State Water Resources Research Institute Program


Project ID: 2011MN288B
Title: Stratigraphic distribution and mineralogical sources of arsenic to Minnesota glacial aquifers
Project Type: Research
Start Date: 6/01/2011
End Date: 5/31/2013
Congressional District: 4th
Focus Categories: Groundwater, Geochemical Processes, Toxic Substances
Keywords: arsenic, glacial aquifer, X-ray absorption spectroscopy, GIS, mineralogy
Principal Investigators: Toner, Brandy Marie; Nater, Edward A (University of Minnesota)
Federal Funds: $ 32,500
Non-Federal Matching Funds: $ 57,488
Abstract: The primary goal of the proposed research is to identify the stratigraphic and mineralogical sources of arsenic (As) to groundwater in west-central and south-central Minnesota (MN). We will generate new geochemical information on the speciation of As in glacial deposits using X-ray absorption spectroscopy and sequential extractions. This information will be integrated with existing hydrogeology and stratigraphy databases to determine the distribution of As species in geologic formations. These results will be reported to MN state agencies with drinking water quality mandates. The research outcomes are sorely needed and have implications for the health of Minnesotans and citizens of communities globally that face As-contaminated water.

Arsenic concentrations in domestic well water throughout large regions of MN exceed the public drinking water system standard (10 µg/L) set by the U.S. EPA in 2001 following review of evidence for increased risk of cancer with consumption of drinking water below 50 µg As/L. The scale of the problem is illustrated by the results of the MN Arsenic Study (MARS): 50% of the 869 domestic wells tested in west-central MN had As concentrations > 10 µg/L, which poses a serious and widespread public health concern. In response to these challenges, the MN well code now requires that each new potable water supply well, estimated at 8,000-12,000 wells annually, be tested for As. Although these tests provide families with important information about drinking water quality, that information comes only after the well has been drilled. While As-removal systems can be purchased by individuals, they are expensive, require maintenance, and do not provide alarms for high As concentrations or system failure. The intent of the proposed research is to help Minnesotans to place their wells where the probability of safe water is highest.

Arsenic concentrations in the solid geological materials composing MN aquifers are not exceptionally high, this seeming paradox is a hallmark of geologically or naturally sourced As contamination in MN and worldwide. Well construction and placement of well screens in the Des Moines Lobe formation are now known to correlate with elevated As concentrations in MN well water. However, the unexplained variability in As concentrations in domestic wells with similar geographic location, depth, and aqueous chemical conditions currently limits our ability to anticipate where safe drinking water is located in the subsurface. Although multiple MN state agencies have studied groundwater chemistry, geology, and hydrogeology in As affected areas, the processes driving As movement from geological materials to drinking water remain elusive. This knowledge gap has consequences for the health of Minnesotans, and it limits the efficacy of public policies directed at wise placement and construction of new wells.

To-date, all scientific evidence supports the conclusion that As in MN glacial aquifers is derived from naturally occurring mineral phases, but the distribution of As-bearing glacial strata and the suite of As-bearing minerals are not known. In the proposed research, we will address this fundamental knowledge gap by measuring the exact form of As present in aquifer, confining layers, and aquifer-confining layer contacts in 20 rotary sonic drill cores that we sampled during 2009 and 2010. We have already invested substantial effort and funds into GIS database construction, field research, laboratory supplies and equipment, analytical instrumentation, and student training for this project. We are requesting 2 years of support for an existing Ph.D. student to complete the spectroscopic and mineralogical measurements, and integrate those data into our GIS database.

Progress/Completion Report, 2011, PDF

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