Arsenic Geochemistry
Arsenic concentrations in the solid geological materials composing MN aquifers are not exceptionally high, yet domestic wells in west-central MN have arsenic concentrations greater than the Environmental Protection Agency allows – this seeming paradox is the hallmark of geologically sourced arsenic contamination. Our research addresses the geochemical form of arsenic (speciation) and the biogeochemical processes that lead to arsenic build up in groundwater.
We are collaborating with the Minnesota Geological Survey to obtain geologic materials from fresh rotary sonic cores. We sample all of the stratigraphic interfaces, especially sand/gravel - glacial till contacts to ~ 200 ft. depth. These interfaces may be critical geochemical zones where arsenic is leached from glacial tills and concentrated in groundwater.
Alan Knaeble (MGS), Sarah Nicholas (UMN graduate student), and Gary Meyer (MGS-PI) inspect new core.
It was pretty difficult for us too - our lab blew in.
The primary goal of this field sampling is to preserve glacial tills for arsenic speciation and geochemistry. Immediately after core recovery, the samples are sealed in heavy mylar film under argon gas in a portable glove box. This is a real challenge when working at 8 F during an Alberta Clipper! During the second day of sampling, the wind blew in our ice house, blew out our heater, and prevented use of the glove box outside.
The van lab.
Geochemistry samples in the glove bag.
This is Sarah's dissertation project. Here she is outside with the samples she selected.
Sarah with the drill rig.
In all, there were 10 new rotary sonic cores drilled during ~ 20 days of drilling operations. These freshly sampled aquifer and till sediments complement on-going work by our group on archived cores obtained from the MN DNR. While the archived cores allow us to integrate our results with information-rich geospatial databases, the long term storage of the cores under oxic conditions is a disadvantage because we are interested in arsenic cycling and speciation. The new samples will allow us to examine arsenic speciation in glacial deposits as well as the microbial ecology of high and low arsenic zones with far fewer artifacts.