Township of Aleppo, PA
Allegheny County
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Table of Contents
Table of Contents
This article is adopted and implemented to achieve the following general purposes and objectives:
A. 
To manage stormwater runoff resulting from land alteration and disturbance activities as required by the Pennsylvania Storm Water Management Act (Act 167 of 1978, as amended).[1]
[1]
Editor's Note: See 32 P.S. § 680.1 et seq.
B. 
To utilize and preserve the desirable existing natural drainage systems and to preserve the flood-carrying capacity of streams.
C. 
To encourage natural infiltration of rainfall to preserve groundwater supplies and stream flows.
D. 
To provide for adequate maintenance of all permanent stormwater management facilities in the municipality.
The provisions of this article shall apply to all subdivisions and land developments, unless specifically exempted or otherwise modified herein.
A. 
General requirements. No final subdivision or land development plan shall be approved, no permit authorizing construction issued, nor 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.
B. 
Exemptions for small developments.
(1) 
At the time of application, the Township shall determine if the subdivision or land development qualifies as a small development and, therefore, is eligible for a simplified stormwater plan submission. For the purposes of this article, a "small development" is any subdivision or land development which results (or will result when fully constructed) in the creation of 3,000 or less square feet of impervious surface area.
(2) 
Small developments shall be exempt from the preparation of a stormwater management plan as specified by Subsection C and D of this section. However, such developments must still provide safe management of stormwater runoff in accordance with the performance standards of § 350-48B of this article and as approved by the Township Engineer. Any stormwater management facilities constructed as part of the development shall be designed to control the peak stormwater runoff in accordance with §§ 350-48 and 350-49 of this article.
(3) 
Applications for small developments shall include a plan which 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. The plan should show accurately site boundaries; contours at two-foot intervals for all sites, with spot elevation for relatively level tracts; location of watershed and/or subarea boundaries on the site (if applicable); and any watercourses, floodplains or existing drainage facilities or structures located on the site.
(4) 
Stormwater management plans for small developments do not have to be prepared by a registered professional engineer or land surveyor. Whenever the submission of runoff calculations is required by the Township Engineer, they shall be prepared in accordance with § 350-49 of this article.
(5) 
The Township Engineer shall review and approve the proposed provisions for stormwater management for a small development. Where the applicant is proposing to connect to an existing storm sewer, the applicant shall demonstrate that sufficient capacity exists in the storm sewer from the point of connection to the point of outlet in the natural drainage system. The Township Engineer shall determine if the proposed development site is part of a larger parcel or tract for which a stormwater management plan was approved previously and, therefore, subject to any specific stormwater management controls contained in the prior plan.
(6) 
For a parcel or tract of land held under single ownership, only one application for a small development as defined above shall be permitted before requiring a stormwater management plan for the entire parcel.
C. 
Stormwater plan contents: preliminary S/LD plan submission.
(1) 
General format. The stormwater plan shall be prepared using the general requirements for plan format contained in this section with the following additions:
(a) 
Watershed location. Provide a locator map showing the development site location within the watershed and watershed sub-basin(s) as identified by the Pennsylvania Department of Environmental Protection. On all site drawings, show the boundaries of the watershed(s) and (where applicable) sub-basin(s) as they are located on the development site and identify watershed name(s) and sub-basin number(s).
(b) 
Floodplain boundaries. Identify one-hundred-year floodplain boundary on the development site (as applicable), as identified on the Township's Flood Insurance Rate Map (FIRM).
(c) 
Natural features. Show all bodies of water (natural and artificial), watercourses (permanent and intermittent), swales, wetlands and other natural drainage features on the development site, or which will be affected by runoff from the development.
(d) 
Soils. Provide an overlay showing soil types and boundaries within the development site (consult county, NRCS, U.S. Geologic Survey for information).
(e) 
Contours. Show existing and final contours at intervals of two feet; in areas with relatively level slope, spot elevation may be used.
(f) 
Stormwater management controls. Show any existing stormwater management or drainage controls and/or structures, such as storm sewers, swales, culverts, etc., which are located on the development site or which are located off site but will be affected by runoff from the development.
(2) 
Professional certification. The stormwater management plan (including all calculations) must be prepared and sealed by a registered professional engineer, or such other professional persons who are qualified to make certification under the laws of Pennsylvania.
(3) 
Runoff calculations. Calculations for estimating predevelopment and post-development discharge rates and for designing proposed stormwater control facilities must be submitted with the stormwater management plan. All calculations shall be prepared using the methods and criteria prescribed by §§ 350-48 and 350-49 of this article.
(4) 
Stormwater controls. All proposed stormwater runoff control measures must be shown on the plan, including methods for collecting, conveying and storing stormwater runoff on site which are to be used both during and after construction. Erosion and sedimentation controls should be shown. The preliminary plan should provide information on the general type, location, sizing, etc., of all proposed facilities and their relationship to the existing watershed drainage system.
(5) 
Easements, rights-of-way, deed restrictions. All existing and proposed easements and rights-of-way for drainage and/or access to stormwater control facilities shall be shown, and the proposed owner identified. Any areas subject to special deed restrictions relative to or affecting stormwater management on the development site shall be shown.
(6) 
Other permits/approvals. A list of any approvals/permits relative to stormwater management that will be required from other governmental agencies (e.g., an obstruction permit from PADEP) and anticipated dates of submission/receipt should be included with the preliminary plan submission. Copies of applications may be requested by the Township where they may be helpful for the stormwater plan review.
(7) 
Maintenance program. The preliminary application shall contain a proposed maintenance plan for all stormwater control facilities, 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 facilities, outlining the type of maintenance activities, probable frequencies, personnel and equipment requirements, and estimated annual maintenance costs.
(c) 
Identify the method of financing continuing operation and maintenance if the facility is to be owned by other than the Township or other governmental agency.
D. 
Stormwater plan contents: final S/LD plan submission.
(1) 
All information pertaining to stormwater management from the preliminary plan, along with any changes.
(2) 
Final maps showing the exact nature and location of all temporary and permanent stormwater management controls, along with design and construction specifications. Details for the construction of all facilities shall be included as part of the construction drawings.
(3) 
A schedule for the installation of all temporary and permanent stormwater control measures and devices.
(4) 
An accurate survey showing all current and proposed easements and rights-of-way and copies of all proposed deed restrictions.
(5) 
A maintenance program establishing ownership and maintenance responsibilities for all stormwater control facilities (identify specific person or entity) and detailing financial requirements and sources of funding. Submit any legal agreements required to implement the maintenance program and copies of the maintenance agreement as specified by § 350-51B of this article.
(6) 
Financial guarantees, consistent with § 350-25 of this chapter, to ensure that all stormwater controls are installed properly and functioning satisfactorily.
A. 
Preapplication phase.
(1) 
During the preapplication phase (see § 350-13 of this chapter), applicants are urged to consult with the Township, the Allegheny County Planning Department, and the County Conservation District on the requirements for safely managing stormwater runoff from the development site in a manner consistent with the Township ordinances and the watershed stormwater management plan; these agencies may be helpful in providing the data that is necessary for preparing the stormwater management plan for the development site.
(2) 
Applicants are encouraged to submit a sketch plan with a narrative description of the proposed stormwater management controls for general guidance and discussion with Township and county agencies.
(3) 
The preapplication phase is not mandatory, and any review comments provided by Township or county agencies are advisory only and do not constitute any legally binding action on the part of the Township or any county agency.
B. 
Preliminary and final stormwater plan reviews.
(1) 
Requirements. Two sets of the stormwater management plan, in accordance with the requirements of § 350-44, will be submitted with the preliminary and final application.
(2) 
Review by the Township Engineer and the County Conservation District. Preliminary and final plans will be reviewed by the Township Engineer and the County Conservation District.
(3) 
Review by County Planning Department. A copy of the preliminary plan, along with all runoff calculations, will be forwarded to the Allegheny County Planning Department. A report of the findings will be returned to the Township within 30 days. No plan will be approved which receives a negative watershed impact review by the county.
(4) 
Notification of affected municipalities. When a plan is submitted for review, municipalities downstream of the proposed project will be notified by the Township in writing. As part of the notification, a date will be established by which any comments from the affected municipalities must be received. Copies of the plans will be made available to the municipalities upon request. Comments received will be submitted to the Planning Commission and the Township Commissioners.
(5) 
Township Engineer review. The Township Engineer shall approve or disapprove the preliminary and final stormwater management plan based on the requirements of the Township ordinances, the standards and criteria of the watershed stormwater management plan, and good engineering practice. The Engineer shall submit a written report, along with supporting documentation, to the Township Planning Commission for consideration as part of the overall plan review.
(6) 
The Township Engineer's decision to approve or disapprove a stormwater management plan shall be final.
(7) 
Approval. No preliminary or final approval for any application involving land disturbance will be granted until a stormwater management plan for the site has been approved.
(8) 
Permits. Where the application requires an obstruction or erosion/sedimentation control permit from PADEP, then final plan approval shall be contingent upon receipt of such permits. However, no building permit shall be issued, or construction started, until the permits are received and copies filed with the Township.
Upon recording of the final plat, the applicant may commence to install or implement the approved stormwater management controls, subject to the provisions of § 350-45B above. If site development or building construction does not begin within 12 months of the date of the final approval of the plan, then before doing so, the applicant shall resubmit the stormwater management plans to verify that no condition has changed within the watershed that would affect the feasibility or effectiveness of the previously approved stormwater management controls. Furthermore, if for any reason development activities are suspended for 12 months or more, then the same requirement for resubmission of the stormwater management plan shall apply. The terms of these subsequent reviews shall be subject to the provisions of Article III of this chapter.
Requests for modifications of the final approved stormwater management controls shall be submitted to the Township Engineer as follows:
A. 
If the request is initiated before construction begins, the stormwater plan must be resubmitted and reviewed according to the procedures in § 350-45 of this article.
B. 
If the request is initiated after construction is underway, the Township Engineer shall have the authority to approve or disapprove the modification, based on field inspection, provided the requested changes in stormwater controls do not result in any modifications to other approved Township land use/development requirements (such as required building setbacks, yards, etc.). A plan modification, in accordance with applicable Township procedures, shall be necessary if any such requirements are affected. The Township Engineer shall submit a record of all approved changes for the stormwater management controls to the Township prior to the acceptance of any improvements by the Township. Modifications must not affect the compliance of the plan with the design standards as set forth in Article IV of this chapter and Article III and § 400-31 of Chapter 400, Zoning.
A. 
General performance standards. The following provisions shall be considered the overriding performance standards against which all proposed stormwater control measures shall be evaluated, and they shall apply in all watersheds in the Township.
(1) 
Any landowner and any person engaged in the alteration or development of land which may affect stormwater runoff characteristics shall implement such measures as are reasonably necessary to prevent injury to health, safety or other property. Such measures shall include such actions as are required:
(a) 
To assure that the maximum rate of stormwater runoff is no greater after development than prior to development activities; or
(b) 
To manage the quantity, velocity and direction of resulting stormwater runoff in a manner which otherwise adequately protects health and property from possible injury.
(2) 
The stormwater management plan for the development site must consider all the stormwater runoff flowing over the site.
(3) 
Where the existing storm sewers are reasonably accessible, proposed developments may be required to connect with the storm sewer system unless insufficient capacity or other reasons can be demonstrated to prevent the connection.
B. 
Stormwater performance standards. The stormwater performance standards contained in this section are intended to implement the standards contained in the Pennsylvania Storm Water Management Act (Act 167 of 1978, as amended).[1] If there is any discrepancy between the provisions of this chapter and the standards of the Act, or subsequent amendments, then the standards of the current Act shall govern.
[1]
Editor's Note: See 32 P.S. § 680.1 et seq.
A. 
Design storms.
(1) 
The two-, ten- and one-hundred-year design storm frequencies shall be used for analyzing stormwater runoff for predevelopment and post-development conditions as well as for designing runoff control facilities in all Township watersheds. The NRCS twenty-four-hour, Type II Rainfall Distribution shall be used for all analyses. The twenty-four-hour rainfall volumes for each of these design storms is shown below:
Design Storm Frequency
Rainfall Depth in Inches
2-year
2.14
10-year
3.24
100-year
4.59
(2) 
For additional information or data on other return periods, consult "Rainfall Duration Frequency Tables for Pennsylvania," published by PADEP Office of Resource Management, Bureau of Dams and Waterways Management, Division of Stormwater Management, Harrisburg, Pennsylvania, February 1983.
B. 
Calculation methods.
(1) 
Development sites. For the purposes of computing peak flow rates, runoff hydrographs, and storage requirements for development sites, the NRCS Soil Cover Complex Method as presented in the most recent version of Technical Release 55 (TR-55), or equal, shall be used.
(2) 
Stormwater collection/conveyance systems. For the purposes of designing storm sewers, open swales and other stormwater runoff collection and conveyance facilities, the Rational Method shall be applied. Rainfall intensities for design shall be obtained from the Pennsylvania Department of Transportation Rainfall Charts, unless otherwise specified by the Township Engineer.
(3) 
Predevelopment conditions. For the purposes of calculating predevelopment peak flow rates, all sites will be considered to be in a heavily forested cover type at the time of development.
C. 
Release rate percentage.
(1) 
Application. All subdivisions and land development activities which result in an increase in the post-development peak rate of stormwater runoff from any outfall on the development site shall be assumed to have a release rate percentage of 100%, unless otherwise specified by the Township Engineer.
(2) 
Definition. The release rate percentage defines the percentage of the predevelopment peak rate of runoff that can be discharged from the site after development. It applies uniformly to all land developments or alterations within a sub-basin, and the post-development rate of runoff discharged from the development site cannot exceed the release rate percentage for the sub-basin in which it is located.
(3) 
Procedure for use. The steps that must be followed to use the release rate percentage for a particular development site are:
(a) 
Compute the predevelopment and post-development runoff hydrographs for the site using the prescribed calculation method for the two-, ten- and one-hundred-year design storms, applying no on-site detention for stormwater management. If the post-development peak runoff rate is less than or equal to the predevelopment peak runoff rate, then additional stormwater control shall not be required. If the post-development peak runoff rate is greater than the predevelopment value, then stormwater detention will be required and proceed to § 350-54B.
(b) 
Multiply the release rate percentage(s) by the predevelopment rate of runoff from the development site to find the allowable release rate from the development site for the two-, ten- and one-hundred-year storm events.
D. 
No harm evaluation.
(1) 
An applicant may seek to exceed the otherwise applicable sub-basin release rate percentage by performing the no harm evaluation, which requires an independent engineering analysis to demonstrate that other reasonable options exist to protect downstream areas from harmful storm runoff impacts.
(2) 
The no harm evaluation shall be prepared by a registered engineer, or land surveyor who is experienced in hydrology and hydraulics, in accordance with the procedures contained in § 350-54 of this article.
(3) 
The analysis for the no harm evaluation shall be submitted to the Township Engineer for review and approval.
A. 
No earthmoving activity, including cuts and fills, excavation, removal of topsoil, trees, or vegetative cover of the land, shall commence until the plans for minimizing soil erosion and sedimentation, both during and after construction, have been approved.
B. 
The erosion and sedimentation plan shall be prepared in accordance with the Pennsylvania erosion and sedimentation regulations (25 Pa. Code Chapter 102) and the standards and specifications of the Allegheny County Conservation District.
C. 
The erosion and sedimentation control plan shall specifically indicate all erosion and sedimentation control measures to be utilized on the site. The plan shall meet the following requirements:
(1) 
The erosion and sedimentation control plan shall be prepared by persons trained and experienced in erosion and sedimentation control methods and techniques.
(2) 
The erosion and sedimentation control plan shall be designed to prevent accelerated erosion and sedimentation and shall consider all factors which contribute to erosion and sedimentation, including, but not limited to, the following:
(a) 
The topographic features of the project area;
(b) 
The types, depth, slope and areal extent of the soils;
(c) 
The proposed alteration to the area;
(d) 
The amount of runoff from the project area and the upstream watershed area;
(e) 
The staging of earthmoving activities;
(f) 
Temporary control measures and facilities for use during earthmoving;
(g) 
Permanent control measures and facilities for long-term protection; and
(h) 
A maintenance program for the control facilities, including disposal of materials removed from the control facilities or project area.
D. 
Proposed erosion/sedimentation control measures shall be submitted with the stormwater management plan as part of the applicant's preliminary and final plans.
E. 
The plan should show the type, location, and application of the proposed erosion/sedimentation control measures and include the calculations and criteria used in designing them.
F. 
Some of the guides to be followed in designing the erosion/sedimentation control measures include:
(1) 
The smallest practicable area of soil should be exposed at any one time during construction, and exposure should be limited to the shortest practicable period of time.
(2) 
Temporary ditches, dikes, vegetation, and/or mulching shall be used to protect critical areas exposed during development.
(3) 
Sediment basins (debris basins, desilting basins, or silt traps) shall be installed and maintained to removed sediment from runoff waters from land undergoing development.
(4) 
Wherever possible, temporary erosion/sedimentation control measures should be designed to serve as part of a site's permanent stormwater management control system.
(5) 
Permanent vegetation and erosion control structures should be installed as soon as practicable during construction activities.
(6) 
Wherever feasible, natural vegetation should be retained and protected, and natural grade alterations kept to a minimum.
A. 
Maintenance responsibilities.
(1) 
The stormwater management plan for the development site shall establish responsibilities for the continuing operation and maintenance of all proposed stormwater control facilities.
(2) 
The Township Commissioners shall make the final determination of the continuing maintenance responsibilities as part of the final application review based on the recommendation of the Planning Commission. The Township Commissioners reserve the right to accept or reject the ownership and operating responsibility of any or all of the stormwater management controls.
B. 
Maintenance agreement.
(1) 
Prior to final approval of the stormwater management plan for the site, the property owner/applicant shall sign and record a maintenance agreement covering all stormwater control facilities which are to be privately owned. The agreement shall have the following stipulations:
(a) 
The owner/applicant shall maintain all facilities in accordance with the approved maintenance schedule and shall keep all facilities maintained in a safe and attractive manner.
(b) 
The owner/applicant shall convey to the Township easements and/or rights-of-way to assure access for periodic inspections by the Township and maintenance, if required.
(c) 
The owner/applicant shall keep on file with the Township the name, address and telephone number of the person or company responsible for maintenance activities. In the event of a change, new information will be submitted to the Township within 10 days of the change.
(d) 
The owner/applicant shall establish any special maintenance funds or other financing sources, in accordance with the approved maintenance plan.
(e) 
If the owner/applicant fails to maintain the stormwater control facilities, following due notice by the Township to correct the problems, the Township shall perform the necessary maintenance or corrective work. The owner/applicant shall reimburse the Township for all costs.
(2) 
Other items may be included in the agreement where determined necessary to guarantee the satisfactory maintenance of all facilities. The maintenance agreement shall be subject to the review and approval of the Township Solicitor.
A. 
The Township Engineer or a designated representative shall inspect the construction of the temporary and permanent stormwater management controls for the development site. The permittee shall notify the Township at least 48 hours in advance of the completion of the following key development phases:
(1) 
At the completion of preliminary site preparation, including stripping of vegetation, stockpiling of topsoil, and construction of temporary stormwater management and erosion control facilities.
(2) 
At the completion of rough grading, but prior to placing topsoil, permanent drainage, or other site development improvements and ground covers.
(3) 
During construction of the permanent stormwater facilities at such times as specified by the Township Engineer.
(4) 
Completion of permanent stormwater management facilities, including established ground covers and plantings.
(5) 
Completion of any final grading, vegetative control measures, or other site restoration work done in accordance with the approved plan and permit.
B. 
No work shall commence on any subsequent phase until the preceding one has been inspected and approved. If there are deficiencies in any phase, the Township Engineer shall issue a written description of the required corrections and stipulate the time by which they must be made.
C. 
If, during construction, the contractor or permittee identifies any site conditions, such as subsurface soil conditions, alterations in surface or subsurface drainage, which could affect the feasibility of the stormwater management design, the Township Engineer shall be notified within 24 hours of the discovery of such condition and request a field inspection. The Township Engineer shall determine if the condition requires a stormwater plan modification.
D. 
In cases where stormwater facilities are to be installed in areas of landslide-prone soils, or where other special site conditions exist, the Township may require special precautions such as soil tests and core borings, full-time resident inspectors, and/or similar measures. All costs of any such measures shall be borne by the developer/subdivider.
A. 
Neither the granting of any approval under the stormwater management provisions of this section, nor the compliance with the provisions of this section, or with any condition imposed by a Township official hereunder, shall relieve any person from any responsibility imposed by law, nor impose any liability upon the Township for damages to persons or property.
B. 
The granting of a permit which includes any stormwater management facilities shall not constitute a representation, guarantee or warranty of any kind by the Township, or by an official, employee or consultant thereof, of the practicability of safety of any structure, use or other plan proposed and shall create no liability upon or cause of action against such public body, official, employee or consultant for any damage that may result pursuant thereto.
Design criteria for stormwater management facilities:
A. 
General design guidelines.
(1) 
Applicants may select runoff control techniques, or combinations of techniques, which are most suitable to control stormwater runoff from the development site. All controls are subject to the approval of the Township Engineer. The Engineer may request specific information on design and/or operating features of the proposed stormwater controls in order to determine their suitability and adequacy in terms of the standards of this chapter.
(2) 
In selecting and designing stormwater management systems and controls, applicants may be guided by the following references:
(a) 
"Urban Hydrology for Small Watersheds," Technical Release No. 55, USDA, Natural Resources Conservation Service, 1975 (or most recent edition).
(b) 
"Soil Erosion and Sedimentation Control Manual," Pennsylvania Department of Environmental Protection, March 1982.
(c) 
"Standards and Specifications for Soil Erosion and Sediment Control," Maryland Water Resources Administration, 1983.
(d) 
"Urban Stormwater Management," Special Report No. 49, American Public Works Administration, 1981.
(e) 
"Water Resources Protection Measures in Land Development, A Handbook," University of Delaware Water Resources Center, April 1974.
(f) 
"Design and Construction of Sanitary and Storm Sewers," WPCF Manual of Practice No. 9, Water Pollution Control Federation, 1970.
(3) 
Methods of stormwater runoff detention and control.
(a) 
The following is a listing of detention and control methods which may be used in stormwater management systems, if appropriate. The choice of control techniques is not limited to those appearing on this list.
[1] 
Detention basins. See standards in Subsection B of this section.
[2] 
Rooftop storage.
[3] 
Parking lot and street storage.
[4] 
Seepage pits, seepage trenches, level spreaders, or other infiltration structures.
[5] 
Porous pavement and concrete lattice block surfaces.
[6] 
Grassed channels and vegetated strips.
[7] 
Routed flow over grass.
[8] 
Decreased impervious area coverage.
(b) 
The use of other control methods which meet the criteria in this section will be permitted when approved by the Township Engineer. Various combinations of methods should be designed to suit the particular requirements of the type of development and the topographic features of the project area.
(4) 
Maintenance of natural drainageways. All natural streams, channels, swales, drainage systems and/or areas of surface water concentration shall be maintained in their existing condition unless an alteration is approved by the Township. All encroachment activities shall comply with the requirements of Chapter 105 (Water Obstructions and Encroachments) of Title 25, Rules and Regulations of the Pennsylvania Department of Environmental Protection.
(5) 
The applicant should consider the effect of the proposed stormwater management techniques on any special soils conditions or geological hazards which may exist on the development site. In the event such conditions are identified on the development site, the Township may require in-depth studies by a competent geotechnical engineer.
B. 
Criteria for stormwater detention facilities.
(1) 
If detention facilities are utilized for the development site, the facility(ies) shall be designed such that the post-development peak runoff rates from the developed site are controlled to those rates defined by the sub-basin release rate percentage or no harm evaluation for the two-, ten- and one-hundred-year design storms.
(2) 
All detention facilities shall be equipped with outlet structures to provide discharge control for the two-, ten- and one-hundred-year storm frequencies. Provisions shall also be made for auxiliary structures that are capable of passing the post-development one-hundred-year storm runoff flows without damaging the facilities.
(3) 
Shared storage facilities, which provide stormwater detention for more than the development site, may be considered within a single sub-basin. Such facilities shall meet the design criteria contained in this section. In addition, 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.
(4) 
Where detention facilities are used, the design of multiple-use facilities, such as ball fields or similar recreational uses, is encouraged wherever feasible.
(5) 
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.
(6) 
Except in approved wet basins, stormwater detention basins will be designed to drain completely. All interior portions of the basin will slope toward the outlet, or low-flow sluice, at a minimum slope of 2%.
(7) 
In general, facilities should be designed to have design water depths as shallow as possible.
(8) 
All detention facilities involving an earth embankment shall be designed with a minimum freeboard of one foot between the peak emergency spillway design flow elevation and the top of the embankment.
(9) 
All embankments will 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 shall require a supporting report from an engineer experienced in the design of earth embankments and shall be constructed under the supervision of the engineer.
(10) 
The outside slopes of the embankment shall not exceed two horizontal to one vertical. The interior slopes of the structure within the pool area should not exceed a slope of three horizontal to one vertical.
(11) 
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 approved by the Township.
(12) 
Each inlet and outlet to the facility shall be provided with erosion control measures approved by the Township.
(13) 
Outlet control structures shall be constructed of reinforced concrete (cast-in-place, precast, or block) and provided with debris grates approved by the Township Engineer.
(14) 
All impoundment areas shall be adequately underdrained to prevent long-term ponding of water.
(15) 
All detention facilities shall be provided with an access road (with a legal easement) for maintenance purposes. Such roads shall be a minimum of 10 feet wide and have a maximum grade of 15%.
(16) 
Control and removal of debris both in the storage facility and in all inlet or outlet devices shall be a design consideration.
(17) 
Inflow and outflow structures, pumping stations, and other structures shall be protected and designed to minimize safety hazards.
(18) 
Landscaping shall be provided for the facility which harmonizes with the surrounding area.
(19) 
An as-built drawing shall be required for each stormwater detention facility constructed. The drawing shall represent an engineering certification of the volume of the facility and the depth vs. storage relationship. This relationship shall be shown on the drawing in table form. The drawing shall be stamped by a registered professional engineer and submitted to the Township within 60 days of the completion of the facility. No facility will be accepted until this requirement has been fulfilled.
C. 
Criteria for collection/conveyance facilities.
(1) 
As a general rule, no stormwater may be discharged to unprotected areas such as hillsides 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 Engineer or be provided with an approved energy dissipation device. Conveyance shall be by pipe or erosion-protected ditch.
(2) 
The design for culverts, pipes and other stormwater conveyance structures shall be consistent with the design of the other stormwater management facilities.
(3) 
All sites shall be graded to provide drainage away from and around structures to prevent potential flooding damage.
(4) 
Lots located on the high side of streets shall extend roof and french drains to a properly sized storm sewer located within the street right-of-way. Low-side lots may extend roof and french drains to a stormwater collection/conveyance system or natural watercourse in accordance with the approved stormwater management plan for the development site.
(5) 
Collection/conveyance facilities should not be installed parallel and close to the top or bottom of major embankments to avoid the possibility of failing or causing the embankments to fail.
D. 
Criteria for dry sumps.
(1) 
All dry sumps designed for accepting surface water from roof or driveway areas shall be designed according to Exhibit No. 4, shown in Appendix No. 1, unless otherwise approved by the Township Engineer.[1]
[1]
Editor's Note: Appendix No. 1 is on file in the Township offices.
(2) 
Each sump shall be designed to store a minimum water volume equivalent to one inch of water covering the tributary area. For example, a sump for a one-thousand-two-hundred-square-foot roof area would be designed to store a water volume of 100 cubic feet. The total storage area, assuming the sump is 50% rock and 50% voids, would be 200 square feet.
(3) 
Dry sumps should be elongated in a three-to-one length to width ratio and be oriented with the long dimension parallel to the contour.
(4) 
Dry sumps must be constructed in undisturbed ground only. No dry sumps shall be permitted in fill material.
(5) 
The minimum distance between a dry sump and the property line shall be 20 feet.
(6) 
Dry sumps shall not be permitted in or upslope of areas determined by the county or other competent person to be susceptible to landslides.
E. 
Disposal of stormwater from roof and driveway drains.
(1) 
Unless otherwise approved by the Township, no stormwater from roofs or driveway drains shall be discharged to the street surface or curb underdrain.
(2) 
Acceptable methods of disposal include properly designed dry sumps, grassed or other ground surfaces with adequate consideration being given to erosion protection, storm sewers, or any other method approved by the Township.