A.
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 17-302:
B.
SWM site plans approved by the municipality, in accordance with § 17-406, 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.
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)
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), 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 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 § 17-303 and the peak rate controls of § 17-304 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
of the adjacent property owner(s). 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 by implementing measures
to:
(a)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(b)
Maintain or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
(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 over karst shall include an evaluation
of measures to minimize adverse effects.
J.
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.
K.
Normally dry, open top storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not less than 24 and not more than 72 hours from the end of
the design storm.
L.
Method of computation. Peak discharge and runoff shall be computed
using:
(1)
For drainage areas of zero to five acres, the recommended method of peak discharge runoff computation is the Rational Method. The design storm rainfall values to be used in the computations shall be in accordance with the PennDOT Drainage Manual, Publication 584, Chapter 7, Appendix A, as now or hereafter amended. Refer to Appendix E for the IDF maps and charts.[1]
[1]
Editor's Note: Said appendix is on file in the Township offices.
(2)
For drainage areas five acres to 0.5 square miles, the recommended
method of peak discharge and runoff computation is the Soil Cover
Complex Method as found in Technical Release 55, Urban Hydrology for
Small Watersheds, as published by Soil Conservation Service, as now
or hereafter amended. Refer to Appendix F for the Fayette County Twenty-Four-Hour
Rainfall Values.[2]
[2]
Editor's Note: Said appendix is on file in the Township offices.
(3)
For drainage areas larger than 0.5 square miles, the recommended
method of peak discharge and runoff computation is Procedure PSU-IV
for Estimating Design Flood Peaks on Ungauged Pennsylvania Watersheds,
as developed by Pennsylvania State University, as now or hereafter
amended.
M.
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/.
N.
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.
O.
Various BMPs and their design standards are listed in the BMP Manual.
A.
Regulated activities that create DIAs smaller than 1,000 square feet
are exempt from the peak rate control and the SWM site plan preparation
requirement of this chapter.
B.
Regulated activities that create DIAs equal to or greater than 1,000
square feet and less than 5,000 square feet are exempt only from the
peak rate control requirement of this chapter.
C.
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 102.
D.
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 102.
E.
Single-family residential dwellings are exempt from providing SWM
plan if one of the identified BMPs is complied with, as provided for
in Appendix C.[1] If the property owner/developer chooses to select another
BMP for a single-family residential dwelling, then he/she shall follow
the requirements of the SWM plan as regulated in this chapter. Single-family
residential dwellings are not exempt from inspections.
[1]
Editor's Note: Said appendix is on file in the Township offices.
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 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)
Do not increase the postdevelopment total runoff volume for all storms
equal to or less than the two-year twenty-four-hour duration precipitation.
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 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.
Areas not covered by a release rate map from an approved Act 167
Stormwater Management Plan:
(1)
Postdevelopment discharge rates shall not exceed the predevelopment
discharge rates for the two-, ten-, twenty-five-, and 100-year twenty-four-hour
storms. If it is shown that the peak rates of discharge indicated
by the postdevelopment analysis are less than or equal to the peak
rates of discharge indicated by the predevelopment analysis for two-,
ten-, twenty-five-, 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.
B.
Areas covered by a release rate map from an approved Act 167 Stormwater
Management Plan:
(1)
For the two-, ten-, twenty-five-, and 100-year storms, the postdevelopment
peak discharge rates will follow the applicable approved release rate
maps. For any areas not shown on the release rate maps, the postdevelopment
discharge rates shall not exceed the predevelopment discharge rates.
