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Chloride Study

The Regional Chloride Impact Study is analyzing the environmental impacts of chloride (salt) on the Region’s surface water and groundwater resources.

Commission staff monitoring chloride levels in a stream

Chloride Impact Study

The Regional Chloride Impact Study is the Region’s foremost comprehensive study to identify significant sources and magnitudes of chloride (salt) in surface water and groundwater resources. The Commission is examining several potential anthropogenic sources that contribute chloride to the environment, including road salt, water softener discharge, septic systems, and fertilizers. Commission staff will develop a plan that encompasses aspects from policy to alternative scenarios to help reduce the adverse effects of chloride on the Region’s freshwater resources.

 

Monitoring Work

Regionwide monitoring began in 2017, as outlined in the study Prospectus. Monitoring work includes:

line art of a stream

Stream Monitoring

Staff conducted continuous monitoring for specific conductance at 41 stream locations throughout the Region. Following a detailed site selection process and in-stream monitoring equipment deployment, a two-year comprehensive data collection period began in October 2018 and concluded in October 2020. Additional data collection at selected sites continued into spring 2021. Monthly grab samples were collected at each site, along with targeted event sampling, to obtain water quality data that include chloride concentrations.

line art of a pond with two round trees behind the pond

Lake Monitoring 

Quarterly sampling was performed at six lakes within the Region. Data collected included temperature, specific conductance, and chloride at various depths. This figure compares the preliminary seasonal chloride profiles for two of the lakes, Moose Lake and Little Muskego Lake.

 

Specific Conductance & Chloride Concentrations

Previous studies have demonstrated that specific conductance is a sound predictor of chloride concentration once a reliable relationship is established. Specific conductance, collected at 5-minute intervals at each monitoring site, is paired with the corresponding chloride concentration obtained from sampling and will be used to develop regression relationships.

 

Preliminary Paired Study Data

This figure shows the preliminary paired study data for all Commission monitoring sites. The best-fit chloride-specific conductance relationships will be used to estimate chloride concentrations based on the observed continuous specific conductance data.

 

Technical Reports

A series of technical reports are being prepared for the study. Four technical reports have been completed so far and can be accessed on this page. The completed technical reports include documentation of the field monitoring effort (TR 61), a literature review of the impacts of chloride to the natural and built environment (TR 62), documentation of the regression evaluation for specific conductance and chloride (TR 64), and legal and policy considerations for chloride management (TR 67).

 

Commission staff are currently developing technical reports for the historical trends in chloride levels in our streams and lakes, the analysis of mass balance of chloride sources in the environment of the Region, and the state-of-the-art practices and technologies affecting chloride in the environment. Draft technical report chapters will be posted on this page for review and comment as they are completed.

Chloride Study Comments

Use the comment box below to submit comments or questions about the Chloride Impact Study at any time during the planning process.