Township of Lower Mount Bethel, PA Part 3 STORMWATER MANAGEMENT REQUIREMENTS

§ 23-301 General Requirements.

[Ord. 2014-03, 9/8/2014]

1. All applicants proposing regulated activities within the Township which do not fall under the exemption criteria contained within § 23-106 of this chapter shall submit a stormwater management plan consistent with this chapter to the Township for review. These criteria shall apply to the total proposed development even if development is to take place in stages. Impervious surface shall include, but not be limited to, any roof, parking or driveway areas and any new streets and sidewalks. All gravel and crushed stone areas shall be assumed to be impervious unless designed as a BMP (e.g., pervious paver blocks, reinforced turf, gravel filled grids, etc.). (Refer to definition of "impervious surface" within Part 2 of this chapter.)

2. All regulated activities in the municipality shall be subject to the stormwater management requirements of this chapter and shall include such measures as necessary to:

A. Protect health, safety, and property;

B. Meet the water quality goals of this chapter by implementing measures to:

(1) Minimize disturbance to floodplains, wetlands, and wooded areas.

(2) Create, maintain, repair or extend riparian buffers.

(3) Avoid erosive flow conditions in natural flow pathways.

(4) Minimize thermal impacts to waters of this commonwealth.

(5) Disconnect impervious surfaces (i.e., disconnected impervious areas, DIAs) by directing runoff to pervious areas, wherever possible.

C. To the maximum extent practicable, incorporate the techniques for low-impact development practices (e.g., protecting existing trees, reducing area of impervious surface, and protecting open space) described in the Pennsylvania Stormwater Best Management Practices Manual, Pennsylvania Department of Environmental Protection (PADEP) No. 363-0300-002 (2006).

3. Storm drainage systems shall be provided to permit unobstructed flow in natural watercourses except as modified by stormwater detention facilities, recharge facilities, water quality facilities, pipe systems or open channels consistent with this chapter.

4. The existing locations of concentrated drainage discharge onto adjacent property shall not be altered without written approval of the affected property owner(s).

5. Areas of existing diffused drainage discharge onto adjacent property shall be managed such that, at minimum, the peak diffused flow does not increase in the general direction of discharge, except as otherwise provided in this chapter. If diffused flow is proposed to be concentrated and discharged onto adjacent property, the developer must document that there are adequate downstream conveyance facilities to safely transport the concentrated discharge to the point of predevelopment flow concentration, to the stream reach or otherwise prove that no harm will result from the concentrated discharge. Areas of existing diffused drainage discharge shall be subject to any applicable release rate criteria in the general direction of existing discharge whether they are proposed to be concentrated or maintained as diffused drainage areas.

6. Easements.

A. Where a site is traversed by watercourses other than those for which a one-hundred-year floodplain is defined by the municipality, there shall be provided drainage easements conforming substantially with the line of such watercourses. The width of any easement shall be adequate to provide for unobstructed flow of storm runoff based on calculations made in conformance with § 23-308 for the one-hundred-year return period runoff and to provide a freeboard allowance of 0.5 foot above the design water surface level. However, in no case shall the easement be less than 30 feet in width. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations which may adversely affect the flow of stormwater within any portion of the easement. Also, periodic maintenance of the easement to ensure proper runoff conveyance shall be required. Watercourses for which the one-hundred-year floodplain is formally defined are subject to the applicable municipal floodplain regulations. Terms of the easement shall prohibit excavation, the placing of fill or structures, landscaping other than that shown on the stormwater management plan, and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Periodic maintenance of the easement shall be required by the landowner to ensure proper runoff conveyance. The developer will retain the easement until such time as one of the following is accomplished:

(1) For subdivisions or land developments, the individual lot owner assumes responsibility for the maintenance of the portion of their property through which the easement passes. The record plan shall contain a description of such easement(s) and notation indicating the maintenance responsibilities.

(2) A homeowner's association or other legal entity approved by the Township, assumes responsibility for the maintenance of the development, including the watercourse easement. The record plan shall contain a description of such easement(s) and notation indicating the maintenance responsibilities.

B. The developer shall provide a deed or deeds of dedication to the Township to permit access to privately owned and maintained improvements to permit the Township to undertake maintenance of such improvements (without any obligation on behalf of the Township to do so) should the developer or responsible party fail to adequately maintain such improvements. All easements offered for dedication shall be accompanied by a metes and bounds description and plot plan prepared by the developer. The Board of Supervisors shall not accept any deed of dedication until an opinion of record title, in form acceptable to the Township Solicitor, prepared by the developer's counsel (who must not be affiliated with the developer, must be licensed to practice law in Pennsylvania and must maintain an office in Pennsylvania), indicating that the easements are free and clear of all liens and of all encumbrances that could adversely affect the Township's ownership or use of such rights-of-way is received from the developer.

7. When it can be shown that, due to topographic conditions, natural drainage swales on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainage swales. Capacities of open channels shall be calculated using the Manning Equation. Work within natural drainageways shall be subject to approval by PADEP through the joint permit application process, or, where deemed appropriate by PADEP, through the general permit process.

8. Any stormwater management facilities regulated by this chapter that will be located in or adjacent to waters of the commonwealth, waters of the United States, or wetlands shall be subject to approval by PADEP and/or U.S. Army Corps of Engineers through the joint permit application process, or, where deemed appropriate by PADEP and/or U.S. Army Corps of Engineers, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the developer or his agent to show that the land in question cannot be classified as wetlands; otherwise, approval to work in the area must be obtained from PADEP and/or U.S. Army Corps of Engineers.

9. Any stormwater management facilities regulated by this chapter that would be located on state highway rights-of-way, or discharge stormwater to facilities located within a state highway right-of-way, shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).

10. Site disturbance and impervious surface shall be minimized. Infiltrating stormwater runoff through seepage beds, infiltration trenches, etc. shall be required, where soil conditions permit, to reduce the size or eliminate the need for retention/detention facilities.

11. Roof drains and sump pumps shall discharge to an infiltration bed, natural watercourse, storm sewer system, or drainage swale. Roof drains and sump pumps shall be connected to a storm sewer, drainage structure, or other approved stormwater conveyance facility that is designed as part of a stormwater management BMP. In no case shall roof drains or sump pumps be connected to a sanitary sewer or permitted to discharge across a sidewalk, walkway, path, or to a street through the curb.

12. Special Requirements for Watersheds Draining to High-Quality (HQ) and Exceptional-Value (EV) Waters. The temperature and quality of water and streams that have been determined to be exceptional value and high quality are to be maintained as defined in Chapter 93, Water Quality Standards, Title 25, Pennsylvania Department of Environmental Protection Rules and Regulations, as may be amended from time to time, and/or any successor provision thereto. Maintaining the multiple values of these special protection waters occurs through maintaining the predevelopment or natural water cycle; not decreasing infiltration and recharge; and not increasing runoff. In so doing, critical temperature considerations are to be provided (optimal temperature control is achieved through infiltration of precipitation to groundwater which maximizes temperature-moderated stream base flow). In those cases where runoff volume control cannot be achieved as per § 23-304, temperature-sensitive BMPs and stormwater conveyance systems are to be used and designed with storage pool areas (drawing outflow from the bottom of the pool) and supply outflow channels shall be shaded with trees. This may require modification of berms for permanent ponds and the relaxation of restrictions on planting vegetation within the facilities, provided that capacity for volumes and rate control is maintained. At a minimum, the southern half of pond shorelines shall be planted with shade or canopy trees within 10 feet of the pond shoreline. In conjunction with this requirement, the maximum slope allowed on the berm area to be planted is 10 to 1. This will lessen the destabilization of berm soils due to root growth. A long-term maintenance schedule and management plan for the thermal control BMPs is to be established and recorded for all development sites.

13. All stormwater runoff shall be pretreated for water quality prior to discharge to surface or groundwater as required by § 23-304 of this chapter.

14. Completed stormwater management facilities, including detention/retention basins, shall be surveyed by a professional land surveyor or engineer licensed in the Commonwealth of Pennsylvania, to verify compliance with the character of stormwater management facilities as depicted on the approved final plan (or subsequently approved revision thereof). As-constructed plans shall be submitted to Lower Mount Bethel Township for review and approval, upon completion of construction of all facilities. Where stormwater management facilities are constructed as part of a subdivision or land development application, the as-built plan must be submitted to, and approved by, Lower Mount Bethel Township prior to the acceptance of any offer of dedication of any public facilities and/or release of financial security for the required maintenance period. Facilities intended for public dedication will not be accepted by Lower Mount Bethel Township until such time the as-built plans have been reviewed and approved by the Township Engineer.

15. The record plan and development agreement for an approved subdivision or land development shall define the ownership and maintenance responsibilities. Specifically, the record plan shall contain a provision permitting access to such easement(s), at any time, for inspection and/or emergency repair/maintenance, by Lower Mount Bethel Township or its designee, of all facilities deemed critical to public welfare. In the event the lot owner or homeowner's association fails to honor their maintenance responsibilities set forth herein, in any manner, Lower Mount Bethel Township shall have the right of entry upon and within the area of the easement to undertake any required corrective or maintenance effort in accordance with § 23-707, Subsection 2C, of this chapter.

16. Post-construction BMPs shall be designed, installed, operated and maintained to meet the requirements of the Clean Streams Law[1] and implementing regulations, including the established practices in 25 Pa. Code Chapter 102 and the specifications of this chapter as to prevent accelerated erosion in watercourse channels and at all points of discharge.

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

17. No approval of any subdivision or land development plan, or issuance of any building, zoning, erosion and sedimentation control and grading permit, occupancy permit, or the commencement of any earth disturbance activities associated with any regulated activities shall commence until approval by the municipality of a plan which demonstrates compliance with the requirements of this chapter.

18. For all regulated earth disturbance activities, erosion and sediment (E&S) control best management practices (BMPs) shall be designed, implemented, operated, and maintained during the regulated earth disturbance activities (e.g., during construction) to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law. Various BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual, No. 363-2134-008, as amended and updated.

19. Erosion and sediment control during land development shall be addressed as required by § 23-303.

20. All best management practices (BMPs) shall conform to the design criteria of this chapter and Pennsylvania Stormwater Management Practices Manual, December 30, 2006.

21. Techniques described in Appendix G (Low-Impact Development) of this chapter[2] are encouraged because they reduce the costs of complying with the requirements of this chapter and the state water quality requirements.

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

22. The Township may, after consultation with the Department of Environmental Protection (PADEP), approve measures for meeting the state water quality requirements other than those in this chapter, provided that they meet the minimum requirements of, and do not conflict with, state law including, but not limited to, the Clean Streams Law.[3]

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

23. Infiltration for stormwater management is encouraged where soils and geology permit, consistent with the provisions of this chapter and, where appropriate, the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D.[4]

[4] Editor's Note: Appendix D is included as an attachment to this chapter.

§ 23-302 Permit Requirements by Other Government Entities.

[Ord. 2014-03, 9/8/2014]

The following permit requirements apply to certain regulated and earth disturbance activities and must be met prior to commencement of regulated and earth disturbance activities, as applicable:

1. All regulated and earth disturbance activities subject to permit requirements by DEP under regulations at 25 Pa. Code Chapter 102.

2. Work within natural drainageways subject to permit by DEP under 25 Pa. Code Chapter 102 and Chapter 105.

3. Any stormwater management facility that would be located in or adjacent to surface waters of the commonwealth, including wetlands, subject to permit by DEP under 25 Pa. Code Chapter 105.

4. Projects that involve use of PennDOT right-of-way, or that involve new discharges onto or toward PennDOT right-of-way, are subject to the requirements, including the permitting requirements, of Title 67, Chapter 441 of the Pennsylvania Code, or any successor provision thereto as may be amended from time to time.

5. 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 DEP under 25 Pa. Code Chapter 105.

§ 23-303 Erosion and Sediment Control During Regulated Earth Disturbance Activities.

[Ord. 2014-03, 9/8/2014]

1. No regulated earth disturbance activities within the municipality shall commence until approval by the municipality of an erosion and sediment control plan for construction activities. Written approval by DEP or a delegated County Conservation District shall satisfy this requirement.

2. An erosion and sediment control plan is required by DEP regulations for any earth disturbance activity of 5,000 square feet or more under Pa. Code § 102.4(b).

3. A DEP NPDES Stormwater Discharges Associated with Construction Activities Permit is required for regulated earth disturbance activities under Pa. Code Chapter 92.

4. Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or County Conservation District must be provided to the municipality before the commencement of an earth disturbance activity.

5. A copy of the erosion and sediment control plan and any permit, as required by DEP regulations, shall be available at the project site at all times.

§ 23-304 Post-Construction Water Quality Criteria.

[Ord. 2014-03, 9/8/2014]

1. No regulated earth disturbance activities within the municipality shall commence until approval by the municipality of a drainage plan which demonstrates compliance with this chapter. This chapter provides standards to meet NPDES permit requirements associated with construction activities and MS4 permit requirements.

2. The water quality volume (WQv) shall be captured and treated with evapotranspiration and/or direct recharge BMPs. The WQv shall be calculated as the difference in runoff volume from predevelopment to post-development for the twenty-four-hour, two-year-return-period storm. This may be calculated using either the Soil-Cover-Complex Method or Rational Method using the two-year rainfall depth as noted in § 23-308, Subsection 3. The effect of closed depressions on the site shall be considered in this calculation.

3. The WQv shall be calculated for each post-development drainage direction on a site for sizing BMPs. Site areas having no impervious cover and no proposed disturbance during development may be excluded from the WQv calculations and do not require treatment.

4. For sites within watersheds with high-quality (HQ) or exceptional-value (EV) waters as designated by DEP, if an applicant is proposing to use a BMP that ponds water on the land surface and may receive direct sunlight, the discharge from that BMP must be treated by infiltration, a vegetated buffer, filter strip, bioretention, vegetated swale or other BMP that provides a thermal benefit to protect the designated waters from thermal impacts.

5. The WQv for a site as a result of the regulated activities must either be treated with infiltration or two acceptable BMPs such as those listed in Subsection 15.

6. Infiltration BMPs shall not be constructed on fill unless the applicant demonstrates that the fill is stable and otherwise meets the infiltration BMP standards of this chapter.

7. The applicant shall document the bedrock type(s) present on the site from published sources. Any apparent boundaries between carbonate and noncarbonate bedrock shall be verified through more detailed site evaluations by a qualified geotechnical professional.

8. For each proposed regulated activity in the watershed where an applicant intends to use infiltration BMPs, the applicant shall conduct a preliminary site investigation, including gathering data from published sources, a field inspection of the site, a minimum of one test pit and a minimum of two percolation tests, as outlined in Appendix H.[1] This investigation will determine depth to bedrock, depth to the seasonal high water table, soil permeability and location of special geologic features, if applicable. This investigation may be done by a certified Sewage Enforcement Officer (SEO), except that the location(s) of special geologic features shall be verified by a qualified geotechnical professional.

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

9. Sites where applicants intend to use infiltration BMPs must meet the following criteria:

A. Depth to bedrock below the invert of the BMP greater than or equal to two feet.

B. Depth to seasonal high water table shall be below the invert of the BMP by a margin, greater than or equal to three feet; except for infiltration of residential roof runoff, where the invert of the BMP must be greater than or equal to two feet from the season high water table.

C. Soil permeability (as measured by the adapted 25 Pa. Code § 73.15; percolation test in Appendix H) greater than or equal to 0.5 inches per /hour and less than or equal to 12 inches per hour.

D. Setback distances or buffers as follows:

(1) One hundred feet from water supply wells, or 50 feet in residential development.

(2) Fifteen feet downgradient or 100 feet upgradient from building foundations; except for residential development, where the required setback is 15 feet downgradient or 40 feet upgradient from building foundations.

(3) Fifty feet from septic system drainfields; except for residential development, where the required setback is 25 feet from septic system drainfields.

(4) Fifty feet from a geologic contact with carbonate bedrock unless a preliminary site investigation is done in the carbonate bedrock to show the absence of special geologic features within 50 feet of the proposed infiltration area.

(5) One hundred feet from the property line unless documentation is provided to show that all setbacks from existing or potential future wells, foundations and drain fields on neighboring properties will be met; except for one- and two-family residential dwellings where the required setback is 40 feet, unless documentation is provided to show that all setbacks from existing or potential future wells, foundations and drain fields on neighboring properties will be met.

10. For entirely noncarbonate sites, if infiltration of the entire WQv is not proposed, the remainder of the WQv shall be treated by acceptable BMPs for each discharge location. Acceptable BMPs are listed in Subsection 15.

A. The preliminary site investigation described in Subsection 8 is required and shall continue on different areas of the site until a potentially suitable infiltration location is found or the entire site is determined to be infeasible for infiltration. For infiltration areas that appear to be feasible based on the preliminary site investigation, the additional site investigation and testing as outlined in Appendix H shall be completed.[2]

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

B. If an applicant proposes infiltration, the municipality may determine infiltration to be infeasible if there are known existing conditions or problems that may be worsened by the use of infiltration.

C. The site must meet the conditions listed in Subsection 9.

11. In entirely carbonate areas, where the applicant intends to use infiltration BMPs, the preliminary site investigation described in Subsection 8 shall be conducted. For infiltration areas that appear feasible based on the preliminary site investigation, the applicant shall conduct the additional site investigation and testing as outlined in Appendix H.[3] The soil depth, percolation rate and proposed loading rate, each weighted as described in § 23-308, along with the buffer from special geologic features, shall be compared to the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D[4] to determine if the site is recommended for infiltration. In addition to the recommendation from Appendix D, the conditions listed in Subsection 9 are required for infiltration in carbonate areas.

Applicants are encouraged to infiltrate the WQv, as calculated in Subsection 10, but are not required to use infiltration BMPs on a carbonate site even if the site falls in the "Recommended" range on the chart in Appendix D. Any amount of volume infiltrated can be subtracted from the overall WQv to be treated by non-infiltration BMPs. If infiltration is not proposed, the full WQv shall be treated by two acceptable BMPs, as specified in Subsection 15.

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

[4] Editor's Note: Appendix D is included as an attachment to this chapter.

12. If a site has both carbonate and noncarbonate areas, the applicant shall investigate the ability of the noncarbonate portion of the site to fully meet this chapter to meet the requirements for WQv for the whole site through infiltration. If that proves infeasible, infiltration in the carbonate area as described in Subsection 11 or two other noninfiltration BMPs as described in Subsection 15 must be used. No infiltration structure in the noncarbonate area shall be located within 50 feet of a boundary with carbonate bedrock, except when a preliminary site investigation has been done showing the absence of special geologic features within 50 feet of the proposed infiltration area.

13. If infiltration BMPs are proposed in carbonate areas, the post-development two-year runoff volume leaving the site shall be 80% or more of the predevelopment runoff volume for the carbonate portion of the site to prevent infiltration of volumes far in excess of the predevelopment infiltration volume.

14. Site areas proposed for infiltration shall be protected from disturbance and compaction except as necessary for construction of infiltration BMPs.

15. If infiltration of the entire WQv is not proposed, the remainder of the WQv shall be treated by two acceptable BMPs in series for each discharge location. Sheet flow draining across a pervious area can be considered as one BMP. Sheet flow across impervious areas and concentrated flow shall flow through two BMPs. If sheet flow from an impervious area is to be drained across a pervious area as one BMP, the length of the pervious area must be equal to or greater than the length of impervious area. In no case may the same BMP be employed consecutively to meet the requirement of this section. Acceptable BMPs are listed below along with the recommended reference for design.

	Best Management Practice	Design Reference NumberC
	BioretentionA	4, 5, 11, 16
	Capture/reuseB	4, 14
	Constructed wetlands	4, 5, 8, 10, 16
	Dry extended detention ponds	4, 5, 8, 12, 18
	Minimum disturbance/minimum maintenance practices	1, 9
	Significant reduction of existing impervious cover	N/A
	Stormwater filtersA (sand, peat, compost, etc.)	4, 5, 10, 16
	Vegetated buffers/filter strips	2, 3, 5, 11, 16, 17
	Vegetated roofs	4, 13
	Vegetated swalesA	2, 3, 5, 11, 16, 17
	Water quality inletsD	4, 7, 15, 16, 19
	Wet detention ponds	4, 5, 6, 8

	NOTES:
	A	This BMP could be designed with or without an infiltration component. If infiltration is proposed, the site and BMP will be subject to the testing and other infiltration requirements in this chapter.
	B	If this BMP is used to treat the entire WQv, then it is the only BMP required because of this BMP's superior water quality performance.
	C	See table below.
	D	Water quality inlets include such BMPs as oil/water separators, sediment traps/catch basin sumps, and trash/debris collectors in catch basins.

	Number	Design Reference Title
	1	"Conservation Design For Stormwater Management — A Design Approach to Reduce Stormwater Impacts From Land Development and Achieve Multiple Objectives Related to Land Use," Delaware Department of Natural Resources and Environmental Control, The Environmental Management Center of the Brandywine Conservancy, September 1997.
	2	"A Current Assessment of Urban Best Management Practices: Techniques for Reducing Nonpoint Source Pollution in the Coastal Zone," Schueler, T. R., Kumble, P. and Heraty, M., Metropolitan Washington Council of Governments, 1992.
	3	"Design of Roadside Channels with Flexible Linings," Federal Highway Administration, Chen, Y. H. and Cotton, G. K., Hydraulic Engineering Circular 15, FHWA-IP-87-7, McLean Virginia, 1988.
	4	"Draft Stormwater Best Management Practices Manual," Pennsylvania Department of Environmental Protection, January 2005.
	5	"Evaluation and Management of Highway Runoff Water Quality," Federal Highway Administration, FHWA-PD-96-032, Washington, D.C., 1996.
	6	"Evaporation Maps of the United States," U.S. Weather Bureau (now NOAA/National Weather Service) Technical Paper 37, Published by Department of Commerce, Washington D.C., 1959.
	7	"Georgia Stormwater Manual," AMEC Earth and Environmental, Center for Watershed Protection, Debo and Associates, Jordan Jones and Goulding, Atlanta Regional Commission, Atlanta, Georgia, 2001.
	8	"Hydraulic Design of Highway Culverts," Federal Highway Administration, FHWA HDS 5, Washington, D.C., 1985 (revised May 2005).
	9	"Low-Impact Development Design Strategies An Integrated Design Approach, Prince Georges County, Maryland Department of Environmental Resources, June 1999.
	10	"Maryland Stormwater Design Manual," Maryland Department of the Environment, Baltimore, Maryland, 2000.
	11	"Pennsylvania Handbook of Best Management Practices for Developing Areas," Pennsylvania Department of Environmental Protection, 1998.
	12	"Recommended Procedures for Act 167 Drainage Plan Design," LVPC, Revised 1997.
	13	"Roof Gardens History, Design, and Construction," Osmundson, Theodore. New York: W.W. Norton & Company, 1999.
	14	"The Texas Manual on Rainwater Harvesting," Texas Water Development Board, Austin, Texas, Third Edition, 2005.
	15	"VDOT Manual of Practice for Stormwater Management," Virginia Transportation Research Council, Charlottesville, Virginia, 2004.
	16	"Virginia Stormwater Management Handbook," Virginia Department of Conservation and Recreation, Richmond, Virginia, 1999.
	17	"Water Resources Engineering," Mays, L. W., John Wiley & Sons, Inc., 2005.
	18	"Urban Hydrology for Small Watersheds," Technical Report 55, U.S. Department of Agriculture, Natural Resources Conservation Service, 1986.
	19	U.S. EPA, Region 1 New England website (as of August 2005) http://www.epa.gov/NE/assistance/ ceitts/stormwater/techs/html.

16. Pretreatment.

A. Stormwater runoff from hot spot land uses shall be pretreated. In no case may the same BMP be employed consecutively to meet this requirement and the requirement in Subsection 15. Acceptable methods of pretreatment are listed below.

	Hot Spot Land Use	Pretreatment Method(s)
	Vehicle maintenance and repair facilities, including auto parts stores	Water quality inlets Use of drip pans and/or dry sweep material under vehicles/equipment Use of absorbent devices to reduce liquid releases Spill prevention and response program
	Vehicle fueling stations	Water quality inlets Spill prevention and response program
	Storage areas for public works	Water quality inlets Use of drip pans and/or dry sweep material under vehicles/equipment Use of absorbent devices to reduce liquid releases Spill prevention and response program Diversion of stormwater away from potential contamination areas
	Outdoor storage of liquids	Spill prevention and response program
	Commercial nursery operations	Vegetated swales/filter strips Constructed wetlands Stormwater collection and reuse
	Salvage yards and recycling facilities*	BMPs that are a part of a stormwater pollution prevention plan under an NPDES permit
	Fleet storage yards and vehicle cleaning facilities*	BMPs that are a part of a stormwater pollution prevention plan under an NPDES permit
	Facilities that store or generate regulated substances*	BMPs that are a part of a stormwater pollution prevention plan under an NPDES permit
	Marinas*	BMPs that are a part of a stormwater pollution prevention plan under an NPDES permit
	Certain industrial uses (listed under NPDES)*	BMPs that are a part of a stormwater pollution prevention plan under an NPDES permit

	NOTES:
	*	Regulated under the NPDES Stormwater Program

B. Design references for the pre-treatment methods, as necessary, are listed below. If the applicant can demonstrate to the satisfaction of the municipality that the proposed land use is not a hot spot, then the pretreatment requirement would not apply.

	Pretreatment Method	Design ReferenceA
	Constructed wetlands	4, 5, 8, 10, 16
	Diversion of stormwater away from potential contamination areas	4, 11
	Stormwater collection and reuse (especially for irrigation)	4, 14
	Stormwater filters (sand, peat, compost, etc.)	4, 5, 10, 16
	Vegetated swales	2, 3, 5, 11, 16, 17
	Water quality inlets	4, 7, 15, 16, 19

	NOTES:
	A	These numbers refer to the Design Reference Title Chart in Subsection 15 above.

17. Use of infiltration BMPs are prohibited on hot spot land use areas unless the applicant can demonstrate that existing and proposed site conditions, including any proposed runoff pretreatment, create conditions suitable for runoff infiltration under this chapter. Examples of hot spots are listed in Appendix K.[5] Stormwater runoff from hot spot land uses shall be pretreated. In no case may the same BMP be employed consecutively to meet this requirement. Guidance regarding acceptable methods of pretreatment is located in Appendix K.

[5] Editor's Note: Appendix K is included as an attachment to this chapter.

18. Stormwater infiltration BMPs shall not be placed in or on a special geologic feature(s). Additionally, stormwater runoff shall not be discharged into existing on-site sinkholes.

19. Applicants shall request, in writing, public water suppliers to provide the Zone I wellhead protection radius, as calculated by the method outlined in the Pennsylvania Department of Environmental Protection Wellhead Protection regulations, for any public water supply well within 400 feet of the site. In addition to the setback distances specified in Subsection 9, infiltration is prohibited in the Zone I radius as defined and substantiated by the public water supplier in writing. If the applicant does not receive a response from the public water supplier, the Zone I radius is assumed to be 100 feet.

20. The volume and rate of the net increase in stormwater runoff from the regulated activities must be managed to prevent the physical degradation of receiving waters from such effects as scour and stream bank destabilization, to satisfy state water quality requirements, by controlling the two-year post-development runoff to a 30% release rate.

21. The municipality may, after consultation with DEP, approve alternative methods for meeting the state water quality requirements other than those in this section, provided that they meet the minimum requirements of and do not conflict with state law, including but not limited to the Clean Streams Law.[6]

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

22. West Nile Guidance Requirements. All wet basin designs shall incorporate biologic controls consistent with the West Nile Guidance found in Appendix L.[7]

[7] Editor's Note: Appendix L is included as an attachment to this chapter.

§ 23-305 Stormwater Management Districts.

[Ord. 2014-03, 9/8/2014]

1. Mapping of Stormwater Management Districts. To implement the provisions of the Lower Mount Bethel Act 167 Stormwater Management Plan, the municipality is hereby divided into stormwater management districts consistent with the Martins/Jacoby Creeks Watershed and Delaware River Sub-Basin 1 Watershed Release Rate Map presented in the plan update. The boundaries of the stormwater management districts are shown on an Official Map which is available for inspection at the municipal office. A copy of the Official Map at a reduced scale is included in Appendix A for general reference.[1]

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

2. Description of Stormwater Management Districts. Two types of stormwater management districts may be applicable to the municipality, namely, "Conditional/Provisional No-Detention Districts" and "Dual Release Rate Districts," as described below.

A. Conditional/Provisional No-Detention Districts. Within these districts, the capacity of the stormwater management facilities (as defined in Part 2) must be calculated to determine if adequate capacity exists. For this determination, the developer must calculate peak flows assuming that the site is developed as proposed and that the remainder of the local watershed is in the existing condition. The developer must also calculate peak flows assuming that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified by this chapter. The larger of the two peak flows calculated will be used in determining if adequate capacity exists. If adequate capacity exists to safely transport runoff from the site to the main channel (as defined in Part 2), these watershed areas may discharge post-development peak runoff without detention facilities. If the capacity calculations show that the "local" runoff conveyance facilities lack adequate capacity, the developer shall either use a 100% release rate control or provide increased capacity of downstream elements to convey increased peak flows consistent with § 23-306, Subsection 16. Any capacity improvements must be designed to convey runoff from development of all areas tributary to the improvement consistent with the capacity criteria specified in § 23-306, Subsection 4. By definition, a storm drainage problem area associated with the "local" runoff conveyance facilities indicates that adequate capacity does not exist. Sites in these districts are still required to meet all of the water quality requirements in § 23-304.

B. Dual Release Rate Districts. Within these districts, the two-year post-development peak discharge must be controlled to 30% of the predevelopment two-year runoff peak. Further, the ten-, twenty-five- and one-hundred-year post-development peak runoff must be controlled to the stated percentage of the predevelopment peak. Release rates associated with the ten- through one-hundred-year events vary from 50% to 100% depending upon location in the watershed.

§ 23-306 Stormwater Management District Implementation Provisions.

[Ord. 2014-03, 9/8/2014]

1. Applicants shall provide a comparative pre- and post-construction stormwater management hydrograph analysis for each direction of discharge and for the site overall to demonstrate compliance with the provisions of this chapter.

2. Any stormwater management controls required by this chapter and subject to a dual release rate criteria shall meet the applicable release rate criteria for each of the two-, ten-, twenty-five- and one-hundred-year return period runoff events consistent with the calculation methodology specified in § 23-308.

3. The exact location of the Stormwater Management District boundaries as they apply to a given development site shall be determined by mapping the boundaries using the two-foot topographic contours provided as part of the drainage plan. The district boundaries as originally drawn coincide with topographic divides or, in certain instances, are drawn from the intersection of the watercourse and a physical feature such as the confluence with another watercourse or a potential flow obstruction (e.g., road, culvert, bridge, etc.). The physical feature is the downstream limit of the subarea and the subarea boundary is drawn from that point up slope to each topographic divide along the path perpendicular to the contour lines.

4. Any downstream capacity analysis conducted in accordance with this chapter shall use the following criteria for determining adequacy for accepting increased peak flow rates:

A. Natural or man-made channels or swales must be able to convey the increased runoff associated with a two-year return period event within their banks at velocities consistent with protection of the channels from erosion.

B. Natural or man-made channels or swales must be able to convey the increased twenty-five-year return period runoff without creating any hazard to persons or property.

C. Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area must be designed in accordance with DEP Chapter 105 regulations (if applicable) and, at minimum, pass the increased twenty-five-year return period runoff.

5. For a proposed development site located within one release rate category subarea, the total runoff from the site shall meet the applicable release rate criteria. For development sites with multiple directions of runoff discharge, individual drainage directions may be designed for up to a one-hundred-percent release rate so long as the total runoff from the site is controlled to the applicable release rate.

6. For a proposed development site located within two or more release category subareas, the peak discharge rate from any subarea shall be the predevelopment peak discharge for that subarea multiplied by the applicable release rate. The calculated peak discharges shall apply regardless of whether the grading plan changes the drainage area by subarea. An exception to the above may be granted if discharges from multiple subareas re-combine in proximity to the site. In this case, peak discharge in any direction may be a one-hundred-percent release rate, provided that the overall site discharge meets the weighted average release rate.

7. For a proposed development site located partially within a release rate category subarea and partially within a conditional/provisional no detention subarea, the size of the predevelopment drainage area on a site may not be changed post-development to create potentially adverse conditions on downstream properties except as part of a "no harm" or hardship waiver procedure.

8. No portion of a site may be regraded between the Martins/Jacoby Creeks Watershed and Delaware River Sub-Basin 1 Watershed and any adjacent watershed except as part of a "no harm" or hardship waiver procedure.

9. Within a release rate category area, for a proposed development site which has areas which drain to a closed depression(s), the design release from the site will be the lesser of: (a) the applicable release rate flow assuming no closed depression(s); or (b) the existing peak flow actually leaving the site. In cases where (b) would result in an unreasonably small design release, the design discharge of less than or equal to the release rate will be determined by the available downstream conveyance capacity to the main channel calculated using § 23-307, Subsection 8Q, and the minimum orifice criteria.

10. Off-site areas which drain through a proposed development site are not subject to release rate criteria when determining allowable peak runoff rates. However, on-site drainage facilities shall be designed to safely convey off-site flows through the development site using the capacity criteria in Subsection 4 and the detention criteria in § 23-307, Subsection 8.

11. For development sites proposed to take place in phases, all detention ponds shall be designed to meet the applicable release rate(s) applied to all site areas tributary to the proposed pond discharge direction. All site tributary areas will be assumed as developed, regardless of whether all site tributary acres are proposed for development at that time. An exception shall be sites with multiple detention ponds in series where only the downstream pond must be designed to the stated release rate.

12. Where the site area to be impacted by a proposed development activity differs significantly from the total site area, only the proposed impact area shall be subject to the release rate criteria. The impact area includes any proposed cover or grading changes.

13. Development proposals which, through groundwater recharge or other means, do not increase either the rate or volume of runoff discharged from the site compared to predevelopment are not subject to the release rate provisions of this chapter.

14. "No Harm" Water Quantity Option. For any proposed development site not located in a Conditional/Provisional No Detention district, the developer has the option of using a less restrictive runoff control (including no detention) if the developer can prove that special circumstances exist for the proposed development site and that "no harm" would be caused by discharging at a higher runoff rate than that specified by the plan. Special circumstances are defined as any hydrologic or hydraulic aspects of the development itself not specifically considered in the development of the plan runoff control strategy. Proof of "no harm" would have to be shown from the development site through the remainder of the downstream drainage network to the confluence of the creek with the Delaware or Lehigh River. Proof of "no harm" must be shown using the capacity criteria specified in Subsection 4 if downstream capacity analysis is a part of the "no harm" justification.

Attempts to prove "no harm" based upon downstream peak flow versus capacity analysis shall be governed by the following provisions:

A. The peak flow values to be used for downstream areas for the design return period storms (two-, ten-, twenty-five- and one-hundred-year-) shall be the values from the calibrated PSRM Model for the Martins/Jacoby Creeks Watershed and Delaware River Sub-Basin 1 Watershed or as calculated by an applicant using an alternate method acceptable to the municipality. The flow values from the PSRM Model would be supplied to the developer by the municipality upon request.

B. Any available capacity in the downstream conveyance system as documented by a developer may be used by the developer only in proportion to his development site acreage relative to the total upstream undeveloped acreage from the identified capacity (i.e., if his site is 10% of the upstream undeveloped acreage, he may use up to 10% of the documented downstream available capacity).

C. Developer-proposed runoff controls which would generate increased peak flow rates at storm drainage problem areas would, by definition, be precluded from successful attempts to prove "no harm," except in conjunction with proposed capacity improvements for the problem areas consistent with Subsection 16.

Any "no harm" justifications shall be submitted by the developer as part of the drainage plan submission per Part 4. Developers submitting "no harm" justifications must still meet all of the water quality requirements in § 23-304.

15. Regional Detention Alternatives. For certain areas within the study area, it may be more cost-effective to provide one control facility for more than one development site than to provide an individual control facility for each development site. The initiative and funding for any regional runoff control alternatives are the responsibility of prospective developers. The design of any regional control basins must incorporate reasonable development of the entire upstream watershed. The peak outflow of a regional basin would be determined based on the required release rate at the point of discharge.

16. Capacity Improvements. In certain instances, primarily within the conditional/provisional no detention areas, local drainage conditions may dictate more stringent levels of runoff control than those based upon protection of the entire watershed. In these instances, if the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then the capacity improvements could be provided by the developer in lieu of runoff controls on the development site. Peak flow calculations shall be done assuming that the local watershed is in the existing condition and then assuming that the local watershed is developed per current zoning and using the specified runoff controls. Any capacity improvements would be designed using the larger of the above peak flows and the capacity criteria specified in Subsection 4. All new development in the entire subarea(s) within which the proposed development site is located shall be assumed to implement the developer's proposed discharge control, if any.

Capacity improvements may also be provided as necessary to implement any regional detention alternatives or to implement a modified "no harm" option which proposes specific capacity improvements to provide that a less stringent discharge control would not create any harm downstream.

§ 23-307 Design Criteria for Drainage Facilities.

[Ord. 2014-03, 9/8/2014]

1. Stormwater runoff which may result from regulated activities listed in § 23-105 shall be controlled by permanent stormwater runoff BMPs that will provide the required standards within Part 3. The methods of stormwater control or best management practices (BMPs) which may be used to meet the required standards are described in this chapter and "Pennsylvania Stormwater Best Management Practice Manual," December 30, 2006, as amended. The choice of BMPs is not limited to the ones appearing in this chapter and the manual; however, any selected BMP must meet or exceed the runoff peak rate requirements of this chapter for the applicable hydrologic district. Further, the developer's selection of BMPs may impact the Township's willingness to accept any offer of dedication, it being noted that the Township is under no obligation to accept ownership and maintenance obligations of any BMPs or improvements required by this chapter.

2. Any stormwater facility located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation.

3. Collection System Standards.

A. Curb Inlets. Curb inlets shall be located at curb tangents on the uphill side of street intersections, and at intervals along the curbline to control the maximum amount of encroachment of runoff on the roadway pavement so that same does not exceed 1/2 of the width of the travel lane during the design storm event. Design and location of curb inlets shall be approved by the Township.

B. Pipe Materials. All storm sewer piping shall be Class III reinforced concrete pipe, except when pipe class and strength is required to be increased in accordance with PennDOT Specifications. Piping shall be saw-cut at ends, as needed, and not hammered or broken. All pipe joints and lift holes must be mortared except where designed for infiltration. For areas where adequate cover can be provided, high-density polyethylene (HDPE) pipe may be used in lieu of concrete pipes. Applicants wishing to use HDPE pipe must provide evidence that the pipe will be manufactured by an "Approved Construction Materials" provider under PennDOT Bulletin 15.

C. Minimum Pipe Size. Minimum pipe diameter shall be 18 inches (or an equivalent flow area of 1.76 square feet).

D. Inlet and Manhole Construction. Inlet and manhole castings and concrete construction shall be equivalent to PennDOT Design Standards. All inlet grates shall be "bicycle safe" heavy-duty structural steel. All storm sewer inlets must be identified with a storm drain marker. Storm drain markers shall be stainless steel affixed to the inlet hood with adhesive, rivets or bolts. (Marker may be bolted to the grate in off-road locations) Marker shall have a minimum diameter of 3 1/2 inches and include "No Dumping — Drains to Waterway" and a fish symbol.

E. Open-end pipes must be fitted with concrete endwalls or wing walls in accordance with PennDOT Standards.

F. Flow velocity. Stormwater collection systems shall be designed to produce a minimum velocity of 3.0 feet per second when flowing full. The maximum permissible velocity shall be 15.0 feet per second. Pipe slopes shall not be less than 0.50%.

G. Inlets and manholes shall be spaced at intervals not exceeding 300 feet, and shall be located wherever branches are connected or sizes are changed, and wherever there is a change in alignment or grade. For drainage lines of at least 36 inches diameter, inlets and manholes may be spaced at intervals not exceeding 400 feet.

H. Storm sewer bedding/backfill requirements shall conform to PennDOT Form 408, latest revision.

I. Inlets shall be located to intercept concentrated runoff prior to discharge over public/private rights-of-way, sidewalks, paths, streets, and driveways.

J. The capacity of all Type "C" inlets shall be based on a maximum surface flow to the inlets of 4.0 cfs, calculated based on the one-hundred-year frequency design storm event. The maximum flow to Type "C" inlets located in low points (such as sag vertical curves) shall include the overland flow directed to the inlet as well as all bypass runoff from upstream inlets. The bypass flow from upstream inlets shall be calculated using inlet efficiency curves included in PennDOT Design Manual Part 2, latest edition. If the surface flow to an inlet exceeds 4.0 cfs, additional inlets shall be provided upstream of the inlet to intercept the excessive surface flow. A Type "C" inlet at a low point of a paved area may be designed to accept a maximum of six cubic feet per second (cfs). Type "M" inlets shall be designed to accept a maximum surface flow of 6 cfs based on the one-hundred-year frequency design storm event. Double inlets will not be permitted where additional pipe and inlets can be placed upstream to intercept excessive surface flow. A maximum of 12 cfs shall be permitted to be collected by a Type "M" inlet located in an isolated pervious area, provided the designer can verify that such an inlet would not cause stormwater to accumulate on any adjacent public or private property, outside of an associated storm sewer easement, and that the depth of the accumulated stormwater would not exceed 12 inches.

K. A minimum drop of two inches shall be provided between the inlet and outlet pipe invert elevations within all inlets and manholes. When varying pipe sizes enter an inlet or manhole, the elevation of crown of all pipes shall be matched.

L. Stormwater pipes shall have a minimum depth of cover of 12 inches (including over the bell) or as designated by the American Concrete Pipe Association (whichever is greater), and in no case shall any part of the pipe project into the road subbase or curb. Where cover is restricted, equivalent pipe arches may be specified in lieu of circular pipe.

M. The capacity of all stormwater pipes shall be calculated utilizing the Manning Equation for open channel flow as applied to closed conduit flow. The Manning's roughness coefficient shall be 0.013 for all concrete pipe. In cases where pressure flow may occur, the hydraulic grade line shall be calculated throughout the storm sewer system to verify that at least one foot of freeboard will be provided in all inlets and manholes for the design storm event.

N. Culverts shall be designed based on procedures contained in Hydraulic Design of Highway Culverts, HDS #5, U.S. Department of Transportation, Federal Highway Administration. Where pressure flow is anticipated in storm sewer pipes (non-open channel flow), the applicant's designer shall be required to calculate the elevation of the hydraulic grade line through the storm sewer system. Wherever the hydraulic grade line elevation exceeds the pipe crown elevation for the design flow, pipes with watertight joints must be specified.

O. Storm sewer structures (i.e., end walls, inlets, and sections, etc.) may not be located on top of, or within 10 feet of electric, communication, water, sanitary sewer, or gas services and/or mains, unless approval is received from the Township and the Authority or utility having jurisdiction over same.

P. Stormwater pipes must be oriented at right angles to electric, water, sanitary sewer, and gas utilities when crossing above or beneath same. Crossing angles of less than 90° will only be permitted at the discretion of the Township. When skewed crossings are permitted, interior angles between alignment of the storm sewer pipe and utility shall not be less than 45°. Vertical and horizontal design of storm sewer must be linear.

Q. Roadway underdrain is required along both sides of all proposed roadways, existing roadways proposed to be widened, and within existing or proposed roadside swales as directed by the Township.

R. Where a public storm sewer system is not located within a right-of-way, or dedicated public property, a 20 feet wide easement shall be established to encompass the storm sewer system. For multiple pipes or utilities, the width of the easement shall be a minimum of 30 feet.

S. A minimum of one foot of freeboard, between the inlet grate and the design flow elevation, shall be provided in all storm sewer systems (inlets and manholes) for the one-hundred-year frequency design storm event.

T. Personal safety grates should be provided on the upstream and downstream end of any culvert pipe, basin outlet pipe or storm sewer discharge pipe.

4. Open Swales and Gutters. Open swales shall be designed on the basis of Manning's Formula as indicated for collection systems with the following considerations:

A. Roughness Coefficient. The roughness coefficient shall be 0.040 for earth swales.

B. Bank Slopes. Slopes for swale banks shall not be steeper than one vertical to four horizontal.

C. Flow Velocity. The maximum velocity of flow as determined by Manning's equation shall not exceed the allowable velocities as shown in the following table for the specific type of material, unless otherwise approved by the Township and the Northampton County Conservation District.

NOTE: Source of the following design criteria is the Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conservation Publication, Erosion and Sediment Control Program Manual.

	Allowable Velocity
	Material		Velocity (feet per second)
	Well-established grass on good soil
	Short pliant bladed grass		4.0 to 5.0
	Bunch grass, soil exposed		2.0 to 3.0
	Stiff-stemmed grass		3.0 to 4.0
	Earth without vegetation
		Fine sand or silt	1.0
	Ordinary firm loam		2.0 to 3.0
	Stiff clay		3.0 to 5.0
	Clay and gravel		4.0 to 5.0
	Coarse gravel		4.0 to 5.0
	Soft shale		5.0 to 6.0
	Shoulders
		Earth	(As defined above)
		Stabilized	6.0
		Paved	10.0 to 15.0

D. Swales shall be stabilized with biodegradable erosion control matting to permit establishment of permanent vegetation. Swales shall be of such shape and size to effectively contain the one-hundred-year, Rational Method design storm, and to conform to all other specifications of the Township.

E. To minimize sheet flow of stormwater across lots located on the lower side of roads or streets, and to divert flow away from building areas, the cross-section of the street as constructed shall provide for parallel ditches or swales or curb on the lower side which shall discharge only at drainage easements, unless otherwise approved by the Township.

F. Gutters and swales adjacent to road paving shall be permitted to carry a maximum flow of four cubic feet per second prior to discharge away from the street surface, unless it is proven to the satisfaction of the Township by engineering calculations that the road slopes or other factors would allow higher gutter or swale capacity.

G. Flows larger than those permitted in gutters and roadside swales may be conveyed in swales outside the required road right-of-way in separate drainage easements, or may be conveyed in pipes or culverts inside or outside the required road right-of-way.

H. Existing and proposed swales shall be provided with underdrains as deemed necessary by the Township should overland seepage result in potential maintenance problems. Underdrains must discharge into a natural drainage channel or stormwater management system.

I. Where drainage swales are used to divert surface waters away from buildings, they shall be sodded, landscaped, or otherwise protected as required and shall be of a slope, shape, and size conforming with the requirements of the Township. Concentration of surface water runoff shall be permitted only in swales, watercourses, retention or detention basins, bioretention areas, or other areas designed to meet the objectives of this chapter.

5. Bridge and Culvert Design. Any proposed bridge or culvert to convey flow within a perennial or intermittent stream shall be designed in accordance with the following principles:

A. Culverts and bridges shall be designed with an open bottom to maintain natural sediment transport and bed roughness, avoiding acceleration of water velocity above the natural (preexisting) condition. Rock (riprap) lining (native material if possible) shall be installed within the culvert as needed to prevent erosion within the structure. Approximate top of rock lining must be at the level of the existing stream bottom so as to maintain normal water level and unimpeded movement of native animal species.

B. Bottom of opening shall be designed to match the bankfull channel condition in terms of width and depth. The cross-sectional area of the bankfull channel (measured at a reference location upstream of the structure) shall be matched with area in the crossing structure.

C. Above the bankfull elevation, the width shall increase a minimum of 30% to disperse the energy of higher flow volumes and avoid undermining of the supporting structure by secondary currents.

D. The total cross-sectional area of the structure opening must be equal to or greater than the flood-prone area (cross-sectional stream area at a depth of twice the maximum bankfull depth, measured at a reference location upstream of the structure). The flood-prone area is approximately equal to the area flooded by a fifty-year return flood.

E. All bridges, culverts, and drainage channels shall be designed to convey a flow rate equal to a one-hundred-year, twenty-four-hour storm (refer to Appendix C[1]). All bridges and culverts shall be designed to convey the one-hundred-year design storm without increasing the extent and depth of the one-hundred-year floodplain.

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

6. Storm Sewer Design.

A. Design flow rate. The storm sewer system shall be designed to carry the one-hundred-year frequency design storm peak flow rate. The drainage area and runoff coefficient to each inlet shall be indicated on the drainage plan. The one-hundred-year flow rate shall be determined by the Rational Method formula:

Q = CIA

	Where:
		Q	=	Peak runoff rate measured in cubic feet per second (cfs)
		C	=	Runoff coefficient: The coefficient of stormwater runoff includes many variables, such as ground slope, ground cover, shape of drainage area, etc.
		I	=	Intensity: Average rainfall intensity in inches per hour for a time equal to the time of concentration (inches per hour).
		A	=	Area: Drainage area in acres (ac).
		Appropriate values for the rainfall intensity can be determined using a method described in Chapter 7, Appendix A of PennDOT Publication 584, as amended.
		*A storm sewer may be designed for the twenty-five-year event, if it can be shown that through a combination of techniques, that the equivalent volume for the one-hundred-year event can be safely directed to a stormwater facility or suitable outfall.

B. Consideration shall be given to future land use changes in the drainage area in selecting the Rational ("C") coefficient. For drainage areas containing several different types of ground cover, a weighted value of "C" shall be used.

C. In determining the peak flow rate to individual storm sewer inlets (or other collection structures), the time of concentration method (as referenced in § 23-308) shall be used for inlet drainage areas in excess of one acre, unless otherwise approved by the Township. For inlet drainage areas less than one acre, a five-minute time of concentration shall be used.

D. In determining the required design flow rate through a storm sewer piping system, if a five-minute time of concentration (storm duration) results in a pipe size exceeding a thirty-inch diameter pipe (or equivalent flow area of 4.9 square feet), the time of concentration approach (as defined herein) shall be used in determining storm duration.

E. Overflow System. An overflow system shall be provided to carry all bypass flow and/or flow in excess of storm sewer design capacity, to the detention basin (or other approved outlet point) when the capacity of the storm sewer system is exceeded. Stormwater runoff will not be permitted to surcharge from storm sewer structures.

7. Grading and Drainage.

A. After completion of rough grading, a minimum of eight inches of topsoil, or the existing depth of topsoil encountered on the site (whichever is greater), shall be returned to remaining disturbed areas prior to final grading and seeding.

B. Lots shall be graded to secure proper drainage away from buildings and to prevent the collection of stormwater in pools. Minimum two-percent slopes shall be maintained away from and around all structures. Separation between the top of foundation wall (or slab) shall comply with Township Construction Code requirements.[2]

[2] Editor's Note: See Ch. 5, Code Enforcement, Part 1, Uniform Construction Code.

C. Construction. The developer shall construct and/or install such drainage structures and/or pipe which are necessary to prevent erosion damage and to satisfactorily carry off such surface waters to the nearest practical street, storm drain or natural watercourse.

D. Excavation. No excavation shall be made with a cut face steeper in slope than four horizontal to one vertical (4:1 = 25%), except under one or more of the following conditions:

(1) The fill is located so that settlement, sliding, or erosion will not result in property damage or be a hazard to adjoining property, streets, alleys or buildings.

(2) A written statement from a professional civil engineer, licensed in the Commonwealth of Pennsylvania and experienced in erosion control, certifying the site has been inspected and that the proposed deviation from the slope specified above will not endanger any property or result in property damage, is submitted to and approved by the Township Engineer.

(3) A concrete, segmental block, or stone masonry wall, constructed in accordance with requirements of Chapter 27, Zoning, and Township Construction Code,[3] is provided to support the face of the excavation.

[3] Editor's Note: See Ch. 5, Code Enforcement, Part 1, Uniform Construction Code.

E. Fill. No fill shall be made which creates any exposed surface steeper in slope than four horizontal to one vertical (4:1 = 25%) except under one or more of the following conditions:

(1) The fill is located so that settlement, sliding, or erosion will not result in property damage or be a hazard to adjoining property, streets, alleys, or buildings.

(2) A written statement from a professional civil engineer, licensed in the Commonwealth of Pennsylvania and experienced in erosion control, certifying the site has been inspected and that the proposed deviation from the slope specified above will not endanger any property or result in property damage, is submitted to and approved by the Township.

(3) A concrete, segmental block, or stone masonry wall, constructed in accordance with Township requirements, is provided to support the face of the excavation.

F. Slopes and Fences. The top or bottom edge of slopes shall be a minimum of five feet from property or right-of-way lines of streets or alleys, in order to permit the normal rounding of the edge without encroaching on the abutting property. Where walls or slopes (steeper than two horizontal to one vertical) are approved under the criteria in this chapter, and are five feet or more in height, a protective fence conforming to the applicable construction code shall be required at the top of the wall (or bank).

G. Cleanup. All lots must be kept free of any debris or nuisances whatsoever during construction.

H. Design of erosion and sedimentation control facilities (particularly stormwater/sediment basins) shall incorporate best management practices as defined herein.

I. Cut-and-fill operations shall be kept to a minimum. Wherever feasible, natural vegetation shall be retained, protected, and supplemented. Cut-and-fills shall not endanger or otherwise adversely impact adjoining property.

J. No grading equipment shall be permitted to be loaded and/or unloaded on a public street, and no grading equipment shall be permitted to travel on or across a public street unless licensed for operation on public thoroughfares.

K. Grading equipment shall not be permitted to within intermittent and perennial streams. Temporary crossing shall only be permitted where application is made, and approval is received, from the Pennsylvania Department of Environmental Protection (where applicable), the Northampton County Conservation District, and Lower Mount Bethel Township.

L. Design of energy dissipation for high volume and/or high-velocity discharge from storm sewer pipes and channels shall be in accordance with Hydraulic Engineering Circular No. 14, "Hydraulic Design of Energy Dissipaters for Culverts and Channels," as published by Department of Transportation, FHWA, when deemed necessary by the Township, and as approved by the Northampton County Conservation District.

M. To control the dissemination of mud and dirt on to public roads and driveways, tire cleaning areas constructed of AASHTO #1 stone (underlain by geotextile structural fabric), at least 50 feet in length, shall be installed at each point of access to the site and individual lots (upon construction of internal streets in a binder condition). Washing stations shall also be set up at every construction entrance in order to wash mud and dirt from exiting vehicles. Appropriate measures must be taken to control runoff from such locations. The developer shall be responsible for the placement of appropriate signage identifying construction entrances and washing stations. Construction entrances shall be maintained by the developer during construction.

N. During construction activities, necessary measures for dust control shall be exercised, including the application of water to higher traffic areas of the site.

O. The developer shall remove any and all mud and debris from any street, road and/or alley. If the same is not removed within 24 hours after verbal notice from the Township to the developer, then, in that event, said mud and debris may be removed from the road, street or alley by the Township at the developer's sole cost and expense, and the developer shall be charged for said expense, plus a 20% surcharge for administrative expenses.

P. Adequate provision shall be made to prevent surface water from damaging the cut face of excavation and the sloping surfaces of fills.

8. Stormwater Detention/Retention Basins.

A. If permanent ponds (retention basins) are proposed, the developer shall demonstrate that such ponds are designed to protect the public's health and safety.

B. During construction, duly authorized representatives of Lower Mount Bethel Township may enter upon any property within the Township to investigate whether construction activity is in compliance with this chapter.

C. When basins are provided, they shall be designed to utilize the natural contours of the land whenever possible. When such design is not practical, the construction of the basin shall utilize slopes as flat as possible to blend the structure into the terrain.

D. Except with the two-year design storm, basins shall be designed so that they return to normal conditions within approximately 24 hours after the termination of the storm, unless the Township determines that downstream conditions may warrant other design criteria for stormwater release.

E. Landscaping and planting in and around the perimeter of basins shall be provided. It shall be aesthetically pleasing and compatible with surrounding land uses, and require minimum maintenance. Proposed landscaping and planting shall also be in accordance with the provisions of this chapter, Chapter 22, Subdivision and Land Development, and Chapter 27, Zoning.

F. If a stormwater management basin will serve as a temporary sediment control device, the temporary sediment control measures shall be shown including perforated riser pipes or stand boxes, filter berms, cleanout stakes and other measures as may be required by Pennsylvania Department of Environmental Protection, Chapter 102, Regulations. Plans for such facilities shall require Northampton County Conservation District approval prior to implementation. Sedimentation basins shall be in place prior to any earthmoving activities within their tributary drainage areas. A note identifying the above criteria shall be required on the record plan of subdivisions and land developments as well as in the development agreement with the Township.

G. Stormwater management basins shall be in place before the creation of any new impervious surfaces on the site.

H. Runoff shall not be directed to any infiltration structure until all tributary drainage areas are stabilized.

I. Where permanent retention (pond) facilities are proposed, there shall be a safety ledge, 10 feet wide, no greater than 15 inches and no less than 12 inches below the permanent water surface level.

J. All basins shall have slopes of four horizontal to one vertical (4:1 = 25%), or flatter on the basin's outer berm and three horizontal to one vertical or less on the basin's inner berm. The top or toe of any slope shall be located a minimum of five feet from any property line. The maximum difference between the top of berm elevation and the invert elevation of the outlet structure shall be seven feet.

K. All portions of a dry detention basin bottom (non wetland) shall have a minimum slope of 2%.

L. All basin embankments shall be placed in lifts not to exceed one foot in thickness and each lift shall be compacted to a minimum of 95% of Modified Proctor Density as established by ASTM D-1557. Prior to proceeding to the next lift, the compaction shall be verified by a Soils Engineer employed by the applicant/developer. Compaction tests shall be run on the leading and trailing edge of the berm along with the top of the berm. Verification of required compaction shall be submitted to the Township prior to utilization of any basin for stormwater management.

M. Emergency overflow facilities/spillways shall be provided within basins in order to convey basin inflow in excess of design flows, out of the basin, or in the event the outlet structure becomes blocked and is unable to convey flow. Emergency spillways discharging over embankments shall be constructed of reinforced concrete checker blocks (on an equivalent approved by the municipal engineer) to protect the berm against erosion. Checker-blocks shall be backfilled with topsoil and stabilized in lawn cover. The checker-block lining shall extend to the toe of the embankment on the outside of the berm, and shall extend to an elevation of three feet below the spillway crest on the inside of the berm. Vegetated spillways may be utilized for spillways constructed entirely on undisturbed ground (e.g., not discharging over fill material). A dense cover of vegetation shall be rapidly established in such spillways by sodding or seeding with a geotextile anchor. The minimum capacity of all emergency spillways shall be equivalent to the peak flow rate of the one-hundred-year, post-development design storm (entering to the basin). Spillway elevations shall be a minimum of one foot above the maximum depth of detained runoff within the basin for the one-hundred-year post-development design storm.

N. In all cases, the discharge end of the basin shall be provided with a properly designed outlet control structure (headwall, orifice structure or other approved flow control structure), culvert pipe, and end wall. Perforated riser pipes alone, without provision for permanent outlet control structure (as stated above) and culvert pipe, are not permitted for permanent basins.

O. The minimum top of basin berm width (at the design elevation) shall be 10 feet. A cutoff trench (keyway) of impervious material shall be provided under all embankments that require fill material. The cutoff trench shall be a minimum of eight feet wide, three feet deep and have side slopes of one horizontal to one vertical.

P. All stormwater detention facilities shall provide a minimum 1.0 foot freeboard above the maximum pool elevation associated with the two- through twenty-five-year runoff events. A one-half-foot freeboard shall be provided above the maximum pool elevation of the one-hundred-year runoff event. The freeboard shall be measured from the maximum pool elevation to the invert of the emergency spillway. The two- through one-hundred-year storm events shall be controlled by the primary outlet structure. An emergency spillway for each basin shall be designed to pass the one-hundred-year return frequency storm peak basin inflow rate with a minimum one-half-foot freeboard measured to the top of basin. The freeboard criteria shall be met considering any off-site areas tributary to the basin as developed, as applicable. If this detention facility is considered to be a dam as per DEP Chapter 105, the design of the facility must be consistent with the Chapter 105 regulations, and may be required to pass a storm greater than the one-hundred-year event.

Q. The minimum circular orifice diameter for controlling discharge rates from detention facilities shall be three inches. Designs where a lesser size orifice would be required to fully meet release rates shall be acceptable with a three-inch orifice, provided that as much of the site runoff as practical is directed to the detention facilities. The minimum three-inch diameter does not apply to the control of the WQv.

R. Antiseep collars or sand filter diaphragms shall be installed around the pipe barrel and shall be centered within the normal saturation zone of the berm. The antiseep collars and their connections to the pipe barrel shall be watertight. The antiseep collars shall be cast-in-place and extend a minimum of two feet beyond the outside of the principal pipe barrel. Precast collars shall be permitted if approved by the Township. A minimum of two collars shall be installed on each basin outlet pipe, and be located a minimum of two feet from any pipe joint.

S. A perforated sediment control structure, sized in accordance with Northampton County Conservation District requirements, shall be provided at each basin outlet structure (if more than one is to be utilized) for sediment control. Sediment control structures shall not be removed until the entire area tributary to the basin has been permanently stabilized and until approved by the Northampton County Conservation District.

T. All basin outlet pipes shall be watertight reinforced concrete having "O" ring joints. All joints and lift holes shall be mortared. Crushed stone bedding/backfill material shall not be utilized through basin berms.

U. A minimum of six inches is required between the top of an outlet structure box and the emergency spillway elevation. Six inches, minimum, is also required between the one-hundred-year water surface elevation and the top of an outlet structure box.

V. Energy-dissipating devices (rock lining/riprap, or other approved materials) shall be provided at all basin outlets and shall be sized in accordance with Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conservation Publication, Erosion and Sediment Control Program Manual, latest revision.

W. Stone gabion baskets and retaining wall systems shall not be utilized in construction of detention/retention basins.

X. Access easements and stabilized drives to stormwater detention facilities shall be provided for maintenance and operation. This access easement shall be cleared and be at least 20 feet in width. Multiple accesses shall be encouraged for major facilities. The developer shall provide access easements and drives of reinforced concrete checker block (backfilled with topsoil and stabilized in lawn cover) or other similar paver acceptable to the Township Engineer, over a six-inch bed of compacted PennDOT type 3A coarse aggregate (or approved equivalent). Accessways to basins shall be a minimum of 10 feet wide and be no steeper in slope than 10 feet horizontal to one foot vertical. In addition, depressed curb and concrete apron shall be provided where the accessway enters a street/driveway and the stabilized driveway shall extend from the bottom of the interior basin berm embankment to the point of access to the basin. Access easements shall be owned and maintained by the individual lot owner(s) or homeowner's association, but shall be established to permit access by Lower Mount Bethel Township or its designee, for inspection and/or maintenance.

Y. Split-rail fence with wire mesh backing is required around all detention or retention basins. Fence shall consist of concrete posts (dual rail), four feet high, with cedar rails (eight feet to 10 feet long), and epoxy-coated wire mesh (earth-tone color) installed six inches above finished grade. Each basin fence installation shall include two points of access with 10 feet wide self-closing, self-latching gates.

Z. All detention/retention basins shall be constructed to meet or exceed the "Construction Specifications" section of the Natural Resource Conservation Service (NRCS): Code No. 378, "Pond" document, as amended.

9. General Design Requirements.

A. Prior to finish grading of a development site and final overlay of streets, roads, and driveways, temporary measures, acceptable to the Township, shall be taken to ensure that all runoff intended to be intercepted and collected by an inlet or other facility, will be collected. The plan shall include such details, notes, or specification including bituminous "eyebrows" at inlets, diversion berms, etc.

B. All stormwater runoff and floodplain calculations and stormwater management facilities design shall be prepared by a professional engineer licensed by and in good standing with the Commonwealth of Pennsylvania.

C. When subdivisions or land developments are submitted to the Township for approval in sections or phases, a complete storm sewer design for the proposed subdivision and land development shall be submitted. The proposed design must include the entire tract and not a portion.

§ 23-308 Calculation Methodology.

[Ord. 2014-03, 9/8/2014]

1. Stormwater runoff from all development sites shall be calculated using either the Rational Method or a Soil Cover Complex Methodology.

2. Methods.

A. Any stormwater runoff calculations shall use generally accepted calculation technique that is based on the NRCS Soil Cover Complex Method. Table 308-1 summarizes acceptable computation methods. Method must be selected by the applicant based on the individual limitations and suitability of each method for a particular site.

B. The Rational Method may be used to estimate peak discharges from drainage areas that contain less than 75 acres. The Rational Method is recommended for drainage areas under 25 acres.

	Table 308-1 Acceptable Computation Methodologies for Drainage Plans
	Method	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 development package based on TR-55)	USDA NRCS	Applicable for land plans within limitations described in TR-55
	HEC-1, HEC-HMS	U.S. Army Corps of Engineers	Applicable where use of full hydrologic computer model is desirable or necessary
	PSRM	Penn State University	Applicable where use of a hydrologic computer model is desirable or necessary; simpler than TR-20 or HEC-1
	Rational Method (or commercial computer package based on Rational Method)	Emil Kuichling (1889)	Applicable sites less than 75 acres, or as approved by the Township Engineer
	Other methods	Varies	Other computation methodologies approved by the Township Engineer

3. All calculations consistent with this chapter using the Soil Cover Complex Method shall use the appropriate design rainfall depths for the various return period storms according to the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 rain data corresponding to the Pen Argyl, Pennsylvania, rain gage, as presented in Table C-4, Appendix C, of this chapter.[1] The SCS Type II rainfall curve from NOAA is found on Figure C-4 in Appendix C of this chapter. This data may also be directly retrieved from the NOAA Atlas 14 website: hdsc.nws.noaa.gov/hdsc/pfds/orb/pa_pfds.html and must be checked at the beginning of each application, as NOAA rainfall curve data is frequently changed. If a hydrologic computer model such as PSRM or HEC-1/HEC-HMS is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours.

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

4. (Reserved)

5. Runoff curve numbers (CN) for both existing and proposed conditions to be used in the Soil Cover Complex Method shall be obtained from Table C-1 in Appendix C of this chapter.[2]

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

6. Runoff coefficients (C) for both existing and proposed conditions for use in the Rational Method are contained in Table C-2 in Appendix C of this chapter.

7. All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from a method outlined in Chapter 7, Appendix A, of PennDOT Publication 584 (as amended). Times of concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS TR-55 (as amended or replaced from time to time by NRCS). Times of concentration for channel and pipe flow shall be computed using Manning's Equation.

8. For the purposes of existing conditions flow rate determination for all subdivision and land development applications, undeveloped land and existing impervious surfaces shall be considered as "meadow" in good condition, unless the natural ground cover generates a lower curve number (CN) or Rational "C" value (e.g., forest), as listed in Table C-1 or C-2 in Appendix C of this chapter. Wooded areas shall use a ground cover of "woods in good condition." An area shall be considered wooded if there is a contiguous canopy of trees existing over an area of 1/4 acre or more.

9. Where uniform flow is anticipated, the Manning Equation shall be used for hydraulic computations, and to determine the capacity of open channels, pipes, and storm sewers. Values for Manning's roughness coefficient (n) shall be consistent with Table C-3 in Appendix C of this chapter.

10. Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this chapter using any hydraulic analysis technique or method accepted by the Township.

11. The design of any stormwater management facilities intended to meet the performance standards of this chapter shall be verified by routing the design storm hydrograph through these facilities using the Storage Indication Method. The design storm hydrograph shall be computed using a calculation method that produces a full hydrograph.

12. The Township has the authority to require that computed existing runoff rates be reconciled with field observations and conditions. If the design professional engineer can substantiate through actual physical calibration that more appropriate runoff and time-of-concentration values should be utilized at a particular site, then appropriate variations may be made upon review and recommendations of the Township Engineer. Calibration shall require detailed gauge and rainfall data for the particular site in question.

13. Infrequent Storm. The rational runoff coefficients given in this chapter are applicable for the one-year through one-hundred-year frequency design storm event. Less frequent, higher-intensity storms require modification of the runoff coefficient because infiltration and other losses have a proportionally smaller effect on runoff (Wright-McLaughlin 1969). The adjustment of the Rational Method for use with major storms shall be made by multiplying the Rational formula by a frequency factor Cw. Cw values are as follows: any event less than the twenty-five-year frequency design storm, use runoff cooefficents (C) designated by superscript "a" in Appendix C, Chart C-2; any event greater than or equal to the twenty-five-year frequency design storm, use runoff cooefficents (C) designated by superscript "b" in Appendix C, Chart C-2.[3]

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

14. The time of concentration (Tc) is the time required for water to flow from the hydraulically most remote point of the drainage area to the point of interest (design point). Use of the Rational formula requires calculation of a Tc for each design point within the drainage basin. For design purposes, the time of concentration may not be less than five minutes. Travel time (Tt) is the time it takes runoff to travel from one location to another in a watershed (subarea) and is a component of time of concentration. Tc is computed by summing all the travel times for consecutive components of the drainage conveyance system.

All time of concentration calculations shall use a segmental approach (Tt) which may include one or all of the flow types below:

A. Sheet flow (overland flow) calculations shall use either the NRCS average velocity chart (Figure 3-1, Technical Release-55, 1975, as amended) or the modified kinematic wave travel time equation (Equation 3-3, NRCS TR-55, June 1986). If using the modified kinematic wave travel time equation, the sheet flow length shall be limited to 50 feet for designs using the Rational Method and limited to 150 feet for designs using the Soil-Cover-Complex Method.

B. Shallow concentrated flow travel times shall be determined from the watercourse slope, type of surface and the velocity from Figure 3-1 of TR-55, June 1986.

C. Open channel flow travel times shall be determined from velocities calculated by the Manning Equation. Bankfull flows shall be used for determining velocities. Manning 'n' values shall be based on the table presented in Appendix C.[4]

[4] Editor's Note: Appendix C is included as an attachment to this chapter.

D. Pipe flow travel times shall be determined from velocities calculated using the Manning Equation assuming full flow and the Manning 'n' values from Appendix C.

15. If using the Rational Method, all predevelopment calculations for a given discharge direction shall be based on a common time of concentration considering both on-site and any off-site drainage areas. If using the Rational Method, all post-development calculations for a given discharge direction shall be based on a common time of concentration considering both on-site and any off-site drainage areas.

16. Infiltration BMP loading rate percentages in the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D shall be calculated as follows:

	All disturbed areas to be made impervious:	Weight at 100%
	All disturbed areas to be made pervious:	Weight at 50%
	All undisturbed pervious areas:	Weight at 0%
	All existing impervious areas:	Weight at 100%

17. Soil thickness is to be measured from the bottom of any proposed infiltration system. The effective soil thickness in the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D is the measured soil thickness multiplied by the thickness factor based on soil permeability (as measured by the adapted 25 Pa. Code § 73.15 percolation test in Appendix H[5]), as follows:

	Permeability Range* (inches per hour)	Thickness Factor
	6.0 to 12.0	0.8
	2.0 to 6.0	1.0
	1.0 to 2.0	1.4
	0.75 to 1.0	1.2
	0.5 to 0.75	1.0

	*	If the permeability rate (as measured by the adapted 25 Pa. Code § 73.15 percolation test in Appendix H) falls on a break between two thickness factors, the smaller thickness factor shall be used.
	Sites with soil permeability greater than 12.0 inches per hour, as measured by the adapted 25 Pa. Code § 73.15 percolation test in Appendix H, are not recommended for infiltration.

A. BMPs designed to store or infiltrate runoff and discharge to surface runoff or pipe flow shall be routed using the storage indication method.

B. BMPs designed to store or infiltrate runoff and discharge to surface runoff or pipe flow shall provide storage volume for the full WQv below the lowest outlet invert.

C. Wet detention ponds designed to have a permanent pool for the WQv shall assume that the permanent pool volume below the primary outlet is full at the beginning of design event routing for the purposes of evaluating peak outflows.

D. The Manning Equation shall be used to calculate the capacity of watercourses. Manning 'n' values used in the calculations shall be consistent with the table presented in Appendix C or other appropriate standard engineering 'n' value resources. Pipe capacities shall be determined by methods acceptable to the municipality.

E. The Pennsylvania DEP, Chapter 105, Rules and Regulations, apply to the construction, modification, operation or maintenance of both existing and proposed dams, water obstructions and encroachments throughout the watershed. Criteria for design and construction of stormwater management facilities according to this chapter may differ from the criteria that are used in the permitting of dams under the Dam Safety Program.

[5] Editor's Note: Appendix H is included as an attachment to this chapter.

§ 23-309 Water Quality Requirements After Regulated Earth Disturbance Activities Are Complete.

[Ord. 2014-03, 9/8/2014]

1. No regulated earth disturbance activities within the Township shall commence until approval by the Township of a plan which demonstrates compliance with state water quality requirements after construction is complete.

2. The BMPs must be designed, implemented, and maintained to meet state water quality requirements and any other more stringent requirements that may be adopted from time to time by the Township or other governmental entity or authority with jurisdiction.

3. To control post-construction stormwater impacts from regulated earth disturbance activities, state water quality requirements may be met by BMPs, including site design, which provide for replication of preconstruction stormwater infiltration and runoff conditions, so that post-construction stormwater discharges do not degrade the physical, chemical or biological characteristics of receiving waters. As described in the PADEP Comprehensive Stormwater Management Policy (#392-0300-002, September 28, 2002), this may be achieved by the following:

A. Infiltration. Replication of preconstruction stormwater infiltration conditions;

B. Treatment. Use of water quality treatment BMPs to filter out the chemical and physical pollutants from the stormwater runoff, and

C. Stream Bank and Streambed Protection. Management of volume and rate of post-construction stormwater discharges to prevent physical degradation of receiving waters (e.g., from scouring).

4. PADEP has regulations that require townships ensure design, implementation, and maintenance of best management practices (BMPs) that control runoff from new development and redevelopment after regulated earth disturbance activities are complete. These requirements include the need to implement post-construction stormwater BMPs with assurance of long-term operations and maintenance of those BMPs.

5. Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate PADEP regional office must be submitted to the Township.

6. BMP operations and maintenance requirements are described in Part 7 of this chapter.