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One option for municipalities includes the potential of providing lime or membrane water softening at the water treatment plant (WTP) in an attempt to eliminate water softening at individual residences. This option assumes that all WTP users would be connected to city drinking water and would have taken their water softener offline. Water softening at the WTP has the potential to be more cost efficient than individual residential water softening for many users.
The MPCA supports any effort to reduce chloride loading to the WWTPs, including encouraging residential users to switch to high efficiency ion exchange softeners. However, the MPCA does not believe that switching residents to high efficiency softeners will automatically allow a WWTP to come into compliance with chloride permit limits. The MPCA is developing a guidance document that will provide WWTPs chloride source reduction methods, treatment alternatives, and permitting strategies that will help WWTPs to come into compliance with the chloride water quality standard. The following steps will help to reduce the amount of salt being discharged to a WWTP:
- Know the hardness level of local water supply.
- Consider whether a water softener is needed and avoid the ongoing expenses if it isn’t. Test water for hardness. Typically water hardness greater than 120 mg/L CaCO3 needs to be softened. See the University of Kentucky’s Guidance: Hard Water- To Soften or Not to Soften for more information.
- Do not over soften. Program the water softener to obtain an optimal level of hardness.
- Uninstall an old timed softener and replace it with a new demand softener. A new demand softener could be optimized to minimize backwashing and the newer model would have a more efficient ion exchange resin.
- If using a timer-based softener, set to recharge at the lowest effective rate and turn it off when on vacation.
- Install a bypass so landscape irrigation water is not softened.
- Consider alternatives to salt-based water softeners.
- Move to centralized water softening using lime rather than salt
Homeowners with water softeners with an on-site septic system, salt reduction strategies should also be taken. Chlorides in on-site septic systems will infiltrate to groundwater and may result in elevated levels of chloride in groundwater which can impact water supplies as well as groundwater recharge of lakes, streams, and wetlands.
Example: Years 1-2
- Monitor chloride in effluent and review past monitoring reports for chloride concentrations.
- Evaluate chloride data and determine if reasonable potential to exceed 230 mg/L exist.
- If potential to exceed 230 mg/L work with MPCA permit staff and create a plan to reduce upstream chloride sources.
Example: Years 3-5
- Identify goals for chloride reductions.
- Develop a compliance schedule if chloride limits are established through NPDES permit.
- Educate industrial dischargers on the importance of reducing chloride in waste streams.
- Educate residents in cities that pre-soften water that they do not need water softeners.
Example: Years 6-10
- Work with water softening companies to offer a trade-in program to upgrade to high efficiency residential water softeners.
- Offer a credit to a city or industrial discharger for reducing chloride concentrations in wastewater.
- Work with municipality to install municipal lime softening at the WTP.