Chloride and Fluoride in Minnesota’s Ground Water Environmental Outcomes Division May 1999 Ground Water Monitoring & What are chloride and fluoride? adding fluoride to municipal water Assessment supplies high in calcium is ineffective. Program Chloride and fluoride are chemicals commonly found in soil and rocks. Although chloride and fluoride belong to What are considered safe levels of the same chemical group (the halogens), chloride and fluoride in ground their behavior in the environment differs. water? Chloride is very mobile in ground water, Neither chloride nor fluoride has a while fluoride is rendered immobile in the health-based drinking water standard. presence of aluminum and iron oxides. Chloride has a secondary maximum Bromide is another halogen; but because contaminant level (SMCL) of 250 mg/L bromine occurs at very low (parts per million). Chloride may impart concentrations in ground water, it is not a bad taste to water. Fluoride has a discussed in this fact sheet. maximum contaminant level (MCL) of 4 mg/L based on potential mottling of What are sources of chloride and teeth. fluoride in ground water? The primary source of chloride is halite How are chloride and fluoride (salt) and brines. Anthropogenic distributed in Minnesota ground (human) sources of chloride include water? fertilizer, road salt, human and animal There were eight exceedances of the waste, and industrial applications. These SMCL for chloride in wells sampled from sources can result in significant the Ground Water Monitoring and concentrations of choride in shallow Assessment Program (GWMAP) ground water because chloride is readily statewide baseline network of 954 wells. transported through the soil. Two of these were in surficial Igneous rocks are a common source of Quaternary aquifers, while four were in fluoride. Fluoride is used in industrial buried Quaternary aquifers. The median processes as a strong acid. It is also a concentration for all aquifers was 2.4 common chemical in phosphorus mg/L, but the distribution between fertilizers. Fluoride is added to many aquifers was uneven. Concentrations municipal water systems to prevent tooth were highest in Cretaceous and surficial decay. Because fluoride precipitates Quaternary aquifers (both had a median when calcium is present in ground water, concentration of 5.8 mg/L) and lowest
Minnesota Pollution Control Agency, 520 Lafayette Rd. N., Saint Paul, MN 55155-4194 (651) 296-6300, toll-free (800) 657-3864, TTY (651) 282-5332 or (800) 657-3864 This material can be made available in alternative formats for people with disabilities. Printed on recycled paper containing at least 20 percent fibers from paper recycled by consumers. Environmental Outcomes Division May 1999 Ground Water Monitoring & Assessment Program in the Jordan Aquifer (0.95 mg/L). These results is also used to assess quality control for ground water suggest different sources for the chloride, with sampling and laboratory analysis. anthropogenic sources likely for the surficial Quaternary aquifers and natural sources for the What are some management strategies for Cretaceous aquifers. reducing risks from chloride? There were only two exceedances of the MCL for Reverse osmosis, ion exchange and distillation are fluoride. The overall median concentration was 0.30 treatment methods for removing chloride from well mg/L. Concentrations were relatively evenly water (see Minnesota Department of Health fact sheet distributed between aquifers. The highest median Home Water Treatment Units). concentration was for the Cretaceous aquifers (0.43 Impacts from anthropogenic sources can be reduced mg/L), and the lowest was for the Cedar Valley by proper management of animal and human wastes Aquifer (0.27 mg/L). and reduced use of road salts. Which aquifers are most sensitive to Additional information, including reports and contamination with chloride and fluoride? distribution maps, can be found on the Minnesota Pollution Control Agency’s Web site at Aquifers can have high concentrations of chloride http://www.pca.state.mn.us/water/groundwater/gwm under a variety of settings. Well-protected aquifers ap/index.html. with large ground water residence times and a source of chloride will have the highest concentrations of chloride. These aquifers include the Cretaceous and buried Quaternary aquifers. Surficial aquifers, however, are also sensitive to contamination from anthropogenic sources. Road salt and animal wastes are the most likely sources of chloride. Even though salt and animal wastes may be distributed on the surface of the land, chloride is readily leached as water infiltrates the soil. No aquifer appears to be sensitive to elevated concentrations of fluoride. There are localized instances of high concentrations. These are a function of minerals that have high concentrations of fluoride.
Why is it important to measure chloride concentrations in ground water? Chloride in shallow ground water is a useful indicator of contamination from human sources. Compared to background concentrations, chloride concentrations are typically elevated in shallow ground water under urban land use, around septic systems, near waste impoundments and occasionally under agricultural fields. It moves with ground water, and is therefore an excellent tracer of contaminant sources. Chloride
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