Modelling Different Types of Stormwater Treatment Facilities Considering Irreducible Concentrations

Abstract

To design Stormwater Treatment Facilities (STFs) properly, we recommend the use of an urban drainage model that should include the calculation of runoff quality, to be based on a detailed land use specification, include site-specific design parameters, calculated outflow concentrations and loads of specified pollutants of relevance for the receiving water. This study compiles minimum outflow concentrations from stormwater databases of different types of STFs (wet ponds, wetlands, biofilters and underground retention basins with filters). These concentration data are used for the suggested values of specific “irreducible concentrations” (Cirr). Suggested Cirr for phosphorus (P) varies from 20–40 μg/l depending on facility type, for copper (Cu) 1.8–4.0 µg/l, for zinc (Zn) 2.0–15 μg/l and for total suspended solids (TSS) 2 900–5 000 μg/l. Corresponding data for 70 substances are compiled in the StormTac database and employed in the urban drainage model StormTac Web. Cirr have significant impact regarding the choice of facility type and its calculated dimensions. This design parameter and the calculated outflow concentrations can be used to investigate the need for combined serial facilities or complemented design elements with more planted vegetation or installed filters. Such elements can be required to decrease Cirr and thereby reach project specific limit outflow concentrations and loads. The suggested data will be further evaluated and updated with respect to more data from different facility types and more substances.