and Potassium in Minnesota’s Ground Environmental Outcomes Division May 1999 Ground Water & What are sodium and potassium? animal wastes. Sodium is more mobile in Assessment than potassium and so it is used often Program Sodium and potassium are chemicals commonly found in and rocks. as an indicator of human impacts to They belong to a of chemicals shallow ground water. Sodium is also a called the “ earth .” common chemical in . Like (, cesium and are also potassium, sodium is gradually released alkali earth metals, but they are not from rocks. Concentrations therefore discussed in this fact sheet because they increase with time. were not frequently detected in ground water.) Sodium and potassium are often What are considered safe levels of associated with chloride and bromide. In sodium and potassium in ground these forms, they readily dissolve in water? water. In soils containing appreciable There are no health-based amounts of clay, these metals are not standards for sodium and potassium. mobile. Sodium and potassium are Neither has a secondary drinking released slowly upon dissolution of standard. Sodium intake may lead to rocks. Consequently, concentrations and be a concern for people increase as residence time in ground with conditions. water increases. How are sodium and potassium What are sources of sodium and distributed in Minnesota ground potassium in ground water? water? Potassium, an important , is Because there are anthropogenic sources strongly held by clay particles in soil. of potassium and sodium, and because Therefore, leaching of potassium through concentrations increase with residence the soil profile and into ground water is time in ground water, concentrations important only on coarse-textured soils. may be elevated in shallow ground water Potassium is common in many rocks. as well as deep aquifers. Median Many of these rocks are relatively soluble concentrations of sodium and potassium and potassium concentrations in ground from the Ground Water Monitoring and water increase with time. Important Assessment Program (GWMAP) anthropogenic sources of sodium include statewide baseline network of 954 wells road and were 9.4 and 2.4 mg/L (parts per

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

million), respectively. Sodium, in particular, was What are some management strategies for unevenly distributed in ground water. Ninety-three reducing risks from sodium and potassium? samples exceeded a concentration of 100 mg/L. Distillation may reduce concentrations of sodium and Concentrations of sodium were highest in the buried potassium. Sodium may lead to hypertension. Ground Quaternary, Galena and Precambrian aquifers and with high concentrations of sodium and lowest in the and St. Peter aquifers. potassium are considered to be “soft” and therefore Concentrations were relatively low in surficial generally desirable for drinking. Quaternary aquifers. This contrasts with chloride, which also has anthropogenic sources and is found at Additional information, including reports and relatively high concentrations in surficial Quaternary distribution maps, can be found on the Minnesota aquifers. Sodium is less mobile than chloride in soil. Pollution Control Agency’s Web site at Potassium is more evenly distributed than sodium http://www.pca.state.mn.us/water/groundwater/gwm among aquifers. Median concentrations ranged from ap/index.html. 0.99 mg/L in the Jordan Aquifer to 5.5 mg/L in Cretaceous aquifers. Concentrations of both chemicals increase from east to west in Minnesota. Differences in geology and increasing residence times are responsible for this distribution.

Which aquifers are most sensitive to contamination with sodium and potassium? Since there are no drinking water standards for sodium or potassium, it is difficult to determine which aquifers might be sensitive to contamination. Surficial Quaternary aquifers do not appear to be impacted by human activity, although concentrations may locally be high due to anthropogenic sources such as animal waste, fertilizer and road salt. Deeper aquifers also have high concentrations resulting from dissolution of aquifer materials.

Why is it important to measure sodium and potassium concentrations in ground water? Sodium and potassium are important in ground water and are used to assess quality control for samples and laboratory analysis. Like , sodium and potassium are often useful for identifying the source of ground water. This may be useful for programs such as Wellhead Protection. Sodium has some utility as a tracer of human and animal waste in shallow ground water.

Sodium and Potassium in Minnesota’s Ground Water Page 2