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Using stable isotopes to trace contamination of the Madison Limestone aquifer by coal AMD, central Montana
Chris Gammons,Allison BrownMontana TechButte, MT
Tom HendersonMT‐DEQ
Simon PoulsonUniv‐Nevada Reno
Gammons, MDOC Conference, May 2012
Lewistown
Great Falls
Giant Spring
50 km0 25
Big Spring
MissouriRiver
Billings
Helena
Butte
MONTANA
Map Detail
MissouriRiver
MissouriRiver
Billings
Helena
Butte
MONTANA
Map Detail
MissouriRiverFig. 1 detail
MissouriRiver
Billings
Helena
Butte
MONTANA
Map Detail
MissouriRiver
MissouriRiver
Billings
Helena
Butte
MONTANA
Map Detail
MissouriRiverFig. 1 detail
N
Great Falls-Lewistown Coal Field
Study area
AMD Problems
Gammons, MDOC Conference, May 2012
• Shallow, undulatory dip of coal beds
• Underground, room & pillar mining
• Most mines worked updip so water would drain by gravity
• In cases where this was not possible, horizontal drains were tunneled to the nearest coulee
• All mining ceased by mid‐1900s
Mining methods
Bituminous, high-S coal
Gammons, MDOC Conference, May 2012
Perched groundwater
Regional groundwater
Madison limestone
Gammons, MDOC Conference, May 2012
Slide courtesy of John Lafave, Montana Bureau Mines and Geology
The Madison Aquifer is an important drinking water source
Giant Spring
Big SpringGammons, MDOC Conference, May 2012
Is AMD from coal mines contaminating the Madison Aquifer?
• Undergraduate research project
• Sample domestic wells completed in Madison in old coal mine towns
• Field parameters (pH, SC, temp, alkalinity)
• ICP‐metals• water isotopes• sulfate isotopes
Undergraduate student Allison Brown sampling a neighbor’s well
Gammons, MDOC Conference, May 2012
Stable Isotope Background
# protons # neutrons Total mass Naturalabundance
18O 8 10 18 0.2%
17O 8 9 17
Isotope preparation
• Add BaCl2 to make BaSO4 precipitate– Filter, rinse, weigh and send to Reno
Stable Isotope Measurement
Isotope Ratio Mass Spectrometer (IRMS)Univ‐Nevada Reno (Dr. Simon Poulson)
Stable Isotope Notation
• δ (in ‰) = (Rsample / Rstandard ‐ 1) ∙1000 • R= ratio of the heavy isotope to light
– E.g., 18O/16O, or 34S/32S• If δ is negative the sample contains less heavy isotope than standard
Previous Work: Gammons et al. 2010 (Chem. Geol., v. 269)
Gammons, MDOC Conference, May 201234S-sulfate, ‰
-20 -10 0 10 20 30
18 O
-sul
fate
, ‰
-15
-10
-5
0
5
10
15
20
Mine drainsGiant SpringBig SpringBelt city wellCoal gw wells
Mississippian seawater
Madison wells, Montana (Plummer et al., 1990)
Jurassic-early Cretaceous seawater
sulfate from coal AMD drains
• Montana Tech:– 21 wells sampled
• MT DEQ– 9 wells sampled
Gammons, MDOC Conference, May 2012
Results 1 (cont.): major ions
Ca2+ Mg2+ Na+ K+ HCO3‐ SO42‐
AB‐1 88.9 38.3 7.8 7.4 460 135
AB‐2 72.9 33.3 9.2 2.9 348 110
AB‐3 70.0 25.2 3.0 1.2 326 95
AB‐4 74.2 25.8 11.9 2.3 370 100
AB‐5 77.0 26.9 12.4 2.5 396 130
AB‐6 70.9 24.8 10.9 2.3 360 85
AB‐7 86.6 47.5 28.2 3.9 476 140
AB‐8 71.1 24.7 10.9 2.3 370 95
AB‐9 72.7 28.7 11.8 2.4 382 105
AB‐10 126 49.5 12.6 3.7 390 345
AB‐11 70.3 26.3 12.9 2.5 364 85
AB‐12 70.2 26.4 11.7 2.4 374 85
80 60 40 20 20 40 60 80
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
C N HCO3 Cl
Mg SO4Mg SO4
Ca Na+K HCO3 Cl
Madison GroupSwift Fm. (Stockett) Mine drains
Results: Water chemistry
• All wells had near‐neutral pH
• Low to moderate TDS
• No major problems with trace metals
Gammons, MDOC Conference, May 2012
34S-sulfate, ‰
-20 -15 -10 -5 0 5 10 15 20
18 O
-sul
fate
, ‰
-15
-10
-5
0
5
10
15
Madison wells: MT TechMadison wells: DEQGiant SpringBig SpringAMD DrainsStockett water
y = 0.709x ‐ 1.175R² = 0.96
• All samples lie on an apparent two component mixing line
• Some wells appear to be dominated by AMD sulfate
Results: Stable Isotopes
Gammons, MDOC Conference, May 2012
34 S
-sul
fate
, ‰
-20
-15
-10
-5
0
5
10
15
20
Madison wells: MT TechAMD DrainsGiant SpringBig SpringStockett waterMadison wells: DEQ
1/SO4, mmol-1
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
18 O
-sul
fate
, ‰
-15
-10
-5
0
5
10
15
Madison wells: MT TechAMD DrainsGiant SpringBig SpringStockett waterMadison wells: DEQ
Madison end‐member
Swift end‐member
AMD
Madison end‐member
Swift end‐memberAMD
A.
B.
• When plot isotopes vs. reciprocal SO4, a 3‐component mixing model emerges
• End‐members:– AMD sulfate– Madison sulfate– “Shallow” sulfate (e.g., Swift Fm.)
Gammons, MDOC Conference, May 2012
older rocks
Kk
Jsm
Jsm
Mbs
KkStockett
Little Belt Mtns
southnorth________
2000
1600
1200
800
Elevation, m
10 km
1000
600
1400
1800
Mm
Gammons, MDOC Conference, May 2012
0 10 20 30 40 50 60 70 80 90 1000
10
20
30
40
50
60
70
80
90
1000
10
20
30
40
50
60
70
80
90
100
% sulfate from local recharge
Madison wells: Montana TechSwift Fm. (Stockett)Madison wells: DEQ Giant SpringBig SpringAMD drains
End‐member mixing calculations
Gammons, MDOC Conference, May 2012
• Spatial variations• Size of bubble correlates to proportion of sulfate from AMD source
Gammons, MDOC Conference, May 2012
Older wells Newer wells
Open Hole Casing with screen
Gammons, MDOC Conference, May 2012
Conclusions• Many of the wells in this study appear to be contaminated with AMD from coal mines– Water is still drinkable– Chemical buffering of Madison Limestone
• “Open hole” wells have higher probability of contamination
• Sulfate isotopes were very useful to trace sources of sulfate in the Madison Aquifer
Gammons, MDOC Conference, May 2012
• Funded through the Montana Tech Undergraduate Research Program
Questions?
Film of Fe-oxidizing bacteriaKate’s Coulee
Gammons, MDOC Conference, May 2012
References• Gammons C.H., Brown A., Poulson S.R., and Henderson T. (in review) Using
stable isotopes (S, O) of sulfate to track contamination of the Madison karst aquifer, Montana, from coal mine drainage. Submitted, March 5, 2012
• Gammons C.H., Duaime T.E., Parker S.R., Poulson S.R., Kennelly P. (2010) Geochemistry and stable isotope investigation of acid mine drainage associated with abandoned coal mines in central Montana, USA. Chemical Geology 269, 100‐112.
Gammons, MDOC Conference, May 2012