Chloride Compliance Study

In 2014, the District contracted with a consulting firm to analyze various options for complying with chloride limits. This study, linked below, provides the basis for chloride sources to the plant and the costs of different compliance options.

Chloride Compliance Study

Salt in the News
Other Research & Reports

Paired Sewershed/Household Water Softener Study - Examines Chloride Reduction Potential of Optimization & Replacement in household settings

Chloride Compliance Plan 2019 and Beyond - Presented to the Commission March 2020 

Annual Reports on Permit Variance

Year Annual Report
2010 Annual Report
2011 Annual Report
2012 Annual Report
2013 Annual Report
2014 Annual Report
2015 Annual Report
2016 Annual Report
2017 Annual Report
2018 Annual Report
2020 Annual Report

Chloride FAQ

Chloride background

Water hardness and water softening

Road de-icing salt

Q: What is chloride?
Chloride is an ion (charged particle) that is most commonly found in sodium chloride, also known as table salt or rock salt. When salt dissolves in water, it separates into sodium (Na+) ions and chloride (Cl-) ions. Chloride can also be found in other compounds, like magnesium chloride and potassium chloride.

Q: Where does chloride come from?
Most chloride that ends up in the MMSD sewer system comes from water softeners, which are found in residential, commercial and industrial buildings. Some industries use salt water in their processes and discharge chloride to the sewer. The sanitary sewer also receives chloride from road salt, but most road salt ends up in lakes, streams and drinking water. Small amounts of chloride come from soaps, detergents, other cleaning products, and food waste.

Q: Why is chloride a concern?
High concentrations of chloride are harmful to freshwater plants and animals. It takes only one teaspoon of salt to bring five gallons of fresh water to the chloride level that starts to affect freshwater life, according to the EPA. Chloride can also interfere with healthy ecosystem processes and kill vegetation (which is why you might see dead grass next to sidewalks where road salt was applied in the winter). 

Q: Can chloride be removed from water?
Technology to remove chloride from water exists -- for example, at desalination plants -- but it is very costly and has other significant disadvantages. Removing chloride from wastewater at Nine Springs Wastewater Treatment Plant would cost hundreds of millions of dollars, which would increase sewer bills by anywhere from 55 to 500%. The treatment process would also result in higher greenhouse gas emissions and energy use. 

Q: How does chloride get in the environment?
From the water softener, chloride is flushed into the sewer where it goes to the wastewater treatment plant. Treatment plants are designed to remove solid particles, like grit and sand; and to biologically degrade organic waste, such as food and human waste. Once chloride is dissolved in water, it cannot be removed by settling, or biologically degraded by standard treatment processes. Chloride that comes to the Nine Springs Treatment Plant passes through the plant to Badfish Creek or Badger Mill Creek and eventually the Sugar River. About one hundred tons of salt pass through the plant to the environment each day. This is equal to the amount of road salt loaded into 20 5-ton salt trucks. This brings up another significant source of chloride, Road Salt.

Q: Is potassium chloride a better choice than sodium chloride for my water softener?
No. Although it consists of potassium instead of sodium, it still contains chloride. There is no advantage to using potassium chloride as your softener salt here in the Madison area. In some of the drier parts of western U.S., crops are regularly irrigated with treated wastewater. Certain crops are sensitive to sodium, and in those areas, they are promoting the use of potassium chloride over sodium chloride.

 Q: What makes hard water hard?
Rainwater that falls is “soft”. It does not contain any minerals. As it percolates through the soil, water dissolves minerals which can include calcium and magnesium. Water with substantial amounts of calcium and magnesium is referred to as “hard water”. 

Q: How do you measure hardness?
Hardness is measured in terms of grains per gallon (g/gal) or milligrams per liter (mg/L). If you were to evaporate one gallon of water that had a hardness of 5 g/gal, the residue would be the equal to one 5-grain aspirin tablet. Laboratories often record hardness as mg/L or parts per million (ppm). One g/gal of hardness is equal to 17.1 mg/L of hardness. In the example above, 5 g/gal equals 85.5 mg/L hardness. Water that is 10 g/gal or more is considered very hard.

Q: What is the problem with hard water?
The minerals in hard water can be deposited as scale on pipes and in hot water heaters. They also chemically interact with soaps and detergents and make them less efficient. For example, it takes 50% to 75% less detergent to clean laundry in soft water than in hard water.

Q: Why is my water hard?
Most drinking water in Dane County comes from groundwater held in a sandstone-dolomite aquifer far below the surface. The wells that supply water for the Madison Water Utility range from 744 feet deep to 1175 feet deep. Dolomite is composed of calcium magnesium carbonate and is the source of the minerals that make our water hard. The hardness of water from the Madison Water Utility is typically 16 to 24 g/gal. Groundwater in northern Wisconsin is 4 to 7 g/gal and is considered moderately hard. You can look up the average water hardness for your address on this map

Q: How is water softened?
Home water softeners have two tanks; a mineral tank that contains a resin in the form of small beads, and a brine tank which holds the sodium chloride (salt) solution. As water flows through the mineral tank, the hard minerals, magnesium (Mg++) and calcium (Ca++) ions, replace sodium (Na+) ions on the resin. This process is called ion exchange. The water that flows out is considered “soft” because sodium ions do not build up on pipes as lime or interfere with detergents and soaps.

Q: What is water softener regeneration, and what does it mean for salt use?
Eventually, the resin reaches its limit as to how much calcium and magnesium it can hold. At this point, the resin is flushed with a strong brine solution from the brine tank. Because of its high salt concentration, the brine washes off the calcium and magnesium and replaces them with sodium. The minerals and brine wash go down the drain and into the sewer system. New salt must be added regularly to the brine tank to replace the salt that is used to regenerate the resin. The regeneration cycle can be initiated by a timer or by demand. A timer regulated softener regenerates the resin after a fixed amount of time regardless of how much water is used. A demand initiated regeneration (DIR) softener either tracks the amount of water used or utilizes a hardness sensor to indicate the resin is near capacity and needs to be regenerated. A DIR softener is the more efficient softener in terms of salt and water usage.

Q: What about water softeners in seasonally-occupied homes? 
For buildings that are only occupied for part of the year, like summer-occupied cabin/cottages, make sure to unplug the softener while you are away. This will prevent it from regenerating while you are away. When you get back, plug it back in and reset the time of day. If any questions come up, call a professional – many times they can help over the phone.

Q: How much salt comes from road de-icing?
Road salt used to de-ice streets and highways is also a significant source of chloride to the environment. Most road salt is applied as pellets or as a sand/salt mixture. We need everyone’s help to reduce the amount of deicing salt used. All the salt that is applied to sidewalks, driveways, roads and parking lots makes its way to our local waterways . Each year, Madison Dane County Public Health publishes the Road Salt Report. These documents quantify the amount of salt being applied to local roads as well as document some of the impacts to our waters. Some estimates show that the local roads use is only about one half of the total road salt applied in our county. The remaining sources are sidewalks, driveways and parking lots. Click here for  video stories on improving winter maintenance.

Q: Can't I just use sand instead of salt on my sidewalk or driveway?
Sand doesn't act the same way as salt, and so it isn't an appropriate substitute for salt as an ice melter. Unlike salt, sand does not melt ice. Sand's function in the winter is to provide traction on top of slippery surfaces. Because road salt doesn't work well below 15 degrees Fahrenheit, sand can be used when it's very cold to help reduce the risk of slipping. It's also important to remember that salt alternatives like sand and beet juice also have environmental impacts, so no matter what substance is used on surfaces in the winter, it's important to use the right amount.

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