Solid-phase arsenic speciation in glacial aquifer sediments of west-central Minnesota, USA

211 Pages·2017·9.32 MB·English

Solid-phase arsenic speciation in glacial aquifer sediments of west-central
Minnesota, USA:
a micro-X-ray absorption spectroscopy approach for quantifying trace-level
speciation

A Dissertation
SUBMITTED TO THE FACULTY OF
UNIVERSITY OF MINNESOTA
BY

Sarah Luella Nicholas

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

Brandy M. Toner, Adviser, Edward Nater, Co-adviser

June 2017
© Sarah Luella Nicholas 2017
Acknowledgements

Funding for my research came from a grant to Professor Toner from the Center for Urban
and Regional Affairs, a grant to Professor Toner from the Office of the Vice President for
Research, and a USGS Water Research Grant to Professor Toner (jointly funded by the
USGS’s Water Resources Research Initiative Program and the Minnesota Agricultural
Experiment Station’s Center for Agricultural Impacts on Water Quality).

Further support came from a Science Fellowship from the UMN Graduate School, the
Allmaras Memorial Fellowship from the Department of Soil, Water, and Climate, and a
Doctoral Dissertation Fellowship from the University of Minnesota – Twin-Cities (UMN)
Graduate School.

Sarah Baldvins and Reba Van Beusekom assisted me in my research when they were
undergraduates. They were funded by the UMN Undergraduate Research Opportunities
Program (UROP).

I would like to thank Alan Knaeble, Gary Meyer, Angela Gowan, Barb Lusardi, and
Harvey Thorleifson at the Minnesota Geological Survey.

I would like to thank synchrotron scientists Matthew Marcus, Sirine Fakra and Josep
Roque-Rosell (Advanced Light Source, ALS, BL10.3.2). The ALS is supported by the
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Director, Office of Science, Office of Basic Energy Sciences, of the U.S. DOE under
Contract No. DE-AC02-05CH11231.

I would also like to thank beamline scientists Mahaling Balasubramanian and Steve
Heald (Advanced Photon Source, APS, PNC/XSD, 20-BM), and Matthew Newville
(APS, 13-BM) for their support of this project. PNC/XSD facilities at the APS, and
research at these facilities, are supported by the U. S. Department of Energy (DOE) -
Basic Energy Sciences, a Major Resources Support grant from NSERC, the University of
Washington, Simon Fraser University, and the APS. Use of the APS is also supported by
the U. S. DOE, Office of Basic Energy Sciences, under Contract DE-AC02-06CH11357.

I would like to thank Sara Baldvins, Lindsey Briscoe, Shahida Quazi, and Ryan
Lesneiwiski (UMN) and Sofia Oufqir (University of Mohamed V-Agdal, Morocco) for
assistance with sample preparation of the archived tills.

Prof. Bernhardt Saini-Eidukat and the department Geological Sciences at North Dakota
State University lent me lab space for the night work on the Clay County samples and
NDSU undergraduate student Lane Folkers assisted me in the field.

I would like to thank Brandi Cron Kammermans, Michael Ottman, Rebecca Sims, Reba
Van Beusekom, and Olga Furmann for their help with the Meeker County enrichment
experiment.
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I would like to thank Brandi Cron Kammermans, Jill Coleman Wasik, Colleen Hoffman,
and Jeff Sorensen for co-staffing the beamline at 10.3.2 with me, and Brandi for taking
me along to 13 ID E in Chicago.

I would like to thank Karl Wirth at Macalester College for his guidance and patience.

I would like to thank my committee: Mindy Erickson, Carrie Jennings, Paul Bloom, and
Edward Nater for their advice, support, and patience.

I would like to thank Professor Peter Croot my post-doctoral advisor at the National
University of Ireland, Galway for allowing me to continue to work on arsenic papers
during the first six months of my post-doctoral work.

I would like to thank Soil, Water, and Climate staff Kari Jarcho, Marjorie Bonse, Joel
Nelson, Thor Sellie, Andy Scobbie, and Dave Ruschy for making the wheels go around.

I would like to thank my parents Kathleen Hall and David Nicholas, my husband Joshua
Lynch and my daughters Maura Nicholas Lynch and Brigid Nicholas Lynch.

Brandy Toner took me on in 2010 when I wanted to come back to science but didn’t
know how. I have her to thank not only for teaching me spectroscopy and low-T
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geochemistry but for sending me to sea in 2013. None of us could have predicted how
that would turn out but it’s been a wonderful experience. I am truly grateful for my time
on team Toner.
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Dedication

For Joshua Lynch

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Abstract
Arsenic (As) is a geogenic contaminant affecting groundwater in geologically diverse
systems. The footprint of the Des Moines Lobe glacial advance in west-central
Minnesota, is a regional nexus of drinking-water wells that exceed the US EPA
maximum contaminant level for arsenic (As>10µgL-1). Arsenic release from aquifer
sediments to groundwater is favored when biogeochemical conditions in aquifers
fluctuate.
The specific objective of this research was to identify the solid-phase sources and
geochemical mechanisms of release of As in aquifers of the Des Moines Lobe glacial
advance. The overarching hypothesis is that gradients in hydrologic conductivity and
redox conditions found at aquifer-aquitard interfaces promote a suite of geochemical
reactions leading to mineral alteration and release of As to groundwater. A microprobe
X-ray absorption spectroscopy (µXAS) approach was developed and applied to rotosonic
drill core samples to identify the solid-phase speciation of As in aquifer, aquitard, and
aquifer-aquitard interface sediments. This approach addressed the low solid-phase As
concentrations, as well as the fine-scale physical and chemical heterogeneity of the
sediments. The solid-phase Fe and As speciation was interpreted using sediment and
well-water chemical data to propose solid-phase As reservoirs and release mechanisms.
The results are consistent with three different As release mechanisms: (1) desorption
from Fe oxyhydroxides, (2) reductive dissolution of Fe oxyhydroxides, and (3) oxidative
dissolution of Fe sulfides. The findings confirm that glacial sediments at the interface
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between aquifer and aquitard are geochemically active zones for As. The diversity of As
release mechanisms is consistent with the geographic heterogeneity observed in the
distribution of elevated-As wells.
Supplementary file “Nicholas dissertation supplementary files 1 to 5.xlsx” was submitted
to the UMN digital conservancy with this thesis. It is an excel workbook with five tables.
Tables 1 and 2 are the complete provenance and citation information for all As and Fe
reference spectra used. Tables 3, 4, and 5 are the reference spectra fits, fractions, and
scores for the sampled spectra from cores OTT3, TG3, and UMRB2.

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Table of Contents

Acknowledgements .............................................................................................................. i
Dedication ........................................................................................................................... v
List of Tables ..................................................................................................................... xi
List of Figures ................................................................................................................... xii
CHAPTER 1. INTRODUCTION – GEOGENIC ARSENIC CONTAMINATION OF
WELL WATER .................................................................................................................. 1
Previous work on arsenic in Minnesota well water ........................................................ 1
Geogenic arsenic contamination of drinking water worldwide ...................................... 2
Geogenic arsenic contamination of drinking water in North America ........................... 3
Well construction ............................................................................................................ 4
Solid-phases sources of arsenic to waters and the importance of speciation .................. 5
CHAPTER 2: SOLID-PHASE ARSENIC SPECIATION IN AQUIFER SEDIMENTS: A
MICRO-X-RAY ABSORPTION SPECTROSCOPY APPROACH FOR
QUANTIFYING TRACE-LEVEL SPECIATION ............................................................. 9
Abstract ......................................................................................................................... 10
2.1. INTRODUCTION ................................................................................................. 11
2.1.1 Arsenic Release Mechanisms in Glacial Aquifers ........................................... 14
2.2. MATERIALS AND METHODS ........................................................................... 18
2.2.1 Regional Setting ............................................................................................... 18
2.2.2 Sample Selection .............................................................................................. 20
2.2.3 Well-Water Chemistry Near the Cores ............................................................ 21
2.2.4 Sample Processing ........................................................................................... 22
2.2.5 Unconsolidated Sediment Chemistry ............................................................... 23
2.2.6 X-ray Absorption Spectroscopy ...................................................................... 24
2.2.7 Analytical Challenges and Approach ............................................................... 27
2.2.8 Arsenic Speciation Mapping ........................................................................... 29
2.2.9 Arsenic and Fe XAS Data Analysis ............................................................... 31
2.3. RESULTS .............................................................................................................. 35
2.3.1 Spatial Analysis of Well Water Chemistry ...................................................... 35
2.3.2 Bulk Chemical Analysis .................................................................................. 36
2.3.3 Solid-phase As and Fe Speciation .................................................................... 37
2.4. DISCUSSION ........................................................................................................ 46
2.4.1 Solid-Phase Source of As to Groundwater ..................................................... 46
2.4.2 Geochemical Processes Liberating As to Waters ........................................... 46
2.4.3 Summary of Geochemical Conditions and Solid-phase Speciation ............... 48
2.5 CONCLUSIONS .................................................................................................... 49
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