The average cost per treated hectare is $530,000 (total project costs are weighted by total project area). The design volume for the majority of the projects is not available.
|Ontario (and Alberta) Green Infrastructure Costs|
|Ontario (and Alberta) Green Infrastructure Costs by Type|
The following table compares cost by LID type for three sources, the Philadelphia CSO control program, the ES UPA BMP database, and the compiled Ontario (and Alberta) tenders noted above. The Philadelphia and the US EPA data both include design storage volume that may be considered for achieving different types of stormwater management goals (i.e., levels of service / performance outcomes).
|Green Infrastructure Costs by Type and Design Volume - Philadelphia CSO Control Program, US EPA BMP Database, and Ontario (and Alberta) Completed Projects|
Some key observations are that porous/permeable pavement has a relatively high cost per drainage area ($/ha), however the cost per storage volume is relatively low for the US EPA datasets - this warrants further review. The Ontario/Alberta porous/permeable pavement costs per area are also relatively high, compared to other types. Just like Ontario/Alberta data, Philadelphia and US EA data shows lowest cost per hectare for infiltration/exfiltration projects. The infiltration/exfiltration cost per storage volume was relatively low for both the US EPA and Philadelphia datasets.
The Philadelphia green infrastructure projects achieve a high volume, equivalent to 38.9 mm over the catchment area draining to it. In contrast, the US EPA storage volumes are equivalent to only 6.6 mm. The Philadelphia projects are sized for 1-2 inches of storage to achieve CSO control. In contrast the US EPA projects are sized to achieve other benefits, such as watershed protection.
While the Philadelphia cost per area is highest at $857,000 per hectare, which is 4.1 times the US EPA database cost of only $208,000 per hectare, the unit cost per storage is in fact less. The Philadelphia unit cost is $22,000 per hectare-mm. The US EPA cost is $32,000 per hectare-mm, reflecting lower cost efficiency for smaller installations perhaps.
Using these unit costs one can estimate the budget required to retrofit green infrastructure into older urban areas to improve stormwater management. In Ontario, the urban area built by 1966 has been estimated to be 110,000 hectares (Ducks Unlimited mapping), and by year 2000 to be 852,000 hectares (provincial SOLRIS land use mapping v2). Assuming that 200,000 hectares require significant storage to achieve flood control in older communities, the retrofit cost would be $171 billion, applying the $857,000/hectare unit cost. Or to provide improved water quality and water balance controls to the year 2000 urban area, the retrofit cost would be $177 billion, applying the $208,000/hectare unit cost. Both of those costs represent considerable sums, given the Ontario stormwater infrastructure deficit of about $6.8 billion - that is the retrofit cost would be over 25 times that current deficit. Given that, a strategic approach to retrofitting older communities is required, including prioritization of retrofit areas, implementing on higher-performance sites (e.g., permeable soils), implementing on highest risk tributaries (sensitive habitat, infrastructure or property risks), and considering the most cost effective measures, e.g., higher volume/centralized facilities that exhibit lower unit costs for storage, and feature types with lowest unit costs (i.e., infiltration/exfiltration facilities, and (to be confirmed) porous/permeable pavement). The operation and maintenance costs associated with porous/permeable pavement should also be considered in the development of a retrofit strategy (i.e., consider full lifecycle costs including both capital and operating costs).