Township of Honey Brook, PA Part 3 STORMWATER MANAGEMENT STANDARDS

§ 20-301 General Requirements.

[Ord. No. 170-2014, 5/14/2014, as amended by Ord. No. 202-2019, 11/13/2019, and by Ord. No. 210-2023, 9/13/2023]

1. Applicants proposing regulated activities in the Municipality which are not exempt under § 20-106 shall submit a stormwater management site plan (SWM site plan) to the Municipality for review and approval in accordance with Parts 3 and 4; SWM site plans approved by the Municipality shall be on site throughout the duration of the regulated activity.

2. 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.

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

A. The Municipality issues approval of a SWM site plan, which demonstrates compliance with the requirements of this chapter; and

B. 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.

4. Neither submission of a 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.

5. 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 § 20-304 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.

6. To the maximum extent practicable, postconstruction 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.

7. For regulated activities with one acre or more of proposed earth disturbance, 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.

A. For regulated activities with one acre or less proposed earth disturbance the applicant shall provide written notification to the affected landowner(s) describing the proposed regulated activity and proposed discharge(s), unless otherwise required by the Municipality.

8. 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 §§ 20-305, 20-306, 20-307, and 20-308). Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.

9. 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.

10. 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 Pa. Code and the Clean Streams Law.[1]

[1] Editor's Note: See 35 P.S. § 691.1 et seq.

11. 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,[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.

12. 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).

13. 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.

14. Hotspots Runoff Controls. Specific structural or pollution prevention practices may be required, as determined to be necessary by the Municipal Engineer, to pretreat runoff from hotspots prior to infiltration. Following is a list of examples of hotspots:

A. Vehicle salvage yards and recycling facilities;

B. Vehicle fueling stations;

C. Vehicle service and maintenance facilities;

D. Vehicle and equipment cleaning facilities;

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

F. Industrial sites based on standard industrial classification codes;

G. Marinas (service and maintenance areas);

H. Outdoor liquid container storage;

I. Outdoor loading/unloading facilities;

J. Public works storage areas;

K. Facilities that generate or store hazardous materials;

L. Commercial container nursery;

M. Contaminated sites/brownfields;

N. Other land uses and activities as designated by the Municipality.

15. 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.

16. Additional Water Quality Requirements. The Municipality may require additional stormwater control measures for stormwater discharges to special management areas including, but not limited to:

A. Water bodies listed as "impaired" by PADEP.

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

C. Areas of known existing flooding problems.

D. 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.).

17. 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.

18. 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.

19. All regulated activities located within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with Honey Brook Township zoning ordinance (Chapter 27), § 27-802, and the Honey Brook Township Floodplain Ordinance (Chapter 8) 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.

20. Disturbance of existing ground cover during construction of the proposed regulated activity is prohibited within 50 feet of top-of-bank of all perennial and intermittent waterways, water bodies (lakes, ponds, etc.) and wetlands, except for activities otherwise approved by state or local agencies (e.g., stream restoration projects, road crossings, subsurface utility projects, etc.). At the Municipal Engineer's discretion, and with Conservation District and PADEP approval where necessary, the non-disturbance buffer may be reduced because of setback or other site constraints, but never be less than 10 feet.

21. All regulated activities shall comply with the riparian corridor and wetland margin provisions of the Honey Brook Township zoning ordinance, §§ 27-805 and 27-806, respectively.

22. The grading, regrading, or other alteration of a property in any manner that alters the existing drainage pattern of the area or increases the rate, volume or manner in which surface runoff leaves a property is prohibited.

§ 20-302 Permit Requirements by Other Governmental Entities.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. 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 Title 25 Pa. Code Chapter 102, or erosion and sediment control requirements of the Municipality.

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

§ 20-303 Erosion and Sediment Control.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

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

A. The Municipality receives documentation that the applicant has received:

(1) A "letter of adequacy" from the Conservation District or other approval from PADEP in compliance with Title 25 Chapter 102 of the Pennsylvania Code 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 Title 25 Chapter 105 of the Pa. Code permits;

(2) A PADEP NPDES Permit for Stormwater Discharges Associated with Construction Activities as required under Title 25 Pa. Code Chapter 92a, if applicable;

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

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

2. 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.

3. Additional erosion and sediment control measures shall be applied where infiltration BMPs are proposed, at a minimum including those required in § 20-306, Subsection 1L.

§ 20-304 Site Design Process.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. 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 regulated impervious surfaces, the applicant shall demonstrate in its SWM site plan (as required in § 20-402, Subsection 1C) 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 § 20-402, Subsection 1B(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 § 20-304, Subsection 1B, 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 § 20-304, Subsection 1B, 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 § 20-304, Subsection 1B and 1C. Appendix 20-C[1] presents additional discussion of "conservation design" and "low-impact development."

[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 §§ 20-305, 20-306, 20-307 and 20-308.

§ 20-305 Water Quality and Runoff Volume Requirements.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. To control postconstruction 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 postconstruction 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 20-C,[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 postconstruction 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 § 20-309, Subsection 5, 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 § 20-306. The infiltration volume required under § 20-306 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 § 20-301, Subsection 16.

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 § 20-304, Subsection 1C, 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.

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

§ 20-306 Infiltration Requirements.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. 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 § 20-305. Infiltration BMPs should be consistent with the design and infiltration period guidelines included in the PA BMP Manual or other PADEP design guidance. If the runoff volume required by § 20-305 cannot be infiltrated, then alternative methods consistent with the PA BMP Manual (as amended) or other PADEP 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 of a minimum of one inch of runoff from all regulated impervious surfaces shall be infiltrated.

C. If the requirements of § 20-306, Subsection 1A or 1B, 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 § 20-306 be considered by the Municipality, in accordance with § 20-109.

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 sub-grade 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, minimum of two 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.

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 Subsection 1M).

(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 § 20-304, Subsection 1C, that are applicable to infiltration;

(2) Be set back at least 25 feet from all buildings and features with sub-grade elements (e.g., basements, foundation walls, etc.), 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 25 feet of a building or feature with sub-grade elements (e.g., basements, foundation walls, etc.), the bottom elevation shall be set below the elevation of the sub-grade element.

(4) Infiltration facilities shall be setback a minimum of 10 feet from any lot line or right-of-way line.

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

(1) When a hotspot 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 "well head protection area" of a public water supply well, as defined and regulated by the Honey Brook Township zoning ordinance, § 27-803, 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 through 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 top and sides of all seepage beds, trenches, or like facilities shall be covered with drainage fabric. Fabric shall be non-woven 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.

§ 20-307 Stream Channel Protection Requirements.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. 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 postconstruction 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 postconstruction 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 § 20-309, Subsection 5, 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.

§ 20-308 Stormwater Peak Rate Control Requirements.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. The applicant shall comply with the following peak flow rate control requirements for all regulated activities including those that involve new development and redevelopment that are not located in the Conestoga River watershed.

A. Postconstruction 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 20-308.1.

Table 20-308.1
Peak Rate Control Standards
(Peak Flow Rate of the Postconstruction Design Storm Shall be Reduced to the Peak Flow Rate of the Corresponding Predevelopment Design Storm Shown in the Table)
Postconstruction Design Storm Frequency (24-Hour Duration)	Predevelopment Design Storm
	New development regulated activities	Redevelopment regulated activities
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 § 20-309, Subsection 5, 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 20-308.1, using the redevelopment ground cover assumptions presented in § 20-309, Subsection 5. 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 non-structural 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.

H. Any portion of the volume control storage that is designed according to the infiltration standards in § 20-305 and § 20-306 and is available within 24 hours from the end of the design storm based on the stabilized infiltration rate and/or the evapotranspiration rate may be also utilized for rate control storage.

I. For regulated activities located within the Conestoga River Watershed, the postdevelopment peak discharge rates shall not exceed a certain percentage of the predevelopment peak discharge rate for the two-, ten-, twenty-five-, fifty- and 100-year (twenty-four-hour duration) storm events as identified on the Conestoga River Watershed Release Rate Map in Appendix 20-G[1] of this chapter, using the ground cover assumptions presented in § 20-309, Subsection 5.

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

§ 20-309 Calculation Methodology.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. Stormwater runoff from all regulated activity sites with a drainage area of greater than five acres shall be calculated using a generally accepted calculation technique(s) that is based on the NRCS Soil Cover Complex Method. Table 20-309.1 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 five acres shall be permitted only upon approval by the Municipal Engineer.

TABLE 20-309.1 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 five acres, or as approved by the Municipality.
Other Methods	Varies	Other computation methodologies approved by the Municipality.

2. 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.

3. 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.

4. Hydrographs may be obtained from NRCS methods such as TR-55, TR20, or from use of the "modified" or "unit hydrograph" rational methods. If "modified" or "unit hydrograph" rational methods are used, the ascending leg of the hydrograph shall have a length equal to three times the time of concentration (3xTc) and the descending leg shall have a length equal to seven times the time of concentration (7xTc) to approximate an SCS Type II hydrograph.

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

A. For regulated activities involving new development, the following ground cover assumptions shall be used:

(1) For areas that are woods (as defined in Part 2 of this chapter), predevelopment calculations shall assume ground cover of "woods in good condition."

(2) For all other areas (including all impervious surfaces), predevelopment calculations shall assume ground cover of "meadow."

B. For regulated activities involving redevelopment, the following ground cover assumptions shall be used:

(1) For areas that are woods (as defined in Part 2 of this chapter), predevelopment calculations shall assume ground cover of "woods in good condition."

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

(3) For areas that are impervious surfaces, predevelopment calculations shall assume at least 20% of the existing impervious surface area to be disturbed as "meadow" ground cover.

C. The applicant shall determine which stormwater standards apply to the proposed regulated activity as follows:

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

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

(3) 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:

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

(b) Apply the redevelopment and new development stormwater standards to the corresponding redevelopment and new development portions of the proposed regulated activity.

6. Runoff curve numbers (CN) for both predevelopment and proposed (postconstruction) conditions to be used in the Soil Cover Complex Method shall be obtained from Table D-1 in Appendix 20-D[1] of this chapter.

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

7. Runoff coefficients (C) for both predevelopment and proposed (postconstruction) conditions for use in the Rational Method shall be obtained from Table D-2 in Appendix 20-D[2] of this chapter.

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

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

9. 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 D-3 in Appendix 20-D[3] of the chapter.

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

10. Runoff calculations shall include the following assumptions:

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

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

§ 20-310 Other Requirements.

[Ord. No. 170-2014, 5/14/2014; as amended by Ord. No. 210-2023, 9/13/2023]

1. 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 20-E, PADEP document 363-0300-001 "Design Criteria - Wetlands Replacement/Monitoring" (as amended)[1], (or contact the Pennsylvania State Cooperative Wetland Center or the Penn State Cooperative Extension Office for design information.)

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

2. 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 six inches 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 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.

3. Any drainage conveyance facility and/or channel not governed by 25 Pa. 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.

4. 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.

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 stormwater management 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.

§ 20-311 Other Conveyance and System Design Standards.

[Ord. No. 170-2014, 5/14/2014, as amended by Ord. 183-2016, 3/9/2016; by Ord. No. 202-2019, 11/13/2019, and by Ord. No. 210-2023, 9/13/2023]

1. Aboveground Storage Facilities. Aboveground storage facilities consist of all stormwater facilities which store, infiltrate/evaporate/transpire, clean or otherwise affect stormwater runoff and the top of which is exposed to the natural environment. Aboveground storage facilities are located above the finished ground elevation. Aboveground storage facilities do not include stormwater management facilities designed for conveyance or cisterns.

A. Design Criteria. Aboveground storage facilities shall comply with the design criteria in Table 20-311.1:

Table 20-311.1
Aboveground Storage Facility Design Criteria
			Facility Depth
			Less than 2 feet	2 feet to 8 feet	Greater than 8 feet
(a)	Embankment geometry
	[1]	Top width (minimum)	5 feet	5 feet	8 feet
	[2]	Interior side slope (maximum)	3:1	3:1	3:1
	[3]	Exterior side slope (maximum)	3:1	3:1	3:1
(b)	Embankment construction
	[1]	Key trench	Not required	Required	Required
	[2]	Pipe collar	Not required	Required	Required
	[3]	Compaction density	Not required	Required	Required
(c)	Internal construction
	[1]	Dewatering feature	Required	Required	Required
	[2]	Pretreatment elements	Not required*	Required	Required
(d)	Outlet structure
	[1]	Pipe size (minimum)	6 inches	15 inches	18 inches
	[2]	Pipe material	SLHDPE, PVC, RCP	RCP	RCP
	[3]	Pipe slope	0.5%	1.0%	1.0%
	[4]	Anticlogging devices	Required	Required	Required
	[5]	Antivortex design	Not required	Required	Required
	[6]	Watertight joints in piping?	No	Yes	Yes
(e)	Spillway requirements
	[1]	Spillway freeboard (minimum)	Not required	6 inches	6 inches
	[2]	Width (minimum)	Not required	10 feet	20 feet
	[3]	Width (maximum)	Not required	50 feet	50 feet
	[4]	Spillway channel design	Not required	Required	Required
	[5]	Routing of 100-year storm	Permitted	Permitted	Permitted

NOTES:

* Pretreatment required for infiltration BMPs unless shown to be unnecessary.

N/A = Not applicable

SLHDPE = Smooth lined high density polyethylene pipe;

PVC = Polyvinyl chloride;

RCP = Reinforced concrete pipe

B. Facility Depth.

(1) For the purposes of the design criteria, the facility depth is defined to be the depth between the bottom invert of the lowest orifice and the invert of the spillway. If there is no spillway, the top of the berm shall be used. For basins with no orifices or outlet structure, the bottom elevation of the basin shall be used.

(2) Facilities with a facility depth greater than eight feet shall not be permitted in residential areas.

(3) Facilities with a facility depth greater than 15 feet require a dam permit from DEP.

C. Embankment Construction.

(1) Impervious core/key trench. An impervious core/key trench, when required, shall consist of a cutoff trench (below existing grade) and a core trench (above existing grade). A key trench may not be required wherever it can be shown that another design feature, such as the use of an impermeable liner, accomplishes the same purpose.

(a) Materials. Materials used for the core shall conform to the Unified Soil Classification GC, SC, CH, or CL and must have at least 30% passing the No. 200 sieve.

(b) Dimensions.

1) The dimensions of the core shall provide a minimum trench depth of two feet below existing grade, minimum width of four feet and side slope of 1H:1V or flatter.

2) The core should extend up both abutments to the ten-year water surface elevation or six inches below the emergency spillway elevation, whichever is lower.

3) The core shall extend four feet below any pipe penetrations through the impervious core. The core shall be installed along or parallel to the centerline of the embankment.

(c) Compaction.

1) Compaction requirements shall be the same as those for the embankment to ensure maximum density and minimum permeability.

2) The core shall be constructed concurrently with the outer shell of the embankment.

3) The trench shall be dewatered during backfilling and compaction operations.

(d) Pipe Collars. All pipe collars, when required, shall be designed in accordance with Chapter 7 of the DEP E&S Manual. The material shall consist of concrete or otherwise non-degradable material around the outfall barrel and shall be watertight. Design calculations shall be provided.

(e) Embankment Fill Material. The embankment fill material shall be taken from an appropriate borrow area which shall be free of roots, stumps, wood, rubbish, stones greater than six inches, frozen or other objectionable materials.

(f) Embankment Compaction. When required, embankments shall be compacted by sheepsfoot or pad roller. The loose lift thickness shall be nine inches or less, depending on roller size, and the maximum particle size is six inches or less (two-thirds of the lift thickness). Five passes of the compaction equipment over the entire surface of each lift are required. Embankment compaction to visible nonmovement is also required.

D. Internal Construction.

(1) Bottom Slope. The minimum bottom slope of facilities not designed for infiltration shall be 2%. A flatter slope may be used if an equivalent dewatering mechanism is provided.

(2) Dewatering Features. When required, dewatering shall be provided through the use of underdrain, surface device, or alternate approved by the Municipal Engineer. If the facility is to be used for infiltration, the dewatering device should be capable of being disconnected and only be made operational if the basin is not dewatering within the required timeframe.

(3) Pretreatment Elements. When required, pretreatment elements shall consist of forebays, or alternate approved by the Municipal Engineer, to keep silt to a smaller portion of the facility for ease of maintenance.

(4) Infiltration Basins. Within basins designed for infiltration, existing native vegetation shall be preserved, if possible. For existing unvegetated areas or for infiltration basins that require excavation, a planting plan shall be prepared in accordance with the Honey Brook Township subdivision and land development ordinance § 22-629 and the PA BMP Manual, and contain plantings that are water-tolerant and which promote infiltration.

(5) Inlet Structures. The invert of an inlet pipe into a basin shall be six inches above the basin floor or lining so that the pipe can adequately drain after rain storms. Inlet and outlet structures shall be separated to the greatest extent possible in order to maximize the flow path through the basin.

E. Outlet Configuration.

(1) For facilities with a depth of two feet or greater, a type D-W endwall or concrete riser box outlet structure shall be provided.

(2) For facilities with a depth less than two feet, no outlet structure is required.

(3) All discharge control devices with appurtenances shall be made of reinforced concrete and stainless steel. Bolts/fasteners shall be stainless steel.

(4) The minimum distance between a proposed basin discharge point including the energy dissipater and a downstream property boundary shall be 25 feet. The setback distance may be adjusted at the discretion of the Municipal Engineer based upon factors such as flow rate, topography, soil conditions, and location of structures.

F. Spillway.

(1) Material. The spillway shall be designed to provide a non-erosive, stable condition when the project is completed. Linings for emergency spillways shall be based upon the maximum velocity in the emergency use condition.

(2) Non-Emergency Use. Use of the spillway to convey flows greater than the fifty-year design storm is permitted.

(3) Emergency Use. The spillway shall be designed to convey the 100-year peak inflow based upon a blocked outlet structure.

(4) When required, freeboard shall be measured from the top of the water surface elevation for emergency use.

G. Breach Analysis. The municipality may require a breach analysis based on site-specific conditions and concern of threat for downstream property. When required, the breach analysis shall be conducted in accordance with the NRCS methodology, the U.S. Army Corps of Engineers methodology (HEC-1) or other methodologies as approved by the municipality.

H. Aboveground stormwater facilities shall be landscaped in accordance with § 22-629, Subsection 6H, of the Honey Brook Township subdivision and land development ordinance.

2. Subsurface Storage Facilities. Subsurface storage facilities consist of all stormwater facilities which store, infiltrate/evaporate/transpire, clean or otherwise affect stormwater runoff and the top of which is not exposed to the natural environment. Subsurface facilities are located below the finished ground elevation. Subsurface facilities do not include stormwater management facilities designed for conveyance.

A. Design Criteria. Subsurface storage facilities shall comply with the design criteria in Table 20-311.2:

Table 20-311.2
Subsurface Storage Facility Design Criteria
			Facility Type
			Infiltration and Storage	Storage without Infiltration
(a)	Facility geometry
	[1]	Depth from surface (maximum)	2 feet less than limiting zone	N/A
	[2]	Loading ratio (maximum)	Per BMP Manual*	N/A
(b)	Distribution system requirements
	[1]	Pipe size (minimum)	4 inches	4 inches
	[2]	Pretreatment	Required	Required
	[3]	Loading/balancing	Required	Not required
	[4]	Observation/access ports	Required	Required
	[5]	Overflow system	Required	Required

* Unless otherwise determined by professional geologic evaluation.

B. Distribution System Requirements.

(1) Pretreatment Requirements. The facility shall be designed to provide a method to eliminate solids, sediment, and other debris from entering the subsurface facility.

(2) Loading/Balancing. The facility shall be designed to provide a means of evenly balancing the flow across the surface of the facility to be used for infiltration.

(3) Observation/Access Ports.

(a) For facilities with the bottom less than five feet below the average grade of the ground surface, a clean-out shall be an acceptable observation port.

(b) For facilities with the bottom five feet or more below the average grade of the ground surface, a manhole or other means acceptable to the municipality shall be provided for access to and monitoring of the facility.

(c) The number of access points shall be sufficient to flush or otherwise clean out the system.

C. Materials.

(1) Pipe Material. Distribution system piping may be PVC, SLHDPE, or RCP.

(2) Stone for Infiltration Beds. The stone used for infiltration beds shall be clean washed, uniformly graded coarse aggregate (AASHTO No. 3 or equivalent approved by the municipality). The void ratio for design shall be assumed to be 0.4.

(3) Backfill Material. Pipes shall be backfilled in accordance with the standards in § 20-311, Subsection 3C(1), unless otherwise approved by the Municipal Engineer.

(4) Lining Material. Non-woven geotextile shall be placed on the tops and sides of subsurface infiltration facilities.

D. Cover.

(1) When located under pavement, the top of the subsurface facility shall be a minimum of three inches below the bottom of pavement subbase.

(2) Where located under vegetative cover, the top of the subsurface facility shall be a minimum of 12 inches below the surface elevation or as required to establish vegetation.

E. In all cases, subsurface facilities shall be designed to safely convey and/or bypass flows from storms exceeding the design storm. An overflow system shall be provided to accommodate flows in excess of design criteria and divert flows to appropriate areas of discharge without damage to property. Design of the overflow system shall be approved by the Municipal Engineer.

3. Conveyance Facilities. Conveyance facilities consist of all stormwater facilities which carry flow, which may be located either above or below the finished grade. conveyance facilities do not include stormwater management facilities which store, infiltrate/evaporate/transpire, or clean stormwater runoff.

A. Design Criteria. Conveyance facilities shall comply with the design criteria in Table 20-311.3 and be sized in accordance with the criteria of § 20-310, Subsection 2:

Table 20-311.3
Conveyance Facility Design Criteria
Location			Within Public Street Right-of-Way	Outside Public Street Right-of-Way
Loading			All	Vehicular loading	Non-Vehicular Loading
(a)	Pipe design
	[1]	Material	RCP	SLHDPE, RCP	SLHDPE, RCP
	[2]	Slope (minimum)	0.5%	0.5%	0.5%
	[3]	Cover	1 foot to stone subgrade	1 foot to stone subgrade	1 foot to surface
	[4]	Diameter (minimum)	15 inches	15 inches	12 inches
	[5]	Street crossing angle	75° to 90°	N/A	N/A
	[6]	Access/maintenance port frequency (maximum)	400 feet	400 feet	400 feet
(b)	Inlet design
	[1]	Material	Concrete	Concrete	N/A
	[2]	Grate depression	2 inches	2 inches	1 inch minimum
(c)	Manhole design
	[1]	Material	Concrete	Concrete	Concrete
(d)	Swale design
	[1]	Freeboard (minimum)	1 foot	N/A	1 foot
	[2]	Velocity (maximum)	Stability check	N/A	Stability check
	[3]	Slope (minimum/maximum)	2%/9%	N/A	2%/9%
	[4]	Side slopes (residential area)	4:1 max	N/A	4:1 max
	[5]	Side slopes (non-residential area)	4:1 max	N/A	3:1 max
	[6]	Bottom width to flow depth ratio	12:1	N/A	12:1
(e)	Outlet design
	[1]	End treatment	Headwall/endwall	N/A	Headwall/endwall or flared end section
	[2]	Energy dissipater	Required	N/A	Required

NOTES:

N/A = Not applicable or no criteria specified

SLHDPE = Smooth lined high density polyethylene pipe

PVC = Polyvinyl chloride

RCP = Reinforced concrete pipe

B. Conveyance pipes, culverts, manholes, inlets and endwalls within the public street right-of-way or proposed for dedication shall conform to the requirements of PennDOT Standards for Roadway Construction, Publication No. 72M. conveyance pipes, culverts, manholes, inlets and endwalls which are otherwise subject to vehicular loading shall be designed for the HS-25 loading condition.

C. Conveyance Pipes.

(1) Backfill Requirements. For all storm sewer pipes, the trench shall be backfilled as follows unless otherwise approved by the Township Engineer.

(a) With PennDOT 2A stone a minimum six inches below and to each side of the pipe and one foot above the pipe crown.

(b) In street right-of-way areas, the remainder of the trench shall be backfilled with select backfill compacted in six-inch lifts.

(c) Outside of street right-of-way areas, the remainder of the trench shall be backfilled with clean fill compacted in eight-inch lifts.

(d) Backfill shall be free of large (not exceeding four inches in any dimension) objectionable or detritus material.

(2) Inlets or manholes shall be placed at all points of changes in the horizontal or vertical directions of conveyance pipes. Curved pipe sections are prohibited.

(3) Access/maintenance ports. An access/maintenance port is required may either be an inlet or manhole.

(4) Watertight joints shall be provided where pipe sections are joined, except for perforated pipe installed as pavement base drain.

(5) The street crossing angle shall be measured between the pipe centerline and the street centerline.

(6) Elliptical pipe of an equivalent cross-sectional area may be substituted in lieu of circular pipe where cover or utility conflict conditions exist.

(7) The roughness coefficient (Manning "n" values) used for conveyance pipe capacity calculations should be determined in accordance with PennDOT Publication 584, PennDOT Drainage Manual, or per the manufacturer's specifications.

(8) 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.

D. Inlets.

(1) All pipes must enter inlets completely through one of the sides. No corner entry of pipes is permitted. Inlet box sizes shall be determined based upon the size of entering/exiting pipes and noted in the storm sewer profiles.

(2) When there is a change in pipe size through an inlet, the top inside elevation of the outlet shall be at or below the top inside elevations of all incoming pipes (i.e., match crowns).

(3) Storm sewer design shall be based upon PennDOT design methods. Inlet efficiency and bypass flow for the 100-year storm shall be determined for all inlets and the gutter flow spread shall not exceed 1/2 the travel lane width, or to a maximum of eight feet where parking is permitted. Honey Brook Township may require that a hydraulic grade line analysis be performed on storm sewer systems.

(4) Flow Depth within Intersections. Within intersections of streets, the maximum depth of flow shall be 1 1/2 inches based on the 100-year storm.

(5) Curbed Streets.

(a) Inlets in streets shall be located along the curbline.

(b) At street intersections, every attempt should be made to place inlets in the tangent and not in the curved portion of the curbing.

(c) All storm sewers within the streets shall not be placed under the curbs or sidewalks.

(d) Top units shall be PennDOT Type "C." The hood shall be aligned with the adjacent curb height.

(6) All inlets placed in paved areas shall have heavy duty bicycle-safe grating consistent with PennDOT Publication 72M, latest edition. A note to this effect shall be added to the SWM site plan or inlet details therein.

(7) Inlets, junction boxes, or manholes greater than five feet in depth shall be equipped with ladder rungs and shall be detailed on the SWM site plan.

(8) Within street rights-of-way and all paved areas, concrete risers or lintels shall be utilized to bring inlet grate elevations up to finished grade.

E. Swales.

(1) A swale shall be considered as any man-made ditch designed to convey stormwater directly to another stormwater management facility or surface waters.

(2) Swales shall be designed to provide a minimum one foot of freeboard for the twenty-five-year design storm flow (twenty-four-hour duration).

(3) Inlets within swales shall have PennDOT Type "M" top units or equivalent approved by the municipal engineer.

(4) Swale capacities and velocities shall be computed using the Manning equation using the following design parameters:

(a) Vegetated Swales.

1) The first condition shall consider swale stability based upon a low degree of retardance ("n" = 0.03);

2) The second condition shall consider swale capacity based upon a higher degree of retardance ("n" = 0.05); and

3) All vegetated swales shall have a minimum slope of 2% unless otherwise approved by the Municipal Engineer.

(b) The "n" factors to be used for paved or riprap swales or gutters shall be based upon accepted engineering design practices, as approved by the Municipal Engineer.

(5) All swales shall be designed to maximize infiltration and concentrate low flows to minimize siltation and meandering, unless geotechnical conditions do not permit infiltration.

(6) Adequate erosion protection and energy dissipation shall be provided along all swales 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 DEP E&S Manual, or other design guidance acceptable to the Municipal Engineer.

(7) Swales shall be stabilized with seed mixes and/or other plantings suitable for the underlying soil conditions and swale function (infiltration/conveyance only).

F. Culverts. In addition to the material requirements in this section, culverts designed to convey waters of the commonwealth may be constructed with either a corrugated metal arch or a precast concrete culvert.

G. Level Spreaders.

(1) Shall discharge at existing grade onto undisturbed vegetation.

(2) Discharge at a depth not exceeding 3.0 inches for a fifty-year, twenty-four-hour design storm.

(3) All level spreaders shall be dressed with a minimum aggregate size of AASHTO no. 1.

H. Energy Dissipaters. Energy dissipaters shall be designed in accordance with the requirements in the DEP E&S Manual and installed at all points where pipes or swales discharge to or from basins and at the discharge point of all conveyance pipes.

I. End Treatments.

(1) Where the connecting pipe has a diameter of 15 inches or greater, headwalls and endwalls shall be provided with a protective barrier device to prevent entry of the storm sewer pipe by unauthorized persons. Such protection devices shall be designed to be removable for cleaning.

(2) Headwalls and endwalls shall be constructed of concrete.

(3) Flared end sections shall be of the same material as the connecting pipe and be designed for the size of the connecting pipe.

J. SWM facilities which qualify as a dam per DEP regulations or facilities deemed a potential threat to the life, safety or welfare of the general public shall be subject to the following requirements:

(1) 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 25 Pa. Code Chapter 105, concerning dam safety. Chapter 105 of 25 Pa. Code may require the safe conveyance of storms larger than 100-year event.

(2) Additional requirements and analysis may be required by the municipality to prove that the proposed facility has been designed to limit the potential risk to the life, safety or welfare of the general public.