The stormwater management plan shall be prepared using the general performance and technical standards requirements for plan format contained in Part 1, the Subdivision and Land Development Ordinance, and in this article with the following additions:
Watershed location map: Provide a key map showing the location of the development site within the watershed(s) and watershed(s) subareas(s). On all site drawings, show the boundaries of the watershed(s) and subarea(s) as they are located on the development site and identify watershed name(s) and subarea number(s). Example: Use a USGS map with the watershed, watershed subareas, and the subject property all outlined and designated.
Subwatershed map: A plan must be submitted showing all the drainage areas and subwatersheds for the pre- and post-development peak runoff calculations. Example: Use the site plan and draw the watersheds and subwatersheds on the plan.
Floodplain boundaries: Identify one-hundred-year floodplain on the development site as shown on the FEMA mapping where applicable. In the case where no FEMA mapping exists for a watercourse that boarders the proposed development site, the applicant's determination of the one-hundred-year floodplain for any watercourse or water body on the development site shall be used.
Natural features: Show all bodies of water (natural and artificial), watercourses (permanent and intermittent), swales, wetlands and other natural drainage courses on the development site, or which will be affected by runoff from the development.
Soils: Provide a map showing soil types and boundaries within the development site (consult county, SCS, U.S. Geologic Survey for information). The soils must be defined on the plan.
Contours: Show existing and final contours at intervals of two feet; in areas with slopes greater than 15%, five-foot contour intervals may be used.
Stormwater management controls: Show any existing stormwater management and/or drainage 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.
Wetlands: Show any areas on the plan which have soils with hydric inclusions, are shown on the National Wetlands Inventory Map and/or support common wetland plants. These areas must be delineated by a registered professional engineer who specializes in this field.
A Soil Erosion and Sedimentation Pollution Control Plan or NPDES Plan in accordance with Chapter 102 of PaDEP Administrative Code Title 25 as authorized by the Clean Streams Law, Act 222, amended, and current Borough Erosion and Sedimentation Control Ordinance must be submitted.
Land cover: Show existing and final land cover classifications as necessary to support and illustrate the runoff calculations performed.
Drainage area delineations: Show the boundaries of the drainage areas employed in the runoff calculations performed.
Stormwater management controls: Show any existing stormwater management or drainage controls and/or structures, such as sanitary and 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.
DEP has regulations that require municipalities to ensure design, implementation and maintenance of best management practices (BMPs) that control runoff from new development and redevelopment after regulated earth disturbance activities are complete. These requirements include the need to implement post-construction with assurance of long-term operations and maintenance of those BMPs.
Stormwater management facilities shall be constructed in accordance with the following minimum specifications:
All workmanship and materials shall conform to the borough construction standards. In addition, all workmanship and materials shall conform to the latest edition of PennDOT Form 408 and be supplied by manufacturers or suppliers listed in PennDOT's Bulletin 15.
All connections to existing storm sewer pipes shall be made by construction of a suitable junction box (inlet or manhole) to provide access for clean-out. No blind connections shall be permitted.
All pipe outlets shall discharge onto a stone riprap blanket to prevent erosion of soil. Riprap shall be sized considering pipe exit velocities plus a factor of safety of 1.5.
The discharge of stormwater runoff shall be to a well-defined drainage course which has a defined bed and bank. If stormwater runoff cannot be discharged to a defined drainage course, documentation of written recorded drainage easement permission from each downstream property owner shall be provided for all properties between the source of discharge and the defined drainage course.
The stormwater management plan (including all calculations) must be prepared, signed and sealed by a registered professional engineer, or land surveyor with training and expertise in hydrology and hydraulics, or such other professional persons as are qualified to make certification under the laws of Pennsylvania. The preparer of the stormwater management plan must fill out and submit Appendix C with said plan.
Editor's Note: Appendix C is included at the end of of this chapter.
Runoff calculations are the acceptable methods of calculation for use in determining the stormwater runoff correspondence with recommendations of the Monongahela River Watershed Plan, prepared by the county, in order to maintain a uniform, watershed wide approach. The following methods for calculating pre- and post-development runoff rates have been stipulated in the standards and criteria of the watershed plan:
Methods of runoff calculations, such as:
All pertinent information used to generate the pre- and post-developed discharge rates must be included with the stormwater management plan. Also, the calculations for the sizing of the stormwater control facilities must be submitted with the stormwater management plan.
All inflow hydrographs to detention facilities must be routed using methodology that analyzes detention storage and outflow simultaneously with respect to time. The modified-puls method or approved equal, as found in Haested Method's Pond 2 or the Army Corps of Engineers HEC-1, is recommended.
The following provisions shall be considered the overriding performance standards against which all proposed stormwater control measures shall be evaluated, and they shall apply to all areas of the borough.
Stormwater shall not be permitted, as a result of development undertaken after adoption of this Part 2 to collect upon any property, or to pass from one property to another in a concentrated flow without benefit of a legal easement, or to cross a public street on the surface.
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:
To assure that the maximum rate of stormwater runoff is no greater after development than prior to development activities; and
To manage the quality, velocity and direction of resulting stormwater runoff in a manner which will not adversely impact the health on, or value of, any affected properties.
In the case of a development in which the total of the building and paved surfaces on the site exceed 10,000 square feet, the developer shall provide as part of the design a stormwater management narrative signed and sealed by an engineer licensed in the Commonwealth of Pennsylvania. The stormwater management narrative shall include an analysis of both pre- and post-developed runoff conditions.
For the analysis of redevelopment projects 20% of the existing impervious surface shall be considered meadow in good condition.
Post-development runoff rates after development shall not exceed the pre-developed runoff rates including the reduction in impervious surface required for redevelopment projects.
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 must be shown on a separate plan. 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.
If the development is to be constructed in stages, the applicant must demonstrate that stormwater facilities will be installed to manage stormwater runoff safely during each stage of development.
A schedule for the installation of all temporary and permanent stormwater control measures and devices shall be submitted.
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. Show any areas subject to special deed restrictions relative to or affecting stormwater management on the development site.
Stormwater management easements are required for all areas used for off site stormwater control, unless a waiver is granted by the municipality.
Stormwater management easements shall be provided by the property owner if necessary for access for inspections and maintenance, or preservation of stormwater runoff conveyance, infiltration, and detention areas and other BMPs, by persons other than the property owner. The purpose of the easement shall be specified in any agreement under Section 405.
If a conservation easement is provided, the long-term ownership, access, maintenance, and use restrictions must be identified on the recording plan.
A list of any approvals/permits relative to stormwater management that will be required from other governmental agencies (e.g., a water obstruction permit from PaDEP or approval from Allegheny County Planning), and anticipated dates of submission/receipt should be included with the preliminary plan submission. Copies of applications must be submitted to the borough.
A list of any permits relative to wetlands along with a wetlands study must be submitted to the borough if wetlands are found on the development site. The wetlands study must be prepared, signed and sealed by a person certified to do such work.
The preliminary application shall contain a proposed maintenance plan for all stormwater control facilities, in accordance with the following:
Identify the proposed ownership entity (e.g., municipality, property owner, a homeowners, association, other management entity).
If ownership is to be an entity other than the borough, include a maintenance program for all facilities, outlining the type of maintenance activities, probable frequencies, personnel and equipment requirements, and estimated annual maintenance costs.
Identify method of financing continuing operation and maintenance if facility is to be owned by other than the borough or other governmental agency.