A.
Regulated activities are subject to the following permitting requirements:
(1)
Regulated activities that propose up to 500 square feet of new
impervious qualify to pay a fee in lieu of completing a stormwater
management plan. Payment of a fee does not alleviate the applicant
from the management of stormwater or the regulatory requirements of
this chapter. This fee shall be determined by resolution.
(2)
Regulated activities that propose 501 to 2,000 square feet of
new impervious area qualify for utilization of the small projects
guide contained within this chapter. See Appendix D.[1]
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
(3)
Regulated activities that propose greater than 2,000 square feet of new impervious area shall be required to submit a stormwater management plan that meets the requirements set forth in § 265-401.
(4)
No regulated activities shall commence until the municipality
issues written approval of a SWM site plan or other applicable authorization
which demonstrates compliance with the requirements of this chapter.
B.
SWM site plans approved by the municipality in accordance with § 265-406, shall be on-site throughout the duration of the regulated activity.
C.
The municipality 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.[2]
[2]
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 (e.g., during construction beginning with initial topsoil removal and through the conversion and operation of all post-construction stormwater management 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. Note: See § 265-1001D.), No. 363-2134-008, as amended and updated.
E.
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 stages.
(2)
For development taking place in stages, 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 § 265-303 and the peak rate controls of § 265-304 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
F.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written approval
of the adjacent property owner(s). Such stormwater flows shall be
subject to the requirements of this chapter. Water discharges cannot
be discharged within 10 feet of the property line unless there is
an existing easement or approval from the neighboring property owner
is obtained.
G.
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:
(3)
Incorporate methods described in the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual. Note: See § 265-1001C.). If methods other than green infrastructure and LID methods are proposed to achieve the volume and rate controls required under this chapter, the SWM site plan must include a detailed justification demonstrating that the use of LID and green infrastructure is not practicable.
H.
The design of all facilities over karst geology shall include an
evaluation of measures to minimize adverse effects.
I.
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.
J.
Normally dry, open-top, storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not more than 72 hours from the end of the design storm.
K.
The design storm volumes to be used in the analysis of peak rates
of discharge should be obtained from the latest version of the Precipitation-Frequency
Atlas of the United States, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland. NOAA's Atlas 145 can be accessed
at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
L.
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.[3] Various BMPs and their design standards are listed in the BMP Manual. (Note: See § 265-1001C.)
[3]
Editor's Note: See 35 P.S. § 691.1 et seq.
and 32 P.S. § 680.1 et seq., respectively.
M.
Financial security for the completion of stormwater management facilities is set forth in § 265-408 of this chapter.
N.
Prior to the full release of financial security, the applicant shall
be responsible for providing a record plan of all stormwater management
facilities included in the approved stormwater management plan. The
record plan and an explanation of any discrepancies with the design
plans shall be submitted to the municipality or its designee for final
approval. The record plan shall include a final certification as required
by Chapter 102 from an engineer, landscape architect, surveyor, or
other qualified person registered in the Commonwealth of Pennsylvania.[4]
[4]
Editor's Note: See 25 Pa. Code Chapter 102.
A.
Agricultural activity is exempt from the SWM site plan preparation
requirements of this chapter, provided that the activities are performed
according to the requirements of 25 Pa. Code Chapter 102.
B.
Forest management and timber operations are exempt from the SWM site
plan preparation requirements of this chapter, provided that the activities
are performed according to the requirements of 25 Pa. Code Chapter
102.
C.
The use of land for domestic (i.e., for a single individual dwelling
unit) gardening and landscaping is exempt from specific approval and
permitting under this chapter so long as such activities comply with
all other applicable ordinances and statutes.
E.
The municipality may deny or revoke any exemption pursuant to this
section at any time for any project that the municipality believes
may pose a threat to public health and safety or the environment.
Green infrastructure and low-impact development practices provided in the BMP Manual (Note: See § 265-1001C.) shall be utilized for all regulated activities wherever possible. Water volume controls shall be implemented using the design storm method in Subsection A or the simplified method in Subsection B below. This chapter establishes that only the design storm method may be used for regulated activities that add greater than 1/2 acre of new impervious area or disturb greater than one acre of total area.
A.
The design storm method (CG-1 in the BMP Manual. Note: See § 265-1001C.) 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.
(2)
For modeling purposes:
(a)
Existing (predevelopment) nonforested pervious areas must be
considered meadow in good condition.
(b)
Twenty percent of existing impervious areas to be disturbed
by the project, when present, shall be considered meadow in good condition
in the model for existing conditions. Regulated activities not requiring
an NDPES permit are exempt from this requirement.
B.
The simplified method (CG-2 in the BMP Manual. Note: See § 265-1001C.) provided below is independent of site conditions and should be used if the design storm method is not followed. This method is not applicable for regulated activities that add greater than 1/2 acre of new impervious area or for projects that require routing 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 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 runoff should be infiltrated.
A.
For computation of predevelopment peak discharge rates, 20% of existing
impervious areas to be disturbed by the project, when present, shall
be considered meadow. Regulated activities not requiring an NDPES
permit are exempt from this requirement.
B.
For areas not covered by a release rate map from an approved Act
167 Stormwater Management Plan: Post-development discharge rates shall
not exceed the predevelopment discharge rates for the one-, two-,
five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour
storm events. If it is shown that the peak rates of discharge indicated
by the post-development analysis are less than or equal to the peak
rates of discharge indicated by the predevelopment analysis for one-,
two-, five-, ten-, twenty-five-, fifty-, and 100-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.
C.
For areas covered by a release rate map from an approved Act 167
Stormwater Management Plan: For the one-, two-, five-, ten-, twenty-five-,
fifty-, and 100-year, twenty-four-hour storm events, the post-development
peak discharge rates will follow the applicable approved release rate
maps. For any areas not shown on the release rate maps, the post-development
discharge rates shall not exceed the predevelopment discharge rates.
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.
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.[2]
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.
G.
Septic drainfields and sewage disposal systems shall not be permitted
within the riparian buffer easement and shall comply with setback
requirements established under 25 Pa. Code Chapter 73.
H.
With the exception of plans that qualify as small projects, riparian
buffers shall be established, enhanced, protected, and maintained
to the greatest extent possible in accordance with the Spring Garden
Township Floodplain Ordinance.[3] All applicable PADEP credits for the implementation of
such buffers may be utilized to meet the requirements of this chapter.
The applicant shall provide all applicable PADEP modules and calculations
when such credits are requested.
I.
Riparian buffers shall meet all applicable dimension requirements
per the Spring Garden Township Floodplain Ordinance. Riparian buffers
are shall be the greatest of 75 feet from the tops of banks of watercourses,
75 feet from boundaries of wetlands, or 25 feet from boundaries of
floodplains, unless more restrictive dimensional requirements are
applicable by PADEP. When these areas are part of a property being
subdivided, developed or redeveloped, to the maximum extent physically
possible, they shall be established, enhanced and/or maintained as
riparian forest buffers to comply with the PA-DEP Riparian Forest
Buffer Guidance.
J.
Riparian buffers are not required for streams which are not hydraulically
connected to the project's drainage area and do not receive runoff
from the project or from any proposed post-construction stormwater
management BMPs.
A.
Off-site areas. 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.
B.
On-site areas. On-site areas proposed to remain undisturbed as part
of the regulated activity, including previously developed areas, shall
be considered as existing conditions.
C.
Downstream hydraulic capacity analysis. Any existing downstream capacity
hydraulic analysis shall be conducted in accordance with this chapter.
(1)
All downstream facilities impacted by the total site area of
the regulated facility shall be studied to determine if the facility
has adequate capacity to handle existing and proposed flows. An impacted
downstream facility is one in which the runoff from the total site
area of the regulated activity comprises more than 50% of the total
flow to such a facility. The study shall end at a perennial stream
unless directed otherwise by the Municipal Engineer. Downstream facilities
include, but are not limited to, man-made or natural swales and open
channels, pipes, inlets, culverts, bridges, and roadways.
(2)
If any private facility is found to be undersized, the applicant
shall be responsible for updating the facility in coordination with
the regulated activity.
(3)
If any public facility is found to be undersized or inadequate,
the applicant shall work with the municipality or state agency on
upgrading the facility in coordination with the regulated activity.
D.
Regional detention alternatives. For certain areas within the study
area, it may be more cost-effective to provide one control facility
for more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives are the responsibility of
prospective developers. The design of any regional control basins
must incorporate reasonable development of the entire upstream watershed.
The peak outflow of a regional basin would be determined on a case-by-case
basis using the hydrologic model of the watershed consistent with
protection of the downstream watershed areas. "Hydrologic model" refers
to the calibrated model as developed for the stormwater management
plan.
E.
Capacity improvements of local drainage networks. In certain instances, local drainage conditions may dictate more stringent levels of runoff control than those based upon protection of the entire watershed. In these instances, if the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then the capacity improvements could be provided by the developer in lieu of runoff controls on the development site. Any capacity improvements would be designed based upon development of all areas tributary to the proposed improvement and the capacity criteria specified in § 265-308. In addition, all new development upstream of a proposed capacity improvement shall be assumed to implement the applicable runoff controls consistent with this chapter except that all new development within the entire subarea(s) within which the proposed development site is located shall be assumed to implement the developer's proposed discharge control if any.
F.
Capacity improvements may also be provided as necessary to implement
any regional or subregional detention alternatives.
G.
Where the potential for groundwater and/or surface water contamination
exists, based on the proposed use of the regulated activity, safeguards
shall be incorporated into the site.
H.
Roof drains and sump pumps shall discharge to infiltration or vegetative
BMPs and, to the maximum extent practicable, satisfy the criteria
for DIAs.
I.
Stormwater runoff shall not be transferred from one watershed to
another unless the watersheds are subwatersheds of a common watershed
that join together within the perimeter of the property. The transfer
of watersheds may be permitted in the event the transfer does not
alter the peak discharge onto downstream lands, or drainage easements
are acquired from the affected landowners.
J.
All storm sewer pipes, culverts, bridges, gutters, and swales (excluding
outfall structures from stormwater management facilities) conveying
water originating only from within the boundaries of the project site
shall be designed for a twenty-five-year storm event. All other storm
sewer pipes, culverts and bridges, gutters and swales (excluding detention
and retention basin outfall structures and excluding sole access structures)
conveying water originating from off-site shall be designed for a
fifty-year storm event. Sole access structures shall be designed to
convey the 100-year storm event without roadway overtopping. Drainage
and access easements shall be provided to encompass the water surface
limits of the 100-year storm event throughout the project site and
to provide access from a public street to the stormwater facility.
Easements shall begin at the furthest upstream property line of the
proposed development in the watershed.
K.
The maximum water depth for aboveground storage facilities shall
not exceed six feet measured at the emergency spillway.
L.
Flow velocities from any storm sewer may not result in erosion of
the receiving channel. Adequate erosion protection shall be provided
along all open channels and at all points of discharge.
M.
For all swales, capacities and velocities shall be computed using
the Manning Equation. The following design considerations shall be
met:
(1)
Two analyses of channel velocity and stability shall be provided
with each swale design. One analysis shall be based upon the swale
in an unvegetated state with control matting, and the second shall
consider the channel in permanent, designed conditions.
(2)
All swales shall have a minimum slope of 1% unless otherwise
approved by the Municipal Engineer.
N.
Design standards: facilities within the public street right-of-way.
(1)
Storm sewer pipes, other than those used for street subbase
underdrains, shall have a minimum diameter of 15 inches. Structural
calculations that address the actual design requirements will be required
where installation conditions merit.
(2)
Storm sewer pipes and culverts shall be installed with a minimum
slope of 0.5%.
(3)
Allowable pipes, culvert, and bridge materials shall be as outlined
in the municipality's construction and material specifications.
(4)
All storm sewer crossings of streets shall not deviate by more
than 15° from perpendicular to the street center line.
(5)
All storm sewer pipes and culverts shall be laid to a minimum
depth of 12 inches from finished subgrade to the crown of the pipe
in paved and grassed areas, or more if specified by the manufacturer.
(6)
Curves or angle points in pipes or box culverts without the
use of an inlet or manhole are prohibited unless preapproved by the
municipality. Tee joints, elbows, and wyes shall be limited for use
in constructing underground detention facilities, underground retention
facilities, underdrain systems, and roof leader collection systems.
(7)
Manholes, inlets, headwalls, endwalls, and end sections shall
conform to the requirements of PennDOT, Publication 408.
(8)
Inlets shall be placed on both sides of the street at low spots,
at a maximum of 600 feet apart along a storm sewer pipe or culvert,
and at points of abrupt changes in the horizontal or vertical directions
of storm sewers. Inlets shall normally be along the curbline at or
beyond the curb radius points. Within the street right-of-way, the
gutter spread based on the twenty-five-year storm event shall be no
greater than 1/2 of the travel lane width and have a maximum depth
of three inches at the curbline. A parking lane shall not be considered
as part of the travel lane. In the absence of pavement markings separating
a travel lane from the parking lane, the parking lane shall be assumed
to be eight feet wide if parking is permitted on the street. At intersections
and access driveways, the depth of flow across the through-streets
and across the access driveways (proposed and existing) shall not
exceed 1 1/2 inches for the twenty-five-year storm event. Manholes
may be substituted for inlets at locations where inlets are not required
to handle surface runoff.
(9)
Placement or use of BMPs within the public street right-of-way
shall only be allowed after municipal approval.
O.
Design standards: facilities outside of the public street right-of-way.
(1)
The design of all BMP facilities shall incorporate best engineering
practices. The design engineer shall utilize all available design
criteria in the BMP Manual to meet the requirements of this chapter
and shall provide all the necessary backup documentation with their
submittal.
(2)
The BMPs must be designed to protect and maintain existing uses
and maintain the level of water quality necessary to protect those
uses in all streams, and to protect and maintain water quality in
special protection streams, as required by statewide regulations at
25 Pa. Code Chapter 93.
(3)
No regulated earth-disturbance activities within the municipality
shall commence until approval by the municipality of a plan that ensures
post-construction stormwater discharges do not degrade the physical,
chemical, or biological characteristics of the receiving waters.
P.
Design standards: subsurface infiltration facilities.
(1)
Positive overflow must be provided in the subsurface infiltration
facility. Overflow structures or pipes must be designed to convey
the inflow capacity of the facility. Note: Volume control credits
may not be used above the lowest invert of the positive overflow structure
or pipe.
(2)
The minimum allowable distance between a subsurface infiltration
facility and structure/building/retaining wall is 10 feet.
(3)
The subsurface infiltration facility must be located at least
two feet above any limiting zone, i.e., seasonal high groundwater
table, bedrock, or poorly infiltrating soils.
(4)
Soils with rates exceeding 10 inches per hour require soil amendments.
During construction, upon reaching the subgrade of the infiltration
facility, a two-foot thick layer of soil amendments must be spread
across the entire facility bottom area, below the designed bottom
of the facility. Soil media infiltration rate must be provided upon
design.
(5)
The infiltration facility must include an acceptable form of
pretreatment before stormwater enters the facility. An acceptable
form of pretreatment includes an inlet with an eighteen-inch sump
and one-inch diameter weep holes. Other forms of pretreatment must
be approved by the Municipal Engineer.
(6)
Subsurface infiltration facilities may not use a geotextile
liner to separate the storage area from the subgrade. Geotextile liners
may only be used on the sides and top. AASHTO Class 1 or Class 2 geotextile
is recommended.
(7)
Subsurface infiltration facilities must contain a cleanout or
observation well near the center of the facility and at the end of
any portion of underdrain. The observation well or cleanout must be
placed at the invert of the stone bed and extend up to grade. Adequate
inspection and maintenance access to the observation well or cleanout
must be provided.
(8)
In subsurface infiltration facilities that include chamber,
pipe, or other storage systems, a sufficient number of access features
must be provided to efficiently inspect and maintain the infiltration
area.
(9)
Perforated distribution pipes must contain a bedding of at least
four inches separating the pipe and subgrade.
(10)
Infiltration testing standards set forth in the appendix shall
be followed when designing a subsurface infiltration facility.[1]
[1]
Editor's Note: See Appendix C, Infiltration Testing, included as an attachment to this chapter.
Q.
Design standards: water-carrying facilities.
(1)
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
facility for the 100-year storm. The greater flow shall govern the
design of the pipe or culvert.
(2)
When a pipe is part of a storm sewer system and crosses the
roadway, it shall be designed as a storm sewer with the same design
storm as the remainder of the drainage system.
(3)
Greater design frequencies may be justified on individual projects.
(4)
A 100-year storm frequency may be required for the design of
the stormwater collection system to ensure that the runoff from the
post-development storm is directed into the intended management facility.
(5)
In general, inlets shall be spaced such that, based upon the
Rational Method, tc = five minutes and ten-year rainfall intensity,
the area contributing to the inlet shall not produce a peak runoff
of greater than four cfs. Also, inlets shall be spaced so that their
efficiency, based upon efficiency curves published by the Pennsylvania
Department of Transportation, is not less than 65%.
(6)
Proposed channels or swales must be able to convey the increased
runoff associated with a proposed 100-year return period event within
their banks at velocities consistent with protection of the channels
from erosion. Acceptable velocities shall be based upon criteria included
in the PADEP Erosion and Sediment Pollution Control Program Manual.
(7)
All other storm sewer manholes and inlets shall have smooth
flow lines grouted.
(8)
Inlets shall be placed on both sides of the street at low spots
and at the upper side of street intersections to prevent stormwater
from crossing an intersection. Other devices such as high-efficiency
grates or perforated pipe may be required if conditions warrant. All
inlets at low points along the roadway shall have an eight-inch curb
reveal and shall be equipped with pavement base drain extending 50
feet in either direction, parallel to the center line of the roadway.
(9)
Headwalls and endwalls shall be used where stormwater runoff
enters or leaves the storm sewer horizontally from a natural or man-made
channel. In all cases where drainage is picked up by means of a headwall,
the pipe shall be designed as a culvert. Inlet and outlet conditions
shall be analyzed. PennDOT type "dw" headwalls and endwalls shall
be utilized for pipes 15 inches and larger in diameter. End sections
shall be utilized for pipes smaller than 15 inches in diameter.
(10)
Guards shall be provided on all intake and outfall structures
as well as outlet structures. The guard bars shall be one-half-inch
diameter galvanized bars on six-inch centers attached to the structure
with three-eights-inch diameter stainless steel anchors. Guards shall
also be provided for any pipe opening, 18 inches in diameter or larger.
(11)
Manholes, inlets, headwalls, and endwalls shall conform to the
requirements of the PennDOT Publication 408, as modified by the municipal
construction and materials standards.
R.
Design standards: detention and retention basins. Permanent detention
and retention basins shall be designed to meet the following standards:
(1)
The maximum permitted depth for detention or retention basins
shall be six feet, measured from the bottom of the emergency spillway
to the lowest point in the basin.
(2)
The minimum top width of all basin embankments shall be eight
feet.
(3)
The maximum permitted inside side slopes for detention or retention
basins shall be four to one vertical. Three-to-one vertical inside
side slopes may be approved upon furnishing an appropriate planting
schedule. The maximum permitted outside side slopes shall be three-to-one
vertical and utilize a seed mix designed for embankments. Areas for
vehicle access shall be provided and encompassed by a twenty-foot-wide
easement and shall have slopes no greater than five-to-one vertical.
The proposed vegetation shall be low-maintenance varieties.
(4)
Any stormwater management facility (i.e., detention basin) designed
to store runoff and requiring a berm or earthen embankment required
or regulated by this chapter shall be designed to provide an emergency
spillway to handle flow up to and including the 100-year, twenty-four-hour
design storm at post-development conditions, assuming the principal
outlet structure to be clogged. The height of the embankment must
be set as to provide a minimum of one foot of freeboard above the
maximum elevation computed. Should any stormwater management facility
require a dam safety permit under PADEP 25 Pa.Code Chapter 105, the
facility shall be designed in accordance with PADEP 25 Pa.Code Chapter
105, and meet the regulations of PADEP 25 Pa.Code Chapter 105, concerning
dam safety which may be required to pass storms larger than the 100-year
event.
(5)
A cutoff trench composed of a four-foot width of impervious
material shall be provided within all basin embankments.
(6)
Where a basin embankment is constructed using fill on an existing
15% or greater slope, the basin must be keyed into the existing grade.
(7)
Fencing. Any aboveground stormwater management detention/retention
facility that is designed to store at least a two-foot depth of runoff
shall be subject to the following fencing requirements:
(a)
The stormwater facility must be completely surrounded by a chain-link
fence of not less than four feet in height. Alternative fences and
barriers may be permitted upon request to and approval by the municipality.
(b)
All gates or doors opening through such enclosure shall be equipped
with a self-closing and self-latching device for keeping the gate
or door securely closed at all times, when not in actual use.
(8)
All outlet structures and emergency spillways shall include
a nonerosive means of energy dissipation at its outlet to assure conveyance
and flow without endangering the safety and integrity of the basin
and the downstream drainage area.
(9)
Plans for infiltration must show the locations of existing and
proposed septic tank infiltration areas and wells. A minimum twenty-five-foot
separation from on-lot disposal systems (OLDS) infiltration areas,
including replacement areas, is desired and will be evaluated by the
municipality on a case-by-case basis. However, the separation shall
not be less than the PADEP required 10 feet. Infiltration rates shall
be based upon perk and probe tests conducted at the site of the proposed
facility.
(10)
Aboveground infiltration facilities shall provide a means of
emergency dewatering of the facilities to the bottom elevation. If
amended soils are used in the facility bottom, an underdrain shall
be placed below or at the bottom of the amended soils to dewater the
amended soils in emergency situations. Dewatering to the top may be
allowed on a case-by-case basis if the circumstance does not allow
for the amended soils to drain properly. Usage of this method shall
require approval of the municipality.
S.
Design standards: rain gardens/bioretention facilities. A rain garden/bioretention
facility is an excavated shallow surface depression or storage area
created by an earthen embankment that is planted with specific native
vegetation to treat and capture runoff and amended soils. Rain gardens
shall meet the following design standards (Note: any SWM facility
exceeding these design standards shall be considered a retention/detention
basin and subject to their design standards):
(1)
The maximum ponding depth shall be 12 inches.
(2)
Infiltration testing standards set forth in Appendix C shall
be followed when designing a rain garden facility.[2]
[2]
Editor's Note: Appendix C is included as an attachment to this chapter.
(3)
The bottom of the rain garden storage area must be located at
least two feet above any limiting zone, i.e., seasonal high groundwater
table, bedrock, or poorly infiltrating soils.
(4)
Pretreatment shall be used in the design of the facility. Pretreatment
can include structures such as sumped and trapped inlets, sediment/grit
chambers or separators, media filters, inlet inserts, or other appropriate
prefabricated or proprietary designs to remove sediment, floatables,
and/or hydrocarbons from stormwater runoff prior to being conveyed
to a rain garden/bioretention basin. A facility may be exempt from
pretreatment at the discretion of the Municipal Engineer.
(5)
Maximum side slopes for surface storage areas shall be 4(H):1(V).
(6)
Any stone storage systems incorporated into the rain garden
design must be separated from the soil media by a geotextile liner.
A geotextile liner shall not be used to separate the stone storage
system from the subgrade. Stone storage systems shall have a level
bottom or use a terraced system if installed along a slope.
(7)
In the event a sand layer is to be used as part of the underground
filtration/storage system, the sand must be placed between the soil
medium and stone storage. All sides of the sand must be separated
by a geotextile liner.
(8)
The planting soil medium must have a minimum depth of 18 inches.
Planting soil shall be a loam soil capable of supporting a healthy
vegetative cover. Soils shall be amended with a composted organic
material. At a minimum, the organic amended soil shall be combined
with 20% to 30% organic material (compost) and 70% to 80% soil base
(topsoil). Amended soils shall be spread throughout the bottom floor
of the facility.
(9)
Underdrains must be provided for all rain gardens and extend
throughout the entire rain garden bottom. Underdrains must be surrounded
by a stone layer with a minimum of four inches above and below the
pipe.
(10)
Rain gardens that are used for volume control credits shall
have an underdrain with a valve that is to remain closed at all times
unless dewatering the facility to perform maintenance.
(11)
A sufficient number of cleanouts must be provided to access
underdrains to allow for maintenance and inspection of the underdrain
pipe.
(12)
Native plants capable of supporting the proposed ponding depth
shall be utilized. The designer shall refer to the PA DEP BMP Manual
for a list of potential native plant species.
A.
Any stormwater facility located on state highway rights-of-way shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
B.
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 of 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.
C.
Any stormwater management facility located within the vicinity of
a floodplain shall be subject to approval in accordance with PADEP
25 Pa.Code Chapter 105, Floodplain Management, of PADEP's rules
and regulations.
D.
The design of all stormwater management facilities shall incorporate
good engineering principles and practices. The municipality shall
reserve the right to disapprove any design that would result in the
occupancy or continuation of adverse hydrologic or hydraulic conditions
within the watershed.
E.
The existing points of concentrated drainage that discharge onto
adjacent property shall not be altered without permission of the adjacent
property owner(s) and shall be subject to any applicable discharge
criteria specified in this chapter. New proposed discharge points
shall be no closer than 10 feet to the property line in which they
are located.
F.
Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this chapter. If the
diffused flow is proposed to be concentrated and discharged onto adjacent
property, 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.
G.
Where a development site is traversed by watercourses, twenty-foot-wide
minimum drainage easements (10 feet from top of the bank out) 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, maintaining
of vegetation in a natural state within the easement shall be required,
except as approved by the appropriate governing authority.
H.
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 joint permit application
process or, where deemed appropriate by PADEP, through the general
permit process.
I.
Roof drains and sump pumps must not be connected to streets, sanitary
or storm sewers, or roadside ditches 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 by the
municipality.
J.
Special requirements for areas falling within defined exceptional
value and high-quality subwatersheds. The temperature and quality
of water and streams that have been declared as exceptional value
and high-quality are to be maintained as defined in 25 Pa.Code Chapter
93, Water Quality Standards, Pennsylvania Department of Environmental
Protection rules and regulations. Temperature-sensitive BMPs and stormwater
conveyance systems are to be used and designed with storage pool areas
and supply outflow channels and should be shaded with trees. This
will require modification of berms for permanent ponds and the relaxation
of restrictions on planting vegetation within the facilities, provided
that capacity for volumes and rate control is maintained. At a minimum,
the southern half on pond shorelines shall be planted with shade or
canopy trees within 10 feet of the pond shoreline. In conjunction
with this requirement, the maximum slope allowed on the berm area
to be planted is 10 to 1. This will lessen the destabilization of
berm soils due to root growth. A long-term maintenance schedule and
management plan for the thermal control BMPs are to be established
and recorded for all development sites within defined exceptional
value and/or high-quality subwatersheds.
Stormwater runoff from all development sites shall be calculated
using the Rational Method, Modified Rational Method, or a soil cover
complex methodology.
A.
Any stormwater runoff calculations involving drainage areas greater
than 200 acres, including on- and off-site areas, shall use a generally
accepted calculation technique that is based on the NRCS Soil Cover
Complex Method. It is assumed that all methods will be selected by
the design professional based on the individual limitations and suitability
of each method for a particular site.
B.
The municipality may allow the use of the Rational Method or Modified
Rational Method to estimate peak discharges from drainage areas that
contain less than 200 acres. When using the Rational Method, an ascending
and descending limb factor of 3 and 7 shall be used, respectively.
C.
All calculations consistent with this chapter using the Soil Cover
Complex Method shall use the appropriate design rainfall depths. If
a hydrologic computer model such as PSRM or HEC-RAS is used for stormwater
runoff calculations, then the duration of rainfall shall be 24 hours.
The SCS Rainfall Type II curve shall be used for the rainfall distribution.
Those projects proposing infiltration structures shall utilize this
method.
D.
When routing a detention basin, the Rational Method or SCS Method
may be used to determine peak rates through the primary outlet structure.
Only the SCS Method may be used to determine the peak water surface
elevation during the 100-year, twenty-four-hour design storm, dictating
the height of the embankment.
E.
Underground storage facilities that solely receive stormwater and
are designed to capture and infiltrate the entire 100-year, twenty-four-hour
SCS runoff volume may have their drainage areas removed from the overall
post-development drainage area(s).
F.
For the purposes of predevelopment flow rate determination, undeveloped
land, including disturbed areas, shall be considered as meadow in
good condition, unless the natural ground cover generates a lower
curve number or rational C value (i.e., forest), as listed in Tables
1 and 2, respectively.[1]
[1]
Editor's Note: Tables 1 and 2 are included as attachments to this chapter.
G.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times of concentration for overland flow
and return periods. Times of concentration for overland flow shall
be calculated using the methodology presented in Chapter 3 of Urban
Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced
from time to time by NRCS). Time of concentration for channel and
pipe flow shall be computed using Manning's Equation.
H.
Runoff curve numbers (CN) for both existing and proposed conditions
to be used in the Soil Cover Complex Method shall be obtained from
Table 1.[2]
[2]
Editor's Note: Table 1 is included as an attachment to this chapter.
I.
Runoff coefficients (c) for both existing and proposed conditions
for use in the Rational Method shall be obtained from Table 2.[3]
[3]
Editor's Note: Table 2 is included as an attachment to this chapter.
J.
Where uniform flow is anticipated, the Manning Equation shall be
used for hydraulic computations such as the capacity of open channels,
pipes, and storm sewers. Values for Manning's roughness coefficient
(n) shall be consistent with Table 3.[4]
[4]
Editor's Note: Table 3 is included as an attachment to this chapter.
K.
The design of any stormwater detention facilities intended to meet
the performance standards of this chapter shall be verified by routing
the design storm hydrograph through these facilities, using either
manual methods or computerized routing. Routing shall be based upon
the modified PULS method; other routing methodologies shall be subject
to the approval of the Municipal Engineer.
L.
The stormwater collection system shall be designed using the peak
discharge computed using the Rational Formula.
In areas of carbonate geology, a geologist shall certify to
the following:
A.
No stormwater management facility will be placed in, over, or immediately
adjacent to the following features:
(1)
Closer than 100 feet from sinkholes;
(2)
Closer than 100 feet from closed depressions;
(3)
Closer than 100 feet from caverns, intermittent lakes, or ephemeral
streams;
(4)
Closer than 50 feet from lineaments in carbonate areas;
(5)
Closer than 50 feet from fracture traces;
(6)
Closer than 25 feet from bedrock pinnacles (surface or subsurface).
B.
Stormwater resulting from regulated activities shall not be discharged
into sinkholes.
C.
If the developer can prove through analysis that the project site is an area underlain by carbonate geology, and such geologic conditions may result in sinkhole formations, then the project site is exempt from recharge requirements as described in § 265-303, Volume control. However, the project site shall still be required to meet all other standards found in this chapter.
D.
It shall be the developer's responsibility to verify if the
project site is underlain by carbonate geology. The following note
shall be attached to all stormwater management plans and signed and
sealed by the developer's geologist: "I,_____, certify that the
proposed stormwater management facility (circle one) is/is not underlain
by carbonate geology."
E.
Whenever a stormwater management facility will be located in an area
underlain by carbonate geology, a geological evaluation of the proposed
location by a geologist shall be conducted to determine susceptibility
to sinkhole formation. The evaluation may include the use of impermeable
liners to reduce or eliminate the separation distances listed in the
BMP Manual. Additionally, the evaluation shall, at a minimum, address
soil permeability, depth to bedrock, seasonally high groundwater table,
susceptibility for sinkhole formation, suitability of stormwater management
facilities, subgrade stability, and maximum infiltration capacity
in depth of water per unit area.
F.
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)
Site evaluation to determine general areas of suitability for
infiltration practices.
(2)
Provide field percolation tests throughout the area proposed
for development to determine appropriate percolation rate and/or hydraulic
conductivity. At least one infiltration test must be included in each
soil group, and at least one infiltration test must be conducted for
every five lots proposed for development. Infiltration tests must
be taken at the location and depth of all proposed infiltration structures.
(3)
Design infiltration structure for required storm volume based
on all available data.
G.
Extreme caution shall be exercised where infiltration is proposed
in geologically susceptible areas, such as strip mine or limestone
areas. 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 study
be performed if necessary. Whenever a basin is 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 carbonate formations shall include
measures to prevent groundwater contamination and, where necessary,
sinkhole formation. The infiltration requirement in the high quality/exceptional
waters shall be subject to the Department's 25 Pa.Code Chapter
93, and antidegradation regulations. A detailed hydrogeologic investigation
may be required by the municipality, and where appropriate, the municipality
may require the installation of an impermeable liner in detention
basins.
A.
As required in § 265-301D, whenever the vegetation and topography are to be disturbed, such activity must be in conformance with PADEP 25 Pa.Code Chapter 105, rules and regulations, Part I, Subpart C, Protection of Natural Resources, Article II, Water Resources, Chapter 102, Erosion Control, and in accordance with the County Conservation District.
B.
It is extremely important that strict erosion and sedimentation control
measures be applied surrounding infiltration structures during installation
to prevent the infiltrative surfaces from becoming clogged. Additional
erosion and sedimentation control design standards and criteria that
must be applied where infiltration BMPs are proposed shall include
the following:
(1)
Areas proposed for infiltration BMPs shall be protected from
sedimentation and compaction during the construction phase so as to
maintain their maximum infiltration capacity.
D.
The developer shall demonstrate that the post-development hydrograph flows during erosion and sedimentation control phase are less than or equal to the predevelopment hydrograph flows to assure the rate and volume of runoff leaving the site is controlled for the two-, five-, and ten-year frequency storms. All calculation methodology shall be in accordance with §§ 265-303 through § 265-309.
E.
In the event a regulated activity falls under the Chapter 102[1] thresholds for requiring a written erosion and sedimentation
plan and/or NPDES permit, the applicant is still required to provide
suitable erosion and sedimentation best management practices to prevent
an illicit discharge caused by erosion during a precipitation event.
[1]
Editor's Note: See 25 Pa. Code Chapter 102.
