- Introduction
- Ch. 1 Stormwater Management Requirements
- Ch. 2 Submission, Review, and Approval Procedures
- Ch. 3 Site Design and Stormwater Management Integration
- Ch. 4 Stormwater Management Practice Guidance
- Ch. 5 Construction Guidance
- Ch. 6 Post-Construction and Operations and Maintenance Guidance
- Appendices
- Download
- Back to Chapters
- Manual Organization and Purpose
- Stormwater Regulations
- Private Development Services
- Stormwater Billing and Incentives
- Stormwater Management in Philadelphia
- Applicability and Submission Process
- Preferred Design Approach
- Back to Chapters
- 1.0 Introduction
- 1.1 Applicability Factors
- 1.2 Stormwater Regulations
- 1.3 Stormwater Retrofits
- Back to Chapter 1
- 1.2.1 Post-Construction Stormwater Management Requirements
- 1.2.2 Erosion and Sediment Control Requirement
- Back to Chapter 1
- 1.3.1 Retrofit Project Applicability and Initiation
- 1.3.2 Retrofit Project Requirements and Guidance
- Back to Chapters
- 2.0 Introduction
- 2.1 Existing Resources and Site Analysis
- 2.2 Review Paths
- 2.3 Review Phases
- 2.4 Expedited Post-Construction Stormwater Management Plan Reviews
- 2.5 PWD’s Development Review Process
- 2.6 PWD’s Role in Philadelphia's Development Process
- 2.7 PWD and Pennsylvania Department of Environmental Protection
- Back to Chapter 2
- 2.2.1 Development Compliance Review Path
- 2.2.2 Development Exemption Review Path
- 2.2.3 Demolition Review Path
- 2.2.4 Stormwater Retrofit Review Path
- Back to Chapter 2
- 2.3.1 Development Compliance Review Path
- 2.3.2 Development Exemption Review Path
- 2.3.3 Demolition Review Path
- 2.3.4 Stormwater Retrofit Review Path
- Back to Chapter 2
- 2.4.1 Disconnection Green Review
- 2.4.2 Surface Green Review
- 2.4.3 Expedited PCSMP Review Process
- Back to Chapter 2
- 2.7.1 National Pollutant Discharge Elimination System Permits
- 2.7.2 Other PA DEP Requirements
- Back to Chapters
- 3.0 Introduction
- 3.1 Site Assessment and Stormwater Management Strategies
- 3.2 Stormwater Management Design
- 3.3 Infiltration Testing and Soil Assessment for SMP Design
- 3.4 How To Show Compliance
- 3.5 Integrated Stormwater Management Examples
- Back to Chapter 3
- 3.0.1 How to Use This Chapter
- 3.0.2 Integrated Site and Stormwater Management Assessment and Design Process Overview
- 3.0.3 Interactions between Design Strategies, Stormwater Regulations, and Review Paths
- Back to Chapter 3
- 3.1.1 Background Site Factors and Site Factors Inventory
- 3.1.2 Site Factors Analysis
- 3.1.3 Integrated Design Approach
- 3.1.4 Non-Structural Design
- 3.1.5 Disconnected Impervious Cover
- 3.1.6 SMP Functions
- 3.1.7 Pollutant- Reducing Practices and Roof Runoff Isolation
- 3.1.8 How to Use SMPs to Comply with the Regulations
- Back to Chapter 3
- 3.2.1 Major SMP Types
- 3.2.2 SMP Hierarchy and Selection Process
- 3.2.3 Placing SMPs in Series
- 3.2.4 Stormwater Management Banking and Trading
- 3.2.5 SMP Design Guidance and General Requirements
- 3.2.6 Loading Ratio Requirements
- 3.2.7 Planting and Vegetation Guidance
- 3.2.8 Operations and Maintenance
- Back to Chapter 3
- 3.3.1 Infiltration Testing and Soil Characterization Plan Development
- 3.3.2 Soil Characterization Requirements
- 3.3.3 Infiltration Testing Requirements
- 3.3.4 Soil Characterization Procedures
- 3.3.5 Infiltration Testing Procedures
- 3.3.6 Evaluation of Infiltration Testing Results
- Back to Chapter 3
- 3.4.1 Regulatory Compliance Documentation Requirements
- 3.4.2 Storm Sewer Design Requirements
- 3.4.3 Calculation Methods and Design Tools
- Back to Chapter 3
- 3.5.1 Commercial Office Building Development
- 3.5.2 Residential Multi-Family Development
- 3.5.3 Full Build-Out
- 3.5.4 Trails
- 3.5.5 Athletic Fields
- 3.5.6 Streets
- Back to Chapters
- 4.0 Introduction
- 4.1 Bioinfiltration/ Bioretention
- 4.2 Porous Pavement
- 4.3 Green Roofs
- 4.4 Subsurface Infiltration
- 4.5 Cisterns
- 4.6 Blue Roofs
- 4.7 Ponds and Wet Basins
- 4.8 Subsurface Detention
- 4.9 Media Filters
- 4.10 Pretreatment
- 4.11 Inlet Controls
- 4.12 Outlet Controls
- Back to Chapter 4
- 4.1.1 Bioinfiltration/ Bioretention Introduction
- 4.1.2 Bioinfiltration/ Bioretention Components
- 4.1.3 Bioinfiltration/ Bioretention Design Standards
- 4.1.4 Bioinfiltration/ Bioretention Material Standards
- 4.1.5 Bioinfiltration/ Bioretention Construction Guidance
- 4.1.6 Bioinfiltration/ Bioretention Maintenance Guidance
- Back to Chapter 4
- 4.2.1 Porous Pavement Introduction
- 4.2.2 Porous Pavement Components
- 4.2.3 Porous Pavement Design Standards
- 4.2.4 Porous Pavement Material Standards
- 4.2.5 Porous Pavement Construction Guidance
- 4.2.6 Porous Pavement Maintenance Guidance
- Back to Chapter 4
- 4.3.1 Green Roof Introduction
- 4.3.2 Green Roof Components
- 4.3.3 Green Roof Design Standards
- 4.3.4 Green Roof Material Standards
- 4.3.5 Green Roof Construction Guidance
- 4.3.6 Green Roof Maintenance Guidance
- Back to Chapter 4
- 4.4.1 Subsurface Infiltration Introduction
- 4.4.2 Subsurface Infiltration Components
- 4.4.3 Subsurface Infiltration Design Standards
- 4.4.4 Subsurface Infiltration Material Standards
- 4.4.5 Subsurface Infiltration Construction Guidance
- 4.4.6 Subsurface Infiltration Maintenance Guidance
- Back to Chapter 4
- 4.5.1 Cistern Introduction
- 4.5.2 Cistern Components
- 4.5.3 Cistern Design Standards
- 4.5.4 Cistern Material Standards
- 4.5.5 Cistern Construction Guidance
- 4.5.6 Cistern Maintenance Guidance
- Back to Chapter 4
- 4.6.1 Blue Roof Introduction
- 4.6.2 Blue Roof Components
- 4.6.3 Blue Roof Design Standards
- 4.6.4 Blue Roof Material Standards
- 4.6.5 Blue Roof Construction Guidance
- 4.6.6 Blue Roof Maintenance Guidance
- Back to Chapter 4
- 4.7.1 Pond and Wet Basin Introduction
- 4.7.2 Pond and Wet Basin Components
- 4.7.3 Pond and Wet Basin Design Standards
- 4.7.4 Pond and Wet Basin Material Standards
- 4.7.5 Pond and Wet Basin Construction Guidance
- 4.7.6 Pond and Wet Basin Maintenance Guidance
- Back to Chapter 4
- 4.8.1 Subsurface Detention Introduction
- 4.8.2 Subsurface Detention Components
- 4.8.3 Subsurface Detention Design Standards
- 4.8.4 Subsurface Detention Material Standards
- 4.8.5 Subsurface Detention Construction Guidance
- 4.8.6 Subsurface Detention Maintenance Guidance
- Back to Chapter 4
- 4.9.1 Media Filter Introduction
- 4.9.2 Media Filter Components
- 4.9.3 Media Filter Design Standards
- 4.9.4 Media Filter Material Standards
- 4.9.5 Media Filter Construction Guidance
- 4.9.6 Media Filter Maintenance Guidance
- Back to Chapter 4
- 4.10.1 Pretreatment Introduction
- 4.10.2 Filter Strips
- 4.10.3 Forebays
- 4.10.4 Swales
- Back to Chapter 4
- 4.11.1 Inlet Control Introduction
- 4.11.2 Flow Splitters
- 4.11.3 Curbless Design/Curb Openings
- 4.11.4 Energy Dissipaters
- 4.11.5 Inlets
- Back to Chapter 4
- 4.12.1 Outlet Control Introduction
- 4.12.2 Orifices
- 4.12.3 Weirs
- 4.12.4 Risers
- 4.12.5 Underdrains
- 4.12.6 Level Spreaders
- 4.12.7 Impervious Liners
- 4.12.8 Micro Siphon Drain Belts
- 4.12.9 Low Flow Devices
- Back to Chapters
- 5.0 Introduction
- 5.1 Construction Inspection
- 5.2 Common Construction Issues
- 5.3 Construction Documentation
- Back to Chapter 5
- 5.1.1 Coordinating Inspections with Other PWD Units
- 5.1.2 Preconstruction Processes
- 5.1.3 Construction Processes
- 5.1.4 Final Inspection
- 5.1.5 Post-Construction Submissions
- Back to Chapter 5
- 5.2.1 Erosion and Sediment-Related Construction Issues
- 5.2.2 Stormwater Management Practice-Related Construction Issues
- Back to Chapters
- 6.0 Introduction
- 6.1 Operations and Maintenance
- 6.2 Stormwater Management Practice Inspection Guidance
- 6.3 Stormwater Credits Program
- Back to Chapter 6
- 6.1.1 Maintenance Requirements for Property Owners
- 6.1.2 Operations and Maintenance Agreements
- Back to Chapters
- Appendix Index
- A. Glossary
- B. Abbreviations
- C. PWD Stormwater Regulations
- D. Watershed Maps
- E. Plan and Report Checklists
- F. Design Guidance Checklists
- G. SMP Maintenance Guide Documents
- H. Infiltration Testing Log
- I. Landscape Guidance
- J. Construction Certification Package
- K. Record Drawing Sample
- L. Standard Details
- Back to Appendices
- Table E-1: General Plan Sheet Requirements
- Table E-2: Existing Conditions Plan Requirements
- Table E-3: Conceptual Stormwater Management Plan Requirements
- Table E-4: Erosion and Sediment Control Plan Requirements
- Table E-5: Standard Erosion and Sediment Control Notes
- Table E-6: Standard Sequence of Construction Notes
- Table E-7: Post-Construction Stormwater Management Plan Report Requirements
- Table E-8: Record Drawing Requirements
- Back to Appendices
- F.1 Stormwater Regulation Compliance
- F.2 Post-Construction Stormwater Management Plan
- F.3 Erosion and Sediment Control
- F.4 Disconnected Impervious Cover
- F.5 Infiltration Testing and Soil Assessment
- F.6 Hydrologic Model and Calculation Methods
- F.7 Bioinfiltration/ Bioretention
- F.8 Porous Pavement
- F.9 Green Roofs
- F.10 Subsurface Infiltration
- F.11 Cisterns
- F.12 Blue Roofs
- F.13 Ponds and Wet Basins
- F.14 Subsurface Detention
- F.15 Media Filters
- F.16 Pretreatment
- F.17 Inlet Controls
- F.18 Outlet Controls
F.9 Green Roofs
F.9.1 Green Roof Plan Standards
- Verify that the plans include an appropriate sequence of construction that is specific to the construction of the green roof. Refer to Section 4.3.5 for guidance. [Section 2.3.1]
- Verify that the plans include an appropriate cross-sectional detail for the green roof. [Section 2.3.1]
- Verify that a roof drainage plan is provided and that the roof drainage is consistent with the green roof design. [Appendix E, Table E-7]
F.9.2 Green Roof Design Standards
- Verify that runoff from impervious roof area onto the green roof is dispersed evenly across the green roof surface and passes through the growing medium either by sheet flow or a level spreading device. [Section 4.3.3, 1]
- Verify that the flow path of runoff across the green roof surface is greater than or equal to the contributing DCIA length. [Section 4.3.3, 2]
- Verify that structural loading is considered for the green roof design, and that the green roof design is coordinated with a licensed structural engineer for both new building construction and retrofits to existing structures. [Section 4.3.3, 3a]
- If runoff estimation calculations are required, verify that the correct curve number for the proposed green roof is used in the calculations. Refer to Table 3.4-2 of the Manual. [Section 4.3.3, 4a]
- If flow routing is required, verify that the rational coefficient used is 0.40. [Section 4.3.3, 4b]
- If flow routing is required, verify that the time of concentration used is six minutes. [Section 4.3.3, 4c]
- Verify that the total amount of impervious surfaces within the designated boundary of the green roof footprint does not exceed 1/3 of the combined area. [Section 4.3.3, 5]
- If runoff is conveyed via piping, verify that a distribution piping manifold embedded in a gravel strip, along with an appropriate detail, is provided on the plans to dissipate energy and promote uniform flow. [Section 4.3.3, 7]
- For green roofs that receive direct (1:1) rainfall only, verify the following:
- The minimum allowable thickness of the green roof growing medium is three inches. This can include both an upper finer-grained medium and a basal coarse granular green roof medium. [Section 4.3.3, 9a]
- Green roofs that meet minimum growing medium thickness requirements are permitted a DCIA reduction equal to the entire area of the green roof. [Section 4.3.3, 9b]
- For green roofs that receive runoff from contributing impervious roof catchments, verify the following:
- Impervious roof areas that direct runoff onto the green roof cannot exceed 50% of the green roof area, which is equivalent to a maximum hydraulic impervious runoff loading ratio of 0.5:1. [Section 4.3.3, 10a]
- The minimum thickness of the green roof growing medium must be calculated as follows, where the “impervious roof area to green roof area” ratio is less than or equal to 0.50: [Section 4.3.3, 10b]
Minimum thickness (in inches) of green roof growing medium = 3 inches + [3 * (Impervious roof area / Green roof area)] - Green roofs that meet minimum growing medium thickness requirements are permitted a DCIA reduction equal to the entire area of the green roof. Impervious roof areas that drain to these green roofs can be also considered as disconnected impervious cover, and, thus, included in the green roof’s DCIA reduction. [Section 4.3.3, 10c]
- In areas that will receive tributary discharge, verify that the plans include specifications that demonstrate that the drainage layer is not a high-transmissivity drainage layer, defined as a layer with a transmissivity of 0.005 m2/s or greater (ASTM D4716). In general, this will exclude peg-style or egg-carton-style geosynthetic sheets. High-transmissivity drainage layers will allow runoff to effectively flow under the green roof, minimizing contact with medium and plant roots. Typical granular aggregate, or coarse granular green roof medium, with a grain-size distribution complying with ASTM gradation No. 7 will satisfy the requirement, as will also a variety of mats and composite drainage layer assemblies. [Section 4.3.3, 10d]
- Verify that any deck built atop a green roof that does not allow for sheet flow runoff is slotted, and that the minimum thickness of growing medium required for the green roof is maintained under the entire extent of the deck. [Section 4.3.3, 10e]
- Verify that the plans indicate that the saturated permeability of the growing medium, in its compacted state [ASTM E2399], is not less than six inches per hour. [Section 4.3.3, 11]
- Verify that a drainage layer is provided and that it prevents ponding of runoff in the growing medium during the ten-minute maximum rainfall rate associated with the one-year, 24-hour storm event. [Section 4.3.3, 13]
- Verify that the contributing area of rooftop to each disconnected discharge point is equal to, or less than, 500 square feet. [Section 4.3.3, 15]
- Verify that details are provided on the plans that demonstrate that all drains and scuppers are covered and protected by an enclosure, typically a square or round chamber with a locking lid. These chambers are designed to prevent clogging of the drains by debris. [Section 4.3.3, 17]
- Verify that the roof drainage system and the remainder of the site drainage system safely convey roof runoff to the storm sewer, combined sewer, or receiving water. [Section 4.3.3, 18]
- Verify that the green roof is designed to allow for safe access and working conditions for green roof inspection and maintenance personnel. This access must be a permanent feature of the building, such as a pilot house, roof hatch, or exterior stairs to the green roof. Retractable, unsecured ladders should not be required for routine maintenance and inspections. The design may include other permanent personal safety measures. For green roofs, designers must specifically assess applicability to Occupational Safety and Health Administration (OSHA) Fall Protection Safety Standards and the American National Standards Institute (ANSI) and American Society of Safety Engineers (ASSE) consensus-based fall protection standards. [Section 4.3.3, 20]
F.9.3 Green Roof Material Standards
- Verify that the green roof growing medium is specified on the plans to be a lightweight mineral material with a minimum of organic material that meets the following specifications: [Section 4.3.4, 2]
- Moisture content at maximum water holding capacity (ASTM E2399 or FLL): 40% to 60% (vol)
- Porosity at maximum water holding capacity (ASTM E2399 or FLL): 10% to 15%
- Density at maximum water holding capacity (ASTM E2399 or FLL): ≤ 85 lb/ft3
- Total organic matter (MSA): 6% to 10% (dry weight)
- pH (MSA): 6.5 to 7.8
- Soluble salts (DPTA saturated media extraction): ≤ 2 mmhos/cm
- Water permeability (ASTM E2399 or FLL): 0.25 in/min to 1.25 in/min
- Grain-size distribution consisting of ≤ 4.5% passing for clay (0.002 mm) and 5% to 15% passing for silt (0.05 mm)
- The nutrients must be initially incorporated in the formulation of a suitable mix for the support of the specified plant materials.
- The medium must withstand freeze/thaw cycles.
- Verify that geotextile is specified on the plans to consist of polypropylene fibers and to meet the following specifications (AASHTO Class 1 or Class 2 geotextile is recommended): [Section 4.3.4, 3]
- Grab Tensile Strength (ASTM-D4632): ≤ 120 lbs
- Mullen Burst Strength (ASTM-D3786): ≥ 225 psi
- Flow Rate (ASTM-D4491): ≥ 95 gal/min/ft2
- UV Resistance after 500 hrs (ASTM-D4355): ≥ 70%
- Heat-set or heat-calendared fabrics are not permitted
- For vegetated cover assemblies with an overall thickness of five inches or greater, verify that the drainage layer is specified on the plans to meet the following specifications: [Section 4.3.4, 4b]
- Abrasion resistance (ASTM-C131-96): ≤ 25% loss
- Soundness (ASTM-C88): ≤ 5% loss
- Porosity (ASTM-C29): ≥ 25%
- Percent of particles passing 1/2-inch sieve (ASTM-C136): ≥ 75%
- The minimum thickness of the granular layer must be two inches. The granular layer may be installed in conjunction with a synthetic reservoir sheet.
- Verify that all waterproof membranes meet appropriate ASTM specifications. PVC membranes must meet ASTM D4434 requirements, EPDM membranes must meet ASTM D4637 requirements, and TPO membranes must meet ASTM D6878 requirements. [Section 4.3.4, 5b]
- Verify that all waterproofing membranes are fully waterproof with properly sealed seams, corners, and protrusions to prevent any intrusion of standing water above the membrane. [Section 4.3.4, 5c]
- Verify that roofing membranes meet all building code requirements and guidelines of the City of Philadelphia. [Section 4.3.4, 5d]
- Verify that the proposed green roof plantings are indicated on the plans and that the proposed plantings and are non-invasive. Refer to Appendix I for plant lists. [Section 4.3.4, 6]
- Verify that sedum sarmentosum, also known as star sedum, gold moss, stringy stonecrop, or graveyard moss, is not proposed. [Section 4.3.4, 9]