The Impact of Urban Development on Water Quality

Principal water pollution sources from urban areas include:

• treated effluents discharged from sewage treatment plants and untreated effluents that bypass sewage treatment plants;
• treated and untreated storm water runoff;
• combined sewer overflows that carry a mixture of untreated sewage and storm water;
• air emissions from incidental and accidental releases and mobile sources; and
• ground water discharges to adjacent receiving waters.

The multi-billion dollar investments in wastewater and combined sewer overflow controls substantially reduced the worst pollution problems during the 1970s to the 1990s. However, most urban and suburban watersheds – including nearshore areas of major Great Lakes cities -- are still not safe for swimming, do not have fish that are completely safe to eat, or do not support diverse biological communities¹. The increase in hardened surfaces from roads, roof tops and parking areas means pollutants enter surface waters via runoff without undergoing treatment, which has a significant impact from a basin wide perspective. For example, recent Canadian estimates indicate that the sum of major storm water-related discharges to the Great Lakes are in excess of 90,000 tonnes/year (~ 100,000 tons/year) of sediment, oil, grease, metals, and other contaminants ².

he expansion of major urban areas in the Great Lakes basin (Figure 1) can be attributed to many factors: population growth; land use preferences (for example, favoring suburban greenfields over urban brownfields); the tendency towards fewer people living in each household, thus necessitating more housing; and large suburban commercial and retail properties with extensive hardened areas for parking and access to highways. Unless these trends are anticipated and managed effectively, the continued expansion of major urban areas in the Great Lakes basin will have serious consequences for Great Lakes water quality.