1.2.2 Water Quality Impacts from Urbanization

As streams flow through urban settings, they are subject to pollutant loading from stormwater runoff, illicit discharges, and streambank and riparian area modifications. Both urban and rural stormwater runoff has been shown to contain many different types of pollutants depending on land use and the nature of the activities occurring on them. The pollutants in runoff can be dissolved in the water or can be attached to solid particles that settle in streambeds, rivers, wetlands, or other waterways. The result is impairment to the quality of and benefits provided by both ground and surface receiving waters.

The 2004 SWMMEW provides the following summary of water quality impacts by land use:
  • Runoff from roads, streets, and highways is concentrated with pollutants primarily from vehicles; typical pollutants in road runoff include: oil and grease, polynuclear aromatic hydrocarbons (PAHs), lead, zinc, copper, cadmium, sediments (soil particles), and road salts and other anti-icers.
  • Runoff from industrial areas typically contains more types of heavy metals, sediments, and a broad range of man-made organic pollutants, including phthalates, PAHs and other petroleum hydrocarbons.
  • Runoff from commercial areas contains concentrated road-based pollutant runoff and may also contain other pollutants typical of industrial and/or residential areas. The accumulation of trace pollutant quantities can prove detrimental during heavy storms.
  • Runoff from residential areas may contribute the same road-based pollutants, as well as herbicides, pesticides, nutrients from fertilizers and animal wastes, and bacteria.


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