Urban Runoff - Pollutants

Pollutants

Water running off these impervious surfaces tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants from roadways and parking lots, as well as fertilizers and pesticides from lawns. Roads and parking lots are major sources of polycyclic aromatic hydrocarbons (PAHs), which are created as combustion byproducts of gasoline and other fossil fuels, as well as of the heavy metals nickel, copper, zinc, cadmium, and lead. Roof runoff contributes high levels of synthetic organic compounds and zinc (from galvanized gutters). Fertilizer use on residential lawns, parks and golf courses is a significant source of nitrates and phosphorus in urban runoff.

Eroding soils or poorly maintained construction sites can often lead to increased sedimentation in runoff. Sedimentation often settles to the bottom of water bodies and can directly affect water quality. Excessive levels of sediment in water bodies can increase the risk of infection and disease through high levels of nutrients present in the soil. These high levels of nutrients can reduce oxygen and boost algae growth while limiting native vegetation growth. Limited native vegetation and excessive algae has the potential to disrupt the entire aquatic ecosystem due to limited light penetration, lower oxygen levels, and reduced food reserves. Excessive levels of sediment and suspended solids have the potential to damage existing infrastructure as well. Sedimentation can increase runoff by plugging underground injection systems, thereby increasing the amount of runoff on the surface. Increased sedimentation levels can also reduce storage behind reservoirs. This reduction of reservoir capacities can lead to increased expenses for public land agencies while also impacting the quality of water recreational areas.

As stormwater is channeled into storm drains and surface waters, the natural sediment load discharged to receiving waters decreases, but the water flow and velocity increases. In fact, the impervious cover in a typical city creates five times the runoff of a typical woodland of the same size.