Composition of urban stormwater

J.S. Gulliver, B.N. Wilson, O. Mohseni, A.J. Erickson, and R.M. Hozalski

The chemical composition of stormwater varies within a storm event. Pollutant concentration is therefore often represented as event mean concentration (EMC), where the EMC is calculated by equation 2.1.

Median concentrations of relevant stormwater constituents are provided in tables 2.1 and 2.2. Two major analyses of urban stormwater throughout the United States (U.S. EPA 1983; Pitt et al., 2004) show that EMCs vary significantly among storms, and that relationships between annual median EMC and land use are weak. The values in tables 2.1 and 2.2 should therefore be used only as rough approximations. Field measurements are required to establish the actual concentration of a given constituent for a given watershed.

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