SAMPLING AND TEMPORAL EFFECTS ON ARSENIC CONCENTRATION IN NEW PRIVATE RESIDENTIAL WELLS IN MINNESOTA

Naturally occurring arsenic is elevated in groundwater throughout Minnesota posing a health risk to an estimated 100,000 private residential water well users. The Minnesota Department of Health is working in collaboration with the U.S. Geological Survey to improve understanding of arsenic mobilization mechanisms and occurrence in well water. Two study goals are to 1) determine whether different water sampling protocols and/or timing of sample collection affect arsenic test results and 2) assess whether the initial arsenic sample is representative of the long-term arsenic concentration for that well.

Three areas (south-central, west-central and northeast Minnesota) with known elevated arsenic concentrations are the focus of the study. A total of 260 newly-constructed private residential water wells were sampled at three distinct times: at the time of well construction to mimic current driller-collected samples; 3 to 6 months after construction; and one year after construction. Initial unfiltered arsenic samples were collected either off the drill rig or from the residential plumbing, according to the method used by the particular well contractor. Other samples were also collected during each sampling event, including filtered arsenic, field parameters, and certain redox-sensitive analytes. Water sampling will be completed September 2016 and statistical analysis completed in 2017.

This poster will present the study design, sampling methodology, and preliminary results. Preliminary results will include a discussion of the geochemical conditions in wells with low arsenic, elevated arsenic, and temporally changing arsenic. A statistical summary and comparison of arsenic results comparing sampling methods and sample timing will also be presented.

Emily Berquist is a Hydrologist with the Minnesota Department of Health Well Management Section. Since joining MDH in 2013, she has been working on a collaborative project with USGS, testing for arsenic and related geochemical parameters in new private wells to understand arsenic occurrence and behavior. Ms. Berquist has a B.S. in Hydrology from St. Cloud State University, with a minor in Geology.