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Township of East Manchester, PA
York County
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Table of Contents
Table of Contents
A. 
General requirements.
(1) 
The developer of any project within the Township, with the exception of those projects exempted from the requirements of this chapter in § 199-8 shall submit an application for and obtain approval of a stormwater management plan.
(2) 
When a project is proposed to be developed in phases or sections and the developer submits stormwater management plans for each section or phase, all proposed temporary facilities required for construction of a section or phase shall be included in the submitted stormwater management plan for that section.
(3) 
Stormwater management facilities located within or affecting the floodplain or any watercourse shall also be subject to the requirements of Chapter 255, Zoning, of the Code of the Township of East Manchester, any ordinance which regulates construction and development within areas of the Township subject to flooding, and any other applicable requirements of Act 166, the Pennsylvania Floodplain Management Act.[1]
[1]
Editor's Note: See 32 P.S. § 679.101 et seq.
(4) 
Runoff from impervious surface areas shall be drained when possible to pervious areas of the project site.
(5) 
Stormwater runoff shall not be transferred from one watershed to another unless the watersheds are subwatersheds of a common watershed which join together within the perimeter of the project site, or the effect of the transfer does not alter the peak discharge onto downstream lands, or drainage easements from the affected landowners are provided.
(6) 
All stormwater runoff flowing over the project site shall be considered in the design of the stormwater management facilities. This includes existing points of concentrated drainage that discharge onto adjacent property. Existing concentrated drainage shall not be relocated and shall be subject to any applicable discharge criteria specified in this chapter.
(7) 
Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses.
(8) 
Other innovative methods for the management of stormwater runoff rates and volumes may also be approved by the Township. Various combinations of methods should be tailored to suit the particular requirements of the type of development and the topographic features of the project site. The following is a partial listing of control methods which can be utilized in stormwater management plans where appropriate and when approved by the Township Engineer.
(a) 
Infiltration pits, infiltration trenches or other infiltration structures.
(b) 
Concrete lattice block surfaces.
(c) 
Grassed channels and vegetated strips.
(d) 
Cisterns and underground reservoirs.
(e) 
Routed flow over grass.
(f) 
Decreased impervious surface coverage.
(g) 
Constructed wetlands.
(h) 
Retention Basins subject to prior Township approval.
(i) 
Roof-top storage.
(j) 
Detention basins (extended or conventional).
(k) 
Other BMPs.
(l) 
Porous pavement.
B. 
Permanent stormwater management standards. The developer shall demonstrate by substantial evidence that the stormwater management facilities for the project will meet or exceed all of the following standards:
(1) 
After installation of impervious or semipervious materials, there shall be no increase in the volume of stormwater runoff being discharged for up to the two-year, twenty-four-hour design storms, predevelopment to postdevelopment, calculated using the Soil Cover Complex Method.
(2) 
After installation of impervious or semipervious materials, the postdevelopment peak rate of stormwater discharges from the project site for all design storms up to an including a one-hundred-year frequency rainfall shall not exceed the predevelopment peak rate discharges from the project site of the same design storms before disturbance. Design storms include: two-year, twenty-four-hour storm; five-year, twenty-four-hour storm; ten-year, twenty-four-hour storm; twenty-five-year, twenty-four-hour storm; fifty-year, twenty-four-hour storm; one-hundred-year, twenty-four-hour storm.
(3) 
The volume and rate of any stormwater discharges allowed by this chapter must be managed to prevent the physical degradation of receiving waters, such as streambank scour and erosion. If a detention facility is proposed that is part of the BMPs approved for a project, the facility(ies) must be designed to provide for the twenty-four-hour extended detention of the two-year, twenty-four-hour storm event (i.e., the stormwater runoff will be released over a minimum of 24 hours for the two-year, twenty-four-hour storm event).
(4) 
The Township shall impose the following additional restrictions on stormwater discharges:
(a) 
When a probable risk to downstream structures or unique natural areas exists or previous (historical) flooding problems could be further aggravated, the Township shall require developer to further restrict peak discharge.
(b) 
The Township shall impose measures to protect against groundwater or surface water pollution from significant pollution producing sources (so called "hot spots," including but not limited to industrial uses, gas stations, fast food an other commercial uses generating large numbers of vehicle trips, and other uses at the determination of the Township) or where the nature of the soils or bedrock underlying a stormwater management facility constitutes substantial risk of contamination, such as carbonate areas. The developer shall install special provisions that act to remove pollutant loadings (including but not limited to filtration devices like sand peat filters, multiple chamber catch basins and inlets, oil separators and others).
(c) 
Where groundwater yields are very low or where a groundwater supply already is heavily used or where maintenance of downstream wetlands is a special concern, the Township shall require that the entire volume of the two-year, twenty-four-hour design storm (3.0 inches in 24 hours) from the project site be retained and infiltrated. If substantial irrigation needs are anticipated, portion of stored stormwater may be reused for irrigation purposes.
A. 
Postdevelopment rates of runoff from any regulated activity shall not exceed the peak release rates of runoff specified in § 199-13 of this chapter. If it is shown, by applications of water quality and groundwater recharge requirements pursuant to §§ 199-17 and 199-18, that the postdevelopment hydrographs are equal to the predevelopment hydrographs to assure the rate and volume of runoff leaving the site is unchanged for two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year storm frequencies, then the requirements of this section will be considered met. Otherwise, the developer shall control the rate and volume for the balance of uncontrolled runoff by satisfying §§ 199-17 and 199-18. If an extended detention or a permanent pool-type stormwater management facility is selected for the treatment of water quality volume, the outlet shall be designed such that one-year, twenty-four-hour postdevelopment runoff volume is released over a twenty-four-hour period. This will also help channel protection. The release of water begins 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 consider and minimize the chances of clogging and sedimentation potential. Orifices smaller than four inches diameter are not recommended.
B. 
Infiltration BMPs must be provided for all development to capture all volume from impervious area associated with development for a three-inch, twenty-four-hour Type II SCS rainfall distribution. See requirements specified in § 199-17.
C. 
Off-site areas which drain through a proposed project site are not subject to release rate criteria when determining allowable peak discharge rates. However, on-site drainage facilities shall be designed to safely convey off-site flows through the project site.
D. 
Any downstream hydraulic capacity analysis conducted in accordance with this chapter shall use the following criteria for determining adequacy for accepting increased peak discharge rates:
(1) 
Natural or man-made channels or swales must be able to convey the increased runoff associated with a one-hundred-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 DEP "Erosion and Sediment Pollution Control Program Manual."
(2) 
Natural or man-made channels or swales must be able to convey increased one-hundred-year return period runoff without creating any hazard to persons or property.
(3) 
Culverts, bridges, storm sewers or any other stormwater management facilities which must pass or convey flows from the tributary area must be designed in accordance with DEP Chapter 105[1] and PennDOT regulations (if applicable) and, at minimum, pass the increased one-hundred-year return period runoff.
[1]
Editor's Note: See 25 Pa. Code § 105.1 et seq.
E. 
For certain areas within the Township, it may be more cost-effective to provide one stormwater management facility for more than one project site than to provide an individual stormwater management facility for each project site. The initiative and funding for any regional runoff control alternatives are the responsibility of prospective developers. The design of any regional control basins must incorporate reasonable development of the entire upstream watershed. The peak outflow of a regional basin would be determined on a case-by-case basis using the hydrologic model, if available, of the watershed consistent with protection of the downstream watershed areas.
A. 
Any stormwater management facility located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
B. 
Any stormwater management facility (i.e., detention basin) designed to store runoff and requiring a berm or earthen embankment required or regulated by this chapter shall be designed to provide an emergency spillway to handle flow up to and including the one-hundred-year postdevelopment conditions. The height of embankment must be set as to provide a minimum 1.0 foot of freeboard above the maximum pool elevation computed when the facility functions for the one-hundred-year postdevelopment 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[1] concerning dam safety.
[1]
Editor's Note: See 25 Pa. Code § 105.1 et seq.
C. 
Any stormwater management facilities regulated by this chapter that would be located in or adjacent to waters of the commonwealth or wetlands shall be subject to approval by DEP through the joint permit application process, or, where deemed appropriate by DEP, the applicable general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the developer or his agent to show that the land in question cannot be classified as wetlands, otherwise approval to work in the area must be obtained from DEP.
D. 
Any drainage conveyance facility and/or channel that does not fall under DEP Chapter 105 regulations,[2] 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.
[2]
Editor's Note: See 25 Pa. Code § 105.1 et seq.
E. 
Storm sewers must be able to convey postdevelopment runoff from a fifty-year design storm without surcharging inlets, where appropriate. Any postdevelopment drainage area that does not naturally convey stormwater runoff to a stormwater management facility shall incorporate a storm sewer system capable of collecting and conveying the stormwater runoff during a one-hundred-year design storm to said facilities. A combination of aboveground and overland conveyance will be accepted without creation of hazardous conditions to any person or property.
F. 
Any earthmoving activities subject to review by the Conservation District must be granted approval of the Conservation District prior to commencing work.
G. 
The design of all stormwater management facilities shall incorporate good engineering principles and practices. The Township shall reserve the right to disapprove any design that would result in the occurrence or continuation of adverse hydrologic or hydraulic conditions within the watershed.
H. 
The existing points of concentrated drainage that discharge onto adjacent property shall be subject to applicable discharge criteria in this chapter. The volume of runoff may not be increased by more than the volume of the two-year return period storm unless an analysis is completed that shows adequate facilities are in place to adequately convey postdevelopment flows. The downstream owners' signatures must be included on the stormwater management plan or a letter of approval acceptable to the Township must be obtained signifying approval to alter the concentrated drainage where inadequate downstream drainage conveyance facilities exist to convey the concentrated discharge. This requirement shall be limited to owners less than 500 yards downstream of the concentrated drainage point. The adequacy of downstream drainage conveyance facilities shall be as determined by the Township Engineer with reference to this chapter. Should the downstream owners refuse to accept the altered discharge, the developer must modify the stormwater management plan so the plan does not increase the drainage area or volume of discharge at the discharge point.
I. 
Areas of existing diffused drainage discharge shall be subject to any applicable discharge criteria in the general direction of existing discharge, whether proposed to be concentrated or maintained as diffused drainage areas, except as otherwise provided by this chapter. If diffused flow is proposed to be concentrated and discharged onto adjacent property, the developer must document that adequate downstream drainage conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding or other harm will result from the concentrated discharge. The downstream owners' signatures must be included on the stormwater management plan or a letter of approval acceptable to the Township must be obtained signifying approval to alter the concentrated drainage where inadequate downstream drainage conveyance facilities exist to convey the concentrated discharge. This requirement shall be limited to owners less than 500 yards downstream of the concentrated drainage point. The adequacy of downstream drainage conveyance facilities shall be as determined by the Township Engineer with reference to this chapter. Should the downstream owners refuse to accept the altered discharge, the developer must modify the stormwater management plan so the plan does not increase the drainage area or volume of discharge at the discharge point.
J. 
Where a project site is traversed by watercourses, drainage easements shall be provided conforming to the line of such watercourses. The terms of the drainage easement shall prohibit excavation, the placing of fill or structures, and any alterations that may adversely affect the flow of stormwater within any portion of the drainage easement. Also, maintenance, including mowing of vegetation within the drainage easement shall be required, except as approved by the appropriate governing authority.
K. 
When it can be shown that, due to topographic conditions, natural drainageways on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainageways. Work within natural drainageways shall be subject to approval by DEP through the joint permit application process, or, where deemed appropriate by DEP, through the general permit process.
L. 
Roof drains must not be connected to streets, sanitary or storm sewers or roadside ditches to promote overland flow and infiltration/percolation of stormwater where advantageous to do so. When it is more advantageous to connect directly to streets or storm sewers, then it shall be permitted on a case-by-case basis by the Township. In no case shall roof drains be positioned in a manner that promotes drainage to adjacent structures or onto adjacent properties.
M. 
Special requirements for areas falling within defined exceptional value and high quality subwatersheds. The temperature and quality of water and streams that have been declared as exceptional value and high quality is to be maintained as defined in Chapter 93, Water Quality Standards, Title 25 of the DEP Rules and Regulations.[3] Temperature sensitive BMPs and stormwater conveyance systems are to be used and designed with storage pool areas and supply outflow channels and should be shaded with trees. This will require modification of berms for permanent ponds and the relaxation of restrictions on planting vegetation within the facilities, provided that capacity for volumes and rate control is maintained. At a minimum, the southern half on pond shorelines shall be planted with shade or canopy trees within 10 feet of the pond shoreline. In conjunction with this requirement, the maximum slope allowed on the berm area to be planted is 10:1. This will lessen the destabilization of berm soils due to root growth. A long-term maintenance schedule and management plan for the thermal control BMPs is to be established and recorded for all project sites within defined exceptional value and/or high quality subwatersheds.
[3]
Editor's Note: See 25 Pa. Code § 93.1 et seq.
N. 
Outlet control shall be accomplished utilizing (six-inch diameter or six-inch width minimum) perforations arranged vertically to provide for positive control of runoff. Outlet controls shall also provide for modification of the orifice to a smaller diameter through the use of removable plates or similar devices.
O. 
Discharges from piping outlets of stormwater management facilities shall be provided with a concrete level spreader to convert point discharge back to simulated sheet flow. The length of the level spreader shall be equal to 10 times the outlet pipe diameter (e.g., an eighteen-inch discharge pipe would require a one-hundred-eighty-inch or fifteen-foot wide level spreader).
P. 
All detention basins shall have a minimum bottom slope of 2% unless infiltration structures are provided. Where infiltration structures are provided an infiltration and/or percolation rate must be sufficient to accept the additional storm load and drain completely as determined by field tests conducted by the owner's professional designer.
Q. 
The permitted depth for detention or retention basins shall be six feet, measured from the bottom of the emergency spillway to the lowest point in the basin.
R. 
The maximum permitted side slopes for detention or retention basins shall be four horizontal to one vertical.
S. 
All stormwater management facilities are considered structures and must comply with applicable building setback requirements as set forth in Chapter 255, Zoning, or other applicable regulations. No part of the discharge structure or piping shall encroach into the setback area.
T. 
Any stormwater detention/retention facility located in or adjacent to a Residential (R-1, R-2 or R-3) District or an Apartment/Office (AO) District shall be subject to the following fencing requirements:
(1) 
Stormwater facility must be completely surrounded by a fence or wall of not less than four feet in height, which shall be so constructed as not to have openings, holes or gaps larger than two inches in any dimension (including the distance between horizontal or vertical pickets in a picket fence).
(2) 
All gates or doors opening through such enclosure shall be equipped with a self-closing and self-latching device for keeping the gate or door securely closed at all times.
(3) 
The fences or walls erected shall further comply with all applicable provisions of Chapter 255, Zoning.
U. 
No stormwater management facilities shall be installed over existing utility mains or services.
V. 
Plans showing outlet control structures shall contain a drainage easement dedication as follows: "An easement is hereby granted to East Manchester Township to access and modify the basin outlet control device at the expense of the developer or owner so as to function within design parameters."
W. 
In general, inlets shall be spaced such that, based upon the Rational Method, time-of-concentration (Tc) = five minutes and fifty-year design storm intensity, the area contributing to the inlet shall not produce a peak discharge of greater than four cubic feet per second. Also, inlets shall be spaced so that their efficiency, based upon efficiency curves published by the PennDOT, is not less than 65%. Additional inlets shall be placed at the upper side of driveway/street intersections to prevent stormwater from discharging onto the roadway. Other devices such as high-efficiency grates or perforated pipe may be required if conditions warrant.
X. 
In all cases where drainage is picked up by means of a head wall, and inlet or outlet conditions control, the pipe shall be designed as a culvert. The minimum diameter of culvert shall be 18 inches. The procedure contained in Hydraulic Engineer Circular Nos. 5 and 13, as prepared by the U. S. Department of Transportation, Federal Highway Administration, Washington, D.C., shall be used for the design of culverts. When a pipe or culvert is intended to convey the discharge from a stormwater management facility, its required capacity shall be computed by the Rational Method and compared to the peak outflow from the stormwater management facility for the fifty-year design storm. The greater flow shall govern the design of the pipe or culvert.
Stormwater runoff from all project sites shall be calculated using either the Rational Method or a Soil Cover Complex Methodology.
A. 
Any stormwater runoff calculations involving drainage areas greater than 200 acres, including on- and off-site areas, shall use generally accepted calculation technique that is based on the NRCS Soil Cover Complex Method. It is assumed that all methods will be selected by the design professional 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.
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 presented in Table 4-1. If a hydrologic computer model such as PSRM or HEC-RAS is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours. The SCS Rainfall Type II curve shall be used for the rainfall distribution. See Table 4-2 and Table 4-3.[1]
[1]
Editor's Note: Said tables are included at the end of the chapter.
C. 
For the purposes of predevelopment flow rate determination, undeveloped land, including disturbed areas, shall be considered as "meadow" in good condition, unless the natural ground cover generates a lower curve number or Rational "C" value (i.e., forest), as listed in Table 4-4.[2]
[2]
Editor's Note: Said table is included at the end of the 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 design storm Curves for PennDOT Design Rainfall Curves. Region 4 curves will apply to the watersheds within the Township. See Table 4-5.[3]
Peak discharge computed using the Rational Method should follow the formula, Q = CIA
Where
Q
=
Peak discharge in cubic feet per second
C
=
Runoff factor expressed as a percent of the total rainfall
I
=
Rainfall intensity in inches per hour
A
=
The drainage area expressed in acres
[3]
Editor's Note: Said table is included at the end of the chapter.
E. 
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 form time to time by NRCS). Time-of-concentration for channel and pipe flow shall be computed using Manning's equation.
F. 
Runoff curve numbers (CN) for both existing and proposed conditions to be used in the Soil Cover Complex method shall be obtained from Table 4-6.[4]
[4]
Editor's Note: Said table is included at the end of the chapter.
G. 
Runoff coefficients (c) for both existing and proposed conditions for use in the Rational Method shall be obtained from Table 4-4.[5]
[5]
Editor's Note: Said table is included at the end of the chapter.
H. 
Where uniform flow is anticipated, the Manning equation shall be used for hydraulic computations such as the capacity of open channels, pipes, and storm sewers. Values for Manning's roughness coefficient (n) shall be consistent with Table 4-7.[6]
[6]
Editor's Note: Said table is included at the end of the 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.
A. 
Maintaining runoff volumes of predevelopment conditions requires groundwater recharge of the areas being developed. Design of the infiltration/recharge stormwater management facilities shall incorporate groundwater recharge to compensate for the reduction in the percolation that occurs when the ground surface is converted to an impervious surface. These measures are required unless the applicant can prove the project site is physically incapable of recharge. If physical limitations exist preventing groundwater recharge, runoff volumes must be reduced through another acceptable BMP proposed by the developer's engineer.
B. 
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 12 inches between the bottom of the facility and the seasonal high-water table and/or bedrock (limiting zones). Limiting zones to be determined by probe hole excavation.
(b) 
An infiltration and/or percolation rate sufficient to accept the additional stormwater load and drain completely as determined by field tests conducted by the owner's professional designer.
(2) 
The size of the recharge facility shall be based upon the following chart:
Seepage Table
Perc Rate
(minutes/inch)
Depth of Stone
(feet)
Minimum Required
Bed Area
15
2.5
*
30
2.5
45
3.15
60
3.15
75
3.62
90
3.62
105
4
120
4
135
4
150
4.25
165
4.25
180+
Fails
Assumed Data:
C = 0.95
Rainfall = 6.00 inches
Bed loading rate 5:1
NOTES:
* The minimum required bed area is determined by dividing the increase in impervious surface by five. For example, a five-hundred-square-foot increase in impervious surface would have a minimum required bed area of 100 square feet.
(3) 
The recharge volume provided at the project site shall be directed to the most permeable soils available.
(4) 
The recharge facility shall be capable of completely infiltrating the impounded water within 48 hours.
C. 
A detailed soils evaluation of the project site shall be performed to determine the suitability of recharge facilities. The evaluation shall be performed by a qualified professional, and at a minimum, address soil permeability, depth to bedrock, susceptibility to sinkhole formation, and subgrade stability. The general process for designing the infiltration BMP shall be:
(1) 
Site evaluation to determine general areas of suitability for infiltration practices.
(2) 
Provide field test to determine appropriate percolation rate and/or hydraulic conductivity.
(3) 
Design infiltration structure for required storm volume based on all available data.
D. 
Extreme caution shall be exercised where infiltration is proposed in geologically susceptible areas, such as strip mine or limestone areas. Extreme caution shall also be exercised where salt or chloride would be a pollutant since soils do little to filter this pollutant and it may contaminate the groundwater. It is also extremely important that the design professional evaluate the possibility of groundwater contamination from the proposed infiltration/recharge facility and recommend a hydrogeologic justification study be performed, if necessary. Whenever a basin will be located in an area underlain by limestone, a geological evaluation of the proposed location shall be conducted to determine susceptibility to sinkhole formations. The design of all facilities over limestone formations shall include measures to prevent ground water contamination and, where necessary, sinkhole formation. The infiltration requirement in the high quality/exceptional waters shall be subject to the DEP's Chapter 93 and Antidegradation Regulations.[1] The Township may require the installation of an impermeable liner in detention basins. A detailed hydrogeologic investigations may be required by the Township.
[1]
Editor's Note: See 25 Pa. Code § 93.1 et seq.
E. 
The Township may require the developer to provide safeguards against groundwater contamination for uses which may cause groundwater contamination, should there be a mishap or spill. It shall be the developer's responsibility to verify if the project site is underlain by limestone. A note shall be included on all stormwater management plans and signed and sealed by the developer's engineer/surveyor/landscape architect/geologist certifying whether any detention or retention basins are underlain by limestone.
F. 
Where porous pavement is permitted for parking lots, recreational facilities, nondedicated streets, or other areas, pavement construction specifications shall be noted on the stormwater management plan.
G. 
Recharge/infiltration facilities may be used in conjunction with other innovative or traditional BMPs, stormwater control facilities, and nonstructural stormwater management alternatives.
A. 
Developed areas will provide adequate storage and treatment facilities necessary to capture and treat stormwater runoff. The recharge volume computed under § 199-17 may be a component of the water quality volume. If the recharge volume is less than the water quality volume, the remaining water quality volume may be captured and treated by methods other than recharge/infiltration BMPs.
(1) 
The water quality volume (WQv) is the storage capacity needed to treat stormwater runoff produced by "P" inches of rainfall (90% rule) from the developed areas of the project site. The following calculation formula is used to determine the storage volume, WQv, in acre-feet of storage:
WQv
=
[(P.O)(Rv)(A)]/12
WQv
=
Water quality volume
P
=
Rainfall amount (3.0 inches)
A
=
Disturbed project area
Rv
=
0.05 + 0.009(I)
I
=
(Impervious area ÷ Total project area) x 100
(2) 
WQv shall be designed as part of a stormwater management facility which incorporates water quality BMPs as a primary benefit of using that facility, in accordance with design specifications contained in "Pennsylvania Handbook of Best Management Practices for Developing Areas". The following factors shall be considered when evaluating the suitability of BMPs used to control water quality at a given project site:
(a) 
Total contributing area;
(b) 
Permeability and infiltration rate of the site soils;
(c) 
Slope and depth to bedrock;
(d) 
Seasonal high-water table;
(e) 
Proximity to building foundations and well heads;
(f) 
Erodibility of soils;
(g) 
Land availability and configuration of the topography;
(h) 
Peak discharge and required volume control;
(i) 
The nature of the pollutant being removed;
(j) 
Maintenance requirements;
(k) 
Creation/protection of aquatic and wildlife habitat;
(l) 
Recreational value;
(m) 
Enhancement of aesthetic and property value.
(3) 
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 consider and minimize the chances of clogging and sedimentation potential. Orifices smaller than four inches in diameter are not recommended.
B. 
The developer may 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 BMPs. Infiltration required in § 199-17 should be accounted for in meeting the requirements of § 199-18A.
A. 
As required in § 199-15F of this chapter, whenever the vegetation and topography are to be disturbed, such activity must be in conformance with Chapter 102, Title 25 of the DEP, Rules and Regulations, Part I,[1] and in accordance with requirements of the Conservation District.
[1]
Editor's Note: See 25 Pa. Code § 102.1 et seq.
B. 
It is extremely important that strict erosion and sedimentation control measures be applied surrounding infiltration structure during installation to prevent the infiltrative surfaces from becoming clogged. Additional erosion and sedimentation control design standards and criteria that must be or are recommended to be applied where infiltration BMPs are proposed shall include the following:
(1) 
Areas proposed for infiltration BMPs shall be protected from sedimentation and compaction during the construction phase, so as to maintain their maximum infiltration capacity.
(2) 
Infiltration BMPs shall not be constructed nor receive runoff until the entire contributory drainage area to the infiltration BMP has received final stabilization.
Areas immediately adjacent to the Township's perennial streams, areas of springs, watercourses where the drainage area to the wetland or watercourse exceeds 75 acres, and areas deemed by the Township to possess environmental value shall be defined as the "riparian buffer zone" or "RBZ". In the RBZ, special requirements as set forth in this section shall apply in order to maintain important natural functions. These RBZ requirements are based on both the heightened sensitivity of the RBZ and the potential to negatively impact the stream system when this RBZ is disturbed, as well as the potential of this RBZ to mitigate to the maximum extent the negative effects of development in areas adjacent to the stream system. The RBZ shall include three sub-zones, Zones 1 through 3, extending landward from the top of the streambank where different requirements are imposed. These RBZs are to be established and protected, as defined below:
A. 
Zone 1, a fifteen-foot setback zone, measured from the top of the bank of the watercourse, where no disturbance of vegetation and soil except for construction of roadway structures or conveyance systems in accordance with the design standards of this chapter and restoration shall occur, in order to shade the stream with natural vegetation, to provide a source of numerous other organic inputs to the aquatic system, to anchor the streambank and floodplain area, and to consume and otherwise remove nitrogen, sediment, and other substances which can adversely affect stream systems.
B. 
Zone 2, a managed buffer zone, extending a distance equal to 35 feet outward from Zone 1 or to the one-hundred-year floodplain boundary, whichever is larger, where disturbance of natural vegetative cover shall be limited to selective logging and other activities which minimally disrupt existing tree cover, in accordance with applicable zoning restrictions, and soil mantle, in order to maximize filtering and overall physical removal of particulate-form pollutants from runoff generated upgradient and to promote subsurface vegetative uptake of nitrogen and other nonparticulate elements from stormwater generated upgraident. The developer shall use land within Zone 2 only for those uses authorized within the one-hundred-year floodplain as allowed in Chapter 255, Zoning, even if portions of Zone 2 are located outside of the one-hundred-year floodplain.
C. 
Zone 3, a zone of 50 feet extending outward from Zone 2; Zone 3 is defined in those cases where up-slope areas adjacent to the RBZ are being disturbed during the development process and where direct discharge of stormwater would otherwise occur, Zone 3 must include level spreading devices as necessary to ensure that any directly discharged stormwater flows are properly distributed as sheet flow. The developer shall avoid channelization and point source discharges.
D. 
An RBZ adjacent to "high quality waters" and "exceptional value waters" designated by DEP shall be subject to the provisions of the most recent edition of DEP's "Special Protection Waters Implementation Handbook." To the extent the Township and DEP requirements are not consistent, the more restrictive requirements shall apply.
E. 
For areas immediately adjacent to the Township's perennial streams, areas of springs, watercourses where the drainage area to the wetland or watercourse less than 75 acres, the RBZ shall be defined as a zone extending 15 feet outward from the top of the bank(s) of the watercourse. Within this area, no disturbance of vegetation and soil except for construction of roadway structures or conveyance systems in accordance with the design standards of this chapter and restoration shall occur, in order to shade the stream with natural vegetation, to provide a source of numerous other organic inputs to the aquatic system, to anchor the streambank and floodplain area, and to consume and otherwise remove nitrogen, sediment, and other substances which can adversely affect stream systems.