A River Runs Through It:
Taconite Mining, Sulfate, and the St. Louis River
Michael E. Berndt
Minnesota DNR/ U of M
MMEW Worshop
June 16, 2015
Biwabik Iron Formation
St. Louis River
Duluth Complex
St. Louis River:
>180 miles long
~1100 foot drop from headwaters
to Lake Superior
9283 km2 Drainage Basin
Sulfate Source Plot for St. Louis River
160
Daily Sulfate Load (metric tons)
140
Mining
Non-Mining
Non-Mining
Mining
120
100
80
Mining Avg
35 tons/day
Non-Mining Avg
15 tons/day
60
40
20
0
J
A
S
O
2010
N
D
J
F
M
A
M
J
J
A
S
O
N
2011
Berndt and Bavin (2012)
2012-2013: Mine Water Research Advisory Panel (MWRAP)
Coordinated studies:
Sediments, water, biology
DOC/Hg/MeHg kinetics
Sulfur cycling, d34S, d18O
Topics for today
• Where does water go when it rains? 
• How does water chemistry change when it
falls on the unaltered landscape?
• How does water chemistry change when it
falls on a taconite mine?
• How does water coming from the landscape
mix with mine water in the St. Louis River?
What lies beneath the landscape?
Where does water go when it rains?
HSPF User’s Manual, v.12.2, 2005
*About 28 inches falls on the landscape annually in this region.
*Little runs off directly to streams, except during bigger storms.
*About 8 inches infiltrates into the groundwater, eventually leaking to streams.
Freshly decaying organic matter is an important reactant.
http://pubs.water.usgs.gov/cir1139
In a mine, ground water leaks into pit. This and precipitation are pumped out.
Freshly decaying organic matter is not usually an important reactant.
Previously buried materials are exposed to oxygen in air.
Topics for today
• Where does water go when it rains?
• How does water chemistry change when it
falls on the unaltered landscape? 
• How does water chemistry change when it
falls on a taconite mine?
• How does water coming from the landscape
mix with mine water in the St. Louis River?
What controls the chemistry?
Water entering the streams takes its
chemistry from the riparian soils, … the
last soils in contact with the water
before it becomes runoff.
(Bishop et al, Hydrol. Proc. 18, 185-189, 2004)
Dissolved Organic Carbon (DOC)
• DOC comes from decaying organic matter
• Composed mostly of Humic and Fulvic acids
• Northern MN waters hold as much as 60 mg/L DOC
Former Dissolved Organic Carbon (DOC),
separated from water
DOC transports iron and other components,
including mercury (Hg), from riparian sediments
into the open water.
Photo-volatilization
Demethylation
Hg2+,
MeHg+
Hg2+,
Fe2+
Hg2+
Sulfate>1
Berndt et al (in prep)
Event occurred following major
rainfall in the non-mining region
Iron is released into streams following big storm events.
Flow
(Event #8)
Iron (Fe)
Flow
Flow
Fe
Fe
2010
2011
Iron Concentration in the St. Louis River at Scanlon Dam
Different flow rates sample the levels in the soil profile in different proportions.
DOC
DOC+ Fe
A – High Flow
DOC+ Fe
B – Medium Flow
Berndt et al. (2014)
Minerals,
microbes, and
decaying biota
DOC
Fe
Minerals,
microbes, and
decaying biota
St. Louis River Basin
Lake Superior
Topics for today
• Where does water go when it rains?
• How does water chemistry change when it
falls on the unaltered landscape?
• How does water chemistry change when it
falls on a taconite mine? 
• How does water coming from the landscape
mix with mine water in the St. Louis River?
Pyrite in Biwabik Fe Formation
Photos from Rod Johnson and Associates (2009) Petrography Report for Mesabi Mining
Iron Sulfide as fracture Filling on mine wall
FeS2 alteration products (Melanterite or
Calcite) along bedding plane
Iron oxide coating on pyrite
grain from aged taconite
mine waste
Length: 10 um
Scale 50 um
Pyrite in mine wastes
After Wunderly et al. (1996)
Pyrite Oxidation:
FeS2 + 3.75O2 + 3.5 H2O = Fe(OH)3 + 2H2SO4
Pyrite
Oxygen
Water
Altered Rind
Sulfuric Acid
A little pyrite oxidation releases a lot of sulfate!
New Taconite Tails
N/A
N/A
~30 Yr Old Taconite Tails
Bavin et al. (2015)
Sulfuric Acid
Pyrite Oxidation:
FeS2 + 3.75O2 + 3.5 H2O = Fe(OH)3 + 2H2SO4
Carbonate Neutralization:
H2SO4 + 2(Mg,Ca)CO3 = 2(Ca++,Mg++) + SO4= + 2HCO3Carbonate
Minerals
Calcium, Magnesium, Sulfate, and Bicarbonate
Slightly “alkaline” (pH>7)
Mg vs SO4 for samples collected in or near mine pits
on the Mesabi Iron Range
Topics for today
• Where does water go when it rains?
• How does water chemistry change when it
falls on the unaltered landscape?
• How does water chemistry change when it
falls on a taconite mine?
• How does water coming from the landscape
mix with mine water in the St. Louis River? 
Jay Cook State Park Swinging Bridge
Thursday, June 21, 2012
Pioneer Press
Kare 11 News
Prior to flood
Skibo
Mile 94
Scanlon
Hydrograph and Sample Dates in 2012
Berndt et al (2014)
Skibo Site Sampling Photos in 2012
Mile 94 Site Sampling Photos in 2012
HSPF = Hydrologic Simulation Program (Fortran)
2014: MPCA commissioned flow model for St. Louis River by Tetratech.
2014-2016: DNR is using the flow model to help quantify mine impacts to chemistry.
Modeled and measured flow at Scanlon Dam
(Rutelonis and Berndt – in prep)
Fraction of water from source
Origin of water in St. Louis River at Scanlon Dam (modeled)
(Rutelonis and Berndt – in prep)
Fraction of water from source
Watershed
Point Sources:
Mining
Non mining
(Rutelonis and Berndt – in prep)
Fraction of water from source
Watershed
Point Sources:
Mining
Non mining
(Rutelonis and Berndt – in prep)
Sulfate vs Magnesium in the St. Louis River in 2012
Upstream site
Berndt et al. (2014)
Fe vs DOC: Upstream and Downstream from Mining Region
36
36
Berndt et al. (2014)
DNR Website
http://www.dnr.state.mn.us/lands_minerals/dnr_so4_research.html
Acknowledgements
•
•
•
•
MWRAP 2012 Scientific Crew
Wes Rutelonis (U of M Graduate Student)
Chuck Regan (MPCA – HSPF modeling)
Hanna Friedlich (Workshop organization)