made to place
inlets in the tangent and not in the curved portion of the curbing.
(c)
All storm sewers within the streets shall not be placed under
the curbs or sidewalks.
(d)
Top units shall be PennDOT Type "C." The hood shall be aligned
with the adjacent curb height.
(6)
All inlets placed in paved areas shall have heavy duty bicycle-safe
grating consistent with PennDOT Publication 72M, latest edition. A
note to this effect shall be added to the SWM site plan or inlet details
therein.
(7)
Inlets, junction boxes, or manholes greater than five feet in
depth shall be equipped with ladder rungs and shall be detailed on
the SWM site plan.
(8)
Within street rights-of-way and all paved areas, concrete risers
or lintels shall be utilized to bring inlet grate elevations up to
finished grade.
E.
Swales.
(1)
A swale shall be considered as any man-made ditch designed to
convey stormwater directly to another stormwater management facility
or surface waters.
(2)
Swales shall be designed to provide a minimum one foot of freeboard
for the twenty-five-year design storm flow (twenty-four-hour duration).
(3)
Inlets within swales shall have PennDOT Type "M" top units or
equivalent approved by the municipal engineer.
(4)
Swale capacities and velocities shall be computed using the
Manning equation using the following design parameters:
(a)
Vegetated Swales.
1)
The first condition shall consider swale stability based upon
a low degree of retardance ("n" = 0.03);
2)
The second condition shall consider swale capacity based upon
a higher degree of retardance ("n" = 0.05); and
3)
All vegetated swales shall have a minimum slope of 2% unless
otherwise approved by the Municipal Engineer.
(b)
The "n" factors to be used for paved or riprap swales or gutters
shall be based upon accepted engineering design practices, as approved
by the Municipal Engineer.
(5)
All swales shall be designed to maximize infiltration and concentrate
low flows to minimize siltation and meandering, unless geotechnical
conditions do not permit infiltration.
(6)
Adequate erosion protection and energy dissipation shall be
provided along all swales 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 DEP E&S Manual, or other design guidance acceptable
to the Municipal Engineer.
(7)
Swales shall be stabilized with seed mixes and/or other plantings
suitable for the underlying soil conditions and swale function (infiltration/conveyance
only).
F.
Culverts. In addition to the material requirements in this section,
culverts designed to convey waters of the commonwealth may be constructed
with either a corrugated metal arch or a precast concrete culvert.
H.
Energy Dissipaters. Energy dissipaters shall be designed in accordance
with the requirements in the DEP E&S Manual and installed at all
points where pipes or swales discharge to or from basins and at the
discharge point of all conveyance pipes.
I.
End Treatments.
(1)
Where the connecting pipe has a diameter of 15 inches or greater,
headwalls and endwalls shall be provided with a protective barrier
device to prevent entry of the storm sewer pipe by unauthorized persons.
Such protection devices shall be designed to be removable for cleaning.
(2)
Headwalls and endwalls shall be constructed of concrete.
(3)
Flared end sections shall be of the same material as the connecting
pipe and be designed for the size of the connecting pipe.
J.
SWM facilities which qualify as a dam per DEP regulations or facilities
deemed a potential threat to the life, safety or welfare of the general
public shall be subject to the following requirements:
(1)
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 25 Pa. Code may require the safe conveyance
of storms larger than 100-year event.
(2)
Additional requirements and analysis may be required by the
municipality to prove that the proposed facility has been designed
to limit the potential risk to the life, safety or welfare of the
general public.
