Chris Ling and Levi Waldron
Published December 21, 2006
Where land is undeveloped, runoff from storms can be absorbed by soil and roots and normally does not cause flooding or other problems except in extreme cases. In cities, however, the extensive construction of roads, parking lots, and buildings diminishes the area of land available to absorb runoff, and it is instead diverted into a storm water system after picking up residues of oil, animal waste, fertilizers, pesticides, road salt, exhaust chemicals, and other contaminants. In many areas, especially with older sewage systems, the storm water combines with sewage in "combined sewers." Ideally, the combined sewer water would be treated before being released, but during heavy rain or melting events, sudden spikes in volume exceeds capacity of the treatment plants, and the excess is released untreated, polluting the waterways where this waste is dumped. This case study documents some of the innovative approaches being undertaken to mitigate this problem in Chilliwack, BC, and Toronto, ON.
Sustainable Development Characteristics
There are a number of approaches to mitigating waste water pollution, ranging from source to end-of-pipe, small to large-scale, low to high-tech, public education, and building large public works. In order to capture a wide range of innovative approaches to reducing the problem, this case study looks at the medium-sized community of Chilliwack, BC and the large urban area of Toronto, ON. How a community treats all of its waste, including waste water, is an essential component of sustainable community development, and indeed adjacent communities, particularly where water systems and watersheds are interconnected .
The Policy and Design Criteria for Surface Water Management in Chilliwack1 is a policy for surface water management that aims to replicate the natural infiltration rate of the land surface to prevent peak flows in flooding in streams within the municipality. The policy is also tied into a process of stream classification based on the water course’s suitability for fish habitat, its flow regime and cross sectional characteristics. A parallel policy to the surface water management is, therefore, the derivation of suitable riparian setbacks to protect stream quality.
The policy aims to transfer the costs of drainage from the city to private developers of new subdivisions and property improvers. This means that developers are responsible for designing systems that retain water within a new development area and release it in a slow and controlled fashion into the soil, and ultimately the natural drainage system. The standard for this has been set at a flow rate of less than 1 litre / sec from the outflow from a subdivision.
The Great Lakes hold one fifth of the world's fresh water, covering 23,000 km2 and draining an area of 745,900 km2, making them ecologically important on a global scale. Its shores are home to 35 million residents, almost half of whom draw their drinking water directly from the lakes (Sierra Legal Defence Fund, 2006). Although some improvements have been made in recent decades, the Great Lakes are still a disposal area for a wide range of industrial, residential, and public effluents. Since only about 1% of the Great Lakes' water is changed every year, the effects of water pollution are cumulative and long-lasting (Gorrie, 2006). Of all the pollution sources in the Great Lakes, one of the most significant is untreated sewage: the 20 cities studied in the Great Lakes Sewage Report Card (Sierra Legal Defence Fund, 2006) dump 92 billion litres of untreated sewage annually into the Great Lakes.
Toronto ranked 12th of these 20 cities for sewage treatment performance, with particularly low performance on combined sewer overflows (containing a mixture of sanitary and storm water), occuring 30-50 times per year for a total of 9 billion litres.
In 2003, in order to mitigate these impacts Toronto embarked on a 25-year, 1 billion dollars Wet Weather Flow Management Master Plan. The basic goal of this plan is to meet the Provincial Water Quality Objectives within the City of Toronto area surface waters. More specifically, it aims to (City of Toronto, 2006):
improve the water quality at public beaches so the water is safely swimmable all summer;
eliminate discharges from combined sewer overflows;
reduce basement flooding caused by the backing up of overflowing sewers;
protect of city infrastructure from stream erosion;
restore degraded local streams;
improve stream water quality;
reduce algae growth along the waterfronts and in streams; and,
restore aquatic habitat.
The plan includes efforts at every stage of the waste water management system: source, conveyance (moving of the waste water), and end-of-pipe facilities. This plan is part of a longer-term 100-year watershed-wide strategy to mitigate the impacts of wet weather flow. The size and population of Toronto present both a significant burden on the local watershed and a particular opportunity to develop new solutions given the significant financial and human resources available to the city.
Critical Success Factors
based on provincial guidance2, and with their support, and the support of federal ministries and consultants from the private sector.
systems approach – operates from the moment water reaches the ground.
considers design issues from watershed scale to individual buildings.
uses research and data to identify critical areas.
the provision of design guidance and open and transparent standards for developers.
Successful implementation of Toronto's 25-year water pollution plan will depend on:
continued and increasing funding for capital projects and ongoing programs from the city and the province. This is critical both to the rate at which projects are completed, and so the city can take advantage of opportunities to replace aging combined sewers with separate storm and sanitary sewers when the pipes need replacing.
success of public education campaigns in promoting less polluting individual habits (ie cleaning up animal waste and not flushing toxic chemicals down drains and sewer grates) and source storm water management such as downspout disconnection, and
continuing political will to improve water quality in Toronto rivers and Lake Ontario.
Community Contact Information
Toronto and Region Conservation Authority Project Manager for the Community Program for Stormwater Management Program
1-416-661-6600 x 5325
Although no monitoring has taken place, the City of Chilliwack officers have observed that flood events have been reduced and water quality has been improved.
The regulatory regime of applying the standards in all new developments, combined with a fair and equal application of the standards meant that local developers agreed to undertake the implementation of the policy once an initial period of complaint and lobbying against the policy was over.
Combination of many different approaches at different levels of the waste water system.
Public education may serve both to reduce individual polluting behaviors and drive support for expensive public works projects.
New Deal for Cities has provided new capital funding for expensive projects such as large overflow storage basins.
Long-term commitment to public education and improvements to existing practice and infrastructure.
Ongoing monitoring will assess the long-term effectiveness of the plan, but it is too early yet to separate normal climatic variations from plan improvements.
What Didn’t Work?
The initial application of the policy on hill slopes was rejected as the infiltration of water into the slope is contrary to geotechnical safety considerations. Therefore, a policy of water retention, not infiltration, was instigated, with water being released into water courses, or pipes down slope and infiltrated elsewhere.
City Operations engineers vetoed the use of open lagoon storage systems due to the increased maintenance costs, liability issues and fears over the West Nile Virus associated with open water.
It was initially hoped that existing developments could be retrofitted, but this has proven difficult to implement due to the costs placed on home owners. As a result, home owners are encouraged to retrofit the drainage system when renovating an existing development and, any extension to the existing building or new buildings must incorporate retention and infiltration drainage.
Large networks of environmentally damaging public infrastructure have been built, which will be expensive and time consuming to upgrade
Beaches may remain too polluted for swimming even after all point sources are controlled. The city spent over $75 million on a huge underground CSO storage tank to protect its western beaches, but they still frequently have too high E. coli levels for swimming. Some evidence suggests that a high waterfowl population and flow from the rivers are now the primary sources of E. coli contamination. The city is now investigating redirecting river flow away from beaches and controlling waterfowl populations. Toronto's rivers continue to be polluted by combined sewer outfalls, within and outside of city limits, and agriculture outside of city limits. New suburban developments in the Humber River headwaters are expected to further degrade the river's water quality (http://www.torontoenvironment.org/westernbeaches).
The free, voluntary downspout disconnection program has been fairly popular, disconnecting about 2,300 homes per year at an average cost of $1,100 per house. At this rate, however, it would take 22 years to reach its target of 40% of downspouts disconnected. City council has proposed mandatory downspout disconnection with 50% of the cost up to $300 covered by the city, which would disconnect 80% of homes within 10 years. This proposal has been sharply criticized by some councillors and others as a veiled tax, and will be going to community consultations. It is yet unclear whether the mandatory program will pass council (http://www.waterkeeper.ca/content/swim/ban_eyed_on_downspouts_tied_to.php).
Financial Costs and Funding Sources
The initial budget for the policy formulation and the development of design criteria ran to approximately $700,000. Half of this was met by the city, the other half through a number of grants including:
Department of Fisheries and Oceansto support the protection of riparian zones for fish habitat.
Support from the provincial government to allow training of fishermen and forestry workers to help with the engineering and biological surveys.
Grant funding from the Real Estate Association of British Columbia.
Money from the provincial government in support of salmon habitat protection and enhancement.
The University of British Columbia also provided resources to help with the initial monitoring and surveying.
Since the implementation of the policy, little financial data are available as much of the implementation costs are incurred by the private sector developers now responsible for the drainage systems. Initial figures for the implementation of a five-year plan were budgeted at $1.7M (Dipak Basu, former Development Engineer for the City of Chilliwack, in a presentation given in 2004 at Royal Roads University), but this budget has now been abandoned as key personnel have retired and the time and resources are not available to do more than keep up with the pace of new development.
Implementation costs are incurred by developers, which are added to their development budgets, and then presumably onto future home owners. The responsibility for maintenance is then passed to the city, or to strata committees depending on the type of development. There is no information on the relative costs of maintenance for the infiltration infrastructure relative to the traditional storm sewer.
The cost of Toronto's 25-year Wet Weather Flow Management Plan is estimated at $40,000,000 per year (http://www.toronto.ca/water/protecting_quality/wwfmmp/pdf/background.pdf). The budget for the first five years of the plan (2003 - 2007), based on the detailed breakdown in the 2004-2005 implementation report (City of Toronto, 2006b) is summarized in table 1. This table does not include an additional $36,000,000 spent on stream restoration, $1,000,000 on shoreline restoration, and $55,510,000 on basement flooding measures. The program is funded by the City of Toronto. Total funding for waste water and water programs is predicted by the city to more than double from $249,500,000 in 2005 to $502,000,000 by 2009 (City of Toronto, 2005).
|Capital Cost ($)||Operating Cost ($)||Total Cost ($)|
|End of Pipe Facilities||38,075,000||9,700,000||47,775,000|
Table 1: Toronto Wet Weather Flow Management Plan costs
Analysis leads to the following observations:
Developers, while unlikely to incur extra costs voluntarily, can be persuaded to take on extra costs provided they and their competitors are given clear guidance and all are treated equally.
A soft engineering approach has potential benefits for ecology and aesthetic landscape concerns. Infiltration areas can be designed to maximise value for wildlife and provide an attractive park like location.
Sustainable drainage is not always entirely compatible with all topographies and geotechnical conditions.
Retrofitting sustainable infrastructure is significantly harder to undertake than implementing such policies in new development. The Toronto case study, however, provides many examples of possible approaches in already developed areas.
A complete waste water management strategy is likely to require both large-scale projects (i.e. upgraded storage and treament facilities) and small-scale projects, such as public education and support for downspout disconnection.
Detailed Background Case Description
Chilliwack is an agricultural community of 70,000 running along the south bank of the Fraser River in BC. The community recognises three creek-based watershed planning areas:
- Hope Slough in the eastern part of the municipality.
- Chilliwack Creek in the central part of the municipality.
- Chilliwack Western Areas.
Throughout the municipality there are 600 km of streams in a land area of 260 km2. The goal of the project was to create an urban form that simulated run-off profiles similar to the natural forest eco-system – or a land surface that is only 10% impermeable. Or to put it another way, a land surface that can infiltrate the first 30mm of rainfall in any precipitation event.
The Department of Fisheries and Oceans' policy of restricting development along riparian zones to protect fish habitat led the City of Chilliwack to formulate classification of streams to allow for development to create appropriate riparian set-backs, and to instigate a more sustainable surface water management system that improved water quality entering water courses and reduced flood events.
Chillwack was selected as a case study for the application of Stormwater Planning: A Guidebook for British Columbia2 funded jointly by the provincial and federal governments, and forms part of the Georgia Basin Ecosystem Initiative. Chilliwack has been concerned about planning for storm water management since 1995, when it released guidelines stating that:
“all new development must restrict flows from the subdivision or development to pre-development volumes.”
The goal of the current policy is to:
“implement integrated stormwater management that maintains or restores the water balance and water quality characteristics of a healthy watershed, manages flooding and geotechnical risks to protect life and property, and improves fish habitat values overtime.”
This is supported by five management objectives.
To manage development to maintain storm water characteristics that emulate the pre-development natural watershed.
To predict the cumulative storm water impacts of development and to integrate this information with other economic, land use and sustainability objectives and policies when considering land use change.
To regulate watershed-specific performance targets for rainfall capture, runoff control, and flood risk management during development, and to refine these targets over time through an adaptive management program.
To identify, by example and pilot studies, means of meeting the performance targets by application of best management practices, and to remove barriers to use of these practices.
To support innovation that leads to affordable, practical stormwater solutions and to increased awareness and application of these solutions.
The policy's goal and objectives are supported by a master planning exercise providing strategic plans for surface water management at creek watershed and sub-watershed levels and a functional plan for individual creek catchment areas.
Design criteria are implemented so that at the site level rain fall is kept on site to allow it to infiltrate into the natural subsurface hydrological systems. At the neighbourhood scale, runoff from a subdivision is held to reduce storm run-off peaks into the municipal drainage system and creek network. This has the goal of reducing flooding in the municipality. These also reflect the severity of rain events. Most rainfall events should be exclusively retained on site and infiltrated into subsurface hydrological system. Moderate events will be stored within neighbourhood in retention ponds, extreme events will be safely conveyed into and through the natural surface water system avoiding flooding in urban areas.
Not only does this reduce flood risk, but it also prevents surface runoff from washing pollutants from road surfaces and residential lots into the creek system. In addition, holding water in the subsurface and on site allows for water recycling by households and aids the recharging of the groundwater. Although this approach, termed the 'water balance approach', has been tested in Chilliwack, to date, private developers have not used it, preferring to implement their own design solutions.
Design lessons from the policy formulation process included the provision of a minimum depth of soil in subdivision landscaping. Careful design of drainage on driveways directs water into soak-a-ways rather than into storm drains. Between 2001 and 2003, pilot projects in five new sub-divisions were implemented to test some of the design criteria. These included:
Removing curbs and gutters from roads.
Installing ‘french drains’ in a grass verge along the road side. At its simplest, a french drain is a trench filled with gravel that allows water to drain away from the surface quickly, but allows the water to infiltrate into the subsurface rather than into a drainage system.
Installing a retention pond at the lowest point of altitude to contain water during larger rainfall events, and releasing it slowly into the natural drainage system.
Landscaping with gentle grades of slope to reduce the loss of soil and sediment into the drainage system.
Narrower roads also have other benefits such as reducing development costs and reducing the amount of clearing of natural vegetation required. The data from the test subdivisions confirmed that the drainage is adequate for all storm events and prevents flooding in the downtown and other sensitive areas.
Since the formulation of the design guide and policy, developers have been obliged to implement water retention and infiltrations systems in all new developments. This has usually been in the form of permeable pipes and storage tanks allowing the slow release of water into the ground and adjacent water courses. There are, however, exceptions to this. On the hillsides within the municipality, infiltration into the soil was not an option as slope stability concerns became an issue. Impermeable concrete storage tanks, therefore, have been used to hold the water, which is then released in a controlled fashion into water courses.
Toronto is a large urban centre of 2.6 million people and a $7.6 billion operating budget (City of Toronto, 2006). Its municipal sewer and storm water systems are extensive: the storm water system is a 4,500km network with 2,600 outfalls (http://www.toronto.ca/water/protecting_quality/wwfmmp/index.htm), connected in an unknown number of locations to the sanitary waste system, which handles 400 billion litres of sewage annually.
Its land base is almost entirely developed except for preserved areas, and residential and commercial development is in the form of re-development of already urban areas, rather than building new subdivisions as seen in Chilliwack. Due to the high degree of existing development in Toronto, and the greater budgetary resources available, the strategies available for waste water pollution mitigation are both limited and more extensive in comparison with those available to Chilliwack.
Goals and Strategies
In developing its Wet Weather Flow Management Master Plan, Toronto considered an extensive list of available strategies and technologies (City of Toronto, 2003):
At source control measures that are at the beginning of a drainage system or generally at the lot level.
Conveyance controls that are located within the drainage system where flows are concentrated and are being conveyed along a corridor.
End-of-pipe controls that are at the end of a flow conveyance route.
Management / operational practices, which are not site specific and are generally “watershed wide” measures.
Special measures that are not actual “control works” but provide an enhancement that will provide a watershed or stream improvement.
This 275-page document outlines 86 different waste water management strategies, explains each one, its mechanism of effectiveness, expected benefits, related management plans, application requirements, proven effectiveness / experience elsewhere, cost considerations, and references for further information. The document also lists which of the 13 objectives of the plan each strategy addresses.
- meet guidelines for water and sediment quality
- virtually eliminate toxics through pollution prevention
- improve water quality in rivers and the lake for beaches that are healthy for swimming
- improve aesthetics
- preserve and re-establish a natural hydrologic cycle
- reduce erosion impacts on habitats and property
- eliminate or minimize threats to life and property from flooding
Natural areas and wildlife
- protect, enhance and restore natural features (eg., wetlands) and functions
- achieve healthy aquatic communities
- reduce fish contamination
- eliminate discharges of sanitary sewage
- reduce infiltration and inflow to sanitary sewers
- reduce basement flooding
It is a comprehensive and valuable resource of available waste water management strategies. Selection and adoption of these strategies is decided by a 24-member steering committee including the public, city councillors and staff, representatives of provincial agencies, and interested NGOs (City of Toronto, 2003b). The committee has selected strategies that include both large and small-scale projects, and both centralized and diffuse (Toronto Water - Community Program for Stormwater Management http://www.toronto.ca/water/news/cpsm/index.htm). There are too many projects to list in this case study, but the following is a brief summary from the 2004-2005 Implementation Report.
- multifaceted advertising campaign to promote individual water pollution reduction through measures such as downspout disconnection, reducing impermeable surface area (i.e. pavement and concrete), cleaning up pet waste, avoiding oil spills from vehicle maintenance, and reducing household use of toxic chemicals.
blue flag program: an international accreditation program for public beaches, which Toronto has sought and earned for several of its beaches, and uses for public education towards individual pollution reduction.
Community Program for Storm water Management (CPSWM): $250,000 per year to fund small-scale, community-led storm water management projects costing between $1,000 and $25,000.
Source Controls and Pollution Reduction
Downspout disconnection program: an advertising program, and provides city staff to disconnect roof downspouts from the sewer system for free. In 2004 and 2005, 3,400 downspouts were disconnected. Downspout disconnection will eventually become mandatory for all homes.
Green roofs: The city has committed to installing green roofs on city buildings where practical, and has adopted a strategy of incentives to private owners to construct or retrofit existing buildings with green roofs.
Rainwater Harvesting (RWH): This refers to using rain water as a resource for non-potable uses such as irrigation and toilet-flushing. In 2005, the city hosted a RWH workshop to identify and promote opportunities, and is working with Exhibition Place to develop a demonstration and public education project, and is promoting the use of RWH in new public and private developments.
Catchbasin cleaning: Catchbasins and storm water inlets are cleaned annually for arterial roads and biannually for local roads to reduce pollution concentrations
Improved street cleaning: Replacing existing street sweepers with regenerative-air type sweepers, which are more effective at reducing runoff toxicity.
Perforated pipe system: Can be installed in newly constructed roadways or roadways being reconstructed to reduce runoff temperature and remove some pollutants contained in roadway storm water. Several of these projects are being planned starting in 2007.
Grass swale and roadside ditches: Only feasible in low-density suburban and rural areas or along highways, as described for Chilliwack. Toronto is "strongly promoting" their use in new suburban developments and their preservation where already existing, and has incorporated them into several road reconstructions.
Sewer separation: Separating combined sanitary and waste water sewer pipes into separate pipes. It is very expensive and causes lengthy road disruptions, so is only being done on a case-by-case basis to reduce basement flooding. As existing sewer pipes need replacing, the city will consider separate storm and sanitary pipes, also on a case by case basis.
Numerous combined sewer overflow (CSO) storage tanks, treatment facilities, or storm water quality control ponds are undergoing environmental assessments to identify and prioritize the opportunities.
The city is researching new waste water treatment technologies in collaboration with the National Water Research Institute, Environment Canada and the Ministry of the Environment (MOE):
- North Toronto High Rate Treatment Facility and the Etobicoke Stormwater Pilot-Scale High-Rate Treatment projects: two pilot projects underway to assess new high-rate treatment technologies.
- Scarborough Terraview Filtration Technology project: an underground sand filtration system feasibility study. Has suffered from large-volume bypasses, but research is ongoing.
- Scarborough Dunker's Flow Balance System: a storage and treatment facility constructed on the lake using a series of plastic curtains suspended from floating pontoons, to create treatment cells. It is a very low-cost facility, but some of the wetland vegetation in the cells was killed by geese and carp. Research is ongoing.
Monitoring pollution levels at outfalls and beaches.
Regular assessment of progress, with major status reports every five years.
Using open lagoons and retention ponds would provide valuable additional benefits for wildlife and aesthetic quality within the landscape – how would a municipality be able to offset some of the maintenance costs, liabilities and concerns over West Nile virus? Note that Toronto Water and Wastewater Services, in collaboration with Toronto Public Health, is conducting a number of pilot projects to investigate alternative, non-chemical methods to control mosquito larvae in catch basins. These include flushing, vacuuming, drilling drainage holes, filter cloths, ultrasound and steam. Further information can be found in this report.
Public concern over water pollution is heightened in Toronto due to recreational use of its rivers and lake, and due to its drinking water being drawn from the lake. How can this same motivation be developed in cities without these same driving factors?
Resources and References
Stephens, K, Graham, P. and D. Reid. (undated). Stormwater Planning: A Guidebook for British Columbia, BC Ministry of Water Land and Air Pollution.
City of Toronto. (2003). List of CSO/Stormwater Control Alternatives (Blue Book).
City of Toronto. (2003b). Toronto’s Water Pollution Solution… The plan behind our plan.
City of Toronto. (2006). 2006 City Budget.
City of Toronto. (2006b). Wet Weather Flow Master Plan Implementation Report 2004-2005.
City of Toronto. (2005). Operating & Capital Budget Summary.
International Joint Commission. (1978). The Great Lakes Water Quality Agreement.
Government of British Columbia, Ministry of Environment, Environmental Protection Division. (2005). Stormwater Planning: A Guidebook for British Columbia.