Township of Daugherty, PA Stormwater Management BMP(s)

The design criteria are intended to elaborate on the Township Code, such as Chapter 88, Grading; Chapter 148, Subdivision and Land Development; Chapter 175, Zoning; and Chapter 64, Uniform Construction Codes, and to complement the Stormwater Management Act, P.L. 864, No. 167. Said Act requires that actions be taken:

To assure that the maximum rate of stormwater runoff is no greater after development than prior to development activities.

To manage the quantity, velocity and direction of resulting stormwater runoff in a manner which otherwise adequately protects health and property from possible injury.

Stormwater management design and construction will conform in general to the applicable recognized national and state acts, manuals, and references such as the Pennsylvania Stormwater Management Act and PennDOT published forms.

All stormwater management plans shall be designed and certified by individuals registered in the Commonwealth of Pennsylvania and qualified to perform such duties.

Where applicable stormwater management BMP(s) shall comply with the requirements of Chapter 105 (Dam Safety and Waterway Management) of Title 25, Environmental Protection, of the Pennsylvania Department of Environmental Protection (DEP), and Section 404 of the Clean Water Act, as authorized by the U.S. Army Corps of Engineers.

Stormwater management BMP(s) that involve a state highway shall be subject to the approval of the Pennsylvania Department of Transportation.

Stormwater runoff from a project site shall flow directly into a natural watercourse or into an existing storm sewer system or onto adjacent properties in a manner similar to the runoff characteristics of the predevelopment flow.

Stormwater runoff shall not be transferred from one watershed to another unless the watersheds are subareas of a larger watershed that are tributary to a common point of interest within or near the perimeter of the property. Transfer of runoff from one watershed to another under any other circumstances shall only be approved at the discretion of the Township. Documentation shall be provided that peak flow rates are not increased following development and there will be no detrimental impact in downstream areas.

All stormwater runoff flowing over the project site shall be considered in the design of the stormwater management BMP(s).

For any stormwater management BMP(s) requiring a permit to be issued by the DEP, said permit, along with supporting report and plans used to secure the permit, shall also be submitted.

Stormwater management standards.

Design storms.

Stormwater management BMP(s) on all development sites shall control the peak stormwater discharge for the two-, ten- and one-hundred-year design storms. For developments larger than three acres, the SCS twenty-four-hour, Type II Rainfall Distribution shall be used for analyzing stormwater runoff in predevelopment and post-development conditions, as well as for designing runoff control facilities (except storm runoff collection and conveyance facilities). For development sites less than three acres, the Rational Method may be utilized to determine peak flows and the Modified Rational Method used for design and routing of runoff control facilities. The rainfall data to be used for SCS TR-55 computations in Daugherty Township are:

	Design Storm Return Period (years)	24-Hour Rainfall Depth (inches)
	2	2.32
	10	3.33
	100	4.73

(NOTE: For additional information or data on other return periods, consult the Rainfall Duration Frequency Tables for Pennsylvania, produced by PA DEP Office of Resource Management, Bureau of Dams and Waterways Management, Division of Stormwater Management, Harrisburg, February 1983, or its most recent update.)

If the Rational Method is used, the Region No. 1, Pennsylvania Rainfall Intensity - Duration - Frequency Chart shown in the Pennsylvania Department of Transportation, Design Manual, Part 2, July 1986, shall be used to determine the rainfall intensity in inches per hour. See chart in Appendix D.

Editor's Note: Appendix D is included at the end of this chapter.

Where, in the judgment of the Township Engineer, the additional volume of stormwater runoff associated with a proposed development site will have a detrimental impact on downstream properties, and/or an existing downstream flood problem is documented, post-development peak flows may be required to be reduced to less than predevelopment peak flows. Under these circumstances, acceptable peak flow rates will be determined at the discretion of the Township Engineer for a given storm event(s) based on existing downstream restrictions. Additional hydrologic studies or analyses may also be required.

Calculation methods.

Development sites. For the purposes of computing peak flow rates, runoff hydrographs and storage requirements for development sites, either the SCS Soil-Cover-Complex Method as presented in the most recent version of Technical Release 55 (TR-55) shall be used or the Rational Method as specified in § 143-16B(1). When the Rational Method is used, the technical data at the end of this chapter shall be used to determine rainfall intensities, time of concentration, and runoff coefficients. The use of alternative hydrologic methodologies may be approved by the Township Engineer if sufficient justification and documentation of their application is provided.

Stormwater collection conveyance facilities.

For the purpose of designing storm sewers, open swales and other stormwater runoff collection and conveyance facilities, the Rational Method shall be utilized. Rainfall intensities for design should be obtained from the Pennsylvania Department of Transportation rainfall charts in Appendixes C through G.

Editor's Note: Appendixes C through G are included at the end of this chapter.

The design storm for storm sewers and swales that will discharge to detention facilities is the one-hundred-year storm. The ten-year design storm for storm systems discharging to detention facilities shall be acceptable, provided it can be documented that runoff exceeding the ten-year capacity of the storm system during a one-hundred-year storm event will ultimately discharge to the detention facility by alternative means, without endangering public safety or damaging private property. The design storm for all other on-site storm sewers or swales is the ten-year storm event, providing that larger storm events will not impact private property. Calculation sheets must be submitted. For storm inlets with multiple inflow pipes and/or bends where energy losses will be significant, inlet control conditions at the entrance to the outflow pipe shall be a design consideration to determine capacity.

All stormwater collection and/or conveyance systems routing water through or around the development site shall be designed for the one-hundred-year storm event, unless it can be documented that said facilities will not create a hazard. A drainage easement shall be provided to contain and convey the one-hundred-year flood event throughout the project site, beginning at the furthest upstream property line of the proposed development in the watersheds.

Predevelopment conditions. The cover type for all sites will be considered to be woods with light underbrush in good hydrologic conditions at the time of proposed development. All hydrologic parameters used to calculate peak flow rates shall use the appropriate coefficients pertaining to these conditions, as recommended in the hydrologic methodologies noted in § 143-16B(3)(a).

Post-development conditions. The hydrologic parameters used to develop peak flow rates shall be reflective of anticipated soil runoff characteristics following grading and development of the site.

Stormwater management BMP(s). Peak runoff rates for all areas within or impacting the project site shall be determined and considered in the design of stormwater management BMP(s). These calculations shall be based on land use, time of concentration and other standard hydrologic parameters.

Allowable release rates. The allowable release rates from stormwater management BMP(s), or a development site in general, shall be less [as per § 143-16B(2)] than or equal to the predevelopment peak runoff rates generated for the site. All stormwater runoff discharged from the site that is not controlled by a stormwater management BMP shall be accounted for in the determination of the allowable release rates for the full range of storm events.

Joint development of control systems. Stormwater control systems may be planned and constructed in coordination by two or more developments so long as they are in compliance with § 143-16.

Small developments. A small development shall be defined as a site that creates less than 5,000 square feet of impervious surface and shall be exempt from the preparation of a detailed stormwater management plan as specified in § 143-16C. However, such developments must still provide safe management of stormwater runoff in accordance with the standards of this article and as approved by the Township.

Applications for small developments shall include a plan that describes, narratively and graphically, the type and location of proposed on-site stormwater management techniques or the proposed connection to an existing storm sewer system.

Runoff calculations, as required at the discretion of the Township, shall be prepared in accordance with the standards of this article.

The Township shall review and approve the proposed provisions for stormwater management for a small development.

Stormwater management plan.

General requirements:

No final subdivision or land development plan shall be approved, no permit authorizing construction issued, or any earthmoving or land disturbance activity initiated until the final stormwater management plan for the development site is approved in accordance with the provisions of this article.

A letter from the Beaver County Conservation District (BCCD) approving the erosion and sedimentation control plan must also be received prior to the initiation of any grading. In the event that submission to the BCCD is not required by the Township, an erosion and sedimentation control plan prepared in accordance with the most recent version of PA DEP Chapter 102, Erosion and Sedimentation Control Program Manual, must be approved by the Township.

Recording of approved operations and maintenance program and related agreements. The owner of any land upon which permanent stormwater facilities will be placed, constructed or implemented, as described in the operations and maintenance plan, shall record the following documents in the Office of the Recorder of Deeds for Beaver County within 30 days of approval of the stormwater management plan by the Township:

The stormwater management plan, or a summary thereof.

Operations and maintenance program agreements under § 143-16C(2)(c)[6][e].

Easements under § 143-16C(5).

[4]

The Township may suspend or revoke any approvals granted for the project site upon discovery of the failure of the owner to comply with this section.

Exemptions. The following activities are specifically exempt from this article:

Use of land for gardening primarily for home consumption.

Use of land for construction of landscaping improvements, provided such improvements do not significantly alter the runoff characteristics for the land.

Agricultural use of lands when operated in accordance with a farm conservation plan approved by the local soil conservation district, or when it is determined by the local soil conservation district that such use will not cause excessive erosion and sedimentation.

Stormwater management report. A written and bound report shall be submitted, including but not necessarily limited to the following information.

Proposed name or identifying title of project, the name and address of the landowner and developer of the project site, as well as the name, address and phone number of the consultant who prepared the stormwater management plan.

Stormwater management report date and date of the latest revision to the report.

Typewritten narrative report that should include sections describing the following items:

Stormwater management report date and date of the latest revision to the report.

Typewritten narrative report that should include sections describing the following items:

[a]

Stormwater management plan objectives.

[b]

Hydrologic procedures used to develop plan.

[c]

Description(s) of predevelopment watershed conditions.

[d]

Description(s) of post-development watershed conditions.

[e]

Description(s) of proposed plan and method(s) to handle post-development runoff.

[f]

Description(s) of proposed detention facility(ies) and proposed outlet control.

[g]

Summary tables for predevelopment and post-development peak flows, detention facility allowable release rates, stage storage outflow characteristics and storm-routing results.

Watershed maps delineating predevelopment and post-development watershed boundaries as well as the flow path and segments used to determine time of concentrations for each watershed.

[4]

All hydrologic and hydraulic computations associated with the stormwater management plan, appended and referenced in the narrative.

[5]

Storm sewer calculations and watershed map delineating all subareas used to size and compute flow for the storm sewer system.

[6]

Operation and maintenance program. The report shall contain a proposed maintenance plan for all stormwater control BMP(s), in accordance with the following:

[a]

Identify the proposed ownership entity (e.g., Township, property owner, homeowners' association, other management entity).

[b]

A maintenance program for all BMP(s), outlining the type of maintenance activities, probable frequencies, personnel and equipment requirements, and estimated annual maintenance costs for the continuing operation and maintenance of all permanent stormwater BMP(s), as follows:

[i]

If a plan includes structures or lots which are to be separately owned and in which streets, sewers and other public improvements are to be dedicated to the Township, stormwater facilities may also be dedicated to and maintained by the Township.

[ii]

If a plan includes operations and maintenance by a single ownership, or if sewers and other public improvements are to be privately owned and maintained, then the operation and maintenance of stormwater BMP(s) shall be the responsibility of the owner or private management entity.

[iii]

The Township shall make the final determination on the continuing operations and maintenance responsibilities. The Township reserves the right to accept or reject the operations and maintenance responsibility for any or all of the stormwater BMP(s).

[c]

The property owner shall sign an operations and maintenance program agreement with the Township covering all stormwater facilities that are to be privately owned. The agreement shall be substantially the same as the agreement in Appendix B of this chapter.

Editor's Note: Appendix B is included at the end of this chapter.

[d]

Other items may be included in the agreement where determined necessary to guarantee the satisfactory operation and maintenance of all permanent stormwater BMP(s). The agreement shall be subject to the review and approval of the Township.

[e]

On or before the issuance of any permits by the Township, and on or before the signing of any operations and maintenance agreement by the Township, and for so long as any stormwater BMP(s) shall remain in existence and be necessary for the collection, distribution, or storage of stormwater, the developer, landowner or designated agent shall provide and maintain financial security to assure compliance with all applicable laws and regulations and the provisions of this chapter of such type and in such amount as the Township Supervisors shall from time to time prescribe.

[f]

A note shall be placed on the recorded plan: "As per the approved stormwater management plan, the Township shall have right of access to the on-site detention facility for the right of maintenance in the event the owner, assigns or heirs do not adequately maintain the facility. The owner, assigns or heirs shall reimburse the Township for all costs associated with said maintenance. The aforementioned rights granted the Township in no way diminish the responsibility of the owner, assigns or heirs of said maintenance, and no liability will be assumed by the Township associated with required access for maintenance purposes."

A copy of the proposed erosion and sedimentation control narrative and plans shall be submitted to the Township. The narrative and accompanying plans shall also be submitted to the Beaver County Conservation District for review and approval.

Stormwater controls. All proposed stormwater runoff control measures must be shown on the development site plans, including methods for collecting, conveying and storing stormwater runoff on site. The preliminary plan should provide information on the general type, location, sizing, etc., of all proposed BMP(s) and their relationship to the existing watershed drainage system.

Easements, rights-of-way, deed restrictions. Stormwater management easements shall be provided by the property owner or developer for access for inspections and maintenance, or the preservation of stormwater runoff conveyance, infiltration, and detention areas and other BMP(s), by persons other than the property owner. The purpose of the easement shall be specified in any agreement under § 143-16C(2)(c)[6][e]. Stormwater management easements are required for all areas used for off-site stormwater control, unless a waiver is granted by the Township Engineer. All existing and proposed easements and rights-of-way for drainage and/or access to stormwater control BMP(s) shall be shown and the proposed owner identified. Drainage easements shall be delineated and recorded for all permanent BMP(s), swales and storm sewers to identify their permanency and provide maintenance access. Any areas subject to special deed restrictions relative to or affecting stormwater management on the development site shall be shown.

Permits/approvals. A list of any permits/approvals relative to stormwater management that will be required from other governmental agencies (e.g., an obstructions permit from PA DEP) and anticipated dates of submission/receipt should be included with the plan submission. Copies of applications may be requested by the Township. All stormwater or drainage-related computations or reports associated with these permit applications shall be submitted to the Township for reference and for review.

One-hundred-year floodplain delineation.

Stormwater management BMP(s) located with or affecting the floodplain of any watercourse shall also be subject to the requirements of Chapter 81, Floodplain Management, as amended from time to time, which regulates construction and development within areas of the Township subject to flooding.

The one-hundred-year floodplain must be delineated on all plans for all watercourses which have a watershed area of 150 acres or greater. Where, in the judgment of the Township, private property or public BMP(s) may be adversely affected by the proposed activity, the one-hundred-year floodplain shall be established for any watercourse.

The one-hundred-year floodplain shall be delineated by one of the following methods:

The FIS study by the Federal Emergency Management Agency (FEMA).

A hydrologic report prepared by an individual registered in the Commonwealth of Pennsylvania to perform such duties. Calculations and channel hydraulic characteristics used to determine floodplain limits shall be provided.

Municipal liability disclaimer. Approval of a stormwater management plan by the Township shall not be construed as an indication that said plan complies with the requirements, laws or standards of any agency of the commonwealth, which may or may not govern said activity.

Design criteria for stormwater detention facilities. The following criteria shall be utilized for the design of proposed detention facilities.

Detention facilities shall be designed such that the post-development peak runoff rates from the developed site are controlled at levels consistent with the allowable release rates determined for the two-, ten- and one-hundred-year design storms.

All detention facilities shall be equipped with outlet structures to provide discharge control for the two-, ten- and one-hundred-year storm events. Provisions shall also be made for auxiliary structures that are capable of passing the post-development one-hundred-year storm peak runoff flows, presuming blockage of all lower flow controls, without damaging the facilities.

Shared storage facilities which provide stormwater detention for more than one development site will be encouraged. Such facilities shall meet the design criteria contained in this section. Runoff from the development sites involved shall be conveyed to the facility in a manner so as to avoid adverse impacts, such as flooding or erosion, to channels and properties located between the development site and the shared storage facilities.

Where detention facilities are used, the design of multiple-use facilities, such as ball fields or similar recreational uses, are encouraged wherever feasible.

As a general rule, detention facilities will be designed as dry basins, although wet facilities will be considered in specific situations where they can be shown to represent a significant amenity to the development and/or the Township. Facilities should be designed to induce water depths as shallow as possible.

Except in approved wet basins, stormwater detention basins will be designed to drain completely. A low-flow channel shall be installed to facilitate the conveyance of storm sewer flows to the basin outlet during frequent storm events. All interior portions of the basin will slope toward the outlet or low-flow channel at a minimum slope of 1%. (Drawing No. 8.7.4.6) (SW-04).

Editor's Note: The drawing is included at the end of this chapter.

All impoundment areas shall be adequately underdrained to prevent long-term ponding of water.

Detention facility outfall pipes shall have a minimum of two antiseepage collars installed along the profile of the pipe. Antiseepage collars shall be constructed of reinforced concrete. (Drawing No. 8.7.4.7) (SW-05).

Editor's Note: The drawing is included at the end of this chapter.

All detention facilities designed with an earthen dam shall provide a minimum of one foot of freeboard between the peak emergency spillway design flow elevation and the top of the embankment.

(9)

Where emergency spillways cannot be excavated into the existing undisturbed ground, they shall be designed and constructed with an approved geotextile fabric lining under the riprap. All riprap spillways shall be provided with a concrete cutoff wall at the spillway design crest elevation (Drawing No. 8.7.4.9) (SW-06.)

Editor's Note: The drawing is included at the end of this chapter.

(10)

All embankments shall be designed according to sound engineering practice for such structures and must meet the approval of the Township. Facilities with a design water depth in excess of 10 feet may require a supporting report from a geotechnical engineer. In general, impoundment areas shall be designed to be contained with areas excavated within existing ground, rather than fill, whenever possible. Impoundment areas designed within fill shall require a supporting report from a geotechnical engineer addressing potential infiltration concerns and recommended solutions.

(11)

The outside slopes of the embankment shall not exceed three horizontal to one vertical. The interior slopes of the structure within the pool area shall not exceed a slope of three horizontal to one vertical. Design of facilities with flatter slopes for aesthetics and as a maintenance consideration are encouraged (Drawing No. 8.7.4.11) (SW-01).

Editor's Note: The drawing is included at the end of this chapter.

Crest of the embankment shall have a minimum width of not less than 10 feet.

(12)

The embankment shall be level along the crest and along the longitudinal center line. In the event that the embankment would be overtopped by stormwater runoff, the flow over the crest and down the downstream slope would be sheet flow rather than being concentrated and eroding away the embankment. No trees shall be planted on the embankment. Should any type of protective fence be placed around the impoundment, the fence shall not be placed on the embankment or across the primary or emergency spillways.

(13)

Except where special erosion protection measures are provided, all disturbed areas will be graded evenly, topped with four inches of topsoil, fertilized, seeded and mulched by methods consistent with PennDOT Publication 408.

(14)

All outfalls to and from the facility shall be provided with end walls and erosion control measures as per § 143-19 [(Drawing No. 8.10a) (SS-02) and (Drawing No. 8. 10b) (SS-04)].

Editor's Note: Drawings cited are included at the end of this chapter.

(15)

Outlet control structures shall be constructed of reinforced concrete (cast-in-place or precast) and shall be recessed into the embankment wherever practical (Drawing No. 8.7.4.15a) (SW-02). Trash racks for low-flow control openings should be designed to provide four to 10 times the area of the low-flow opening and facilitate debris removal and maintenance (Drawing No. 8.7.4.15b) (SW-03).

Editor's Note: Drawings cited are included at the end of this chapter.

(16)

An access easement with a minimum width of 20 feet to all stormwater detention facilities shall be provided to the Township. This access shall be improved with a cartway having a minimum width of 10 feet and a maximum grade of 15%. The access easement shall include a statement on the recorded plan from the owner/operator of the facility granting access to the Township as noted in § 143-16C(5).

(17)

Detention facilities that are designed as sedimentation facilities during construction operations shall be desilted and regraded to original design dimensions and have all temporary sedimentation-control devices removed prior to their conversion to detention facilities. Low-flow channels and underdrains should be installed with the conversion of the facility.

(18)

In subdivisions or projects that are constructed in phases with individual detention facilities employed as sedimentation basins, said facilities shall be converted to their ultimate use as stormwater management facilities as soon as their tributary areas are stabilized per BCCD standards. This conversion may be requested by the Township, with supportive corroboration from the Beaver County Conservation District, and shall be implemented as outlined in the approved erosion and sedimentation control plan.

(19)

An as-built drawing shall be required for each stormwater detention facility constructed. The drawing shall represent certification of the volume of the facility and the depth-versus-storage relationship, as well as the elevational relationships and dimensions of flow controls, including emergency spillways, as appropriate. These relationships shall be shown on the drawing in table form or in report form. In the event that these relationships vary from the computations provided in the approved plan, revised storm routings may be required, at the discretion of the Township. The as-built drawing shall be stamped by a registered professional engineer or surveyor and submitted to the Township within 60 days of the completion of the facility. No facility will be approved until this as-built drawing has been approved by the Township.

Design criteria for collection/conveyance facilities.

As a general rule, no stormwater may be discharged to unprotected areas such as hillsides or fills without special erosion and/or energy-dissipation controls being installed. Stormwater shall either be conveyed to the nearest established stream channel as approved by the Township or provided with an approved energy-dissipation device. Conveyance shall be by pipe or erosion-protected ditch.

The design for culverts, pipes and other stormwater conveyance structures shall be consistent with the design of the other stormwater management facilities. In the event that these structures are to be permitted by the PA DEP or PennDOT, the design criteria required by the state agency shall be utilized.

All sites shall be graded to provide drainage away from and around structures to prevent potential flooding damage.

Collection/conveyance facilities should not be installed parallel to or close to the top or bottom of major embankments to avoid the possibility of embankment failure, with the exception of those facilities specifically designed to prohibit stormwater runoff from eroding slopes or prevent runoff from damaging downstream properties.

Stormwater shall be collected and conveyed from upslope areas in a manner designed to prevent damage to downslope property(ies) consistent with appropriate engineering standards. This system shall be identified by permanent easements with the party responsible for maintenance identified.

Disposal of stormwater from roof, foundation and driveway drains.

Individual lots that are required to provide for on-lot stormwater management BMP(s) per the stormwater management plan shall be identified on the recorded plan(s) for the subdivision.

No roof, driveway or foundation drains shall be discharged onto the right-of-way of any street or the pavement of any street. They may be connected to the street stormwater collection system of pipes or inlets. All residential dwellings not connected to a private or public stormwater collection and management system shall install a stormwater containment and disposal system at the direction of the Township in accordance with Drawing No. 8.7.6.2 (SS-13 and SS-13A).

Editor's Note: Drawings are included at the end of this chapter.

Other acceptable methods of disposal include underground tanks, infiltration devices, storm sewers, large-diameter pipe-chamber systems and grassed or other ground surfaces, provided adequate consideration is given to erosion protection, or any other method approved by the Township.

At no time will any roof, driveway or foundation drains be allowed to be connected to the sanitary sewer line.

The use of splash blocks is permitted. The location of the splash-block discharge must be a minimum of five feet from foundations and five feet from the property line. Exceptions to this method may be permitted in the instance of townhouses or similar structures where common property lines exist. No stormwater runoff may be directed in such a manner as to disturb or damage neighboring properties.

Houses located on the low side of the road can use a solid pipe or corrugated pipe (minimum of four inches diameter) to the rear of the lot to a point of discharge onto a rock apron (size and dimensions to be specified) not less than 10 feet from the adjacent neighboring property line, provided said discharge has been accounted for within the approved stormwater management plan and the discharge does not impact downstream property owners.

Lots shall be graded in such a manner as to divert stormwater runoff away from adjacent property and structures consistent with appropriate engineering standards.

Predevelopment conditions.

For the purposes of calculating predevelopment peak flow rates, all sites will be considered to be woods with light underbrush in good hydrologic condition at the time of proposed development.

For the purposes of calculating predevelopment peak flow rates, all lands shall be considered to be in good hydrologic condition.

Methods of calculations of runoff.

The methods of computation used to determine peak discharge and runoff shall be:

The USDA Soil Conservation Service Soil-Cover-Complex Method as set forth in the latest edition of Urban Hydrology for Small Watersheds, Technical Release No. 55, as published by SCS, or the Rational Method, when approved by the Engineer for small sites.

The Rational Method of Q equals CIA where Q is the peak discharge of the watershed in cubic feet per second, C is the coefficient of runoff as per runoff coefficients found in Appendix F,

Editor's Note: Appendix F is included at the end of this chapter.

I is the intensity of rainfall in inches per hour, and A is the area of watershed in acres. If the Rational Method is used, the overland velocity versus watercourse slope chart, Appendix E

Editor's Note: Appendix E is included at the end of this chapter.

shall be used to determine the average overland velocity.

If the SCS Twenty-Four-Hour, Type II Rainfall Distribution is used, the rainfall depths in inches for each of the design storms is shown below:

	Design Storm Frequency (years)	Rainfall Depth (inches)
	2	2.32
	10	3.33
	100	4.73

NOTE: For additional information or data on other return periods, consult Rainfall Duration Frequency Tables for Pennsylvania, published by PA DEP Office of Resource Management, Bureau of Dams and Waterways Management, Division of Stormwater Management, Harrisburg, Pennsylvania, February 1983, or its most recent update.

Editor's Note: Appendix D is included at the end of this chapter.

Runoff calculations shall include a hydrologic and hydraulic analysis indicating volume and velocities of flow and the grades, sizes and capacities of water-carrying structures, sediment basins, retention and detention structures and sufficient design information to construct such facilities. Runoff calculations shall also indicate both predevelopment and post-development rates for peak discharge of stormwater runoff from the project site.

Design standards for water-carrying facilities.

All storm sewer pipes, culverts and bridges (excluding detention and retention basin outfall structures) conveying water originating only from within the boundaries of the project site shall be designed for a ten-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 the one-hundred-year storm event, unless it can be demonstrated that said facilities will not create a hazard. Natural drainage easement shall be provided to contain and convey the one-hundred-year frequency flood throughout the project site. Easements shall begin at the furthest upstream property line of the proposed development in a watershed.

The capacities of storm sewers and open swales or channels shall be computed from the Manning Equation.

Additional engineering analysis may be required by the Township Engineer.

Discharging stormwater off the property to an existing facility will require supporting calculations to prove the adequacy of the downstream facilities. The developer, subject to Township approval, may elect to upgrade downstream facilities to accommodate the generated runoff.

All storm sewer pipes, culverts, bridges, outlet structures and emergency spillways shall include a satisfactory means of dissipating the energy of flow at its outlet to assure conveyance of flow without endangering the safety and integrity of the downstream drainage area.

Design standards for detention facilities.

All detention facilities shall be equipped with outlet structures capable of providing discharge control for the two-, ten- and one-hundred-year storm frequencies. Provisions shall also be made for auxiliary structures, spillways and pipe that are capable of passing the post-development one-hundred-year storm runoff flows without endangering the detention facilities.

All detention facilities constructed with earth embankments shall be designed and constructed with a minimum freeboard elevation of one foot between the peak emergency spillway design flow elevation and the top of the embankment.

All detention facility embankments shall have a minimum top width levee of 10 feet, interior slopes of not less than 3:1 and exterior slopes of not less than 2:1.

If the Rational Method is used, the design storm duration will be the one that requires the maximum storage. Such a storm will be determined by analyzing various rainfall durations to determine the maximum storage required.

A stage/discharge table for the detention facilities shall be provided.

A storage/elevation table for the detention facilities shall be provided.

Calculations, planimeter readings or other data to document storage/elevation table shall be provided.

All outlet structures and emergency spillways shall include a satisfactory means of dissipating the energy of flow at its outlet to assure conveyance of flow without endangering the safety and integrity of the basin and the downstream drainage area.

(9)

To ensure that the detention system will not become a health hazard or public nuisance, means shall be provided to drain the pond completely.

Stormwater management plan contents. The following items shall be included as part of the stormwater management plan:

Written and bound report including the following information:

Proposed name or identifying title of project.

Name and address of the landowner and developer of the project site.

Name, address and phone number of the consultant who prepared the stormwater management plan.

Stormwater management report date and date of the latest revision to the report.

(e)

Typewritten narrative outlining the objectives of the proposed stormwater management plan.

(f)

Stormwater runoff calculations for both predevelopment and post-development conditions.

(g)

If the maintenance responsibility for the detention system shall remain with the developer and his successor in title, a legal agreement will be recorded with the final plat to that effect.

(h)

An ownership and maintenance program that clearly sets forth the ownership and maintenance responsibility of all temporary and permanent stormwater management BMP(s) and erosion and sedimentation control facilities, including:

Description of temporary and permanent maintenance requirements.

Identification of a responsible individual, corporation, association or other entity for ownership and maintenance of both temporary and permanent stormwater management and erosion sedimentation control facilities.

Establishment of suitable easements for access to all BMP(s).

[4]

Establishment of a graded roadway from public highway to the detention facilities suitable for maintenance equipment access as per §§ 143-16D(16) and 143-16C(5).

Plans showing the following information:

Proposed name or identifying title of project.

Name of the landowner and developer of the project site.

Name and address of consultant who prepared the stormwater management plan.

Plan date and date of the latest revision to the plan.

(e)

Location map. A key map showing the development site location at a minimum scale of 2,000 feet to the inch shall be provided.

(f)

The names, locations and dimensions of streets, buildings, watercourses, bodies of water, swales, drainage facilities, tree masses, significant trees, wetlands and other existing or proposed features on the site or which will be affected by runoff from the development.

(g)

Existing and final contours with sufficient detail to show all stormwater surface drainage. The location of the bench mark and the datum used shall also be indicated.

(h)

The boundaries of the watershed(s) and (where applicable) subbasin(s) as they are located on the development site and identifying name(s) or number(s).

(i)

The watershed and subbasin areas.

(j)

Tract boundaries showing distances and bearings.

(k)

Soil types and boundaries as designated by the USDA SCS Soil Survey of Beaver County.

(l)

The location of the flow path utilized to estimate the predevelopment and post-development time of concentration shall be shown and identification of each flow segment on the topographic plan.

One-hundred-year floodplain delineation.

Stormwater management facilities located within or affecting the floodplain of any watercourse shall also be subject to the requirements of Chapter 81, Floodplain Management, as amended from time to time, which regulates construction and development within areas of the Township subject to flooding.

The one-hundred-year floodplain must be delineated on all plans for all watercourses which have a watershed area of 150 acres or greater. Where, in the judgment of the Township Engineer, private property or public facilities may be adversely affected by the proposed activity, the one-hundred-year floodplain shall be established for any watercourse.

The one-hundred-year floodplain shall be delineated by one of the following methods:

A hydrologic report prepared by the Federal Emergency Management Agency (FEMA).

A hydrologic report prepared by an individual registered in the Commonwealth of Pennsylvania to perform such duties.

Township liability disclaimer. Approval of a stormwater management plan by the Township shall not be construed as an indication that said plan complies with the requirements, laws or standards of any agency of the commonwealth which may or may not govern said activity.

Outlet structures in detention basins. Outlet structures in detention basins shall be constructed with reinforced concrete; Drawing Nos. 8.7.4.15a (SW-02) and 8.7.5. (SW-08).

Editor's Note: Drawings are included at the end of this chapter.

Detention basin low-flow channels. Detention basin low-flow channels shall be constructed in accordance with Detention Basin Low-Flow Channel, Drawing No. 8.7.4.6. (SW-04).

Editor's Note: The drawing is included at the end of this chapter.

Detention basin outlet pipes. Detention basin outlet pipes shall have two or more antiseep collars; Drawing Nos. 8.7.4.7 and 8.7.4.11. (SW-05 and SW-01).

Editor's Note: Drawings are included at the end of this chapter.

§ 143-17 Storm sewer trench.

All storm sewer pipes shall be installed in accordance with the standard in Drawing No. 8.8, Typical Storm Trench Detail,

Editor's Note: See SS-01, Drawing No. 8.8, included at the end of this chapter.

where located under all proposed pavements.

§ 143-18 Cradles and reinforcements for sewers.

All cradles and reinforcements for sewers shall be approved by the Engineer.

§ 143-19 Headwall/end wall.

Concrete headwalls and splash aprons shall be constructed in accordance with the construction standard in Drawing No. 8.10a, Standard Type D-2 End Wall Detail (SS-02), at the outfall of all storm sewers. Where watercourses are piped and filled, concrete headwall and splash aprons shall be constructed at both ends of the pipe. Riprap shall be placed at end walls in accordance with Drawing No. 8.10b, Rip-Rap Detail Storm Sewer Outfall (SS-04).

Editor's Note: Drawings are included at the end of this chapter.

Riprap. All riprap used for outlet protection, bank stabilization or other means of protection shall be designed and installed in accordance with specifications outlined in PennDOT Publications 408 and 72.

§ 143-20 Concrete encasement and anchors for sewers.

All concrete encasement and anchors for sewers shall be in accordance with Drawing No. 8.11, Concrete Encasement and Anchors for Sewers (SS-14),

Editor's Note: The drawing is included at the end of this chapter.

and approved by the Engineer.

§ 143-21 Connections for drop manholes.

All connections for drop manholes shall be approved by the Engineer.

§ 143-22 Design criteria for stormwater collection/conveyance facilities.

For the purpose of designing storm sewers, open swales and other stormwater runoff collection and conveyance facilities, the Rational Method shall be applied. Rainfall intensities for design should be obtained from the Pennsylvania Department of Transportation rainfall charts. The design storm for storm sewers is 10 years. The design storm for storm sewer outfall channels is 10 years. Calculation sheets must be submitted, except as follows: where it is required to collect and convey the one-hundred-year event to the detention facilities, the storm sewers shall be sized as required to accommodate such an event without overflowing onto the ground surface and in compliance with Drawing No. 8.10b, Rip-Rap Detail (SS-04).

Editor's Note: The drawing is included at the end of this chapter.

§ 143-23 Location of collection/conveyance facilities.

Collection/conveyance facilities should not be installed parallel and close to the top or bottom of a major embankment to avoid the possibility of damage to the facility due to embankment failure or of damage to the embankment due to facility failure.

§ 143-24 Storm sewer outfall channels and drainage swales.

Permissible velocities of various channel linings (vegetation, rock-lined, riprap, gabions), Drawing No. 8.15 (SD-04), shall be in accordance with Chapter 4 of the Erosion and Sediment Pollution Control Program Manual published by the Pennsylvania Department of Environmental Protection. Storm sewer outfall channels shall be trapezoidal or triangular shape with side slopes not to exceed two horizontal to one vertical (ratio). Storm sewer outfall channels shall be designed in accordance with Chapter 13 of the Pennsylvania Department of Transportation Design Manual Part 2 — Publication 13, Section 13.3, entitled "Watercourse Erosion Protection." Where drainage swales or open channels are used, they shall be suitably designed for ease of maintenance.

§ 143-25 Springs.

Any springs encountered during construction shall be piped and connected to the storm sewer system or extended to a natural watercourse, as may be approved by the Township Engineer.

§ 143-26 Roof and foundation drains.

No roof or foundation drains shall be discharged onto the right-of-way of any street or the pavement of any street. They may be connected to the street stormwater collection system of pipes or inlets. All residential dwellings not connected to a private or public stormwater collection and management system shall install a stormwater containment and disposal system in accordance with Drawing No. 8.7.6.2 (SS-13 and SS-13A).

Editor's Note: Drawings are included at the end of this chapter.

§ 143-27 Erosion and sediment control.

No regulated earth disturbance activities within the Township shall commence until approval by the Township of an erosion and sediment control plan for construction activities.

Any earth disturbance activity of 5,000 square feet or more shall comply with the regulations issued by the Pennsylvania Department of Environmental Protection (DEP) requiring the preparation and approval of an erosion and sediment control plan, 25 Pa. Code § 102.4(b).

A DEP NPDES construction activities permit is required for any earth disturbance of one acre or more with a point source discharge to surface waters or the Township's storm sewer system or five acres or more regardless of the planned runoff (hereinafter collectively referred to as "regulated earth disturbance activities"). This includes earth disturbance on any portion of, part of, or during any stage of, a larger common plan of development.

Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or county conservation district must be provided to the Township. The issuance of an NPDES construction permit [or permit coverage under the statewide general permit (PAG-2)] satisfies the requirements § 143-27A.

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

§ 143-28 Prohibited discharges.

No person in the Township shall allow, or cause to allow, stormwater discharges into the Township's separate storm sewer system which are not composed entirely of stormwater, except as provided in § 143-28B below and discharges allowed under a state or federal permit.

Discharges which may be allowed, based on a finding of the Township that the discharge(s) do not significantly contribute to pollution of surface waters of the commonwealth, are:

Discharges from fire-fighting activities;

Potable water sources including dechlorinated waterline and fire hydrant flushings;

Irrigation drainage;

Routine external building washdown (which does not use detergents or other compounds);

Air-conditioning condensate;

Water from individual residential car washing;

Springs;

Water from crawl space pumps;

(9)

Uncontaminated water from foundation or from footing drains;

(10)

Flows from riparian habitats and wetlands;

(11)

Lawn watering;

(12)

Pavement washwaters where spills or leaks of toxic or hazardous materials have not occurred (unless all spill material has been removed) and where detergents are not used;

(13)

Dechlorinated swimming pool discharges; and

(14)

Uncontaminated groundwater.

In the event that the Township determines that any of the discharges identified in § 143-28B above significantly contribute to pollution of waters of the commonwealth, or is so notified by DEP, the Township will notify the responsible person to cease the discharge.

Upon notice provided by the Township under § 143-28C hereof, the discharger will have a reasonable time, as determined by the Township, to cease the discharge, consistent with the degree of pollution caused by the discharge.

Nothing in this section shall affect a discharger's responsibilities under state law.

§ 143-29 Prohibited connections.

The following connections are prohibited, except as provided in § 143-28B:

Any drain or conveyance, whether on the surface or subsurface, which allows any nonstormwater discharge, including sewage, process wastewater, and wash water, to enter the separate storm sewer system, and any connections to the storm drain system from indoor drains and sinks.

Any drain or conveyance connected from a commercial or industrial land use to the separate storm sewer system which has not been documented in plans, maps or equivalent records and approved by the Township.

§ 143-30 Post-construction runoff control requirements.

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

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

The BMP(s) must be designed to protect and maintain existing uses (e.g., drinking water use; cold water fishery use) and maintain the level of water quality necessary to protect those uses in all streams and to protect and maintain water quality in special protection streams, as required by statewide regulations at 25 Pa. Code Chapter 93 (collectively referred to herein as "state water quality requirements").

To control post-construction stormwater impacts from regulated earth disturbance activities, state water quality requirements can be met by BMP(s), 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:

Infiltration: replication of preconstruction stormwater infiltration conditions;

Treatment: use of water quality treatment BMP(s) to ensure filtering out of chemical and physical pollutants from the stormwater runoff; and