Thomas Larm and Anna Wahlsten from StormTac corporation have written a scientific paper that has been published  in “Journal of Civil Engineering and Architecture”, 2019. The paper “Applying the Parameter “Irreducible Concentration” in Modelling of Stormwater Treatment Facilities” compiles minimum outflow concentrations from stormwater databases of different types of stormwater treatment facilities (e.g. swales, wet ponds, wetlands, biofilters and underground retention basins with filters). These data are used for the suggested values of specific “irreducible concentrations” (Cirr). The minimum outflow concentrations or “irreducible concentrations” (Cirr) refer to a stormwater treatment facility’s inability to reduce pollutant concentrations below a certain level. Cirr has 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.

We recommend the use of a 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 to design stormwater treatment facilities (STFs) for the receiving water.

The paper is available from “Downloads/Publications”.