A. 
Applicants proposing regulated activities in the municipality that do not fall under the exemption criteria shown in § 101-6 shall submit a drainage plan consistent with this chapter and any respective Act 167 stormwater management plan(s) to the municipality 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 § 101-19 to ensure maintenance of the natural hydrologic regime, to promote groundwater recharge, and to protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with Article IV of this chapter.
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 § 101-21G 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 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 municipality shall be designed, implemented, operated, and maintained to meet the purposes of this chapter, through these two elements:
(1) 
Erosion and sediment control during 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 municipality shall commence until the requirements of this chapter are met.
N. 
Post-construction water quality protection shall be addressed as required by § 101-21.
O. 
Operations and maintenance of permanent stormwater BMPs shall be addressed as required by Article VII.
P. 
All 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 municipality.
Q. 
Techniques described in Appendix C, Low-Impact Development Practices,[1] of this chapter shall be considered because they reduce the costs of complying with the requirements of this chapter and the state water quality requirements.
[1]
Editor's Note: Said appendix is on file in the Borough offices.
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's 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) 
Streambank 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 A.[2]
[2]
Editor's Note: Said appendix is on file in the Borough offices.
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 encroaches on a state highway right-of-way or requires access from a state highway shall be subject to approval by PennDOT.
E. 
Culverts, bridges, storm sewers, or any other facilities which must pass or convey flows from the tributary area and any facility which may constitute a dam are subject to a permit from DEP under 25 Pa. Code Chapter 105.
A. 
No regulated earth disturbance activities within the municipality shall commence until the municipality receives an approval from the Conservation District of an erosion and sediment control plan for construction activities.
B. 
DEP has regulations that require an erosion and sediment control plan for any earth disturbance activity of 5,000 square feet or more, under 25 Pa. Code § 102.4(b).
C. 
In addition, under 25 Pa. Code Chapter 92,[1] a DEP permit for stormwater discharges associated with construction activities is required for land disturbances greater than one acre.
[1]
Editor's Note: Chapter 92 was reserved 10-8-2010. See now 25 Pa. Code Ch. 92a.
D. 
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.
E. 
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.
F. 
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. Additional measures, such as placement of orange construction fencing around proposed infiltration BMPs during construction to minimize or eliminate traffic overtop of these areas, and the temporary sealing off of pipes and inlet connections to infiltration BMPs to prevent sediment clogging, should be given consideration.
(2) 
Infiltration BMPs shall not be constructed nor receive runoff until the entire drainage area contributory 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 D, Table D-4,[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: Said appendix is on file in the Borough offices.
(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 municipal 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, stream buffers, hydrologic soil groups, wooded areas, and potential infiltration areas. Land development, any existing recharge areas, and other requirements outlined in the municipal SALDO shall also be included.[2]
[2]
Editor's Note: See Ch. 102, Subdivision and Land Development.
(2) 
Establish a stream buffer according to § 101-21G.
(3) 
Prepare a draft project layout avoiding sensitive areas identified in § 101-19B(1).
(4) 
Identify site-specific existing conditions drainage areas, discharge points, recharge areas, and hydrologic soil groups A and B (areas conducive to infiltration). Infiltration should still be considered in well-draining soils listed as hydrologic soil group C, but additional soils testing should be performed to verify on-site conditions and placement of these BMPs.
(5) 
Evaluate nonstructural stormwater management alternatives:
(a) 
Minimize earth disturbance.
(b) 
Minimize impervious surfaces.
(c) 
Disconnect large impervious surfaces.
(6) 
Satisfy the groundwater recharge (infiltration) objective, § 101-20, and provide for stormwater pretreatment prior to infiltration.
(7) 
Provide for water quality protection in accordance with § 101-21, Water quality requirements.
(8) 
Provide streambank erosion protection in accordance with § 101-22, Streambank erosion requirements.
(9) 
Conduct an existing conditions runoff analysis.
(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, to ensure the remaining site development has no surface or point discharge.
(11) 
Conduct a proposed conditions runoff analysis based on the final design.
(12) 
Manage any remaining runoff prior to discharge through detention, bioretention, direct discharge, or other structural control.
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 that may be designed to compensate for the runoff from parking areas. These measures are required to be consistent with § 101-3 and to take advantage of utilizing any existing recharge areas. 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. Appropriate soils testing and/or geotechnical evaluation should be included as part of any documentation for infiltration BMPs. If it can be physically accomplished, then the volume of runoff to be infiltrated shall be determined from § 101-20A(2).
A. 
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., SHWT, 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 recharge (infiltration) volume (Rev) between 24 hours to 72 hours.
(d) 
Pretreatment shall be provided prior to infiltration.
(2) 
The size of the infiltration facility shall be based upon the net two-year volume approach, where the recharge (infiltration) volume (Rev) to be captured and infiltrated shall be the volume difference between the predevelopment two-year, twenty-four-hour storm event and post-development two-year, twenty-four-hour storm event.
(3) 
The recharge volume calculated using this section is the minimum volume the applicant must control through an infiltration BMP facility. However, if a site has areas of soils where additional volume of recharge can be achieved, the applicant is encouraged to infiltrate as much of the stormwater runoff from the site as possible.
B. 
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 may not 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 recharge volume (Rev) based on field-determined capacity at the level of the proposed infiltration surface.
(4) 
If on-lot infiltration structures are proposed by the applicant's design professional, it must be demonstrated to the municipality that the soils are conducive to infiltrate on the lots identified.
C. 
Stormwater hotspots. Below is a list of examples of designated hotspots. If a site is designated as a hotspot, it has important implications for how stormwater is managed. First and foremost, untreated stormwater runoff from hotspots 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 hotspot category (the entire WQv must still be treated). Second, a greater level of stormwater treatment shall be considered at hotspot sites to prevent pollutant washoff after construction. The Environmental Protection Agency's (EPA) NPDES stormwater program requires some industrial sites to prepare and implement a stormwater pollution prevention plan.
(1) 
Examples of hotspots:
(a) 
Vehicle salvage yards and recycling facilities.
(b) 
Vehicle fueling stations.
(c) 
Vehicle service and maintenance facilities.
(d) 
Vehicle and equipment cleaning facilities.
(e) 
Fleet storage areas (bus, truck, etc.).
(f) 
Industrial sites based on Standard Industrial Codes.
(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 hotspots:
(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.
(3) 
While large highways (average daily traffic volume [ADT] greater than 30,000) are not designated as stormwater hotspots, it is important to ensure that highway stormwater management plans adequately protect groundwater.
D. 
Extreme caution shall be exercised where infiltration is proposed in SWPAs as defined by the local municipality or water authority.
E. 
Infiltration facilities shall be used in conjunction with other innovative or traditional BMPs, stormwater control facilities, and nonstructural stormwater management alternatives.
F. 
Extreme caution shall be exercised where salt or chloride would be a pollutant, such as municipal salt storage, 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. Specific consideration should be given to the particular type of salt or deicing material to be stored within this watershed in regards to its potential long-term effects on the soils.
G. 
The infiltration requirement in HQ or EV waters shall be subject to the Department's Chapter 93 antidegradation regulations.[1]
[1]
Editor's Note: See 25 Pa. Code Chapter 93.
H. 
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 municipality.
I. 
The municipality 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.
The applicant shall comply with the following water quality requirements of this article:
A. 
No regulated earth disturbance activities within the municipality shall commence until approval by the municipality of a plan that demonstrates compliance with post-construction state water quality requirements.
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 municipality.
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 the filtering out of the chemical and physical pollutants from the stormwater runoff; and
(3) 
Streambank and streambed protection: management of volume and rate of post-construction stormwater discharges to prevent physical degradation of receiving waters (e.g., from scouring).
D. 
Storage and treatment facilities.
(1) 
Developed areas shall provide adequate storage and treatment facilities necessary to capture and treat stormwater runoff. If site conditions allow for infiltration, the water quality volume and the recharge volume are the same volume and may be managed in a single facility. If infiltration cannot be physically accomplished, the water quality volume should be calculated using the net two-year volume approach described in § 101-20A(2). In this case, the water quality volume may be captured and treated by methods other than infiltration BMPs.
(2) 
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 E.[1]
[1]
Editor's Note: Said appendix is on file in the Borough offices.
(3) 
The water quality volume shall take a minimum of 24 hours to be discharged from a BMP facility. Release of the water quality volume 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 that include EV and HQ waters, the temperature and quality of water and streams shall be maintained through the use of temperature-sensitive BMPs and stormwater conveyance systems.
F. 
To accomplish the above, the applicant shall submit original and innovative designs to the Municipal 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 10 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 B of the Pennsylvania Stormwater Best Management Practices Manual, latest version, for plant lists.) if the applicable rear or side yard setback is less than 50 feet or a stream traverses the site, the buffer width may be reduced to 25% of the setback and/or to a minimum of five 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. This does not include lakes or wetlands.
H. 
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office must be provided to the municipality. The issuance of an NPDES construction permit (or permit coverage under the statewide general permit [PAG-2]) satisfies the requirements of § 101-21A.
A. 
In addition to the control of water quality volume (in order to minimize the impact of stormwater runoff on downstream streambank 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 (post two-year to the pre one-year). 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 of the BMP shall be three inches in diameter where possible, and a trash rack shall be installed to prevent clogging. On sites with small drainage areas contributing 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 orifice.
A. 
Peak rate control. For all areas of the Borough, the design storm criteria for peak runoff rate control are designed to reduce the post-development peak flow to the predevelopment peak flow. Development sites must control proposed conditions runoff rates to the existing conditions runoff rates for the two-, five-, ten-, twenty-five-, fifty-, and 100-year storm events.
B. 
The calculated peak discharges within the Borough 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 100% release rate, provided that the overall site discharge meets the weighted average release rate.
C. 
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.
D. 
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 peak rate control standards noted above. In other words, unimpacted areas bypassing the stormwater management facilities would not be subject to the peak rate control standards.
E. 
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 West Conshohocken Borough:
(1) 
Meet the full requirements specified by Subsections A through D; 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.
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 101-24 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. Note that successors to the methods listed in Table 101-24 are also acceptable, such as WinTR55 for TR-55 and WinTR20 for TR-20. The municipality may allow the use of the Rational Method to estimate peak discharges from drainage areas that contain less than 200 acres. The Soil Cover Complex Method shall be used for drainage areas greater than 200 acres.
Table 101-24 Acceptable Computation Methodologies for Stormwater Management Plans
Method
Developed by
Applicability
TR-20 (or commercial computer package based on TR-20)
USDA NRCS
Applicable where use of full hydrology computer model is desirable or necessary
TR-55 (or commercial computer package based on TR-55)
USDA NRCS
Applicable for land development plans where limitations described in TR-55
HEC-1/HEC-HMS
U.S. Army Corps of Engineers
Applicable where use of a full hydrologic computer is desirable or necessary
PSRM
Penn State University
Applicable where use of a hydrologic 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 municipality and/or Municipal Engineer
Other methods
Varies
Other computation methodologies approved by the municipality and/or Municipal 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 D-1 in Appendix D of 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.
[1]
Editor's Note: Said appendix is on file in the Borough offices.
C. 
The following criteria shall be used for runoff calculations:
(1) 
For development sites not considered redevelopment, the ground cover used in determining the existing conditions flow rates shall be as follows:
(a) 
Wooded sites shall use a ground cover of "woods in good condition." A site shall be considered to be a wooded site where a biological community dominated by trees and other woody plants exists that covers an area of 10,000 square feet or more and contains at least 100 trees with at least 50% of those trees having a dbh of two inches or greater. I would not call this a wooded site (one two-inch tree every 10 feet).[2]
[2]
Editor's Note: So in original.
(b) 
The undeveloped portion of the site, including agriculture, bare earth, and fallow ground, shall be considered as "meadow in good condition," unless the natural ground cover generates a lower curve number (CN) or Rational "C" value (i.e., woods) as listed in Table D-2 or D-3 in Appendix D of this chapter.[3]
[3]
Editor's Note: Said appendix is on file in the Borough offices.
(c) 
Off-site land use conditions used to determine storm flows for designing storm facilities shall be based on existing land uses assuming winter or poor land cover conditions.
(2) 
For development considered redevelopment sites, the ground cover used in determining the existing conditions flow rates for the developed portion of the site shall be based upon actual land cover conditions.
D. 
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration for overland flow and return periods presented in the appropriate curves from the PennDOT Storm-Duration-Frequency Chart. (Region 4 is included in Figure D-1. The user should refer to the Atlas 14, Volume 2, Storm-Duration-Frequency Chart.) 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.
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 D-2 in Appendix D of this chapter.[4]
[4]
Editor's Note: Said appendix is on file in the Borough offices.
F. 
Runoff coefficients (c) for both existing and proposed conditions for use in the Rational Method shall be obtained from Table D-3 in Appendix D of this chapter.
G. 
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 accepted published values.
H. 
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.
I. 
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 municipality 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. 
Stormwater facilities.
(1) 
All wet basin designs shall incorporate biologic controls consistent with the West Nile guidance.
(2) 
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 100-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 100-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 100-year event.[1]
[1]
Editor's Note: See 25 Pa. Code Chapter 105.
(3) 
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.
(4) 
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.
(5) 
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 twenty-five-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 identified floodplain areas must be able to convey runoff from a 100-year design storm. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.
(6) 
Adequate erosion protection shall be provided along all open channels and at all points of discharge.
(7) 
The design of all stormwater management facilities shall incorporate sound engineering principles and practices. The municipality reserves the right to disapprove any design that would result in construction in or continuation of a stormwater problem area.
(8) 
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 the following (at a minimum):
(a) 
The maximum water depth shall not exceed six feet for a detention basin. A facility designed to have a permanent pool (i.e., retention basin) shall not exceed a maximum permanent water depth of two feet and shall be enclosed within a fence approved by the Borough Engineer.
(b) 
The minimum top width of all dams/embankments/berms shall be 10 feet.
(c) 
The interior side slopes shall not be greater than five horizontal to one vertical. The top or toe of any slope shall be located a minimum of five feet from a property line.
(d) 
All basins shall be structurally sound and shall be constructed of sound and durable materials. The completed structure and the foundation of all basins shall be stable under all probable conditions of operation. An emergency spillway shall be provided for the basin and shall be capable of discharging the 100-year peak rate of runoff that enters the basin after development, in a manner that will not damage the integrity of the facility and will not create a downstream hazard. Where practical, the emergency spillway shall be constructed in undisturbed ground. Emergency spillways shall be constructed of concrete pavers, gabions, or other similar materials approved by the Borough Engineer. An easement for inspection and repair shall be provided when the conveyance structure crosses property boundaries.
(e) 
All basins not including groundwater recharge and/or water quality storage shall include an outlet structure to permit draining the basin to a completely dry position between 24 hours and 72 hours following the end of the design rainfall, unless the Borough Engineer finds that the downstream conditions may warrant other design criteria for stormwater release. All basins that do include groundwater recharge and/or water quality storage shall include an outlet structure to permit draining the basin to the level of the groundwater recharge and/or water quality storage between 24 hours and 72 hours following the end of the design rainfall.
(f) 
A cutoff trench of relatively impervious material shall be provided beneath all embankments requiring fill material. The keyway shall be a minimum of eight feet wide and a minimum of three feet deep and have 1:1 side slopes.
(g) 
All structures passing through detention basin embankments shall have properly spaced antiseep collars installed around the pipe barrel within the normal saturation zone of the detention basin berms. The antiseep collars and their connections to the pipe barrels shall be watertight. The antiseep collars shall extend a minimum of two feet in all directions beyond the outside of the principal pipe barrel. The maximum spacing between collars shall be 14 times the minimum projection of the collar measured perpendicular to the pipe. A minimum of two antiseep collars shall be installed on each outlet pipe.
(h) 
All discharge control devices with appurtenances shall be made of reinforced concrete and stainless or hot dip galvanized steel. Bolts/ fasteners are to be stainless or galvanized steel.
(i) 
The minimum slope within a basin that does not include groundwater recharge and/or water quality storage shall be 2% positive grade to the low flow channel.
(j) 
Design storms for the computation of retention basin (where approved) volumes shall be based upon a twenty-four-hour storm with 100-year return period (a storm with a 1% chance of occurrence each year).
(k) 
The effect on downstream areas if the basin embankment fails shall be considered in the design of all basins. Where possible, the basin shall be designed to minimize the potential damage caused by such failure of the embankment.
(l) 
All structures (detention basins, cisterns, etc.), other than those used for groundwater recharge volume and water quality volume, must completely drain between 24 hours and 72 hours after the end of the design storm, unless the Borough Engineer finds that downstream conditions may warrant other design criteria for stormwater release.
(m) 
Soils used for the construction of basins shall have low erodibility factors ("K" factors).
(n) 
Unless permitted by the Floodplain Administrator, stormwater management facilities shall not be located within floodplains or within the identified floodplain areas or alluvial soils.
(o) 
Detention basins shall be designed to facilitate regular maintenance, mowing and periodic silt removal and reseeding. Shallow broad basins are preferred to steep-sided basins.
(p) 
All detention and retention basin embankments shall be placed in eight-inch maximum lifts to a minimum 95% dry density. Prior to proceeding to the next lift, compaction shall be checked by the Borough Engineer or an approved soils engineer, who shall provide the Borough Engineer with a written report. Compaction tests shall be performed using the Modified Proctor Method in accordance with ASTM D-1577. Compaction tests shall be run on the leading and trailing edge as well as the top of the berm.
(9) 
Minimum floor elevations for all structures that would be affected by a basin, other temporary impoundments, or open conveyance systems where ponding may occur shall be two feet above the 100-year water surface. If basement or underground facilities are proposed, detailed calculations addressing the effects of stormwater ponding on the structure and waterproofing and/or floodproofing design information shall be submitted for approval.
(10) 
A concentrated discharge of stormwater to an adjacent property shall be within an existing natural drainageway or watercourse, or otherwise an easement shall be required.
(11) 
All groundwater recharge facilities shall be designed to empty between 24 hours and 72 hours. All water quality facilities shall be designed so that water is released slowly for a minimum of 24 hours subsequent to any storm event. All infiltration, detention or retention facilities the volume of which will be used for stormwater management (predevelopment versus post-development) shall be designed to empty between 24 hours and 72 hours subsequent to any storm event. Volumes that will not be available within 24 hours subsequent to any storm event shall not be used for stormwater management (predevelopment versus post-development).
B. 
Stormwater conveyance systems.
(1) 
General.
(a) 
Storm sewers, culverts, bridges and related installations shall be provided:
[1] 
To permit unimpeded flow of natural watercourses and in such a manner as to protect the natural character of the watercourses and to provide regulated discharge;
[2] 
To insure adequate drainage of all low points along the line of streets; and
[3] 
To intercept stormwater runoff along streets at intervals reasonably related to the extent and grade of the area drained and to prevent substantial flow of water across intersections.
(b) 
All storm sewer system components shall conform to current PennDOT standards.
(c) 
Drainage structures which drain watershed areas in excess of 1/2 square mile (320 acres), or which have a span of eight feet or more, shall be designed for a maximum expected runoff as calculated using the Soil Conservation Service Technical Release 55, "Urban Hydrology for Small Watersheds (less than 2,000 acres)."
(d) 
The design storm for the above structures shall be a 100-year storm. A water obstruction permit shall be obtained from the Pennsylvania Department of Environmental Protection for the waterway opening before final design is undertaken.
(e) 
The cartway over the culvert or bridge shall be as wide as the ultimate width of the roadway approaches. Additional width may be required to provide sidewalk on one or both sides of the cartway.
(2) 
Storm sewer design and construction requirements.
(a) 
All storm sewer pipes, culverts and bridges (excluding detention and retention basin outfall structures), gutters and swales conveying water originating only from within the boundaries of the development site shall be designed for a twenty-five-year storm event. All storm sewer pipes, culverts and bridges (excluding detention and retention basin outfall structures) conveying water originating from off site shall be designed for a fifty-year storm event. Drainage easements shall be provided to contain and convey the 100-year-frequency flood throughout the development site. Easements shall begin at the furthest upstream property line of the proposed development site in a watershed.
(b) 
All storm sewer pipes and inlets intended to drain to detention facilities shall be designed to accommodate the 100-year storm if the bypass or overflow runoff will not reach the basin by overland flow. In cases where the bypass or overflow runoff will flow over land, a stable swale shall be constructed to accommodate the excess runoff.
(c) 
Storm sewer pipes, other than those used as roof drains, detention basin underdrains, and street subbase underdrains shall have a minimum diameter of 18 inches and be made of reinforced concrete pipe, smooth lined corrugated polyethylene pipe, or approved equivalent. Where installation conditions merit, structural calculations that address the actual design requirements will be required.
(d) 
Storm sewer pipes and culverts shall be installed on sufficient slopes to provide a minimum velocity of three feet per second when flowing full.
(e) 
All storm sewer pipe and culverts shall be laid to a minimum depth of two feet from finished subgrade to the crown of pipe in paved areas and two feet from finished grade to the crown of pipe in grassed areas.
(f) 
Curves in pipes or box culverts without an inlet or manhole are prohibited. Tee joints, elbows and wyes are also prohibited.
(g) 
Manholes, inlets, headwalls and endwalls proposed for dedication or located along streets or subject to vehicular traffic shall conform to the requirements of the PennDOT, Bureau of Design, Standards for Roadway Construction, in effect at the time the design is submitted, or as otherwise modified by the municipality.
(h) 
Headwalls and endwalls shall be used where stormwater runoff enters or leaves the storm sewer horizontally from a natural or man-made channel. PennDOT Type "DW" headwalls and endwalls shall be utilized.
(i) 
Stormwater roof drains, sump pumps, and pipes shall not directly discharge water into a street right-of-way or discharge into a sanitary sewer or storm sewer.
(j) 
All existing and natural watercourses, channels, drainage systems, wetlands and areas of surface water concentration shall be maintained in their existing condition unless an alteration is approved by the municipality and any other necessary approving body.
(k) 
Flow velocities from any storm sewer may not result in erosion of the receiving channel.
(l) 
Minimum pipe size is 18 inches.
(m) 
Minimum pipe slope shall be 0.005 foot/foot.
(n) 
Minimum drop across junctions shall be two inches. At changes in pipe diameter, pipe crowns shall be matched at junctions (manhole, inlet or junction box).
(o) 
Maximum distance between junctions shall be 300 feet.
(p) 
Runoff to proposed storm sewers and inlets shall be calculated using the Rational Method.
(q) 
The time of concentration to inlets for grate capacity calculations shall be assumed five minutes.
(r) 
All storm sewer systems shall be analyzed for both inlet and outlet control (including tailwater effects) by using the equations and nomographs as shown in the FHA's Hydraulic Design Services No. 5. In lieu of this, computer programs that calculate the actual hydraulic grade line for the storm sewer system can be used, provided all losses (friction, bend, junction, etc.) are taken into account. Documentation for the program must be submitted for approval.
(s) 
Inlet capacities shall be calculated using PennDOT or manufacturer's nomographs. Documentation for manufacturer's nomograph must be provided to the Borough Engineer.
(t) 
Manning "n" values used for design of pipes and culverts shall be in accordance with accepted published values.
(u) 
All storm sewer crossings of streets shall be perpendicular to the street center line, to the maximum extent possible.
(v) 
Storm facilities not located within a public right-of-way shall be contained in and centered within an easement. Easements shall follow property boundaries where possible.
(w) 
Adequate erosion protection shall be provided along all open channels and at all points of discharge.
(3) 
Shoulders in cut areas (without swales).
(a) 
Water flowing in the shoulder shall not encroach more than 2/3 the shoulder width during a twenty-five-year-frequency storm of five-minute duration.
(b) 
The maximum velocity as determined by Manning's Equation shall not exceed the allowable velocities for the specific type of shoulder material.
(c) 
Inlets shall be provided to control the shoulder encroachment and water velocity.
(4) 
Swales adjacent to shoulders.
(a) 
Swales in cut areas shall be designed to prevent the passage of water on the cartway during a twenty-five-year-frequency storm of five-minute duration.
(b) 
The maximum velocity as determined by Manning's Equation shall not exceed the allowable velocities for the specific type of shoulder material.
(5) 
Curb sections.
(a) 
The maximum encroachment of water on the roadway pavement shall not exceed three inches in depth at the curb during a twenty-five-year-frequency storm of five-minute duration.
(b) 
Inlets shall be provided to control the encroachment of water on the pavement.
(6) 
Inlets: general.
(a) 
At street intersections, inlets shall be placed in the tangent portion, rather than the curved portion, of the curbing.
(b) 
If the capacity of the shoulder, swale, curb section, or depressed median section exceeds the assumed inlet capacities, the inlet capacities shall govern the spacing of inlets.
(c) 
If the capacity of the shoulder, swale, curb section, or depressed median section is less than the inlet capacities, then the shoulder, swale, curb section or depressed section capacity shall govern the spacing of inlets.
(7) 
Energy dissipaters. Energy dissipaters shall be placed at the outlets of all storm sewer pipes, culverts, and bridges where flow velocities exceed maximum permitted channel velocities as specified below:
(a) 
Three feet per second where only sparse vegetation can be established and maintained because of shade or soil condition.
(b) 
Four feet per second where normal growing conditions exist and vegetation is to be established by seeding.
(c) 
Five feet per second where a dense, vigorous sod can be quickly established or where water can be temporarily diverted during establishment of vegetation. Netting and mulch or the equivalent methods for establishing vegetation shall be used.
(d) 
Six feet per second where there exists a well-established sod of good quality.
(8) 
Swales. The following conditions shall be met for all swales:
(a) 
Capacities and velocities shall be computed using the Manning Equation. The design parameters shall be as follows:
[1] 
Vegetated swales shall meet the following two design considerations:
[a] 
The first shall consider swale stability based upon a lowdegree of retardance ("n" = 0.03).
[b] 
The second shall consider swale capacity based upon a high degree of retardance ("n" = 0.05).
[2] 
All vegetated swales shall have a minimum slope of 1% unless approved by the Municipal Engineer.
[3] 
The "n" factors to be used for paved or riprap swales or gutters shall be based upon accepted engineering design practices as approved by the municipality.
(b) 
All swales shall be designed to concentrate low flows to minimize siltation and meandering.
A. 
In order to protect and improve water quality, a riparian buffer easement shall be created and recorded as part of any subdivision or land development that encompasses a riparian buffer.
B. 
Except as required by Chapter 102, the riparian buffer easement shall be measured to be the greater of the limit of the 100-year floodplain or a minimum of 35 feet from the top of the streambank (on each side).
C. 
Minimum management requirements for riparian buffers.
(1) 
Existing native vegetation shall be protected and maintained within the riparian buffer easement.
(2) 
Whenever practicable invasive vegetation shall be actively removed and the riparian buffer easement shall be planted with native trees, shrubs and other vegetation to create a diverse native plant community appropriate to the intended ecological context of the site.
D. 
The riparian buffer easement shall be enforceable by the municipality and shall be recorded in the appropriate County Recorder of Deeds office, so that it shall run with the land and shall limit the use of the property located therein. The easement shall allow for the continued private ownership and shall count toward the minimum lot area a required by zoning, unless otherwise specified in the Municipal Zoning Ordinance.[1]
[1]
Editor's Note: See Ch. 113, Zoning.
E. 
Any permitted use within the riparian buffer easement shall be conducted in a manner that will maintain the extent of the existing 100-year floodplain, improve or maintain the stream stability, and preserve and protect the ecological function of the floodplain.
F. 
The following conditions shall apply when public and/or private recreation trails are permitted within riparian buffers:
(1) 
Trails shall be for nonmotorized use only.
(2) 
Trails shall be designed to have the least impact on native plant species and other sensitive environmental features.
G. 
Septic drainfields and sewage disposal systems shall not be permitted within the riparian buffer easement and shall comply with setback requirements established under 25 Pa. Code Chapter 73.