A. 
All computations used in conjunction with the analysis and design of stormwater management facilities shall be based on one or more of the following methods, or as otherwise approved in advance by the Township:
(1) 
TR-55-Soil Conservation Service (SCS) Technical Release No. 55.
(2) 
TR-20-Soil Conservation Service (SCS) Technical Release No. 20.
(3) 
Modified rational method.
(4) 
Penn State runoff model.
(5) 
Virginia Tech/Penn State runoff model.
B. 
These methods for determining peak discharge shall be used to:
(1) 
Determine predevelopment runoff conditions;
(2) 
Analyze the impact of development; and
(3) 
Perform calculations in the design of any detention/retention facilities used in controlling runoff.
C. 
The SCS, Type II rainfall distribution shall be used for all analyses. The design storm frequencies for the watershed are:
Design Storm
24 Hour Rainfall Depth
1-year
1.97
2-year
2.35
5-year
2.88
10-year
3.30
25-year
3.90
50-year
4.40
100-year
5.20
D. 
Predevelopment conditions: The cover type for all sites will be considered to be the dominant land cover during the five-year period immediately preceding a proposed regulated activity:
(1) 
For the purposes of predevelopment peak flow rate and volume determination, existing nonforested pervious areas conditions shall be considered as meadow (good condition). Forested land areas shall be considered in good condition.
(2) 
For the purposes of predevelopment peak flow rate and volume determination, 20% of existing disturbed impervious area, when present, shall be considered meadow (good condition).
E. 
Post-development conditions: The hydrologic parameters used to develop peak flow rates shall be reflective of anticipated soil runoff characteristics following grading and development of the site.
F. 
Time of concentration: The minimum time of concentration for any watershed shall be five minutes. A minimum five-minute time of concentration may be assumed for any post-development watershed. Calculations must be provided for all predevelopment times of concentrations. A minimum time of concentration cannot be assumed for predevelopment conditions.
G. 
The use of the basic rational method in estimating runoff may be employed in the design of the storm sewer conveyance system within the development. The storm sewer system shall be interpreted as the conduits, culverts, inlets and appurtenant features for the conveying of stormwater to, through or from a development site to the point of final discharge or control facility. The rational method shall not be used in the analysis of stormwater runoff from the development in its entirety or in conjunction with the design of any retention/detention facilities or other runoff control measures.
H. 
Points of interest for analysis of pre- and post-development runoff must be selected to demonstrate compliance with the requirements of §§ 71A-16 and 71A-17 is achieved at all points where runoff exits the perimeter of the property.
I. 
Stormwater runoff shall not be transferred from one watershed to another unless the watersheds are sub-areas of a larger watershed that are tributary to a common point of interest within or near the perimeter of the property. Transfer of runoff from one watershed to another under any other circumstances shall only be approved at the discretion of the Township. Documentation shall be provided that peak flow rates are not increased following development and there will be no detrimental impact in downstream areas.
J. 
The stormwater management plan shall consider all of the stormwater runoff flowing over the project site. Runoff calculations shall be made to ensure that runoff from the fully development upstream watershed area (based on the Comprehensive Plan) can be accommodated by the pipes, drainage easements and watercourses, etc., on the site.
A. 
All stormwater collection and conveyance facilities (pipes, swales, and structures) shall be designed for a 100-year design storm event, unless the runoff would naturally drain overland to a stormwater detention facility, in which case a twenty-five-year design storm event may be used. The hydraulic gradeline must be a minimum of two feet below the surface elevation of structures and within the pipe. Swales and channels shall provide at least one foot of freeboard above the energy gradeline. Backwater effects of pipes discharging under surcharge conditions shall be included.
B. 
Runoff calculations shall include complete hydrology and hydraulic analysis of all downstream swales and pipe facilities to permanent stream discharge point, to the municipal boundary or connection to a state- or county-owned conveyance system.
C. 
Manholes shall not be spaced more than 400 feet apart for pipe sizes up to 24 inches in diameter and not more than 650 feet apart for larger pipe sizes.
D. 
No public stormwater pipe shall be less than 15 inches in diameter that conveys surface runoff. The minimum pipe slope shall be 1.0% grade or maintain velocity of two feet per second. For public storm sewer systems, only pipes related to construction of stormwater BMPs may be less than 15 inches in diameter.
E. 
All workmanship and materials shall conform to the Township's construction standards. In addition, all workmanship and materials shall conform to the latest edition of PennDOT Form 408 and be supplied by manufacturers or suppliers listed in PennDOT's Bulletin 15. No stormwater facility shall be enclosed or covered over until the Township has field reviewed the construction. All construction materials used in storm sewers shall be tested by a qualified testing laboratory, if required by the Township. The cost for such test shall be borne by the developer.
F. 
Manhole and inlet castings shall conform to the Pennsylvania Department of Transportation Form 408 and PennDOT Standards for Roadway Construction. Inlet grates shall be bicycle safe. Frames and grates shall be cast iron or structural steel. Concrete frames shall not be permitted.
G. 
All connections to existing storm sewer pipes shall be made by construction of a suitable junction box (inlet or manhole) to provide access for cleanout. No blind connections shall be permitted.
H. 
The discharge of stormwater runoff shall be to a well-defined drainage course, which has a defined bed and bank. If stormwater runoff cannot be discharged to a defined drainage course, documentation of written permission from each downstream property owner shall be provided for all properties between the source of discharge and the defined drainage course. The use of level spreaders or similar BMPs that promote sheet flow may be permitted if the applicant provides documentation that the peak post-development 100-year discharge is no greater than predevelopment two-year discharge and a letter from the Geotechnical Engineer of Record regarding slope stability of the downstream area is provided. Use of a level spreader requires a waiver to be granted by the Township.
I. 
Easements for stormwater management facilities shall be required to have a minimum width of 20 feet. Where a subdivision or land development is, or will be, traversed by a watercourse, there shall be provided a stormwater or drainage easement of a width sufficient for the purpose, but not less than 20 feet. The stormwater detention facilities must be provided within a drainage easement. An access easement must be provided from the public right-of-way to the stormwater detention facility with a minimum width of 20 feet.
(1) 
Operation and management plans for stormwater management approved pursuant to 25 Pa. Code § 102 after the date of this section shall be recorded as a restrictive deed covenant that runs with the land.
(2) 
If a conservation easement is provided the long-term ownership, access, maintenance, and use restrictions must be identified on the recording plan.
J. 
No property owner shall obstruct or alter the flow, location or carrying capacity of a stream, channel or drainage swale to the detriment of any other property owner, whether upstream or downstream. All subdivision and/or land development plans containing streams, channels, drainage swales, storm sewers or other conveyance systems that cross property boundaries, existing or proposed, or whose discharge crosses such boundaries shall contain a note stating the above.
K. 
All roof drains shall discharge to an on-lot sump or to a storm sewer system, which is controlled by a detention pond. Outlets from roof drain sumps shall not discharge directly onto fill slopes. Outlets shall not discharge directly to the gutter line of any street. All pipes from roof drains shall be a minimum four-inch Schedule 40 ABS, PVC or SDR 35 pipe. Four-inch Schedule 40 PVC or ABS pipe is required for a distance of 10 feet from the foundation of the dwelling. No stormwater drainage system shall be permitted to discharge into any sanitary sewer system. No pipes shall be permitted to be constructed through any curbing on any public street.
L. 
Intersections of private driveways and public streets. Stormwater drainage facilities shall be placed where each private driveway intersects with a public street. The design shall be approved by the Township and shall meet the following requirements: The facility shall be placed to maintain the flow line of the stormwater drainage facility in the public street.
(1) 
Where an apron gutter is to be utilized, said apron gutter shall be designed and constructed in accordance with the Township's Standard Details.
(2) 
Where reinforced concrete, metal or tile pipe is to be used beneath the driveway, said pipe shall not be less than 15 inches in diameter and shall extend across the full width of the driveway and beyond the driveway for a distance determined by the Township. The pipe shall be installed with flared end sections and shall be designed to support H-15 loading and any other imposed loadings necessary without structurally damaging the system. The installation of the pipe shall be in accordance with the adopted Township's Standard Details.
A. 
All retention/detention facilities shall be equipped with multistage outlet structures to provide discharge control for each designated storm frequency. Provisions shall also be made to safely pass the post-development 100-year storm runoff in the event of an outlet structure failure without damaging or impairing the continued function of the facilities (i.e., impairing the continued function of) the facilities. The facility(ies) must have an emergency outlet which is able to discharge the post-development 100-year peak flow. Should any stormwater management facilities qualify as a dam under PaDEP Chapter 105 criteria, the facility shall be designed in accordance with those regulations and meet the regulations concerning dam safety.
B. 
Any stormwater management facility designed to store runoff shall provide an emergency spillway designed to convey the unattenuated 100-year post-development peak rate flow with a blocked primary outlet structure and an inundation stormwater to the invert elevation of the spillway, with a minimum one-foot freeboard to the crest of the embankment.
C. 
Woody vegetation shall not be permitted on the embankments or within 25 feet of the emergency spillway.
D. 
Fencing at least four feet in height shall be required for a storage facility if directed by the Township.
E. 
Side slopes of storage facilities shall not exceed a ratio of 3:1 horizontal to vertical dimension. The crest of the embankment shall have a minimum width of not less than 10 feet.
F. 
The facility shall be equipped with an access road at least 10 feet wide and with a maximum of grade of 15%. Access roads greater than 12% grade must be paved. Access roads 12% or less shall have a minimum six inches depth non-eroding aggregate surface. An access easement with a minimum width of 20 feet to all stormwater detention facilities shall be provided. The access easement shall include a statement on the recorded plan from the owner/operator of the facility granting access to the Township.
G. 
All stormwater facility outlet structures shall have suitable gaskets to prevent leakage and piping of water through the facility embankment. All storm pipe installed through the facility embankment must be constructed of reinforced concrete pipe. Use of high-performance polypropylene pipe may be permitted with documentation of pipe manufacturer's backfill requirements.
H. 
A geotechnical investigation report for the construction of the stormwater detention/retention and infiltration facilities must be provided, including design recommendation for embankment construction, interior and exterior slopes, drainage swales and infiltration areas.
I. 
Basin outlet structures shall have nonclogging trash racks over all design openings. Periodic cleaning of debris from trash racks shall be included in the operation and maintenance plan.
J. 
Inlet structures and outlet structures shall be separated to the greatest extent possible in order to maximize the flow path through the basin.
K. 
Detention ponds shall be designed to be integrated into the overall site design and incorporate landscaping features, fountains and passive recreational amenities such as benches and pathways to provide an aesthetic and functional facility that fits within the character of the Township. When aesthetic and passive recreational amenities are incorporated into the design of the detention pond, the detention pond may be calculated as a part of the required open space as required elsewhere in this chapter. Side slopes of such facilities shall not exceed 4:1 horizontal to vertical dimension.
L. 
BMPs must be designed to protect and maintain existing uses (e.g., drinking water use; cold water fishery use) and maintain the level of water quality necessary to protect those uses in all streams, and to protect and maintain water quality in "special protection" streams, as required by statewide regulations at 25 Pa. Code, Chapter 93 (collectively referred to herein as "state water quality requirements").