Jovian Design - Permeable Surface Stormwater Management Feasibility Study

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Myself and colleagues studied the feasibility of permeable surfaces for the City of London during a Consulting Project.

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Jovian Design - Permeable Surface Stormwater Management Feasibility Study

  1. 1. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY FINAL REPORT APRIL 2010 City of London Engineering Review Division Environmental & Engineering Services Disclaimer: This report is an academic exercise conducted by graduate students from the University of Western Ontario. Jovian Design is a fictional entity and has been created only for the purposes of this exercise. WONDERLAND POWER CENTRE, LONDON, ONTARIO, CANADA
  2. 2. DANIEL BITTMAN | ANIRUDDHA DHAMORIKAR | STEVEN DIXON | JENNA SIMPSON | SYED ZAIDI
  3. 3. April 23, 2010 Lois Burgess, P.Eng. Division Manager Engineering Review Division Environmental & Engineering Services City of London Ismail Abushehada, Ph.D., P. Eng. Development Services Engineer Engineering Review Division Environmental & Engineering Services City of London RE: Final Report: Permeable Surface Stormwater Management Feasibility Study: Wonderland Power Centre, London, Ontario, Canada Dear Ms. Burgess and Mr. Abushehada, The following document is the Final Report of the Permeable Surfaces Stormwater Management Feasibility Study that has been requested by the Engineering Review Division of the Environmental and Engineering Services Department of the City of London. It has been a pleasure to work with both of you and we would like to extend our thanks for your continued support throughout this project. Sincerely, Jenna Simpson, Project Manager Jovian Design 1151 Richmond Street, London, Ontario, Canada N6A 3K7
  4. 4. i Table of Contents Table of Contents............................................................................................................................................................................ i Table of Tables .............................................................................................................................................................................vii Table of Figures ...........................................................................................................................................................................viii Glossary of Terms..........................................................................................................................................................................ix List of Abbreviations......................................................................................................................................................................xii Executive Summary .....................................................................................................................................................................xiii 1. Introduction ................................................................................................................................................................................ 1 1.1 General................................................................................................................................................................................. 1 1.2 Urbanization in the City of London ........................................................................................................................................ 2 2. City of London Development Objectives..................................................................................................................................... 4 2.1 Introduction........................................................................................................................................................................... 4 2.2 Official Plan for the City of London........................................................................................................................................ 4 2.3 Needs & Guidelines .............................................................................................................................................................. 4 3. Project Approach & Methodology ............................................................................................................................................... 5 3.1 Introduction........................................................................................................................................................................... 5 3.2 Site Visit Preparation ............................................................................................................................................................ 5 3.3 Site Visit................................................................................................................................................................................ 5 3.4 Site Context .......................................................................................................................................................................... 5 3.5 City of London Development Objectives ............................................................................................................................... 5 3.6 Surface Analysis................................................................................................................................................................... 5 3.7 Stormwater Management Inventory ...................................................................................................................................... 5 3.8 Permeable Surface Research, Analysis & Summary............................................................................................................. 5
  5. 5. ii 3.9 Net Water Savings................................................................................................................................................................ 5 3.10 Financial Analysis............................................................................................................................................................... 6 3.11 Conclusions & Recommendations ...................................................................................................................................... 6 4. Site Context – Wonderland Power Centre.................................................................................................................................. 7 5. Surface Analysis ........................................................................................................................................................................ 9 5.1 Introduction........................................................................................................................................................................... 9 5.2 Study Area Surfaces............................................................................................................................................................. 9 5.2.1 Roofs ............................................................................................................................................................................. 9 5.2.2 Parking Lots and Low-Traffic Roadways ...................................................................................................................... 10 5.2.3 Sidewalks..................................................................................................................................................................... 11 5.2.4 Medians ....................................................................................................................................................................... 11 5.2.5 Stormwater Management Facilities .............................................................................................................................. 12 5.2.6 Other Surfaces............................................................................................................................................................. 12 6. Stormwater Management Inventory ......................................................................................................................................... 14 6.1 Introduction......................................................................................................................................................................... 14 6.2 Construction of Bradley Avenue SWM Facility.................................................................................................................... 14 6.3 Servicing Capacity of Bradley Avenue SWM Facility .......................................................................................................... 14 6.4 Subsurface Conditions........................................................................................................................................................ 16 6.5 Maintenance of the SWM Facility ....................................................................................................................................... 16 7. Permeable Surfaces Overview................................................................................................................................................. 17 7.1 Introduction......................................................................................................................................................................... 17 7.2 Permeable Asphalt ............................................................................................................................................................. 19 7.2.1 Introduction .................................................................................................................................................................. 19 7.2.2 Function and Application.............................................................................................................................................. 19
  6. 6. iii 7.2.3 Durability ...................................................................................................................................................................... 20 7.2.4 Maintenance................................................................................................................................................................. 21 7.2.5 Cost.............................................................................................................................................................................. 21 7.2.6 Benefits and Limitations ............................................................................................................................................... 21 7.3 Permeable Concrete........................................................................................................................................................... 22 7.3.1 Introduction .................................................................................................................................................................. 22 7.3.2 Function and Application .............................................................................................................................................. 23 7.3.3 Durability ...................................................................................................................................................................... 27 7.3.4 Maintenance................................................................................................................................................................. 27 7.3.5 Cost.............................................................................................................................................................................. 28 7.3.6 Benefits and Limitations ............................................................................................................................................... 28 7.3.7 Supplementary Cementitious Materials ........................................................................................................................ 29 7.4 Permeable Pavement De-icing agents................................................................................................................................ 29 7.5 Green Roofs ....................................................................................................................................................................... 31 7.5.1 Introduction .................................................................................................................................................................. 31 7.5.2 Function and Application .............................................................................................................................................. 31 7.5.3 Durability ...................................................................................................................................................................... 34 7.5.4 Maintenance................................................................................................................................................................. 34 7.5.5 Cost.............................................................................................................................................................................. 35 7.5.6 Extensive Green Roofs................................................................................................................................................. 36 7.5.7 Intensive Green Roofs.................................................................................................................................................. 37 7.5.8 Benefits and Limitations ............................................................................................................................................... 38 7.5.9 Public Policy................................................................................................................................................................. 38 7.6 Additional Benefits of Permeable Surfaces ......................................................................................................................... 38
  7. 7. iv 7.6.1 Urban Heat Island ........................................................................................................................................................ 38 7.6.2 LEED ........................................................................................................................................................................... 40 8. Product Analysis ...................................................................................................................................................................... 41 8.1 Introduction......................................................................................................................................................................... 41 8.2 PICP................................................................................................................................................................................... 41 8.3 Concrete & Asphalt............................................................................................................................................................. 41 8.4 Green Roofs....................................................................................................................................................................... 42 9. Net Water Savings ................................................................................................................................................................... 44 9.1 Introduction......................................................................................................................................................................... 44 9.2 Wonderland Power Centre ................................................................................................................................................. 45 9.2.1 Scenario 1a: 100% Pervious Coverage of Hard Surfaces using Permeable Asphalt or Porous Concrete and Extensive Green Roofs ......................................................................................................................................................................... 45 9.2.2 Scenario 1b: 75% Pervious Coverage of Hard Surfaces using Permeable Asphalt or Porous Concrete and Extensive Green Roofs ......................................................................................................................................................................... 46 9.2.3 Scenario 1c: 50% Pervious Coverage of Hard Surfaces Using Permeable Asphalt or Porous Concrete and Extensive Green Roofs ......................................................................................................................................................................... 46 9.2.4 Scenario 1d: 25% Pervious Coverage of Hard Surfaces Using Permeable Asphalt or Porous Concrete and Extensive Green Roofs ......................................................................................................................................................................... 46 9.2.5 Scenario 2a: 100% Pervious Coverage of Hard Surfaces using PICP and Extensive Green Roofs.............................. 49 9.2.6 Scenario 2b: 75% Pervious Coverage of Hard Surface using PICP and Extensive Green Roofs ................................. 49 9.2.7 Scenario 2c: 50% Pervious Coverage of Hard Surfaces using PICP and Extensive Green Roofs................................ 49 9.2.8 Scenario 2d: 25% Pervious Coverage of Hard Surfaces using PICP and Extensive Green Roofs................................ 50 9.3 Net-Water Savings Analysis Summary ............................................................................................................................... 50 10. Financial Analysis .................................................................................................................................................................. 52 10.1 Introduction....................................................................................................................................................................... 52
  8. 8. v 10.2 Net Present Value & Equivalent Annual Cost.................................................................................................................... 52 10.2.1 Net Present Value and Prorated Net Present Value ................................................................................................... 52 10.3 Equivalent Annual Cost..................................................................................................................................................... 53 10.4 Product Comparisons ....................................................................................................................................................... 53 10.5 Wonderland Power Centre................................................................................................................................................ 55 10.6 Additional Economic Benefits............................................................................................................................................ 57 10.6.1 Monetary Value of Environmental Benefits................................................................................................................. 57 11. Conclusions............................................................................................................................................................................ 59 11.1 Durability........................................................................................................................................................................... 59 11.2 Net water Savings............................................................................................................................................................. 59 11.3 Financial Analysis ............................................................................................................................................................. 60 11.4 Summary .......................................................................................................................................................................... 61 12. Recommendations ................................................................................................................................................................. 63 12.1 Durability........................................................................................................................................................................... 63 12.2 Net Water Savings............................................................................................................................................................ 63 12.3 Financial Analysis ............................................................................................................................................................. 63 12.4 Additional Recommendations ........................................................................................................................................... 63 References................................................................................................................................................................................... 64 Appendices .................................................................................................................................................................................. 75 Appendix A. 1: Site Context ...................................................................................................................................................... 76 Appendix A. 2: Surface Analysis............................................................................................................................................... 77 Appendix A. 3: Stormwater Management Inventory .................................................................................................................. 78 Appendix B. 1: Product Analysis............................................................................................................................................... 79 Appendix B. 2: Net Water Savings: Calculations....................................................................................................................... 80
  9. 9. vi Appendix B. 3: Financial Analysis: Calculations........................................................................................................................ 94 Appendix C: Project Timeline ................................................................................................................................................... 99
  10. 10. vii Table of Tables Table 1: Surface Analysis for the WPC Study Site ......................................................................................................................... 9 Table 2: Bradley Avenue SWM facility volume summary.............................................................................................................. 14 Table 3: SWM facility discharge and storage summary for varying rain events............................................................................. 15 Table 4: Factors affecting infiltration rates of permeable concrete products ................................................................................. 23 Table 5: Base storage capacity of PICP and CGP........................................................................................................................ 25 Table 6: Applications of pervious concrete ................................................................................................................................... 26 Table 7: Comparison between extensive and intensive green roof systems................................................................................. 33 Table 8: Component costs of extensive green roofs assuming an existing building with sufficient loading capacity, roof hatch and ladder access ................................................................................................................................................................ 36 Table 9: Component cost of intensive green roofs assuming an existing building with sufficient loading capacity, roof hatch and ladder access ................................................................................................................................................................ 37 Table 10: Comparison of feasibility parameters for various permeable products .......................................................................... 43 Table 11: Runoff coefficients........................................................................................................................................................ 45 Table 12: Comparison of runoff reductions for conventional and permeable surfaces at the WPC: Pavement and green roofs.... 48 Table 13: SWM facility volume reduction resulting from pervious surface coverage at the WPC: Pavement and green roofs....... 48 Table 14: Comparison of runoff reductions for conventional and permeable surfaces at the WPC: PICP and green roofs ........... 51 Table 15: SWM facility volume reduction resulting from pervious surface coverage at the WPC: PICP and green roofs .............. 51 Table 16: Financial comparisons of different surfaces.................................................................................................................. 55 Table 17: Financial comparisons of different surface applications at the WPC ............................................................................. 57 Table 18: Financial benefits of green roofs in Toronto, Ontario assuming 50 Million m2 of available roof space........................... 58 Table 19: Overall product comparisons ........................................................................................................................................ 62
  11. 11. viii Table of Figures Figure 1: The relationship between impervious and pervious area and extent of sewerage ........................................................... 2 Figure 2: Study Area ...................................................................................................................................................................... 8 Figure 3: Roof surfaces in the WPC Study Area showing a) asphalt shingles on a commercial building, b) low-sloped impervious roof on a commercial building, and c) clay tiles on a commercial building .................................................................... 10 Figure 4: Asphalt surfaces in the WPC Study Area ...................................................................................................................... 11 Figure 5: Commercial concrete sidewalks in the WPC Study Area............................................................................................... 11 Figure 6: Medians are dispersed throughout commercial parking lots to help guide traffic and provide aesthetic relief from dominating impervious pavements ............................................................................................................................... 12 Figure 7: Stormwater Management Pond adjacent to the WPC showing a) an inflow culvert, b) a near full pond, overflow spillway and forebay, c) and emergency spillway ...................................................................................................................... 12 Figure 8: Other surfaces within the WPC include a) roofed shopping cart corrals and b) landscaped areas................................. 13 Figure 9: Interaction between rainwater and tradition/conventional pavement.............................................................................. 18 Figure 10: Interaction between rainwater and permeable pavement ............................................................................................ 18 Figure 11: Typical cross-section of a permeable asphalt surface ................................................................................................. 19 Figure 12: Winter performance vs. general indicators, including runoff control, pollution control, and level of integration, for different stormwater components ................................................................................................................................. 21 Figure 13: a) PICP, b) CGP, c) PC............................................................................................................................................... 22 Figure 14: Typical installation for exfiltration................................................................................................................................. 24 Figure 15: Typical installation of porous concrete surface............................................................................................................ 26 Figure 16: Typical cross-section of a green roof........................................................................................................................... 31 Figure 17: Rural and urban heat characteristics........................................................................................................................... 39
  12. 12. ix Glossary of Terms Annual Precipitation – The annual total precipitation is the sum of the rainfall and the assumed water equivalent of the snowfall for a given year (Natural Resources Canada, 2003) Asphalt – Also known as conventional asphalt; an impermeable surface comprised of asphalt cement and coarse aggregates, including stone, sand, and gravel compacted together (Freemantle, 1999) Baseflow – Water that, having infiltrated the soil surface, percolates to the groundwater table and moves laterally to reappear as surface runoff (University of Florida, 2010) Biodegradation – The breaking down of organic and inorganic substances by biological action, a process usually involving bacteria and fungi (Fischel, 2001) Bradley Avenue Stormwater Management Facility – The Stormwater Management Facility at Wonderland Power Centre Concrete – Also known as conventional concrete; an impermeable construction material comprised usually of Portland cement, and other materials, including aggregates, water, and chemical admixtures (ICPI, 2008) Client – Also known as the City of London; the City; Environmental & Engineering Services Department, Engineering Review Division Consultant – Jovian Design; the Design team De-icing Agent – A snow and ice control strategy for prevention of a strong bond between frozen precipitation or frost and a pavement surface by application of a chemical freezing point depressant prior to or during a storm (Fischel, 2001) Eutrophication – The enrichment of water with nutrients, such as phosphorus resulting in the increase in numbers of aquatic algae in the water (Fischel, 2001) Evapotranspiration – The merging of evaporation (movement of free water molecules away from a wet surface into air that is less saturated) and transpiration (movement of water vapour out through the pores in vegetation) into one term (Christopherson, 2005) Exfiltration – A loss of water from a drainage system as the result of percolation or absorption into the surrounding soil (HydroCAD, 2009) Freeze-thaw – A weathering process in which intermittent periods of freezing and thawing act upon a substance, leading to its gradual breakdown by forces of water crystal expansion and contraction (Christopherson, 2005) Green Roof – A roof with a vegetative cover, used passively to address environmental issues in mainly urban settings (Kosreo & Ries, 2007) Green Space – Areas generally planted with trees, shrubs, herbaceous perennials and decorative grasses, rocks, and water features; used mainly for aesthetics and recreation
  13. 13. x Groundwater – Water beneath the surface that is beyond the soil-root zone; a major source of potable water (Christopherson, 2005) Impermeable Surfaces – Consist of surfaces which restrict infiltration of precipitation due to decreased drainage capacity (Shuster et al., 2005) Infiltration – Also known as percolation; water access to subsurface regions of soil moisture storage through penetration of the soil surface (Christopherson, 2005) Leadership in Energy and Environmental Design (LEED) – A green building rating system that encourages and accelerates the global adoption of sustainable green building and development practices through the creation and implementation of universally accepted performance criteria (CaGBC, 2004) Low-Traffic Urban Roadways – Roads and access roadways generally characterized by low to moderate speeds and low to moderate volumes of automobiles per day Median – A raised structure used to organize and direct automobile traffic, as well as to provide shade and enhance aesthetic value to commercial parking lots (Celestian & Martin, 2003) Permeable Surfaces – Consist of a variety of types of pavement, pavers and other devices that provide stormwater infiltration while serving as a structural surface (University of Florida, 2008) Permeable Asphalt – Also known as porous or pervious asphalt; an adaptation of conventional asphalt in which fine sediments are removed, resulting in a network of continuously linked voids to allow the passage of fluids through the surface (Beecham, 2007; Boving, 2008) R-value – A commercial unit used to measure the effectiveness of thermal insulation. The R-value of the insulator is defined as 1 divided by the thermal conductance per inch (Rowlett, 2002) Rational Method – An equation that postulates a proportionality between peak discharge and rainfall intensity (Dingman, 2002) Return Period – The frequency with which one would expect, on average, a given precipitation event to recur (Cornell University, 2007) Roof – A cover used to protect the interior and structural components of a building from weather elements, particularly precipitation Sidewalk – A raised structure used to provide a suitable transit route and safe place for pedestrians to walk Storm Drain – An opening that leads to an underground pipe or open ditch for transporting surface runoff, separate from a sanitary sewer or wastewater system (Environmental Services Water Quality Division, 2009) Stormwater Management (SWM) Facilities – Facilities designed to temporarily collect runoff from localized storm
  14. 14. xi sewer systems after a rainfall or snowmelt event (Ministry of Environment [MOE], 2003) Stormwater Runoff – Excessive water, derived from precipitation or snowmelt that ultimately reaches a drainage area (Oke, 2006) Toxicity – The potential of a chemical or compound to cause adverse effects on living organisms (Fischel, 2001) Urban Heat Island – An effect caused by the warming of urban centres in comparison to rural areas as a result of increasing surface characteristics which may augment surrounding atmospheric temperatures (U.S. Environmental Protection Agency, 2009) Urbanization – The physical growth of urban areas as a result of global change, in which individuals move from rural communities to more dense urban areas (Barrow, 2003) Water Table – The upper surface of groundwater; the contact point between the zone of saturation and aeration in an unconfined aquifer (Christopherson, 2005)
  15. 15. xii List of Abbreviations AAR - alkali–aggregate reaction CaCl2 – calcium chloride CAD – Canadian dollars CaGBC - Canadian Green Building Council CGP – concrete grid pavers CMA – calcium magnesium acetate COTA – City of Toronto Act EAC – Equivalent Annual Cost GTA – Greater Toronto Area GGBFS – ground granulated blast furnace slag ICPI – Interlocking Concrete Pavement Institute KCl – potassium chloride LEED – Leadership in Energy and Environmental Design MgCl2 – magnesium chloride NaCl – sodium chloride NPV – Net Present Value O&M – operation and maintenance OEPA – Ontario Environmental Protection Act PC – porous concrete PICP – permeable interlocking concrete pavers SCM – supplementary cementitious materials SS – Sustainability Site SWM – stormwater management TRCA – Toronto and Region Conservation Authority UHI – Urban Heat Island effect USD – US dollars WPC – Wonderland Power Centre
  16. 16. xiii Executive Summary The Engineering and Review Division, Environmental and Engineering Services Department of the City of London has retained Jovian Design to undertake a Permeable Surfaces Stormwater Management Feasibility Study. The primary purpose of this study is to evaluate the durability, net water reduction and financial feasibility of permeable surfaces compared to conventional materials, using the following project scope: The Consultants will research permeable surfaces and compare permeable products to existing conventional materials. The purpose of this comparison is to determine the effectiveness of each product including permeability, cost and durability while ensuring that the development objectives of the City are met. The Wonderland Power Centre will be assessed as a sample of this comparison. Peer reviewed journal articles and other literature show that permeable surfaces are in many instances feasible for large scale developments such as the Wonderland Power Centre. Primary research supported these findings. Several permeable product contractors and distributors operate within Southern Ontario and offer products that are locally feasible in terms of cost, net-water savings, and durability. Comparative product analyses for local permeable pavements, pavers, and green roof companies showed that not only are these products readily available in Southern Ontario, but that the lifespan and maintenance requirements of these products are competitive with conventional pavements and roofing systems. All permeable products proved to reduce the volume of stormwater runoff when compared to conventional surfaces. Within the scope of the permeable surfaces analyzed, different product typologies offered varying levels of infiltration. Depending on the level of integration and combination of permeable products, the volume of water being sent to stormwater facilities can be reduced by up to 62% in ideal conditions. This, in turn, can represent a direct cost savings for new developments, as the size of planned stormwater management facilities can be reduced. Most permeable products proved to be more expensive than conventional materials. However, depending on the proposed application and surface area, some permeable products are very similar in Net Present Value and Equivalent Annual Cost to their conventional counterparts. In the case of using porous concrete for sidewalks, a general cost savings was discovered compared to using conventional concrete for the same application. Properly installed and maintained permeable pavements also have the potential to reduce Urban Heat Island effects, improve driving safety, encourage urban tree and plant growth, gain LEED credits, reduce stormwater quantity and enhance water quality. There may also be financial savings due to the benefits of stormwater reduction, including the impact on combined sewer overflow, improvement in air quality, reduction in direct energy use and other environmental and social benefits such as the aesthetic improvement of urban landscapes, and increased property values.
  17. 17. xiv
  18. 18. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 1 1. Introduction 1.1 General Jovian Design (Consultants) was retained by the Engineering Review Division, Environmental and Engineering Services Department of the City of London (Client) to undertake a permeable surface stormwater management feasibility study. The intent of this project is to evaluate the feasibility of various permeable technologies in comparison to conventional impermeable materials, as described in the Project Scope below, using the Wonderland Power Centre in London, Ontario as a baseline study. This analysis will help determine the feasibility of implementing permeable surfaces. Initially, a project proposal was developed by the Consultant and refined in consultation with the Client to better reflect the expectations of the City. Under the guidance of Dr. Omar Ouda, the Consultants: a) Developed a comprehensive site inventory for the Wonderland Power Centre including site context, surface analysis and a stormwater management inventory b) Conducted a literature review of permeable surfaces to outline the function and application, durability, maintenance, cost, and benefits and limitations of each permeable surface type, as well as other pertinent information c) Contacted several local distributors and contractors in order to gather primary information about permeable products available in Southern Ontario d) Analyzed the net water savings capacity of each permeable product e) Conducted a financial analysis of each permeable product f) Developed conclusions and recommendations to reflect the findings of the Feasibility Study This Study was completed as a result of contributions from a number of individuals from various organizations. The Consultants would therefore like to thank the following: Project Scope The Consultants will research permeable surfaces and compare permeable products to existing conventional materials. The purpose of this comparison is to determine the effectiveness of each product including permeability, cost and durability while ensuring that the development objectives of the City are met. The Wonderland Power Centre will be assessed as a sample of this comparison.
  19. 19. JOVIAN DESIGN Page | 2 Ismail Abushehada, Ph.D., P. Eng. City of London Michal Kuratczyk, M.Acc. Deloitte Lois Burgess, P.Eng. City of London Connor Malloy Duo Building Ltd. Darcy Decaluwe Stone in Style Omar Ouda, Ph.D., P.Eng, PMP University of Western Ontario Vito Frijia Southside Group Denis Taves, OALA Gardens in the Sky Carol Hayward City of London Jarrett Woodward Grand River Natural Stone Ltd. 1.2 Urbanization in the City of London The City of London is located in the heart of south-western Ontario, within close proximity to both Lake Huron and Lake Erie. The City‟s population of more than 350,000 is expected to grow steadily over the next two decades (Statistics Canada, 2006). The City has also undergone significant growth over the last 15 years due to a persistent developmental strategy (City of London, 2010). Increased impervious surface area is a consequence of urbanization, in which there may be significant ensuing effects on the hydrologic cycle (Shuster et al., 2005; Barnes et al., 2002). This increasing proportion of impervious surface creates shorter lag times between the arrival of precipitation and consequent high runoff rates and total flow volume (Shuster et al., 2005). As a result, a municipality‟s sewershed or stormwater management system may be put under increasing pressure in order to compensate for this additional volume of runoff (Figure 1). Figure 1: The relationship between impervious and pervious area and extent of sewerage Source: Shuster et al., 2005. Increasing stress on existing stormwater infrastructure provides incentive for municipalities like the City of London to explore the feasibility of innovative strategies such as the implementation of permeable surfaces. Stormwater management facilities present an opportunity for the City to implement strategies that address municipal economic, social, and environmental interests. Currently there are approximately 85 stormwater facilities in London and over 100 more are planned for future developments.
  20. 20. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 3 These systems are expensive to build and maintain, with facilities costing millions of dollars each. Permeable surfaces can potentially improve the cost effectiveness of storm water management systems, thereby alleviating pressure on municipal financial resources. In addition, the implementation of permeable surfaces can result in environmental and social benefits. Increasing urbanization and subsequent Urban Heat Island effect, among other things, make the implementation of permeable surfaces attractive to forward-thinking municipalities.
  21. 21. JOVIAN DESIGN Page | 4 2. City of London Development Objectives 2.1 Introduction One objective of this Study is to establish a basis for the inclusion of permeable surface stormwater management systems as part of the City of London Design Standards or urban design guidelines. Although there is a wide range of permeable products on the North American market, not all products are suitable for the City of London or meet the City‟s development goals and objectives. As there are currently no specific design standards in London pertaining to permeable surfaces, the Consultants have developed a list of applicable development guidelines in order to aid in the evaluation of available permeable products. 2.2 Official Plan for the City of London The Official Plan for the City of London contains objectives and policies to guide physical development within the municipality (City of London, 2010). It provides direction for the allocation of land use and provision of municipal services and facilities in order to promote orderly urban growth and compatibility among land uses. Although the Official Plan‟s primary function is to establish policies for the physical development of the City of London, it also has regard for relevant social, economic and environmental matters. As such, various sections of the Official Plan were examined in order to help determine the City of London‟s development needs and establish support for the implementation of permeable surfaces within the City. 2.3 Needs & Guidelines The following provisions are necessary for parking, roadways, sidewalks and related developments in the City of London: Accommodate low-level traffic and heavy vehicular loads such as fire engines, delivery trucks, and heavy machinery Allow for seasonal maintenance and snow clearing Provide easy access and use by handicapped persons The following objectives should be considered when evaluating permeable surfaces: Enhance hydrology, geomorphology and water quality by protecting and promoting groundwater recharge Enhance the pedestrian environment while providing easy access and use by all and promoting public safety Minimize inconvenience and damage from surface ponding and flooding Maximize the cost effectiveness of stormwater management facilities Minimize water and energy consumption through resource conservation, landscaping and innovative design features and servicing techniques Promote the reuse and recycling of wastes Protect, maintain and improve surface and groundwater quality and quantity
  22. 22. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 5 3. Project Approach & Methodology 3.1 Introduction The following is an account of the methodology used to complete this Report and develop conclusions and recommendations. A detailed project plan timeline can be found in Appendix C. 3.2 Site Visit Preparation Maps and satellite images were gathered from online databases to begin the initial geographic analysis of the Study Site. 3.3 Site Visit The Consultants travelled to the Study Site to perform a visual analysis of the Wonderland Power Centre for the purposes of the Surface Analysis and Stormwater Management Inventory (below). 3.4 Site Context Following the Site Visit, a brief report discussing the existing land use patterns and geographic location of the Study Site was developed. 3.5 City of London Development Objectives A list of applicable development objectives for the implementation of permeable surfaces was developed based on discussions with the Client and reviews of policies and design standards governing development within the City of London. 3.6 Surface Analysis Using the City of London Public Zoning Map and the findings from the Site Visit and Site Context, a detailed Surface Analysis was conducted for the Wonderland Power Centre. 3.7 Stormwater Management Inventory Functional drawings of the Wonderland Power Centre were provided by the Clients. Using this resource and information gathered from online databases, the Consultants assessed the stormwater facility on the Study Site with regard to its service capacity, lifespan, and required maintenance. 3.8 Permeable Surface Research, Analysis & Summary A review of the current literature on permeable surfaces, green roofs and stormwater management approaches and techniques was conducted. Research was primarily focused on the typology, water retention capacity, durability and cost of permeable surfaces and green roofs. The Consultants also contacted several local distributors and contractors in order to gather primary information about permeable products available in Southern Ontario. Findings from the Permeable Surface Research, Analysis & Summary are found throughout this Report, most notably in the Permeable Surface Overview and Product Analysis. 3.9 Net Water Savings A comparative analysis of the net water savings of each type of permeable surface and green roof was conducted using known runoff coefficients and the calculations found within the Surface Analysis of this Report.
  23. 23. JOVIAN DESIGN Page | 6 The water retention capacity of the existing Study Site and stormwater retention pond was calculated as a baseline, and different permeable surface coverage scenarios were formulated. 3.10 Financial Analysis The current capital costs, operational and maintenance costs, and potential savings from the reduction of stormwater management facilities as a result of each permeable surface were compared using the Net Present Value and Equivalent Annual Cost financial calculations. 3.11 Conclusions & Recommendations Conclusions and recommendations were formulated based on the findings outlined in this Report. The function and application, durability, maintenance, cost, and benefits and limitations of all permeable pavement and green roof options were considered.
  24. 24. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 7 4. Site Context – Wonderland Power Centre The Wonderland Power Centre (WPC) is located in the southeast corner of Wonderland Road and Southdale Road in London, Ontario. Designated as a “Commercial Policy Area” in Schedule A of the City of London Official Plan (Appendix A) (City of London, 2006), the WPC is a fully occupied regional shopping centre, covering approximately 20 hectares of commercial land (Southside Group, 2008). The WPC is bound by the Westmount Estates and Westmount Estates II high density residential buildings (Tricar, 2010) to the east, Southdale Road to the north and Wonderland Road to the west. The site is mirrored by a similar commercial development, the Westwood Power Centre, across Wonderland Road which utilizes the same stormwater management (SWM) facility. To the immediate south of the WPC commercial development is the “Old Wonderland Mall” property. This area has been included as part of the Study Site (Figure 2). It is important to note that although the entire SWM watershed includes the Westwood Power Centre, the Study Site used in this Report only includes the fully developed Wonderland Power Centre, the Old Wonderland Mall, and the SWM facility itself. From an aerial perspective, the WPC can be divided into four general types of hard surfaces: paved parking lots and/or roadways; concrete sidewalks; roofs, and; landscaped areas. As seen in the map below, the majority of the WPC interior is paved asphalt parking spaces or roadways. The perimeter of the site is lined with commercial developments (the majority of which have low-sloped roofs), and there are small landscaped medians dispersed throughout the site. Perhaps most notably, the south-eastern corner of the Study Site contains the stormwater management facility that collects runoff for the entire Study area. With the exception of the soft, landscaped surfaces sparsely located throughout the Site, the Study Area is composed entirely of hard surfaces that do not allow water to permeate into the underlying soil. This is explored in further detail in the following section. It is important to note that the WPC is only intended to provide a baseline analysis for this Feasibility Study.
  25. 25. JOVIAN DESIGN Page | 8 Figure 2: Study Area LEGEND Entire Study Area WPC & Old Wonderland Mall Commercial Areas Stormwater Management Facility Stormwater Management Watershed Modified from: City of London, 2010
  26. 26. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 9 5. Surface Analysis 5.1 Introduction The Study Area covers approximately 220,000 m2 of land (Table 1), of which approximately 70% is comprised of impermeable surfaces. In other words, more than two-thirds of all precipitation that falls on the site may begin to flow as urban runoff, with minimal, if any vegetative buffers to intercept it. This is a substantial amount of surface flow, and therefore requires a catchment area (i.e., SWM facility) of sufficient size to store the excess water and mitigate further runoff. The cost to build such structures generally requires a significant amount of funds for municipalities and, ultimately, taxpayers (AECOM, 2009). The primary impermeable surfaces examined in this section of the Report include roofs, parking lots and low-traffic roadways, and sidewalks. Other surfaces that will be examined include medians, green spaces, and temporary structures (e.g., shopping cart corrals). Calculations for this analysis were completed through on-site investigations and satellite interpretation using a modified City of London Public Zoning Map (Appendix A). 5.2 Study Area Surfaces 5.2.1 Roofs The primary function of roofs is to protect the interior and structural components of a building from weather elements, particularly precipitation. Roofs within the Wonderland Power Centre are the second most prevalent surface, making-up approximately 20% of the entire Study Area. Approximately 17% of the Study Area is comprised of low- sloped, commercial roofs, whereas sloped or pitched roofs represent approximately 2% of the Study Site. Table 1: Surface Analysis for the WPC Study Site The low-sloped roofs are generally sealed with an impervious asphalt layer, while pitched roofs are generally covered with impervious asphalt shingles (e.g., Loblaw Superstore) or other highly impervious materials such as clay tiles (e.g., Angelo‟s Italian Bakery and Deli). In both instances, precipitation is directed from the roof to a drainage system consisting of gutters, downspouts, and piping, and ultimately to the surface below (either impermeable asphalt or cement, or permeable grass surfaces which allow infiltration). Vegetated green roofs may act as an intermediate step to this process, intercepting Surface Analysis for the Wonderland Power Centre Surface Type Area (m2 ) Area (%) Low-sloped Roofs 37,550 17 Sloped Roofs 5,193 2 Parking Lots/Roadways 96,161 44 Sidewalks 14,812 7 Medians 9,987 5 SWM Pond 42,983 19 Others (e.g., Green Space; Temporary Structures) 14,098 6 TOTAL 220,784 100
  27. 27. JOVIAN DESIGN Page | 10 precipitation and helping to reduce runoff from reaching the SWM facility (VanWoert et al., 2005). Figure 3: Roof surfaces in the WPC Study Area showing a) asphalt shingles on a commercial building, b) low-sloped impervious roof on a commercial building, and c) clay tiles on a commercial building 5.2.2 Parking Lots and Low-Traffic Roadways The principal function of parking lots is to accommodate a steady volume of visitors and their automobiles. Parking lots within the WPC site are the most significant surface typology, composing more than 40% of the entire Study Area. Part of this percentage includes a series of low-traffic roadways connecting the parking lots together. Generally located around the peripheries of parking lots and buildings, these features are primarily coated with impermeable asphalt, but may also include concrete pavement as well. Porous pavements, including permeable asphalt, porous concrete, Permeable Interlocking Concrete Pavers (PICP) and grid pavers, may be used to divert urban runoff from SWM facilities, as precipitation is able to pass through the paved surfaces and recharge groundwater sources or the water table (Beecham, 2007; Boving, 2008). a b c
  28. 28. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 11 Figure 4: Asphalt surfaces in the WPC Study Area 5.2.3 Sidewalks The main function of sidewalks is to provide a suitable transit route and safe place for pedestrians to travel, by separating them from vehicular traffic. Raised sidewalks within the Wonderland Power Centre represent an overall surface composition of close to 7% of the entire Study Area. Sidewalks are generally composed of impermeable concrete pavement which prevents percolation of precipitation and snow melt (Bean et al., 2007). Permeable pavers and porous concrete may be used to help alleviate the stress of surface runoff on SWM facilities by increasing infiltration rates on site. Although they make up a small percentage of the total area of the WPC, sidewalks may be the most feasible surface to change, while acting as a consistent penetrable buffer. Figure 5: Commercial concrete sidewalks in the WPC Study Area 5.2.4 Medians The primary function of medians is to organize and direct automobile traffic, as well as to provide shade and enhance the aesthetic value of commercial parking lots (Celestian & Martin, 2003). Medians within the Wonderland Power Centre are the least prevalent surface, making-up slightly more than 4% of the entire Study Area. They are sparsely located within each parking section, and generally contain trees, shrubs, herbaceous perennials, ornamental grasses, and in some cases decorative stone or mulches. These decorated medians are not considered to be “hard” surfaces, and therefore may effectively catch and store incident precipitation due to their vegetative nature and soil-based structure. However, due to their elevation (i.e., about 4 to 6
  29. 29. JOVIAN DESIGN Page | 12 inches off the ground), medians generally do not help reduce stormwater runoff or flow over the parking lots. Figure 6: Medians are dispersed throughout commercial parking lots to help guide traffic and provide aesthetic relief from dominating impervious pavements 5.2.5 Stormwater Management Facilities The main function of a SWM facility is to store runoff from precipitation and snow melt, which may otherwise lead to flooding or erosion, and adversely affect water quality (MOE, 2003). The SWM facility used to mitigate runoff at the Wonderland Power Centre makes up nearly 20% of the entire Study Area. More detail on this facility can be found in the Stormwater Inventory section of this Report. Figure 7: Stormwater Management Pond adjacent to the WPC showing a) an inflow culvert, b) a near full pond, overflow spillway and forebay, c) and emergency spillway 5.2.6 Other Surfaces Landscaped green spaces within the Wonderland Power Centre site represent slightly more than 6% of the Study Area. These spaces are generally composed of trees, a b c
  30. 30. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 13 shrubs, herbaceous perennials and decorative grasses, rocks, and maintained grass lawns. Although their function is mainly for aesthetic and recreational purposes, urban green spaces may help alleviate the problem of surface runoff by increasing infiltration rates and acting as a penetrable buffer (Benedict & McMahon, 2002). Landscaped green spaces may be intensified to provide a more significant role or function, both as an aesthetic tool and as a buffer, especially in commercial and residential zones where impermeable surfaces generally dominate. Temporary structures, including roofed shopping cart corrals and seasonal greenhouses are also present within the Study Area. Figure 8: Other surfaces within the WPC include a) roofed shopping cart corrals and b) landscaped areas
  31. 31. JOVIAN DESIGN Page | 14 6. Stormwater Management Inventory 6.1 Introduction The WPC is wholly serviced by the Bradley Avenue Stormwater Management Facility within the Pincombe Drain catchment area (Appendix A). A Stormwater Management Inventory is required to assess the present condition and required maintenance of the SWM facility at the Wonderland Power Centre. As such, functional designs, entitled Final Stormwater Management Report for the Bradley Avenue Stormwater Management Facility were obtained from the City of London Engineering and Review Division, and used to assess the servicing capacity, present condition and required maintenance of the SWM facility. 6.2 Construction of Bradley Avenue SWM Facility The total projected cost for the Bradley Avenue SWM facility was $2,456,660 of which the cost for construction of inlet/outlet sewers was $636,660 (AECOM, 2009). Prior to construction, on-site siltation and erosion control measures were taken in order to prevent the transportation of eroded soils off-site into downstream properties or watercourses. These measures included the installation of 140m of regular duty silt fences and 300m of heavy duty silt fences. A sediment trap of approximately 70m x 20m x 1m was constructed adjacent to the SWM Facility, to store sediment deposition. 6.3 Servicing Capacity of Bradley Avenue SWM Facility The City of London averages 987mm of precipitation per year (Environment Canada, 2010). As illustrated in Table 2, the Bradley Avenue SWM facility has a total stormwater retention capacity of 45,238m3 . Generally speaking, the facility has a total permanent volume of 7.500m3 , with a drawdown time of 72 hours (Development Engineering, 2005). Table 2: Bradley Avenue SWM facility volume summary Bradley Avenue SWM Facility Volume Summary Water Quality Volume Required Provided Permanent pool volume per hectare based on protection level and imperviousness (MOE) 115 m3 /ha 118 m3 /ha Total Permanent pool volume 5615 m3 7500 m3 Total SWM Facility Volume – 45238 m3 Baseflow and Erosion Volume Required Provided Total storage volume per hectare 200 m3 /ha 160 m3 /ha Total baseflow and erosion volume 12685 m3 10147 m3 Source: Development Engineering, 2005
  32. 32. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 15 Table 3 summarizes the return period of flooding as used in the Bradley Avenue SWM facility modeling. The stormwater discharge into the SWM facility, for return periods of 2, 5, 10, 25, 50, 100 and 250 years has been tabulated and the volume corresponding to the respective flooding events has been calculated (Development Engineering, 2005). In the event of a 250 year storm (6 hour duration), 26,524 m3 of the SWM facility will be utilized. This number represents approximately 59% of the total volume of the facility at 45,238 m3 . Thus, the anticipated single-event volume utilization from the SWM facility is less than the maximum available storage volume (Development Engineering, 2005). Table 3: SWM facility discharge and storage summary for varying rain events Discharge and Storage Summary for 2-250 Year Rainfall Events Return Period Discharge into SWM facility (m3 /s) Discharge from SWM facility (m3 /s) Storage volume utilization (m3 ) Pond elevation/depth (m) 2 year 5.90 0.28 13271 266.08 5 year 7.68 0.85 16380 266.27 10 year 8.86 1.51 17713 266.35 25 year 10.08 2.24 19288 266.44 50 year 11.05 2.42 20429 266.51 100 year 11.72 2.56 21571 266.58 250 year 15.01 3.10 26524 266.86 Source: Development Engineering, 2005 However, given that the SWM facility carries a constant volume, frequent storm events can surpass the maximum capacity, leading to the submergence of the existing discharge outlets and a subsequently slow release of water from the SWM facility (Development Engineering, 2005).
  33. 33. JOVIAN DESIGN Page | 16 6.4 Subsurface Conditions A subsurface analysis was carried out at the WPC site in order to install standpipes and the groundwater table was discovered to be 7.9m to 8.1m below the surface (Development Engineering, 2005). According to Brown (2008), these depths are suitable for the installation of permeable surfaces, which require a groundwater table of at least 1.1m to 1.5m from the surface. 6.5 Maintenance of the SWM Facility The maintenance responsibilities for the Bradley Avenue SWM facility are separated into general maintenance, sediment maintenance and sediment disposal (Development Engineering, 2005). General maintenance is carried out three or four times a year. The activities include weed control, grass cutting and outlet pipe opening maintenance. Sediment maintenance is carried out when the sediment removal efficiency is reduced by 5%. Sediment disposal is carried out after a sediment chemical analysis is completed. The Ministry of Environment guidelines for Use at Contaminated Sites in Ontario and the Ontario Environmental Protection Act (OEPA), Regulation 347, Schedule 4 Leachate Test, Ref. 15 provide the applicable guidelines for determining sediment disposal options (Development Engineering, 2005). Inspection is carried out at least once per month during dry weather, and a Sediment & Erosion Control Maintenance & Monitoring Report is completed (Development Engineering, 2005). Annual maintenance costs for the SWM facility at the WPC is estimated at $20,000 per year (Weber, 2010).
  34. 34. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 17 7. Permeable Surfaces Overview 7.1 Introduction The level of urbanization is rising; by 2030 it is expected that 83% of people in developed countries will live in urban areas (Mentens, Raes & Hermy, 2005). Urbanization results in the displacement of cropland, grassland and forests by the implementation of impervious surfaces. This greatly intensifies stormwater runoff, diminishing groundwater recharge and enhancing stream channel and river erosion (Mentens, Raes & Hermy, 2005). Permeable surfaces are surfaces which allow water to percolate or travel through their structure into the underlying ground layer, thereby relieving pressures on traditional stormwater management systems (SWITCH, 2007). The advancement of new technologies has brought many new permeable products onto the market; including porous asphalt, permeable concrete, green roofs and other emerging technologies. If properly installed and maintained, permeable pavements are typically designed to handle as much as 70-80% of annual rainfall (Metropolitan Area Planning Council, 2010).
  35. 35. JOVIAN DESIGN Page | 18 Figure 9: Interaction between rainwater and tradition/conventional pavement Modified from: Sansalone et al., 2008, p. 667) Traditionally-paved surfaces do not allow for the natural infiltration of water into the underlying soil for the purposes of groundwater recharge (Sansalone, Kuang & Ramieri, 2008). Rather, rainfall is carried over the surface of pavements as runoff (Figure 9), and must be captured using municipal stormwater management infrastructure. In addition to the negative environmental impacts associated with impermeable surfaces (i.e., the movement of pollutants into natural systems and increasing runoff peaks and volumes), impermeable surfaces are also a costly economic expenditure (Sansalone et al., 2008; Gilbert & Clausen, 2006). As urbanization increases, so too does the need for increased stormwater infrastructure. The development of a new individual stormwater management facility for a city the size of London can cost anywhere between just over $1 million (CAD) to just under $7 million (CAD); including land acquisition, construction of ponds, and necessary piping systems (AECOM, 2009). Permeable surfaces, on the other hand, serve as more environmentally conscious, low-impact development materials for rainwater runoff control (Figure 10) (Sansalone, Figure 10: Interaction between rainwater and permeable pavement Modified from: Sansalone et al., 2008, p. 667)
  36. 36. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 19 et al., 2008). Although some surfaces have higher porosities than others, they all work to restore the in situ hydrology of a site by reducing runoff, filtering and treating infiltrating runoff and reducing thermal pollution and temperature (Sansalone et al., 2008). By reducing the rate and quantity of stormwater runoff, permeable pavements reduce the demand on stormwater treatment facilities (Landers, 2008), thereby reducing costs for capital infrastructure, maintenance and operation (SWITCH, 2007). 7.2 Permeable Asphalt 7.2.1 Introduction Conventional asphalt is comprised of asphalt cement and coarse aggregates, including stone, sand, and gravel compacted together (Freemantle, 1999). Traditionally, this media consists of impermeable substances which do not allow precipitation or surface runoff to infiltrate into the soil or rock beds. A novel solution to impervious asphalt was first developed in the 1970s, in which fine sediments (e.g., sand with a grain size less than 0.075 mm in diameter) were removed, resulting in a network of continuously linked voids to allow the passage of fluids through the pavement surface and ultimately to groundwater sources or the water table (Beecham, 2007; Boving, 2008). 7.2.2 Function and Application Walker (2006) suggests that the permeable asphalt surface (e.g., approximately 5 to 10 cm in depth with 15-25% voids or pore space) should be generally underlain by a top filter course (e.g., 5 cm of 1.3 cm crushed stone aggregate), a reservoir course (determined by the average storage volume, structural capacity, or frost depth; usually an 20 or 23 cm minimum with aggregates between 4 and 7.5 cm in size with 40% voids is recommended), an optional bottom filter course, filter fabric (e.g., geotextile fabric) and subgrade material consisting of larger aggregates that acts as a temporary storage capacity to hold the collected water (Walker, 2006). Figure 11 shows a typical cross-section of a permeable asphalt surface. Figure 11: Typical cross-section of a permeable asphalt surface Source: Fancher & Townsen, 2003 Many factors must be taken into account before a project can be proposed or designed using permeable asphalt, including local soil characteristics, local topography, climate, and traffic loading (Brattebo & Booth, 2003). For instance, it is recommended that permeable asphalt pavement be used on sites with gentle slopes (e.g., surface grade less than 5%), permeable soils (i.e., well drained or moderately well drained), and relatively deep water table and bedrock levels (Gunderson, 2008; Beecham, 2007). Conventional asphalt is largely used as a material to construct highways, roadways, airfields, and parking lots. Alternatively, permeable asphalt pavement is appropriate for
  37. 37. JOVIAN DESIGN Page | 20 low-traffic applications such as walkways, low-traffic streets, and along highway shoulders (Freemantle, 1999; Brattebo & Booth, 2003). 7.2.3 Durability The lifespan of a parking lot situated in a northern climate, and made from conventional pavements is approximately 15 years (EPA, 2009). A properly designed, installed, and maintained permeable asphalt pavement, on the other hand, may have a lifespan of 20 to 30 years (Gunderson, 2008). The regional climate of Southwestern Ontario, and specifically London, presents many obstacles to the effectiveness of permeable asphalt pavement due to cold weather. For instance, Backstrom and Bergstrom (2000) found that at freezing point, the infiltration capacity of porous asphalt was about 40% lower (7.4 mm/min) than that near 20o C (19 mm/min) due to ice formation within the pores. The authors also found that exposure to snowmelt conditions (i.e., freeze-thaw) over a two day period further reduced this capacity up to 90%. As a result, typical snowmelt conditions for porous asphalt may only yield an estimated 1-5 mm/min infiltration capacity (Backstrom & Bergstrom, 2000; Stenmark, 1995). However, several confounding variables found during experimentation may be at fault for the overall poor performance. Firstly, the asphalt pieces were taken from a field site which had been in operation for two years. Secondly, the asphalt was not cleaned; nor were the pore spaces unclogged before testing. Thirdly, no apparent de- icing agents of any sort were used during experimentation, which may have melted snow and ice more quickly, allowing water to effectively infiltrate the media. Despite the results of this Study, many researchers maintain that porous asphalt pavement performs relatively well in cold weather climates compared to conventional design (Gunderson, 2008; Roseen & Ballestero, 2008; Roseen et al., 2009; Backstrom and Viklander, 2000). These researchers argue that porous asphalt, and other low impact development designs, have a high level of functionality during winter months and that frozen filter media, generally, do not reduce performance. Figure 12 shows winter performance of different stormwater components.
  38. 38. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 21 Figure 12: Winter performance vs. general indicators, including runoff control, pollution control, and level of integration, for different stormwater components Source: Backstrom and Viklander, 2000 7.2.4 Maintenance Due to the nature of porous asphalt pavement, regular inspection for surface clogging must be undertaken, especially after large storm events, which may also increase sandy discharge (Beecham, 2007). In cases of clogged or reduced surface porosity, the pavement can be cleaned by a vacuum sweeper or pressure washer 2 to 4 times per year to avoid build-up of debris, and to prevent potential decreases in infiltration capacity (Bean et al., 2007; Balades et al., 1995). For large commercial developments, however, this implies an additional cost that should be taken into consideration when comparing product types. Dust and sand tends to clog the pores of porous asphalt surfaces and severely restrict percolation through the top layer of the system (Bean et al., 2007; Balades et al., 1995). It stands to reason that these surfaces may not be suitable candidates for areas adjacent to partially landscaped locations where significant erosion may take place, or jurisdictions which use sand, and even salt, as a de-icing agent in winter. A liquid de-icer is therefore recommended as it drains out with the snow and ice during melting, leaving the porosity of the pavement largely intact (Walker, 2006). 7.2.5 Cost The cost of porous asphalt pavement installation is similar in cost to conventional asphalt, and one of the least expensive compared to the other permeable surfaces (Boving, 2008). It is estimated that the cost for porous asphalt pavement is approximately $5.50 to $10.76 (USD) per metre squared (EPA, 2009). However, the underlying stone bed is usually more expensive than those found in a conventional sub- base, due to the greater depths of aggregates required (Beecham, 2007). Special training or techniques are not generally required for application of porous asphalt, as the laying process is similar to that of conventional asphalt (Walker, 2006). 7.2.6 Benefits and Limitations The key advantage of permeable asphalt is that it retains stormwater onsite, which may decrease surface runoff with low peak discharge (Bean et al., 2007; Rushton, 2001). It may also act as a potential water quality treatment process by intercepting the contaminants of urban stormwater runoff
  39. 39. JOVIAN DESIGN Page | 22 prior to infiltration into soil (Beecham, 2007; Brattebo & Booth, 2003; Bean et al., 2007). Another possible benefit of using porous asphalt in cold weather climates is that melted water infiltrates through the media before it freezes, which may cause fewer problems with slipperiness and black ice related accidents, for example, during cold nights (Backstrom & Bergstrom, 2000). Parking lots and roads tend to be sources of water pollution because of their extensive impervious surfaces, in which most precipitation that falls becomes urban runoff. Motor vehicles are a constant source of pollutants, the most significant being gasoline, motor oil, polycyclic aromatic hydrocarbons (found in the combustion by-products of gasoline, as well as in asphalt sealants used to maintain parking lots), and heavy metals (Bean et al., 2007; Rushton, 2001; Boving et al., 2008). According to a cold climate study by Backstrom and Viklander (2000), cold vehicle engines produce 2 to 8 times more potentially harmful particles than does a warm engine, which may accumulate on impermeable surfaces and be subject to runoff, with implications for water contamination. Another study by Boving et al. (2008) suggests that porous asphalt is effective at removing organic and metal contaminants. However, permeable asphalt surfaces, which allow liquid infiltration, may lead to possible ground contamination within the surface of the parking lot. Although this process can filter the water, contaminants may seep directly into groundwater, especially where there is groundwater abstraction downstream for drinking water (Howard & Beck, 1993; Legret & Colandini, 1999). 7.3 Permeable Concrete 7.3.1 Introduction Concrete in the form of permeable interlocking concrete pavers (PICP), concrete grid pavers (CGP) and porous concrete (PC) (Figure 13) is commonly used to increase surface infiltration rates, thereby mitigating stormwater from conventional stormwater systems (Bean, Hunt, & Bidelspach, 2007a). Infiltration rates depend on a number of factors, including the type of permeable concrete product that is applied, soil infiltration rate, and installation of the permeable concrete product (i.e. the aggregate material that is used as a filler, and the size and type of sub-base that is installed) (Table 4) (Bean et al., 2007a). Figure 13: a) PICP, b) CGP, c) PC Source: Bean et al., 2007b
  40. 40. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 23 Results from runoff studies indicate that permeable concrete pavements may not only reduce runoff, but also eradicate runoff entirely under certain rainfall depths, intensities, maintenance conditions, antecedent conditions and designs (Bean et al., 2007b). Table 4: Factors affecting infiltration rates of permeable concrete products Factors Affecting Infiltration Rates of Permeable Concrete Products Product Site (m2 ) Slope (%) Soil Thickness of Permeable Surface (mm) Filler Base Base (mm) SIR (mm/h) CGP 630 0.5 Kalmia sandy soil 90 Coarse grade sand Yes; sand 50 580 PC 370 0.33 Seagate fine graded sand 200 NA No NA 230 PICP 740 0.4 Bay Meade sandy soil 76 NA Yes; stone & gravel 275 20 X 1013 PICP 120 NA Loamy sand soil 76 NA Yes; stone & gravel 275 40 X 1013 SIR = Surface Infiltration Rate; Source: Bean et al., 2007a 7.3.2 Function and Application PICP is defined as concrete block pavers that, when in place, create voids located at the corners and midpoints of the pavers, allowing water to infiltrate through an aggregate material (Bean et al., 2007b). CGP is defined as concrete blocks with inner voids between the blocks that permit water to infiltrate in the same way as PICP. PC is defined as altered standard concrete, as fine aggregate has been removed from the standard mix, permitting interconnected
  41. 41. JOVIAN DESIGN Page | 24 void spaces to form during curing, thus allowing water to infiltrate through the material (Bean et al., 2007b). 7.3.2.1 Function and Application of PICP and CGP The primary difference between permeable pavers and conventional pavers is base materials and void space (Bean et al., 2007b; Unilock, 2009). Permeable paver systems use crushed, angular, open-graded aggregate base materials that have a void space or porosity of approximately 40%. Base storage capacities depend on a number of factors including rainfall and base depth (Table 5) (Unilock, 2009). The proper installation of the base is very important to the optimal function of PICP and CPG systems (Smith, 2006). Figure 14 illustrates the appropriate installation of a typical exfiltration system including base compositions and measurements. This system fully exfiltrates, by infiltrating water directly into the base and extruding it to the soil. Overflows are managed through perimeter drainage to swales, bio-retention areas or storm sewer inlets. Partial exfiltration systems are less common than full exfiltration systems and include drainage by perforated pipes. In this case, excess water is drained from the base by pipes to sewers or a stream (Smith, 2006). Figure 14: Typical installation for exfiltration Source: Uni-EcoLocTech, 2008 The application of PICP and CGP products depend on the specific material that is being used as well as the location of the project. Unilock, a company that sells permeable pavers, manufactures its products to meet the ASTM C936 standard which allows the product to support semi-truck traffic, heavy-traffic and high-load environments (Unilock, 2009). The application of Unilock products varies greatly. Over 107.6 million metres squared of Unilock permeable pavers have been installed throughout Canada and the U.S. Applications include parks and municipal commons, commercial parking and vehicular areas, government and municipal facilities, streets and streetscapes, stadiums, condominiums and others (Unilock, 2009). Because of the structural integrity of CGP, this material is intended for light- duty use such as over-flow parking areas, being occasionally
  42. 42. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 25 used in parking lots, and in access to emergency lanes (Smith, 2006). Table 5: Base storage capacity of PICP and CGP Base Storage Capacity of Permeable Interlocking Concrete Pavers and Concrete Grid Pavers Criteria Rainwater Harvest Volume Base Storage Capacity Surplus/(Deficit) Storage Rainfall (mm/hr) Surface Area (m2 ) Base Depth (cm) Void Space (m3 ) (m3 ) (m3 ) % Used 25 4,047 30 40% 103 493 391 20.8% 25 4,047 46 40% 103 740 637 13.9% 89 4,047 30 40% 360 493 134 72.9% 89 4,047 46 40% 360 740 380 48.6% 12 4,047 61 40% 520 986.5 473 52.1% 188 4,047 46 40% 761 740 (21) 102.8% Source: Unilock, 2009 7.3.2.2 Function and Application of PC PC is a paste composed of water and cementitious materials that forms a thick coating around aggregate particles (Tennis, Leming, & Akers, 2004). Void space is created by adding little or no sand which results in a system that is highly permeable and drains quickly. The hardened concrete contains between 15% and 25% voids that typically allow flow rates of approximately 34 mm/s, although it can be much higher (Figure 15) (Tennis, et al., 2004).
  43. 43. JOVIAN DESIGN Page | 26 Figure 15: Typical installation of porous concrete surface Source: National Ready Mixed Concrete Association, 2010 PC can be applied in a variety of settings. It can be used in parking lots, tennis courts, greenhouses and as pervious base layers under heavy duty pavements (Table 6) (Tennis et al., 2004). Properly installed PC can achieve strengths in excess of 20.5 MPa and flexural strengths of more than 53.5 MPa. This strength is more than sufficient for most low- volume pavement applications, including high axle loads for garbage truck and emergency vehicles such as fire trucks (Tennis et al., 2004). As PC matures, its compressive strength increases (Park & Tia, 2003). Special mix designs, structural designs and placement techniques can be altered to accommodate more demanding applications (Tennis et al., 2004). Table 6: Applications of pervious concrete Applications of Porous Concrete Low-volume pavements Artificial reefs Residential roads, alleys, and driveways Slope stabilization Sidewalks and pathways Well linings Parking lots Tree grates in sidewalks Low water crossings Foundations/floors for greenhouses, fish hatcheries, aquatic amusement centres, and zoos Tennis courts Hydraulic structures Subbase for conventional concrete pavements Swimming pool decks Patios Pavement edge drains Walls (including load-bearing) Groins and seawalls Source: Tennis et al., 2004
  44. 44. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 27 7.3.3 Durability 7.3.3.1 Durability of PICP PICP is particularly durable and has the capacity to withstand high traffic areas and climatic uncertainty (Toronto and Region Conservation Authority [TRCA], 2007). A study by the TRCA (2007) indicated that permeable pavement continued to function normally throughout the winter months during winter rain events, with minor amounts of infiltrate measures even during very cold periods. 7.3.3.2 Durability of CGP CGP is recommended for light-duty use, thus applications vary (Pavers by Ideal, 2005). Certain CGP products have the capacity to withstand harsh winter climates and are “snow-plough safe.” Freeze-thaw conditions have no demonstrated effect on certain CGP products (Pavers by Ideal, 2005). 7.3.3.3 Durability of PC PC is often criticized for its vulnerability to freeze-thaw conditions (Tennis et. al., 2008). However, freeze-thaw resistance depends on the saturation level of the voids in the concrete at the time of freezing. Because PC drains rapidly, saturation is often prevented from occurring. In fact, evidence suggests that snow-covered pervious concrete melts quicker as voids in the material allow snow to thaw more quickly than conventional pavements. Different factors improve durability of PC in freeze-thaw conditions. For example, entrained air in the PC paste can dramatically improve freeze-thaw protection. Placement also plays an important role as specific installation is recommended in freeze-thaw environments (Tennis et. al., 2008). PC can be susceptible to the effects of aggressive chemicals in soils or water, such as acids and sulphates (Tennis et. al., 2008). If isolated from high-sulphate soils and groundwater, PC can be used. Abrasion resistance is also a concern as PC has a rough surface texture and open structure. PC can be particularly problematic where snowploughs are used to clear pavements although studies indicate that PC can allow snow to melt faster thus requiring less ploughing (Tennis et. al., 2008). 7.3.4 Maintenance 7.3.4.1 Maintenance of PICP, CGP and PC Clogging can occur as a result of fine particle accumulation in the void spaces of permeable pavements (Bean, Hunt, Bidelspach & Burak, 2004). The rate of clogging increases as more fine particles (fines) are trapped since smaller particles trap larger particles. In most cases, clogging reduces surface infiltration rates. Clogging can be limited, however, through regular maintenance, either by a vacuum sweeper or pressure washing thereby improving surface infiltration rates from unmaintained infiltration rates (Bean et al., 2007b; Smith, 2006). Clogging can also be limited through strategic site placement away from disturbed soil areas. One study concluded that maintenance was vital to sustaining high surface infiltration rates of CGP in particular (Bean et al., 2007b). Without maintenance, the median average infiltration rate of CGP was 4.9 cm/h; while with maintenance, the median infiltration rate was 8.6 cm/h (Bean et al., 2007b).
  45. 45. JOVIAN DESIGN Page | 28 The study also concluded that the selected site of permeable pavement applications was a significant factor in preserving high surface infiltration rates (Bean et al., 2007b). In particular, locating PICP and PC away from disturbed soil areas was of great importance in maintaining high surface infiltration rates. The authors of this particular study also found that permeable pavements installed in sandy soil environments maintained relatively high surface infiltration rates, regardless of pavement age or type (Bean et al., 2007b). Bean et al. (2007b) suggest that a storage layer improves runoff reduction potential. Keeping the permeable surface free of fine particles, performing regular maintenance and construction on sandy, in situ soils may also increase runoff reduction potential. In climates where snow removal equipment is employed, damage can occur to PICP and CGP. This may require the replacement of damaged blocks thereby increasing maintenance costs. 7.3.5 Cost 7.3.5.1 Cost of PICP, CGP, and PC The cost of permeable concrete pavement varies according to location, distributor, and scope of project (among other factors). For example, PICP is generally more expensive than conventional asphalt or concrete pavements that rely on a stormwater collection pond (Interlocking Concrete Pavement Institute [ICPI], 2008). PICP may be cost-effective in a new development where regulations limit impervious cover and space is limited. Because PICP and other permeable pavements may not require a collection pond as large as impervious-paved surfaces, space can be used more efficiently (ICPI, 2008). 7.3.6 Benefits and Limitations PICP and CPG have the capacity to remove pollutants, improving the quality of exfiltrate (Tennis et al., 2008). The material allows the rainfall to percolate into the ground where soil chemistry and biology are able to “treat” the polluted water naturally. This results in the reduction or elimination of stormwater retention areas. Also, “groundwater and aquifer recharge is increased, peak flow through drainage channels is reduced and flooding is minimized” (Tennis et. al., 2008, p.4). PICP is also easy to replace as individual pavers can be removed in the event of damage (Park & Tia, 2003). This results in lower replacement costs and lessens the negative environmental impact of large scale product replacement (Hirshorn, 2010). PC has the capacity to remove pollutants from infiltrate at high rates (Park & Tia, 2003). Pollutant removal rates are variable as water purification can be affected by the size of aggregate and void content in the PC paste. One study indicates that PC composed of a smaller size of aggregate and a higher void content greatly removes total nitrogen (T- N, mg/l) and total phosphorous (T-P, mg/l) from the test water in comparison to PC pastes with a larger size aggregate and a lower void content. Smaller sized aggregate and higher void content increase the surface area of the concrete‟s porosity. The composition of the PC paste can largely affect the ability of the material to remove pollutants (Park & Tia, 2003).
  46. 46. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 29 Permeable surfaces should not be used in locations with high pollutant loads. These locations include commercial nurseries, recycling facilities, fuelling stations, industrial storage, marinas, some outdoor loading facilities, public works yards, hazardous materials generators (if containers are exposed to rainfall), vehicle service and maintenance areas and vehicle and equipment washing and steam cleaning facilities (Hirshorn, 2010). Permeable paving should also not be used in high traffic and/or high speed areas as permeable paving has lower load-bearing capacity that conventional pavement (Hirshorn, 2010). 7.3.7 Supplementary Cementitious Materials The National Ready Mixed Concrete Association (2008) claimed that the construction industry is committed to continuous environmental improvement through process innovation and product standards that lead to reduced environmental impact. One method of improving product standards is through the mixing of Portland cement with supplementary cementitious materials (SCMs) for various uses. Bouzoubaâ and Foo (2005) contend that SCMs, including fly ash, ground granulated blast furnace slag (GGBFS), silica fume and natural pozzolans can be mixed with Portland cement. These blended cements are less energy intensive and made with by-products or wastes. Therefore, they reduce the solid waste burden on landfills and offer performance benefits for certain applications (Committee E- 701 Materials for Concrete Construction, 2001). One of the main objectives of increasing the use of SCMs in concrete production is to reduce the release of CO2 associated with the production of each cubic meter of concrete (Bouzoubaâ & Fournier, 2005). SCMs were used mainly due to their low costs and performance-enhancing aspects. Fly ash is used in various concrete applications because of improvement in workability, reduction of heat of hydration, increased water tightness and ultimate strength, and enhanced resistance to sulphate attack (especially in western Canada) and alkali– aggregate reaction (AAR) throughout Canada (Bouzoubaâ & Fournier, 2005). The use of SCMs in the cement and concrete industries can render benefits in engineering, economic, and ecological terms (Malhotra & Mehta, 1996). Engineering benefits of the incorporation of SCMs into a concrete mixture include improvement in the workability and the reduction of the water. This mixing enhances the ultimate strength, permeability, and durability to chemical attack along with an improved resistance to thermal cracking. In terms of residential application, concrete is used in basement walls and floors, driveways, steps, sidewalks and a small amount of concrete products such as paving blocks, retaining walls, and masonry blocks. Specifically, SCMs have proven to be very effective in producing durable, freeze-thaw tolerant sidewalks (Bouzoubaâ & Fournier, 2005). 7.4 Permeable Pavement De-icing agents In many northern countries, such as Canada and the USA, one of the main de-icing agents of choice for safe driving conditions in municipal areas is common salt (sodium chloride) because of its cost effectiveness (Liu et al., 2006). Urbanization leads to increases in impervious surfaces and
  47. 47. JOVIAN DESIGN Page | 30 complex systems, such as roads, parking lots, and sidewalks that receive chemical de-icer to keep them free of ice and snow during winter (Daley et al., 2009). As a result of these larger surfaces, additional road salts are required which may adversely affect soil and vegetation systems, human health, as well as the quality of water systems (e.g., groundwater and streams) due to increased levels of Cl- (Williams et al., 2005; Williams et al., 1999). The Greater Toronto Area alone applies more than 100,000 tonnes of salt each winter (Williams et al., 1999) and approximately 5 million tonnes of sodium chloride are consumed each year in Canada for de-icing roles (Environment Canada and Health Canada, 2001). If high enough concentrations of these road salts reach groundwater zones, contamination can occur and negatively affect drinking water quality, fresh water systems, and aquatic ecosystems (Ramakrishna & Viraraghavan, 2005). De-icing salts, particularly NaCl contribute ions to the soil, altering pH and the soil‟s chemical composition, which may lead to vegetative stress and disrupt plant function (Bogemans et al., 1989; Guntner & Wilke; Trombulak & Frissell, 2000). NaCl is also an environmental concern because of its toxicity to aquatic organisms; its alterations to soil structure and decreased permeability (Ramakrishna & Viraraghavan, 2005; Fischel, 2001); and its adverse effects on human health (Environment Canada and Health Canada, 2001). The main human impact of ingesting large amounts of salt is hypertension leading to cardiovascular disease, which could account for thousands of deaths a year in Canada and the USA (Feig & Paya, 1998). In the past few years, high levels of sodium and chloride (>2000 mg/L) have been found in many shallow groundwater wells in and around the GTA where urbanization is greater than 80% (Williams et al., 1999). In general, only wells or reservoirs near salt-treated surfaces or salt storage facilities are most likely to become susceptible to salt infiltration, whereby road salts can enter drinking water supplies by migrating through soil into groundwater or by runoff and drainage directly into surface water (Werner & diPretoro, 2006). Due to concerns of clogged pores by sand and salt, a liquid de-icer is therefore recommended for use on permeable pavements as it drains out with the snow and ice during melting, leaving the porosity of the pavement largely intact (Walker, 2006). However, less research has been devoted towards liquid de-icers, including CaCl2, KCl, and MgCl2 (Ramakrishna & Viraraghavan, 2005). Generally the chloride ions of these substances have similar environmental impacts as rock salt (NaCl), but have been found to present less toxicity to aquatic organisms, as well as having a limited impact on human health (Fischel, 2001). Another option for snow and ice removal on permeable pavement is the liquid form of calcium magnesium acetate (CMA) which may provide the most environmentally friendly, although a more expensive alternative to sodium chloride, while leaving the porosity of the pavement largely intact. CMA is an organic de-icing agent which may largely be broken down by biodegradation (Fischel, 2001; Ramakrishna & Viraraghavan, 2005). There is, however, some concern that the acetate-based de-icer has the potential to cause
  48. 48. PERMEABLE SURFACE STORMWATER MANAGEMENT FEASIBILITY STUDY APRIL 2010 Page | 31 oxygen depletion in rivers, streams, and lakes; however, it is hoped that the agent breakdown before such an occurrence (Fischel, 2001; Ramakrishna & Viraraghavan, 2005). There is also some debate over pH alterations and the corrosive potential caused by the agent (Ramakrishna & Viraraghavan, 2005). Due to CMA containing phosphorous and nitrogen, eutrophication may occur to nearby water bodies, and as a result adversely affect aquatic ecosystems (Fischel, 2001). 7.5 Green Roofs 7.5.1 Introduction Roof surfaces account for a large portion of impervious cover in urban areas. Establishing vegetation on roof-tops, known as green roofs, is one method of recovering lost green space that can aid in mitigating stormwater runoff (van Woert, et al., 2005). A green roof, i.e., a roof with a vegetative cover (Figure 16), is one passive technique that can be used to address environmental issues in an urban setting (Kosareo & Ries, 2007). Green roofs have been a standard construction practice in many countries for hundreds, if not thousands of years, mainly due to the excellent insulative qualities of the combined plant and soil layers (sod) (Peck & Kuhn, n.d.). In the cold climates of Iceland and Scandinavia, sod roofs helped to retain heat, while in warm countries such as Tanzania, green roofs keep buildings cool. Canadian examples of early green roofs, imported by the Vikings and later the French colonists, can be found in the provinces of Newfoundland and Nova Scotia (Peck & Kuhn, n.d.). Figure 16: Typical cross-section of a green roof Source: Kosareo & Ries, 2007 7.5.2 Function and Application Green roofs are an emerging strategy for mitigating stormwater runoff. They offer numerous benefits such as: Stormwater mitigation; insulation for buildings; an increase in the life span of a typical roof by protecting the roof components from exposure to ultraviolet rays, extreme temperatures and rapid temperature fluctuations; filtration of harmful air pollutants; an aesthetically pleasing environment to live and work in; habitat for a range of organisms, and; the potential to reduce Urban Heat Island effect (van Woert et al., 2005). However, many consider stormwater runoff mitigation to be the primary function of green roofs due to the prevalence of impervious surfaces in urban areas (van Woert et al., 2005). Furthermore, green roofs have the potential to improve thermal performance of a roofing system through shading and evapotranspiration, thus reducing a building‟s energy demand for space conditioning (Kiu & Baskaran, 2003).

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