Chloride and wastewater facilities
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.
- Chloride Work Group policy proposal for Minnesota: Recommendations for addressing chloride in municipal wastewater effluent (wq-wwprm2-24)
- Differences between schedules of compliance and streamlined municipal chloride variances in wastewater permitting (wq-wwprm2-72)
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.
- Streamlined chloride variance pollutant minimization program (wq-wwprm2-88)
- Strategy for municipal chloride reduction and minimization (wq-wwprm2-71)
- Editable version: Strategy for municipal chloride reduction and minimization (wq-wwprm2-71)
- Example: Chloride management plan - Village of Paddock Lake, WI (wq-wwprm2-82)
Chloride standard variances for wastewater facilities
- Chloride variance request form (wq-wwprm2-10e)
- Eligibility tool for streamlined chloride variance approach (wq-wwprm2-17)
- Instructions on Eligibility tool for streamlined chloride variance approach (wq-wwprm2-17a)
- Alternatives for addressing chloride in wastewater effluent (wq-wwprm2-18)
- Chloride variance framework for preliminary determination (wq-wwprm2-105)
Chloride and 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).
Municipal stormwater permittees must:
Cities and townships must distribute educational materials or equivalent outreach to residents, businesses, commercial facilities, and institutions, focused on the impacts of deicing salt, methods to reduce its use, and proper storage.
At permittee owned/operated salt storage areas proper salt storage BMPs should be implemented such as: covering or storing salt indoors on an impervious surface; and implementing practices to reduce exposure when transferring material from salt storage areas (e.g., sweeping, diversions, and/or containment).
Regulatory mechanism(s) of cities and townships must require proper salt storage at commercial, institutional, and non-NPDES permitted industrial facilities.
Include permittee owned/operated salt storage areas in a written or mapped facilities inventory.
Implement a written snow and ice management policy for individuals that perform winter maintenance activities for the permittee. The policy must establish practices and procedures for snow and ice control operations (e.g., plowing or other snow removal practices, sand use, and application of deicing compounds).
All individuals that perform winter maintenance activities for the permittee should receive training that includes the importance of protecting water quality, BMPs to minimize the use of deicers, and tools and resources to assist in winter maintenance. The permittee may use training materials from MPCA's Smart Salting training.
TMDL reporting requirements
If the permittee has an applicable waste load allocation (WLA) where a reduction in pollutant loading is required for chloride:
- They must document the amount of deicer applied each winter maintenance season to all permittee owned/operated surfaces.
- Conduct an assessment of the permittee's winter maintenance operations to reduce the amount of deicing salt applied to permittee owned/operated surfaces and determine current and future opportunities to improve BMPs. The permittee may use the Agency's Smart Salting Assessment Tool or other available resources and methods to complete this assessment. The permittee must document the assessment.
See the Minnesota Stormwater Manual for guidance on completing your TMDL reporting form.
For more information, visit the general municipal stormwater permit requirements.
A recorded discussion about the new chloride management requirements in the 2020 MS4 permit and the tools, resources, and training available to assist permit holders in meeting these new requirements.
Minnesota success stories. Learn more about Minnesota entities that have reduced salt use. 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.
Wisconsin Salt Wise has some compelling case studies of organizations that have reduced salt use, either using less de-icing salt or less water softener salt.