Researcher Melinda Erickson finds cause, effect and treatment in well water arsenic contamination research
Over a million Minnesotans depend on private wells for drinking water, which makes recent news of arsenic found in groundwater important. About half of new private wells have detectable arsenic in their well water, and about 150,000 people use groundwater sources with arsenic concentrations exceeding the U.S. Environmental Protection Agency’s drinking water standard.
Melinda Erickson, a research hydrologist with the U.S. Geological Survey and Water Resources Science Program faculty, led a project to better understand locations of high groundwater arsenic concentrations in Minnesota, identify reasons for arsenic mobilization, and find ways to drill wells with lower risk of arsenic contamination.
By evaluating the effects of geochemical changes that occurr after well installation, researchers are better able to predict high arsenic levels and locations. “Knowing where the greatest risk lies is helpful in getting water treatment information into the right hands” says Erickson. Results varied depending on geology and geography. Wells in glacial aquifers in northwestern and central Minnesota had a higher risk of high arsenic and increasing arsenic concentration in newly drilled wells. Bedrock wells in the northeastern part of the state had lower risk of high arsenic, but when arsenic was high it was sometimes very high (8x the EPA standard), with little or no change in arsenic levels over time in newly drilled wells.
Well drilling contractor sampling methods were also analyzed with regard to water sampling and other protocols by Erickson's team and Emily Berquist, a Minnesota Department of Health hydrologist. More stable results were recorded several months after well construction, rather than the regulatory standard of four weeks. Assessing protocols for water quality testing was a prime outcome of this portion of the project.
Erickson's team developed a boosted regression tree (BRT) statistical model to assess the relation between arsenic concentration and hydrogeologic, geochemical, and well-construction factors. They found that location, soil geochemistry and well construction all play a part in how and if arsenic finds its way into drinking water wells. Project results reveal a new and important finding from an arsenic probability model: Controllable well construction choices (not just location or depth) influence arsenic concentrations in drinking water from wells.
For well owners who do discover arsenic in their water, there are multiple treatment options to reduce arsenic concentrations. To choose the right treatment system, it helps to understand what else is in the water (the water’s geochemistry) and what type of arsenic is present. The Minnesota Department of Health website provides resources for identifying contaminants and effective treatment systems.
This research was funded by the State of Minnesota Clean Water Fund through the Minnesota Department of Health and the U.S. Geological Survey Cooperative Matching Funds. The work was also supported by the National Science Foundation Graduate Research Fellowship Program and an internship provided through the Graduate Research Internship Program (GRIP).
Recent project publications:
Erickson, ML, HF Malenda, EC Berquist. 2018. How or when samples are collected affects measured arsenic concentration in new drinking water wells. Groundwater, 56(6), pp 921-933.
Erickson, ML, HF Malenda, EC Berquist, JD Ayotte. 2019. Arsenic concentrations after drinking water well installation: Time-varying effects on arsenic mobilization. Science of the Total Environment, 678. pp 681-691.
Erickson, ML, SM Elliott, CA Christenson, and AL Krall. 2018. Predicting geogenic arsenic in drinking water wells in glacial aquifers, north-central USA: accounting for depth-dependent features. Water Resources Research 54(12).