Any regulated activity that meets the following exemption criteria is exempt from the provisions of this chapter only to the extent specifically provided for herein. These criteria shall apply to the total project even if the project is 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 set forth in §
199-7A(10) and
(12) through
(18), or as necessary to meet the intent of this chapter, or compliance with any NPDES permit requirements. Exemption shall not relieve the applicant from implementing such measures as are necessary to protect health, safety, and property. This exemption shall not relieve the applicant from meeting the requirements for water quality and groundwater recharge or special requirements for high quality (HQ) and exceptional value (EV) watersheds.
A. Regulated activities that create impervious areas equal to or less
than 750 square feet calculated on a cumulative basis from the date
of enactment of this chapter are exempt from the peak rate control
and the stormwater management site plan preparation requirements of
this chapter. Upon exceeding this cumulative exemption, the impervious
areas created from the date of exceedance forward shall not be exempted
from the requirements of this chapter, except as otherwise set forth
in this chapter. The Township may deny this exemption in situations
where the location of impervious area will discharge any concentrated
stormwater runoff onto a downslope property or directly into the waters
of the commonwealth.
B. Regulated activities that create DIAs equal to or less than 1,000
square feet are exempt from the peak rate control and the stormwater
management site plan preparation requirements of this chapter. This
exemption shall be applied on a project basis and not a cumulative
basis.
C. Regulated activities that create DIAs greater than 1,000 square feet
and equal to or less than 5,000 square feet are exempt only from the
peak rate control requirement of this chapter. This exemption shall
be applied on a project basis and not a cumulative basis.
D. Agricultural activities such as growing crops, rotating crops, tilling
of soil and grazing animals and other such activities when performed
in accordance with a conservation plan or erosion and sedimentation
control plan approved by the Conservation District shall be exempt
from the rate control and stormwater management site plan provisions
of this chapter. Construction of new buildings or the addition of
impervious area shall not be considered an agricultural activity for
purposes of this exemption.
E. Forest management operations, which are following the DEP's
management practices, contained in its publication "Soil Erosion and
Sedimentation Control Guidelines for Forestry," or any successor publication,
and are operating under an erosion and sedimentation control plan
approved by the Conservation District, shall be exempt from the rate
control and stormwater management site plan provisions of this chapter.
Construction of new buildings or the addition of impervious area shall
not be considered forest management activity for purposes of this
exemption.
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.
G. Emergency maintenance work performed for the protection of public
health, safety and welfare. A written description of the scope and
extent of any emergency work performed shall be submitted to the Township
within 24 hours of the commencement of the activity. If the Township
determines the work is not an emergency, then the work shall cease
immediately and the requirements of this chapter shall be addressed
as applicable.
H. Any maintenance to an existing stormwater management system made
in accordance with plans and specifications approved as part of an
O&M plan or by the Township Engineer.
I. Regulated activities exempted from SWM site plan requirements are
not subject to review and approval for the volume control requirements
of this chapter. It shall be the landowner's responsibility to
assure compliance with the volume control requirements. The Township
may at its discretion require drawings and calculations in sufficient
detail to show proposed volume controls of this chapter are met.
J. The Township may deny or revoke any exemption pursuant to this section
at any time for any project that the Township determines poses a threat
to public health, safety, property or the environment.
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 to or less than one acre
that do not require hydrologic routing to design the stormwater management
facilities, this chapter establishes no preference for either methodology;
therefore, the applicant may select either methodology with Township
concurrence.
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) The stormwater management plan shall 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.
(b)
Twenty percent of the existing impervious area of a project
site, when present, shall be considered meadow in the model for existing
conditions.
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) The stormwater management plan shall provide for the capture of 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 structures 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.
(4) This method is exempt from the requirements of §
199-10, Rate controls.
For the purposes of the county Act 167 plan elements, contained
within the IWRP, and this chapter, design policy pertaining to stormwater
management facilities for PennDOT 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 DEP. As stated in DM-2.13.7.D (Act 167 and Municipal
Ordinances), PennDOT 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-2.13.7.0 (Project Categories) discusses
the anticipated impact on the quality, volume, and rate of stormwater
runoff. Where standards in the Act 167 elements of the IWRP and this
chapter are impractical, PennDOT 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. For the purposes of the Act
167 elements in the IWRP and this chapter, road maintenance activities
are regulated under 25 Pa. Code Chapter 102.
Stormwater runoff from all project sites shall be calculated
using either the 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. The Township may allow the use
of the rational method to estimate peak discharges from drainage areas
that contain less than 200 acres.
B. The design storm volumes and precipitation intensities to be used
in the analysis of discharge or runoff shall be obtained from the
Precipitation-Frequency Atlas of the United States, Atlas 14, Volume
2, Version 3.0, U.S. Department of Commerce, National Oceanic and
Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological
Design Studies Center, Silver Spring, Maryland. NOAA's Atlas
14 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/.
C. For computation of predevelopment flow rates, 20% of the existing
impervious area of a project site, when present, shall be considered
meadow. 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 Table 1 and Table 2, respectively.
Peak discharge computed using the rational method should follow
the formula, Q = CIA
Where:
|
Q
|
=
|
Peak discharge in cubic feet per second
|
C
|
=
|
Runoff factor expressed as a percent of the total rainfall
|
I
|
=
|
Rainfall intensity in inches per hour
|
A
|
=
|
The drainage area expressed in acres
|
D. 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 form time to time
by NRCS). Time-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
Table 1.
F. Runoff coefficients (c) for both existing and proposed conditions
for use in the rational method shall be obtained from Table 2.
G. 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.
H. Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this chapter using any generally
accepted hydraulic analysis technique or method.
I. 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.