Assessment of Urban Stormwater Chloride and its Impact on Surface Water Trends

In this project, we seek to provide a comprehensive characterization of chloride (Cl) in surface runoff of streams and storm drains across Minnesota cities, towards developing a predictive understanding of the watershed, waterbody, climate, and stormwater management factors that influence chloride transport (magnitude, variability, and timing) in storm drains and streams.

The work would build on a large Twin Cities metro (TCMA) stormwater monitoring dataset assembled by the PIs in a current MSRC project by incorporating non-TCMA stream monitoring datasets and time series data (salt application, continuous discharge and conductivity logging) to better understand road salt retention and lag times, and factors influencing chloride trends across a gradient of urban land cover, drainage networks and salt inputs. We would apply these new analyses to an assessment of vulnerability of urban receiving waters to chloride pollution by surface runoff, by developing predictive relationships to identify high-risk water bodies for the large number that have not yet been assessed, addressing a key knowledge gap. Other applications of the results include development of procedures for estimation of chloride lost from surface runoff to groundwater by infiltration, including through BMPs, and for investigation of the influence of salt application reductions and chloride loss to groundwater on chloride trends in selected urban lakes. The proposed work would produce an improved characterization of chloride in surface runoff in MN and provide assessment tools to practitioners to identify areas of MN cities where attention should be paid to BMP siting and vulnerability of lake and stream health.

Projected outcomes

  • An improved understanding of the magnitude and timing of chloride in surface runoff in MN, and of characteristics of watersheds, waterbodies, climate, and stormwater BMPs driving chloride pollution;
  • Predictive relationships for runoff chloride, applied to urban watersheds across MN to provide a method to assess vulnerability of lakes and streams to chloride pollution, in particular where little or no assessment has been done previously;
  • Using results in a demonstration of a method to assess chloride loss to infiltration, including in structural BMPs, to assess the potential impact of BMPs on chloride loading and inform future research to reduce salt contamination of shallow groundwater;
  • Development of a method to assess the potential impacts on surface water chloride trends of management actions, including reduction of road salt use and/or construction of stormwater BMPs.