Urban Area Dry Diffuse Pollutants Washoff Composition
This chapter presents the characteristics of urban area dry pollutants buildup and subsequent washoff in stormwater in Perth, Western Australia. Accumulated dust and dirt (DD) and stormwater runoff were sampled and analyzed for associated pollutants. The study concludes that total DD and associated pollutants present significant temporal and spatial variations. Surface texture was found to be an important factor in pollutant buildup, which can affect the initial and maximum DD loadings on the surfaces. The antecedent dry period had pronounced effects on dry solids (DD and associated pollutants). Suspended solids (SS), zinc (Zn) and copper (Cu) washoff loads from impervious areas had significant variations among the test areas. Washoff concentration variations of total phosphorus (TP), nitrite and nitrate (NO2+NO3) were insignificant among test areas. The dissolved fraction of total phosphorus and NO2+NO3 was between 22 to 43% and 50 to 62%, respectively. It was observed that the initial mass of dry pollutants from impervious surfaces was much greater than the observed washoff load. Only minor portions of dry pollutants (DD and associated pollutants) were available for washoff. The available washoff load was between 0.5 to 3.5% for TP, Zn and Cu of the total dry pollutants initially accumulated on the catchments impervious areas. No correlation was found between washoff load and inter-event dry period.
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