A.
For all Level 1 to Level 4 applications, the submission of the stormwater
management permit application provided in Appendix B[1] is required. No regulated activity associated with a Level
1 to Level 3 application shall commence unless a stormwater management
permit application is approved by Foster Township. Although proposed
earth disturbance projects with an earth disturbance of less than
2,000 square feet and an impervious area of less than 625 square feet
have no submission requirements, these projects must still comply
with this section of this chapter.
[1]
Editor's Note: Appendix B is included as an attachment to this chapter.
B.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 192-11:
(1)
Preparation and implementation of an approved SWM site plan is required.
An SWM site plan is required for a Level 4 application only.
(2)
No regulated activities shall commence until Foster Township issues
written approval of an SWM site plan which demonstrates compliance
with the requirements of this chapter.
C.
SWM site plans approved by Foster Township, in accordance with § 192-21, shall be on-site throughout the duration of the regulated activity.
D.
Foster Township may 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.
E.
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),§ 192-37B No. 363-2134-008
(April 15, 2000), as amended and updated.
F.
For Level 3 and Level 4 applications, the implementation of the volume controls in § 192-12 is required. For Level 2 applications, the implementation of the volume controls of Appendix E[3] is required unless the disconnected impervious area (DIA)
requirements of Appendix C.1[4] are implemented or the subject lot is associated with an existing approval as described in § 192-5C.
[3]
Editor's Note: Appendix E is included as an attachment to this chapter.
[4]
Editor's Note: Appendix C.1 is included as an attachment to this chapter.
G.
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, only the proposed
impervious area on the parcel must be considered and summed to determine
the plan preparation and approval requirements of this chapter.
(4)
For redevelopment projects in which the existing site is disturbed,
the entire proposed site is subject to the plan preparation and approval
requirements of this chapter. Existing conditions are considered to
be the existing site immediately prior to disturbance, and 20% of
the existing impervious area must be considered as meadow in good
condition for all stormwater calculations. For redevelopment projects
in which the existing site is already controlled by a stormwater management
facility, the requirement to consider 20% of existing impervious area
as meadow is waived, provided the existing facility meets the water
quality, volume, and peak rate standards and criteria of this chapter.
H.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written permission
of the adjacent property owner(s). Such stormwater flows shall be
subject to the requirements of this chapter. If written permission
cannot be obtained from the adjacent property owner (proof must be
submitted that the applicant attempted to obtain written permission),
the applicant must successfully demonstrate that the proposed discharge:
(1)
Qualifies for a "common law flowage easement," as defined by Pennsylvania
courts. Pennsylvania courts have upheld a common law right to discharge
stormwater to adjoining properties downstream "because water is descendible
by nature, the owner of the dominant or superior heritage has an easement
in the servient or inferior tenement for the discharge of all waters
which by nature rise in or flow or fall upon the superior." To qualify
for a "common law flowage easement," as defined by this chapter, the
applicant must demonstrate that the discharge will not result in a
significant increase in volume of stormwater on the downstream property,
will not create a channel for the water to flow where it does not
flow naturally, and also provide evidence that all attempts to obtain
written permission of the downstream property owner have failed.
(2)
Will not cause accelerated erosion or damage to the proposed flow
area and/or adjoining properties. The applicant must utilize methods
recommended by PADEP to demonstrate that erosion and damage will not
occur on adjoining properties.
(3)
Shall be located at least 20 feet from the downstream property line
of the subject property.
I.
All regulated activities shall include measures to:
(1)
Protect health, safety, and property;
(2)
Meet the water quality goals of this chapter by implementing measures
outlined in the Pennsylvania Stormwater Best Management Practices
Manual (BMP Manual)§ 192-37A 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 this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
J.
The design of all facilities over karst and mined areas shall include
an evaluation of measures to minimize adverse effects.
K.
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.
L.
Storage facilities, to the greatest extent possible and at the discretion
of the Foster Township Engineer, shall completely drain both the volume
control and rate control capacities over a period of time not less
than 24 hours and not more than 72 hours from the end of the design
storm.
M.
Storage facilities shall incorporate features to maximize the length
of the flow path and increase the travel time through the facility.
N.
The design storm volumes to be used in the analysis of peak rates
of discharge should be obtained from the Precipitation-Frequency Atlas
of the United States, Atlas 14, Volume 2, Version 3.0, U.S. Department
of Commerce, National Oceanic and Atmospheric Administration (NOAA),
National Weather Service, Hydrometeorological Design Studies Center,
Silver Spring, Maryland. NOAA's Atlas 14 can be accessed at:
http://hdsc.nws.noaa.gov/hdsc/pfds/.§ 192-37E
O.
Q.
Sump pump drains, roof drains and foundation drains.
(1)
All drains shall connect to an existing infiltration or vegetative
BMP if a BMP exists within the subject property outbound. If a drain
is to be connected to a proposed underground infiltration BMP, evidence
must be submitted to the Township that the existing soil in the area
of the proposed BMP is suitable for infiltration.
(2)
If an infiltration or vegetative BMP does not exist within the subject
property outbound, all drains should be directed to a Township roadside
swale if a swale exists adjacent to a roadway and positive drainage
can be achieved. If a swale does not existing adjacent to a Township
roadway and no other acceptable discharge can be achieved on the property,
the discharge point of the drain shall be a minimum of 15 feet (20
feet may be required to comply with DIA requirements) from the shoulder
of the Township roadway and shall be on a pervious ground surface
to minimize the possibility of the freezing of water on the roadway
in the winter months.
(3)
Discharges to wetland areas are encouraged; however, the discharge
shall be a minimum of five feet from the wetland boundary to avoid
the requirement of state or federal permitting and to avoid the inundation
of the drain outfall.
(4)
Sump pump discharges shall be a minimum of 10 feet from the foundation
of the building from where the water is being pumped out to prevent
the recycling of water back into the foundation drains of the building.
(5)
All drain outlets shall be a minimum of 20 feet from any property
line with the exception of the front property line.
(6)
The isolation distances of this subsection may be slightly modified
at the discretion of the Township Engineer if the applicant can demonstrate
that no adverse downstream stormwater impact is being created or worsened.
A.
Regulated activities that create impervious areas or earth disturbance
shall adhere to Table III.1 to meet the requirements of this chapter.
The larger of the two areas determines the applicable requirements
of this chapter (i.e., if only 500 square feet of impervious area
is proposed, but 15,000 square feet of earth disturbance, the requirements
follow Row 3 of Table III.1).
|
Table III.1. Stormwater Management Requirements and Exemptions.
| ||||
|---|---|---|---|---|
|
Proposed Impervious Area
(square feet)
|
Proposed Total Earth Disturbance
(square feet)
|
Chapter Exemptions
|
Stormwater Management Requirements
|
Required Submissions to Municipality*
|
|
625 to 1,250
|
2,000 to 5,000
|
Level 1: Ensure § 192-10 general requirements are met
|
Sketch
| |
|
1,250 to 5,000***
|
5,000 to 10,000***
|
Level 2: Disconnected impervious area (DIA) as in Appendix C.1[1]
|
Appendix C.1 Worksheet and Sketch
| |
|
or
|
or
| |||
|
Level 2: Capture and control first 1 inch of runoff over proposed
impervious areas as in Appendix E[2]
|
Appendix E worksheet and sketch
| |||
|
5,000 to 10,000**
|
10,000 to 20,000**
|
Level 3: Capture and permanently remove the first 2 inches of runoff over proposed impervious areas as in § 192-12B of this chapter
|
Appendix D[3] worksheet and sketch
| |
|
> 10,000
|
> 20,000
|
None
|
Level 4: All requirements of this chapter
|
SWM site plan
|
|
*
|
In addition to the stormwater management permit application
provided in Appendix B[4]
|
|
**
|
Regardless of the proposed amount of impervious area and earth
disturbance, all land developments shall require a Level 4 application
|
|
***
|
For Level 2 applications for existing lots governed by previous approvals, see § 192-5C
|
[1]
Editor's Note: Appendix C.1 is included as an attachment to this chapter.
[2]
Editor's Note: Appendix E is included as an attachment to this chapter.
[3]
Editor's Note: Appendix D is included as an attachment to this chapter.
[4]
Editor's Note: Appendix B is included as an attachment to this chapter.
B.
Agricultural activity is exempt from the rate control and SWM site
plan preparation requirements of this chapter, provided the activities
are performed according to the requirements of 25 Pa. Code Chapter
102.
C.
Forest management and timber operations are exempt from the rate
control and SWM site plan preparation requirements of this chapter,
provided the activities are performed according to the requirements
of 25 Pa. Code Chapter 102.
D.
Exemptions from any provisions of this chapter shall not relieve the applicant from the requirements in § 192-10A through Q. (i.e., if an applicant proposes an impervious area less than 625 square feet or an earth disturbance of less than 2,000 square feet although there is no formal submittal required by the Township, it is the applicant's responsibility to comply with § 192-10 of this chapter.)
The low-impact development practices provided in the BMP Manual§ 192-37A shall be utilized for all regulated
activities to the maximum extent practicable. Water volume controls
shall be implemented using the Design Storm Method in Subsection A
or the Simplified Method in Subsection B below. For all regulated
activities that require submission of a formal SWM site plan, both
the Design Storm Method and the Simplified Method shall be calculated;
the larger control volume based on the two calculations shall be controlled.
Subsection C below provides requirements for mined, karst, or other
geologically limiting areas where infiltration shall not occur.
A.
The Design Storm Method (CG-1 in the BMP Manual§ 192-37A) is applicable to any size of regulated activity. This method requires
detailed modeling based on site conditions.
(1)
Do not increase the post-development total runoff volume for all
storms equal to or less than the two-year, twenty-four-hour duration
precipitation.
B.
When Design Storm Method CG-1 guidelines are not used, the Simplified
Method (CG-2 in the BMP Manual§ 192-37A) has been modified to accommodate two inches of permanently removed
runoff volume. This method (provided below) is independent of site
conditions and should be used if the Design Storm Method is not followed.
For new impervious surfaces:
(1)
The first two inches 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.
(2)
Wherever possible, infiltration facilities should be designed to
accommodate infiltration of the entire permanently removed runoff;
however, in all cases, at least the first 0.5 inch of the permanently
removed runoff should be infiltrated.
(3)
Facilities, to the greatest extent possible and subject to the Township
Engineer's discretion, shall be designed to drain the permanently
removed runoff volume in a period no less than 24 hours and no greater
than 72 hours.
(4)
Runoff volume in excess of two inches shall be safely conveyed to
existing stormwater collection systems or streams, in the direction
of the existing drainagecourse.
C.
Before infiltration is proposed on a site, site conditions shall
be evaluated by a qualified design professional through subsurface
investigation and testing to determine if site conditions are suitable
to support proposed infiltration facilities to manage runoff. If it
is determined that infiltration is not feasible due to physical constraints
of the site, or will adversely impact the environment as demonstrated
by the presence of acid mine drainage, sinkhole formation, or other
serious environmental issues, then the above volume controls must
be achieved through surface BMP mitigation. Reference the BMP Manual§ 192-37A for alternative mitigation measures
that do not require infiltration.
A.
Areas not covered by the Stormwater Management District Map contained
in Appendix F.1[1] of this chapter:
|
Post-development discharge rates shall not exceed the predevelopment
discharge rates for the one- through 100-year, twenty-four-hour storms.
If it is shown that the peak rates of discharge indicated by the post-development
analysis are less than or equal to the peak rates of discharge indicated
by the predevelopment analysis for one - through 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.
|
[1]
Editor's Note: Appendix F.1 is included as an attachment to this chapter.
B.
Areas covered by the Stormwater Management District Map contained
in Appendix F.1 of this chapter:
|
For the one- through 100-year storms, the post-development peak
discharge rates will follow the Nescopeck Creek Watershed Stormwater
Management District Map. For any areas not shown on the Nescopeck
Creek Watershed Stormwater Management District Map, the post-development
discharge rates shall not exceed the predevelopment discharge rates.
|
A.
Any stormwater management facility located with a state highway right-of-way
shall be subject to approval by the Pennsylvania Department of Transportation.
B.
Any facilities that constitute water obstructions (e.g., culverts,
bridges, outfalls, or stream enclosures), and any work involving wetlands
as directed in PADEP Chapter 105 regulations, as amended, shall be
designed in accordance with Chapter 105 and will require a permit
from PADEP. Any facility that constitutes a dam as defined in PADEP
Chapter 105 regulations may require a permit under dam safety regulations.
C.
Any stormwater conveyance facility that does not fall under Chapter
105 regulations must be able to convey, without damage to the drainage
structure or roadway, runoff from the twenty-five-year design storm.
Stormwater conveyance facilities outleting from stormwater management
detention/infiltration facility shall be designed to convey the 100-year
design flow from that structure. Roadway crossings located within
designated floodplain areas must be able to convey runoff from a 100-year
design storm.
D.
Storm sewers must be able to convey post-development runoff from
a twenty-five-year design storm without surcharging inlets, where
appropriate. No storm sewer shall be smaller than 15 inches in diameter
within a public right-of-way. Twin twelve-inch culverts are permitted
to convey stormwater underneath a single-family residential driveway
within a Foster Township right-of-way. All culverts and inlet structures
shall be sized so that the calculated headwater for the design storm
does not flood the adjacent roadway. All such structures shall maintain
a zero-point-five-foot freeboard between the headwater and the edge
of shoulder.
E.
Detention and infiltration facilities shall be designed to conform to the release rate requirements of § 192-13.
F.
An emergency spillway capable of passing the peak 100-year, twenty-four-hour,
post-development inflow to a detention basin shall be provided, assuming
the primary outfall of the basin is blocked. A minimum of one foot
of freeboard shall be provided to the top of the basin berm to the
water surface at the emergency spillway. Also, the invert of the emergency
spillway must be specified at least 0.1 foot above the 100-year water
surface in the basin. In lieu of the one-foot freeboard requirement,
the emergency spillway shall pass two times the peak 100-year inflow
with no freeboard requirement. All emergency spillways shall be suitably
stabilized to prevent erosion. Alternate designs for emergency spillways
may be considered by the Township at the discretion of the Township
Engineer for underground detention/infiltration structures or aboveground
infiltration basins/rain gardens without a primary outlet structure.
G.
The top of a detention basin berm shall be a minimum of eight feet
wide. Where the basin depth from top of berm to invert of outfall
structure exceeds 10 feet, the top of berm shall be a minimum of 10
feet wide. Infiltration basins and rain gardens without a primary
outlet structure shall have a minimum berm width of six feet.
H.
The exterior and interior slopes of all detention basin cuts and
fills shall be a minimum of three horizontal to one vertical. A 2.5
horizontal to one vertical slope may be allowed at the discretion
of the Township Engineer if specific site constraints warrant a steeper
slope.
I.
A concrete outlet structure with metal-grate trash rack bolted to
the top shall be used as principal detention basin outlet. The outlet
structure should be of dimension to allow interior access for cleaning
and maintenance.
J.
In no case shall an outlet structure orifice be smaller than 3.0
inches in dimension.
K.
All earth fill shall be free of wood, stumps, brush, roots, and other
organic material subject to decomposition. Also, no fill shall be
permitted that contains any stones larger than three inches measured
in any direction.
L.
Areas where the fill is to be placed shall be scarified prior to
placement. Fill material for the embankment of detention and infiltration
basins shall be placed in maximum twelve-inch lifts, and each lift
should be compacted with a roller to at least 95% of the maximum density
obtained from compaction tests performed by the appropriate method
in ASTM D698. Furthermore, the center of the embankment shall contain
a clay core of relatively impervious material.
M.
An easement to allow maintenance crews access to all basins and outlet
areas shall be established. The limits of such easement shall be 15
feet from the outside toe of all dams and embankments and top of all
basin side slopes and shall be connected to a public right-of-way.
The accessway from the basin to a public street shall be a twelve-inch-thick
2A material road or equivalent surface of a minimum width of 10 feet.
N.
All basins shall be sodded or topsoiled (at a six-inch minimum depth)
and seeded, including the bottom, side slopes, berms and embankments.
O.
Adequate erosion protection shall be provided along all open channels,
embankments and at all points of discharge.
P.
Drainage pipes shall have a minimum slope of 0.5%.
Q.
All open-ended pipes with a diameter of 12 inches or greater shall
be fitted with concrete end walls or prefabricated end sections. All
end walls, end sections or inlets shall be constructed and installed
in accordance with PennDOT standards.
R.
Manholes, cleanouts or inlets shall be used at all changes in horizontal
alignment, at changes in vertical alignment and at all pipe junctions.
No run of pipe shall exceed 400 feet in length without appropriate
measures to provide cleanout. Inlets shall be spaced at intervals
to achieve desired capacity based on the methods outlined in PennDOT
Design Manual 2.
S.
All wet pond or retention basin designs shall incorporate biological
controls to control mosquitoes.
T.
Anti-seep collars and an inner core of relatively impervious material
(clay) shall be provided under all stormwater detention/infiltration
basin berms. Watertight anti-seep collars shall be installed around
discharge pipes at intervals not to exceed 24 feet and shall extend
a minimum of two feet beyond the outside of the pipe.
U.
All inlets shall have a sump of a minimum of one foot and shall have
weep holes covered with geotextile fabric to provide complete drainage
of the inlet. All inlets shall be constructed on a base of a minimum
of 12 inches of 2A material.
V.
Inlets over four feet in depth shall have ladder rungs.
W.
The design of all stormwater management facilities shall incorporate
sound engineering principles and practices. Foster Township shall
reserve the right to disapprove any design that would result in the
occupancy or continuation of an adverse hydrologic or hydraulic condition.
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. Foster Township may approve
the use of the Modified Rational Method to estimate peak discharges
from drainage areas that contain less than 200 acres.
B.
All calculations consistent with this chapter using the Soil Cover
Complex Method shall use the appropriate design rainfall depths for
the various return period storms presented in Precipitation-Frequency
Atlas of the United States, Atlas 14, Volume 2, Version 3.0, U.S.
Department of Commerce, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland. NOAA's Atlas 14 can be accessed
at: http://hdsc.nws.noaa.gov/hdsc/pfds/§ 192-37E.
C.
For the purposes of predevelopment flow rate determination, undeveloped
land 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).
D.
All calculations using the Modified Rational Method shall use rainfall
intensities consistent with appropriate times of concentration for
overland flow and return periods from the design storm curves from
PA Department of Transportation design rainfall curves. 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. Times of concentration for channel and pipe flow shall
be computed using Manning's equation.
E.
Runoff curve numbers (CN) for both existing and proposed conditions
to be used in the Soil Cover Complex Method shall be obtained from
Urban Hydrology for Small Watersheds, NRCS, TR-55, as amended.
F.
Runoff coefficients (c) for both existing and proposed conditions
for use in the Rational Method shall be obtained from the PADEP Erosion
and Sediment Pollution Control Manual, latest edition.
G.
Where uniform flow is anticipated, Manning's equation shall be used
for hydraulic computations and to determine the capacity of open channels,
pipes, and storm sewers. Values for Manning's roughness coefficient
(n) shall be obtained from the PADEP Erosion and Sediment Pollution
Control Manual, latest edition. Outlet structures for stormwater management
detention/infiltration facilities shall be designed to meet the performance
standards of this chapter using any generally accepted hydraulic analysis
technique or method.
H.
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 the Storage-Indication
Method. For drainage areas greater than 20 acres in size, the design
storm hydrograph shall be computed using a calculation method that
produces a full hydrograph. Foster Township may approve the use of
any generally accepted full hydrograph approximation technique which
shall use a total runoff volume that is consistent with the volume
from a method that produces a full hydrograph.
I.
Foster Township has the authority to require that computed existing
runoff rates be reconciled with field observations and conditions.
If the designer can substantiate through actual physical calibration
that more appropriate runoff and time-of-concentration values should
be utilized at a particular site, then appropriate variations may
be made upon review and recommendations of the Municipal Engineer.
Calibration shall require detailed gauge and rainfall data for the
particular site in question.
