A. 
Applicants proposing regulated activities in Neshaminy Creek and Delaware River South Watersheds which do not fall under the exemption criteria shown in § 430-302 shall submit a drainage plan consistent with the Neshaminy Creek and Delaware River South Watershed Stormwater Management Plan to the Township for review. The stormwater management criteria of this chapter shall apply to the total proposed development even if development is to take place in stages.
B. 
The applicant is required to find practicable alternatives to the surface discharge of stormwater, the creation of impervious surfaces and the degradation of waters of the commonwealth, and must maintain as much as possible the natural hydrologic regime.
C. 
The drainage plan must be designed consistent with the sequencing provisions of § 430-504 to ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with Article IV of this chapter.[1]
[1]
Editor's Note: Amended at time of adoption of Code (see Ch. 1, General Provisions, Art. I).
D. 
Stormwater drainage systems shall be designed in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities or open channels consistent with this chapter.
E. 
Existing points of concentrated drainage that discharge onto adjacent property shall not be altered in any manner which could cause property damage without permission of the affected property owner(s) and shall be subject to any applicable discharge criteria specified in this chapter.
F. 
Areas of existing diffused drainage discharge, whether proposed to be concentrated or maintained as diffused drainage areas, shall be subject to any applicable discharge criteria in the general direction of existing discharge, except as otherwise provided by this chapter. If diffused drainage discharge is proposed to be concentrated and discharged onto adjacent property, the applicant must document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding or other impacts will result from the concentrated discharge.
G. 
Where a development site is traversed by existing streams, drainage easements shall be provided conforming to the line of such streams. The terms of the easement shall conform to the stream buffer requirements contained in § 430-506G of this chapter.
H. 
Any stormwater management facilities regulated by this chapter that would be located in or adjacent to waters of the commonwealth or delineated wetlands shall be subject to approval by DEP through the joint permit application or the environmental assessment approval process or, where deemed appropriate, by the DEP general permit process. When there is a question as to whether wetlands may be involved, it is the responsibility of the applicant or his agent to show that the land in question cannot be classified as wetlands, otherwise approval to work in the area must be obtained from DEP.
I. 
Any proposed stormwater management facilities regulated by this chapter that would be located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
J. 
Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, etc., is encouraged where soil conditions permit in order to reduce the size or eliminate the need for detention facilities or other structural BMPs.
K. 
All stormwater runoff shall be pretreated for water quality prior to discharge to surface water or groundwater.
L. 
All regulated activities within the Township shall be designed, implemented, operated and maintained to meet the purposes of this chapter, through these two elements:
(1) 
Erosion and sediment control during the earth disturbance activities (e.g., during construction); and
(2) 
Water quality protection measures after completion of earth disturbance activities (i.e., after construction), including operations and maintenance.
M. 
No regulated earth disturbance activities within the Township shall commence until the requirements of this chapter are met.
N. 
Post-construction water quality protection shall be addressed as required by § 430-506.
O. 
Operations and maintenance of permanent stormwater BMPs shall be addressed as required by Article VIII.
P. 
All best management practices (BMPs) used to meet the requirements of this chapter shall conform to the state water quality requirements and any more stringent requirements as set forth by the Township.
Q. 
Techniques described in Appendix E to this chapter (Low-Impact Development Practices)[2] shall be considered because they reduce the costs of complying with the requirements of this chapter and the state water quality requirements.
[2]
Editor's Note: Appendix E is included as an attachment to this chapter.
R. 
In selecting the appropriate BMPs or combinations thereof, the applicant shall consider the following:
(1) 
Total contributing area.
(2) 
Permeability and infiltration rate of the site soils.
(3) 
Slope and depth to bedrock.
(4) 
Seasonal high-water table.
(5) 
Proximity to building foundations and wellheads.
(6) 
Erodibility of soils.
(7) 
Land availability and configuration of the topography.
(8) 
Peak discharge and required volume control.
(9) 
Stream-bank erosion.
(10) 
Effectiveness of the BMPs to mitigate potential water quality problems.
(11) 
The volume of runoff that will be effectively treated.
(12) 
The nature of the pollutant being removed.
(13) 
Maintenance requirements.
(14) 
Creation/protection of aquatic and wildlife habitat.
(15) 
Recreational value.
S. 
The applicant may meet the stormwater management criteria through off-site stormwater management measures as long as the proposed measures are in the same subwatershed as shown in Appendix D to this chapter.[3]
[3]
Editor's Note: Appendix D is included as an attachment to this chapter.
T. 
All best management practices (BMPs) used to meet the requirements of this chapter shall conform to the state water quality requirements and any more stringent requirements as determined by the Township.
The following permit requirements may apply to certain regulated earth disturbance activities and must be met prior to commencement of regulated earth disturbance activities, as applicable:
A. 
All regulated earth disturbance activities subject to permit requirements by DEP under regulations at 25 Pa. Code Chapter 102.
B. 
Work within natural drainageways subject to permit by DEP under 25 Pa. Code Chapter 105.
C. 
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.
D. 
Any stormwater management facility that would be located on a state highway right-of-way, or require access from a state highway, shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
E. 
Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area and any facility which may constitute a dam subject to permit by DEP under 25 Pa. Code Chapter 105.
A. 
No regulated earth disturbance activities within the Township shall commence until the Township approves an erosion and sediment control plan for construction activities.
B. 
DEP has regulations that require an erosion and sediment control plan under 25 Pa. Code § 102.4(b).
C. 
The Bucks County Conservation District shall review and approve any earth disturbance activity of 1,000 square feet or more.
D. 
In addition, under 25 Pa. Code Chapter 92,[1] a DEP NPDES construction activities permit is required for regulated earth disturbance activities when there is land disturbance greater than one acre.
[1]
Editor's Note: Chapter 92 of the Pa. Code was reserved 10-8-2010. See now 25 Pa. Code Ch. 92a, National Pollutant Discharge Elimination System (NPDES) Permitting, Monitoring and Compliance.
E. 
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 Township.
F. 
A copy of the erosion and sediment control plan and any required permit, as required by DEP regulations, shall be available on the project site at all times.
G. 
Additional erosion and sediment control design standards and criteria are recommended to be applied where infiltration BMPs are proposed. They shall include the following:
(1) 
Areas proposed for infiltration BMPs shall be protected from sedimentation and compaction during the construction phase to maintain maximum infiltration capacity. Barriers such as orange construction fencing should be used to protect and keep construction traffic in the area where infiltration BMPs are proposed. Inlet or pipes that are installed to these systems should be completely sealed or protected and monitored until the drainage areas are completely stabilized.
(2) 
Infiltration BMPs shall not be constructed nor receive runoff until the entire contributory drainage area to the infiltration BMP has achieved final stabilization.
A. 
The design of all regulated activities shall include the following to minimize stormwater impacts.
(1) 
The applicant shall find practicable alternatives to the surface discharge of stormwater, such as those listed in Appendix B to this chapter, Table B-5,[1] the creation of impervious surfaces and the degradation of waters of the commonwealth, and must maintain as much as possible the natural hydrologic regime of the site.
[1]
Editor's Note: Appendix B is included as an attachment to this chapter.
(2) 
An alternative is practicable if it is available and capable of implementation after taking into consideration existing technology and logistics in light of overall project purposes and other Township requirements.
(3) 
All practicable alternatives to the discharge of stormwater are presumed to have less adverse impact on quantity and quality of waters of the commonwealth unless otherwise demonstrated.
B. 
The applicant shall demonstrate that the regulated activities were designed in the following sequence. The goal of the sequence is to minimize the increases in stormwater runoff and impacts to water quality resulting from the proposed regulated activity:
(1) 
Prepare an existing resource and site analysis map (ERSAM), showing environmentally sensitive areas, including but not limited to steep slopes, ponds, lakes, streams, wetlands, hydric soils, vernal pools (aka "natural springs"), stream buffers, hydrologic soil groups, land development, any existing recharge areas, potential infiltration areas or permeable soil areas and other requirements outlined in Chapter 440, Subdivision and Land Development, shall also be included.
(2) 
Establish a stream buffer according to § 430-506G.
(3) 
Prepare a draft project layout avoiding sensitive areas identified in § 430-504B(1) and minimizing total site earth disturbance as much as possible. The ratio of disturbed area to the entire site area and measures taken to minimize earth disturbance shall be included in the ERSAM.
(4) 
Identify site-specific existing conditions drainage areas, discharge points, recharge areas and hydrologic soil groups A and B (areas conducive to infiltration).
(5) 
Evaluate nonstructural stormwater management alternatives:
(a) 
Minimize earth disturbance.
(b) 
Minimize impervious surfaces.
(c) 
Break up large impervious surfaces.
(6) 
Satisfy groundwater recharge (infiltration) objective (§ 430-505) and provide for stormwater pretreatment prior to infiltration.
(7) 
Provide for water quality protection in accordance with § 430-506, Water quality requirements.
(8) 
Provide stream-bank erosion protection in accordance with § 430-507, Stream-bank erosion requirements.
(9) 
Determine the watershed and management district the site falls into (Appendix D to this chapter[2]) and conduct an existing conditions runoff analysis.
[2]
Editor's Note: Appendix D is included as an attachment to this chapter.
(10) 
Prepare final project design to maintain existing conditions drainage areas and discharge points, to minimize earth disturbance and impervious surfaces and, to the maximum extent possible, ensure the remaining site development has no surface or point discharge.
(11) 
Conduct a proposed conditions runoff analysis based on the final design that meets the management district requirements (§ 430-508).
(12) 
Manage any remaining runoff prior to discharge, through detention, bioretention, direct discharge or other structural control.
A. 
Maximizing the groundwater recharge capacity of the area being developed is required. Design of the infiltration facilities shall consider groundwater recharge to compensate for the reduction in the recharge that occurs when the ground surface is disturbed or impervious surface is created. It is recommended that roof runoff be directed to infiltration BMPs which may be designed to compensate for the runoff from parking areas or driveways. These measures are required to be consistent with § 430-103 and take advantage of utilizing any existing recharge areas.
B. 
Infiltration may not be feasible on every site due to site-specific limitations such as soil type. If it cannot be physically accomplished, then the design professional shall be responsible to show that this cannot be physically accomplished. Soils testing and geotechnical evaluation of the site soils should be performed and submitted to verify that the infiltration requirements cannot be met. If it can be physically accomplished, then the volume of runoff to be infiltrated shall be determined from § 430-505C(2), depending on demonstrated site conditions, and shall be the greater of the two volumes.
C. 
Minimum requirements. Infiltration BMPs shall meet the following minimum requirements:
(1) 
Infiltration BMPs intended to receive runoff from developed areas shall be selected based on suitability of soils and site conditions and shall be constructed on soils that have the following characteristics:
(a) 
A minimum depth of 24 inches, preferably 36 inches, between the bottom of the BMP and the top of the limiting zone (e.g., seasonal high-water table, groundwater, bedrock, etc.).
(b) 
An infiltration rate sufficient to accept the additional stormwater load and dewater completely as determined by field tests conducted by the applicant's design professional.
(c) 
The infiltration facility shall be capable of completely infiltrating the retention (infiltration) volume (Rev) within four days (96 hours).
(d) 
Pretreatment shall be provided prior to infiltration.
(e) 
The requirements for recharge are applied to all disturbed areas, even if they are ultimately to be an undeveloped land use such as grass, unless the applicant can demonstrate through construction sequencing and use of special construction techniques and machinery that this is not the case. Studies have found that compaction of the soils during disturbance reduces their infiltrative capacity.
(2) 
The recharge volume (Rev) shall be computed by first obtaining the infiltration requirement using methods in either Subsection C(2)(a) or (b), then multiplying by the total proposed impervious area. The overall required recharge volume for a site is computed by multiplying total impervious area by the infiltration requirement.
(a) 
NRCS Curve Number equation. The following criteria shall apply.
[1] 
The NRCS runoff shall be utilized to calculate infiltration requirements (P) in inches.
Equation 405.1
For zero runoff: P = I (Infiltration) (inch) = (200/CN) - 2
Where:
P
=
I = infiltration requirement (inches)
CN
=
SCS (NRCS) curve number of the existing conditions contributing to the recharge facility
[2] 
This equation can be displayed graphically in, and the infiltration requirement can also be determined from, Figure 405.1.
[3] 
The recharge volume (Rev) required would therefore be computed as:
Rev = I (inches) * percent impervious area (square feet)/12 (inches) = cubic feet (cf)
An asterisk (*) in equations denotes multiplication.
(b) 
Annual recharge water budget approach.
[1] 
Within the Neshaminy Creek Watershed it has been determined that infiltrating 0.6 inches of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of Subsection C(2)(a) cannot be achieved, then 0.6 inches of rainfall shall be infiltrated from all impervious areas, up to an existing site conditions curve number of 77. Above a curve number of 77, Equation 405.1 or the curve in Figure 405.1 should be used to determine the infiltration requirement.
Where:
I
=
0.6 inches
The recharge volume (Rev) required would therefore be computed as: Rev = I (inches)/12 (inches) * impervious area (square feet) = cubic feet (cf)
Figure 405.1.
Infiltration Requirement Based upon NRCS Curve Number for the Neshaminy Creek Watershed:
430 Figure 405p1.tif
[2] 
Within the Delaware River South Watershed, it has been determined that infiltrating 0.5 inches of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of Subsection C(2)(a) cannot be achieved, then 0.5 inches of rainfall shall be infiltrated from all impervious areas, up to an existing site conditions curve number of 81. Above a curve number of 81, Equation 405.1 or the curve in Figure 405.2 should be used to determine the infiltration requirement.
Where:
I
=
0.5 inches
The recharge volume (Rev) required would therefore be computed as: Rev = I (inches)/12 (inches) * impervious area (square feet) = cubic feet (cf)
Figure 405.2.
Infiltration Requirement Based upon NRCS Curve Number for the Delaware River South Watershed:
Required Infiltration (I) in inches by NRCS CN
430 Figure 405p2.tif
(3) 
The recharge values derived from these methods are the minimum volumes the applicant must control through an infiltration/recharge BMP facility. However, if a site has areas of soils where additional volume of infiltration can be achieved, the applicant is encouraged to recharge as much of the stormwater runoff from the site as possible.
D. 
Soils. A detailed soils evaluation of the project site shall be required to determine the suitability of infiltration facilities. The evaluation shall be performed by a qualified design professional and, at a minimum, address soil permeability, depth to bedrock and subgrade stability. The general process for designing the infiltration BMP shall be:
(1) 
Analyze hydrologic soil groups as well as natural and man-made features within the site to determine general areas of suitability for infiltration practices. In areas where development on fill material is under consideration, conduct geotechnical investigations of subgrade stability; infiltration is not permitted to be ruled out without conducting these tests.
(2) 
Provide field tests such as double-ring infiltrometer or hydraulic conductivity tests (at the level of the proposed infiltration surface) to determine the appropriate hydraulic conductivity rate. Percolation tests are not recommended for design purposes.
(3) 
Design the infiltration structure for the required retention (Rev) volume based on field-determined capacity at the level of the proposed infiltration surface.
(4) 
Where the recharge volume requirement cannot be physically accomplished due to the results of the field soils testing, supporting documentation and justification shall be supplied to the Township with the drainage plan.
(5) 
If on-lot infiltration structures are proposed by the applicant's design professional, it must be demonstrated to the Township that the soils are conducive to infiltrate on the lots identified.
E. 
Stormwater hot spots. Following is a list of examples of designated hot spots. If a site is designated as a hot spot, it has important implications for how stormwater is managed. First and foremost, untreated stormwater runoff from hot spots shall not be allowed to recharge into groundwater where it may contaminate water supplies. Therefore, the Rev requirement shall not be applied to development sites that fit into the hot spot category (the entire WQv must still be treated). Second, a greater level of stormwater treatment shall be considered at hot spot sites to prevent pollutant washoff after construction. The EPA's NPDES stormwater program requires some industrial sites to prepare and implement a stormwater pollution prevention plan.
(1) 
Examples of hot spots:
(a) 
Vehicle salvage yards and recycling facilities.
(b) 
Vehicle fueling stations.
(c) 
Vehicle service and maintenance facilities.
(d) 
Vehicle and equipment cleaning facilities.
(e) 
Fleet storage areas (bus, truck, etc.).
(f) 
Industrial sites (based on Standard Industrial Codes defined by the United States Department of Labor).
(g) 
Marinas (service and maintenance).
(h) 
Outdoor liquid container storage.
(i) 
Outdoor loading/unloading facilities.
(j) 
Public works storage areas.
(k) 
Facilities that generate or store hazardous materials.
(l) 
Commercial container nursery.
(m) 
Other land uses and activities as designated by an appropriate review authority.
(2) 
The following land uses and activities are not normally considered hot spots:
(a) 
Residential streets and rural highways.
(b) 
Residential development.
(c) 
Institutional development.
(d) 
Office developments.
(e) 
Nonindustrial rooftops.
(f) 
Pervious areas, except golf courses and nurseries [which may need an integrated pest management (IPM) plan].
(3) 
While large highways [average daily traffic volume (ADT) greater than 30,000] are not designated as a stormwater hot spot; however, it is important to ensure that highway stormwater management plans adequately protect groundwater.
F. 
Extreme caution shall be exercised where infiltration is proposed in source water protection areas as defined by the local township or water authority.
G. 
Infiltration facilities shall be used in conjunction with other innovative or traditional BMPs, stormwater control facilities, and nonstructural stormwater management alternatives.
H. 
Extreme caution shall be exercised where salt or chloride (municipal salt storage) would be a pollutant since soils do little to filter this pollutant and it may contaminate the groundwater. The qualified design professional shall evaluate the possibility of groundwater contamination from the proposed infiltration facility and perform a hydrogeologic justification study if necessary.
I. 
The infiltration requirement in high quality or exceptional value waters shall be subject to the Department's Chapter 93 antidegradation regulations.
J. 
An impermeable liner will be required in detention basins where the possibility of groundwater contamination exists. A detailed hydrogeologic investigation may be required by the Township.
K. 
The Township shall require the applicant to provide safeguards against groundwater contamination for land uses that may cause groundwater contamination should there be a mishap or spill.
In addition to all other applicable provisions of this chapter, an applicant shall also comply with the following water quality requirements of this article.
A. 
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 post construction is complete.
B. 
The BMPs shall be designed, implemented and maintained to meet state water quality requirements, and any other more stringent requirements as determined by the Township.
C. 
To control post-construction stormwater impacts from regulated earth disturbance activities, state water quality requirements can 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 the receiving waters. As described in the DEP Comprehensive Stormwater Management Policy (No. 392-0300-002, September 28, 2002), this may be achieved by the following:
(1) 
Infiltration: replication of preconstruction stormwater infiltration conditions;
(2) 
Treatment: use of water quality treatment BMPs to ensure filtering out of the chemical and physical pollutants from the stormwater runoff; and
(3) 
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 and downcutting).
D. 
Developed areas shall provide adequate storage and treatment facilities necessary to capture and treat stormwater runoff.
(1) 
The retention volume computed under § 430-505 may be a component of the water quality volume if the applicant chooses to manage both components in a single facility. If the retention volume is less than the water quality volume, the remaining water quality volume may be captured and treated by methods other than infiltration BMPs. The required water quality volume (WQv) is the storage capacity needed to capture and treat a portion of stormwater runoff from the developed areas of the site produced from 90% of the average annual rainfall (P).
(2) 
To achieve this goal, the following criterion is established:
(a) 
The following calculation formula is to be used to determine the water quality storage volume, (WQv), in acre-feet of storage for the Neshaminy Creek, Little Neshaminy Creek, and Delaware South River watersheds:
Equation 406.1
WQv = [(P)(Rv)(A)]/12
Where:
WQv
=
Water Quality Volume (acre-feet)
P
=
1.00 inch for Neshaminy Creek Watershed
P
=
2.04 inches for the Delaware River South Watershed (Region 5) (obtained from PennDOT Field Manual, May 1986)
P
=
Rainfall amount equal to 90% of events producing this rainfall (inches)
A
=
Area of the project contributing to the water quality BMP (acres)
Rv
=
0.05 + 0.009(1), where 1 is the percent of the area that is impervious surface [(impervious area/A) * 100]
(b) 
This volume requirement can be accomplished by the permanent volume of a wet basin or the detained volume from other BMPs. Where appropriate, wet basins shall be utilized for water quality control and shall follow the guidelines of the BMP manuals referenced in Appendix F to this chapter.[1]
[1]
Editor's Note: Appendix F is included as an attachment to this chapter.
(c) 
Release of water can begin at the start of the storm (i.e., the invert of the water quality orifice is at the invert of the facility). The design of the facility shall provide for protection from clogging and unwanted sedimentation.
E. 
For areas within defined special protection subwatersheds which include exceptional value (EV) and high quality (HQ) waters, the temperature and quality of water and streams shall be maintained through the use of temperature-sensitive BMPs and stormwater-conveyance systems. For other waters, use of temperature-sensitive BMPs and stormwater-conveyance systems should be considered as temperature can negatively impact water quality and stream health.
F. 
To accomplish the above, the applicant shall submit original and innovative designs to the Township Engineer for review and approval. Such designs may achieve the water quality objectives through a combination of different BMPs.
G. 
If a perennial or intermittent stream passes through the site, the applicant shall create a stream buffer extending a minimum of 50 feet to either side of the top-of-bank of the channel. The buffer area shall be maintained with and encouraged to use appropriate native vegetation. (Refer to Appendix H of Pennsylvania Handbook of Best Management Practices for Developing Area for plant lists.) If the applicable rear or side yard setback is less than 50 feet, the buffer width may be reduced to 25% of the setback to a minimum of 10 feet. If an existing buffer is legally prescribed (i.e., deed, covenant, easement, etc.) and it exceeds the requirements of this chapter, the existing buffer shall be maintained.
H. 
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office must be provided to the Township.
I. 
Design of BMPs used for water quality control shall be in accordance with design specifications outlined in the Pennsylvania Stormwater Best Management Practices Manual (Draft, January 2005) or other applicable manuals. The following factors shall be considered when evaluating the suitability of BMPs used to control water quality at a given development site:
(1) 
Total contributing drainage area.
(2) 
Permeability and infiltration rate of the site soils.
(3) 
Slope and depth to bedrock.
(4) 
Seasonal high-water table.
(5) 
Proximity to building foundations and wellheads.
(6) 
Erodibility of soils.
(7) 
Land availability and configuration of the topography.
(8) 
Peak discharge and required volume control.
(9) 
Stream-bank erosion.
(10) 
Efficiency of the BMPs to mitigate potential water quality problems.
(11) 
The volume of runoff that will be effectively treated.
(12) 
The nature of the pollutant being removed.
(13) 
Maintenance requirements.
(14) 
Creation/protection of aquatic and wildlife habitat.
(15) 
Recreational value.
(16) 
Enhancement of aesthetic and property value.
J. 
To accomplish the above, the applicant shall submit original and innovative designs to the Township for review and approval. Such designs may achieve the water quality objectives through a combination of BMPs.
A. 
In addition to the control of water quality volume (in order to minimize the impact of stormwater runoff on downstream stream-bank erosion), the primary requirement is to design a BMP to detain the proposed conditions two-year, twenty-four-hour design storm to the existing conditions one-year flow using the SCS Type II distribution. Additionally, provisions shall be made (such as adding a small orifice at the bottom of the outlet structure) so that the proposed conditions one-year storm takes a minimum of 24 hours to drain from the facility from a point where the maximum volume of water from the one-year storm is captured (i.e., the maximum water surface elevation is achieved in the facility). Release of water can begin at the start of the storm (i.e., the invert of the water quality orifice is at the invert of the facility).
B. 
The minimum orifice size in the outlet structure to the BMP shall be three inches in diameter where possible, and a trash rack shall be installed to prevent clogging. On sites with small contributing drainage areas to this BMP that do not provide enough runoff volume to allow a twenty-four-hour attenuation with the three-inch orifice, the calculations shall be submitted showing this condition. Orifice sizes less than three inches can be utilized, provided that the design will prevent clogging of the intake.
C. 
In conditional direct discharge districts (District C) only (see § 430-508), the objective is not to attenuate the storms greater than the two-year recurrence interval. This can be accomplished by configuring the outlet structure not to control the larger storms or by a bypass channel that diverts only the two-year stormwater runoff into the basin or, conversely, diverts flows in excess of the two-year storm away from the basin.
A. 
The Neshaminy Creek Watershed peak rate requirements and districts are as follows:
(1) 
In order to implement the provisions of the Neshaminy Creek Watershed Stormwater Management Plan, Middletown Township is hereby divided into stormwater runoff districts, whereby specific peak release rates have been established. The districts are as follows:
Stormwater Runoff Peak Rate Districts
RR-1
100% release rate
RR-3
75% release rate
DD
Provisional direct discharge
LR
Provisional lower reaches 100% release rate
(2) 
The exact location of the stormwater runoff peak rate district boundaries as they apply to a given development site shall be determined by mapping the boundaries using the two-foot or five-foot topographic contours provided as part of the stormwater management plan developed for the site. 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 (road, culvert, bridge, etc.) to the topographic divide consistent with topography. The location of the stormwater management district boundary on a stormwater management plan shall be reviewed and verified by the Township Engineer.
(3) 
Additional stormwater design standards and criteria.
(a) 
In addition to the peak runoff rate requirements specified in Subsection A(1) above, the erosion and sedimentation control (§ 430-503), the nonstructural project design (§ 430-504), the groundwater recharge (§ 430-505), the water quality (§ 430-506), and the stream-bank erosion (§ 430-507) requirements shall be implemented. Standards for managing runoff from each subarea in the Neshaminy Creek Watershed for the two-, five-, ten-, twenty-five-, fifty- and one-hundred-year design storms are shown on the map in Appendix D.[1] Development sites located in each of the stormwater runoff peak rate districts must control proposed conditions runoff rates to existing conditions runoff rates or percentages thereof.
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
(b) 
General. Proposed conditions rates of runoff from any regulated activity shall not exceed the peak release rates of runoff from existing conditions for the design storms specified on the Stormwater Management District Watershed Map (Appendix D to this chapter[2] and § 430-508A(1) of this chapter.
[2]
Editor's Note: Appendix D is included as an attachment to this chapter.
(c) 
District boundaries. The boundaries of the stormwater runoff peak rate districts are shown on an official map that is available for inspection at the Township office and County Planning offices. A copy of the official map at a reduced scale is included in Appendix D to this chapter.[3] The exact location of the stormwater runoff peak rate district boundaries as they apply to a given development site shall be determined by mapping the boundaries using the two-foot topographic contours (or most accurate data required) provided as part of the drainage plan.
[3]
Editor's Note: Appendix D is included as an attachment to this chapter.
(d) 
Sites located in more than one district. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall meet the runoff peak rate/management district criteria for the district in which the discharge is located. 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 recombine in proximity to the site. In this case, peak discharge in any direction may follow runoff peak rate/Management District A criteria, provided that the overall site discharge meets the runoff peak rate/management district criteria for which the discharge is located.
(e) 
Off-site areas. Off-site areas that 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.
(f) 
Site areas. Where the site area to be impacted by a proposed development activity differs significantly from the total site area, only the proposed impact area utilizing stormwater management measures shall be subject to the management district criteria. In other words, unimpacted areas bypassing the stormwater management facilities would not be subject to the runoff peak rate/management district criteria.
(g) 
Provisions must also be made for safely passing the runoff greater than that occurring from the one-hundred-year design storm.
(h) 
For proposed development sites located partially within a release rate district and partially within a provisional direct discharge district, in no event shall a significant portion of the site area subject to the release rate control be drained to a discharge point(s) located in the provisional direct discharge district. All runoff from the site will be subject to the water quality requirement as stated in § 430-506 of this article.
(i) 
Alternate criteria for redevelopment sites. For redevelopment sites, one of the following minimum design parameters shall be accomplished, whichever is most appropriate for the given site conditions as determined by Township Engineer;
[1] 
Meet the full requirements specified by Table 508-1 and Subsection A(3)(a) through (i); or
[2] 
Reduce the total impervious surface on the site by at least 20%, based upon a comparison of existing impervious surface to proposed impervious surface.
B. 
Delaware River South Watershed has been divided into stormwater management districts as shown on the Watershed Map in Appendix D.[4] In addition to the requirements specified below, the erosion and sedimentation control (§ 430-503), the nonstructural project design (§ 430-504), the groundwater recharge (§ 430-505), the water quality (§ 430-506), and the stream-bank erosion (§ 430-507) requirements shall be implemented.
(1) 
Standards for managing runoff from each subarea in the Delaware River South Watershed is shown below. Development sites located in each of the A, B or C, Districts must control post-development runoff rates to predevelopment runoff rates for the design storms as follows:
Table 508-1
District
Design Storm Post Development
Design Storm Predevelopment
A
2-year
1-year
5-year
5-year
10-year
10-year
25-year
25-year
50-year
50-year
100-year
100-year
B
2-year
1-year
5-year
2-year
10-year
5-year
25-year
10-year
50-year
50-year
100-year
100-year
C*
2-year
1-year
5-year
2-year
*
In District C, development sites which can discharge directly to the Delaware River South main channel or major tributaries or indirectly to the main channel through an existing stormwater drainage system (i.e., storm sewer or tributary) may do so without control of post-development peak rate of runoff greater than the five-year storm. Sites in District C will still have to comply with the groundwater recharge criteria, the water quality criteria, and stream-bank erosion criteria. If the post-development runoff is intended to be conveyed by an existing stormwater drainage system to the main channel, assurance must be provided that such system has adequate capacity to convey the flows greater than the two-year predevelopment peak flow or will be provided with improvements to furnish the required capacity. When adequate capacity in the downstream system does not exist and will not be provided through improvements, the post-development peak rate of runoff must be controlled to the predevelopment peak rate as required in District A provisions (i.e., ten-year post-development flows to ten-year predevelopment flows) for the specified design storms.
(2) 
Post-development peak rates of runoff from any regulated activity shall meet the peak release rates of runoff prior to development for the design storms specified on the Stormwater Management District Watershed Map (Appendix D[5]) and Subsection B(1).
[5]
Editor's Note: Appendix D is included as an attachment to this chapter.
(3) 
The boundaries of the Delaware River South Stormwater Management Districts are shown on an official stormwater district map that is available for inspections at the Township office. A copy of the map at a reduced scale is included in Appendix D.[6] 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 (or most accurate data required) provided as part of the drainage plan.
[6]
Editor's Note: Appendix D is included as an attachment to this chapter.
(4) 
For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall be the predevelopment peak discharge for that subarea as indicated in Subsection B(1). 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 recombine 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.
(5) 
Off-site areas that 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.
(6) 
Site areas. Where the area of a site being impacted by a proposed development activity differs significantly from the total site area, only the proposed impact area utilizing stormwater management measures shall be subject to the management district criteria. Unimpacted or undisturbed areas that do flow into or are bypassing the stormwater management facilities would not be subject to the management district criteria.
(7) 
For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less restrictive runoff control (including no detention) if the applicant can prove that no harm would be caused by discharging at a higher runoff rate than that specified by the plan. The no-harm option is used when a applicant can prove that the post-development hydrographs can match predevelopment hydrographs, or if it can be proved that the post-development conditions will not cause increases in peaks at all points downstream. Proof of no harm would have to be shown based upon the following downstream impact evaluation, which shall include a downstream hydraulic capacity analysis consistent with Subsection B(8) to determine if adequate hydraulic capacity exists. The land applicant shall submit to the Township this evaluation of the impacts due to increased downstream stormwater flows in the watershed.
(a) 
The downstream impact evaluation shall include hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications due to the proposed development upon a dam, highway, structure, natural point of restricted stream flow, or any stream channel section, established with the concurrence of the Township.
(b) 
The evaluation shall continue downstream until the increase in flow diminishes due to additional flow from tributaries and/or stream attenuation.
(c) 
The peak flow values to be used for downstream areas for the design return period storms (two-, five-, ten-, twenty-five-, fifty- and one-hundred-year) shall be the values from the calibrated model for the Delaware River South Watershed. These flow values can be obtained from the watershed plan.
(d) 
Applicant-proposed runoff controls that 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 B(9).
(e) 
Financial considerations shall not constitute grounds for granting a no-harm exemption.
(f) 
Capacity improvements may be provided as necessary to implement the no-harm option which proposes specific capacity improvements to provide that a less stringent discharge control would not create any harm downstream.
(g) 
No-harm justifications shall be submitted by the applicant as part of the drainage plan submission per Article IV.
(8) 
Any downstream hydraulic 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 one-and-one-half-year return period event within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the Department of Environmental Protection's Erosion and Sediment Pollution Control Program Manual.
(b) 
Natural or man-made channels or swales must be able to convey 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 the Department of Environmental Protection's Chapter 105 regulations (if applicable) and, at minimum, pass the increased twenty-five-year return period runoff.
(9) 
Regional detention alternatives.
(a) 
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 applicants.
(b) 
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 on a case-by-case basis using the hydrologic model of the watershed consistent with protection of the downstream watershed areas. "Hydrologic model" refers to the calibrated model as developed for the stormwater management plan. It is a requirement that, even if regional basins are proposed for the water quantity control, that the water quality, stream-bank erosion and recharge criteria be accomplished on site, or as close to the source of the runoff as possible.
[4]
Editor's Note: Appendix D is included as an attachment to this chapter.
A. 
Stormwater runoff from all development sites with a drainage area of greater than 200 acres shall be calculated using a generally accepted calculation technique that is based on the NRCS Soil-Cover-Complex Method. Table 509-1 summarizes acceptable computation methods, and the method selected by the design professional shall be based on the individual limitations and suitability of each method for a particular site. The Township may allow the use of the Rational Method to estimate peak discharges from drainage areas that contain less than 200 acres. The Soil-Complex Method shall be used for drainage areas greater than 200 acres.
Table 509-1
Acceptable Computation Methodologies for Stormwater Management 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 package based on TR-55)
USDA NRCS
Applicable for land development 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)
For sites less than 200 acres, or as approved by the Township and/or Township Engineer
Other methods
Varies
Other computation methodologies approved by the Township and/or Township Engineer
B. 
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 region in which they are located as presented in Table B-1 in Appendix B-1 to this chapter.[1] 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. The Alternating Block Method shown in Figure B-1, or the SCS Type II S Curve, Figure B-3, in Appendix B[2], shall be used for the rainfall distribution.
[1]
Editor's Note: Appendix B-1 is included as an attachment to this chapter.
[2]
Editor's Note: Appendix B is included as an attachment to this chapter.
C. 
For the purposes of existing conditions flow rate determination, the undeveloped portion of the site shall be considered as meadow in good condition, unless the natural ground cover generates a lower curve (CN) number or Rational C value (i.e., forest), as listed in Table B-2 or B-3 in Appendix B to this chapter.[3] For the developed portion of the site, the CN or C value shall be based upon actual land cover conditions.
[3]
Editor's Note: Appendix B is included as an attachment to this chapter.
D. 
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods from the Region 5 Curves from the Pennsylvania Department of Transportation Storm-Duration-Frequency Chart (Figure B-4).[4] 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.
[4]
Editor's Note: See Appendix B which is included as an attachment to this chapter.
E. 
Runoff curve numbers (CN) for both existing and proposed conditions to be used in the Soil-Cover-Complex Method shall be obtained from Table B-2 in Appendix B to this chapter.[5]
[5]
Editor's Note: Appendix B is included as an attachment to this chapter.
F. 
Runoff coefficients (c) for both existing and proposed conditions for use in the Rational Method shall be obtained from Table B-3 in Appendix B to this chapter.[6]
[6]
Editor's Note: Appendix B is included as an attachment to this chapter.
G. 
The designer shall consider that the runoff from proposed sites graded to the subsoil will not have the same runoff conditions as the site under existing conditions, even after topsoiling or seeding. The designer shall increase his proposed condition CN or "C" to better reflect proposed soil conditions.
H. 
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 B-4 in Appendix B to this chapter.[7]
[7]
Editor's Note: Appendix B is included as an attachment to this chapter.
I. 
Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this chapter using any generally accepted hydraulic analysis technique or method.
J. 
The design of any stormwater detention 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. The Township may approve the use of any generally accepted full hydrograph approximation technique that shall use a total runoff volume that is consistent with the volume from a method that produces a full hydrograph.
A. 
Any stormwater facility located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
B. 
All wet basin designs shall incorporate biologic controls consistent with the West Nile virus guidance found in Appendix G.[1]
[1]
Editor's Note: Appendix G is included as an attachment to this chapter.
C. 
Any stormwater management facility (i.e., detention basin) required or regulated by this chapter, designed to store runoff and requiring a berm or earthen embankment, shall be designed to provide an emergency spillway to handle flow up to and including the one-hundred-year proposed conditions. The height of embankment must provide a minimum one foot of freeboard above the maximum pool elevation, computed when the facility functions for the one-hundred-year proposed conditions inflow. Should any stormwater management facility require a dam safety permit under DEP Chapter 105, the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety. Chapter 105 may be required to pass storms larger than the one-hundred-year event.
D. 
Any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls or stream enclosures), and any work involving wetlands governed by DEP Chapter 105 regulations (as amended or replaced from time to time by DEP), shall be designed in accordance with Chapter 105 and will require a permit from DEP.
E. 
Any other drainage conveyance facility that does not fall under Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm with a minimum one foot of freeboard measured below the lowest point along the top of the roadway. Any facility that constitutes a dam as defined in DEP Chapter 105 regulations may require a permit under dam safety regulations. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.
F. 
Any drainage conveyance facility and/or channel not governed by Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the one-hundred-year design storm. Conveyance facilities to or exiting from stormwater management facilities (i.e., detention basins) shall be designed to convey the design flow to or from that structure. Roadway crossings located within designated floodplain areas must be able to convey runoff from a one-hundred-year design storm. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.
G. 
Storm sewers must be able to convey proposed conditions runoff from a one-hundred-year design storm without surcharging inlets, where appropriate.
H. 
Adequate erosion protection shall be provided along all open channels, and at all points of discharge.
I. 
The design of all stormwater management facilities shall incorporate sound engineering principles and practices. The Township reserves the right to disapprove any design that would result in construction in or continuation of a stormwater problem area.