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

Chloride Research

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

Chloride FAQ

Q: What is chloride?
A: 
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?
A:
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?
A: 
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?
A: 
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?
A: 
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?
A:
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?
A:
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?
A:
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?
A:
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?
A:
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. The following map shows water hardness across the United States.

Q:How is Water Softened?
A:
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 the Regeneration Cycle?
A:
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:How much salt comes from road de-icing?
A:
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.

What Can I Do?

  • Check to see how your softener is calibrated. Some softeners are preset for the highest hardness setting at the factory. This setting may be as high as 30 grains. Reset the hardness actual hardness, generally between 16 and 22 grains.
  • Soften only the hot water in your home. This reduces the demand for soft water and therefore reduces the amount of salt that is getting into our local waters.
  • When you add salt, look at the water level. About 18-inches of water in the bottom of your salt tank is right, if the water is higher, you could be wasting salt and water during each regeneration. If you see higher water, call in a water quality professional – a small repair could keep you from buying and hauling unnecessary salt to your softener.
  • Have your softener optimized by a water quality professional. Let the professional know that you want your softener optimized to use the least salt. They will review your use patterns, the hardness of your water and then make any adjustments needed.
  • If you are looking for a new water softener that removes over 4000 grains of hardness per pound of salt used. Make sure your softener uses a meter or a sensor to trigger regeneration. If possible, look for a dual tank system and/or reduce your ‘reserve capacity’ to as close to zero as possible. Newer, high-efficiency softeners will use considerably less salt and less water. The added benefit is that you will know you are helping to protect our environment right here in Dane County.

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