A. 
All stormwater management, collection, conveyance, erosion control, and floodplain considerations shall be accomplished in accordance with the following provisions:
(1) 
Prior to the final approval or commencement of any regulated activity within the jurisdiction of this chapter, the developer shall submit a stormwater management site plan to the Township for approval.
(a) 
When plan applications, whether preliminary or final, are submitted in sections, a detailed stormwater management site plan for the entire project site shall be submitted. This detailed plan shall demonstrate how the stormwater of the proposed section will relate to the entire development. The amount and velocity at the discharge point of the section shall be included in the data submitted. If temporary facilities are required for construction of a section, such facilities shall be included in the submitted plans.
(b) 
The type, location, and extent of all erosion and sedimentation control measures shall be shown on an erosion and sedimentation control plan that conforms to the requirements of the Soil Erosion and Sediment Control Manual of the Pennsylvania Department of Environmental Protection and the erosion and sedimentation control design standards of this chapter.
(c) 
An operation and maintenance agreement, in recordable form acceptable to the Township, that clearly sets forth the ownership, operation and maintenance responsibility of all temporary and permanent stormwater management facilities and erosion and sedimentation control facilities as provided for in Article VII, Administration. The intent of these regulations is to provide private operation and maintenance of stormwater management and erosion and sedimentation control facilities, including regular inspection of the areas to assure proper maintenance and care of all stormwater management facilities in accordance with their design.
[Amended at time of adoption of Code (see Ch. 1, General Provisions, Art. I)]
(d) 
A written report shall be submitted that includes the following information:
[1] 
General description of the development site, including a description of existing natural and hydrologic features and any environmentally sensitive areas.
[2] 
General description of the overall stormwater management concept for the project, including a description of permanent stormwater management techniques, structural and nonstructural BMPs to be employed.
[3] 
Construction specifications of the materials to be used for structural stormwater management facilities.
[4] 
Stormwater runoff calculations for both predevelopment and post-development conditions.
[5] 
An erosion and sedimentation control plan narrative that conforms to the requirements of the Soil Erosion and Sediment Control Manual of the Pennsylvania Department of Environmental Protection and provides a description of all erosion and sedimentation control measures, temporary as well as permanent, including the staging of earth moving activities, sufficient in detail to clearly indicate their function.
[6] 
For all proposed detention basins and retention basins, except temporary sedimentation basins, the documentation shall include a plotting or tabulation of storage volumes with corresponding water surface elevations and the outflow rates for those water surfaces.
[7] 
For all proposed detention basins and retention basins, except temporary sediment basins, documentation shall set forth the design hydrograph, the routing method or a method of equal caliber acceptable to the Township Engineer, utilized to determine the function of the basin.
(2) 
All stormwater runoff flowing over the project site shall be considered in the design of the stormwater management facilities.
(3) 
Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities or open channels consistent with this chapter.
(4) 
Where a development site is traversed by watercourses, a drainage easement shall be provided conforming substantially to the line of such watercourses.
(a) 
The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations that may affect adversely the flow of stormwater within any portion of the easement.
(b) 
Maintenance of vegetation within the easement shall be required.
(5) 
The PADEP, Chapter 105, Rules and Regulations, apply to the construction, modification, operation or maintenance of both existing and proposed water obstructions and encroachments throughout the watershed, including work in wetlands. Inquiries on permit requirements or other concerns shall be addressed to PADEP's regional office.
(6) 
When it can be shown that, due to topographic conditions, natural drainageways on the development site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainageways. Work within natural drainageways shall be subject to approval by PADEP.
(7) 
Any stormwater management facilities or any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures, etc.) that are regulated by this chapter, that will be located in or adjacent to waters of the commonwealth (including wetlands), shall be subject to approval by PADEP. When there is a question whether wetlands may be involved, it is the responsibility of the applicant or his agent to show that the land in question cannot be classified as wetlands; otherwise, approval to work in the area must be obtained from PADEP.
(8) 
Should any stormwater management facility require a dam safety permit under PADEP Chapter 105, the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety which may be required to pass storms larger than one-hundred-year event.
(9) 
No detention basin, storm pipe, or swale or any other stormwater management facility shall discharge directly onto any publicly used Township, state or private road but shall discharge into a culvert under or along the road.
(10) 
Any stormwater management facilities regulated by this chapter that will be located on, or discharged onto state highway rights-of-way shall be subject to approval by PennDOT.
(11) 
Stormwater management facilities located within or affecting the floodplain of any watercourse shall comply with the requirements of the floodplain regulations provided in Chapter 350, Zoning, or any future ordinances regulating construction or development within areas of the Township subject to flooding.
(12) 
The minimum floor elevations for all structures that would be affected by a basin, other temporary impoundments, or open conveyance systems where ponding may occur shall be two feet above the one-hundred-year water surface.
(a) 
If basement or underground facilities are proposed, detailed calculations addressing the effects of the stormwater ponding on the structure and water-proofing and/or flood proofing design information shall be provided for review and approval.
(13) 
All existing and natural watercourses, channels, drainage systems and areas of surface water concentration shall be maintained in their existing condition unless an alteration is approved by the appropriate regulatory agency.
(14) 
Stormwater management facilities intended to receive and infiltrate runoff from regulated activities shall be selected based on suitability of soils and site conditions and shall be constructed on soils that have the following characteristics:
(a) 
Infiltration testing shall be conducted in accordance with BMP Manual.
(b) 
Acceptable soil will have a percolation rate of at least 0.1 inch per hour and not more than 10 inches per hour (after application of the appropriate safety factor from the BMP manual).
(c) 
A minimum separation of 24 inches of acceptable soil between the bottom of the facility and the limiting zone, unless it is demonstrated to the satisfaction of the Township that the selected BMP has design criteria which allow for a smaller separation.
(d) 
A stabilized infiltration rate sufficient to accept the additional stormwater load and drain completely as determined by field tests conducted by the applicant's professional designer.
[1] 
The stabilized infiltration rate is to be determined in the same location and within the same soil horizon as the bottom of the infiltration facility.
[2] 
The stabilized infiltration rate is to be determined as specified in the BMP Manual.
(e) 
The Township shall be notified 24 hours prior to infiltration tests being conducted as to provide an opportunity for the Township to witness the tests.
(15) 
Stormwater discharge points onto an adjacent property shall comply with the following:
(a) 
Stormwater flows onto adjacent property shall not be created, relocated, or peak rate increased without written notification of the adjacent property owner(s) by the developer including the establishment of an easement.
(b) 
Stormwater runoff from a project site shall flow directly into a natural watercourse or into an existing storm sewer system. If neither of these is available, the applicant shall obtain an easement from the downstream landowner(s) to allow the site's runoff discharge to reach a natural watercourse or an existing storm sewer system through the easement. If an easement is obtained, post-developed flow characteristics must be similar to the runoff characteristics (spread, velocity, and peak rate) of the predeveloped flows. The easement from the downstream property owner(s) shall be to allow for a piped storm sewer system, an overland flow system, or a combination of the two. The downstream system design shall conform to the design requirements of this chapter.
(c) 
When the applicant provides verification that the downstream landowner(s) refuses to grant an easement at reasonable terms in the sole opinion of the Township, the site shall be designed such that the discharge from the applicant's site shall be in a nonerosive, sheet flow condition. For all design year storms, including the one-hundred-year storm, runoff from the applicant's site shall flow onto the adjacent property in a manner similar to the runoff characteristics (spread, velocity, and peak rate) of the predeveloped flow. The use of level spreaders is prohibited.
(d) 
Stormwater runoff shall not be transferred from one watershed to another unless the watersheds are subwatersheds of a common watershed which join together within the perimeter of the property, or both of the following apply:
[1] 
The effect of the transfer does not alter the peak discharge (in conformance with the requirements of the Act 167 Plan) onto adjacent lands; and
[2] 
Drainage easements from the affected landowners are provided.
[a] 
For the purposes of this subsection, affected landowners shall include all landowners receiving runoff that was transferred from one watershed to another watershed that does not join together within the perimeter of the project site, from the point of discharge from the project site to the location in the watershed where the transferred runoff discharges to a receiving watercourse located within the watershed that the runoff was transferred from.
(16) 
Unless an alternate design is submitted to the Township for review, and said design is prepared by a licensed (in the Commonwealth of Pennsylvania) geologist or geotechnical engineer:
(a) 
No stormwater facilities shall be placed in, over or within a distance that will impact the following features:
[1] 
Sinkholes.
[2] 
Closed depressions.
[3] 
Lineaments in carbonate areas.
[4] 
Fracture traces.
[5] 
Caverns.
[6] 
Intermittent streams.
[7] 
Ephemeral streams.
[8] 
Bedrock pinnacles (surface or subsurface).
(b) 
The minimum isolation distance from stormwater management facilities to the listed geologic features shall be as follows:
[1] 
One hundred feet from the rim of sinkholes or closed depressions;
[2] 
One hundred feet from disappearing streams;
[3] 
Fifty feet from lineaments or fracture traces;
[4] 
Twenty-five feet from surface or identified subsurface pinnacles.
(c) 
Stormwater runoff from any regulated activity shall not be discharged into sinkholes.
(d) 
It shall be the developer's responsibility to verify if the development is underlain by carbonate geology. The certificate provided in the Appendix[1] shall be attached to all stormwater management site plans and signed and sealed by the developer's qualified professional.
[1]
Editor's Note: The appendix is included as an attachment to this chapter.
(e) 
Whenever a stormwater facility will be located in an area underlain by carbonate geology, a geological evaluation of the proposed location by a registered professional geologist shall be conducted to determine subsurface conditions, including soil permeability, depth to bedrock, subgrade stability, and susceptibility to sinkhole formation.
(f) 
Impermeable liners may be used to reduce or eliminate the separation distances listed in § 286-25A(16)(a) and (b).
(17) 
The calculated peak rates of runoff for stormwater originating on the project site must meet one of the following conditions for all watersheds flowing from the project site:
(a) 
Match predevelopment hydrograph.
[1] 
Developers and/or landowners are encouraged to provide infiltration facilities or utilize other techniques which will allow the post-development one-hundred-year hydrograph to match the predevelopment one-hundred-year hydrograph, along all parts of the hydrograph, for the development site.
[2] 
To match the predevelopment hydrograph, the post-development peak rate must be less than or equal to the predevelopment peak rate, and the post-development runoff volume must be less than or equal to the predevelopment volume for the same storm event.
[3] 
A shift in hydrograph peak time of up to five minutes and a rate variation of up to 5% at a given time may be allowable to account for the timing effect of BMPs used to manage the peak rate and runoff volume.
[4] 
Incorporating the volume control requirements as given in Article V, Stormwater Management Standards, can be used as part of this option.
(b) 
Where the predevelopment hydrograph cannot be matched, the calculated peak rates of runoff for stormwater originating on the project site must meet the following conditions, for all watersheds flowing from the project site:
[1] 
The two year post-development rate of runoff (peak flow) from any regulated activity shall be less than or equal to 50% of the calculated two year predeveloped rate (peak flow) except where:
[a] 
The regulated activity is filed as a minor land disturbance activity; or
[b] 
The proposed activity involves the subdivision of five or less single family residential lots, either initially or cumulatively from the date of the adoption of this chapter, and providing no new streets are proposed.
[2] 
Where an application meets one of the above exceptions, the two year post-developed rate of runoff (peak flow) shall be less than or equal to the calculated two year predeveloped rate of runoff (peak flow).
[3] 
Post-development runoff from any regulated activity shall not exceed the peak rates of runoff prior to development for all other design storms (five-, ten-, twenty-five-, fifty-, and one-hundred-year storm events).
(c) 
Developers have the option to propose a regional stormwater management plan or participate in a regional stormwater management plan developed by others.
[1] 
A regional stormwater management plan may include off-site volume and rate control, as appropriate and supported by a detailed design approved by the Township.
[2] 
A regional stormwater management plan must meet all of the volume and rate control standards required by this chapter for the area defined by the regional stormwater management plan, but not necessarily for each individual development site.
[3] 
Appropriate agreements must be established to ensure the requirements of this chapter and the requirements of the regional stormwater management plan are met.
(18) 
Areas proposed for infiltration BMPs shall be protected from sedimentation and compaction during the construction phase to maintain maximum infiltration capacity. Staging of earthmoving activities and selection of construction equipment shall consider this protection.
(19) 
Infiltration BMPs shall not be constructed nor receive runoff from disturbed areas until the entire contributory drainage area to the infiltration BMP has achieved final stabilization.
(20) 
If structure foundations, basements, or other underground facilities (whether on site or off site) would be affected by saturated soil due to a nearby stormwater management facility, detailed calculations addressing the impact of the saturated soil, and water-proofing design information, where applicable, shall be submitted for approval.
B. 
In the case of any dispute in the methodology used in the design of any stormwater management site plan and/or in the presentation of such information, the Supervisors shall make the final determination on the design criteria, methodology, and form of presentation.
Methods shall be selected by the qualified person based on the individual limitations and suitability of each method for a particular site. The methods of computation used to determine peak discharge and runoff shall be:
A. 
The Soil-Cover-Complex Method (as set forth in the latest edition of Urban Hydrology for Small Watersheds, Technical Release No. 55 as published by NRCS, formerly SCS) shall be used for all detention facilities with a drainage area greater than or equal to 60 acres. This method is recommended for design of stormwater management facilities and where stormwater runoff volume must be taken into consideration.
B. 
The Rational Method may be used for drainage areas up to 60 acres. Extreme caution should be used by the qualified person if the watershed has more than one main drainage channel, if the watershed is divided so that hydrologic properties are significantly different in one watershed versus the other, if the time of concentration exceeds 60 minutes, or if stormwater runoff volume is an important factor. The combination of rational method hydrographs based on timing shall be prohibited.
C. 
The Rational Method shall be used for all:
(1) 
Collection facilities;
(2) 
Conveyance facilities.
D. 
Any other method approved by the Township Engineer.
E. 
If the NRCS/SCS Method (also known as Soil-Cover-Complex Method) is used, the design storm volumes to be used in the analysis of peak rates of discharge 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/orb/pa_pfds.html.
(1) 
Provide the rainfall used for the two-, ten-, twenty-five-, fifty-, and one-hundred-year twenty-four-hour storm events. Rainfall values vary throughout the county depending on location.
(2) 
Provide the location (longitude and latitude) or a description of the location for which the rainfall applies.
(3) 
If rainfalls from more than one location are used, provide the methodology by which the design rainfall was calculated.
(4) 
Antecedent Moisture Condition 1 shall be used in areas of carbonate geology.
(5) 
Antecedent Moisture Condition 2 shall be used in all other areas.
(6) 
A Type II distribution shall be used in all areas.
F. 
If the Rational Method is used, the NOAA Atlas 14 data (see Subsection E above) shall be used to determine the rainfall intensity in inches per hour based on the information for the five through sixty-minute duration storm events.
G. 
Hydrographs may be obtained from NRCS methods such as TR-55, TR-20, or from use of the modified or unit hydrograph rational methods.
(1) 
If modified or unit hydrograph rational methods are used, the ascending leg of the hydrograph shall have a time of three times the time of concentration (3xTc) and the descending leg shall have a time of seven times the time of concentration (7xTc) to approximate an NRCS/SCS type 2 hydrograph.
H. 
Runoff Coefficients "C" and Curve Numbers "CN" shall be based on the charts contained in the Appendix[1].
[1]
Editor's Note: The Appendix is included as an attachment to this chapter.
I. 
Times of concentration shall be based on the following design parameters:
(1) 
Sheet flow. The maximum length for each reach of sheet or overland flow before shallow concentrated or open channel flow develops is 150 feet. Flow lengths greater than 100 feet shall be justified based on the actual conditions at each development site. Sheet flow may be determined using the nomograph in the Appendix, or the Manning's kinematic solution shown in the Sheet Flow section of Worksheet No. 1 in the Appendix.
(2) 
Shallow concentrated flow. Travel time for shallow concentrated flow shall be determined using Average Velocities For Estimating Travel Time for Shallow Concentrated Flow nomograph from TR-55, Urban Hydrology for small watersheds in the Appendix.
(3) 
Open channel flows. At points where sheet and shallow concentrated flows concentrate in field depressions, swales, gutters, curbs, or pipe collection systems, the travel times and downstream end of the development site between these design points shall be based upon Manning's Equation and/or acceptable engineering design standards as determined by the Township Engineer.
J. 
For the purpose of calculating predevelopment peak discharges, all runoff coefficients, both on site and off site, shall be based on actual land use assuming summer or good land conditions. Post-development runoff coefficients for off-site discharges used to design conveyance facilities shall be based on actual land use assuming winter or poor land conditions.
K. 
Design of on-site conveyance systems calculations may use the Rational Method of Q=CIA where Q is the peak discharge of the watershed in cubic feet per second, C is the coefficient of runoff, I is the intensity of rainfall in inches per hour, and A is the area of the watershed in acres; or any other method approved by the Township.
L. 
Runoff calculations shall include a hydrologic and hydraulic analysis indicating volume and velocities of flow and the grades, sizes, and capacities of water-carrying structures, sediment basins, and retention and detention structures and sufficient design information to construct such facilities. Runoff calculations shall also indicate both predevelopment and post-development rates for peak discharge of stormwater runoff from the project site.
M. 
Runoff calculations will also be made to ensure that the runoff from the upstream watershed area can be accommodated by the pipes, drainage easements, watercourses, etc., on the site.
N. 
Runoff calculations will also be made to ensure that the runoff from the project site can be accommodated by the receiving pipes, drainage easements, watercourses, etc., downstream from the site.
O. 
Peak rate control is not required for off-site runoff. Off-site runoff may be bypassed around the site ,provided all other discharge requirements are met. If off-site runoff is routed through rate control facilities, runoff coefficients for off-site discharges used to design those rate control facilities shall be based on actual land use assuming winter or poor land conditions.
A. 
The applicant shall meet requirements as contained in 25 PA Code, Chapters 92a and 102 as required and applicable as follows:
[Amended at time of adoption of Code (see Ch. 1, General Provisions, Art. I)]
(1) 
The implementation and maintenance of erosion and sediment control BMPs.
(2) 
Development of written plans.
(3) 
Submission of plans for approval.
(4) 
Obtaining erosion and sediment control and NPDES permits.
(5) 
Maintaining plans and permits on site.
B. 
Evidence of any necessary plan or permit approval for land disturbance activities from PADEP or the Lancaster County Conservation District must be provided to the Township.
C. 
A copy of the notice of termination for NPDES permits shall be provided to the Township once accepted by Lancaster County Conservation District.
D. 
Construction of temporary roadways (e.g., for utility construction, timber harvesting, etc.) shall comply with all applicable standards for erosion and sedimentation control and stream crossing regulations under 25 PA Code, Chapters 102 and 105.
E. 
The erosion and sedimentation control plan shall be submitted to the Lancaster County Conservation District for approval and shall address the following, as applicable:
(1) 
Design of the roadway system, including haul roads, skid roads, landing areas, trails, and storage and staging areas.
(2) 
Runoff control structures (e.g., diversions, culverts, detention ponds, etc.).
(3) 
Stream crossings for both perennial and intermittent streams.
(4) 
Access to public roadways, including design of rock construction entrance for mud and debris control.
(5) 
A remediation plan for restoring the disturbed area through regrading, topsoil placement, reseeding, and other stabilization techniques, as required.
F. 
The following principles shall be applied to the design plan and construction schedule to minimize soil erosion and sedimentation:
(1) 
Stripping of vegetation, grading or other soil disturbance shall be done in a manner that will minimize soil erosion.
(2) 
Whenever feasible, natural vegetation shall be retained and protected.
A. 
All storm sewer pipes, grass waterways, open channels, swales, and other water-carrying facilities that service drainage areas within the site shall be designed to convey the twenty-five-year storm event unless in the opinion of the Township or Township Engineer the character of development and potential for damage warrant design for the fifty- or one-hundred-year storm.
B. 
Stormwater management facilities that convey off-site water through the site shall be designed to convey the fifty-year storm event.
C. 
All developments shall include provisions that allow for the overland conveyance and flow of the post-developed one-hundred-year storm event without damage to public or private property.
D. 
Conveyance facilities shall comply with the design criteria in the following table:
Conveyance facility design criteria
Location
Within Public Street Right-Of-Way
Outside Public Street Right-Of-Way
Loading
All
Vehicular Loading
Non-Vehicular Loading
Pipe design
Material
SLHDPE, RCP
SLHDPE, RCP
SLHDPE, RCP
Slope (minimum)
0.5%
0.5%
0.5%
Cover
1 foot to stone subgrade
1 foot to stone subgrade
1 foot to surface
Diameter (minimum)
18 inches
18 inches
18 inches
Street crossing angle
90°
90°
N/A
Access/maintenance port frequency (maximum)
400 feet
400 feet
400 feet
Inlet design
Material
Concrete
Concrete
N/A
Grate depression
N/A
N/A
6 inches w/20:1 approach slope
Manhole design
Material
Concrete
Concrete
Concrete
Swale design
Freeboard (minimum)
6 inches
N/A
6 inches
Velocity (maximum)
Stability check
N/A
Stability check
Slope (minimum)
2%
2%
2%
Side slopes (residential area)
4:1 max
N/A
4:1 max
Side slopes (nonresidential area)
4:1 max
N/A
3:1 max
Bottom width to flow depth ratio
12:1
N/A
12:1
Pipe Inlet/Outlet design
End treatment
Concrete Headwall/endwall
Headwall/endwall or flared end section
Headwall/endwall or flared end section
Energy dissipater
Required
N/A
Required
E. 
All storm sewer pipes, culverts, manholes, inlets, endwalls and end sections shall be constructed in accordance with Pennsylvania Department of Transportation Publication 408, as modified by Rapho Township.
F. 
Storm sewer pipes, culverts, manholes, inlets, endwalls, and end sections proposed for dedication or located along streets shall conform to the requirements of the Pennsylvania Department of Transportation, Bureau of Design, Standards for Roadway Construction, Publication No. 72, in effect at the time the design is submitted, as modified by Rapho Township.
G. 
The roughness coefficient (Manning "n" values) used for conveyance pipe capacity calculations shall be determined in accordance with PennDOT Publication 584, PennDOT Drainage Manual, or per the manufacturer's specifications.
H. 
Inlets shall be placed along streets as follows:
(1) 
On both sides of streets at low spots.
(2) 
At all changes in the horizontal or vertical direction of storm sewers.
(3) 
At points where the flow in gutters exceeds three inches.
(4) 
At or beyond the curb radius points at intersections.
(a) 
For the purpose of inlet location at intersections, the depth of flow shall be considered for each gutter.
(b) 
At intersections, the depth of flow for the twenty-five-year storm across the through streets shall not exceed one inch.
(5) 
Inlets shall be depressed below the grade of the road-side swale or ground surface as indicated in the above design chart.
(6) 
An access/maintenance port may either be an inlet or manhole.
(7) 
Manholes may be substituted for inlets at locations where inlets are not required to collect surface runoff.
I. 
Material consistency and placement depths for storm sewer pipe backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations, further providing it should be free of large (not exceeding six inches in any dimension) stone, rock, or other objectionable or detritus material.
J. 
Within the public street right-of-way, the gutter spread based on the twenty-five-year storm shall be no greater than 1/2 of the travel lane and have a maximum depth of three inches at the curbline. A parking lane shall not be considered as part of the travel lane.
K. 
Inlets or manholes shall be placed at all points of changes in the horizontal or vertical directions of conveyance pipes. Curved pipe sections are prohibited.
L. 
All inlets placed in paved areas shall have heavy duty bicycle-safe grating consistent with PennDOT Publication 72M, latest edition. A note to this effect shall be added to the stormwater management site plan or inlet details therein.
M. 
Inlets, junction boxes, or manholes greater than five feet in depth shall be equipped with nonaluminum ladder rungs and shall be detailed on the stormwater management site plan.
N. 
Where the connecting pipe has a diameter 18 inches or greater, headwalls and endwalls shall be provided with a protective barrier device to prevent entry of the storm sewer pipe by unauthorized persons. Such protection devices shall be designed to be removable for cleaning.
O. 
Flow velocities from any storm sewer shall not result in a degradation of the receiving channel.
P. 
Energy dissipaters shall be placed at the outlets of all storm sewer pipes where flow velocities exceed maximum permitted channel velocities.
Q. 
The capacities of swales shall be computed from the Manning Equation using the following design parameters: Permissible open channel velocities and design standards shall be in accordance with good engineering practice as documented in the Engineering Field Manual for Conservation Practices, USDA, SCS, or in Design Charts for Open-Channel Flow, Hydraulic Design Series No. 3, U.S. Department of Transportation.
(1) 
Vegetated swales:
(a) 
The first condition shall consider swale stability based upon a low degree of retardance ("n" = 0.03);
(b) 
The second condition shall consider swale capacity based upon a higher degree of retardance ("n" = 0.05); and
(2) 
The "n" factors to be used for paved or riprap swales or gutters shall be based upon accepted engineering design practices, as approved by the Township Engineer.
(3) 
All swales shall be designed to maximize infiltration and concentrate low flows to minimize siltation and meandering, unless geotechnical conditions do not permit infiltration.
A. 
Aboveground storage facilities shall consist of all stormwater facilities which store, infiltrate/evaporate/transpire, clean, release, or otherwise affect stormwater runoff and the top of which is exposed to the natural environment. Aboveground storage facilities shall be located above the finished ground elevation. Aboveground storage facilities do not include stormwater management facilities designed for conveyance or cisterns.
B. 
Facilities with a facility depth greater than eight feet shall not be permitted in residential areas.
C. 
Aboveground storage facilities shall comply with the design criteria in the following table:
Aboveground storage facility design criteria
Facility Depth
Less than 2 feet
2 feet to 6 feet
Greater than 6 feet
Embankment Geometry
Top width (minimum)
2 feet
5 feet
8 feet
Interior side slope (maximum)
3:1
5:1
5:1
Exterior side slope (maximum)
3:1
3:1
3:1
Embankment construction
Clay/Impervious Core
Not required
Required
Required
Pipe collar
Not required
Required
Required
Compaction density
Not required
Required
Required
Internal Construction
Dewatering feature
N/A
Required
Required
Pretreatment elements
Not required*
Required
Required
Outlet Structure
Pipe size (minimum) (inches)
12
18
18
Pipe material
SLHDPE, PVC, RCP
SLHDPE, RCP
SLHDPE, RCP
Anticlogging devices
Required
Required
Required
Antivortex design
Not required
Required
Required
Watertight joints in piping?
Yes
Yes
Yes
Spillway Requirements
Spillway freeboard (minimum) (inches)
3
6
12
Width (minimum) (feet)
5
10
20
Width (maximum) (feet)
20
50
50
Spillway channel design
Required
Required
Required
Routing of one-hundred-year storm
Permitted
Permitted
Permitted
*Pretreatment is required for infiltration BMPs unless shown to be unnecessary.
N/A = Not applicable
SLHDPE = Smooth lined high density polyethylene pipe; PVC = Polyvinyl chloride;
RCP = Reinforced concrete pipe
D. 
If required, pretreatment elements shall be designed according to the BMP manual.
E. 
All aboveground storage facilities shall be structurally sound and shall be constructed of sound and durable materials.
(1) 
All discharge control devices with appurtenances shall be made of reinforced concrete and stainless steel.
(2) 
Bolts/fasteners shall be stainless steel.
(3) 
The completed structure and the foundation of all basins shall be stable under all probable conditions of operation.
(4) 
Spillways shall be capable of discharging the peak discharge of a post-development one-hundred-year storm event through the emergency spillway facilities, in a condition that assumes the primary outlet(s) are blocked, which will not damage the integrity of the facility or the downstream drainage areas.
(5) 
Use of the spillway to convey flows greater than the fifty-year design storm shall be permitted.
F. 
The effect on downstream areas if the aboveground storage facility embankment fails shall be considered in the design of all basins. The basin shall be designed to minimize the potential damage caused by such failure of the embankment.
G. 
An easement shall be provided from the spillway outfall to a natural or artificial watercourse.
H. 
The maximum depth of water for aboveground storage facilities without restricted access shall not exceed six feet.
(1) 
Access to basins with a maximum depth of water greater than six feet shall be restricted by fencing that will discourage access.
I. 
Aboveground storage facilities without restricted access shall have impoundment areas with side slopes no greater than the horizontal to vertical ratios in the design chart.
(1) 
Access to basins with steeper side slopes than those shown in the chart shall be restricted by fencing that will discourage access.
J. 
All detention basins shall include an outlet structure to permit draining the Rate Control Volume within 24 hours, exclusive of BMP storage.
K. 
All outlet structures and emergency spillways shall include a satisfactory means of dissipating the energy of flow at its outlet to assure conveyance of flow without endangering the safety and integrity of the basin and the downstream drainage area.
L. 
A clay/impervious core shall consist of a cutoff trench (below existing grade) and a core trench (above existing grade).
(1) 
A clay/impervious core may not be required wherever the facility depth is less than two feet.
(2) 
Materials used for the clay/impervious core shall conform to the Unified Soil Classification GC, SC, CH, or CL and must have at least 30% passing the No. 200 sieve.
(3) 
The dimensions of the clay/impervious core shall provide a minimum trench depth of two feet below existing grade, minimum width of four feet and side slope of 1H:1V or flatter.
(4) 
The clay/impervious core should extend up to the twenty-five-year water surface elevation or six inches below the emergency spillway elevation, whichever is lower.
(5) 
The clay/impervious core shall extend four feet below any pipe penetrations through the impervious core.
(6) 
The core shall be installed along or parallel to the center line of the embankment.
(7) 
Compaction requirements for the clay/impervious core shall be the same as those for the embankment to assure maximum density and minimum permeability.
M. 
All pipe collars, if required, shall be designed in accordance with Chapter 7 of the PADEP Erosion and Sediment Control Manual. The material shall consist of concrete or otherwise nondegradable material around the outfall barrel and shall be watertight.
N. 
The embankment fill material shall be free of topsoil, organic material, roots, stumps, wood, rubbish, stones greater than six inches, frozen or other objectionable materials.
O. 
The minimum freeboard for spillways shall be provided above the one-hundred-year design elevation of the water surface at the emergency spillway in a condition that assumes the primary outlet(s) is (are) blocked.
P. 
The minimum bottom slope of facilities not designed for infiltration shall be 1%. A flatter slope may be used if an equivalent dewatering mechanism is provided.
Q. 
If required, dewatering shall be provided through the use of underdrain, surface device, or an alternate approved by the Township Engineer. If the facility is to be used for infiltration, the dewatering device should be capable of being disconnected and only be made operational if the basin is not dewatering within the required time frame.
R. 
Within basins designed for infiltration, a planting plan shall be prepared in accordance with this chapter and the BMP Manual.
Stormwater runoff volume controls shall be designed using the Design Storm Method (CG-1 in the BMP Manual) as follows:
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 post-development total runoff volume shall not increase for all storms equal to or less than the two-year twenty-four-hour storm event.
(2) 
For modeling purposes:
(a) 
Existing (predevelopment) nonforested pervious areas must be considered meadow in good condition.
(b) 
20% of existing impervious area, when present, shall be considered meadow in good condition in the model for existing conditions.
(c) 
The maximum loading ratio for volume control facilities in Karst areas shall be:
[1] 
3:1 impervious drainage area to infiltration area and 5:1 total drainage area to infiltration area.
[2] 
The maximum loading ratio for volume control facilities in non-Karst areas shall be 5:1 impervious drainage area to infiltration area and 8:1 total drainage area to infiltration area.
B. 
Any portion of the volume control storage that meets the following conditions may also be used as rate control storage:
(1) 
Volume control storage that depends on infiltration and is designed according to the infiltration standards in this chapter and the BMP Manual.
(2) 
The volume control storage which will be used for rate control is that storage which is available within 24 hours from the end of the design storm based on the stabilized infiltration rate and/or the evapotranspiration rate.
C. 
Volume control BMPs and pretreatment elements shall be designed in accordance with the BMP Manual and the soil and infiltration testing requirements of Article V, Stormwater Management Standards.
D. 
All applicable worksheets from Chapter 8 of the BMP Manual must be used when establishing volume controls.
A. 
Subsurface storage facilities shall consist of all stormwater facilities which store, infiltrate/evaporate/transpire, clean, release, or otherwise affect stormwater runoff and the top of which is not exposed to the natural environment. Subsurface facilities shall be located below the finished ground elevation. Subsurface facilities shall not include stormwater management facilities designed for conveyance.
B. 
Subsurface storage facilities shall comply with the design criteria in the following table:
Subsurface storage facility design criteria
Facility Type
Infiltration and Storage
Storage without Infiltration
Facility Geometry
Depth from surface (maximum)
2 feet less than limiting zone
N/A
Loading ratio (maximum)
Per BMP Manual*
N/A
Distribution System Requirements
Pipe size (minimum) (inches)
4
4
Loading/balancing
Required
Required
Observation/access ports
Required
Required
*
Unless otherwise determined by professional geologic evaluation
C. 
The facility shall be designed according to the BMP Manual to provide pretreatment to eliminate solids, sediment, and other debris from entering the subsurface facility.
D. 
The facility shall be designed to provide a means of evenly balancing the flow across the surface of the facility to be used for infiltration.
E. 
Observation/access ports shall be provided for all subsurface storage facilities as follows:
(1) 
For facilities with the bottom less than five feet below the average grade of the ground surface, a clean-out shall be an acceptable observation port.
(2) 
For facilities with the bottom five feet or more below the average grade of the ground surface, a manhole or other means acceptable to the Township shall be provided for access to and monitoring of the facility.
(3) 
The number of access points shall be sufficient to flush or clean out the system.
F. 
Storage and distribution system piping shall be PVC, SLHDPE, or RCP.
G. 
The stone used for infiltration beds shall be clean washed, uniformly graded coarse aggregate. The void ratio for design shall be assumed to be 40%.
H. 
Material consistency and placement depths for backfill shall be (at a minimum) per all applicable pipe manufacturer's recommendations.
(1) 
Backfill material shall be free of large (not exceeding six inches in any dimension) stone, rock, or other objectionable or detritus material.
(2) 
Select nonaggregate backfill material should be indigenous to the surrounding soil material for nonvehicular areas.
(3) 
Backfill material within vehicular areas shall comply with the requirements of the governing municipal road/street or subdivision and land development ordinance.
(4) 
If the design concept includes the migration of runoff through the backfill to reach the infiltration facility, the material shall be well drained, free of excess clay or clay-like materials and generally uniform in gradation.
I. 
Nonwoven geotextiles shall be placed on the bottom, all sides and top of subsurface infiltration facilities.
J. 
When located under pavement, the top of the subsurface facility shall be a minimum of three inches below the bottom of pavement subbase. Where located under vegetative cover, the top of the subsurface facility shall be a minimum of 12 inches below the surface elevation or as required to establish vegetation.
K. 
Subsurface facilities shall be designed to safely convey and/or bypass flows from storms exceeding the design storm.