Irreducible concentrations (Cirr) is the minimum outflow concentrations, a Stormwater Treatment Facility´s (STF’s) inability to reduce pollutant concentrations below a certain level.

Site-specific design parameters, such as Cirr, have great impacts on the design
and choice of type of stormwater treatment facilities.

This is described further in the reviewed conference paper “Modelling different types of stormwater treatment facilities considering irreducible concentration”, by Larm T. and Wahlsten A., presented during the conference “11th International Conference on Urban Drainage Modelling” (UDM), Palermo, Italy, Sept. 23-26, 2018.

Updated values of Cirr for many different substances and types of facilities are presented in the StormTac database and are limplemented in the stormwater & recipient model StormTac Web.

The paper and the updated database can be downloaded from this web page.