Township of East Manchester, PA Stormwater Management Standards

General requirements.

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 site plan (SWM site plan). SWM site plans approved by the Township in accordance with this chapter shall be on site throughout the duration of the regulated activity. Although not a requirement of this chapter, prior to proceeding with stormwater management site plan preparation and submission, the developer is encouraged to request a preapplication meeting with the Township Engineer and a staff member of the Conservation District to discuss the plan concept and responsibility for submission of required documents and information.

(2)

When a project is proposed to be developed in phases or sections and the developer submits stormwater management site 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 site 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 the Zoning Ordinance,[1] 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.[2]

[1]

Editor's Note: See Ch. 255, Zoning.

[2]

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 and BMPs. 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)

Stormwater management site plans approved by the Township shall be on site throughout the duration of the regulated activity.

(9)

The Township may, after consultation with DEP, approve measures for meeting the state water quality requirements other than those in this chapter, provided that they are consistent with the IWRP and meet the minimum requirements of, and do not conflict with, state law, including, but not limited to, the Clean Streams Law.[3] The Township shall maintain a record of consultations with DEP pursuant to this subsection.

[3]

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

(10)

For all regulated activities, erosion and sediment control BMPs shall be designed, implemented, operated, and maintained during the regulated activities, i.e., during construction, to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law. Various BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual (E&S Manual) 2, No. 363-2134-008 (April 15, 2000), as amended and updated.

(11)

For all regulated activities, implementation of the volume controls in § 199-9 is required, unless specifically exempted under § 199-8, or exempted by an approved modification request as specified in § 199-38 of this chapter.

(12)

Impervious areas:

(a)

The measurement of impervious areas shall include all of the impervious areas in the total proposed development even if development is to take place in phases.

(b)

For development taking place in phases, all phases of the project must be considered in determining conformance with this chapter.

(c)

For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls § 199-9 and the peak rate controls of § 199-10 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.

(13)

Stormwater runoff onto adjacent property shall not be created, increased, decreased, relocated, or otherwise altered without written notification of the adjacent property owner(s). Such stormwater runoff shall be subject to the requirements of this chapter.

(14)

All regulated activities shall be conducted in such a way as to:

(a)

Protect health, safety, and property;

(b)

Meet the water quality goals of this chapter, as stated in § 199-2 (Purpose) by implementing measures to:

[1]

Minimize disturbance to floodplains, wetlands, wooded areas, and existing vegetation.

[2]

Maintain or extend riparian buffers.

[3]

Avoid erosive flow conditions in natural flow pathways.

[4]

Minimize thermal impacts to waters of this commonwealth.

[5]

Disconnect impervious surfaces by directing runoff to pervious areas, wherever possible.

[6]

Minimize soil disturbance and compaction. Topsoil, if removed, shall be replaced to a minimum depth equal to its depth prior to removal or four inches, whichever is greater. Additional topsoil may be required for vegetation other than sod.

(c)

To the maximum extent practicable, incorporate the techniques for low-impact development practices described in the BMP Manual. If methods other than green infrastructure and LID methods are proposed to achieve the volume and rate controls required under this chapter, the SWM site plan must include a detailed justification demonstrating that the use of LID and green infrastructure is not practicable.

(15)

The design of all facilities in areas of carbonate geology or karst topography shall include an evaluation of measures to minimize adverse effects, including hydrogeologic studies if required by the Township.

(16)

Infiltration BMPs shall be spread out, made as shallow as practicable, and located to maximize use of natural on-site infiltration features while still meeting the other requirements of this chapter. In addition, infiltration structure BMPs shall include pretreatment BMPs where appropriate.

(17)

All storage facilities shall completely drain both the volume control and rate control capacities over a period of time not less than 24 hours and not more than 72 hours from the end of the design storm. However, any infiltration structure at such facility is exempt from the minimum twenty-four-hour standard, i.e., may infiltrate in a shorter period of time, so long as none of the stormwater flowing into the infiltration structure is discharged directly into the surface waters of the commonwealth. (Inordinately rapid infiltration rates may indicate the presence of large fractures or other conditions for which an additional soil buffer may be required.)

(18)

The design storm volumes and precipitation intensities to be used in the analysis of discharge or runoff shall be obtained from the Precipitation-Frequency Atlas of the United States, Atlas 14, Volume 2, Version 3.0, U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland. NOAA's Atlas 14 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/.

(19)

For all regulated activities, BMPs shall be designed, implemented, operated, and maintained to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code, the Clean Streams Law, and Act 167.

(20)

All stormwater management facilities and regulated activities shall be conducted and located in accordance with the setback requirements of Chapter 238 (Water Supply) also known as the "East Manchester Well Ordinance."

(21)

Various BMPs and their design standards are listed in the BMP Manual.

Permanent stormwater management standards. The developer shall demonstrate by substantial evidence that the stormwater management facilities and BMPs for the project will meet or exceed all of the following standards:

(1)

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).

(2)

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 the 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 and 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 from the project site be retained and infiltrated. If substantial irrigation needs are anticipated, a portion of stored stormwater may be reused for irrigation purposes.

§ 199-8 Exemptions from stormwater management site plan requirements.

Any regulated activity that meets the following exemption criteria is exempt from the provisions of this chapter only to the extent specifically provided for herein. These criteria shall apply to the total project even if the project is to take place in phases. The date of enactment of this chapter shall be the starting point from which future development and the respective proposed impervious surface computations shall be cumulatively considered and regulated. Exemption shall not relieve an applicant from implementing such measures as set forth in § 199-7A(10) and (12) through (18), or as necessary to meet the intent of this chapter, or compliance with any NPDES permit requirements. Exemption shall not relieve the applicant from implementing such measures as are necessary to protect health, safety, and property. This exemption shall not relieve the applicant from meeting the requirements for water quality and groundwater recharge or special requirements for high quality (HQ) and exceptional value (EV) watersheds.

Regulated activities that create impervious areas equal to or less than 750 square feet calculated on a cumulative basis from the date of enactment of this chapter are exempt from the peak rate control and the stormwater management site plan preparation requirements of this chapter. Upon exceeding this cumulative exemption, the impervious areas created from the date of exceedance forward shall not be exempted from the requirements of this chapter, except as otherwise set forth in this chapter. The Township may deny this exemption in situations where the location of impervious area will discharge any concentrated stormwater runoff onto a downslope property or directly into the waters of the commonwealth.

Regulated activities that create DIAs equal to or less than 1,000 square feet are exempt from the peak rate control and the stormwater management site plan preparation requirements of this chapter. This exemption shall be applied on a project basis and not a cumulative basis.

Regulated activities that create DIAs greater than 1,000 square feet and equal to or less than 5,000 square feet are exempt only from the peak rate control requirement of this chapter. This exemption shall be applied on a project basis and not a cumulative basis.

Agricultural activities such as growing crops, rotating crops, tilling of soil and grazing animals and other such activities when performed in accordance with a conservation plan or erosion and sedimentation control plan approved by the Conservation District shall be exempt from the rate control and stormwater management site plan provisions of this chapter. Construction of new buildings or the addition of impervious area shall not be considered an agricultural activity for purposes of this exemption.

Forest management operations, which are following the DEP's management practices, contained in its publication "Soil Erosion and Sedimentation Control Guidelines for Forestry," or any successor publication, and are operating under an erosion and sedimentation control plan approved by the Conservation District, shall be exempt from the rate control and stormwater management site plan provisions of this chapter. Construction of new buildings or the addition of impervious area shall not be considered forest management activity for purposes of this exemption.

Domestic gardening and landscaping are exempt from specific approval and permitting under this chapter so long as those activities are associated with one, and only one, dwelling unit and the activities comply with all other applicable ordinances and statutes.

Emergency maintenance work performed for the protection of public health, safety and welfare. A written description of the scope and extent of any emergency work performed shall be submitted to the Township within 24 hours of the commencement of the activity. If the Township determines the work is not an emergency, then the work shall cease immediately and the requirements of this chapter shall be addressed as applicable.

Any maintenance to an existing stormwater management system made in accordance with plans and specifications approved as part of an O&M plan or by the Township Engineer.

Regulated activities exempted from SWM site plan requirements are not subject to review and approval for the volume control requirements of this chapter. It shall be the landowner's responsibility to assure compliance with the volume control requirements. The Township may at its discretion require drawings and calculations in sufficient detail to show proposed volume controls of this chapter are met.

The Township may deny or revoke any exemption pursuant to this section at any time for any project that the Township determines poses a threat to public health, safety, property or the environment.

§ 199-9 Volume controls.

The-low impact development practices provided in the BMP Manual shall be utilized for all regulated activities to the maximum extent practicable. Water volume controls shall be implemented using the Design Storm Method in Subsection A or the Simplified Method in Subsection B below. For regulated activity areas equal to or less than one acre that do not require hydrologic routing to design the stormwater management facilities, this chapter establishes no preference for either methodology; therefore, the applicant may select either methodology with Township concurrence.

The Design Storm Method (CG-1 in the BMP Manual) is applicable to any size of regulated activity. This method requires detailed modeling based on site conditions.

(1)

The stormwater management plan shall not increase the post-development total runoff volume for all storms equal to or less than the two-year, twenty-four-hour-duration precipitation.

(2)

For modeling purposes:

(a)

Existing (predevelopment) nonforested pervious areas must be considered meadow.

(b)

Twenty percent of the existing impervious area of a project site, when present, shall be considered meadow in the model for existing conditions.

The Simplified Method (CG-2 in the BMP Manual) provided below is independent of site conditions and should be used if the Design Storm Method is not followed. This method is not applicable to regulated activities greater than one acre or for projects that require design of stormwater storage facilities. For new impervious surfaces:

(1)

The stormwater management plan shall provide for the capture of at least the first two inches of runoff from all new impervious surfaces.

(2)

At least the first one inch of runoff from new impervious surfaces shall be permanently removed from the runoff flow, i.e., it shall not be released into the surface waters of this commonwealth. Removal options for the first one inch of runoff include reuse, evaporation, transpiration, and infiltration.

(3)

Wherever possible, infiltration structures should be designed to accommodate infiltration of the entire permanently removed runoff; however, in all cases at least the first 0.5 inch of the permanently removed stormwater runoff shall be infiltrated.

(4)

This method is exempt from the requirements of § 199-10, Rate controls.

§ 199-10 Rate controls.

For computation of predevelopment flow rates, 20% of the existing impervious area of a project site, when present, shall be considered meadow. 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 1 and Table 2,[1] respectively.

[1]

Editor's Note: Said tables are included as attachments to this chapter.

For areas not covered by a release rate map from an approved Act 167 stormwater management plan: Post-development flow rates shall not exceed the predevelopment flow rates for the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour storms. If it is shown that the peak discharge rates indicated by the post-development analysis are less than or equal to the peak discharge rates indicated by the predevelopment analysis for one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour storms, then the requirements of this section have been met. Otherwise, the developer shall provide additional controls as necessary to satisfy the peak discharge rate requirement.

For areas covered by a release rate map from an approved Act 167 stormwater management plan: For the one-, two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour storm events, the post-development peak discharge rates will follow the applicable approved release rate maps. For any areas not shown on the release rate maps, the post-development discharge rates shall not exceed the predevelopment discharge rates.

§ 199-11 Stormwater management facilities for Pennsylvania Department of Transportation and Pennsylvania Turnpike Commission roadways and associated facilities.

For the purposes of the county Act 167 plan elements, contained within the IWRP, and this chapter, design policy pertaining to stormwater management facilities for PennDOT roadways and associated facilities is provided in Section 13.7 (Antidegradation and Post Construction Stormwater Management Policy) of PennDOT Publication No. 13M, Design Manual Part 2 (August 2009), as developed, updated, and amended in consultation with the DEP. As stated in DM-2.13.7.D (Act 167 and Municipal Ordinances), PennDOT roadways and associated facilities shall be consistent with Act 167 plans. DM-2.13.7.B (Policy on Antidegradation and Post Construction Stormwater Management) was developed as a cooperative effort between PennDOT and DEP. DM-2.13.7.0 (Project Categories) discusses the anticipated impact on the quality, volume, and rate of stormwater runoff. Where standards in the Act 167 elements of the IWRP and this chapter are impractical, PennDOT may request assistance from DEP, in consultation with the county, to develop an alternative strategy for meeting state water quality requirements and the goals and objectives of the Act 167 elements within the IWRP. For the purposes of the Act 167 elements in the IWRP and this chapter, road maintenance activities are regulated under 25 Pa. Code Chapter 102.

§ 199-12 Design criteria.

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.

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 100-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 100-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 and PennDOT regulations (if applicable) and, at minimum, pass the increased 100-year return period runoff.

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. Any regional management plan must be a covenant or restriction running with the land that shall be set forth in a recorded agreement approved by the Township.

§ 199-13 Regulation governing stormwater management facilities.

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 100-year post-development conditions, assuming the principal outlet structure to be clogged. The height of embankment must be set as to provide a minimum 1.0 foot of freeboard above the maximum pool elevation computed for the clogged orifice condition. Should any stormwater management facility require a dam safety permit under 25 Pa. Code Chapter 105, the facility shall be designed in accordance with 25 Pa. Code Chapter 105 concerning dam safety.

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.

Any drainage conveyance facility and/or channel that does not fall under DEP Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the 100-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 100-year design storm. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.

Storm sewers must be able to convey post-development runoff from a fifty-year design storm without surcharging inlets, where appropriate. Any post-development 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 100-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.

Any earthmoving activities subject to review by the Conservation District must be granted approval of the Conservation District prior to commencing work.

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.

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 post-development flows. The downstream owner(s)' signatures must be included on the stormwater management site 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 owner(s) 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 owner(s) refuse to accept the altered discharge, the developer must modify the stormwater management site plan so the plan does not increase the drainage area or volume of discharge at the discharge point.

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 owner(s)' signatures must be included on the stormwater management site 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 owner(s) 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 owner(s) refuse to accept the altered discharge, the developer must modify the stormwater management site plan so the plan does not increase the drainage area or volume of discharge at the discharge point.

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.

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.

Roof drains and sump pumps, wherever feasible, shall discharge to infiltration or vegetative BMPs and 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.

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. 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 to 1. This will lessen the destabilization of berm soils due to root growth. A long-term maintenance schedule and management plan for the thermal control BMPs is to be established and recorded for all project sites within defined exceptional value and/or high quality subwatersheds.

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.

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 180-inch- or fifteen-foot-wide level spreader).

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.

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.

The maximum permitted side slopes for detention or retention basins shall be four horizontal to one vertical.

All stormwater management facilities are considered structures and must comply with applicable building setback requirements as set forth in the Zoning Ordinance[1] or other applicable regulations. No part of the discharge structure or piping shall encroach into the setback area.

[1]

Editor's Note: See Ch. 255, Zoning.

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)

The 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 the Zoning Ordinance.

No stormwater management facilities shall be installed over existing utility mains or services.

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."

In general, inlets shall be spaced such that, based upon the rational method, time-of-concentration (Tc) equals 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 (cfs). 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.

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 the 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.

§ 199-14 Calculation methodology.

Stormwater runoff from all project sites shall be calculated using either the rational method or a soil cover complex methodology.

Any stormwater runoff calculations involving drainage areas greater than 200 acres, including on- and off-site areas, shall use a 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.

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

[1]

Editor's Note: Said tables are included as attachments to this chapter.

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.

Runoff curve numbers (CN) for both existing and proposed conditions to be used in the soil cover complex method shall be obtained from Table 1.[2]

[2]

Editor's Note: Said table is included as an attachment to this chapter.

Runoff coefficients (c) for both existing and proposed conditions for use in the rational method shall be obtained from Table 2.[3]

[3]

Editor's Note: Said table is included as an attachment to this chapter.

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 3.[4]

[4]

Editor's Note: Said table is included as an attachment to this chapter.

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.

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.

§ 199-15 Groundwater recharge (infiltration/recharge/retention).

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.

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 calculated by a qualified professional in accordance with a stormwater management site plan.

(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.

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.

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 groundwater 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. The Township may require the installation of an impermeable liner in detention basins. A detailed hydrogeologic investigation may be required by the Township.

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 site 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.

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 site plan.

Recharge/infiltration facilities may be used in conjunction with other innovative or traditional BMPs, stormwater control facilities, and nonstructural stormwater management alternatives.

§ 199-16 Water quality and stream protection.

Developed areas will provide adequate storage and treatment facilities necessary to capture and treat stormwater runoff. The recharge volume computed under § 199-15 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)(Rv)(A)]/12
WQv	=	Water quality volume
P	=	Rainfall amount (two-year, twenty-four-hour Type II SCS rainfall distribution) (in inches)
A	=	Disturbed project area (in acres)
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 the BMP Manual. 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 wellheads;

(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.

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 § 199-15 should be accounted for in meeting the requirements of § 199-16A.

§ 199-17 Erosion and sedimentation requirements.

As required in § 199-13E 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, and in accordance with requirements of the Conservation District.

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.

§ 199-18 Riparian Buffer Zone (RBZ).

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 subzones, 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:

(1)

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.

(2)

Zone 2, a managed buffer zone, extending a distance equal to 35 feet outward from Zone 1 or to the 100-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 upgradient. The developer shall use land within Zone 2 only for those uses authorized within the 100-year floodplain as allowed in the Zoning Ordinance,[1] even if portions of Zone 2 are located outside of the 100-year floodplain.

[1]

Editor's Note: See Ch. 255, Zoning.

(3)

Zone 3, a zone of 50 feet extending outward from Zone 2; Zone 3 is defined in those cases where upslope 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.

(4)

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.

For areas immediately adjacent to the Township's perennial streams, areas of springs, and watercourses where the drainage area to the wetland or watercourse is 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.

§ 199-18.1 Riparian buffers.

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.

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).

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.

The riparian buffer easement shall be enforceable by the Township 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. 255, Zoning.

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.

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.

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.