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;~ Wiz' ~"`~ s ~~° taos ~~ ~ .~"` °~m .""'~` 4~...... ~ ~ ~ ~ ~ _ S 'F by Melinda Erickson, WRS Graduate Student Research conducted by Water Re- sources Science Ph.D. candidate Melinda Erickson comes at a crucial time in the struggle to identify and understand arsenic-contaminated groundwater. The U.S. federal drinking water standard for arsenic was changed from 50 mg/L to 10 mg/L in 2001. Public water systems must comply with the new standard by January 2006. This change will have a direct effect on the estimated 250,000 to 350,000 people in Minnesota who use a public or private drinking well supply with arsenic concen- trations over 10 mg/L. Erickson, under the supervision of her advisor Randal Barnes (Civil Engineering), is completing her dissertation research on arsenic occurrence and geochemistry in upper Midwest and Minnesota ground water. The two keys to Erickson's research are understanding the geochemical mechanisms governing arsenic in ground water, and understanding the relationship between the geology/hydrogeology and arsenic concentration in ground water. The results of her research are permitting better characterization of spatial variability of arsenic in ground water, as well as model- ing and prediction of temporal variability of arsenic in ground water. Arsenic contamination in upper Midwestern ground water is widespread, naturally occurring, and associated with the lateral extent of northwest source late Wisconsin-aged (Des Moines lobe) glacial drift. Contrary to previous assumptions,. arsenic concentrations in ground water do not appear to be directly related to arsenic concentrations in sediment. However, according to Erickson's research, there is a link between well characteristics and increased risk of high arsenic levels in private wells. In west-central Minnesota, private wells that have relatively short screens set close to the upper confining till unit are more likely to have elevated arsenic concentrations than otherwise comparable private wells. Erickson's research has better defined the areas of the state and the types of private wells that are most at-risk for arsenic contamination. In the future, public health education can be focused in areas that are most in need of arsenic testing. Additionally, new guidelines could be developed to change common private well- dnllingpractices. Well drillers could be encouraged to set well screens routinely farther away from the till unit overlaying the sandy aquifer and to use longer screens in private wells- Although it was hypothesized that arsenic concentrations in a new well would change over time because constructing a well changes the geochemical environment of the aquifer, this hypothesis proved to be false- Arsenic concentrations in new wells vary over time in a manner similar to arsenic concentrations in older wells. This result has provided the answer to one of the questions that had been delaying the promulgation of a rule to test all new domestic wells in Minnesota for arsenic: If an arsenic sample is required for a new well, when should the well be sampled so that the measurement is representative of the typical arsenic concentration2 It is now known that an arsenic sample can be collected from a new well whenever it is most convenient because arsenic concen- trations in new wells do not increase or decrease systematically over time. In collaboration with Minnesota Department of Health engineers and hydrogeologists, Erickson identified two potential low-cost public water system options to combat arsenic contaminated groundwater, developed methodologies fog evaluating the viability of the low-cost compliance options, and proved that the methodologies are effective in evaluating these low-cost options on a community- by-community basis. The Minnesota Department of Health is already using bot} the `site investigation' methodology and a prescribed temporal sampling scheme on a regular basis in Minnesota communities that have elevated arsenic concentrations in their water supply. Implementing a viable, low-cost arsenic compliance option allows communities to avoid building an unnecessary and expensive community water treatment plant. A detailed article about this arsenic research is presented in the Spring 2004 edition. of the CUBA Reporter, which is available online at www.cura.umn.edu/ reporter. htrril#archive. Financial support for this project was provided by the Water Resources Center and the Center for Urban and Regional Affairs at the University of Minnesota, the Minnesota Department of Health, and the U.S. Geological Survey. Karla Peterson anc Richard Soule (Minnesota Department of Health) collaborated on portions of the research. WRS continued from page 1 household-scale nutrient modeling. Otto replaces Johanna Schussler as the Student Editor of the Minnegram. He received a B.S. in Civil and Environmental Engineer- ing from the University of Iowa and has spent the last four years working as a civil engineer in Chicago. Otto is advised by John Nieber. Schram is working with her advisor, Jim Perry (Fisheries, Wildlife, and Conservation Biology), on the Sarita wetland project. She received a B.S. in Biology from Iowa State University. Ray Newman and Erik Brown assume the roles of Director of Graduate Studies and Associate Director of Graduate Studies, respectively. For more information about the WRS program, visit the WRS Web site at http://wrs.coafes.umn.edu. 5 September 2004