Water permit holders and chloride

Chloride and wastewater facilities

Mankato wastewater treatment plant

Much of Minnesota has hard water, which prompts people to use water softeners. Water softeners need salt (which contains chloride) to recharge their softening capacity, and the resulting salty brine is discharged to municipal wastewater treatment plants in most cities. The plants are not designed to remove chloride from wastewater, so the chloride ends up in the receiving water, usually a lake, river, or stream.

The MPCA has required several wastewater treatment plants (WWTPs) to monitor for chloride in their discharge since 2009. So far, more than 100 Minnesota WWTPs have the potential to contribute levels of chloride higher than allowed by the standard, which is 230 mg/L for chronic levels and 860 mg/L for acute levels.

The common approach to reduce pollutants in wastewater is to assign a limit in facility permits, requiring WWTPs to adjust or invest in their processes so they can lower the amount of the specific pollutant in the wastewater. However, there is no economically feasible way for plants to remove chloride from wastewater. The only available method (reverse osmosis) is hugely expensive both to install and maintain.

The MPCA commissioner formed a work group of community representatives to study the chloride problem. This group of eight municipal representatives and two consultant engineers made recommendations that were approved in June 2017.

Whatever permitting tool is chosen, the goal is the same: Reduce the amount of chloride and other salts entering the wastewater plant. Work continues on the best ways to achieve this. MPCA has developed a strategy to help municipal permittees start developing a plan.

Chloride standard variances for wastewater facilities

Chloride and stormwater

De-icing salt dried up around a storm drain

Industrial stormwater

Industrial stormwater permittees must:

  • Enclose or cover storage piles of salt or piles containing salt to prevent exposure to precipitation, except where stormwater is routed to a sanitary sewer, sump, or other proper collection system (i.e., not the stormwater drainage system) or the lack of enclosure or cover is authorized under a separate NPDES/SDS permit.
  • Control exposure resulting from the adding or removing material with appropriate measures (e.g. good housekeeping, diversions, and containment).

For more information, read the general industrial stormwater permit requirements:

Municipal stormwater: TMDL reporting requirements

See the Minnesota Stormwater Manual for guidance on completing your TMDL reporting form.

Success stories

Many of the winter maintenance staff who have attended the Smart Salting training — both from cities and counties and from private companies — have used their knowledge to reduce salt use and save their money for their organizations. Learn more about Minnesota entities that have reduced salt use:

Wisconsin Salt Wise also has some compelling case studies of organizations that have reduced salt use, either using less de-icing salt or less water softener salt.