Use of Microbial Source Tracking for Informed Guidance on Disinfection Practices of Wastewater Effluent Impacting Recreational Waters
Rick Wietersen, Rock County Public Health Department, Rick.Wietersen@co.rock.wi.us
Lynne Diebel, Friends of Badfish Creek Watershed, Chapter of Rock River Coalition
Kayley Janssen, Wisconsin State Lab of Hygiene
Martin Collins, Wisconsin State Lab of Hygiene
Janis Baumann, Rock County Public Health Department
Badfish Creek, a 22-mile stream in rural Dane and Rock Counties, is a popular year round recreational stream, which does not freeze as approximately half of the stream’s flow is wastewater effluent. Municipal wastewater discharge permits issued by DNR often only require disinfection during warm weather months and sometimes grant a variance requiring no disinfection at all. Since 2016, tests by Rock County Public Health Department have shown the highest levels of E.coli during winter months. Determining the source of E. coli has been challenging as this stream has several point and non-point sources. A 2020-2021 study by Friends of Badfish Creek Watershed and Rock County Public Health Department used Microbial Source Tracking (MST) conducted at the WI State Lab of Hygiene to determine the source of E.coli, a common indicator of fecal pollution. The MST results from this study suggested that the primary source of E.coli was from humans. These results provided guidance for the DNR to increase UV wastewater disinfection by three additional months for one of the largest wastewater districts in Wisconsin. Site-specific MST can be a valuable tool to provide guidance for making informed decisions on disinfection practices where disinfection is not required year round, especially where effluent may impact recreational waters.