Minnesota has an increasing salty water problem that poses a threat to its freshwater fish and other aquatic life, despite being more than 1,000 miles from the nearest ocean. Salt in the form of chloride is finding its way to lakes and rivers from road salt runoff and water softener discharge. It’s what some call a double-whammy, being a cold-weather state that needs to treat roads for icy conditions and having naturally hard groundwater that people need to soften.
Minnesota has worked for several years to decrease road salt runoff, especially in urban areas. See MPCA's Road salt and water quality webpage.
And now the state is starting to focus on chloride in water softener discharge. Much of Minnesota has hard water, prompting people to use water softeners. These softeners require salt to operate. In most cities, these softeners discharge to the municipal wastewater treatment plant. These plants are not designed to remove chloride in the wastewater and it ends up discharging to the receiving water, usually a river in Minnesota.
Chloride in water is a tough problem to solve. It takes only a small amount — 1 teaspoon per 5 gallons of water — to pollute water permanently. At high concentrations, chloride can harm fish and plant life. But there’s no easy and affordable way to remove chloride in wastewater. It would require reverse osmosis, the same process used to produce water for laboratory use, which is technically difficult as well as costly.
Based on a new study reducing chloride in wastewater means reducing salt used in softeners.
That means cities either:
- Provide water already softened, thus eliminating the need for individual softeners
- Implement a program to put high-efficiency softeners into use
The above options can also be expensive and require large-scale change by residents and businesses. And in most cases, the use of high-efficiency softeners, alone, will not result in sufficient reductions to meet the water quality standard.
The MPCA has required several WWTPs to monitor for chloride in their discharge since 2009. So far, more than 100 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 discharge is to assign a limit on pollutants in facility permits, requiring WWTPs to invest in new processes and/or equipment. In the case of chloride, however, the agency knew there was no simple solution.
MPCA Commissioner John Linc Stine directed staff to form a work group of community representatives to:
- Study the chloride problem
- Make recommendations on how to implement the standard in municipal wastewater permits (The agency will continue to work on chloride in industrial wastewater permits on a case-by-case basis.)
The group consisted of 8 municipal representatives and 2 consultant engineers. Members met several times from December 2016-April 2017. The group, represented by David Lane, environmental manager for the Rochester Water Reclamation Plant, made its recommendation to the MPCA Advisory Committee.
- Chloride Work Group Policy Proposal for Minnesota: Recommendations for addressing chloride in municipal wastewater effluent (wq-wwprm2-24)
MPCA staff should use a decision tree developed by the group to decide whether the agency will assign a chloride limit in a WWTP’s permit with an associated schedule of compliance, or consider a variance to allow time to determine a solution.
- Factors in the decision tree include:
- Is a reduction in chloride needed?
- Is the facility close to meeting the standard?
- Is construction needed to meet the chloride limit?
- Is the solution economically feasible?
- For variances, the MPCA has developed a streamlined application tool that includes a spreadsheet calculator to determine affordability. The Chloride Work Group recommends the agency allow municipalities to use the spreadsheet tool.
- Allow variances when the cost of treatment is too high.
- Waive the current variance application fee of $10,850 if municipalities use the streamlined application.
- Reissue variances when permits are reissued if there are no changes in the economics of the solution.
- Use best management practices to minimize a plant’s contribution to chloride concentrations. For example, some plants may be able to use different products for phosphorus removal that will also lead to lower chloride concentrations.
- Plants with variances must still have alternative limits in their permits to prevent “backsliding” or making chloride levels higher.
The same recommendations would apply to other salty parameters such as bicarbonates and total dissolved solids.
Work group members also said the process was a good one, and the MPCA should consider similar work groups in the future. They noted the collaboration among the agency, communities and consultants in working on the chloride problem together. They also liked that MPCA staff from both the permitting program and limits program were involved in the process.
Commissioner Stine is taking the recommendations into consideration and will communicate his decision in a memo to staff. That decision will be communicated to permit holders through the On Point newsletter and through MPCA staff working with municipalities.