A.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 113-13.
B.
SWM site plans approved by the Township, in accordance with § 113-23, shall be on site throughout the duration of the regulated activity.
C.
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.[1] The Township shall maintain a record of consultations
with DEP pursuant to this subsection.
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
D.
For all regulated earth-disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth-disturbance activities, i.e., during construction,
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 Erosion and Sediment Pollution Control Program Manual (E&S
Manual) 2, No. 363-2134-008 (April 15, 2000), as amended and updated.
F.
Impervious areas.
(1)
The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in phases.
(2)
For development taking place in phases, the entire development plan
must be used in determining conformance with this chapter.
(3)
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in § 113-14 and the peak rate controls of § 113-15 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
G.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written notification
of the adjacent property owner(s). Such stormwater flows shall be
subject to the requirements of this chapter.
H.
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, as stated in § 113-3, Purpose, by implementing measures to:
(a)
Minimize disturbance to floodplains, wetlands, wooded areas,
and existing vegetation.
(b)
Maintain or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(f)
Minimize soil disturbance and compaction. Topsoil, if removed,
shall be replaced to a minimum depth equal to its depth prior to removal
or four inches, whichever is greater. (Additional topsoil may be needed
for vegetation other than sod.)
(3)
To the maximum extent practicable, incorporate the techniques for
low-impact development practices described in the Pennsylvania Stormwater
Best Management Practices Manual (BMP Manual).
I.
The design of all facilities in areas of carbonate geology or karst
topography shall include an evaluation of measures to minimize adverse
effects, including hydro-geologic studies if required by the Township.
J.
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. In addition,
infiltration BMPs shall include pretreatment BMPs where appropriate.
K.
All natural streams, channels, swales, drainage systems and/or areas of surface water concentration shall be maintained in their existing condition unless an alteration is approved by the Township. All encroachment activities shall comply with the requirements of Pennsylvania DEP, 25 Pa. Code Chapter 105 (Water Obstructions and Encroachments), Rules and Regulations of Pennsylvania DEP. Any approvals or permits issued do not relieve compliance as referenced in § 113-8, Compatibility with other requirements.
L.
Storage facilities, designed as such, shall completely drain both
the volume control and rate control capacities over a period of time
not less than 24 hours and not more than 72 hours from the end of
the design storm. However, 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, so long as none of the stormwater flowing
into the infiltration facility is discharged directly into the surface
waters of the commonwealth. (Inordinately rapid infiltration rates
may indicate the presence of large fractures or other conditions for
which an additional soil buffer may be required.)
M.
The design storm volumes and precipitation intensities to be used
in the analysis of discharge or runoff shall be obtained from the
Precipitation-Frequency Atlas of the United States, Atlas 14, Volume
2, Version 3.0, U.S. Department of Commerce, National Oceanic and
Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological
Design Studies Center, Silver Spring, Maryland. NOAA's Atlas 14 can
be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
N.
For all regulated activities, SWM 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, the Clean Streams Law, and the Storm Water Management Act.
O.
Various BMPs and their design standards are listed in the BMP Manual.
P.
All work shall be in accordance with the Township's Construction
and Materials Specifications.
Any regulated activity that meets the following exemption criteria
is exempt from the part(s) of this chapter as specified herein. However,
the requirements of the Ordinance shall otherwise remain in effect.
The criteria for exemption in this section apply to the total development
proposed, including instances in which the development is proposed
to take place in phases. The date of enactment of this chapter shall
be the starting point from which future development and the respective
proposed impervious surface computations shall be cumulatively considered
and regulated. Exemption shall not relieve an applicant from implementing
such measures as necessary to meet the intent of this chapter, or
compliance with any NPDES permit requirements.
A.
Regulated activities that create DIAs equal to or less than 1,000
square feet are exempt from the peak rate control and the SWM site
plan preparation requirements of this chapter.
B.
Regulated activities that create DIAs greater than 1,000 square feet
and equal to or less than 5,000 square feet are exempt only from the
peak rate control requirement of this chapter.
C.
Agricultural activity is exempt from the rate control and SWM site
plan preparation requirements of this chapter, provided the activities
are performed according to the requirements of 25 Pa. Code 102.
D.
Forest management and timber operations are exempt from the rate
control and SWM site plan preparation requirements of this chapter,
provided the activities are performed according to the requirements
of 25 Pa. Code 102.
E.
Domestic gardening and landscaping are exempt from specific approval
and permitting under this chapter so long as those activities are
associated with one, and only one, dwelling unit and the activities
comply with all other applicable ordinances and statutes.
G.
The Township may deny or revoke any exemption pursuant to this section
at any time for any project that the Township determines poses a threat
to public health, safety, property or the environment.
[Added 10-27-2022 by Ord. No. 22-09]
B.
Waivers
or modifications of the requirements of this chapter may be approved
by the municipality if enforcement will exact undue hardship because
of peculiar conditions pertaining to the land in question, provided
that the modifications will not be contrary to the public interest
and that the purpose of this chapter is preserved. Cost or financial
burden shall not be considered a hardship. Modification may be considered
if an alternative standard or approach will provide equal or better
achievement of the purpose of this chapter. A request for modifications
shall be in writing and accompany the stormwater management site plan
submission. The request shall provide the facts on which the request
is based, the provision(s) of this chapter involved and the proposed
modification.
C.
No waiver
or modification of any regulated stormwater activity involving earth
disturbance greater than or equal to one acre may be granted by the
municipality unless that action is approved in advance by the Department
of Environmental Protection (DEP) or the delegated county conservation
district.
The low-impact development practices provided in the BMP Manual
shall be utilized for all regulated activities to the maximum extent
practicable. Water volume controls shall be implemented using the
Design Storm Method in Subsection A or the Simplified Method in Subsection
B below. For regulated activity areas equal or less than one acre
that do not require hydrologic routing to design the stormwater facilities,
this chapter establishes no preference for either methodology; therefore,
the applicant may select either methodology on the basis of economic
considerations, the intrinsic limitations on applicability of the
analytical procedures associated with each methodology, and other
factors.
A.
The Design Storm Method (CG-1 in the BMP Manual) is applicable to
any size of regulated activity. This method requires detailed modeling
based on site conditions.
(1)
Do not increase the post-development total runoff volume for all
storms equal to or less than the two-year twenty-four-hour duration
precipitation.
B.
The Simplified Method (CG-2 in the BMP Manual) provided below is
independent of site conditions and should be used if the Design Storm
Method is not followed. This method is not applicable to regulated
activities greater than one acre or for projects that require design
of stormwater storage facilities. For new impervious surfaces:
(1)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(2)
At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow, i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options for the first one inch of runoff include reuse, evaporation,
transpiration, and infiltration.
(3)
Wherever possible, infiltration facilities should be designed to
accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 0.5 inch of the permanently
removed stormwater runoff shall be infiltrated.
A.
For computation of predevelopment peak discharge rates, 20% of the
existing impervious area of a project site, when present, shall be
considered meadow.
B.
Post-development discharge rates shall not exceed the predevelopment
discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty-,
and one-hundred-year twenty-four-hour storms. 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 one-, two-, five-, 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.
[Added 10-27-2022 by Ord. No. 22-09]
A.
In order
to protect and improve water quality, a riparian buffer easement shall
be created and recorded as part of any subdivision or land development
that encompasses a riparian buffer.
B.
Except as otherwise required by § 113-12, the riparian buffer easement shall be measured to be the greater of the limit of the 100-year floodplain or a minimum of 35 feet from the top of the streambank (on each side).
C.
Minimum
management requirements for riparian buffers.
(1)
Existing native vegetation shall be protected and maintained within
the riparian buffer easement.
(2)
Whenever practicable, invasive vegetation shall be actively removed
and the riparian buffer 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 buffer easement shall be enforceable by the municipality
and shall be recorded in the appropriate 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 required by zoning, unless otherwise specified in the municipal
Zoning Ordinance.[1]
E.
Any
permitted use within the riparian buffer easement shall be conducted
in a manner that will maintain the extent of the existing 100-year
floodplain, improve or maintain the stream stability, and preserve
and protect the ecological function of the floodplain.
A.
For the purposes of the Act 167 Stormwater Management (Plan) elements,
contained within the York County Integrated Water Resources Plan,
and this chapter, design policy pertaining to stormwater management
facilities for Pennsylvania Department of Transportation (PennDOT)
and Pennsylvania Turnpike Commission (PTC) roadways and associated
facilities is provided in Section 13.7 (Antidegradation and Post Construction
Stormwater Management Policy) of PennDOT Publication No. 13M, Design
Manual Part 2 (August 2009), as developed, updated, and amended in
consultation with the Pennsylvania Department of Environmental Resources
(DEP). As stated in DM-2.13.7.D (Act 167 and Municipal Ordinances),
PennDOT and PTC roadways and associated facilities shall be consistent
with Act 167 Plans. Dm-2.13.7.B (Policy on Antidegradation and Post
Construction Stormwater Management) was developed as a cooperative
effort between PennDOT and DEP. DM-2.13.7.C (Project Categories) discusses
the anticipated impact on the quality, volume, and rate of stormwater
runoff.
B.
Where standards in the Act 167 elements of the IWRP and this chapter
are impractical, PennDOT or the PTC may request assistance from DEP,
in consultation with the county, to develop an alternative strategy
for meeting state water quality requirements and the goals and objectives
of the Act 167 elements within the IWRP.
C.
For the purposes of the Act 167 elements in the IWRP and this chapter,
road maintenance activities are regulated under 25 Pa. Code Chapter
102.
A.
Predevelopment vs. post-development.
(1)
The peak discharge of the calculated post-development runoff to an
adjacent property shall be less than or equal to the calculated predevelopment
runoff. Pre- and post-development comparisons shall be made for all
points of impact.
(2)
The Type II twenty-four-hour storm distribution rainfall event values
are as follows:
|
Frequency
|
Rainfall1
(inch/24 hour)
| |
|---|---|---|
|
1
|
2.46
| |
|
2
|
2.98
| |
|
5
|
3.81
| |
|
10
|
4.55
| |
|
25
|
5.68
| |
|
50
|
6.67
| |
|
100
|
7.79
| |
|
1or latest NOAA data
|
(3)
Runoff calculations for the pre- and post-development comparison
shall be based upon the peak flow from a one-, two-, five-, ten-,
twenty-five-, fifty-, and one-hundred-year storm frequency. The peak
discharges and volumes of runoff shall be determined by using the
Modified Rational Method for watersheds less than 10 acres, and for
larger watersheds, the latest version of Technical Release No. 55,
Urban Hydrology for Small Watersheds, or an acceptable engineering
method, subject to Township approval.
(4)
Off-site areas which drain through a proposed development site are
not subject to release rate criteria when determining allowable peak
runoff rates. However, on-site, drainage facilities shall be designed
to safely convey off-site flows through the development site.
(5)
See Appendix C[1] for runoff coefficients and runoff curve numbers.
[1]
Editor's Note: Said appendix is included at the end of this chapter.
B.
Design storm for collection facilities.
(1)
The design of stormwater management collection facilities that service
drainage areas within the site shall be based upon the peak flow from
a twenty-five-year storm frequency event.
(2)
All developments shall include design provisions that allow for the
overland conveyance of the post-development one-hundred-year peak
flows through the site without damage to any private or public property.
C.
Method of calculations. Runoff calculations for on-site stormwater
conveyance facilities shall be based upon the Rational Method or an
acceptable engineering design method, subject to Township approval.
Hydraulic grade line calculations shall be provided to demonstrate
that inlet surcharging does not occur. When conveyance facilities
discharge directly to a basin, the basin shall be assumed to be one-third
full for the purpose of computing the hydraulic grade line for the
collection system.
D.
Criteria, methodology and assumptions. Appropriate values for time
of concentration, and rainfall intensity shall be from the latest
edition of the Commonwealth of Pennsylvania, Department of Transportation
Publication 584 (refer to Appendix No. 7).[2] Use of other criteria, methodology, assumptions, references,
calculation methods and/or computer modeling may be accepted, provided
detailed design information and programming with references are submitted
and approved by the Township.
[2]
Editor's Note: See also Appendix D included at the end of this chapter.
E.
Stormwater basins.
(1)
Retention basins and detention basins shall be designed with a minimum
one-foot freeboard above the design elevation of the one-hundred-year
water surface at the emergency spillway. Additionally, basins shall
be designed to safely discharge the one-hundred-year peak discharge
of a post-development storm event through an emergency spillway in
a manner which will not damage the integrity of the basin.
(2)
Basins shall not be located over any existing or proposed utility
line.
(3)
The Modified PULS Method of calculating routing or an acceptable
engineering design method, subject to Township approval, shall be
used for detention basins.
(4)
Basins shall be constructed and maintained to insure the design capacity
after sedimentation has taken place.
(5)
Basin discharge outlets shall be designed to release runoff in a
condition which reflects predevelopment characteristics.
(6)
Basins which are not designed to release all stormwater shall be
specifically identified as retention basins or permanent pond basins.
All other basins shall have provisions for de-watering, particularly
the bottom, and shall not create swampy and/or unmaintainable conditions.
Low-flow channels shall be used to de-water the bottom of a basin.
A minimum slope of 2% or a paved low-flow channel of at least 1% shall
be provided. Discharge structures shall be designed to eliminate the
possibility of blockage during operation.
(7)
Basins which are located in or adjacent to a residential zone and
viewed by the Township as a potential hazard to the public safety
shall be completely surrounded by a fence or wall of not less than
four feet in height. The fence or wall shall not have an opening or
gap larger than two inches and be provided with a self-closing and
self-latching gate.
F.
Earthfill dams.
(1)
Basins which are designed with earthfill dams shall be designed by
a registered professional engineer with experience in earth-filled
dams and shall incorporate the following minimum standards:
(a)
The maximum water depth (measured from the base to the crest
of the emergency spillway) shall not exceed six feet, unless approved
by waiver of the Township.
(b)
The minimum top width of all dams shall be five feet, unless
approved by waiver of the Township.
(c)
The side slopes of earthfill dams shall not be steeper than
three horizontal to one vertical on both sides of the embankment.
(d)
Basins without restricted access shall have impoundment areas
with side slopes no greater than five horizontal to one vertical.
(e)
A cutoff trench of impervious material shall be provided under
all dams.
(f)
All pipes and culverts through dams shall be reinforced concrete
and have properly spaced concrete cutoff collars.
(g)
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 and/or one foot above the five-hundred-year water surface.
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.
(2)
The Township may, upon recommendation of the Township Engineer, impose
additional requirements on earthfill dams for the safety and welfare
of the Township.
G.
Capacities. The capacities of the pipes, gutters, inlets, culverts,
outlet structures, and swales shall consider all possible hydraulic
conditions. The following are minimum design standards:
(1)
Grass swales and roadside gutters shall consider both the channel
velocity and stability.
(2)
The "n" factors to be used for paved or riprap swales or gutters
shall be based on the latest edition of the Pennsylvania Department
of Transportation's Publication 584.
(3)
The "n" factors for corrugated metal pipe shall be based upon the
manufacturer's standard. The use of corrugated metal pipe shall not
be allowed in areas prone to sinkholes.
(4)
The velocity to be used in the design of any piped stormwater conveyance
system shall be a minimum of 2 1/2 feet per second.
(5)
Inlets, culverts, and basin discharge systems shall be designed for
the worst case condition. Inlet capacity shall be based on design
standards provided by the latest edition of the Pennsylvania Department
of Transportation's Publication 584. If acceptable information is
not available, inlets in non-ponding areas shall be designed for a
maximum capacity of five cubic feet per second. Where ponding occurs,
inlet capacity shall be based on accepted engineering design practices.
Culvert design shall consider either inlet/outlet control or a combination
of hydraulic losses through the system, whichever is greater. In all
cases where drainage is picked up by means of a head wall, and inlet
or outlet conditions control, the pipe shall be designed as a culvert.
The minimum diameter of culvert shall be 18 inches. The procedure
contained in Hydraulic Engineer Circulars No. 5 and No. 13, as prepared
by the United States Department of Transportation, Federal Highway
Administration, Washington, D.C., shall be used for the design of
culverts. When a pipe or culvert is intended to convey the discharge
from a stormwater management facility, its required capacity shall
be computed by the Rational Method and compared to the peak outflow
from the stormwater management facility for the fifty-year storm.
The greater flow shall govern the design of the pipe or culvert. Basin
discharge systems shall be designed to the same standards as culverts.
If it cannot be readily determined which hydraulic condition controls,
the basin discharge rate shall be based on the highest possible discharge
rating curve with the basin capacity sized to store the excessive
storm runoff based on the lowest possible discharge rating curve.
H.
Stormwater flow along streets and access drives.
(1)
Inlets shall be along the curbline and are not permitted along the
curb radius at an intersection. When possible, inlets shall be located
away from the side lot property line to avoid conflicts with driveways.
For the purpose of inlet placement, curb, gutter, or roadside swale,
the ten-year storm frequency with a five-minute time-of-concentration
shall be used. Gutter spread shall not exceed 1/2 the travel lane.
(2)
Calculations shall be provided demonstrating the peak flow for the
ten-year frequency storm crossing the center line of a local road
or driveway intersection. The total top width of flow, including the
spread into the driveway or local road, shall not exceed eight feet.
(3)
In no case shall inlets be spaced more than 500 feet apart and function
at less than sixty-five-percent efficiency based on the criteria in
the PennDOT Design Manual.
I.
Manhole locations. Manholes shall not be spaced more than 500 feet
apart. Additionally, manholes shall be placed at points of changes
in the horizontal or vertical direction of storm sewers. Inlets may
be substituted for manholes where they will serve a useful purpose.
J.
Alignment requirement. If less than a forty-eight-inch pipe diameter,
curves in pipes or box culverts, without an inlet or manhole are prohibited.
Tee joints, elbows, and wyes are always prohibited.
K.
Minimum pipe size. Stormwater management pipe collection and conveyance
systems shall have a minimum diameter of 15 inches.
L.
Material specifications. All material and installations must comply
with the Township's Construction and Materials Specifications Manual.
M.
Surface flow characteristics. The maximum swale, gutter, or curb
velocity of stormwater runoff shall be maintained at levels which
result in a stable condition both during and after construction.
(1)
The following are considered characteristics of a stable condition:
(a)
It neither aggrades nor degrades beyond tolerable limits.
(b)
The channel banks do not erode to the extent that the channel
cross section is changed appreciably.
(c)
Sediment bars do not develop.
(d)
Erosion does not occur around culverts and bridges or elsewhere.
(e)
Gullies do not form or enlarge due to the entry of uncontrolled
stormwater runoff.
(2)
Grass-lined channels.
(a)
Grass-lined channels shall be considered stable if the calculated
velocity does not exceed the allowable velocities shown below:
[1]
Three feet per second where only sparse vegetation can be established
and maintained because of shade or soil condition.
[2]
Four feet per second where normal growing conditions exist and
vegetation is to be established by seeding.
[3]
Five feet per second where a dense, vigorous sod can be quickly
established or where water can be temporarily diverted during establishment
of vegetation. Netting and mulch or other equivalent methods for establishing
vegetation shall be used.
[4]
Six feet per second where there exists a well-established sod
of good quality.
(b)
Where swale bends occur, the allowable velocities listed above
shall be divided by the following factors:
|
Degree of Bend
|
Velocity
| |
|---|---|---|
|
0 to 30
|
1.50
| |
|
30 to 60
|
1.75
| |
|
60 to 90
|
2.00
| |
|
90 and over
|
2.50
|
(c)
The above grass-lined channel flows may be exceeded if the designer
can provide acceptable supportive design criteria as proof of erosion
prevention.
(3)
Where the velocity of stormwater runoff exceeds the allowable velocity,
erosion protection must be provided. The method of erosion protection
proposed must be supported by the appropriate design information and/or
references. The design of erosion protection shall be in accordance
with the requirements of the latest edition of the Pennsylvania Department
of Environmental Protection "Erosion and Sediment Control Best Management
Practice (BMP) Manual".
(4)
Sump pump discharges and, similarly, roof drains will be directed
to lawn areas away from residences, into areas that will surface drain
to conveyance structures (e.g., swales and storm sewer collection
systems). Sump pump discharges and roof drains shall not discharge
directly into collection systems located within a public right-of-way.
N.
Infiltration BMPs shall meet the following minimum requirements:
(1)
Infiltration BMPs intended to receive runoff from developed areas
shall be selected based on suitability of soils and site conditions
and shall be constructed on soils that have the following characteristics:
(a)
A minimum depth of 12 inches between the bottom of the facility
and the seasonal high water table and/or bedrock (limiting zones).
Limiting zones to be determined by probe hole excavation.
(b)
An infiltration and/or percolation rate sufficient to accept
the additional stormwater load and drain completely as determined
by field tests conducted by the owner's professional designer.
(2)
The recharge volume provided at the site shall be directed to the
most permeable soils feasible.
(3)
The recharge facility shall be capable of completely infiltrating
the impounded water within 72 hours.
(4)
A detailed soils evaluation of the project site shall be performed
to determine the suitability of recharge facilities. The evaluation
shall be performed by a qualified professional, and, at a minimum,
address soil permeability, depth to bedrock, susceptibility to sinkhole
formation, and subgrade stability. The general process for designing
the infiltration BMP shall be:
(5)
Extreme caution shall be exercised where infiltration is proposed
in geologically susceptible areas such as strip mine or limestone
areas. Extreme caution shall also be exercised where salt or chloride
would be a pollutant since soils do little to filter this pollutant
and it may contaminate the groundwater. It is also extremely important
that the design professional evaluate, the possibility of groundwater
contamination from the proposed infiltration/recharge facility and
recommend a hydro-geologic justification study be performed if necessary.
Whenever a basin will be located in an area underlain by limestone,
a geological evaluation of the proposed location shall be conducted
to determine susceptibility to sinkhole formations. The design of
all facilities over limestone formations shall include measures to
prevent ground water contamination and, where necessary, sinkhole
formation. The infiltration requirement in the high quality/exceptional
waters shall be subject to the Department's Chapter 93 and Antidegradation
Regulations. The Township may require the installation of an impermeable
liner in detention basins. A detailed hydro-geologic investigations
may be required by the Township.
(6)
The Township may require the Developer to provide safeguards against
groundwater contamination for uses which may cause groundwater contamination,
should there be a mishap or spill. It shall be the developer's responsibility
to verify if the site is underlain by limestone. The following note
shall be attached to all drainage plans and signed and sealed by the
developer's engineer/surveyor/landscape architect/geologist:
|
I, __________ certify that the proposed detention basin (circle
one) is/is not underlain by limestone.
|
(7)
Where pervious pavement is permitted for parking lots, recreational
facilities, non-dedicated streets, or other areas, pavement construction
specifications shall be noted on the plan.
O.
Phasing Plans. When applications are submitted in phases, and if
temporary facilities are required for construction of a phase, such
facilities shall be included in the submitted plans. All phases of
development must comply with the provisions of this chapter. In the
event temporary measures cannot adequately handle the stormwater runoff;
the main outfall line shall be included as part of the construction
of the proposed phase.
P.
Floodplain. All stormwater management plans shall conform with the
floodplain standards specified in the West Manchester Township Zoning
Ordinance, as amended.
Q.
Easements. When considered appropriate, easements shall be provided
where stormwater or surface water drainage facilities are existing
or proposed, whether located within or beyond the boundaries of the
property. Easements for maintenance of pipes and culverts shall run
from outlet to inlet. Normal lot grading will not require easements.
Swales which receive runoff from more than one other lot must be provided
with an easement. Easements shall have a minimum width of 30 feet
and shall be adequately designed to provide area for the collection
and discharge of water; the maintenance, repair, and reconstruction
of the drainage facilities; and the passage of machinery for such
work. Consideration should be given for wider easements where situations
warrant. The terms of the easement shall prohibit excavation, the
placing of fill or structures, and any alterations that may adversely
affect the flow of stormwater within any portion of the easement.
When considered appropriate, easements shall include a description
of an ownership and maintenance program, in a recordable form, that
clearly sets forth responsibility for all temporary and permanent
stormwater management facilities.
R.
Sinkhole-prone areas.
(1)
All stormwater management plans shall limit surface water runoff
and the intrusion of concentrated flow of surface water into the subsurface.
Facilities that are required as part of the stormwater management
plan shall include storm drains with watertight gasketed joint conduits
or adequately lined drainage swales and the collection of surface
water flow on pavements into drop inlets connected to a watertight
gasketed joint stormwater conduit or adequately lined drainage swales.
The stormwater conduit must discharge into lined detention basins.
(2)
Approved stormwater conduits include HDPE, PVC, and concrete, with
watertight rubber gaskets at each joint. The use of corrugated metal
pipe is not permitted. Construction of the piping system must follow
all other applicable ordinances. Where rock is encountered at or above
the planned conduit design grade the rock shall be undercut and over
excavated a minimum of one foot and backfilled with a compacted fine
grained soil.
(3)
All detention facilities in areas of sinkhole prone soil shall be
lined. The liner used in a detention basin may consist of a clay liner,
a composite synthetic and soil liner or a synthetic liner. The type
of liner required shall depend on the condition of the detention basin
bottom and the probability of sinkhole occurrence resulting from the
construction of the detention basin. The use of a low-flow channel
may also be required, depending on the duration and frequency of stormwater
discharge into the detention basin. Subsurface detention systems must
be in leak proof tanks or piping. The Township Engineer shall make
the final determination as to what is an acceptable form of liner
for the proposed detention basins.
(4)
Additional items that must be included in the stormwater management
plan include details with regard to the sealing of all pavement curbs
and gutters, manholes and drop inlets.
S.
Pennsylvania Department of Transportation. Any stormwater management
facility located on state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
T.
Waters of the commonwealth or wetlands. Any stormwater management facilities regulated by this chapter that would be located in or adjacent to waters of the commonwealth or wetlands shall be subject to approval by Pennsylvania DEP through the Chapter 105 process. When there is a question whether wetlands may be involved, it is the responsibility of the developer or his agent to show that the land in question cannot be classified as wetlands, otherwise approval to work in the area must be obtained from Pennsylvania DEP.
