Holding ponds for waste water treatment for the city of Janesville.

MN Impact: Research will Help Uncover Sources of High Chloride Levels in Water

August 26, 2019

Objective

Research will uncover new information that will help to develop strategies to manage chloride levels in surface and ground waters.

Issue

High chloride levels in surface waters and groundwater are an emerging concern in Minnesota as they negatively impact aquatic and plant life.   

What has been done

About 50 Minnesota water bodies have chloride levels that exceed state water quality standards. Previous research has shown road salt is a major source of chloride, particularly in urban areas, but chloride discharge from water softener use had not been quantified but was believed to be a major source due to water hardness across the state being high.

Sara Heger and her team at the Water Resources Center performed a mass budget for wastewater treatment plants (WWTPs) with chloride monitoring data to estimate chloride discharged from household and commercial water softeners relative to other household, commercial and industrial sources.

Results

At the statewide level, household and commercial water softening were estimated to contribute 65 percent of WWTP chloride discharge. Industries were also major sources, contributing 22 percent. Human excreta, household product use, background chloride concentrations, chlorination, and other commercial processes contributed less than 5 percent of the chloride load.

The results show water softeners are major sources of chloride and show that increasing efficiency of water softener salt use could be a viable strategy to manage chloride levels in wastewater and receiving waters [Multistate No. NE1545].