PM07 Pollutant Chemistry Transport, Cycling and Fate
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(PM078) Urban Stormwater Runoff as a Source of Polycyclic Aromatic Hydrocarbons (PAHs) to southern California coastal environments.

Tiefenthaler, L1, Stein, E1, 1 Southern California Coastal Water Research Project, Westminster, CA, USA

ABSTRACT- Urban stormwater runoff is a major source of pollution in waterways. Polycyclic aromatic hydrocarbons (PAHs), which form during the incomplete combustion of petroleum, wood, and oil are one of many pollutants that have been documented in urban stormwater. Most storm water monitoring programs measure total PAH mass emissions at the bottom of the watershed being assessed. Few studies have documented temporal patterns of emissions of individual PAH compounds from specific land uses. The objectives of this study were (1) to characterize the concentrations and composition of PAH compounds in stormwater as a function of land use and (2) to estimate directly the input of PAHs to the coastal environment in southern California via stormwater by these different land uses. We measured the concentration of 26 PAHs from seven different land use types over five storm events in the Los Angeles River and Santa Monica Bay watersheds. In addition, runoff samples were also collected from eight mass emission sites (in-river) during seven different storm events. For each site-event we collected ten to twelve individual samples that allowed us to construct a pollutograph of PAH concentration over the duration of each storm. Concentrations of total PAHs at both land use and mass emission sites varied widely ranging from 31.1 to 11,585.6 ng/L. However, in all cases approximately 30% of the total PAH load was discharged in the first 20% of the storm flow. Pyrene, fluoranthene, phenanthrene, and chrysene, were the predominant PAHs detected during this study, comprising approximately 50% of the 26 PAH compounds analyzed. Total PAH flow weighted mean (FWM) concentrations in stormwater were higher at high density residential, commercial and industrial (mixed) land uses. The observations in this study indicate the need for knowledge on spatial and temporal patterns of PAH loading in stormwater to make better management practice decisions (BMP).

Key words: pahs, stormwater, mass emissions, land use

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