A.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 158-14:
B.
SWM site plans approved by the Township, in accordance with § 158-24, shall be on site throughout the duration of the regulated activity.
C.
The Township may, after consultation with and approval by DEP, approve
measures for meeting the state water quality requirements other than
those in this chapter, provided that they meet the minimum requirements
of, and do not conflict with, state law including, but not limited
to, the Clean Streams Law.[1] The Township shall maintain a record of correspondence
with DEP pursuant to this paragraph.
[1]
Editor's Note: See 35 P.S. §§ 691.1 through
691.1001
D.
For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities, i.e., during construction,
to meet the purposes and requirements of this chapter and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law. Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual) 2, No. 363-2134-008 (April 15, 2000), as amended and updated.
F.
Impervious areas:
(1)
The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in phases.
(2)
For development taking place in phases, the entire development plan
must be used in determining conformance with this chapter.
(3)
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in § 158-15 and the peak rate controls of § 158-16 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
G.
Stormwater flows onto adjacent property shall not be created, increased,
decreased, relocated, or otherwise altered without written notification
to the adjacent property owner(s), a copy of which notice shall be
provided to the municipality. Such stormwater flows shall be subject
to the requirements of this chapter.
H.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property;
(2)
Meet the water quality goals of this chapter, as stated in § 158-3, Purpose, by implementing measures to:
(a)
Minimize disturbance to floodplains, wetlands, wooded areas,
and existing vegetation.
(b)
Maintain or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(f)
Minimize soil disturbance and compaction. Topsoil, if removed,
shall be replaced to a minimum depth equal to its depth prior to removal
or a six-inch minimum depth, whichever is greater, with a maximum
required depth of eight inches. (Additional topsoil may be needed
for vegetation other than sod.)
(3)
To the maximum extent practicable, incorporate the techniques for
low-impact development practices described in the Pennsylvania Stormwater
Best Management Practices Manual (BMP Manual).
I.
The design of all facilities in areas of carbonate geology or karst
topography shall include an evaluation of measures to minimize adverse
effects, including hydrogeologic studies if required by the Township.
J.
Infiltration BMPs shall be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter. In addition,
infiltration BMPs shall include pretreatment BMPs where appropriate.
K.
Normally dry, open-top storage facilities, designed as such, shall
completely drain both the volume control and rate control capacities
over a period of time not more than 96 hours from the end of the design
storm. Infiltration facilities shall be designed to infiltrate in
not less than 24 hours; however, any designed infiltration at such
facilities is exempt from the minimum twenty-four-hour standard, i.e.,
may infiltrate in a shorter period of time, so long as none of the
stormwater flowing into the infiltration facility is discharged directly
into the surface waters of the Commonwealth. (Inordinately rapid infiltration
rates may indicate the presence of large fractures or other conditions
for which an additional soil buffer may be required.)
L.
The design storm volumes and precipitation intensities to be used
in the analysis of discharge or runoff shall be obtained from the
Precipitation-Frequency Atlas of the United States, Atlas 14, Volume
2, Version 3.0, U.S. Department of Commerce, National Oceanic and
Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological
Design Studies Center, Silver Spring, Maryland, as amended, updated,
or replaced from time to time. NOAA's Atlas 14 can be accessed at:http://hdsc.nws.noaa.gov/hdsc/pfds/.
M.
N.
Various BMPs and their design standards are listed in the BMP Manual.
O.
For any new development or redevelopment, to the maximum extent practicable,
stormwater BMPs shall be utilized to reduce the discharge of nitrogen,
phosphorus and sediment.
Any regulated activity that meets the following exemption criteria
is exempt from the part(s) of this chapter as specified herein. However,
the requirements of this chapter shall otherwise remain in effect.
The criteria for exemption in this section apply to the total development
proposed, including instances in which the development is proposed
to take place in phases. The date of enactment of this chapter shall
be the starting point from which future development and the respective
proposed impervious surface computations shall be cumulatively considered
and regulated. Exemption shall not relieve an applicant from implementing
such measures as necessary to meet the intent of this chapter, or
compliance with any NPDES Permit requirements.
A.
New impervious surface creation shall be based on impervious surfaces
being created from and after the effective date of this chapter by
past and present owners on the project site. New impervious surface
created by owners of easements and rights-of-way located on the project
site shall not be considered in the calculation.
B.
Regulated activities that create impervious areas equal to or less
than those set forth on Table 158-14.1 (cumulative of all regulated
activities from and after the effective date of this chapter) shall
be exempt from the SWM site plan preparation requirements of this
chapter, provided that the activity will not adversely affect downstream
property owners and will not cause erosion. The Township reserves
the right to have its designee make the determination of adverse effect
after review of the application and review of the proposed site.
(1)
Subject to the Requirements of § 158-111 of this chapter, and notwithstanding the provisions of this Subsection B and Table 158-14.1 activities that would otherwise be regulated activities pursuant to this chapter but are 100 square feet or less shall be exempt from the permitting, stormwater management site plan preparation, volume and peak rate control, and Township review and approval provisions of this chapter. The activities in this subsection are not cumulative.
C.
Regulated activities that create impervious areas less than or equal to 5,000 square feet (cumulative of all regulated activities from and after the effective date of this chapter) but do not qualify for an exemption from SWM site plan preparation requirements per § 158-14B of this chapter may qualify for submission of a simplified SWM site plan per § 158-19F of this chapter. The Township's designee shall determine if a simplified SWM site plan may be submitted in lieu of a full SWM site plan (per § 158-19 of this chapter) after review of the stormwater management permit application and the proposed site. The simplified SWM site plan must demonstrate that the proposed activity will not adversely affect adjoining property owners or cause erosion.
D.
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, and no adverse impacts to adjoining property owners will occur because of stormwater runoff.
E.
Forest management and timber operations may be 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, and no adverse impacts to adjoining property owners will occur because of stormwater runoff.
F.
Domestic gardening and landscaping are exempt from specific approval
and permitting under this chapter so long as those activities are
associated with one, and only one, dwelling unit and the activities
comply with all other applicable ordinances and statutes.
H.
The Township may deny or revoke any exemption pursuant to this section
at any time for any project that poses a threat to public health,
safety, property or the environment.
|
Table 158-14.1
| ||
|---|---|---|
|
Existing Lot Size
|
Maximum New Impervious Area Cumulative per § 158-14B
| |
|
0 to 0.25 acres
|
250 square feet
| |
|
Greater than 0.25 to 0.50 acres
|
500 square feet
| |
|
Greater than 0.50 to 0.75 acres
|
750 square feet
| |
|
Greater than 0.75 acres
|
1,000 square feet
| |
The low-impact development practices provided in the BMP Manual
shall be utilized for all regulated activities to the maximum extent
practicable. Water volume controls shall be implemented using the
Design Storm Method in Subsection A or the Simplified Method in Subsection
B below. For regulated activity areas equal or less than one acre
that do not require hydrologic routing to design the stormwater facilities,
this chapter establishes no preference for either methodology; therefore,
the applicant may select either methodology on the basis of economic
considerations, the intrinsic limitations on applicability of the
analytical procedures associated with each methodology, and other
factors.
A.
The Design Storm Method (CG-1 in the BMP Manual) is applicable to
any size of regulated activity. This method requires detailed modeling
based on site conditions.
(1)
No plan shall increase the post-development total runoff volume for
all storms equal to or less than the two-year, twenty-four-hour duration
precipitation to more than the predevelopment total runoff volume.
(2)
For modeling purposes:
(a)
Existing (predevelopment) nonforested pervious areas must be
considered meadow.
(b)
Twenty percent of the existing impervious area of a project
site, when present, shall be considered meadow in the model for existing
conditions, if the existing impervious area is being altered by the
proposed regulated activity.
B.
The Simplified Method (CG-2 in the BMP Manual) provided below is
independent of site conditions and should be used if the Design Storm
Method is not followed. This method is not applicable to regulated
activities greater than one acre or for projects that require design
of stormwater storage facilities.
|
For new impervious surfaces:
|
(1)
Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
(2)
At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow, i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options for the first one inch of runoff include reuse, evaporation,
transpiration, and infiltration.
(3)
Wherever possible, infiltration facilities should be designed to
accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 0.5 inch of the permanently
removed stormwater runoff shall be infiltrated.
A.
For computation of predevelopment peak discharge rates, 20% of the
existing impervious area of a project site, when present, shall be
considered meadow, if the existing impervious area is being altered
by the proposed regulated activity.
B.
Post-development discharge rates shall not exceed the predevelopment
discharge rates for the one-, two-, five-, ten-, twenty-five-, fifty-,
and one-hundred-year twenty-four-hour storms. If it is shown that
the peak rates of discharge indicated by the post-development analysis
are less than or equal to the peak rates of discharge indicated by
the predevelopment analysis for one-, two-, five-, ten-, twenty-five-,
fifty- and one-hundred-year, twenty-four-hour storms, then the requirements
of this section have been met. Otherwise, the applicant shall provide
additional controls as necessary to satisfy the peak rate of discharge
requirement.
A.
For the purposes of the Act 167 Stormwater Management (Plan) elements
contained within the York County Integrated Water Resources Plan and
this chapter, design policy pertaining to stormwater management facilities
for Pennsylvania Department of Transportation (PennDOT) and Pennsylvania
Turnpike Commission (PTC) roadways and associated facilities is provided
in Section 13.7 (Antidegradation and Post-Construction Stormwater
Management Policy) of PennDOT Publication No. 13M, Design Manual Part
2 (August 2009), as developed, updated, and amended in consultation
with the Pennsylvania Department of Environmental Protection (DEP).
As stated in DM-2.13.7.D (Act 167 and Township ordinances), PennDOT
and PTC roadways and associated facilities shall be consistent with
Act 167 Plans. DM-2.13.7.B (Policy on Antidegradation and Post-Construction
Stormwater Management) was developed as a cooperative effort between
PennDOT and DEP.DM-2.13.7.C (Project Categories) discusses the anticipated
impact on the quality, volume, and rate of stormwater runoff.
B.
Where standards in the Act 167 elements of the IWRP and this chapter
are impractical, PennDOT or the PTC may request assistance from DEP,
in consultation with the county, to develop an alternative strategy
for meeting state water-quality requirements and the goals and objectives
of the Act 167 elements within the IWRP.
A.
Stormwater collection system. The stormwater collection system shall
be designed and approved based upon the following criteria:
(1)
Peak discharge shall be computed using the Rational Formula:
|
Q = CIA
| ||||
|
Where:
| ||||
|
Q =
|
Peak discharge in cubic feet per second.
| |||
|
C =
|
Runoff factor expressed as a percent of the total water falling
on an area.
| |||
|
I =
|
The rate of rainfall for the time of concentration of the drainage
area in inches per hour for a given storm frequency (rainfall intensity).
| |||
|
A =
|
The drainage area expressed in acres.
| |||
|
The runoff factor "C" is a percentage factor which represents
the proportion of the total quantity of water falling on the area
that remains as runoff.
| ||||
(2)
The runoff factors for various types of drainage areas, as presented
in the following table, shall be used for design.
|
Runoff Factors for the Rational Equation
| ||
|---|---|---|
|
Type of Drainage Area or Surface
|
Runoff Factor "C"
| |
|
Impervious surfaces, such as but not limited to roof surface,
pavement, concrete or bituminous concrete, gravel
|
0.95
| |
|
Cultivated field
|
0.40
| |
|
Lawn
|
0.25
| |
|
Meadow
|
0.20
| |
|
Wooded
|
0.15
| |
|
NOTES:
| ||
|---|---|---|
|
1.
|
Consideration should be given to future land use changes in
the drainage area in selecting the "C" factor.
| |
|
2.
|
For drainage area containing several different types of ground
cover, a weighted value of "C" factor must be used.
| |
|
3.
|
In special situations where sinkholes, stripped abandoned mines,
etc., exist, careful evaluation shall be given to the selection of
a suitable runoff factor with consideration given to possible reclamation
of the land in the future.
| |
(3)
Rainfall intensity "I" shall be per § 158-13L according to the following:
(a)
Storm frequency.
[2]
When a pipe or culvert is intended to convey the discharge from
a stormwater management facility, its required capacity shall be computed
by the Rational Method and compared to the peak outflow from the stormwater
management facility for the one-hundred-year storm. The greater flow
shall govern the design of the pipe or culvert.
[3]
A one-hundred-year design storm frequency may be required for
design of the stormwater collection system to insure that the resultant
stormwater runoff from the post-development design storm is directed
into the stormwater management facility.
[4]
In all cases where drainage is collected by means of a head
wall or pipe end, the pipe shall be designed as a culvert. The minimum
diameter of the culvert shall be 18 inches. The minimum diameter of
storm sewer shall be 15 inches, when located in a public right-of-way
or easement.
[5]
Where the collection system may be under inlet or outlet control,
the Township Engineer may request additional calculations, such as
but not limited to hydraulic grade lines.
(b)
Storm duration.
[1]
A five-minute storm duration shall be used if this duration
does not result in a maximum expected discharge that exceeds the capacity
of a thirty-inch pipe.
[2]
If a five-minute storm duration results in a pipe size exceeding
30 inches, the time of concentration approach shall be used in determining
storm duration.
(4)
Inlet placement. In general, catch basins shall be placed as required
by hydraulic capacity. For design purposes, a capture ratio (intercepted
flow/design flow) of 70% or greater is required. However, the width
of flow in a street cannot exceed 1/2 of the travel lane. In any event,
the maximum distance between conveyed inlets shall not exceed 400
feet.
(5)
Pipe and swale capacity.
(a)
Manning's equation shall be used for the design of all storm
sewer pipes and for open channel design:
|
V = 1.486 R2/3 S1/2
n
| ||||
|
Where:
| ||||
|
V =
|
Velocity of the water in feet per second.
| |||
|
R =
|
Hydraulic radius which is equal to the net effective areas (A)
divided by the wetted perimeter (W.P.):
| |||
|
R =
|
A
W.P.
| |||
|
The wetted perimeter is the lineal feet of the drainage facility
cross-section which is wetted by the water.
| ||||
|
S =
|
Slope of the hydraulic gradient (for approximation, use the
water surface slope in a wetted stream and the stream bed slope in
dry stream or the pipe slope).
| |||
|
n =
|
The roughness coefficient. Roughness coefficients are as follows:
| |||
|
Value of Manning's Roughness Coefficient – n
| ||
|
Rip-rap
|
0.040
| |
|
Grass-lined channel
|
0.035
| |
|
Bare earth channel
|
0.020
| |
|
Paved bituminous channel
|
0.016
| |
|
Concrete
|
0.012
| |
|
Turf reinforcement matting (TRM)
|
Per manufacturer's recommendation
| |
(b)
The maximum permitted velocity in a lined or unlined swale shall
be in accordance with the USDA Engineering Field Manual, Pennsylvania
DEP, applicable Pennsylvania codes and state law, whichever is less.
(c)
The maximum permitted velocity in storm sewer pipe is 20 FPS.
If 20 FPS is exceeded, the pipe must be anchored in accordance with
the following table:
|
Velocity of Flow
(feet per second)
|
Anchor Spacing
(feet)
| |
|---|---|---|
|
20-24.99
|
20
| |
|
25-30
|
10
| |
|
Under no circumstances shall flow velocity exceed 30 FPS.
| ||
B.
Stormwater management facilities. The plan shall be designed and
approved based upon the following criteria:
(1)
General. For drainage areas 320 acres or larger the peak discharge
and runoff shall be computed using the soil-cover complex method contained
in "Urban Hydrology for Small Water Sheds," Technical Release No.
55, published by the Engineering Division, Soil Conservation Services,
United States Department of Agriculture, dated June 1986 or latest
revision, except as modified herein. For drainage areas less than
320 acres the Modified Rational Method may be utilized. Alternate
methods of analysis may be considered if approved by the Township
Engineer.
(2)
Outflow determination.
(a)
The maximum permitted stormwater discharge, in cubic feet per second, from any site shall not exceed the calculated peak discharge from the site at predevelopment ground cover and soil conditions for all design storms specified in § 158-16B. For the purpose of this chapter, predevelopment groundcover conditions shall be assumed to be "meadow" for all nonforested pervious areas as defined in "Urban Hydrology for Small Water Sheds," Technical Release No. 55, published by Engineering Division, Soil Conservation Service, United States Department of Agriculture, dated June 1986 or latest revision; or if using the Modified Rational Method, a "C" factor of 0.20 shall be used for meadow conditions for all nonforested pervious areas. For existing impervious surfaces see § 158-16A. The maximum permitted stormwater discharge shall be calculated using the SCS method or alternative method approved by the Township Engineer for rainfalls having recurrence intervals of one, two, five, 10, 25, 50 and 100 years. Time of concentration (Tc) should be calculated using the SCS segmental approach in accordance with the current recommendations by SCS. For the purpose of this chapter, the rainfall depths shall be per § 158-13L.
(c)
If alternate methods of analysis are utilized, the design storms
recurrence interval in years shall be the same as used in the SCS
TR-55 Method.
(3)
Minimum required detention storage. The minimum required detention
storage shall be determined by routing the approved post-development
hydrographs through the stormwater management facility, 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 Township Engineer.
(4)
Emergency spillway. Emergency spillways or overflow structures shall
be designed to pass the peak flow resulting from a one-hundred-year
recurrence interval design storm computed at post-development conditions,
assuming that the principal outlet structure is nonfunctional. All
retention basins and detention basins shall provide an emergency spillway.
Emergency spillways shall be located in cut where feasible; if not,
adequate permanent stabilization is required. All emergency spillways
shall be permanently stabilized for the design peak flow rate and
velocity.
(5)
Minimum bottom slope. All detention basins shall have a minimum bottom
slope of 2% if not being utilized for infiltration purposes.
(6)
Side slopes. The maximum side slopes for detention or retention basins
shall be three horizontal to one vertical in cut and four horizontal
to one vertical in fill.
(7)
Freeboard. The stormwater management facility shall have a minimum 1/2 foot of freeboard determined after routing the one-hundred-year recurrence interval design storm per § 158-18B(4) or a minimum of one foot of freeboard above the normal one-hundred-year storm routing elevation, whichever is greater.
(8)
Seepage trench. All stormwater management detention basins shall
provide as a minimum a two-foot-wide by ten-foot-long by six-foot-deep
seepage trench in the bottom of the basin near the outlet control
structure in accordance with the stormwater permit application, unless
field conditions deem the seepage trench nonfunctional and concurred
by the Township Engineer. This seepage trench is not required if the
basin is being utilized for infiltration purposes.
(9)
Fencing, trash racks and installation of childproof facilities may
be required by the Township.
