Peeling back the Pavement - POLIS Water Sustainability Project

Photo: Capital Regional District, BC
BOX 1: WHY SHOULD WE CARE ABOUT STORMWATER?
We don’t normally think of rainfall as pollution. But, we have built our cities in a way that
transforms rainwater into an agent of environmental and human harm: stormwater runoff.
Stormwater runoff causes a large proportion of urban water pollution. In Washington
State, for example, the United States Environmental Protection Agency estimates
that more than 100,000 pounds of toxic chemicals are washed into Puget Sound via
stormwater runoff every day.
The transformation of rainwater into polluted stormwater occurs in stages as it flows
through our urban spaces. The first stage is the creation of “hard” surfaces in cities,
such as roofs, driveways, patios, sidewalks, parking lots, and road networks.
In the second stage, heavy metals, PCBs, oils, grease, antifreeze, solvents, pesticides,
herbicides, fertilizers, road salt, detergents, and pet waste collect across the urban
landscape. When heavy rains sweep across a city’s hard surfaces, these pollutants are
picked up and washed away.
The last salmon documented in Bowker Creek in British Columbia’s
Capital Regional District. Due to urbanization and stream
degradation, the creek no longer supports salmon populations.
But, there is no “away.”
In the final stage, the
storm drainage system
rapidly conveys the
polluted runoff—often
without treating it—to
the nearest body of
water where it is flushed
into the aquatic ecosystem.
Stormwater runoff
impacts urban ecosystems.
It can destroy the
spawning grounds of
salmon and other fish, decrease stream baseflows, erode stream banks, and increase
the water temperature of streams. Numerous studies link rapid decline in water quality
and stream health to uncontrolled stormwater runoff from areas in which the total
impervious surface area exceeds 10 per cent of the total watershed area (known as
“The 10% Rule”).
To make things worse, in older municipalities stormwater runoff and sewage may be
carried in the same pipe, which means bodies of water can become contaminated
with fecal coliforms. An even bigger risk occurs when stormwater mixes with sewage
and contaminates drinking water supplies. This is an issue in many places and fixing
it may necessitate the expenditure of millions—or even billions—of dollars. For example,
the cleanup costs of the stormwater-related impacts at Ontario’s 16 Remedial
Action Plan sites were estimated to be $2.5 billion. Sources on page 65
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