Township of West Vincent, PA Article III Stormwater Management Standards

§ 302-13 General requirements.

A. Applicants proposing regulated activities in the Municipality which are not exempt under § 302-6 shall submit a stormwater management site plan (SWM site plan) to the Municipality for review and approval in accordance with Articles III and IV. SWM site plans approved by the Municipality shall be on site throughout the duration of the regulated activity.

B. The stormwater management and runoff control criteria and standards in this chapter shall apply to the total proposed regulated activity, even if it is to take place in stages. The measurement of impervious surfaces shall include all of the impervious surfaces in the total proposed regulated activity even if the development is to take place in stages.

C. No regulated activity within the Municipality shall commence until:

(1) The Municipality issues approval of an SWM site plan which demonstrates compliance with the requirements of this chapter; and

(2) The applicant has received a letter of adequacy or approval for the erosion and sediment control plan review by the Municipality and the conservation District (if required), and has received all other local, state and federal permit approvals required for the project involving the regulated activity.

D. Neither submission of an SWM site plan under the provisions herein nor compliance with the provisions of this chapter shall relieve any person from responsibility for damage to any person or property otherwise imposed by law.

E. The applicant shall design the site to minimize disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall apply the procedures set forth in § 302-16 for the overall site design and for selection, location and design of features and BMPs to be used to comply with the requirements of this chapter.

F. To the maximum extent practicable, post-construction stormwater shall be discharged within the drainage area of the same stream or water body receiving the runoff prior to construction of the proposed regulated activity.

G. Existing drainage peak rate discharges up to and including the 100-year storm and the volume of runoff up to and including the two-year storm onto or through adjacent property(ies) or downgradient property(ies), including diffuse drainage discharge, shall not be altered in any manner by regulated activities under this chapter without written permission from and, where applicable as determined by the Municipality, an easement and agreement with the affected landowner(s) for conveyance of discharges onto or through their property(ies). Altered stormwater discharges shall be subject to any applicable discharge criteria specified in this chapter.

H. Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to water quality and volume control, infiltration, stream channel protection, or peak flow rate control requirements (as presented in §§ 302-17, 302-18, 302-19 and 302-20). Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.

I. If site conditions preclude capture of runoff from limited portions of the disturbed area for achieving water quality volume control standards, stream channel protection standards, and the two-year, five-year, and ten-year storm event peak runoff rate reduction standards for new development required by this chapter, the applicant shall propose alternate methods to mitigate the bypass of the BMPs, subject to the approval of the Municipal Engineer. In no case shall resulting peak rate be greater than the predevelopment peak rate for the equivalent design storm.

J. For all regulated activities, erosion and sediment control BMPs shall be designed, implemented, operated and maintained during the regulated activities (i.e., during construction) as required to meet the purposes and requirements of this chapter; to meet the erosion and sediment control requirements of the Municipality, if applicable; and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law.

K. For all regulated activities, permanent BMPs and conveyances shall be designed, implemented, operated and maintained to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code, the Clean Streams Law, and the Storm Water Management Act.

L. The design of all BMPs and conveyances shall incorporate sound engineering principles and practices in a manner that does not aggravate existing stormwater problems as identified by the Municipality. The Municipality reserves the right to disapprove any design that would result in construction in an area affected by existing stormwater problem(s) or continuation of an existing stormwater problem(s).

M. Existing wetlands, either on the site or on an adjacent property, shall not be used to meet the minimum design requirements for stormwater management or stormwater runoff quality treatment. Stormwater discharges to existing wetlands shall not degrade the quality or hydrologic integrity of the wetland.

N. Hot spots runoff controls. Specific structural or pollution prevention practices may be required, as determined to be necessary by the Municipal Engineer, to pretreat runoff from hot spots prior to infiltration. Following is a list of examples of hot spots:

(1) Vehicle salvage yards and recycling facilities;

(2) Vehicle fueling stations;

(3) Vehicle service and maintenance facilities:

(4) Vehicle and equipment cleaning facilities;

(5) Fleet storage areas (bus, truck, etc.);

(6) Industrial sites based on Standard Industrial Classification Codes;

(7) Marinas (service and maintenance areas);

(8) Outdoor liquid container storage;

(9) Outdoor loading/unloading facilities;

(10) Public works storage areas;

(11) Facilities that generate or store hazardous materials;

(12) Commercial container nursery;

(13) Contaminated sites/brownfields;

(14) Other land uses and activities as designated by the Municipality.

O. Contaminated and brownfield sites. Where BMPs may contribute to the migration of contaminants in groundwater, the water quality and runoff volume, stream channel protection, and peak rate control standards shall be met; however, at the Municipal Engineer's discretion, the minimum infiltration requirement may be reduced or eliminated commensurate with the contaminated area and the required water quality and runoff control measures may be increased to mitigate the reduced infiltration requirement for the contaminated area.

P. Additional water quality requirements. The Municipality may require additional stormwater control measures for stormwater discharges to special management areas, including, but not limited to:

(1) Water bodies listed as "impaired" by PADEP.

(2) Any water body or watershed with an approved total maximum daily load (TMDL).

(3) Areas of known existing flooding problems.

(4) Critical areas with sensitive resources (e.g., state-designated special protection waters, cold water fisheries, carbonate geology or other groundwater recharge areas that may be highly vulnerable to contamination, drainage areas to water supply reservoirs, etc.).

Q. Applicants shall utilize the Pennsylvania Stormwater Best Management Practices Manual (PA BMP Manual), as amended, or other sources acceptable to the Municipal Engineer, for testing and design standards for BMPs; and where there is a conflict with the provisions of this chapter, the most restrictive applies.

R. For areas underlain by Karst or carbonate geology that may be susceptible to the formation of sinkholes and other Karst features, the location, type and design of infiltration BMPs shall be based on a site evaluation conducted by a qualified licensed professional and based on the PA BMP Manual (as amended) or other design guidance acceptable to the Municipal Engineer.

S. All regulated activities located within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with Article XVI, Floodplain Conservation Overlay District, of Chapter 390, Zoning, of the Township's Code, and shall be designed to maintain the flood-carrying capacity of the floodway such that the base flood elevations are not increased, either upstream or downstream. The natural conveyance characteristics of the site and the receiving floodplain shall be incorporated into the stormwater management practices proposed for the site.

T. All regulated activity shall comply with Chapter 390, Zoning, of the Township's Code, with respect to stream buffers.

§ 302-14 Permit requirements by other governmental entities.

The following permit or other regulatory requirements may apply to certain regulated activities and shall be met prior to (or as a condition of) final approval by the Municipality of the SWM site plan and prior to commencement of any regulated activities, as applicable:

A. All regulated activities subject to permit or regulatory requirements by PADEP under regulations at 25 Pa. Code Chapter 102, or erosion and sediment control requirements of the Municipality.

B. Work within natural drainageways subject to permit by PADEP under 25 Pa. Code Chapter 105.

C. Any BMP or conveyance that would be located in or adjacent to surface waters of the commonwealth, including wetlands, subject to permit by PADEP under 25 Pa. Code Chapter 105.

D. Any BMP or conveyance that would be located on or discharge to a state highway right-of-way, or require access to or from a state highway and be subject to approval by PennDOT.

E. Culverts, bridges, storm sewers, or any other facilities which must pass or convey flows from the tributary area and any facility which may constitute a dam subject to permit by PADEP under 25 Pa. Code Chapter 105.

§ 302-15 Erosion and sediment control.

A. No regulated activity within the Municipality shall commence until:

(1) The Municipality receives documentation that the applicant has received:

(a) A letter of adequacy from the Conservation District or other approval from PADEP in compliance with 25 Pa. Code Chapter 102 of an erosion and sediment control plan for construction activities for projects where the area of disturbance exceeds one acre, where pond dredging is involved, or when the disturbance is associated with activities described under 25 Pa. Code Chapter 105 permits;

(b) A PADEP NPDES permit for stormwater discharges associated with construction activities as required under 25 Pa. Code Chapter 92a, if applicable;

(c) Evidence of any other permit(s) or approvals required for the regulated activities; and

(2) An erosion and sediment control plan has been approved by the Municipality, if required.

B. A copy of the erosion and sediment control plan and any required permit(s), as required by PADEP regulations, shall be available on the site at all times.

C. Additional erosion and sediment control measures shall be applied where infiltration BMPs are proposed, at a minimum including those required in § 302-18M.

D. An erosion and sediment control plan shall be submitted with the Preliminary and Final plan subdivision and land development applications and with applications for grading permits for regulated activities that are not exempt under § 302-6. Such plan shall be submitted in accordance with the standards of the Pennsylvania Department of Environmental Protection Erosion and Sediment Pollution Control Manual, as amended, and the Special Protection Waters Implementation Handbook, as amended, and in compliance with the most current review requirements of the Chester County Conservation District, and in compliance with the following provisions:

(1) Upon recommendation from the Municipal Engineer, the Municipality may require the submission of plans, regardless of their size or other outside review requirements, to the Chester County Conservation District for review and approval. In such a case, approval by the Chester County Conservation District shall be required before final approval of a subdivision or land development; the issuance of a grading permit in the case of a minor subdivision; or the issuance of a grading permit for a regulated activity that is not exempt under § 302-6.

(2) Measures to minimize soil erosion and sedimentation shall meet the standards and specifications contained in the Pennsylvania Department of Environmental Protection, Soil Erosion and Sediment Pollution Control Manual, as amended and the Pennsylvania Clean streams Law, Chapter 102, Erosion and Sedimentation Control Rules and Regulations, as amended and the specifications contained herein. The Municipal Engineer or other duly authorized agent shall ensure compliance with the appropriate specifications.

(3) The Municipality may require measures to be incorporated into the plan for erosion and sediment Pollution control in addition to and/or more stringent than those required by the PADEP Manual, or by the Chester County Conservation District.

(4) The disturbed area and the duration of exposure shall be kept to a practical minimum and the disturbed soils shall be stabilized within four days after earth disturbances cease.

(a) The erosion control and stormwater management structures and systems shall be installed in accordance with the approved sequence of construction and shall be completed as quickly as possible; and

(b) If runoff from a project area discharges to a stream that is classified as Special Protection (High Quality or Exceptional Value) as designated by 25 Pa. Code Chapter 93, Water Quality Standards, as amended, more stringent criteria shall be used to design best management practices for that site in accordance with the Erosion and Sediment Pollution Control Program Manual. All graded surfaces shall be stabilized immediately upon completion of an earth disturbance activity, or any stage or phase of an activity, and, shall be watered, tended, and maintained as necessary until growth is well established.

(5) Whenever feasible, natural vegetation shall be retained, protected and supplemented.

(6) Sediment-laden water shall be trapped by the use of erosion and sediment control best management practices (BMP) such as inlet protection, sediment basins, sediment traps, or similar measures until the disturbed area is permanently stabilized and BMP removal is approved by the Chester County Conservation District. Accumulated sediment shall be removed to ensure continued adequate capacity in the BMPs in accordance with the PADEP Manual.

(7) There shall be no increase in discharge of sediment or other solid material from the site as a result of stormwater runoff.

(8) Erosion and sedimentation control BMPs, whether temporary or permanent, such as vegetation and mulch, earthen berms, waterbars, diversion terraces, rock filter berms, rock construction entrances, sediment basins, silt fences, and the like, appropriate to the scale of operations, shall be constructed, stabilized and functional before site disturbance (other than the minimal site disturbance necessary to install the BMPs) begins within the tributary areas of those BMPs, and whenever any situation is created which would contribute to increased soil erosion.

(9) Earthmoving operations shall be minimized where possible and practicable to preserve desirable natural features and the topography of the site.

(10) Stripping of vegetation, re-grading or other development shall be done in such a way that will minimize soil erosion.

(11) Land disturbance shall be limited to the actual construction site and an access strip. The amount of disturbed area and the duration of exposure shall be kept to a practical minimum. Disturbed areas shall be stabilized immediately upon completion of an earth disturbance activity or any stage or phase of an activity with an appropriate BMP.

(12) Temporary vegetation and/or mulching shall be used to protect critical areas during development ("critical areas" shall be construed to mean those portions of a site which are extremely vulnerable to soil erosion);

(13) Until the site is stabilized, all best management practices for erosion and sediment pollution control must be maintained properly. Maintenance must include inspections of all best management practices after each runoff event, and on a weekly basis. All preventive and remedial maintenance work, including cleanout, repair, replacement, regrading, reseeding, remulching and renetting must be performed immediately.

(14) If erosion and sediment pollution control best management practices fail to perform as expected, replacement best management practices or modifications of those installed will be required as determined by the Municipal Engineer.

(15) Should it be necessary, any pumping of sediment-laden water shall be through a sediment control BMP, such as a sediment basin or a pumped water filter bag discharging over non-disturbed areas.

(16) All earth disturbance activities shall proceed in accordance with the approved sequence of construction or staging of earth moving activities as it may be called. Each stage shall be completed before any following stage is initiated. Clearing and grubbing shall be limited to only those areas described in each stage.

(17) Responsibility.

(a) Whenever sedimentation is caused by the removal of vegetation, regrading or other development, it shall be the responsibility of the applicant or applicant's agent causing such sedimentation to remove it from all adjoining surfaces, drainage systems and watercourses and to repair any damage at his or her expense within a time period acceptable to the Township.

(b) All required drainage and erosion control improvements, whether temporary or permanent, shall be installed by the applicant or applicant's agent, at their expense, and in accordance with applicable requirements.

(18) Erosion and sediment control plan contents. An erosion and sediment control plan shall accompany preliminary and final plan subdivision and land development applications and applications for grading permits for regulated activities that are not exempt under § 302-6. It shall be prepared by a design professional experienced in stormwater management and soil erosion control, and in accordance with federal, state, county and Township requirements and regulations.

(a) The erosion and sediment control plan shall contain, at a minimum, the following information:

[1] A description of proposed earthmoving, grading, temporary erosion and sedimentation control facilities, and the relationship to permanent stormwater management facilities;

[2] Proposed alterations to the project area, including changes to the surface and vegetative cover, areas of cut and fill, structures, roads, paved areas and buildings;

[3] A description of the staging of earthmoving activities, including the staging of cover removal and all cuts and fill, and installation of erosion and sediment control facilities and practices;

[4] Details and specifications for all erosion and sediment control measures to be utilized in conjunction with the installation of improvements, including streets, storm sewers, underground utilities, sewer and water lines, buildings, driveways, parking areas, recreational facilities and other structures shall be described; and

[5] The program of operations to convert erosion and sedimentation controls to permanent stormwater management facilities, along with a schedule of the relative time sequence of activities.

(b) A narrative description and a map illustrating temporary and permanent control measures and facilities to be used during earthmoving. The description shall include the following information:

[1] The type, location and dimensions of each measure and/or facility to be used, along with its purpose;

[2] Design considerations and calculations of control measures and facilities;

[3] Facilities or measures to be used to protect trees and existing vegetation;

[4] Facilities or measures to prevent tracking of mud by construction vehicles.

(c) A narrative description of the maintenance procedures for temporary control facilities and the ownership arrangements, including the methods and frequency of removal and ultimate disposal site for sediments and other material removed from control facilities both during and upon completion of the project.

(d) The Soil erosion and sediment control plan shall be available at all times on the construction site. The applicant or applicant's agent shall be responsible for correcting any stormwater runoff problems that arise from the subdivision or land development, even if final approval has been granted. The Township reserves the right to order a cease and desist of all construction where runoff problems arise.

(e) The following practices shall be required for all subdivisions, land developments, and/or grading plan where applicable, as determined by the Township Engineer:

[1] Silt fence or compost filter socks shall be installed on each graded lot down-slope of the disturbed area prior to any lot disturbance. Straw bale barriers shall not be used.

[2] The appropriate erosion and sedimentation BMPs shall be placed at all inlets, headwalls, basin outlets and similar drainage structures during the construction period in order to prevent sediment from entering any watercourse, storm drainage system, or system that does not discharge to an erosion and sedimentation BMP, adjoining property, or other areas downstream.

[3] Each individual lot or unit within a subdivision, or each building within a land development shall incorporate temporary on lot berms designed to act as sediment traps and to capture and reduce runoff. These shall be located to protect environmentally sensitive areas and downstream properties, and shall be required during construction. The top width of the berms shall be a minimum of three feet, with side slopes of a 3:1 maximum.

[4] Rock construction entrances shall be placed at all entrances to construction areas. Rock construction entrances shall be of sufficient width and length to prevent transportation of sediment off of the construction site or shall incorporate other features to do so.

[5] Temporary and permanent seeding and mulch specifications shall be noted on all plans. The specifications shall include lime and fertilizer rates of application, as well as other provisions regarding procedures and materials. All locations where earthmoving has ceased for more than four days shall be stabilized with temporary seeding or mulch.

[6] During roadway grading, water bars shall be installed on all roadway subgrades to prevent erosion of the subgrades. The water bars shall divert stormwater runoff to an appropriate best management practice.

[7] The crushed stone base course for driveways, roadways and parking areas shall be applied immediately after grading procedures, in order to prevent erosion of the subgrade. All construction and trade vehicles must access a site by the crushed stone driveway and not across the unstabilized earth area. Construction vehicles shall not track mud onto paved drives or roads.

[8] Drainage swales and ditches, and all slopes greater than three to one shall be protected against erosive velocities with erosion and sedimentation BMPs, such as erosion control blanket or other material, as determined by the Township Engineer.

§ 302-16 Site design process.

The applicant shall design the site to minimize the disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. For regulated activities with 10,000 or more square feet of proposed earth disturbance or 2,000 or more square feet of proposed impervious surfaces, the applicant shall demonstrate in its SWM site plan (as required in § 302-25C) that the design sequence, objectives and techniques described below were applied to the maximum extent practicable in the site design of the regulated activity while complying with all other requirements of this chapter. The site design shall:

A. First, identify and delineate all existing natural resources and natural and man-made hydrologic features listed in § 302-25B(8) that are located within the site, or receive discharge from, or may be impacted by the proposed regulated activity.

B. Second, provide a prioritized listing of these resources and features to identify:

(1) Those to be incorporated into the site design in a manner that provides protection from any disturbance or impact from the proposed regulated activity;

(2) Those to be protected from further disturbance or impact but for which the proposed regulated activity will provide improvement to existing conditions;

(3) Those that can be incorporated into and utilized as components of the overall site design in a manner that protects or improves their existing conditions while utilizing their hydrologic function within the limits of their available capacity (e.g., for infiltration, evapotranspiration, or reducing pollutant loads, runoff volume or peak discharge rates, etc.) to reduce the need for or size of constructed BMPs; and

(4) Those that may be considered for alteration, disturbance or removal.

C. Third, develop the site design to achieve the following:

(1) Recognize and incorporate the priorities identified in Subsection B of this section as the basis for the proposed site layout, grading, construction, and permanent ground cover design;

(2) Minimize earth disturbance (both surface and subsurface);

(3) Maximize protection of or improvement to natural resources and special management areas;

(4) Minimize the disturbance of natural site hydrology, in particular natural drainage features and patterns, discharge points and flow characteristics, natural infiltration patterns and characteristics, and natural channel and floodplain conveyance capacity;

(5) Incorporate natural hydrologic features and functions identified in Subsection B of this section into the site design to protect and utilize those features and their hydrologic functions to reduce the need for or size of constructed BMPs;

(6) Maximize infiltration and the use of natural site infiltration features, patterns and conditions, and evapotranspiration features;

(7) Apply selective grading design methods to provide final grading patterns or preserve existing topography in order to evenly distribute runoff and minimize concentrated flows;

(8) Minimize the cumulative area to be covered by impervious surfaces and:

(a) Minimize the size of individual impervious surfaces;

(b) Separate large impervious surfaces into smaller components;

(c) Disconnect runoff from one impervious surface to another; and

(d) Utilize porous materials in place of impervious wherever practicable.

(9) Minimize the volume and peak discharge rates of stormwater generated;

(10) Avoid or minimize stormwater runoff pollutant loads and receiving stream channel erosion;

(11) Locate infiltration and other BMPs:

(a) At or as near to the source of generation as possible; and

(b) At depths that are as shallow as possible.

(12) Prioritize the selection and design of BMPs as follows:

(a) Nonstructural and vegetation BMPs; then

(b) Structural (surface and subsurface) BMPs.

(13) For flow volumes requiring conveyance from the source of generation to a BMP for management, give preference to open-channel conveyance techniques that provide infiltration and water quality benefits and landscaped-based management in common open space areas, where practicable; and

(14) Consider additional guidance for incorporating natural hydrology into the site and BMP designs, methods and techniques that support the objectives of Subsections B and C of this section. Appendix B presents additional discussion of conservation design and low-impact development.[1]

[1] Editor's Note: Said appendix is included as an attachment to this chapter.

D. The procedures set forth above shall be utilized to the maximum extent practicable for the overall site design and selection, location and design of features and BMPs to be used to comply with the requirements of §§ 302-17, 302-18, 302-19 and 302-20.

§ 302-17 Water quality and runoff volume requirements.

To control post-construction stormwater impacts from regulated activities and meet State Water Quality Requirements, BMPs shall be provided in the site design that replicate predevelopment stormwater infiltration and runoff conditions, such that post-construction stormwater discharges do not degrade the physical, chemical or biological characteristics of the receiving waters. The green infrastructure and low-impact development (LID) practices provided in the PA BMP Manual, as well as the guidance on green infrastructure, LID and conservation design (CD) provided in Appendix B,[1] shall be utilized for all regulated activities wherever possible. The applicant shall comply with the following water quality and runoff volume requirements for all regulated activities, including all new development and redevelopment activities:

A. The post-construction total runoff volume shall not exceed the predevelopment total runoff volume for all storms equal to or less than the two-year, twenty-four-hour duration precipitation (design storm). The water quality and runoff volume to be managed shall consist of any runoff volume generated by the proposed regulated activity over and above the predevelopment total runoff volume and shall be captured and permanently retained or infiltrated on the site. Permanent retention options may include, but are not limited to, reuse, evaporation, transpiration, and infiltration.

B. For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 302-21D of this chapter.

C. The design of the stormwater management facility outlet shall provide for protection from clogging and unwanted sedimentation.

D. BMPs that moderate the temperature of stormwater shall be used to protect the temperature of receiving waters.

E. Water quality improvement shall be achieved in conjunction with achieving the infiltration requirements of § 302-18. The infiltration volume required under § 302-18 may be included as a component of the water quality volume. If the calculated water quality and runoff volume is greater than the volume infiltrated, then the difference between the two volumes shall be managed for water quality and runoff volume control through other techniques or practices but shall not be discharged from the site.

F. Runoff from the disturbed area shall be treated for water quality prior to entering existing waterways or water bodies. If a stormwater management practice does not provide water quality treatment, then water quality BMPs shall be utilized to provide Pretreatment prior to the runoff entering the stormwater management practice.

G. The Municipality may require additional water quality and runoff control measures for stormwater discharging to special management areas such as those listed in § 302-13P.

H. When the regulated activity contains or is divided by multiple drainage areas, the water quality and runoff volume shall be separately addressed for each drainage area.

I. Weighted averaging of runoff coefficients shall not be used for manual computations or input data for water quality and runoff volume calculations.

J. Areas located outside of the site (i.e., areas outside of the regulated activity) may be excluded from the calculation of the water quality and runoff volume requirements.

K. Water quality and volume control practices shall be selected and designed to meet the criteria of § 302-16C that apply to water quality and volume control.

L. Evapotranspiration may be quantified and credited towards meeting volume requirements according to the PADEP Post Construction Stormwater Management (PCSM) Spreadsheet and Instructions (December 2020) or the most recent guidance from PADEP.

M. Infiltration which occurs during a rainfall event shall not be credited toward meeting infiltration volume requirements.

[1] Editor's Note: Said appendix is included as an attachment to this chapter.

§ 302-18 Infiltration requirements.

Providing for infiltration consistent with the natural hydrologic regime is required to compensate for the reduction in the recharge that occurs when the ground surface is disturbed or impervious surface is created or expanded. The applicant shall achieve the following infiltration requirements:

A. For regulated activities involving both new development and redevelopment, infiltration should be designed to accommodate the entire water quality and runoff volume required in § 302-17. Infiltration BMPs should be consistent with design and infiltration period guidelines included in the PA BMP Manual or other PA DEP design guidance. If the runoff volume required by § 302-17 cannot be infiltrated, then alternative methods consistent with the PA BMP Manual (as amended) or other PA DEP guidance, such as the Managed Release Concept, may be used to manage this volume with approval from the Municipal Engineer.

B. For regulated activities involving both new development and redevelopment, the volume as specified in § 302-17A from all regulated impervious surfaces shall be infiltrated.

C. If the requirements of Subsection § 302-18A or § 302-18B of this section cannot be physically accomplished, then the applicant shall be responsible for demonstrating with data or calculations to the satisfaction of the Municipal Engineer why this infiltration volume cannot be physically accomplished on the site (e.g., shallow depth to bedrock or limiting zone, open voids, steep slopes, etc.) and what alternative volume can be infiltrated.

D. Only if a minimum infiltration of the first 0.5 inch of runoff volume cannot be physically accomplished on the site, shall a waiver from this § 302-18 be considered by the Municipality, in accordance with § 302-9, Waivers.

E. If site conditions preclude capture of runoff from portions of the impervious surfaces, the infiltration volume for the remaining area shall be increased an equivalent amount to offset the loss.

F. When a project contains or is divided by multiple watersheds, the infiltration volume shall be separately addressed for each watershed.

G. Existing impervious surfaces located in areas outside of the site (i.e., outside of the regulated activity) may be excluded from the calculation of the required infiltration volume.

H. A detailed soils evaluation of the site shall be conducted by a qualified professional and, at a minimum, shall address soil permeability, depth to bedrock, and subgrade stability. The general process for designing the infiltration BMP shall be conducted by a qualified licensed professional and shall be consistent with the PA BMP Manual (as amended) (or other guidance acceptable to the Municipal Engineer) and, in general, shall:

(1) Analyze hydrologic soil groups as well as natural and man-made features within the site to determine general areas of suitability for infiltration practices. In areas where development on fill material is under consideration, conduct geotechnical investigations of subgrade stability; infiltration may not be ruled out without conducting these tests.

(2) Provide field tests such as double-ring infiltrometer or other hydraulic conductivity tests (at the elevation of the proposed infiltration surface) to determine the appropriate hydraulic conductivity rate. Standard septic/sewage percolation tests are not acceptable for design purposes.

(3) Design the infiltration facility for the required retention (infiltration) volume based on field-determined infiltration capacity (and apply safety factor as per applicable design guidelines) at the elevation of the proposed infiltration surface.

(4) On-lot infiltration features are encouraged; however, it shall be demonstrated to the Municipal Engineer that the soils are conducive to infiltration on the identified lots.

(5) Tests shall be conducted at the proposed bottom elevation of an infiltration BMP. At a minimum, two tests per infiltration BMP or one test per 1,000 square feet of infiltration area, whichever is greater, shall be provided.

(6) Soil analysis and infiltration test methods and test locations shall be submitted to the Township Engineer for review and approval prior to testing. The Township Engineer shall observe all testing and will require that specific test pits and percolation data be obtained in order to approve test result data and ensure that the proposed infiltration systems will function as designed.

I. Infiltration BMPs shall be selected based on suitability of soils and site conditions and shall be constructed on soils that have the following characteristics:

(1) A minimum depth of 24 inches between the bottom of the BMP and the top of the limiting zone. Additional depth may be required in areas underlain by Karst or carbonate geology (see § 302-18M).

(2) An infiltration rate sufficient to accept the additional stormwater volume and drain completely as determined by field tests conducted by the applicant.

(3) The infiltration facility shall completely drain the retention (infiltration) volume within three days (72 hours) from the end of the design storm.

J. All infiltration practices shall:

(1) Be selected and designed to meet the criteria of § 302-16C that are applicable to infiltration;

(2) Be set back at least 25 feet from all buildings and features with subgrade elements (e.g., basements, foundation walls, etc.), and at least 10 feet from property lines or right-of-way boundaries, unless otherwise approved by the Municipal Engineer;

(3) For any infiltration practice that collects runoff from shared or multiple features and that is located within 50 feet of a building or feature with subgrade elements (e.g., basements, foundation walls, etc.), the bottom elevation shall be set below the elevation of the subgrade element.

K. Infiltration facilities shall, to the maximum extent practicable, be located to avoid introducing contaminants to groundwater:

(1) When a hot spot is located in the area draining to a proposed infiltration facility, an evaluation of the potential of groundwater contamination from the proposed infiltration facility shall be performed, including a hydrogeologic investigation (if necessary) by a qualified licensed professional to determine what, if any, pretreatment or additional design considerations are needed to protect groundwater quality.

(2) When located within a wellhead protection area of a public water supply well, infiltration practices shall be in conformance with the applicable approved source water protection assessment or source water protection plan.

(3) The applicant shall provide appropriate safeguards against groundwater contamination for land uses that may cause groundwater contamination should there be a mishap or spill.

L. During site construction, all infiltration practice components shall be protected from compaction due to heavy equipment operation or storage of fill or construction material. Infiltration areas shall also be protected from sedimentation. Areas that are accidentally compacted or graded shall be remediated to restore soil composition and porosity. Adequate documentation to this effect shall be submitted to the Municipal Engineer for review. All areas designated for infiltration shall not receive runoff until the contributory drainage area has achieved final stabilization.

M. Consideration of infiltration BMPs for areas underlain by Karst or carbonate geology is encouraged, but only where the design, supporting calculations, results of soils or other site investigations or other documentation are provided to the Municipality demonstrating that the potential or likelihood of subsidence or sinkholes is minimal. Evaluation of site conditions and infiltration design shall rely on guidance in the PA BMP Manual (as amended) or other guidance acceptable to the Municipal Engineer.

N. Groundwater quality of the carbonate aquifer shall be protected from infiltration of pollutants. At a minimum, stormwater runoff from hotspots (i.e., sources of significant pollutant runoff) shall first be discharged through a water quality BMP(s) to remove pollutants prior to infiltration. Where soil characteristics are insufficient to provide removal of pollutants from sources other than hotspots, stormwater runoff shall first be discharged though a water quality BMP(s) to remove pollutants prior to infiltration.

O. Where sediment transport in the stormwater runoff is anticipated to reach the infiltration system, appropriate permanent measures to prevent or collect sediment shall be installed prior to discharge to the infiltration system.

P. Where roof drains are designed to discharge to infiltration practices, they shall have appropriate measures to prevent clogging by unwanted debris (for example, silt, leaves and vegetation). Such measures shall include but are not limited to leaf traps, gutter guards and cleanouts.

Q. All infiltration practices shall have appropriate positive overflow controls.

R. No sand, salt or other particulate matter may be applied to a porous surface material for winter ice conditions.

S. The following procedures and materials shall be required during the construction of all subsurface facilities:

(1) Excavation for the infiltration facility shall be performed with equipment that will not compact the bottom of the seepage bed/trench or like facility.

(2) The bottom of the bed and/or trench shall be scarified prior to the placement of aggregate.

(3) Only clean aggregate with documented porosity, free of fines, shall be allowed.

(4) The tops, bottoms and sides of all seepage beds, trenches, or like facilities shall be covered with drainage fabric. Fabric shall be nonwoven fabric acceptable to the Municipal Engineer.

(5) Stormwater shall be distributed throughout the entire seepage bed/trench or like facility, and provisions for the collection of debris shall be provided in all facilities.

(6) Perforated distribution pipes connected to centralized catch basins and/or manholes with provision for the collection of debris shall be provided in all facilities. The perforated pipes shall distribute stormwater throughout the entire seepage bed/trench, or like facility.

(7) Recharge facilities shall be designed in accordance with infiltration system guidelines of DEP BMP Manual Appendix C Protocol 2, as amended.

(8) The Municipal Engineer shall be permitted to inspect construction methods. Shop drawings shall be submitted for all materials utilized in recharge facilities.

T. All infiltration facilities which service more than one lot and are considered a common facility shall have an easement provided to the Township for future access if necessary.

§ 302-19 Stream channel protection requirements.

For regulated activities involving new development with one or more acres of earth disturbance, the applicant shall comply with the following stream channel protection requirements to minimize stream channel erosion and associated water quality impacts to the receiving waters:

A. The peak flow rate of the post-construction two-year, twenty-four-hour design storm shall be reduced to the predevelopment peak flow rate of the one-year, twenty-four-hour duration precipitation, using the SCS Type II distribution.

B. To the maximum extent practicable, and unless otherwise approved by the Municipal Engineer, the post-construction one-year, twenty-four-hour storm flow shall be detained for a minimum of 24 hours and a maximum not to exceed 72 hours from a point in time when the maximum volume of water from the one-year, twenty-four-hour storm is stored in a proposed BMP (i.e., when the maximum water surface elevation is achieved in the facility). Release of water can begin at the start of the storm (i.e., the invert of the orifice is at the invert of the proposed BMP).

C. For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 302-21D of this chapter.

D. The minimum orifice size in the outlet structure to the BMP shall be three inches in diameter unless otherwise approved by the Municipal Engineer, and a trash rack shall be installed to prevent clogging. For sites with small drainage areas contributing to the BMP that do not provide enough runoff volume to allow a twenty-four-hour attenuation with the three-inch orifice, the calculations shall be submitted showing this condition.

E. When the calculated orifice size is below three inches, gravel filters (or other methods) are recommended to discharge low-flow rates subject to the Municipal Engineer's satisfaction. When filters are utilized, maintenance provisions shall be provided to ensure filters meet the design function.

F. All proposed stormwater management facilities shall make use of measures to extend the flow path and increase the travel time of flows in the facility.

G. When a regulated activity contains or is divided by multiple drainage areas, the peak flow rate control shall be separately addressed for each drainage area.

§ 302-20 Stormwater peak rate control requirements.

The applicant shall comply with the following peak flow rate control requirements for all regulated activities including those that involve new development and redevelopment.

A. Post-construction peak flow rates from any regulated activity shall not exceed the predevelopment peak flow rates as shown for each of the design Storms specified in Table 308.1.

Table 308.1 Peak Rate Control Standards
(Peak flow rate of post-construction design storm shall be reduced to the peak flow rate of corresponding predevelopment design storm shown in the table.)
	Predevelopment Design Storm
Post-Construction Design Storm Frequency (24-hour duration)	New Development Regulated Activities	Redevelopment Regulated Activities
1-year	75% (0.75) of the year	1-year
2-year	1-year	2-year
5-year	2-year	5-year
10-year	2-year	10-year
25-year	25-year	25-year
50-year	50-year	50-year
100-year	100-year	100-year

B. For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 302-21D of this chapter.

C. For regulated activities involving only redevelopment, no peak flow rate controls are required when and only if the total regulated impervious surface area is at least 20% less than the total existing impervious surface area to be disturbed by the regulated activity. In all cases where this requirement is not met, the redevelopment regulated activity shall achieve the peak flow rate controls presented in Table 308.1, using the redevelopment ground cover assumptions presented in § 302-21D. This design criterion for redevelopment is only permitted with approval of Municipal Engineer. It shall result in no impact on downstream properties.

D. Only the area of the proposed regulated activity shall be subject to the peak flow rate control standards of this chapter. Undisturbed areas for which the discharge point has not changed are not subject to the peak flow rate control standards.

E. Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to peak flow rate control requirements. Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.

F. When a regulated activity contains or is divided by multiple drainage areas, the peak flow rate controls shall be separately addressed for each drainage area.

G. The effect of structural and nonstructural stormwater management Practices implemented as part of the overall site design may be taken into consideration when calculating total storage volume and peak flow rates.

§ 302-21 Calculation methodology.

A. Stormwater runoff from all regulated activity sites with a drainage area of greater than one acre shall be calculated using a generally accepted calculation technique(s) that is based on the NRCS Soil-Cover-Complex Method. Table 309.1 summarizes acceptable computation methods. The method selected for use shall be based on the individual limitations and suitability of each method for a particular site. The use of the Rational Method to estimate peak discharges for drainage areas greater than one acre shall be permitted only upon approval by the Municipal Engineer.

Table 309.1 Acceptable Computation Methodologies for SWM site plan
Method	Developed by	Applicability
TR-20 (or commercial computer package based on TR-20)	USDA NRCS	Applicable where use of full hydrology computer model is desirable or necessary
TR-55 (or commercial computer package based on TR-55)	USDA NRCS	Applicable for land development plans where limitations described in TR-55 are met
HEC-1/HEC-HMS	US Army Corps of Engineers	Applicable where use of a full hydrologic computer model is desirable or necessary
Rational Method (or commercial computer package based on Rational Method)	Emil Kuichling (1889)	For sites up to 1 acre, or as approved by the Municipality
Other methods	Varies	Other computation methodologies approved by the Municipality

B. All calculations using the Soil-Cover-Complex Method shall use the appropriate design rainfall depths for the various return period storms consistent with this chapter. Rainfall depths used shall be 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 Atlas 14) values consistent with a partial duration series. When stormwater calculations are performed for routing procedures or infiltration, water quality and runoff volume functions, the duration of rainfall shall be 24 hours.

C. All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration (duration) and storm events with rainfall intensities obtained from NOAA Atlas 14 partial duration series estimates, or the latest version of the PennDOT Drainage Manual (PDM Publication 584). Times of concentration shall be calculated based on the methodology recommended in the respective model used. Times of concentration for channel and pipe flow shall be computed using Manning's equation.

D. The applicant shall utilize the following ground cover assumptions for all predevelopment water quality and runoff volume, infiltration volume and peak flow rate calculations:

(1) For regulated activities involving new development, the following ground cover assumptions shall be used:

(a) For areas that are woods (as defined in Article II of this chapter), predevelopment calculations shall assume ground cover of woods in good condition.

(b) For all other areas (including all impervious surfaces and areas of cultivation), predevelopment calculations shall assume ground cover of meadow.

(2) For regulated activities involving redevelopment, the following ground cover assumptions shall be used:

(a) For areas that are woods (as defined in Article II of this chapter), predevelopment calculations shall assume ground cover of woods in good condition.

(b) For areas that are not woods or not impervious surfaces, predevelopment calculations shall assume ground cover of meadow.

(c) For areas that are impervious surfaces, predevelopment calculations shall assume at least 40% of the existing impervious surface area to be disturbed as meadow ground cover.

(3) The applicant shall determine which stormwater standards apply to the proposed regulated activity as follows:

(a) Stormwater standards for new development shall apply to all proposed regulated activities that involve only new development activities as defined in this chapter.

(b) Stormwater standards for redevelopment shall apply to all proposed regulated activities that involve only redevelopment activities as defined in this chapter.

(c) At the discretion of the Municipal Engineer, regulated activities that involve a combination of both new development and redevelopment activities, as defined in this chapter, may either:

[1] Apply the stormwater standards (redevelopment or new development) that are associated with the activity that involves the greatest amount of land area; or

[2] Apply the redevelopment and new development stormwater standards to the corresponding redevelopment and new development portions of the proposed regulated activity.

E. Runoff curve numbers (CN) for both predevelopment and proposed (post-construction) conditions to be used in the Soil-Cover-Complex Method shall be obtained from Table C-1 in Appendix C of this chapter. All those areas to be disturbed during construction shall be assumed to be reduced one Hydrologic Soil Group Category level during post-development runoff calculations (i.e., HSG B is reduced to HSG C and so forth). This requirement does not apply to regulated activities involving redevelopment.

F. Runoff coefficients (C) for both predevelopment and proposed (post-construction) conditions for use in the Rational Method shall be obtained from Table C-2 in Appendix C of this chapter. All those areas to be disturbed during construction shall be assumed to be reduced one Hydrologic Soil Group Category level during post-development runoff calculations (i.e., HSG B is reduced to HSG C and so forth). This requirement does not apply to regulated activities involving redevelopment.

G. Weighted averaging of runoff coefficients shall not be used for manual computations or input data for water quality and runoff volume calculations.

H. Hydraulic computations to determine the capacity of pipes, culverts and storm sewers shall be consistent with methods and computations contained in the Federal Highway Administration Hydraulic design Series Number 5 (Publication No. FHWA-NHI-01-020 HDS No. 5, as amended). Hydraulic computations to determine the capacity of open channels shall be consistent with methods and computations contained in the Federal Highway Administration Hydraulic Engineering Circular Number 15 (Publication No. FHWA-NHI-05-114 HEC 15, as amended). Values for Manning's roughness coefficient (n) shall be consistent with Table C-3 in Appendix C of this chapter.

I. Runoff calculations shall include the following assumptions:

(1) Average antecedent moisture conditions (for the Soil-Cover-Complex Method only for example, TR-55, TR-20).

(2) A Type II distribution storm (for the Soil-Cover-Complex Method only for example, TR-55, TR-20).

§ 302-22 Other requirements.

A. Any BMP intended to hold standing water for four days or longer shall be designed to incorporate biologic controls consistent with the West Nile Guidance found in Appendix D, PADEP document 363-0300-001 "Design Criteria - Wetlands Replacement/Monitoring" (as amended), or contact the Pennsylvania State Cooperative Wetland Center or the Penn State Cooperative Extension Office for design information.

B. Any stormwater basin required or regulated by this chapter designed to store runoff and requiring a berm or earthen embankment shall be designed to provide an emergency spillway to safely convey flow up to and including the 100-year proposed conditions. At the discretion of the Municipal Engineer, the requirement to provide an emergency spillway may be waived for stormwater basins on residential lots with a drainage area less than one acre. The height of embankment shall provide a minimum 1.0 foot of Freeboard above the maximum pool elevation computed when the facility functions for the 100-year proposed conditions inflow. Should any BMP require a dam safety permit under 25 Pa. Code Chapter 105 regulations, the facility shall be designed in accordance with and meet the regulations of Chapter 105 concerning dam safety. Chapter 105 of Title 25 of the Pennsylvania Code may require the safe conveyance of storms larger than 100-year event.

C. Any drainage conveyance facility and/or channel not governed by 25 Pa. Code Chapter 105 regulations shall be designed to convey, without damage to the drainage facility or roadway, runoff from the twenty-five-year storm event. Larger storm events (fifty-year and 100-year storms) shall also be safely conveyed in the direction of natural flow without creating additional damage to any drainage facilities, nearby structures, or roadways.

D. Conveyance facilities to or exiting from stormwater management facilities (i.e., detention basins) shall be designed to convey the design flow to or from the facility.

E. Roadway crossings or structures located within designated floodplain areas shall be able to convey runoff from a 100-year design Storm consistent with Federal Emergency Management Agency National flood Insurance Program floodplain management requirements.

F. Any stormwater management facility located within a PennDOT right-of-way shall comply with PennDOT minimum design standards and permit submission and approval requirements.

G. Adequate erosion protection and energy dissipation shall be provided along all open channels and at all points of discharge. Design methods shall be consistent with the Federal Highway Administration Hydraulic Engineering Circular Number 11 (Publication No. FHWA-IP-89-016, as amended) and the PADEP Erosion and Sediment Pollution Control Program Manual (Publication No. 363-2134-008, as amended), or other design guidance acceptable to the Municipal Engineer.

§ 302-23 Other conveyance and system design standards.

Any design must also comply with any other existing Township ordinances, including, but not limited to, the West Vincent Township Subdivision and Land Development Ordinance (see Chapter 315 of the Township's Code).

A. Detention and retention facility design requirements.

(1) All detention/retention basins shall be designed to detain the peak rate of water resulting from the site for all design storms up to and including the fifty-year frequency rainfall. Design storms shall be routed through the basin facilities, excluding in the design calculations, the volume of the basin required for stormwater infiltration/recharge.

(2) The following setbacks are required for stormwater management facilities:

(a) Stormwater retention or detention basins shall be located at least 25 feet from any structure, whether existing or proposed.

(b) Stormwater retention or detention basins shall be located at least 25 feet from any property boundary or right-of-way.

(c) Stormwater retention or detention basins shall be located at least 50 feet from existing wetlands, or the banks of existing streams.

(d) Recharge systems shall be located at least 25 feet from any basement wall and 25 feet from wastewater treatment areas.

(e) Any recharge system designed to handle runoff from any commercial or industrial impervious parking or outside storage area shall be a minimum of 50 feet from any water supply well or any wastewater treatment area.

(3) Riser. A riser or other acceptable outfall shall be provided at the outlet of all detention basins. The riser shall be constructed of precast or poured-in-place concrete with controlled orifices. A trash rack or similar appurtenance shall be provided to prevent debris from entering the riser. All risers shall have a concrete base attached with a watertight connection. The base shall be of sufficient weight to prevent flotation of the riser.

(4) Landscaping. All stormwater control systems, whether existing or proposed, shall be planted to effectively naturalize areas so as to become an integral and harmonious element in the local landscape. No trees shall be planted in the earthfill of berms or dams.

(5) Emergency spillway. Whenever possible, the emergency spillway for detention basins shall be constructed on undisturbed ground. All emergency spillways shall be constructed so that the detention basin berm is protected against erosion with a permanent erosion control blanket. The minimum capacity of all emergency spillways shall be such that the capacity of the emergency spillway equals the peak flow rate from the 100-year design storm. Emergency spillway linings shall extend along the upstream and downstream berm embankment slopes. The upstream edge of the emergency spillway lining shall extend to a minimum of two feet below the spillway crest elevation. The downstream edge of the spillway lining shall, at minimum, extend to a distance of 10 feet beyond the toe of the berm embankment. The emergency spillway shall not discharge over earthen fill and/or easily erodible material.

(6) Anti-seep collars. Anti-seep collars shall be installed around the principal pipe barrel within the normal saturation zone of the detention basin berms. The anti-seep collars and their connections to the pipe barrel shall be watertight. The anti-seep collars shall extend a minimum of two feet beyond the outside of the principal pipe barrel. The maximum spacing between collars shall be 14 times the minimum projection of the collar measured perpendicular to the pipe.

(7) Freeboard. Any stormwater basin required or regulated by this chapter designed to store runoff and requiring a berm or earthen embankment shall be designed to provide an emergency spillway to safely convey flow up to and including the 100-year proposed conditions. The height of embankment shall provide a minimum 1.0 foot of freeboard above the design flow depth of the emergency spillway. Should any BMP require a dam safely permit under PA Chapter 105 regulations, the facility shall be designed in accordance with and meet the regulations of PA Chapter 105 concerning dam safety. PA Chapter 105 may require the safe conveyance of storms larger than 100-year event.

(8) Slope of detention basin embankment. The maximum slope of earthen detention basin embankments shall meet the requirements contained in this subsection. Whenever possible, the side slopes and basin shape shall be amenable to the natural topography. Straight side slopes and rectangular basins shall be avoided.

(9) Width of berm. For dams less than 10 feet high, a minimum top width of six feet is required, For dams 10 feet to 15 feet in height, a top width of 10 feet is required. For dams greater than 15 feet in height, the top width shall be designed by a professional engineer.

(10) Slope of basin bottom. In order to ensure proper drainage of the detention basin, a minimum grade of 2% shall be maintained for all sheet flow. A minimum grade of 1% shall be maintained for all channel flow. The Township Engineer may approve the use of a flat (0%) bottom accompanied with appropriate water tolerant landscape plantings to promote water quality and groundwater recharge.

(11) Energy dissipaters. Energy - dissipating devices (rip-rap, end sills. etc.) shall be placed at all basin outlets. Any pipe or other component which discharges directly into the basin shall be equipped with energy-dissipating devices and shall outlet into the bottom of the basin.

(12) Landscaping and grading of detention basin. All landscaping and grading standards shall be as follows:

(a) Cuts. No excavation shall be made with a cut face steeper than three horizontal to one vertical, except under the condition that the material in which the excavation is made is sufficiently stable to sustain a slope of steeper than three horizontal to one vertical. A written statement to that effect is required from an engineer and must be submitted and approved by the Municipal Engineer. The statement shall affirm that the site has been inspected and that the deviation from the slope should not result in injury to persons or damage to property. Retaining walls shall be required if a stable slope cannot be maintained. Any retaining wall design must be signed and sealed by a professional engineer. The toe of the slope or headwall of any cut must be located a minimum of five feet from property lines.

(b) Fills. No fills shall be made which creates any exposed surfaces steeper in slope than three horizontal to one vertical, except where the fill is located so that settlement, sliding, or erosion will not result in property damage or be a hazard to adjoining property, streets, or buildings. A written statement is required from an engineer certifying that s/he has inspected the site and that any proposed deviation from the slope specified above should not endanger any property or result in property damage, and must be submitted to and approved by the Municipal Engineer.

[1] A concrete or stone masonry wall designed and constructed in accordance with these specifications and standards may be required to support the face of the fill where the above specified slopes are exceeded.

[2] The top of any fill or toe of the slope of any fill shall be located 25 feet from any property line with the exception of a downstream property line where the toe of the embankment shall be placed a sufficient distance to allow for energy-dissipating devices, but in no case less than 40 feet unless approved otherwise by the Township.

(c) Planting requirements. All areas proposed for recreational use, whether active or passive, shall be planted to effectively naturalize the areas to become an integral and harmonious element in the natural landscape.

(d) Drainage channels and retention areas. All storm drainage channels and retention areas, whether existing or proposed, shall be graded and planted to effectively naturalize areas so as to become an integral and harmonious part of the landscape by contour and type of plant material employed.

(13) Easements for all basins and storm pipes not located within the public street right-of-way shall be provided in accordance with § 302-37.

(14) Any BMP intended to hold standing water for four days or longer shall be designed to incorporate biologic controls consistent with the West Nile Guidance found in PADEP document 363-0300-001 "Design Criteria - Wetlands Replacement/Monitoring" (as amended), (or contact the Pennsylvania State Cooperative Wetland Center or the Penn State Cooperative Extension Officer for design information).

(15) A profile shall be provided on the plan of the berm embankment and outlet structure indicating the embankment top elevation, embankment side slopes, top width embankment emergency spillway elevation, riser dimensions, pipe barrel dimensions, and dimensions and spacing of anti-seep collars.

B. Drainage and conveyance system design requirements.

(1) Design flow rate. The storm drain system shall be designed to carry a twenty-five-year peak flow rate, and a fifty-year peak flow rate at the sump area. The design twenty-five-year peak flow rate into each inlet shall be indicated on the stormwater management plan. The twenty-five-year flow rate shall be determined by the rational formula, Q = CIA.

Where:
Q	=	Peak runoff rate, cubic feet per second (CFS);
C	=	Runoff coefficient equal to the ratio of the runoff rate to the average rate of rainfall over a time period equal to the time of concentration;
I	=	Average rainfall intensity to inches per hour for a time equivalent to the time of concentration;
A	=	Drainage area in acres.

Approximate values for the runoff coefficient and runoff intensity can be found in the Commonwealth of Pennsylvania, Department of Transportation, PennDOT Drainage Manual Publication 584, as amended.

(2) Overflow system, An overflow system shall be provided to carry flow to the detention basin when the capacity of the storm drain pipe system is exceeded. The overflow system shall be of sufficient capacity to carry the difference between the 100-year and the twenty-five-year peak flow rates without creating additional damage to any drainage facilities, structures or roadways.

(3) Inlet capacity. All inlets must be designed to accommodate the twenty-five-year peak flow rate. The designer must submit capture/bypass calculations for each inlet and include these calculations in the stormwater report. As a minimum, the storm drainage system serving a street shall be designed to collect water at any point where three cubic feet to five cubic feet per second is accumulated, and at the bottom of all vertical grades, and immediately upgrade of all street intersections. The system shall discharge any collected water into the nearest practical drainage channel or storm system. The capacity of each inlet shall be indicated on the stormwater plan. The capacity of all C, M, or S type inlets shall be determined from the following sources:

Commonwealth of Pennsylvania

Department of Transportation

Design Manual, Part 2

Highway Design, Chapter 10

(4) Summary table. A table shall be provided on the plan summarizing storm sewer information including, inlet numbers, inlet pipes, elevation of all grates and pipe inverts, pipe diameters and lengths, pipe material, etc. A similar table shall be provided summarizing the design information for all temporary and permanent drainage channels.

(5) Roadway crossings or structures located within designated floodplain areas shall be able to convey runoff from a 100-year design storm consistent with Federal Emergency Management Agency National flood Insurance Program - floodplain management Requirements.

(6) Any facility located within a PennDOT right-of-way shall comply with PennDOT minimum design standards and permit submission and approval requirements.

(7) Adequate erosion protection and energy dissipation shall be provided along all open channels and at all points of discharge. Design methods shall be consistent with the Federal Highway Administration Hydraulic Engineering Circular Number 11 (Publication No. FHWA-IP-89-016, as amended) and the PADEP Erosion and Sediment Pollution Control Program Manual (Publication No. 363-2134-008, as amended), or other design guidance acceptable to the Municipal Engineer.

(8) Straight pipe selections. Wherever possible, all storm drain pipes shall be designed to follow straight courses. No angular deflections of storm sewer pipe sections in excess of 5° shall be permitted. No vertical curves shall be permitted in the storm drain pipe system.

(9) Minimum grade and size. All storm drain pipes shall be designed to maintain a minimum grade of 1/2%. All storm pipes shall have a minimum inside diameter of 15 inches, except that pipes under a twenty-five-foot-deep or greater fill shall not be less than 24 inches, or a cross-sectional area of 453 square inches.

(10) Pipe material and thickness. All storm sewers shall meet PennDOT standards for service life and proper class and thickness to support the above fill material. Pipe type and joint specifications shall be noted on the plans and shall be in accordance with PennDOT standards.

(11) Pipe capacity. The capacity of all pipe culverts shall, as a minimum, provide the required carrying capacity as determined by the following source:

United States Department of Transportation

Federal Highway Administration

Hydraulic Design Series Number 5

Hydraulic Design of Highway Culverts, 3rd Edition.

(12) Pipe arches. Where headroom is restricted, equivalent pipe arches may be used in lieu of circular pipes.

(13) Allowable headwater depth. At all inlets or manholes, the maximum allowable headwater depth shall be one foot below the top of the inlet grate of the manhole cover.

(14) Horizontal pipe deflections. A manhole or inlet shall be provided at all horizontal deflections in the storm pipe system exceeding 5°.

(15) Inlet boxes shall conform to PennDOT Standard Drawings and Publication 408, latest edition. Inlets shall be permanently marked with the phrase "No dumping - drains to creek" with metal medallion style signs or other method approved by the Municipal Engineer.

(16) Minimum and maximum cover. A minimum of 18 inches of cover shall be maintained over all storm drain pipes, unless the pipe manufacturer allows less cover for the specific location and expected loading. The top of storm drain pipes shall be at least 1/2 foot below subgrade elevation.

(17) Culverts and drainage channels.

(a) Design flow standards. All culverts and drainage channels shall be designed to carry a flow rate equal to a fifty-year, twenty-four-hour storm (NRCS, Technical Release No. 55).

(b) Erosion prevention. All drainage channels shall be designed to prevent the erosion of the bed and bank areas. The flow velocity in all vegetated drainage channels shall not exceed three feet per second to prevent erosion unless special provisions approved by the Municipal Engineer are made to protect banks and channel bottoms against erosion. Suitable bank stabilization shall be provided where required to prevent erosion of the drainage channels. Where storm sewers discharge into existing drainage channels at an angle greater than 30° from parallel with the downstream channel flow, the far side bank shall be stabilized by the use of rip-rap or masonry, and/or concrete walls. The stabilization shall be designed to prevent erosion and frost heave under and behind the stabilizing media.

(c) Maximum side slope. Any vegetated drainage channel requiring mowing of the vegetation shall have a maximum grade of three horizontal to one vertical of those areas to be mowed.

(d) Design standard. Because of the critical nature of the vegetated drainage channels, the design of all vegetated channels shall, at a minimum, conform to the design procedures outlines in the PADEP manuals. Several acceptable sources outline procedures for non-vegetated drainage channels, including the following:

Bureau of Public Roads

Hydraulic Engineering Circular No. 5

Hydraulic Charts for the Selection of Highway Culverts

Federal Highway Administration

Hydraulic Engineering Circular No. 13

Hydraulic Design of Improved Inlets for Culverts

(e) Reference to publications and source documents in this section shall be deemed to include any amendments and revisions thereof.

(18) Easements for all drainage and conveyance systems, existing or proposed, not located within the public street right-of-way, shall be provided per § 302-43.

(19) Residential subdivisions or development. Drainage channels shall be provided to intercept stormwater along property lines at locations where runoff from a lot would drain onto an adjacent lot. These channels shall be designed to convey stormwater to a suitable discharge point or the storm sewer system. Storm inlets shall be designed and located in new residential developments to capture stormwater that drains from one lot to another lot. Stormwater drainage channels shall not convey stormwater across more than two adjacent lots without being captured by a storm inlet and piping.