American Society of Civil Engineers

Pollutant Mass Flushing Characterization of Highway Stormwater Runoff from an Ultra-Urban Area

by Kelly R. Flint, (Res. Asst., Dept. of Civ. and Envir. Engrg., Univ. of Maryland, College Park, MD 20742) and Allen P. Davis, (corresponding author), F.ASCE, (Prof., Dept. of Civ. and Envir. Engrg., Univ. of Maryland, College Park, MD 20742 E-mail:

Journal of Environmental Engineering, Vol. 133, No. 6, June 2007, pp. 616-626, (doi:

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Document type: Journal Paper
Abstract: Water quality of highway stormwater runoff from an ultra-urban area was characterized by determining the event mean concentration (EMC) for several pollutants and by evaluating pollutant flushing. Thirty-two storm events were monitored between June 2002 and October 2003. Mean EMCs in mg/L were 0.035, 0.11, 0.22, 1.18, 420, 3.4, 0.14, 1.0, and 0.56 for Cd, Cu, Pb, Zn, total suspended solids (TSS), total Kjeldahl nitrogen (TKN), NO2 — N, NO3 — N, and TP. First flush as defined by flushing of 50% of the total pollutant mass load in the first 25% of the event runoff volume occurred in 33% of the storm events for NO-2, 27% for TP, 22% for NO–3 and TKN, 21% for Cu, 17% for TSS, 14% for Zn, and 13% for Pb. Median values for the mass flushed in the first 25% of runoff volume were greater than the mass flushed in any 25% portion beyond the first for all pollutants. The mass in later 25% volume portions were greater than in the first 25% volume in at least 17% of the events for all pollutants, indicating that a significant amount of the pollutant load can be contained in later portions of the runoff volume. Nonetheless, management of the first 1.3 mm (1/2 in.) of runoff was able to capture 81 — 86% of the total pollutant mass.

ASCE Subject Headings:
Heavy metals
Highways and roads
Stormwater management
Suspended solids
Urban areas
Water pollution