A. 
For all regulated activities, unless preparation of an SWM site plan is specifically exempted in § 338-11:
(1) 
Preparation and implementation of an approved SWM site plan is required.
(2) 
No regulated activities shall commence until the municipality issues written approval of an SWM site plan, which demonstrates compliance with the requirements of this chapter.
B. 
SWM site plans approved by the municipality in accordance with this chapter 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.[1]
[1]
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) 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.
E. 
For all regulated activities, implementation of the volume controls in § 338-12 is required.
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) 
Any areas in the design to be designated initially as gravel or crushed stone shall be assumed to be impervious in preparation of a plan for conformance with this chapter.
(4) 
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 § 338-12 and the peak rate controls of § 338-13 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) by the developer. 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) 
Incorporate the techniques for green infrastructure and low-impact development practices described in the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual).1
[Amended 11-15-2022 by Ord. No. 2022-03]
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. 
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, United States Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland. NOAA's Atlas5 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/.
M. 
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,[2] and the Storm Water Management Act.[3]
[2]
Editor's Note: See 35 P.S. § 691.1 et seq.
[3]
Editor's Note: See 32 P.S. § 680.1 et seq.
N. 
Various BMPs and their design standards are listed in the BMP Manual1.
A. 
Regulated activities that result in cumulative earth disturbances of less than 5,000 square feet are exempt from the requirements in § 338-13 (Rate controls) and Article IV [Stormwater Management (SWM) Site Plan Requirements] of this chapter. Without limiting the general applicability of this provision, a phased project will be considered to result in cumulative earth disturbance of 5,000 square feet or more if the total from all phases exceeds the threshold, regardless of the amount of earth disturbance in any particular phase.
[Amended 11-15-2022 by Ord. No. 2022-03]
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 § 338-10D through L.
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.
[Added 11-15-2022 by Ord. No. 2022-03]
A. 
If the municipality determines that any requirement under this chapter cannot be achieved for a particular regulated activity, the municipality may, after an evaluation of alternatives, approve measures other than those in this chapter, subject to § 338-11.1B and C.
B. 
Waivers or modifications of the requirements of this chapter may be approved by the municipality if enforcement will exact undue hardship because of peculiar conditions pertaining to the land in question, provided that the modifications will not be contrary to the public interest and that the purpose of the chapter is preserved. Cost or financial burden shall not be considered a hardship. Modification may be considered if an alternative standard or approach will provide equal or better achievement of the purpose of the chapter. A request for modifications shall be in writing and accompany the stormwater management site plan submission. The request shall provide the facts on which the request is based, the provision(s) of the chapter involved and the proposed modification.
C. 
No waiver or modification of any regulated stormwater activity involving earth disturbance greater than or equal to one acre may be granted by the municipality unless that action is approved in advance by the Department of Environmental Protection (DEP) or the delegated County Conservation District.
[Amended 11-15-2022 by Ord. No. 2022-03]
The green infrastructure and low-impact development practices provided in the BMP Manual1 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 Manual1) 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.
(2) 
For modeling purposes:
(a) 
Existing (predevelopment) nonforested pervious areas must be considered meadow in good condition.
(b) 
Twenty percent of existing impervious area, when present, shall be considered meadow in good condition in the model for existing conditions.
B. 
The Simplified Method (CG-2 in the BMP Manual1) 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 hydrologic routing to 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.
(4) 
This method is exempt from the requirements of § 338-13, Rate controls.
A. 
General. Postdevelopment 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 postdevelopment 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.
B. 
Runoff rates. There shall be no increase in the peak rate of stormwater runoff discharge from any activity covered by the chapter following the completion of the activity (postdevelopment conditions) over the rate that would have occurred from the land prior to the activity (predevelopment conditions). This criterion shall apply to the total activity even if the activity is to take place in stages.
(1) 
Off-site areas which drain through a proposed development site are not subject to the control standard when determining allowable peak runoff rates. However, on-site drainage facilities shall be designed to safely convey off-site flows through the development site.
(2) 
Where the site area to be impacted through a proposed development activity differs significantly from the total site area, only the proposed impact area shall be subject to the runoff criteria.
C. 
Storm frequencies. Stormwater management facilities on all development sites shall control the peak stormwater discharge for the given storm frequencies. The USDA NRCS twenty-four-hour, Type II Rainfall Distribution shall be used for analyzing stormwater runoff for both pre and post-development conditions. The twenty-four-hour total rainfall for these storm frequencies in the watershed shall be obtained from the Precipitation-Frequency Atlas of the United States, Atlas5, United States Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland. NOAA's Atlas5 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/.
D. 
Calculation methods.
(1) 
Development sites. For the purpose of computing peak flow rates and runoff hydrographs from development sites, calculations shall be performed using one of the following: USDA NRCS publications, Technical Release (TR) 55 or 20, HEC I or Penn State Runoff Model (PSRM) or Modified Rational Method. Under special circumstances, other computation methods may be used subject to the approval of the Township Engineer.
(2) 
Stormwater collection/conveyance facilities. For the purposes of designing storm sewers, open swales and other stormwater runoff collection and conveyance facilities, the Rational Method or other method as approved by the Township Engineer may be applied. Rainfall intensities for design should be obtained from the Pennsylvania Department of Transportation rainfall charts.
(3) 
Routing of hydrographs through detention/retention facilities for the purpose of designing those facilities shall be accomplished using the Modified-Puls Method or other recognized reservoir routing method subject to the approval of the Township Engineer.
(4) 
Predevelopment conditions. Predevelopment conditions shall be assumed to be those which exist on any site at the time prior to the commencement of development activities. NRCS runoff curve numbers selected for use in the calculations shall accurately reflect existing conditions subject to the approval of the Township Engineer. The hydrologic conditions for all areas with pervious cover (i.e., fields, woods, lawn areas, pastures, cropland, etc.) shall be assumed to be in good condition, and the lowest recommended NRCS runoff curve number (CN) shall be applied for all pervious land uses within the respective range for each land use and hydrologic soil group. Impervious cover shall include, but not be limited to, any roof, parking, or driveway areas, and any new streets and sidewalks. Any areas designed to initially be gravel or crushed stone shall be assumed to be impervious for the purposes of these criteria.