61.15.1. 
A stormwater management site plan shall be required for each subdivision, land development and regulated activity, unless exempted. The stormwater management site plan shall demonstrate effective control of stormwater runoff and compliance with the stormwater management requirements, standards and design criteria of this chapter. The stormwater management site plan shall be an integral part of each subdivision and land development plan at the preliminary and final plan stage. For the purposes of this section of this chapter, the following activities are defined as regulated activities and shall be considered as land development for regulation by this chapter:
1. 
Construction of new or additional impervious surfaces (sidewalks, driveways, parking lots, etc.); and
2. 
Installation of new impervious surfaces where gravel exists; and
3. 
Renovation of existing impervious surfaces which currently do not have a stormwater management facility; and
4. 
Construction of new buildings or additions to existing buildings; and
5. 
Diversion or piping of any natural or man-made stream channel; and
6. 
Installation of stormwater management facilities or appurtenances thereto; and
7. 
Alteration of conditions that may increase or alter natural drainage from the existing site.
61.16.1. 
For all regulated activities, unless preparation of an SWM site plan is specifically exempted:
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.
3. 
The Municipality must be notified of construction operations prior to commencement so that an inspection can be completed.
4. 
After the installation of the facility, the overseeing professional engineer (design engineer) should submit a letter indicating that the facility was installed per the approved plan.
61.16.2. 
SWM site plans approved by the Municipality shall be on site throughout the duration of the regulated activity.
61.16.3. 
These standards apply to the landowner and any person engaged in regulated activities.
61.16.4. 
Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by SWM BMPs or open channels consistent with this chapter.
61.16.5. 
If diffused flow is proposed to be concentrated and discharged onto adjacent property with permission from the receiving property owner, the developer must document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding or other harm will result from the concentrated discharge, and downstream easements shall be established to provide drainage paths for concentrated discharge. Maximum use shall be made of the existing on-site natural and man-made stormwater management facilities.
61.16.6. 
A concentrated discharge of stormwater to an adjacent property shall be within an existing watercourse or otherwise an easement shall be required. Pipe outlets shall also be provided with erosion-resistant material or energy dissipaters to calm the anticipated velocity and discharge of stormwater.
61.16.7. 
Discharge points from any facility must be 15 feet from any property line with adequate BMPs to ensure no channelizing of flows onto neighboring property.
61.16.8. 
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. [1]Various BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual (E&S Manual), No. 363-2134-008, as amended and updated.
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
61.16.9. 
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 proposed impervious area on the parcel is subject to the requirements of this chapter.
4. 
Any gravel or crushed stone surface existing prior to the issuance of this chapter is to be assumed as pervious surface.
5. 
Any areas proposed to be gravel or crushed stone shall be considered impervious.
6. 
The anticipated flooded surface area occurring within the site shall be considered as impervious.
61.16.10. 
Stormwater flows onto adjacent or downstream property shall not be created, increased, decreased, relocated, impeded, or otherwise altered without written notification of the affected property owner(s). Notification shall include a description of the proposed development and the stormwater flows that are being created, increased, decreased, relocated, impeded, or otherwise altered. Adjacent property shall at a minimum include any property having a shared boundary with the subject property of the SWM site plan; however, if in the judgment of the designated plan reviewer additional properties might be affected, additional notifications may be required. Proof of notification (signed postal receipt, for example) shall be included as part of the SWM plan submission to the Municipality. Such stormwater flows shall be subject to the requirements of this chapter.
61.16.11. 
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 methods described in the Pennsylvania Stormwater Best Management Practices Manual (BMP Manual). If methods other than green infrastructure and LID methods are proposed to achieve the volume and rate controls required under this chapter, the SWM site plan must include a detailed justification, acceptable to the designated plan reviewer, demonstrating that the use of LID and green infrastructure is not practicable.
61.16.12. 
Infiltration BMPs should be dispersed throughout the project site at strategic locations, 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. If infiltration is utilized, appropriate percolation test results must be provided.
61.16.13. 
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.
61.16.14. 
The design storm precipitation depths to be used in the analysis of peak rates of discharge shall be as obtained in PennDOT's Drainage Manual, Publication 584, Appendix 7A; or obtained from the latest version of the Precipitation-Frequency Atlas of the United States, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland. NOAA's Atlas 145 can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
61.16.15. 
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.
61.16.16. 
Various BMPs and their design standards are listed in the BMP Manual.
61.16.17. 
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.[4]
[4]
Editor's Note: See 35 P.S. § 691.1 et seq.
61.16.18. 
Stormwater management facilities which involve a state highway shall be subject to the approval of PennDOT.
61.16.19. 
Stormwater management facilities which involve a county highway or a county facility shall be subject to the approval of Allegheny County.
61.16.20. 
Minimization of impervious surfaces and maximization of infiltration of runoff through seepage beds, infiltration trenches, etc., are encouraged, where soil conditions permit, to reduce the size or eliminate the need for detention facilities.
61.16.21. 
Where a development site is traversed by watercourses other than permanent streams, drainage easements shall be provided conforming to the line of such watercourses. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Also, maintenance, including mowing of vegetation within the easement, shall be required, except as approved by the appropriate governing authority.
61.16.22. 
The Pa. Code, Title 25, 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 the DEP, Bureau of Waterways Engineering and Wetlands, in Harrisburg.
61.16.23. 
When it can be shown that, due to topographic conditions, natural drainageways on the 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 DEP through the joint permit application process, or, where deemed appropriate by DEP, through the general permit process.
61.16.24. 
Stormwater resulting from regulated activities shall not be discharged into sinkholes.
61.16.25. 
To the maximum extent practicable, incorporate the techniques for low-impact development practices described in the BMP Manual.
61.17.1. 
Regulated activities that result in an increase in the proposed impervious area less than 400 square feet, if there were no previous impervious surface additions after May 1, 2017 (regardless if the existing surface is impervious), are exempt from the requirements of this chapter.
61.17.2. 
Proposed impervious area between 400 square feet and 1,000 square feet of earth disturbance must submit an SWM site plan to the Municipality, which shall consist of the items and related supportive material needed to determine compliance with Section 61.18, Small projects.
61.17.3. 
Agricultural activity is exempt from the SWM site plan preparation requirements of this chapter, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.
61.17.4. 
Forest management and timber operations are exempt from the SWM site plan preparation requirements of this chapter, provided the activities are performed according to the requirements of 25 Pa. Code Chapter 102.
61.17.5. 
Roadway resurfacing and maintenance projects which do not increase or change the impervious area/type and underground infrastructure projects are exempt from the provisions of this chapter, provided the activities meet the requirements of all other municipal, state and federal requirements.
61.17.6. 
Exemptions from any provisions of this chapter shall not relieve the applicant from the requirements in Section 61.15.
61.17.7. 
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.
61.17.8. 
Voluntary green stormwater infrastructure (GSI) retrofit projects that are solely intended to better manage runoff from existing development and are not part of new development or redevelopment are exempt from the stormwater management provisions of this chapter. This does not exempt such projects from any other municipal, state, or federal regulation.
61.18.1. 
Table 1 presents the Municipality's stormwater management requirements for small projects. For projects that propose additional impervious area to a parcel, the total proposed impervious area on the parcel is subject to the requirements of this chapter. Impervious area is described in Section 61.16.9.
Table 1 - Stormwater Management Requirements
No.
Square Feet of Proposed Impervious Surface
Stormwater Management Requirement
1
Less than 400
No requirements if there were no previous impervious surface additions after May 1, 2017
2
400 to 1,000 (small project)
Capture and detain the first 2 inches of any storm event
3
Greater than 1,000
Comply with requirements of this chapter
61.18.2. 
Stormwater management for small projects will consist of capturing and detaining the first two inches of any storm event. For small projects, consider the following:
1. 
Two inches of rain results in the following volumes that need to be captured and detained:
400 sq. ft. * 2 in./(12 in./ft.) * 7.48 gal/cu. ft. = 499 gal., approximately 500 gallons of detention storage.
1,000 sq. ft. * 2 in./(12 in./ft.) * 7.48 gal/cu. ft. = 1247 gal., approximately it 1,250 gallons of detention storage.
2. 
Therefore, small project detention requirements range from 500 gallons to 1,250 gallons.
61.18.3. 
Capture and detention can be accomplished by a variety of methods, including, but not limited to:
1. 
Rain barrels (could be drained through a soaker hose).
2. 
Rain gardens.
3. 
Stone sumps (dry wells) and infiltration trenches filled with clean, AASHTO No. 3 stone, 40% void space.
4. 
Other methods as approved by the municipal staff.
5. 
A combination of methods.
61.18.4. 
In all cases, the detention method must be designed to drain all accumulated runoff not less than 24 hours and not more than 72 hours after the end of the storm event. Appropriate soil percolation conditions must be available for stone sumps and rain gardens, and demonstrated by percolation tests.
61.18.5. 
A maintenance agreement must be signed by the property owner to ensure the proper, continual inspection and maintenance of the capture and detention method.
61.18.6. 
The property owner must submit the following stormwater management information for review by the Municipality staff:
1. 
A written description of the proposed project, including the dimensions of all proposed impervious surfaces.
2. 
A scale drawing showing existing and proposed features of the property.
3. 
A written description of the proposed stormwater management methods.
4. 
Dimensioned drawings of the proposed stormwater management methods and their locations.
5. 
A list of proposed impervious surfaces and their square footage.
6. 
Supporting documentation, such as assumptions, calculations, rain barrel size, stone size, percolation tests, etc.
7. 
Draft operation and maintenance agreement.
61.18.7. 
Construction of the proposed improvements will not begin prior to receiving approval of the stormwater management plan from the Municipality.
61.19.1. 
Stormwater management planning and stormwater management facilities shall be designed and constructed in accordance with the following.
61.19.2. 
General standards.
1. 
The design of all stormwater management facilities shall incorporate sound engineering principles and practices.
2. 
All stormwater runoff flowing over the development site shall be considered in the design of the stormwater management facilities.
3. 
Runoff from impervious areas shall be drained to pervious areas of the development site and the stormwater management control facilities.
4. 
Stormwater runoff from a development site shall flow directly into a natural watercourse, into an existing storm sewer system or onto adjacent properties in a manner similar to the runoff characteristics of the predevelopment flow.
5. 
A concentrated discharge of stormwater to an adjacent property shall be within an existing watercourse or storm sewer system and enclosed within an easement. All discharges must be to stable areas or conveyances. If the existing waterway or drainage system is not stable, a design must be proposed that, when implemented, will ensure a stable conveyance. Downstream easements are required to be established to provide drainage paths for concentrated discharge. Design and construction shall preclude erosion, sedimentation, flooding or similar damage.
6. 
Where a development site is traversed by watercourses, drainage easements shall be provided conforming to the line of such watercourses. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Also, maintenance, including mowing of vegetation within the easement, shall be required, except within BMP areas where mowing is not desired. The drainage easement shall adequately contain the anticipated inundation associated with the identified 100-year floodplain, or be depicted 50 feet from the top of the channel bank for undefined floodplain areas.
7. 
Any stormwater management facilities regulated by this chapter that would be located in or adjacent to waters of the commonwealth or wetlands shall be subject to approval by DEP. When there is a question whether wetlands may be involved, it is the responsibility of the developer 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 DEP.
8. 
Any stormwater management facilities regulated by this chapter that would discharge to state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT). Stormwater detention basins, retention basins, infiltration basins and similar structures shall maintain a ten-foot isolation from a PennDOT right-of-way.
9. 
Stormwater facilities that are not located within a street right-of-way shall be centered within an adequate easement of no less than 20 feet in width. Easements shall follow property lines where possible and are to be provided with bearing and distance descriptions that tie to known points and shall close on individual lots.
10. 
A variety of methods for stormwater detention and retention are available for use. These include surface detention, subsurface detention, use of existing facilities (ponds, etc.) or a combination thereof. Subsurface detention shall be utilized only where the subsurface is stable, the area is not prone to sinkholes or landslides, and all underground pipes are sealed to prevent leaks.
11. 
Storage of equivalent stormwater runoff for a portion of a property may be considered in lieu of storage of generated runoff, provided:
a. 
The site is located so that it is physically impossible to detain runoff from the proposed facilities or drainage problems exist upgrade that would impact upon the site or downgrade properties.
b. 
The impact of generated runoff discharging off site from the subdivision or land development is determined by the Municipal Engineer to be negligible and not detrimental to adjacent properties.
c. 
Implementation of equivalent storage shall be determined applicable and feasible by the Municipal Engineer.
12. 
Storm sewer pipes, culverts, manholes, inlets, endwalls, end sections, and other stormwater management facilities shall be designed and constructed in accordance with the requirements of the Pennsylvania Department of Transportation, Design Manual Part 2, Highway Design, Publication 13, including amendments thereto, unless specifications are otherwise provided herein. Structures and their installation within or directly connected to existing or intended public rights-of-way shall conform to the current PennDOT Publication 72M and Publication 408, Roadway Construction Standards.
13. 
Headwalls and endwalls shall be used where stormwater runoff enters or leaves the storm sewer horizontally from a natural or man-made channel. PennDOT Type "DW" headwalls and endwalls shall be utilized. Reinforced concrete flared end sections are also acceptable, but galvanized metal or polyethylene flared end sections are prohibited. All headwalls and endwalls and flared end sections with pipes of twelve-inch or greater diameter shall be protected from child entry by placing removable stainless steel bars (and compatible mounting hardware), spaced four inches apart, across the opening. Periodic inspection and clearing of debris from such structures is the responsibility of the owner.
61.20.1. 
Any stormwater management facility designed to store stormwater runoff and requiring a berm or earthen embankment (i.e., detention or retention basin) shall be designed to provide an emergency spillway to convey the 100-year post-development peak flow rate tributary to the basin. The use of inlets and pipes are prohibited for the emergency spillway. Stormwater runoff from existing natural swales and/or other existing drainage conveyors shall not be directed towards or intercepted by the stormwater management facilities. The height of embankment must be set as to provide a minimum 1.0 foot of freeboard above the maximum pool elevation computed when the entire 100-year peak flow rate to the structure passes through the spillway. Rain gardens, with a maximum water depth of 12 inches, shall be exempt from this requirement; however, conveyance of the 100-year peak discharge must be shown to be conveyed in a stable condition. The criteria for design and construction of stormwater management facilities are not the same criteria that are used in the permitting of dams under the DEP Dam Safety Program. Depending upon the physical characteristics of a dam, a dam permit may be required, and the design will have to meet the provisions of Pa. Code, Title 25, Chapter 105. Depending on the physical characteristics of a dam, the design could require that anywhere from a 100-year to a probable maximum flood (PMF) storm event be considered. Retention and detention basins shall be designed and constructed according to the following minimum standards:
1. 
The maximum water depth to the base of the emergency spillway shall not exceed six feet in residential areas. Depths up to eight feet are permitted in nonresidential projects, provided minimum six-foot-high fencing is provided around the basin when depths exceed six feet.
2. 
The minimum top width of dams shall be five feet for impoundments draining five acres or less and eight feet minimum width for impoundments with drainage areas of or exceeding five acres.
3. 
The side slopes of earth fill dams shall not be less than three horizontal to one vertical on both sides of the embankment. However, any portion of the inside berm of an unfenced basin above a proposed water depth of three feet shall have a maximum side slope of five horizontal to one vertical. All pond areas, including bottoms of non-water-quality ponds, side slopes and top of berms, shall be provided with a minimum four inches of topsoil and shall be mulched and seeded with Formula B in accordance with PennDOT Publication 408. All areas to receive topsoil should be scarified 12 inches deep before topsoil placement. Protect from erosion until vegetation is 70% established.
4. 
All basins shall be structurally sound and shall be constructed of sound and durable materials. The completed structure and the foundation of all basins shall be stable under all probable conditions of operation.
5. 
A cutoff or key trench of impervious material shall be provided under all basin berms.
6. 
All discharge control devices with appurtenances (except discharge pipes) shall be made of reinforced concrete and stainless or hot dip galvanized steel. Bolts/fasteners are to be stainless or galvanized steel. Smooth lined corrugated polyethylene pipe may be used for discharge piping.
7. 
Concrete, polyethylene or welded galvanized steel anti-seep collars compatible with the discharge pipe shall be placed around all basin discharge pipes to increase the seepage length along the pipe by 15% within the saturated zone of the pipe based on a 4:1 phreatic line. The connection of the anti-seep collar to the discharge pipe shall be completely watertight.
8. 
Basin principal spillway outlet structures shall consist of stainless steel orifice plates and mounting hardware, galvanized or reinforced concrete riser and discharge pipe, and welded structural steel inlet grates with a bituminous coating. Smooth lined corrugated polyethylene pipe may be used for discharge piping. Principal spillways with riser pipes where the designed water depth is deeper than 0.4 times the diameter of the riser shall have an anti-vortex device to prevent reduced capacity of the riser.
9. 
All basin intake and discharge structures shall be protected from frost-related movement by the construction of a concrete footer with a minimum depth of 36 inches below finished grade level.
10. 
Minimum floor elevations for all structures that would be affected by a basin or storm conveyance system shall be two feet above the 100-year water surface elevation.
11. 
An emergency spillway shall be provided to safely pass the peak flow rate of the incoming 100-year storm, with one foot of freeboard between the maximum pool elevation and the top of the embankment and in a manner which will not damage the integrity of the facility and will not create a downstream hazard. The maximum pool elevation shall be established using the weir equation through the spillway while ignoring discharge flows from the principal spillway and storage volume within the basin. Routing calculations for rate control structures discharging to the ground surface shall ignore exfiltration or infiltration discharges from the structure.
12. 
Where practical, the emergency spillway shall be constructed in undisturbed ground. An easement for inspection and repair shall be provided when the conveyance structure crosses property boundaries. Downstream drainage easements from the emergency spillway may be required.
13. 
Except for retention basins, permanent ponds and wetlands, all basins shall have dewatering features such as low flow channels or tile fields. Low flow channels shall be provided with reinforced matting extending two feet beyond the channel. All detention basins shall include an outlet structure designed to completely drain the basin within 24 hours following the end of the design rainfall. However, basins containing groundwater recharge and/or water quality storage shall include an outlet structure designed to fully drain the recharge and/or water quality volume in no less than 24 hours or more than 72 hours.
14. 
Basin discharges to proposed or existing conveyance systems shall require evidence of adequate capacity in the receiving facility.
15. 
The minimum slope of any detention basin bottom surface shall be 1% positive grade toward the outlet, along all flow paths except those basins specifically designed to provide infiltration of stormwater in conformance with the water quality standards.
16. 
Detention basin length or basin flow path length shall be at least two times the basin width to facilitate water treatment and infiltration.
17. 
In areas of carbonate geology, retention and detention basins shall:
a. 
Be placed at least 100 feet from the rim of any sinkhole or closed depression; and
b. 
Be placed a minimum of 25 feet from rock outcroppings or pinnacles; and
c. 
Not discharge into a sinkhole; and
d. 
Be designed and located to prevent groundwater contamination and sinkhole formation, including the use of impermeable liners (see specifications below) where deemed necessary to avoid or abate such problems. The construction of clay liners shall not qualify as an impermeable liner.
e. 
Be constructed under the supervision of a professional engineer or professional geologist licensed by the commonwealth. A professionally sealed as-built construction report, and plan including relative dates, name(s) of contractor(s), methods of construction, and verification of conformance to plan specifications and good engineering practices shall be provided to the Municipality prior to bond reduction requests related to the basin(s).
18. 
The impermeable liner shall be constructed to meet the following minimum requirements.
a. 
The minimum liner required is 30 mil high-density polyethene (HDPE) and must be UV-resistant. Actual individual liner specifications shall be provided by the manufacturer for each individual pond.
b. 
The liner must be placed on a layer of fine-grained soil that has been rolled with a smooth drum roller in both directions to produce a smooth level base for the liner. The soil may not contain sharp angular rock or other debris that could puncture the liner, and must meet all manufacturers' specifications for a liner bedding. All vegetation, roots, and grass must be removed, and any cracks or voids shall be filled.
c. 
If rock is encountered in the bedding area, this rock must be excavated to a depth of six inches below the liner and backfilled with a fine-grained soil. This area should then be covered with geotextile fabric, extending three feet beyond the limits of the rock outcrop before placing the pond liner.
d. 
Installation of the liner may only take place when the ambient temperature is within the manufacturer's specifications. The number of field seams shall be minimized by requiring factory fabrication of large panels. Any field seams performed must be in accordance with the manufacturer's specifications.
e. 
All structures (i.e., headwalls, pipes, outlet structures) which come in contact with the liner must have a waterproof seal installed to prevent leaks around the structure. These seals shall be installed per the manufacturer's recommendations.
f. 
A minimum of 12 inches of earth cover shall be placed over the lining. Soil containing sharp jagged rocks, roots, debris, or any other material that may puncture the liner shall not be used as cover material.
g. 
The liner must be installed to a minimum height of the 100-year floodwater elevation in the facility.
19. 
Basins shall not be divided by a property line.
20. 
Vertical pipes, inlets, and other surface water receiving structures shall be installed with trash racks.
61.21.1. 
Pipes, curbs, gutters, manholes, inlets, headwalls, endwalls, streets, and other stormwater conveyance facilities shall be designed and constructed in accordance with the following:
1. 
Pipe trenching and backfilling shall be in accordance with the requirements of the Pennsylvania Department of Transportation, Publication 408 and Roadway Construction Drawings, current edition, unless the manufacturer's specifications and the Municipal Engineer authorize alternative procedures. All trench backfill within existing or proposed dedicated street right-of-way areas shall be 100% crushed aggregate backfill to the subbase elevation of the street paving. Such crushed aggregate backfill shall be supplied and placed in accordance with PennDOT specifications, Publication 408.
2. 
Pipe sizes and type shall be in accordance with the approved drawings. Minimum pipe size for drainage facilities to be dedicated for municipal ownership shall be 15 inches in diameter, and the type shall be smooth lined high-density polyethylene pipe (HDPEP), or reinforced concrete pipe (RCP) or approved equivalent.
3. 
Pipes shall be constructed and set to line and grade as shown on approved drawings. All pipes shall be laid on straight runs between drainage structures. Minimum pipe slope shall be 1.0%.
4. 
Pipes shall be provided with a minimum of 12 inches of cover from the top of pipe barrel to bottom of base course. In unpaved areas, one foot of cover is required to the finished grade.
5. 
Hauling shall not be permitted over pipe with less than four feet of cover.
6. 
All pipe outlets shall be discharged to natural or man-made waterways and shall be provided with reinforced concrete headwalls or pipe end sections. Pipe outlets shall also be provided with an erosion-resistant material or energy dissipators to calm the anticipated velocity and discharge of stormwater. All pipe outlet structures shall be protected from frost-related movement by the construction of a concrete footer with a minimum depth of 30 inches below finished grade level.
7. 
Underdrains, pavement base drains, or combination storm sewer and underdrains shall be provided at low points, cut sections, poorly drained areas and other areas which are required to provide adequate subsurface drainage to protect the integrity of the street.
8. 
All storm sewers which cross a street shall be perpendicular to the street center line or within 30° of perpendicular. Vertical and horizontal isolation conflicts with other utilities shall be avoided. Storm sewers within a street shall not cross underneath a curb, especially at curb radii locations.
9. 
A concentrated discharge of stormwater to an adjacent property shall be within an existing watercourse or otherwise an easement shall be required. Pipe outlets shall also be provided with erosion-resistant material or energy dissipaters to calm the anticipated velocity and discharge of stormwater.
10. 
For contributing watersheds of less than 100 acres, a twenty-five-year design storm shall be the minimum used for all constructed facilities, including roadside gutters or swale. For contributing watersheds of 100 acres or more, a 100-year design storm (at least) or storm as required by the Pennsylvania Department of Environmental Protection, Division of Dams and Encroachment Regulations, whichever is more restrictive, shall be used for all constructed facilities, such as culverts, piping and major swales or water courses.
61.22.1. 
Inlet tops shall be precast concrete top units conforming to the Pennsylvania Department of Transportation, Publication 408, current edition, and as detailed on the Roadway Construction Standards RC-45M drawings, providing an eight-inch curb reveal from the gutter grade point. Type "C" inlets with ten-inch hoods that provide a two-inch sump condition may be used with approval from the Director of Engineering. Type "M" inlets shall be used in off-street conditions.
61.22.2. 
The maximum allowable spread of water shall be 1/2 of a through travel lane. Design calculations are required to document the capacity and spacing. Inlets shall be analyzed for collection efficiency, and bypass flows from upstream structures shall be accounted for in inlet spacing design.
61.22.3. 
All inlets over four feet in depth shall be provided with steps for accessibility. Inlets shall be placed along the curbline, gutter line, or edge of paving.
61.22.4. 
All inlets in paved areas shall have vane grates.
61.22.5. 
Inlets shall be located at tangents on the uphill side of street intersections.
61.22.6. 
All inlets shall be constructed with concrete flow channels cast in place in the bottom of each inlet.
61.22.7. 
Inlets and manholes shall not be spaced more than 300 feet apart. Manholes or inlets are required at all points of horizontal or vertical pipe deflection.
61.22.8. 
Manhole covers shall have a minimum of thirty-inch diameter entryway clearance.
61.23.1. 
All channels shall be lined with adequate channel lining material, regardless of the designed velocity or shear stress. Maximum permitted channel velocities are:
1. 
Three feet per second where only sparse vegetation can be established.
2. 
Four feet per second under normal conditions where vegetation is to be established by seeding or sodding.
3. 
Velocities may not exceed four feet per second for newly constructed grass channels, unless appropriately designed and approved by the Allegheny County Conservation District.
4. 
The following conditions shall be met for all swales:
a. 
Swales shall be designed using Manning's equation. Vegetated swales shall be designed based upon accepted "n" factors for the anticipated degree of vegetative retardance. The maximum allowable velocity for an established grass swale is four feet per second.
b. 
The "n" factors to be used for paved or riprap swales or gutters shall be based upon accepted engineering design practices as specified by PennDOT or approved by the Engineer.
c. 
Swale side slopes shall be 2:1 minimum. Side slopes for grass-covered swales which will be mowed shall be 3:1 minimum.
d. 
All swales shall be designed to concentrate low flows to minimize siltation and meandering.
e. 
All vegetated swales shall have a minimum longitudinal slope of 2% unless approved by the Municipal Engineer.
f. 
Swales shall be centered within a minimum twenty-foot-wide easement.
61.24.1. 
Provisions for stormwater volume reductions are required for areas being developed. Design of the stormwater BMPs shall give consideration to providing groundwater recharge to compensate for the reduction in the percolation that occurs when the ground surface is paved and roofed over. These groundwater recharge measures are required wherever feasible. Soils used for the construction of basins shall have low-erodibility factors ("K" factors).
61.24.2. 
The low-impact development practices provided in the Pennsylvania Stormwater BMP Manual shall be utilized for all regulated activities to the maximum extent practicable using one of the following methods:
1. 
The Design Storm Method (CG-1 in the BMP Manual) is applicable as a method to any size of regulated activity. This method requires detailed modeling based on site conditions. The following shall be incorporated into the CG-1 method:
a. 
Reduce the post-development total runoff volume by 10% of predevelopment total runoff volume for all storms equal to or less than the two-year, twenty-four-hour duration precipitation.
b. 
At least the first one inch of runoff from the net increase in 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. If the developer provides justification that the listed removal options are not feasible, and the designated plan reviewer agrees, runoff shall be detained in a facility designed for a twenty-four- to seventy-two-hour dewatering time in an area with a dedicated stormwater system.
c. 
For modeling purposes:
[1] 
Existing (predevelopment) nonforested pervious areas must be considered meadow in good condition.
[2] 
Twenty percent of existing impervious area, when present, shall be considered meadow in good condition in the model for existing conditions.
2. 
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:
a. 
Stormwater facilities shall capture at least the first two inches of runoff from the net increase in impervious surfaces.
b. 
At least the first one inch of runoff from the net increase in 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. If the developer provides justification that the listed removal options are not feasible, and the designated plan reviewer agrees, runoff shall be detained in a facility designed for a twenty-four-hour dewatering time in an area with a dedicated stormwater system.
c. 
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.
61.25.1. 
Stormwater runoff calculations for all development sites and regulated activities shall be calculated in accordance with the following computation methodologies:
Method
Accepted Calculation Methods Applicability
Soil Cover Complex Method (formerly SCS)
Acceptable for all watersheds. Preferred for watersheds > 3 acres and for use with detention basin routings.
Rational Method
Acceptable for small watersheds and residential underground absorption systems. Recommended for watersheds < 3 acres.
TR-20, USDA Soil Conservation Service
Acceptable for all watersheds, especially where full hydrologic computer model is desired.
HEC-1 U.S. Army Corps of Engineers
Acceptable for all watersheds, especially where full hydrologic computer model is desired.
61.25.2. 
Selection of the method of calculation by the design professional shall be based upon the limitations and suitability of each method for the development site. The Municipal Engineer should be consulted for method alternatives and applicability.
61.25.3. 
Stormwater event criteria.
1. 
All runoff calculations shall be completed in accordance with the standard guidelines for the selected method of calculation.
2. 
Rational Method. The PennDOT Storm Intensity-Duration-Frequency Chart shall be used. Where stormwater runoff hydrographs are produced using the Rational Method, the provided storage volume shall be verified with a critical duration analysis that investigates similar storm occurrences with extended durations and applicable intensities to determine the anticipated maximum elevation to occur in the storage facility for each required storm event.
3. 
Soil Cover Complex Method. The Soil Conservation Service Type II, twenty-four-hour rainfall distribution shall be used in conjunction with the rainfall depths from NOAA Atlas 14.
a. 
Stormwater runoff control criteria.
[1] 
Stormwater management shall be accomplished by controlling post-development runoff rates to 90% predevelopment runoff rates for the two-year, five-year, ten-year, twenty-five-year, and 100-year storms.
b. 
Assumptions and criteria.
[1] 
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, 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 development site.
[2] 
All predevelopment calculations, unless in woodland, shall be based upon the assumption of meadow in good hydrologic condition. Wooded areas shall utilize forest/woodland cover coefficients. Where the site contains existing impervious surface, up to 50% of the impervious area may be considered as an existing predevelopment condition. Runoff coefficients and curve numbers shall be selected from the tables in the appendix.
[3] 
Drainage areas tributary to sinkholes or closed depressions shall be excluded from the modeled analysis defining predevelopment flows. If left undisturbed during construction, activities in areas draining to closed depressions may also be removed from peak runoff rates and post-development analysis. New additional contributing runoff shall not be directed to existing sinkholes or closed depressions.
[4] 
Runoff calculations for the predevelopment and post-development comparison shall evaluate all stormwater events listed within the stormwater runoff control criteria.
[5] 
Post-development analysis shall consider open areas of possible water impoundments receiving rainfall (such as detention basins, rain gardens, etc.) to have an impervious cover area of the maximum surface storage area of the water surface correlating to the storm event of interest.
[6] 
Design of stormwater facilities shall be verified by routing the storm event hydrographs through the facilities using the Storage Indication Method. Routings of Rational Method hydrographs shall determine the critical duration corresponding to the highest peak water surface elevation in the detention facility based on extended runoff inflows for each control storm event, or consist of a methodology approved by the Municipal Engineer. The combination of Rational Method hydrographs based on timing shall be prohibited.
[7] 
Predevelopment and post-development time-of-concentration paths shall be delineated on topographic mapping with the end and beginning of segments clearly identified, as well as the lengths and corresponding end elevations used for each segment. The post-development time of concentration shall never be greater than the predevelopment time of concentration for any watershed or subwatershed. Times of concentration shall be based upon the following:
[a] 
The maximum length of overland sheet flow shall be 100 feet before shallow concentrated or open channel flow develops and shall be justified using the methodology presented in Chapter 3 of the NRCS Technical Release 55 (TR-55) to include the following.
[b] 
Travel time for shallow concentrated flows shall utilize the NRCS methodology.
[c] 
Overland flows which are concentrated within field depressions, swales, gutters, curbs or pipe collection systems shall be designed using Manning's Equation for time of concentration criteria for open channel conditions between these design points using Manning's n values per the current edition of PennDOT Publication 584.
[8] 
Storm sewer pipes, culverts, gutters, inlets, outlets and swales shall be designed and constructed in accordance with the standards of the PennDOT Design Manual, Part 2, Highway Design (latest edition), including the following requirements:
Facility
Minimum Post-Development Peak Discharge Requirement
Pipes, gutters and swales, culverts, streets, cross drains and low points
25-year storm (Area < 100AC) and 100-year storm (Area > 100AC)
Bridges and stream crossings
100-year storm
[9] 
All stormwater collection facilities shall investigate and account for bypass scenarios.
[10] 
Conveyance of the 100-year storm event in a safe manner with acceptable hydraulic elevations shall be verified for all systems that:
[a] 
May affect improvements such as buildings, etc.
[b] 
All drainage areas directed to stormwater facilities used for post rate management.
[11] 
Swales shall be designed utilizing Manning's Equation to insure adequate capacity, control of velocity and swale stability. Calculations shall support swale stability for initial conditions (prior to established vegetation) and long-term conditions for the required peak flow rate. Vegetated swales shall have a minimum longitudinal slope of 2% and maximum side slopes of 3:1, unless specifically designed as a BMP structure. Culvert design shall investigate, at a minimum, inlet, barrel and outlet control conditions.
c. 
Calculation process.
[1] 
A general procedure recommended for site evaluation and stormwater design is as follows:
[a] 
Evaluate factors influencing stormwater runoff, with a goal of limiting earth disturbance, minimizing grading, and reducing or dispersing impervious surfaces.
[b] 
Satisfy the volume control requirements.
[c] 
Meet water quality (BMP) standards, preferably with BMPs near the source of the runoff.
[d] 
Calculate and satisfy peak runoff objective, considering all measures other than detention basins.
[e] 
Size detention basins accordingly.
[f] 
Demonstrate compliance with pre-development hydrograph requirements.
61.26.1. 
Goals and objectives.
1. 
Preserve existing natural features, especially those which store, infiltrate or filter water runoff.
2. 
Infiltrate rainfall to recharge the groundwater table.
3. 
Use physical (structural) and biological or vegetative (nonstructural) filtration of water runoff to reduce pollutants and remove sediment.
4. 
Moderate water runoff velocities to minimize erosion and damage to downstream aquatic habitat.
5. 
Integrate BMPs into the site layout to perform a water quality function and complement the developed use of the site.
6. 
Enhance site aesthetics through the use of a variety of BMP techniques and components.
7. 
Maximize collection and treatment of small storm event (first flush) stormwater runoff which contains the highest concentration of pollutants.
8. 
Utilize a system of BMP facilities and groundwater recharge devices throughout the site.
61.26.2. 
General standards.
1. 
Water quality shall be maintained through the requirement for BMP design components for all subdivisions, land developments and regulated activities, except where other provisions of this chapter provide for plan or stormwater design exemptions. Revision or expansion projects requiring land development approval with stormwater design shall include measures to retrofit the site with BMPs to maintain or improve the water quality of the stormwater discharges.
2. 
The required volume control, specified elsewhere herein, shall be detained and treated within BMPs for all areas of the site to be developed.
3. 
Site designs shall minimize earth disturbance and the generation of stormwater runoff while maximizing pervious areas for treatment of stormwater.
4. 
All BMPs shall be sized to capture the required control volume, designed according to the BMP criteria within this chapter, constructed properly and maintained regularly.
5. 
Stormwater runoff which is directly discharged to wetlands, streams, ponds, high-quality or exceptional value watersheds or which originates from land uses or activities with higher potential for pollutant loadings (such as auto salvage yards, vehicle service areas, loading/unloading areas, truck centers, etc.) require the use of additional or specific structural BMPs for pollution prevention and maintenance of water temperatures and quality.
6. 
Place BMPs near the source of stormwater runoff and treat runoff from impervious surfaces before mixing with runoff from less contaminated sources.
7. 
Use native vegetation and water-tolerant plants. Trees and shrubs shall not be planted on stormwater facility embankments or in other areas where roots may endanger pipes, embankments, headwalls, endwalls, spillway structures or other structural facilities.
8. 
All impervious area runoff shall be directed to BMPs. The volume control shall be provided within each watershed or subwatershed to provide the intended treatment for upstream runoff. Volume control credit will not be allowed toward noncontributing runoff areas.
9. 
BMP categories used within these regulations are 1) ponds, 2) wetlands, 3) infiltration systems, 4) filtering systems, and 5) open channels. The design criteria subsection listed hereafter provides specific descriptions of the BMPs within these classifications. Where effectiveness can be demonstrated, alternative BMP designs and concepts may be utilized.
10. 
Site designs shall include measures to reduce stormwater velocities and collect sediment near the source of the water runoff so that BMPs can be effective in treating water quality and maintenance can be reduced. Recommended facilities are forebays, energy dissipators, outlet stabilization structures, inlet protection devices, level spreaders, and flow splitters.
11. 
Carbonate geology (limestone) areas require careful evaluation for appropriate BMP design. Facility depths should be minimized and impermeable liners will be required.
12. 
Forebays and micropools are recommended for ponds and required for wetlands. Forebays and micropools should each contain approximately 10% of the required water volume. Forebays should be at least 10 feet long and be baffled from the main basin with a berm of riprap or similar material, to a depth of one foot below the water quality volume level, to insure an indirect flow path. Additionally, when forebays are used, a minimum of 90% of the discharge into the facility shall be directed into the forebays.
13. 
All ponds and wetlands shall be surrounded by a riparian buffer strip of a minimum 25 feet in width. Streams shall be bordered by a riparian buffer strip, a minimum of 25 feet or the width of the floodplain, whichever is greater. All PA DEP standards for buffer strips are required.
14. 
Planting of wetland plants is required within created wetlands and encouraged in ponds and other applicable BMPs. Fringe wetland plants may be used on aquatic benches or within shallow pools, while emergent wetlands vegetation should be planted along the side slopes and facility edges.
15. 
Infiltration, filtering or other BMP systems which are designed to treat the required control volume from small storms shall be preceded by a flow splitter or equivalent bypass device to route larger water volumes around the system.
16. 
All underground stone and sand BMP systems shall be lined with geotextile fabric on the sides, bottom and top (double layer on top), have a flat bottom, be underlain by a minimum of two feet of soil or sand above the seasonal high-water table and be placed a minimum of 10 feet horizontally from building foundation walls.
17. 
Infiltration systems with stone shall utilize AASHTO No. 1 (No. 4) stone and assume a maximum of 40% voids area.
18. 
Grass swales should be designed with a flat channel bottom at least two feet in width, with a longitudinal slope of 1% to 2%. If grass swale slopes exceed 4%, check dams or similar water velocity modifiers should be used.
61.26.3. 
Design criteria.
1. 
The following site factors should be considered in selecting and designing the appropriate BMPs:
a. 
Total contributing area.
b. 
Permeability and infiltration rate of the site soils.
c. 
Slope and depth to bedrock.
d. 
Seasonal high-water table.
e. 
Proximity to building foundations and wellheads.
f. 
Erodibility of soils.
g. 
Land availability and configuration of the topography.
2. 
The following factors should be evaluated when determining the suitability of BMPs for a development site:
a. 
Peak discharge and required volume control.
b. 
Stream bank erosion.
c. 
Efficiency of the BMPs to mitigate potential water quality problems.
d. 
The volume of runoff that will be effectively treated.
e. 
The nature of the pollutant being removed.
f. 
Maintenance requirements.
g. 
Creation/protection of aquatic and wildlife habitat.
h. 
Recreational value.
i. 
Enhancement of aesthetic and property value.
61.27.1. 
All subdivision and land development plans which propose earthmoving activity shall include erosion and sediment pollution control design to satisfy the requirements of Chapter 102, Pennsylvania Department of Environmental Protection, 25 Pa. Code Chapter 92 and/or 102, and the Pennsylvania Clean Streams Law (35 P.S. § 691.1 et seq.), and to prevent soil erosion, sediment and other pollutants from entering streams, lakes and neighboring properties.
61.28.1. 
In order to protect and improve water quality, a riparian corridor easement shall be created and recorded as part of any subdivision, land development or stormwater management plan that encompasses a riparian corridor.
61.28.2. 
Except as otherwise required by 25 Pa. Code Chapter 102, the riparian corridor easement shall be measured to be the greater of the limit of the 100-year floodplain or 35 feet from the top of stream bank (on each side).
61.28.3. 
Minimum management requirements for riparian corridors.
1. 
Existing native vegetation shall be protected and maintained within the riparian corridor easement.
2. 
Whenever practicable, invasive vegetation shall be actively removed, and the riparian corridor easement shall be planted with native trees, shrubs and other vegetation to create a diverse native plant community appropriate to the intended ecological context of the site.
61.28.4. 
The riparian corridor easement shall be enforceable by the Engineer and shall be recorded in the Allegheny County Recorder of Deeds Office, so that it shall run with the land and shall limit the use of the property located therein. The recorded easement shall be superior to all liens of record. The easement shall allow for the continued private ownership and shall count toward the minimum lot area as required by zoning.
61.28.5. 
Any permitted use within the riparian corridor easement shall be conducted in a manner that will maintain the extent of the existing 100-year floodplain, improve or maintain the stream stability, and preserve and protect the ecological function of the floodplain.
61.28.6. 
The following conditions shall apply when public and/or private recreation trails are permitted within riparian corridors:
1. 
It is preferred that trails be designed to be permeable and for nonmotorized use only; however, impermeable trails are permitted, provided they have adequate drainage.
2. 
Trails shall be designed to have the least impact on native plant species and other sensitive environmental features.
61.28.7. 
Septic drain fields and sewage disposal systems shall not be permitted within the riparian corridor easement and shall comply with setback requirements established under 25 Pa. Code Chapter 73.
61.28.8. 
Stormwater drainage pipes shall be permitted within the riparian buffer easement, but they shall cross the easement in the shortest practical distance. Other structural stormwater management facilities are not permitted within the riparian buffer easement.
61.28.9. 
New sanitary sewage conveyance pipes shall be permitted within the riparian buffer easement, but the easement shall not be used as a linear utility easement. Pipes shall cross the easement in the shortest practical distance.
61.28.10. 
Existing utilities may remain and be maintained as required.