A.
A stormwater management site plan shall be required for each subdivision, land development and regulated activity, unless exempted by § 172-29. The stormwater management site plan shall demonstrate effective control of stormwater runoff and compliance with the stormwater management requirements, standards and design criteria of this chapter. The stormwater management site plan shall be an integral part of each subdivision and land development plan at the preliminary and final plan stage. For the purposes of this section of the chapter, the following activities are defined as regulated activities and shall be considered as land development (in addition to subdivision and land development) for regulation by this chapter:
(1)
Construction of new or additional impervious or semipervious surfaces
(driveways, parking lots, etc.); and
(2)
Construction of new buildings or additions to existing buildings;
and
(3)
Diversion or piping of any natural or man-made stream channel; and
(4)
Installation of stormwater management facilities or appurtenances
thereto.
(5)
Alteration of conditions that may increase or alter natural drainage
from the existing site.
B.
Additionally, subdivisions, land developments, and regulated activities
shall be in compliance with all stormwater management plans within
East Hanover Township watersheds.
A.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this 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.
B.
On parcels regulated under this chapter, 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, and concurrence by the adjacent property
owner. Such stormwater flows shall be subject to the requirements
of this chapter.
C.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by SWM
BMPs or open channels consistent with this chapter.
D.
If diffused flow is proposed to be concentrated and discharged onto
adjacent property with permission from the receiving property owner,
the developer must document that adequate downstream conveyance facilities
exist to safely transport the concentrated discharge, or otherwise
prove that no erosion, sedimentation, flooding or other harm will
result from the concentrated discharge and downstream easements shall
be established to provide drainage paths for concentrated discharge,
maximum use shall be made of the existing on-site natural and man-made
stormwater management facilities.
E.
For all regulated activities, SWM BMPs shall be 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 (35 P.S. § 691.1 et seq.), and the
Storm Water Management Act (32 P.S. § 680.1 et seq.).
F.
Various BMPs and their design standards are listed in the Pennsylvania
Stormwater Best Management Practices Manual (BMP Manual).
G.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 172-29:
(1)
Preparation and implementation of an approved SWM site plan is required.
(2)
No regulated activities shall commence until East Hanover Township
issues written approval of an SWM site plan, which demonstrates compliance
with the requirements of this chapter.
(3)
The Township Engineer shall determine if an SWM site plan is required
or if an SWM site plan exemption is warranted.
H.
SWM site plans approved by East Hanover Township shall be on site
throughout the duration of the regulated activity.
I.
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.
J.
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 § 172-23 and the peak rate controls of § 172-25 do not need to be applied to existing impervious areas that are not being altered by the proposed regulated activity.
(4)
In all drainage areas where disturbance is taking place and new impervious
surface is added, up to 50% of the existing impervious area may be
utilized in the pre-development coverage calculation.
(5)
The anticipated flooded surface area occurring within the site shall
be considered as impervious.
K.
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)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(b)
Maintain or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of the commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(f)
To the maximum extent practicable, incorporate the techniques
for low-impact development practices described in the BMP Manual.
L.
The design of all facilities over karst geology shall include an
evaluation of measures to minimize adverse effects, such as sinkholes
and groundwater contamination.
M.
Infiltration BMPs should be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter.
N.
Normally dry, open top, storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not less than 24 and not more than 72 hours from the end of
the design storm.
O.
Those proposing regulated activities which do not fall under the exemption criteria provided in § 172-29, shall submit an SWM site plan, consistent with this chapter, to the East Hanover Township Engineer for review. In applying the exemption criteria set forth in § 172-29, the total proposed development is to be calculated, even if the development is to take place in phases. For the purposes of the exemption, impervious surface shall include, but not be limited to, any roof, parking or driveway areas and any new streets and sidewalks. Any areas designed to be gravel or crushed stone shall be assumed to be impervious for the purposes of the exemption criteria in § 172-29.
P.
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 DEP through the joint permit application
process or, where deemed appropriate by DEP, the general permit 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 DEP. A wetlands report, prepared
by a qualified professional, shall be submitted whenever wetlands
are disturbed.
Q.
Roof drains shall not be connected to streets, sanitary or storm
sewers or roadside ditches to promote overland flow and infiltration/percolation
of stormwater. When it is more advantageous to connect directly to
streets or storm sewers, then it shall be permitted on a case by case
basis by East Hanover Township.
R.
Stormwater management facilities, which involve a State Highway,
shall be subject to the approval of PennDOT.
S.
Minimization of impervious surfaces and infiltration of runoff through
seepage beds, infiltration trenches, etc., are encouraged, where soil
conditions permit, to reduce the size or eliminate the need for detention
facilities.
T.
Where a development site is traversed by watercourses other than
permanent streams, drainage easements shall be provided conforming
to the line of such watercourses. 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. Also, maintenance, including mowing of vegetation
within the easement shall be required, except as approved by the appropriate
governing authority.
U.
Title 25 Pa. Code, Chapter 105, Rules and Regulations, apply to the
construction, modification, operation or maintenance of both existing
and proposed water obstructions and encroachments throughout the watershed,
including work in wetlands. Inquiries on permit requirements or other
concerns shall be addressed to the DEP, Bureau of Waterways Engineering
in Harrisburg. Mailing Address: PA Department of Environmental Protection,
Bureau of Waterways Engineering, PO Box 8460, Harrisburg, PA 17105-8460.
Site Address: 400 Market Street, 3rd Floor Rachel Carson State Office
Building, Harrisburg, PA, 17101.
V.
When it can be shown that, due to topographic conditions, natural
drainageways on the site cannot adequately provide for drainage, open
channels may be constructed conforming substantially to the line and
grade of such natural drainageways. Work within natural drainageways
shall be subject to approval by DEP through the joint permit application
process, or, where deemed appropriate by DEP, through the general
permit process.
W.
Stormwater resulting from regulated activities shall not be discharged
into sinkholes.
X.
To the lowest extent possible, incorporate the techniques for low-impact
development practices described in the BMP Manual.
A.
East Hanover Township is located within the Swatara Creek Watershed.
The East Hanover Township Board of Supervisors have adopted standards
concerning design criteria for this watershed based on Lebanon County
guidelines and as recommended by Act 167, the Pennsylvania Storm Water
Management Act, 32 P.S. § 680.1 et seq.
B.
As of the adoption date of this chapter, the Swatara Creek Watershed
is considered to be the only stormwater management district in the
Township.
C.
Implementation of these provisions shall be subject to the following
requirements:
(1)
Post-development rates of runoff from any subdivision, land development,
or regulated activity shall meet the peak release rates of runoff
prior to development that are specified within the design criteria
and calculation methodology.
(2)
Stormwater runoff should not be transferred from one watershed to another. If a transfer cannot be avoided, the peak discharge limits of the receiving watershed shall be satisfied in accordance with Subsection A above.
(3)
Additional stormwater management districts may be established by
the East Hanover Township Board of Supervisors as new watershed or
sub-watershed studies are completed. Upon adoption of those new watershed
districts or plans by East Hanover Township, the applicable design
criteria within the watershed plan shall be satisfied by owners and
developers of the affected land.
(4)
Off-site areas. Off-site areas that drain through a proposed development
site are not subject to release rate criteria when determining allowable
peak runoff rates. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site for the
one-hundred-year event.
(5)
Site areas. Where the site area to be impacted by a proposed development
activity differs significantly from the total site area, only the
proposed impact area utilizing stormwater management measures shall
be subject to the management district criteria. In other words, unimpacted
areas bypassing the stormwater management facilities would not be
subject to the management district criteria.
(6)
Adequate erosion protection shall be provided along all open channels,
and at all points of discharge.
Stormwater management planning and stormwater management facilities
shall be designed and constructed in accordance with the following:
A.
General standards.
(1)
The design of all stormwater management facilities shall incorporate
sound engineering principles and practices.
(2)
All stormwater runoff flowing over the development site shall be
considered in the design of the stormwater management facilities.
(3)
Runoff from impervious areas shall be drained to pervious areas of
the development site and the stormwater management control facilities.
(4)
Stormwater runoff from a development site shall flow directly into
a natural watercourse, into an existing storm sewer system or onto
adjacent properties in a manner similar to the runoff characteristics
of the pre-development flow.
(5)
A concentrated discharge of stormwater to an adjacent property shall
be within an existing watercourse or storm sewer system and enclosed
within an easement. All discharges must be to stable areas or conveyances.
If the existing waterway or drainage system is not stable, a design
must be proposed that when implemented, will ensure a stable conveyance.
Downstream easements are required to be established to provide drainage
paths for concentrated discharge. Design and construction shall preclude
erosion, sedimentation, flooding or similar damage.
(6)
Where a development site is traversed by watercourses, drainage easements
shall be provided conforming to the line of such watercourses. 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. Also, maintenance,
including mowing of vegetation within the easement shall be required,
except within BMP areas where mowing is not desired. The drainage
easement shall adequately contain the anticipated inundation associated
with the identified one-hundred-year floodplain, or be depicted 50
feet from the top of the channel bank for undefined floodplain areas.
(7)
When it can be shown that, due to topographic conditions, natural
drainageways on the site cannot adequately provide for drainage, open
channels may be constructed conforming substantially to the line and
grade of such natural drainageways. Work within natural drainageways
shall be subject to approval by PADEP through the Chapter 105 permit
process, or, where deemed appropriate by PADEP, through the general
permit process.
(8)
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 PADEP, through the joint permit application
process or, where deemed appropriate by PADEP, the general permit
process. When there is a question whether wetlands may be involved,
it is the responsibility of the 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 PADEP.
(9)
Any stormwater management facilities regulated by this chapter that
would discharge to state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
Stormwater detention basins, retention basins, infiltration basins
and similar structures shall maintain a ten-foot isolation from PennDOT
right-of-way.
(10)
Minimization of impervious surfaces and infiltration of runoff
through infiltration beds, infiltration trenches, etc., is encouraged,
where soil conditions permit, to reduce the size or eliminate the
need for detention facilities.
(11)
Roof drains shall not be connected to streets, sanitary or storm
sewers or roadside ditches so as to promote overland flow and infiltration/percolation
of stormwater where advantageous to do so. When it is more advantageous
to connect directly to streets or storm sewers, then it shall be permitted
on a case by case basis, based upon adequate justification to be provided
by the applicant.
(12)
Stormwater management facilities and discharges shall not be
located within sinkhole prone areas of carbonate geology, including
areas containing sinkholes, closed depressions, fractured limestone
traces and limestone rock outcrops.
(13)
Stormwater facilities that are not located within a street right-of-way
shall be centered within an adequate easement of no less than 20 feet
in width. Easements shall follow property lines where possible and
are to be provided with metes and bounds descriptions that tie to
known points and shall close on individual lots.
(14)
A variety of methods for stormwater detention and retention
are available for use. These include surface detention, subsurface
detention, use of existing facilities (ponds, etc.) or a combination
thereof. Subsurface detention shall be utilized only where the subsurface
is stable, the area is not prone to sinkhole formation, and all underground
pipes are sealed to prevent leaks.
(15)
Storage of equivalent stormwater runoff for a portion of a property
may be considered in lieu of storage of generated runoff provided:
(a)
The site is located so that it is physically impossible to detain
runoff from the proposed facilities or drainage problems exist upgrade
that would impact upon the site or downgrade properties.
(b)
The impact of generated runoff discharging off site from the
subdivision or land development is determined by the Township Engineer
to be negligible and not detrimental to adjacent properties.
(c)
Implementation of equivalent storage shall be determined applicable
and feasible by the Township Engineer.
(16)
Storm sewer pipes, culverts, manholes, inlets, endwalls, endsections,
and other stormwater management facilities shall be designed and constructed
in accordance with the requirements of the Pennsylvania Department
of Transportation, Design Manual Part 2 Highway Design, Publication
13, including amendments thereto, unless specifications are otherwise
provided herein. Structures and their installation within or directly
connected to existing or intended public rights-of-way shall conform
to the current PennDOT Pub 72M, Roadway Construction Standards.
(17)
Headwalls and endwalls shall be used where stormwater runoff
enters or leaves the storm sewer horizontally from a natural or man-made
channel. PennDOT Type "DW" headwalls and endwalls shall be utilized.
Galvanized metal end sections are also acceptable, but polyethylene
flared end sections are prohibited. All headwalls and endwalls and
flared end sections with pipes of 12-inch or greater diameter shall
be protected from child entry by placing removable stainless steel
bars (and compatible mounting hardware), spaced four inches apart
across the opening.
Any stormwater management facility designed to store stormwater
runoff and requiring a berm or earthen embankment (i.e., detention
or retention basin) shall be designed to provide an emergency spillway
to handle the one-hundred-year post-development peak flow rate tributary
to the basin. The use of inlets and pipes are prohibited for the emergency
spillway. Stormwater runoff from existing natural swales and/or other
existing drainage conveyors shall not be directed towards or intercepted
by the stormwater management facilities. The height of embankment
must be set as to provide a minimum 1.0-foot of freeboard above the
maximum pool elevation computed when the entire one-hundred-year peak
flow rate to the structure passes through the spillway. Rain gardens,
with a maximum water depth of 12 inches, shall be exempt from this
requirement; however, conveyance of the one-hundred-year peak discharge
must be shown to be conveyed in a stable condition. The criteria for
design and construction of stormwater management facilities are not
the same criteria that are used in the permitting of dams under the
DEP Dam Safety Program. Depending upon the physical characteristics
of a dam, a dam permit may be required and the design will have to
meet the provisions of 25 Pa. Code Chapter 105. Depending on the physical
characteristics of a dam, the design could require that anywhere from
a one-hundred-year to a probable maximum flood (PMF) storm event be
considered. Retention and detention basins shall be designed and constructed
according to the following minimum standards:
A.
The maximum water depth to the base of the emergency spillway shall
not exceed six feet in residential areas. Depths up to eight feet
are permitted in nonresidential projects, provided minimum six-foot
high fencing is provided when depths exceed six feet.
B.
The minimum top width of dams shall be three feet for all impoundments
draining one acre or less, five feet for impoundments draining one
to five acres, and eight feet minimum width for impoundments with
drainage areas of or exceeding five acres.
C.
The side slopes of earth fill dams shall not be less than three horizontal
to one vertical on both sides of the embankment. However, any portion
of the inside berm of an unfenced basin above a proposed water depth
of three feet shall have a side slope of five horizontal to one vertical
or flatter. All pond areas, including bottoms of non-water quality
ponds, side slopes and top of berms, shall be provided with a minimum
four inches of topsoil and shall be mulched and seeded with formula
B in accordance with PennDOT publication 408, § 804. All
areas to receive topsoil should be scarified 12 inches deep before
topsoil placement.
D.
All basins shall be structurally sound and shall be constructed of
sound and durable materials. The completed structure and the foundation
of all basins shall be stable under all probable conditions of operation.
An emergency spillway shall be provided for the basin and shall be
capable of discharging the one-hundred-year peak rate of runoff which
enters the basin after development, in a manner which will not damage
the integrity of the facility and will not create a downstream hazard.
Where practical, the emergency spillway shall be constructed in undisturbed
ground. An easement for inspection and repair shall be provided when
the conveyance structure crosses property boundaries. Downstream drainage
easements from the emergency spillway may be required.
E.
A cutoff or key trench of impervious material shall be provided under
all basin berms.
F.
All discharge control devices with appurtenances (except discharge pipes) shall be made of reinforced concrete and stainless or hot dip galvanized steel. Bolts/fasteners are to be stainless or galvanized steel. Discharge pipes shall conform to the requirements of § 172-18.
G.
Concrete, polyethylene or welded galvanized steel anti-seep collars
compatible with the discharge pipe shall be placed around all basin
discharge pipes to increase the seepage length along the pipe by 15%
within the saturated zone of the pipe based on a 4:1 phreatic line.
The connection of the anti-seep collar to the discharge pipe shall
be completely watertight.
H.
Basin principal spillway outlet structures shall consist of stainless
steel orifice plates (and mounting hardware), galvanized or reinforced
concrete riser and discharge pipe, and welded structural steel inlet
grates (with a bituminous coating). Smooth lined corrugated polyethylene
pipe may be used for discharge piping. The use of PVC pipe is prohibited
for basin discharge piping except for small applications. Principle
spillways with riser pipes where the designed water depth is deeper
than 0.4 times the diameter of the riser, shall have an anti-vortex
device to prevent reduced capacity of the riser.
(Example, if the top of an 18 inches riser is 100.00, the riser
shall have an anti-vortex device if the water is higher than 100.00
+ [(18*0.4)/12] = 100.60). Materials used for design shall be specified
on the plans.
I.
All pipes and culverts through dams shall have properly spaced cutoff
collars or anti-seep collars.
J.
Minimum floor elevations for all structures that would be affected
by a basin or storm conveyance system shall be two feet above the
one-hundred-year water surface elevation.
K.
An emergency spillway shall be provided to safely pass the peak flow
rate of the incoming one-hundred-year storm, with one foot of freeboard
between the maximum pool elevation and the top of the embankment.
The maximum pool elevation shall be established using the weir equation
through the spillway while ignoring discharge flows from the principal
spillway and storage volume within the basin. Routing calculations
for rate control structures discharging to the ground surface shall
ignore exfiltration or infiltration discharges from the structure.
L.
Except for retention basins, permanent ponds and wetlands, all basins
shall have dewatering features such as low flow channels or tile fields.
Low flow channels shall be provided with reinforced matting extending
two feet beyond the channel. All detention basins shall include an
outlet structure designed to completely drain the basin within 24
hours following the end of the design rainfall. However, basins containing
groundwater recharge and/or water quality storage shall include an
outlet structure designed to fully drain the recharge and/or water
quality volume in no less than 24 hours or more than 72 hours.
M.
Basin discharges to proposed or existing conveyance systems shall
require evidence of adequate capacity in the receiving facility.
N.
The minimum slope of any detention basin bottom surface shall be
2% positive grade toward the outlet, along all flow paths except those
basins specifically designed to provide infiltration of stormwater
in conformance with the water quality standards of this chapter.
O.
Detention basin length or basin flow path length shall be at least
two times the basin width to facilitate water treatment and infiltration.
P.
In areas of carbonate geology, retention and detention basins shall:
(1)
Be placed at least 100 feet from the rim of any sinkhole or closed
depression; and
(2)
Be placed a minimum of 25 feet from rock outcroppings or pinnacles;
and
(3)
Not discharge into a sinkhole; and
(4)
Be designed and located to prevent groundwater contamination and
sinkhole formation, including the use of impermeable liners where
deemed necessary to avoid or abate such problems. The construction
of clay liners shall conform to the minimum requirements included
in the Appendix.[1]
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
(5)
Be constructed under the supervision of a professional engineer or
professional geologist licensed by the commonwealth. A professionally
sealed as-built construction report, and plan including relative dates,
name(s) of contractor(s), methods of construction, and verification
of conformance to plan specifications and good engineering practices
shall be provided to the East Hanover Township Planning Department
prior to bond reduction requests related to the basin(s).
Q.
Basins shall not be divided by a property line.
R.
Vertical pipes, inlets, and other surface water receiving structures
shall be installed with trash racks.
Pipes, curbs, gutters, manholes, inlets, headwalls, endwalls,
streets, and other stormwater conveyance facilities shall be designed
and constructed in accordance with the following:
A.
Pipes.
(1)
Pipe trenching and backfilling shall be in accordance with the requirements
of the Pennsylvania Department of Transportation, Publication 408
and Roadway Construction Drawings, current edition, unless manufacturer's
specifications and the Township Engineer authorize alternative procedures.
(2)
Pipe sizes and type shall be in accordance with the approved drawings.
Minimum pipe size for drainage facilities to be dedicated for municipal
ownership shall be 15 inches in diameter and the type shall be corrugated
galvanized metal pipe (CMP), smooth lined high density polyethylene
pipe (HDPEP), reinforced concrete pipe (RCP) or approved equivalent.
(3)
Pipes shall be constructed and set to line and grade as shown on
approved drawings. All pipes shall be laid on straight runs between
drainage structures.
(4)
Pipes shall be provided with a minimum of 12 inches of cover from
the top of pipe barrel to bottom of base course. In unpaved areas,
one foot of cover is required to the finished grade.
(5)
Backfilling shall be to four feet above the top of the proposed pipe
elevation or to subgrade, whichever is less, before excavating for
the pipe. Additionally, hauling shall not be permitted over pipe with
less than four feet of cover.
(6)
All pipe outlets shall be discharged to natural or man-made waterways
and shall be provided with reinforced concrete headwalls or pipe end
sections. Pipe outlets shall also be provided with an erosion resistant
material or energy dissipaters to calm the anticipated velocity and
discharge of stormwater.
(7)
Underdrains, pavement base drains, or combination storm sewer and
underdrains shall be provided at low points, cut sections, poorly
drained areas and other areas which, in the opinion of the Township
Engineer, are required to provide adequate subsurface drainage to
protect the integrity of the street.
(8)
All storm sewers which cross a street shall be perpendicular to the
street center line or within 30° of perpendicular. Vertical and
horizontal isolation conflicts with other utilities shall be avoided.
Storm sewers within a street shall not cross underneath a curb, especially
at curb radii locations.
(9)
A concentrated discharge of stormwater to an adjacent property shall
be within an existing watercourse or otherwise an easement shall be
required. Pipe outlets shall also be provided with erosion resistant
material or energy dissipaters to calm the anticipated velocity and
discharge of stormwater.
A.
Inlet tops shall be precast concrete top units conforming to the
Pennsylvania Department of Transportation, Publication 408, current
edition, and as detailed on the Roadway Construction Standards RC-45M
drawings providing an eight-inch curb reveal from the gutter grade
point. Type "C" inlets with 10 inches hoods that provide a two-inch
sump condition may be used with approval from the Township Engineer.
The maximum allowable spread of water shall be 1/2 of a through travel
lane. Design calculations are required to document the capacity and
spacing. Inlets shall be analyzed for collection efficiency and bypass
flows from upstream structures shall be accounted for in inlet spacing
design. The efficiency of storm inlets shall be supported with calculations
based on the FHWA HEC-22. Yard inlets and other nondedicated inlets
may be designed with alternative components, subject to Township Engineer
approval.
B.
All inlets over four feet in depth shall be provided with steps for
accessibility. Inlets shall be placed along the curbline, gutter line,
or edge of paving.
C.
All inlets in paved areas shall have bicycle safe grates.
D.
All inlets shall be constructed with concrete flow channels cast
in-place in the bottom of each inlet.
E.
Inlets and manholes shall not be spaced more than 400 feet apart.
Manholes or inlets are required at all points of horizontal or vertical
deflection.
All new catch basins located in street right-of-way must be
marked with high performance preformed thermoplastic markings. Two
layer combination with blue/white contrast. Bottom thermoplastic is
blue with top layer white. Markings to say "NO DUMPING!" on the first
line and "INTO STORM DRAIN" on the second line. Specify Pre-mark® PLUS storm drain marking, or equal. Size shall
be 29 inches by five inches.
All channels shall be lined with adequate channel lining material,
regardless of the designed velocity or shear stress. Maximum permitted
channel velocities are:
A.
Three feet per second where only sparse vegetation can be established.
B.
Four feet per second under normal conditions where vegetation is
to be established by seeding or sodding.
C.
Velocities may not exceed four feet per second for newly constructed
grass channels, unless appropriately designed and approved by the
Lebanon County Conservation District.
D.
For lined water-carrying channels, the following velocities are permitted:
(1)
Minimum six-inch rock riprap up to six f.p.s.
(2)
Minimum nine-inch rock riprap up to eight f.p.s.
(3)
Asphalt: up to seven f.p.s.
(4)
Durable bedrock: up to eight f.p.s.
(5)
Twelve-inch riprap: up to nine f.p.s.
(6)
Concrete or steel: up to 12 f.p.s.
(7)
The normal maximum velocity of open channel flows shall not exceed
10 f.p.s.
E.
The following conditions shall be met for all swales:
(1)
Swales shall be designed using Manning's equation. Vegetated swales
shall be designed based upon accepted "n" factors for the anticipated
degree of vegetative retardance. The maximum allowable velocity for
an established grass swale is four feet per second.
(2)
The "n" factors to be used for paved or rip-rap swales or gutters
shall be based upon accepted engineering design practices as approved
by the Township Engineer.
(3)
Swale side slopes shall be 2:1 minimum. Side slopes for grass covered
swales which will be mowed shall be 3:1 minimum.
(4)
All swales shall be designed to concentrate low flows to minimize
siltation and meandering.
(5)
All vegetated swales shall have a minimum slope of 1% unless approved
by the Township Engineer.
(6)
Swales shall be centered within a minimum twenty-foot wide easement.
A.
All streets shall be so designed to provide for the discharge of
surface water from their rights-of-way.
B.
The slope of the crown on proposed streets shall be of an inch per
foot. Slope of the center line grade shall be at least 1%. On curbed
streets, the right-of-way beyond the street shall be sloped toward
the street at of an inch per foot.
C.
Adequate facilities shall be provided at low points along streets
and where necessary to intercept runoff.
D.
Pipes and basin outlets shall not discharge directly onto or be conveyed
onto a public street.
E.
The maximum allowable spread of water on proposed streets shall be
1/2 of a through travel lane or one-inch less than the curb depth,
whichever is less.
F.
Driveway intersections with streets shall be designed so that street
flows are not diverted onto driveways.
G.
Water flows across street intersections shall not exceed one inch
in depth.
H.
Stormwater roof drains, sump pumps, and pipes, shall not directly
discharge water into a street right-of-way or discharge into a sanitary
sewer or storm sewer.
A.
Provisions for stormwater volume reductions are required for areas
being developed. Design of the stormwater BMPs shall give consideration
to providing groundwater recharge to compensate for the reduction
in the percolation that occurs when the ground surface is paved and
roofed over. These groundwater recharge measures are required wherever
feasible. Soils used for the construction of basins shall have low-erodibility
factors ("K" factors).
B.
The low impact development practices provided in the Pennsylvania Stormwater 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 B(1) or the Alternate Method in Subsection B(2) below.
(1)
The Design Storm Method (CG-1 in the Pennsylvania Stormwater BMP
Manual) is applicable to any size of regulated activity. See Appendix[1] for CG-1 Worksheets 1–5, which shall be used to
perform the required calculations. This method requires detailed modeling
based on site conditions.
(a)
Do not increase the post-development total runoff volume to
surface waters of the Commonwealth for all storms equal to or less
than the two-year twenty-four-hour duration precipitation.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
(2)
The Alternate Method provided below should only be used where the
volume control requirements of the Design Storm Method are not attainable.
See the Appendix[2] for Worksheets 7 and 8, which shall be used to perform
the required calculations.
(a)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(b)
At least the one-first inch of run off from new impervious surfaces
shall be permanently removed from the runoff flow (i.e., it shall
not be released into the surface waters of this commonwealth). Removal
options include reuse, evaporation, transpiration, and infiltration.
(c)
Wherever possible, infiltration facilities should be designed
to accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first one-half inch of the permanently
removed runoff should be infiltrated.
[2]
Editor's Note: Said appendix is included as an attachment to this chapter.
(3)
Stormwater Calculation Process (as outlined in the PADEP Pennsylvania
Stormwater Management Best Management Practices Manual, current version)
(a)
Stormwater Calculation Process - nonstructural BMPs.
[1]
Step 1: Provide General Site information (Worksheet 1).
[2]
Step 2: Identify sensitive natural resources, and if applicable,
identify which areas will be protected (Worksheet 2).
[3]
Step 3: Incorporate nonstructural BMPs into the stormwater design.
Quantify the volume benefits of nonstructural BMPs (Worksheet 3).
|
Proceed to design storm method.
|
(b)
For Design Storm Method:
[1]
Step 4: Estimate the increased volume of runoff for the two-year
storm event, using the soil cover complex Curve Number method. Combining
Curve Numbers for land areas proposed for development with Curve Numbers
for areas unaffected by the proposed development into a single weighted
curve number is NOT acceptable. Runoff volume should be calculated
based on land use and soil types (Worksheet 4).
[2]
Step 5: Design and incorporate structural and nonstructural
BMPs that provide volume control for the two-year volume increase
indicated on Worksheet 4. Provide calculations and documentation to
support the volume estimate provided by BMPs. For nonstructural BMPs,
provide nonstructural BMP checklists to demonstrate that BMPs are
appropriate. Indicate the volume reduction provided by BMPs (Worksheet
5). Note: If the designer is unable to incorporate the two-year volume
increase after all feasible BMP options have been considered, the
designer proceeds to the Alternate Method described below.
[3]
Step 6: Provide detailed routing analysis to demonstrate peak rate control for the one-year through one-hundred-year storm events. This routing should consider the benefits of BMPs. Provide additional detention capacity if needed. Note: there are no exemptions from the peak rate analysis except as permitted under § 172-29.
|
Proceed to Water Quality Calculations (Step 7). See § 172-24.
|
(c)
For Alternate Method:
[1]
Step 4: Capture the first two inches of runoff from all contributing
impervious surfaces. The first one-inch of runoff should be permanently
removed and not be released to the surface waters of the commonwealth.
The other one inch of runoff should be detained. Compute runoff volumes
using Worksheet 7.
[2]
Step 5: Design and incorporate structural and nonstructural
BMPs that provide permanent removal for the PRV and extended detention.
The removal options for PRY include reuse, evaporation, transpiration,
and infiltration. Infiltration for the first 0.5 inch is encouraged.
Documentation to support the computations for volumes can be provided
using Worksheet 8. For nonstructural BMPs, checklists can be used
to demonstrate that selected BMPs are appropriate. Indicate the volume
reduction provided by BMPs on Worksheet 8.
[3]
Step 6: Provide detailed routing analysis to demonstrate peak rate control for the one-year through one-hundred-year storm events. This routing should consider the benefits of BMPs. Note: There are no exemptions from the peak rate analysis except as permitted under § 172-29.
|
Proceed to Water Quality Calculations (Step 7). See § 172-24.
|
C.
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 24 inches between the bottom of the facility
and the seasonal high water table and/or bedrock (limiting zones).
(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 developer's/landowner's professional
designer.
D.
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:
(1)
Analyze hydrologic soil groups as well as natural and man-made features
within watershed to determine general areas of suitability for infiltration
practices.
(2)
Provide field test(s) to determine appropriate percolation rate and/or
hydraulic conductivity.
(3)
Design infiltration structure for required storm volume based on
field determined capacity at the level of the proposed infiltration
surface.
E.
Extreme caution shall be exercised where infiltration is proposed
in geologically susceptible areas such as 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 hydrogeologic
justification study be performed if necessary. Whenever an SWM BMP
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 SWM BMPs over limestone
formations shall include measures to prevent groundwater contamination
and, where necessary, instability resulting from sinkhole formation.
The Township may require the installation of an impermeable liner
in SWM basins. A detailed hydrogeologic investigation may be required
by the Township.
(1)
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.
(2)
It shall be the developer's responsibility to verify if the site
is underlain by limestone. The following note shall be attached to
all SWM site plans and signed and sealed by the developer's engineer/surveyor/landscape
architect/geologist:
______________________, certify that the proposed detention
basin (circle one) is/is not underlain by limestone.
F.
If the developer's professional consultant can prove through analysis
that the development site is located in an area underlain by carbonate
geology, and such geologic conditions would likely result in sinkhole
formations, then the site may be exempted from groundwater recharge
requirements. However, the development site shall be required to meet
all other hydrologic and water quality management standards as mandated
by this chapter.
G.
Where pervious pavement is proposed for parking lots, recreational
facilities, nondedicated streets, or other areas, pavement construction
specifications shall be noted on the plan.
H.
Recharge/infiltration facilities may be used in conjunction with
other innovative or traditional BMPs, stormwater control facilities,
and nonstructural stormwater management alternatives.
A.
Water quality calculations:
(1)
Step 7: Determine if the stormwater management design complies with
either the Design Storm Method or the Alternate Method. If volume
compliance is achieved under either of these methods, proceed to Step
8. If compliance is not achieved, proceed to Step 10.
(2)
Step 8: Determine if at least 90% of the disturbed site area is controlled
by a BMP (maximum disturbed, uncontrolled area of 10%). To be considered
"controlled" by a BMP, the disturbed area must either drain to a structural
BMP (or series of BMPs) or be offset by a preventive BMP, such as
reduced imperviousness or landscape restoration. If at least 90% of
the disturbed area is controlled, proceed to Step 9; else proceed
to Step 11.
(3)
Step 9: Total Suspended Solids (TSS) and Total Phosphorus (TP) requirements
are considered met. Demonstrate use of specific nitrate prevention/reduction
BMPs (Worksheet 10 in Appendix G). If the required BMPs (two primary
or four secondary or one primary and two secondary) are proposed within
the stormwater management plan, then the water quality requirement
for nitrate is achieved. If the required BMPs are not proposed, proceed
to Step 10.
(4)
Step 10: If volume control is not met using either the Design Storm
Method or Alternate Method, demonstrate use of specific BMPs for pollutant
prevention. Worksheet II in Appendix G.
(5)
Step 11: Estimate pollutant load from disturbed areas of the site,
excluding preventive measures (if proposed). Worksheet 12 in Appendix
G.
(6)
Step 12: Calculate pollutant load reductions with the proposed structural
BMPs. Worksheet 13 in Appendix G. If target load reductions are achieved
for TSS, TP, and nitrate, then the water quality requirements are
met.
A.
Stormwater runoff calculations for all development sites and regulated
activities shall be calculated in accordance with the following computation
methodologies:
B.
Accepted calculation methods.
|
Method (a)
|
Applicability
|
|---|---|
|
Soil Cover Complex Method
|
Acceptable for all watersheds (formerly SCS)Preferred for watersheds
> 10 acres and for use with detention basin routings
|
|
Rational Method
|
Acceptable for small watersheds and residential underground
absorption systems (see Storm Event Criteria below). Recommended for
watersheds <10 acres
|
|
TR-20, USDA Department of Environmental Protection
|
Acceptable for all watersheds, especially where full hydrologic
computer model is desired
|
|
HEC-1 U.S. Army Corps of Engineers
|
Acceptable for all watersheds, especially where full hydrologic
computer model is desired
|
|
(a)
|
Selection of the method of calculation by the design professional
shall be based upon the limitations and suitability of each method
for the development site. The Township Engineer should be consulted
for method alternatives and applicability.
|
C.
Storm event criteria.
(1)
All runoff calculations shall be completed in accordance with the
standard guidelines for the selected method of calculation.
(a)
Rational method. Rainfall intensities shall be obtained from
NOAA Atlas 14 or from the PennDOT Storm Intensity-Duration-Frequency
Chart provided in the Appendix.[1] Where stormwater runoff hydrographs are produced using
the Rational Method, the method shall be "modified" to create a triangular
hydrograph with the ascending leg of the hydrograph having a length
equal to three times the time of concentration (3xTc) and the descending
leg having a length equal to seven times the time of concentration
(7xTc) to approximate an SCS type II hydrograph. Alternate "modified"
rational methods shall be subject to acceptance by the Township Engineer.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
(b)
Soil cover complex method. The Soil Conservation Service Type
II, twenty-four-hour rainfall distribution shall be used in conjunction
with the rainfall depths from NOAA Atlas 14 or consistent with the
following table.
(2)
Established twenty-four hour rainfall depths for the various storm
events throughout East Hanover Township are:
|
Design Storm Frequency
(years)
|
Rainfall
(inches)
|
|---|---|
|
1
|
2.5
|
|
2
|
3.0
|
|
5
|
4.0
|
|
10
|
4.8
|
|
25
|
5.3
|
|
50
|
6.0
|
|
100
|
6.7
|
D.
Stormwater runoff control criteria. Stormwater management shall be
accomplished by controlling post-development runoff rates to pre-development
runoff rates for the storm events listed as follows:
|
Post-development Design Storm
(years)
|
Pre-development Design Storm
(years)
|
|---|---|
|
2
|
1
|
|
5
|
2
|
|
10
|
5
|
|
25
|
25
|
|
100
|
100
|
E.
Assumptions and criteria.
(1)
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 pre-development
and post-development rates for peak discharge of stormwater runoff
from the development site.
(2)
All pre-development calculations, unless in woodland, shall be based
upon the assumption of meadow in good hydrologic condition. Wooded
areas shall utilize forest/woodland cover coefficients. Where the
site contains existing impervious surface, up to 50% of the impervious
area may be considered as an existing pre-development condition. Runoff
coefficients and curve numbers shall be selected from the tables in
the appendix.
(a)
Drainage areas tributary to sinkholes or closed depressions
shall be excluded from the modeled analysis defining pre-development
flows. If left undisturbed during construction, activities areas draining
to closed depressions may also be removed from peak runoff rates and
post development analysis. New additional contributing runoff shall
not be directed to existing sinkholes or closed depressions.
(3)
Runoff calculations for the pre- and post-development comparison shall evaluate all stormwater events listed within the stormwater runoff control criteria § 172-25F.
(4)
Post-development analysis shall consider open areas of possible water
impoundments receiving rainfall (such as detention basins, rain garden,
etc.) to have an impervious cover area of the maximum surface storage
area of the water surface correlating to the storm event of interest.
(5)
Design of stormwater facilities shall be verified by routing the
storm event hydrographs through the facilities using the storage indication
method. Routings of rational method hydrographs shall determine the
critical duration corresponding to the highest peak water surface
elevation in the detention facility based on extended runoff inflows
for each control storm event, or consist of a methodology approved
by the Township Engineer. The combination of rational method hydrographs
based on timing shall be prohibited.
(6)
Pre- and post-development time-of-concentration paths shall be delineated
on topographic mapping with the end and beginning of segments clearly
identified as well as the lengths and corresponding end elevations
used for each segment. The post-development time-of-concentration
shall never be greater than the pre-development time-of-concentration
for any watershed or subwatershed. Times of concentration shall be
based upon the following:
(a)
The maximum length of overland sheet flow shall be 100 feet
before shallow concentrated or open channel flow develops and shall
be justified using the methodology presented in Chapter 3 of the NRCS
Technical Release 55 (TR-55) to include the following. For pre-development
conditions, the sheet flow Manning's n value of 0.24 (dense grasses),
0.40 (woods light underbrush) and 0.80 (woods dense underbrush) shall
be used. For post development sheet flow over proposed mowed areas
the Manning's n value shall be 0.15. All other Manning's n assignments
shall follow generally accepted standards.
(b)
Travel time for shallow concentrated flows shall utilize the
NRCS Methodology using the Velocity Factor Kv (NEH-4 Figure 15.2)
in feet/sec.; 20.3 (paved), 16.1 (unpaved), 15.0 (grassed waterway),
7.0 (short grass), 5.0 (woodland) and 2.5 (woodland with heavy litter).
|
The travel time is calculated as Tt = L/V and V = Kv*S1/2
|
|
Where:
| |
|
Tt = travel time (sec)
| |
|
L = length (ft)
| |
|
V = Velocity (ft/sec)
| |
|
Kv = applicable factor
| |
|
S = path slope (ft/ft)
| |
(c)
Overland flows which are concentrated within field depressions,
swales, gutters, curbs or pipe collection systems shall be designed
using Manning's Equation for time of concentration criteria for open
channel conditions between these design points using acceptable Manning's
n values.
(7)
Storm sewer pipes, culverts, gutters, inlets, outlets and swales
shall be designed and constructed in accordance with the standards
of the PADOT Design Manual, Part 2, Highway Design (latest edition),
including the following requirements:
|
Facility
|
Minimum Post Development Peak Discharge Requirements
|
|---|---|
|
Pipes, gutters and swales
|
10-year storm
|
|
Culverts and cross drains
|
25-year storm
|
|
Bridges and stream crossings
|
100-year storm
|
(a)
All stormwater collection facilities shall investigate and account
for bypass scenarios.
(8)
Swales shall be designed utilizing Manning's Equation to insure adequate
capacity, control of velocity and swale stability. Calculations shall
support swale stability for initial conditions (prior to established
vegetation) and long term conditions for the required peak flow rate.
Vegetated swales shall have a minimum longitudinal slope of 1% and
maximum side slopes of 3 to 1, unless specifically designed as a BMP
structure. Culvert design shall investigate, at a minimum, inlet,
barrel and outlet control conditions.
F.
Calculation process. A general procedure recommended for site evaluation
and stormwater design is as follows:
(1)
Evaluate factors influencing stormwater runoff, with a goal of limiting
earth disturbance, minimizing grading, and reducing or dispersing
impervious surfaces.
(3)
Meet water quality (BMP) standards, preferably with BMPs near the source of the runoff (see § 172-24).
(4)
Calculate and satisfy peak runoff objective, considering all measures
other than detention basins.
(5)
Size detention basins accordingly.
(6)
Demonstrate compliance with pre-development hydrograph requirements.
A.
Goals and objectives.
(1)
Preserve existing natural features, especially those which store,
infiltrate or filter water runoff.
(2)
Infiltrate rainfall to recharge the groundwater table.
(3)
Use physical (structural) and biological or vegetative (nonstructural)
filtration of water runoff to reduce pollutants and remove sediment.
(4)
Moderate water runoff velocities to minimize erosion and damage to
downstream aquatic habitat.
(5)
Integrate BMPs into the site layout to perform a water quality function
and compliment the developed use of the site.
(6)
Enhance site aesthetics through the use of a variety of BMP techniques
and components.
(7)
Maximize collection and treatment of small storm event (first flush)
stormwater runoff which contains the highest concentration of pollutants.
(8)
Utilize a system of BMP facilities and groundwater recharge devices
throughout the site.
B.
General standards.
(1)
Water quality shall be maintained through the requirement for BMP
design components for all subdivisions, land developments and regulated
activities within East Hanover Township, except where other provisions
of this chapter provide for plan or stormwater design exemptions.
Also exempted are minor subdivisions such as lot additions, lot revisions,
division of existing buildings and other plans where no new construction
or development is proposed. Revision or expansion projects requiring
land development approval with stormwater design shall include measures
to retrofit the site with BMPs to maintain or improve the water quality
of the stormwater discharges.
(2)
The required volume control, specified elsewhere herein, shall be
detained and treated within BMPs for all areas of the site to be developed.
(3)
Site designs shall minimize earth disturbance and the generation
of stormwater runoff while maximizing pervious areas for treatment
of stormwater.
(4)
All BMPs shall be sized to capture the required control volume, designed
according to the BMP criteria within this chapter, constructed properly
and maintained regularly.
(5)
Stormwater runoff which is directly discharged to wetlands, streams,
ponds, high quality or exceptional value watersheds or which originates
from land uses or activities with higher potential for pollutant loadings
(such as auto salvage yards, vehicle service areas, loading/unloading
areas, truck centers, etc.) may require the use of additional or specific
structural BMPs for pollution prevention and maintenance of water
temperatures and quality.
(6)
Place BMPs near the source of stormwater runoff and treat runoff
from impervious surfaces before mixing with runoff from less contaminated
sources.
(7)
Use native vegetation and water tolerant plants. Trees and shrubs
shall not be planted on stormwater facility embankments or in other
areas where roots may endanger pipes, headwalls, endwalls, spillway
structures or other structural facilities.
(8)
All impervious area runoff shall be directed to BMPs. The volume
control shall be provided within each watershed or sub watershed to
provide the intended treatment for upstream runoff. Volume control
credit will not be allowed toward noncontributing runoff areas.
(9)
BMP categories used within these regulations are 1) Ponds 2) Wetlands
3) Infiltration Systems 4) Filtering Systems, and 5) Open Channels.
The Design Criteria subsection listed hereafter provides specific
descriptions of the BMPs within these classifications. Where effectiveness
can be demonstrated, alternative BMP designs and concepts may be utilized.
(10)
Site designs shall include measures to reduce stormwater velocities
and collect sediment near the source of the water runoff so that BMPs
can be effective in treating water quality and maintenance can be
reduced. Recommended facilities are forebays, energy dissipaters,
outlet stabilization structures, inlet protection devices, level spreaders,
and flow splitters.
(11)
"A" type soils (very permeable) may require installation of
a clay, bentonite or poly liner where water retention is designed,
such as with ponds and wetlands.
(12)
Carbonate geology (limestone or dolomite bedrock) areas require
careful evaluation for appropriate BMP design. Facility depths should
be minimized and liners may be required.
(13)
Forebays and micropools are recommended for ponds and required
for wetlands. Forebays and micropools should each contain approximately
10% of the required water volume. Forebays should be at least 10 feet
long and be baffled from the main basin with a berm of rip rap or
similar material, to a depth of one foot below the water quality volume
level, to ensure an indirect flow path. Additionally, when forebays
are used, a minimum of 90% of the discharge into the facility shall
be directed into the forebays.
(14)
All ponds and wetlands shall be surrounded by a riparian buffer
strip of a minimum 25 feet in width. Streams shall be bordered by
a riparian buffer strip, a minimum of 25 feet or the width of the
floodplain, whichever is greater.
(15)
Planting of wetland plants is required within created wetlands
and encouraged in ponds and other applicable BMPs. Fringe wetland
plants may be used on aquatic benches or within shallow pools, while
emergent wetlands vegetation should be planted alongside slopes and
facility edges.
(16)
Infiltration, filtering or other BMP systems which are designed
to treat the required control volume from small storms shall be preceded
by a flow splitter or equivalent bypass device to route larger water
volumes around the system.
(17)
All underground stone and sand BMP systems shall be lined with
geotextile fabric on the sides, bottom and top, (double layer on top)
have a level (flat) bottom, be underlain by a minimum of two feet
of soil or sand above the seasonal high water table and be placed
a minimum of 10 feet horizontally from building foundation walls.
(18)
Infiltration systems with stone shall utilize AASHTO No. 1 or
AASHTO No. 3 stone and assume a maximum of 40% voids area.
(19)
Grass swales should be designed with a flat channel bottom at
least two feet in width, with a longitudinal slope of one to 2%. If
grass swale slopes exceed 4%, check dams or similar water velocity
modifiers should be used.
C.
Design criteria.
(1)
The following site factors should be considered in selecting and
designing the appropriate BMPs:
(2)
The following factors should be evaluated when determining the suitability
of BMPs for a development site:
(a)
Peak discharge and required volume control.
(b)
Stream bank erosion.
(c)
Efficiency of the BMPs to mitigate potential water quality problems.
(d)
The volume of runoff that will be effectively treated.
(e)
The nature of the pollutant being removed.
(f)
Maintenance requirements.
(g)
Creation/protection of aquatic and wildlife habitat.
(h)
Recreational value.
(i)
Enhancement of aesthetic and property value.
D.
Examples.
(1)
Ponds (Basins) are enhancements to conventional detention basins,
usually containing a pool of water to perform the BMP function of
capturing pollutants to improve the water quality of the discharge.
Specific pond types and guidelines are:
(a)
Wet retention pond. A permanent pool of standing water, normally
containing a perimeter aquatic bench of six inches to 18 inches in
depth, where pollutants are removed through sedimentation and plant
absorption.
(b)
Extended detention pond. A basin designed to temporarily hold
stormwater for an extended period of time to facilitate physical settling
of pollutants. These facilities may be normally dry, contain a shallow
marsh, have a small wet pool, and often contain a combination of these
features. Extended detention ponds usually include a vegetated forebay
that is baffled from the main basin with a rip rap mound, a small
sized outlet for the water quality storm discharge, a primary outlet
for large storm events and a benched basin for varying water depths.
(c)
Multiple pond. A pond system containing a series of two or more
pools or cells to create a longer pollutant removal pathway.
(d)
Rain garden. An excavated shallow (maximum pending depth of
12 inches) surface depression planted with specially selected native
vegetation to treat and capture runoff.
(2)
Wetlands may be constructed to contain an environment of shallow
marsh where pollutants can be removed through a combination of settling,
absorption, retention, plant uptake and biological decomposition.
Wetland designs are best suited for larger watersheds and must be
accompanied by a landscaping plan which specifies plant species, planting
arrangement, bed preparation and operation/maintenance requirements.
Additionally, wetlands shall be planted with three or more plant species
for diversity and survival, plus at least 50% of the wetland area
must be planted and maintained in plant cover. Specific wetland types
and guidelines are:
(a)
Shallow wetlands. These systems are configured with several
varying levels of marsh areas, containing a meandering water pathway
from the forebay to a micropool at the outlet. Water depths usually
range from six inches to 18 inches.
(b)
Pocket wetlands. Wetlands for small locations where a seasonal
high water table is needed to help sustain the water elevations.
(3)
Infiltration systems are designed to capture stormwater runoff and
infiltrate it into the ground. These systems are best adapted for
small drainage areas and effectively reduce runoff volume, remove
many pollutants, recharge the groundwater and contribute to maintaining
stream baseflows. Specific infiltration system types and guidelines
are:
(a)
Infiltration trench. Shallow excavations that are lined with
geotextile fabric and filled with stone to create an underground water
reservoir, which gradually percolates into the surrounding subsoil.
Infiltration trenches are especially useful for connection to roof
drains. Larger trenches will require an under drain to a stormwater
conveyance system.
(b)
Infiltration basin. A large, open depression (basin), which
collects stormwater for percolation. The basin surface should be vegetated
with deep rooted plants to enhance infiltration. Soils, slope, geology
and hydrogeology may restrict use of these basins.
(c)
Porous pavement. Low traffic or overflow parking areas may be
designed with porous pavement, a porous asphalt layer which permits
runoff to drain into an underground stone area where it can infiltrate
into the subsoil.
(d)
Depressed pervious area. These facilities are useful for capturing
runoff within a parking lot island. They are designed lower than the
surrounding areas, contain permeable soils with a filtration system
or a beehive drain and often contain an underdrain for excess runoff.
Plants, shrubs and trees enhance performance and aesthetics. Contributing
parking areas require curb cuts, curbs with weep holes or similar
design to facilitate runoff discharge to the pervious area.
(4)
Filtering systems are effective for filtering sediment and other
pollutants from runoff by passing it through sand, soil, sand/soil
mix, vegetation, a structural filter or any combination thereof. Filtered
runoff is then infiltrated or drained to other on-site facilities.
These systems may be integrated into landscaped areas and parking
islands where plantings will add aesthetic enhancements. Specific
filtering system types and guidelines are:
(a)
Sand filter. An underground chamber or bed with sand designed
to filter pollutants as water drains through it, with an underdrain
system for discharge of the filtered water to a stormwater conveyance
system.
(b)
Bioretention system. These designs utilize a mixture of sand
and permeable soil underneath a planted, landscaped depression to
collect and treat surface water runoff. Bioretention areas are especially
advantageous for parking lot islands and snow storage locations.
(c)
Riparian buffer strip. Along streams, wetlands and ponds, an
area of land which is vegetated with a combination of trees, shrubs
and herbaceous plants. This land strip is designed to protect the
water resource by filtering pollutants, improving the habitat and
cooling the waterways by shading. The riparian buffer strip shall
include the one-hundred-year floodplain, or be a minimum of 25 feet
wide from the edge of the normal water level, whichever is greater.
(d)
Vegetated filter strip. These BMPs are characterized by grass
or low growing vegetation on a uniformly sloped area which is designed
to intercept sheet flow water runoff between an impervious surface
and the stormwater conveyance facilities. Vegetated filter strips
reduce water velocities and trap sediment and pollutants. They require
good vegetation and soil permeability and should be avoided on steep
slopes. They are best used along small parking lots, should be a minimum
of 20 feet wide in the direction of water flow, and normally are designed
equal in size to the impervious area draining to the filter strip.
(e)
Vegetated swale. A broad, shallow, low gradient swale with a
dense stand of medium height vegetation, which is designed to trap
pollutants and promote infiltration.
(f)
Water quality inlet. Underground boxlike structure, such as
an oil/grit separator, which is used to remove sediment and hydrocarbons
from water runoff originating from parking lots and heavy traffic
areas with the potential for petroleum discharges. These facilities
are used close to the source of the runoff and currently include other
products such as Stormceptor and Vortechnics.
(5)
Open channels convey, filter and percolate stormwater runoff. They
are often used as an alternative to, or component of, a storm sewer
system. Specific open channel types and guidelines are:
(a)
Grass swale. Grass swales filter pollutants as stormwater runoff
is drained to other areas. These facilities are best combined with
other BMPs and may include check dams or minor depression storage
to reduce water velocity and encourage infiltration. An underbedding
of mixed sand and soil with a pipe or stone underdrain will improve
the use for infiltration and groundwater recharge.
(b)
Lined channel. Rip rap, concrete or other erosion resistant
material may be used to line a channel to prevent scouring and degradation
of a water carrying channel.
(6)
Additional information and requirements. The information, guidelines
and requirements of this section of this chapter are intended to provide
guidance in the design, construction, operation, and maintenance of
BMPs to protect water quality throughout East Hanover Township. It
is recognized that BMP technology is relatively new and, therefore
subject to continuing modifications and improvements. As such these
regulations provide for considerable design flexibility, provided
the design is consistent with the standards listed in this chapter.
Additionally, it is further intended that comprehensive handbooks
and design manuals for BMPs shall be utilized and relied upon for
guidance. Recommended sources of information are as follows:
(a)
Pennsylvania Stormwater Best Management Practices Manual, effective
date December 30, 2006.
(b)
2000 Maryland Stormwater Design Manual, Volumes I and II, prepared
by the Maryland Department of the Environment.
(c)
Minnesota Urban Small Sites BMP Manual, printed July 2001 by
the St. Paul Metropolitan Council Environmental Services.
(d)
D.E.P. Erosion and Sedimentation Pollution Control Program Manual,
dated March 2000 from PA DEP.
[Amended at time of adoption of Code (see Ch. 1, General
Provisions, Art. I)]
All subdivision and land development plans which propose earthmoving
activity shall include erosion and sediment pollution control design
to satisfy the requirements of Chapter 102 Pennsylvania Department
of Environmental Protection 25 Pa. Code Chapter 92a and/or 102 and
the PA Clean Streams Law (35 P.S. § 691.1 et seq.) and to
prevent soil erosion, sediment and other pollutants from entering
streams, lakes and neighboring properties. In order to demonstrate
and maintain compliance with erosion and sediment pollution control
requirements, subdividers and land developers shall:
A.
Prior to earth moving or subdivision/land development plan approval,
obtain erosion and sediment pollution control design approval from
the Lebanon County Conservation District.
B.
Obtain applicable NPDES approvals or permits through the Lebanon
County Conservation District and the PA DEP, and maintain plans and
permits on site.
C.
Install required erosion and sediment pollution control facilities
prior to the start of construction and maintain said facilities during
the construction period.
D.
Preserve and protect natural vegetation where possible.
E.
Adhere to approved erosion and sediment pollution control design
requirements and NPDES standards.
F.
Inspect weekly and after each runoff event and maintain all erosion
and sediment pollution control facilities to insure their effectiveness.
Accumulated sediment shall be promptly removed and disturbed areas
shall be reseeded or stabilized.
G.
Design, install and maintain facilities in accordance with the PA
DEP Erosion and Sediment Pollution Control Program Manual, March 2000,
as amended.
H.
Include standard erosion and sediment control notes on all plans,
as per the list within the Appendix.[1]
[1]
Editor's Note: Said Appendix is included as an attachment to this chapter.
J.
Construction of temporary roadways (for utility construction, timber
harvesting, etc.) shall comply with all applicable standards for erosion
and sedimentation control and stream crossing regulations under 25
Pa. Code Chapters 102 and 105. The erosion and sedimentation control
plan shall be submitted to the Lebanon County Conservation District
for approval and shall address the following, as applicable:
(1)
Design of roadway systems, including all roads, skid roads, landing
areas, trails, and storage and staging areas.
(2)
Runoff control structures (e.g., diversions, culverts, detention
ponds, etc.).
(3)
Stream crossings for both perennial and intermittent streams.
(4)
Access to public roadways, including design of rock construction
entrance for mud and debris control.
(5)
A remediation plan for restoring the disturbed area through re-grading,
topsoil placement, reseeding, and other stabilization techniques as
required.
K.
Additional erosion and sedimentation control design standards and
criteria that must be applied where infiltration BMPs are proposed
include the following:
(1)
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase, as to maintain their
maximum infiltration capacity.
(2)
Infiltration BMPs shall be protected from receiving sediment laden
runoff.
(3)
The type of protection for infiltration BMPs shall be identified
(i.e., orange construction fence surrounding the perimeter of the
BMP).
L.
Maintenance during development of a project shall be the responsibility
of the developer and/or landowner and shall include, but not be limited
to:
(1)
Removal of silt and debris from basins, traps, inlet protection,
silt fencing, or other structures or measures when capacity of those
structures is reached.
(2)
Periodic maintenance of temporary control facilities such as replacement
of straw bale dikes, straw filters or similar measures.
(3)
Establishment or reestablishment of vegetation by seeding and mulching
or sodding of scoured areas or areas where vegetation is not successfully
established.
(4)
Installation of necessary controls to correct unforeseen problems
caused by storm events within design frequencies.
(5)
The contractor or developer shall be responsible for removal of all
temporary measures and installation of permanent measures upon completion
and stabilization of the project.
M.
Total maximum daily load (TMDL) requirements.
(1)
Agricultural activities contributory to a watershed within East Hanover
Township containing an established nonpoint source (agriculture) TMDL,
shall be conducted in compliance with Chapter 102 (Erosion and Sediment
Control), Chapter 91, § 91.36 (general provisions related
to manure management) and Act 38 (3 Pa.C.S.A. § 501,
nutrient management).
(2)
This section shall apply to agricultural activities conducted in
watersheds where TMDLs are established in the future.
