A.
Preparation of a SWM site plan is required for all regulated activities, unless preparation and submission of the SWM site plan is specifically exempted according to § 230-51 or the activity qualifies as a small project.
B.
No regulated activities shall commence until the Township issues
unconditional written approval of a SWM site plan or stormwater permit.
C.
SWM site plans approved by the Township, in accordance with § 230-55, shall be on site throughout the duration of the regulated activity.
D.
The Township may, after consultation with DEP, approve measures for
meeting the state water quality requirements other than those in this
chapter, provided that they meet the minimum requirements of, and
do not conflict with, state law including, but not limited to, the
Clean Streams Law. The Township shall maintain a record of consultations
with DEP pursuant to this subsection. Where an NPDES permit for stormwater
discharges associated with construction activities is required, issuance
of an NPDES permit shall constitute satisfaction of consultation with
DEP.
E.
For all regulated activities, erosion and sediment control and stormwater
management BMPs 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 and the Clean
Streams Law. Various BMPs and their design standards are listed in
the E&S Manual and the BMP Manual.
F.
Developers have the option to propose a regional stormwater management plan or participate in a regional stormwater management plan developed by others. A regional stormwater management plan may include offsite volume and rate control, as appropriate and supported by a detailed design approved by the Township in accordance with § 230-31D. A regional stormwater management plan must meet all of the volume and rate control standards required by this chapter for the area defined by the regional stormwater management plan, but not necessarily for each individual development site, Appropriate agreements must be established to ensure the requirements of this chapter and the requirements of the regional stormwater management plan are met.
G.
Unless prohibited by Chapter 285, Zoning, or any ordinance which regulates construction and development within the areas of the Township subject to flooding, and any other applicable requirements of the Floodplain Management Act, stormwater management facilities located in the floodplain are permitted when designed and constructed in accordance with the provisions of the BMP Manual, regulatory requirements and the requirements of this chapter.
H.
Impervious areas:
(1)
The measurement of impervious area shall include all of the impervious
areas in the total proposed development even if development is to
take place in stages or phases.
(2)
For development taking place in stages or phases, the entire development
plan must be used in determining conformance with this chapter.
(3)
Any areas designed to initially be gravel or crushed stone shall
be assumed to be impervious.
I.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property;
(2)
Meet the water quality goals of this chapter by implementing measures
to:
(a)
Protect and/or improve the function of floodplains, wetlands,
and wooded areas.
(b)
Protect and/or improve native plant communities including those
within the riparian corridor.
(c)
Protect and/or improve natural drainageways from erosion.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(f)
Reduce or prevent to the maximum extent practicable the discharge
of a pollutant, polluted stormwater or an illicit discharge to the
MS4.
[Added 9-12-2022 by Ord. No. 268]
J.
The design of all SWM facilities over karst shall include an evaluation
of measures to minimize adverse effects.
K.
Infiltration BMPs shall be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter. Infiltration
BMPs shall include pretreatment BMPs unless shown to be unnecessary.
L.
Infiltration BMPs intended to receive runoff from developed areas
shall be selected based on suitability of soils and development 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 facility and
the limiting zone, unless it is demonstrated to the satisfaction of
the Township that the selected BMP has design criteria which allow
for a smaller separation.
(2)
A stabilized infiltration rate sufficient to accept the additional
stormwater load and drain completely as determined by field tests
conducted by the applicant's professional designer.
M.
The calculation methodology to be used in the analysis of volume and peak rates of discharge shall be as required in § 230-35.
N.
A planting plan is required for all vegetated stormwater BMPs.
(1)
Native or naturalized/non-invasive vegetation suitable to the soil
and hydrologic conditions of the development site shall be used unless
otherwise specified in the BMP Manual.
(2)
Invasive vegetation may not be included in any planting schedule.
(3)
The limit of existing, native vegetation to remain shall be delineated
on the plan along with proposed construction protection measures.
(4)
Prior to construction, a tree protection zone shall be delineated
at the dripline of the tree canopy. All trees scheduled to remain
during construction shall be marked; however, where groups of trees
exist, only the tress on the outside edge need to be marked. A forty-eight-inch-high
snow fence or forty-eight-inch-high construction fence mounted on
steel posts located eight feet on center shall be placed along the
tree protection boundary. No construction, storage of material, temporary
parking, pollution of soil, or regrading shall occur within the tree
protection zone.
(5)
All planting shall be performed in conformance with good nursery
and landscape practice. Plant materials shall conform to the standards
recommended by the American Association of Nurseryman, Inc. in the
American Standard of Nursery Stock.
O.
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity. Staging of earthmoving activities and selection of construction
equipment should consider this protection.
P.
Infiltration BMPs shall not be constructed nor receive runoff from
disturbed areas until the entire contributory drainage area to the
infiltration BMP has achieved final stabilization.
Q.
A minimum ten-foot-wide access easement shall be provided for all
stormwater facilities with tributary areas equal or greater than 1,000
square feet and not located within a public right-of-way. Easements
shall provide for ingress and egress to a public right-of-way.
R.
Drainage easements shall be provided where the conveyance, treatment,
or storage of stormwater, either existing or proposed, is identified
on the SWM site plan. Drainage easements shall be provided to contain
and convey the one-hundred-year frequency flood.
S.
The Township may require additional stormwater control measures for
stormwater discharges to special management areas including but not
limited to:
(1)
Water bodies listed as "impaired" on Pennsylvania's Clean Water Act
303(d)/305(b) Integrated List.
(2)
Any water body or watershed with an approved total maximum daily
load (TMDL).
(3)
Critical areas with sensitive resources (e.g., state-designated special
protection waters, cold water fisheries, carbonate or other groundwater
recharge areas highly vulnerable to contamination, drainage areas
to water supply reservoirs, source water protection zones, etc.).
T.
Roof drains and sump pumps shall be tributary to infiltration or
vegetative BMPs. Use of catchment facilities for the purpose of reuse
is also permitted.
U.
Nonstructural BMPs shall be utilized for all regulated activities
unless proven to be impractical.
V.
Incorporate
methods described in the BMP Manual. If methods other than green infrastructure
and low-impact development (LID) methods are proposed to achieve the
volume and rate controls required under this chapter, the SWM site
plan must include a detailed justification demonstrating that the
use of LID and green infrastructure is not practicable.
[Added 9-12-2022 by Ord. No. 268]
W.
Stormwater
flows onto adjacent property shall not be created, increased, decreased,
relocated, or otherwise altered without written notification to the
adjacent property owner(s). Such stormwater flows shall be subject
to the requirements in this chapter.
[Added 9-12-2022 by Ord. No. 268]
X.
Stormwater
management facilities such as permanent basins that are to be conveyed
to a homeowners' association shall not be conveyed to the homeowners'
association until such time as the stormwater management facilities
have been inspected and approved by the Township and the DEP NPDES
notice of termination has been officially received.
[Added 9-12-2022 by Ord. No. 268]
Volume control BMPs are intended to maintain existing hydrologic conditions for small storm events by promoting groundwater recharge and/or evapotranspiration as described in this section. Runoff volume controls shall be implemented using the design storm method described in Subsection A below, or through continuous modeling approaches or other means as described in the BMP Manual. Small projects may use the method described in § 230-32B to design volume control BMPs.
A.
The design storm method is applicable to major land disturbance activity.
This method requires detailed modeling based on site conditions.
(1)
Do not increase the post development total runoff volume for all
storms equal to or less than the two-year twenty-four-hour storm event.
(2)
For modeling purposes:
(a)
Existing (predevelopment) nonforested pervious areas must be
considered meadow in good condition.
(b)
When the existing project site contains impervious area, 20%
of existing impervious area to be disturbed shall be considered meadow
in good condition in the model for existing conditions.
(c)
The maximum loading ratio for volume control facilities in Karst
areas shall be 3:1 impervious drainage area to infiltration area and
5:1 total drainage area to infiltration area. The maximum loading
ratio for volume control facilities in non-Karst areas shall be 5:1
impervious drainage area to infiltration area and 8:1 total drainage
area to infiltration area. A higher ratio may be approved by the Township
if justification is provided. Hydraulic depth may be used as an alternative
to an area based loading ratio if the design hydraulic depth is shown
to be less than the depth that could result from the maximum area
loading ratio.
B.
Volume control for small projects.
(1)
At least the first one inch of runoff from new impervious surfaces
or an equivalent volume shall be permanently removed from the runoff
flow; i.e., it shall not be released into the surface waters of this
commonwealth. Removal options include reuse, evaporation, transpiration
and infiltration.
(2)
Wherever possible, infiltration facilities should be designed to
accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 1/2 inch of the permanently
removed runoff should be infiltrated.
C.
A detailed geologic evaluation of the development site shall be performed in areas of carbonate geology to determine the design parameters of recharge facilities. A report shall be prepared in accordance with § 230-45A.
D.
Storage facilities, including normally dry, open top facilities,
shall completely drain the volume control storage over a period of
time not less than 24 hours and not more than 72 hours from the end
of the design storm. Any designed infiltration at such facilities
is exempt from the minimum twenty-four-hour standard, i.e., may infiltrate
in a shorter period of time, provided that none of this water will
be discharged into waters of this commonwealth.
E.
Any portion of the volume control storage that meets all of the following
criteria may also be used as rate control storage:
(1)
Volume control storage that depends on infiltration is designed according to the infiltration standards in § 230-31.
(2)
The volume control storage which will be used for rate control is
that storage which is available within 24 hours from the end of the
design storm based on the stabilized infiltration rate and/or the
evapo-transpiration rate.
F.
Volume control storage facilities designed to infiltrate shall avoid
the least permeable hydrologic soil group(s) at the development site
to the greatest extent practicable.
Rate control for large storms, up to the one-hundred-year event,
is essential to protect against immediate downstream erosion and flooding.
A.
Match predevelopment hydrograph. Applicants shall provide infiltration facilities or utilize other techniques which will allow the post-development one-hundred-year hydrograph to match the predevelopment one-hundred-year hydrograph, along all parts of the hydrograph, for the development site. To match the predevelopment hydrograph, the post development peak rate must be less than or equal to the predevelopment peak rate, and the post development runoff volume must be less than or equal to the predevelopment volume for the same storm event. A shift in hydrograph peak time of up to five minutes and a rate variation of up to 5% at a given time may be allowable to account for the timing affect of BMPs used to manage the peak rate and runoff volume. "Volume control" volumes as given in § 230-32 above may be used as part of this option.
B.
Where the predevelopment hydrograph cannot be matched, one of the
following shall apply:
(1)
For areas not covered by a release rate map from an approved Act
167 Plan:
Post development discharge rates shall not exceed the predevelopment
discharge rates for the two-, ten-, twenty-five-, fifty-, and one-hundred-year
twenty-four-hour storm events*. If it is shown that the peak rates
of discharge indicated by the post development analysis are less than
or equal to the peak rates of discharge indicated by the predevelopment
analysis for two-, ten-, twenty-five-, fifty-, and one-hundred-year
twenty-four-hour storms*, then the requirements of this section have
been met. Otherwise, the applicant shall provide additional controls
as necessary to satisfy the peak rate of discharge requirement.
*A twenty-four-hour SCS type II storm or an IDF Curve Rational Method storm. See Table III-1 in § 230-35.
(2)
For areas covered by a release rate map from an approved Act 167
Plan:
For the two-, ten-, twenty-five-, fifty-, and one-hundred-year
storm events*, the post development peak discharge rates will follow
the applicable approved release rate maps.
A twenty-four-hour SCS type II storm or an IDF Curve Rational Method storm. See Table III-1 in § 230-35.
C.
Normally dry, open top, storage facilities shall completely drain
the rate control storage over a period of time less than or equal
to 24 hours from the peak one-hundred-year water surface design elevation.
D.
A variety of BMPs should be employed and tailored to suit the development
site. The following is a partial listing of BMPs which can be utilized
in SWM systems for rate control where appropriate:
(1)
Decreased impervious surface coverage.
(2)
Routed flow over grass.
(3)
Grassed channels and vegetated strips.
(4)
Bio-retention areas (rain gardens).
(5)
Concrete lattice block or permeable surfaces.
(6)
Seepage pits, seepage trenches or other infiltration structures.
(7)
Rooftop detention.
(8)
Parking lot detention.
(9)
Cisterns and underground reservoirs.
(10)
Retention basins.
(11)
Detention basins.
(12)
Other methods as may be found in the BMP Manual, as approved
by Township.
A.
Runoff from impervious areas shall be drained to pervious areas within
the development site, unless the site has 85% or more impervious cover
and is a redevelopment, in which case the portion of the site that
discharges to pervious areas shall be maximized.
B.
Stormwater runoff from a development site to an adjacent property
shall flow directly into a natural drainageway, watercourse, or into
an existing storm sewer system, or onto adjacent properties in a manner
similar to the runoff characteristics of the predevelopment flow.
The applicant must provide proof to the Township Engineer that he
or his agent has informed the immediate downstream property owner
of the effects of the stormwater discharge from the proposed development.
C.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written notification
of the adjacent property owner(s) by the developer. Such stormwater
flows shall be subject to the requirements of this chapter, including
the establishment of a drainage easement. Copies of all such notifications
shall be included in SWM site plan submissions.
D.
Existing on-site natural and man-made SWM facilities shall be used
to the maximum extent practicable.
E.
Stormwater runoff shall not be transferred from one sub-watershed
to another unless they are sub-watersheds of a common watershed that
join together within the perimeter of the development site and the
effect of the transfer does not alter the peak discharge onto adjacent
lands.
F.
Minimum floor elevations for all structures that would be affected
by a basin, other temporary impoundments, or open conveyance systems
where ponding may occur shall be two feet above the one-hundred-year
water surface elevation. If basement or underground facilities are
proposed, detailed calculations addressing the effects of stormwater
ponding on the structure and waterproofing and/or floodproofing design
information shall be submitted for approval.
G.
All stormwater conveyance facilities (excluding detention, retention,
and wetland basin outfall structures) shall be designed to convey
a twenty-five-year storm event*. All stormwater conveyance facilities
(excluding detention, retention, and wetland basin outfall structures)
conveying water originating from offsite shall be designed to convey
a fifty-year storm event*. Safe conveyance of the one-hundred-year
runoff event* to appropriate peak rate control BMPs must be demonstrated
in the design.
*A twenty-four-hour SCS Type II storm or an IDF Curve Rational
Method storm.
H.
Erosion protection shall be provided along all open channels, and
at all points of discharge. Flow velocities from any storm sewer may
not result in erosion of the receiving channel.
I.
Roof drains shall not be connected to streets, sanitary or storm
sewers or roadside ditches.
A.
Any stormwater runoff calculations involving drainage areas greater
than 200 acres and time of concentration (Tc) greater than 60 minutes,
including on- and off-site areas, shall use generally accepted calculation
techniques based on the NRCS soil-cover complex method.
B.
Stormwater runoff from all development sites shall be calculated
using either the modified rational method, a soil-cover-complex methodology,
or other method acceptable to the Township. Table III-1 summarizes
acceptable computation methods. It is assumed that all methods will
be selected by the design professional based on the individual limitations
and suitability of each method for a particular development site.
Table III-1
Acceptable Computation Methodologies for Stormwater Management
Plans
| |||
---|---|---|---|
Method
|
Method Developed By
|
Applicability
| |
TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
| |
Win TR-55 (or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
| |
HEC-1/HEC-HMS
|
US Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
| |
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For development sites less than 200 acres, Tc<60 minutes
or as approved by the Township
| |
EFH2
|
USDA NRCS
|
Applicable in rural and undeveloped areas subject to the program
limits
| |
Other methods
|
Varies
|
Other methodologies approved by the Township
|
C.
If the SCS method is used, Antecedent Moisture Condition 1 is to
be used in areas of carbonate geology, and Antecedent Moisture Condition
2 is to be used in all other areas. A type II distribution shall be
used in all areas.
D.
If the Rational Method is used, the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 data (see Subsection B above) or PennDOT Publication 584 "PennDOT Drainage Manual," 2008 Edition, or latest, shall be used to determine the rainfall intensity in inches per hour based on the information for the five-through sixty-minute duration storm events.
E.
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.
F.
Runoff calculations shall include a hydrologic and hydraulic analysis
indicating volume and velocities of flow and the grades, sizes, and
capacities of water-carrying structures, sediment basins, retention
and detention structures and sufficient design information to construct
such facilities. Runoff calculations shall also indicate both predevelopment
and post-development rates for peak discharge of stormwater runoff
from all discharge points.
G.
For the purpose of calculating predevelopment peak discharges, all
runoff coefficients, both on-site and off-site, shall be based on
actual land use assuming summer or good land conditions. Post-development
runoff coefficients for on-site discharges used to design conveyance
facilities shall be based on actual land use assuming winter or poor
land conditions.
H.
Criteria and assumptions to be used in the determination of stormwater
runoff and design of management facilities are as follows:
(1)
Runoff coefficients shall be based on the information contained in Appendix B-1 and B-2[1] if the actual land use is listed in those appendices.
If the actual land use is not listed in these appendices, runoff coefficients
shall be chosen from other published documentation, and a copy of
said documentation shall be submitted with the SWM site plan.
[1]
Editor's Note: Said appendixes are included as attachments
to this chapter.
(2)
A sample worksheet for calculating Tc is provided in Appendix B-4. Times of concentration (Tc) shall be based on the following design parameters:
(a)
Sheet flow: The maximum length for each reach of sheet or overland flow before shallow concentrated or open channel flow develops is 150 feet. Flow lengths greater than 100 feet shall be justified based on the actual conditions at each development site. Sheet flow may be determined using the nomograph in Appendix B-3,[2] or the Manning's kinematic solution shown in the sheet flow section of Worksheet No. 1 in Appendix B-4.[3]
(b)
Shallow concentrated flow: Travel time for shallow concentrated flow shall be determined using Figure 3-1 from TR-55, Urban Hydrology for small watersheds, as shown in Appendix B-5.[4]
[4]
Editor's Note: Said appendixes are included as attachments
to this chapter.
(c)
Open channel flows: At points where sheet and shallow concentrated
flows concentrate in field depressions, swales, gutters, curbs, or
pipe collection systems, the travel times to downstream end of the
development site between these design points shall be based upon Manning's
Equation and/or acceptable engineering design standards as determined
by the Township Engineer.
(3)
The developer may use stormwater credits for nonstructural BMPs in
accordance with the BMP Manual. The allowable reduction will be determined
by the Township.
(4)
Peak rate control is not required for off-site runoff. Off-site runoff
may be by-passed around the site provided all other discharge requirements
are met. If offsite runoff is routed through rate control facilities,
runoff coefficients for off-site discharges used to design those rate
control facilities shall be based on actual land use assuming winter
or poor land conditions.
I.
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.
Supporting documentation and calculations must be submitted for review
and approval.
J.
The sizing of stormwater management facilities for residential subdivisions shall be based on the maximum impervious coverage permitted by Chapter 285, Zoning, for those lots that are 15,000 square feet or less in size. Within residential subdivisions where lots are greater than 15,000 square feet in size the design for the stormwater management facilities must specifically identify the square footage of impervious coverage assumed for each lot and a note must be provided on the plan to be recorded that indicates the amount used for the design of the SWM facilities within the subdivision.
A.
In order to protect and improve water quality, a riparian corridor
easement shall be created and recorded as part of any subdivision
or land development that encompasses a riparian corridor.
B.
Except as otherwise required by Chapter 102, the width of the riparian
corridor easement shall be established as the greatest of the following:
(1)
A specified distance from the top of each stream bank, based on stream
order, as given in Table 1, as determined by PaDEP.
(2)
The limit of the one-hundred-year floodplain. Twenty-five feet from
riparian wetland boundary, if present.
Table 1
Minimum Buffer Widths by Stream Order
| |
---|---|
Stream Order
|
Buffer Width
(feet)
|
1 to 2
|
35
|
3 to 4
|
50
|
Over 4
|
75
|
C.
Minimum management requirements for riparian corridors.
(1)
Existing native vegetation shall be protected and maintained within
the riparian corridor easement.
(2)
Whenever practicable invasive vegetation shall be actively removed
and the riparian corridor easement shall be planted with native trees,
shrubs and other vegetation to create a diverse native plant community
appropriate to the intended ecological context of the site.
D.
The riparian corridor easement shall be enforceable by the Township and shall be recorded in the Lancaster County Recorder of Deeds Office, so that it shall run with the land and shall limit the use of the property located therein. The easement shall allow for the continued private ownership and shall count toward the minimum lot area as required by Chapter 285, Zoning, unless otherwise specified in Chapter 285.
E.
Any permitted use within the riparian corridor easement shall be
conducted in a manner that will maintain the extent of the existing
one-hundred-year floodplain, improve or maintain the stream stability,
and preserve and protect the ecological function of the floodplain.
G.
Septic drainfields and sewage disposal systems shall not be permitted
within the Riparian Corridor Easement and shall comply with setback
requirements established under 25 Pa. Code Chapter 73.
H.
Required
riparian buffers, upon being planted and permanently established with
the required vegetation, shall be professionally inspected, and certified
by a qualified professional that the established vegetation meets
the requirements of the approved planting plan including required
native vegetation, permanent establishment, free from invasives, and
other such requirements.
[Added 9-12-2022 by Ord. No. 268]
A.
Aboveground storage facilities. Aboveground storage facilities consist
of all SWM 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 SWM facilities designed for conveyance or
cisterns.
(1)
Design criteria. Aboveground storage facilities shall comply with
the design criteria in the following table:
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)
|
2 feet
|
5 feet
|
8 feet
| ||
[2]
|
Interior side slope (maximum)
|
2:1
|
3:1
|
5:1
| ||
[3]
|
Exterior side slope (maximum)
|
2:1
|
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
|
N/A
|
Required
|
Required
| ||
[2]
|
Pretreatment elements
|
Not required*
|
Required
|
Required
| ||
(d)
|
Outlet Structure
| |||||
[1]
|
Pipe size (minimum)
|
6 inches
|
12 inches
|
15 inches
| ||
[2]
|
Pipe material
|
SLHDPE, PVC, RCP
|
SLHDPE, RCP
|
RCP
| ||
[3]
|
Anticlogging devices
|
Required
|
Required
|
Required
| ||
[4]
|
Antivortex design
|
Not required
|
Required
|
Required
| ||
[5]
|
Watertight joints in piping?
|
No
|
Yes
|
Yes
| ||
(e)
|
Spillway Requirements
| |||||
[1]
|
Spillway freeboard (minimum)
|
Not required
|
3 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 one-hundred-year storm
|
Permitted
|
Permitted
|
Permitted
|
*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
|
(2)
Facility depth.
(a)
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.
(b)
Facilities with a facility depth greater than eight feet shall
not be permitted in residential areas.
(c)
Facilities with a facility depth greater than 15 feet require
a dam permit from DEP.
(3)
Embankment construction.
(a)
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.
[1]
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.
[2]
Dimensions.
[a]
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.
[b]
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.
[c]
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.
[3]
Compaction.
(b)
Pipe collars. All pipe collars, when required, shall be designed
in accordance with Chapter 7 of the E&S Manual. The material shall
consist of concrete or otherwise non-degradable material around the
outfall barrel and shall be watertight.
(c)
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.
(d)
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 (2/3 of the lift thickness). Five passes
of the compaction equipment over the entire surface of each lift is
required. Embankment compaction to visible nonmovement is also required.
(4)
Internal construction.
(a)
Bottom slope. The minimum bottom slope of facilities not designed
for infiltration shall be 1%. A flatter slope may be used if an equivalent
dewatering mechanism is provided.
(b)
Dewatering features. When required, dewatering shall be provided
through the use of underdrain, surface device, or alternate approved
by the Township 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.
(c)
Pretreatment elements. When required, pretreatment elements
shall consist of forebays, or alternate approved by the Township Engineer,
to keep silt to a smaller portion of the facility for ease of maintenance.
(d)
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 § 230-31N and the BMP Manual which is designed to promote infiltration.
(5)
Outlet configuration.
(a)
For facilities with a depth of two feet or greater, a type D-W
endwall or riser box outlet structure shall be provided.
(b)
For facilities with a depth less than two feet, no outlet structure
is required.
(c)
All discharge control devices with appurtenances shall be made
of reinforced concrete and stainless steel. Bolts/fasteners shall
be stainless steel.
(6)
Spillway.
(a)
Material. The spillway shall be designed to provide a non-erosive,
stable condition when the project is completed.
(b)
Non-emergency use. Use of the spillway to convey flows greater
than the fifty-year design storm is permitted.
(c)
Emergency use. The spillway shall be designed to convey the
one-hundred-year peak inflow.
(d)
When required, freeboard shall be measured from the top of the
water surface elevation for emergency use.
(7)
Breach analysis. The Township 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 US Army Corps of Engineers methodology
(HEC-1) or other methodologies as approved by the Township.
B.
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.
(1)
Design criteria. Subsurface storage facilities shall comply with
the design criteria in the following table:
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
|
*Unless otherwise determined by professional geologic evaluation.
|
(2)
Distribution system requirements.
(a)
Pretreatment requirements. The facility shall be designed to
provide a method to eliminate solids, sediment, and other debris from
entering the subsurface facility.
(b)
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.
(c)
Observation/access ports.
[1]
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.
[2]
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 Township shall be provided for access to and monitoring of the
facility.
[3]
The number of access points shall be sufficient to flush or
otherwise clean out the system.
(3)
Materials.
(a)
Pipe material. Distribution system piping may be PVC, SLHDPE,
or RCP.
(b)
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 Township). The void ratio for
design shall be assumed to be 0.4.
(c)
Backfill material. Material consistency and placement depths for backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations, further providing it should be free of large (not exceeding six inches in any dimension) objectionable or detritus material. Select non-aggregate material should be indigenous to the surrounding soil material for nonvehicular areas. Backfill within vehicular areas shall comply with this section unless otherwise specified in governing municipal road/street or Chapter 240, Subdivision and Land Development. Furthermore, if the design concept includes the migration of runoff through the backfill to reach the infiltration facility, the material shall be well drained, free of excess clay or clay-like materials and generally uniform in gradation.
(d)
Lining material. Nonwoven geotextiles shall be placed on the
sides and top of subsurface infiltration facilities. No geotextiles
shall be placed on the bottom of subsurface infiltration facilities.
(4)
Cover.
(a)
When located under pavement, the top of the subsurface facility
shall be a minimum of three inches below the bottom of pavement subbase.
(b)
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.
(5)
Subsurface facilities shall be designed to safely convey and/or bypass
flows from storms exceeding the design storm.
C.
Conveyance facilities. Conveyance facilities consist of all SWM facilities
which carry flow, which may be located either above or below the finished
grade. Conveyance facilities do not include SWM facilities which store,
infiltrate/evaporate/transpire, or clean stormwater runoff.
(1)
Design criteria. Conveyance facilities shall comply with the design
criteria in the following table:
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
|
SLHDPE, RCP
|
PVC, SLHDPE, RCP
|
PVC 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
|
8 inches
| ||
[5]
|
Street crossing angle
|
75° to 90°
|
N/A
|
N/A
| ||
[6]
|
Access/ maintenance port frequency (maximum)
|
400 feet
|
400 feet
|
600 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)
|
6 inches
|
N/A
|
6 inches
| ||
[2]
|
Velocity (maximum)
|
Stability check
|
N/A
|
Stability check
| ||
[3]
|
Slope (minimum)
|
1%
|
N/A
|
1%
| ||
[4]
|
Side slopes (residential area)
|
4:1 max
|
N/A
|
4:1 max
| ||
[5]
|
Side slopes (nonresidential 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
|
N/A = Not applicable or no criteria specified
| |
---|---|
SLHDPE = Smooth lined high density polyethylene pipe; PVC =
Polyvinyl chloride;
| |
RCP = Reinforced concrete pipe
|
(2)
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.
(3)
Conveyance pipes.
(a)
Backfill requirements. Backfill material. Material consistency and placement depths for backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations, further providing it should be free of large (not exceeding six inches in any dimension) objectionable or detritus material. Select non-aggregate material should be indigenous to the surrounding soil material for nonvehicular areas. Backfill within vehicular areas shall comply with this section unless otherwise specified in governing municipal road/street or Chapter 240, Subdivision and Land Development.
(b)
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.
(c)
Access/maintenance ports. An access/maintenance port is required;
may either be an inlet or manhole.
(d)
Watertight joints shall be provided where pipe sections are
joined, except for perforated pipe installed as pavement base drain.
(e)
The street crossing angle shall be measured between the pipe
centerline and the street centerline.
(f)
Elliptical pipe of an equivalent cross-sectional area may be
substituted in lieu of circular pipe where cover or utility conflict
conditions exist.
(g)
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.
(4)
Inlets.
(a)
All pipes must enter inlets completely through one of the sides.
No corner entry of pipes is permitted.
(b)
Within the public street right-of-way, the gutter spread based
on the twenty-five-year storm shall be no greater than 1/2 of the
travel lane and have a maximum depth of three inches at the curb line.
A parking lane shall not be considered as part of the travel lane.
In the absence of pavement markings separating a travel lane from
the parking lane, the parking lane shall be assumed to be seven feet
wide if parking is permitted on the street.
(c)
Flow depth within intersections. Within intersections of streets,
the maximum depth of flow shall be 1.5 inches based on the twenty-five-year
storm.
(e)
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.
(f)
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.
(5)
Swales.
(a)
A swale shall be considered as any man-made ditch designed to
convey stormwater directly to another SWM facility or surface waters.
(b)
Inlets within swales shall have PennDOT Type "M" top units or
equivalent approved by the municipal engineer.
(c)
Swale capacities and velocities shall be computed using the
Manning equation using the following design parameters:
[1]
Vegetated swales.
[a]
The first condition shall consider swale stability
based upon a low degree of retardance ("n" = 0.03);
[b]
The second condition shall consider swale capacity
based upon a higher degree of retardance ("n" = 0.05); and
[c]
All vegetated swales shall have a minimum slope
of 1% unless otherwise approved by the Township Engineer.
[2]
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 Township Engineer.
(d)
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)
Culverts. In addition to the material requirements in this section,
culverts designed to convey waters of this commonwealth may be constructed
with either a corrugated metal arch or a precast concrete culvert.
(8)
Energy dissipaters. Energy dissipaters shall be designed in accordance
with the requirements in the E&S Manual.
(9)
End treatments.
(a)
Where the connecting pipe has a diameter of 18 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.
(b)
Headwalls and endwalls shall be constructed of concrete.
(c)
Flared end sections shall be of the same material as the connecting
pipe and be designed for the size of the connecting pipe.
D.
SWM facilities which qualify as a dam under 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)
Facilities which qualify as a dam under DEP regulation shall obtain
the required permit through DEP and design the facility in accordance
with DEP standards.
(2)
Additional requirements and analysis may be required by the Township
to prove that the proposed facility has been designed to limit the
potential risk to the life, safety or welfare of the general public.
A.
Capture and reuse facilities include those SWM facilities which capture
stormwater within a site and store the water for reuse through rainwater
harvesting, which includes, but is not limited to, irrigation reuse,
potable water reuse, and toilet flushing reuse. Water storage facilities
for use with capture and reuse facilities include, but are not limited
to, cisterns and rain barrels.
B.
Design requirements. Capture and reuse facilities shall meet all
of the following design standards.
(1)
Calculations shall be provided for all of the following:
(a)
Reuse of water to insure adequate capacity is available for
storage of follow-up rainfall events.
(b)
Verification of conveyance pipe capacity for water to enter
the facility, including roof leaders.
(c)
The water storage facility shall be designed to store the runoff
volume of a one-hundred-year storm event for the area which it serves.
(2)
The reuse of water shall require not less than 5% of the total storage
volume to be drawn out of the tank on a daily basis. The applicant
shall specifically identify the use and/or method for withdrawal of
the stored volume and shall provide the estimated volume of water
which will be used by the proposed method.
(3)
The water storage container shall be protected from direct sunlight
to minimize algae growth.
(4)
Water storage containers shall be watertight with smooth interior
surfaces.
(5)
Every water storage facility shall be provided with an overflow or
emergency spillway. The overflow shall be designed to discharge away
from buildings and other structures and toward existing natural or
man-made channels, other stormwater facilities or vegetated slopes.
(7)
Maintenance responsibilities for water storage and reuse facilities
shall include flushing the storage units to remove any accumulated
sediment, and the inside surfaces shall be brushed and thoroughly
disinfected.
(8)
Water shall not be allowed to freeze in the devices.
[Amended 9-12-2022 by Ord. No. 268]
A.
Amended
soils. Areas with amended soils shall be restricted for use within
the bottom of rain gardens and stormwater management basins that are
within a stormwater or drainage easement identified on a recorded
plan to ensure that the future owners of such facilities are aware
of the restrictions associated with the amended soil areas.
B.
All amended
soils specified within BMP basins shall be required to be certified
for use to meet water quality and water recharge provisions. If on-site
soils are utilized as part of the amended soils, the topsoil shall
be certified including acceptable permeability, PH, clay content,
etc.
C.
No development
or earth-moving activities shall involve uses, activities or improvements
which would entail encroachment into, the regrading of, or the placement
of fill in wetlands in violation of state or federal regulations.
[Added 9-12-2022 by Ord. No. 268]
A.
The developer
shall reserve easements where stormwater management facilities, floodplains
or wetlands are existing or proposed, whether located within or beyond
the boundaries of the project site. If stormwater management facilities,
floodplains or wetlands are to be installed or created beyond the
boundary of the property, the developer shall provide the Township
with all necessary easements, in a form acceptable to the Township
Solicitor, clearly demonstrating that the developer has the right
to install stormwater management facilities on such adjoining property
and/or create floodplains or wetlands upon such adjoining property.
B.
Easements
shall have a minimum width of 20 feet and shall be adequately designed
to provide area for (a) the collection and discharge of water, (b)
the maintenance, repair and reconstruction of all stormwater management
facilities, (c) the passage of machinery for such work, and (d) the
preservation of floodplains and wetlands. The easements shall clearly
identify who has the right of access and the responsibility of maintenance.
C.
Stormwater
management facilities shall be centered within the easement.
D.
To the
fullest extent possible, easements shall be centered on or be adjacent
to lot lines.
E.
Nothing
shall be placed, planted, set, or put within the area of an easement
that would adversely affect the function of the easement or conflict
with the easement agreement.