Geochemical Heterogeneity of
Groundwater in Uncontaminated
and Contaminated Aquifers
Jean M. Bahr
University of Wisconsin - Madison
Hydrogeologists expect spatial variations
in concentrations at contaminated sites
“A” Aquifer Water
Levels and TCE
Plumes, 1983
But “background” concentrations often
determined by a single upgradient well
Background
well
Take Home Messages
• Groundwater chemistry at “pristine”
sites can vary temporally and
spatially at local scales
• Geochemical signatures can help to
delineate local flow paths
• Geochemical heterogeneity at a local
scale reflects a combination of
distinct flow paths and reactions
Case Studies
• Discharge zone in WI Central Sands
• Discharge zones in a glacial aquifer of
Northern WI
• Fractured dolomite in Door Co., WI
• Fractured shale at Oak Ridge, TN
• Pristine and plume transects at a site
of BTEX contamination near Sparta WI
Current and Former Students
•
•
•
•
•
•
•
•
•
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Lucy Chambers Meigs
Lynn Raue Dean
Rod Rustad
Elizabeth Keating
Gerilynn Moline
Madeline Schreiber
Jodi Vandervelden
Maureen Muldoon
Peter Taglia
Ingrid Ekstrom
Geology 729 Classes
Discharge zone in Wisconsin’s Central Sands
Lucy Chambers
Meigs
Multilevel Construction and Installation
Miniature Multilevel Installation
Completed Miniature Multilevels
Field sampling and analysis
Colorimetric kits for DO, Fe, NO3 and others
Ditch
Injection
Well
1.0
1.0
mm64-3
0.8
0.8
Bromide
Nitrate
mm58-4
0.6
0.6
C/Co
C/Co
Bromide
Nitrate
0.4
0.4
0.2
0.2
0.0
0.0
0
6
12
18
24
30
0
Time (Days)
6
12
18
Time (Days)
64
58
24
30
mm38
ml8
mm7
mm20
Ditch
ml9
10 feet
mm38
ml8
mm7
mm20
Ditch
ml9
10 feet
ml 8
mm 7 & 20
Fe
Fe
5
Fe
(mg/l)
(mg/l)
0
mm 38
ml 9
0
10
5
(mg/l)
10
0
1035
1035
1035
1030
1030
1030
1025
1025
1025
1020
1020
1020
1015
1015
1015
1010
1010
1010
1005
1005
1005
1000
1000
1000
5
10
ml 8
mm 7 & 20
Fe
Fe
5
Fe
(mg/l)
(mg/l)
0
mm 38
ml 9
0
10
5
(mg/l)
10
0
1035
1035
1035
1030
1030
1030
1025
1025
1025
1020
1020
1020
1015
1015
1015
1010
1010
1010
1005
1005
1005
1000
1000
1000
5
10
mm 7 & 20
ml 8
Ca/Mg
0
2
mm 38
ml 9
Ca/Mg
0
4
2
Ca/Mg
0
4
1035
1035
1035
1030
1030
1030
1025
1025
1025
1020
1020
1020
1015
1015
1015
1010
1010
1010
1005
1005
1005
1000
1000
1000
2
4
mm 7 & 20
ml 8
Ca/Mg
0
2
mm 38
ml 9
Ca/Mg
0
4
2
Ca/Mg
0
4
1035
1035
1035
1030
1030
1030
1025
1025
1025
1020
1020
1020
1015
1015
1015
1010
1010
1010
1005
1005
1005
1000
1000
1000
2
4
mm 7 & 20
ml 8
Ca/Mg
0
2
mm 38
ml 9
Ca/Mg
4
0
2
Ca/Mg
4
0
1035
1035
1035
1030
1030
1030
1025
1025
1025
1020
1020
1020
1015
1015
1015
1010
1010
1010
1005
1005
1005
1000
1000
1000
2
4
Discharge zones in a glacial aquifer
of Northern Wisconsin
Elizabeth Keating
Middle Site
Lower Site
Reactions Simulated
Dissolution
Plag + 5 H+  Ca2+ + clay + 3[cations]+
Fe(OH)3 +3H+  Fe3+ + 3H2O
Acid/Base
CO32- + H+  HCO3H2CO3  HCO3- + H+
Redox
Fe2+  Fe3+ + e1/2 O2 + 2H+ + 2e-  H2O
Calibration Parameters
• Hydraulic conductivity zones
• Plagioclase dissolution rate
constant
• Electron source rates for
different electron acceptors
Lower Site
Streambed +
Hillslope
Middle Site
Streambed +
Hillslope
Upper Site
1
0
9
4
Fractured dolomite in Door Co., Wisconsin
Bissen Quarry
Maureen
Muldoon
Fracture Mapping
Elevation (ft)
Multilevel 17, Bissen Quarry
May 1996
July 1996
October 1996
Elevation (ft)
90
80
70
60
0
20
40
SO4 (mg/l)
60
80
Multilevel 14-4, Bissen Quarry
140
Cloride (mg/l)
120
100
80
60
40
20
0
0
100
200
300
400
Time (days) starting May 5 1996
500
Fractured shale at Oak Ridge, Tennessee
Water table
a)
Horizontal gradient
grid N
Shallow bedrock
grid N
true N
true N
45
vector mean=200
vector mean=180
Horizontal flow direction
b)
grid N
grid N
true N
true N
45
vector mean=249
vector mean=180
July 8, 1994
January 3, 1995
A'
A2
1
A1
A'
1
z
z
x
x
+52
+48
4
4
-20 -15
2
-20
-13
2
3
3
1
2
3
4
hydraulic gradient
calculated flow direction
bedding orientation
horizontal reference line
Ca-HCO3
Ca-Na-HCO3
Na-Ca-HCO3
Na-Ca-HCO3-SO4
Na-HCO3
Pine Ridge sample
mixing line
January 1995
Ca-Mg-SO4
Mg
Ca
cations
Ca-Mg-SO4
Mg
SO4
Na+K HCO3+CO3
July 1995
Cl Ca
anions
SO4
Na+K
cations
HCO3+CO3
Cl
anions
Hydrochemical Facies from Multilevel Samples
Spatial Distribution of Hydrochemical Facies
Approx. horizontal flow direction
1
z
x
+48
+3
5
-18
-20 -15
4
2
3
1
2
3
4
hydraulic gradient
calculated flow direction
bedding orientation
x-axis reference line
5 range of inferred flow directions
from hydrochemical facies
BTEX plume in sandy aquifer, Fort McCoy
Pete Taglia
Maddy Schreiber
Locations of Uncontaminated and
Contaminated Transects
260
MLA1
DO
NO3
ML1
Tarr Creek
MLA3
Eighth Ave
Ninth Ave
Uncontaminated Transect
ML3
ML2
258
256
shallow
shallow
int
254
int
252
deep
250
deep
248
0
5
10
0
5
10
0
5
10
mg/l
0
5
10
0
5
10
Fe(II)
260
SO4
258
256
shallow
shallow
int
254
int
252
deep
250
deep
248
0
40
80
0
40
80
0
40
mg/l
80
0
40
80
0
40
80
Contaminant Profiles
benzene
ML5
toluene
ML6
256
ML4
Tarr Creek
258
MLA2
Eighth Ave
BTEX
254
252
250
248
1E-41E-30.01 0.1 1
10 1E-41E-30.01 0.1 1
10 1E-41E-30.01 0.1 1
log concentration mg/l
10 1E-41E-30.01 0.1 1
10
MLA2
258
ML6
ML5
ML4
DO
NO3
256
shallow, BTEX
254
252
int
250
deep
shallow, BTEX
int
deep
248
0
5
10
0
5
mg/l
10
0
5
10
0
5
10
Fe(II)
258
SO4
256
shallow, BTEX
shallow, BTEX
254
int
deep
int
252
250
deep
248
0
40
80
0
40
80
mg/l
0
40
80
0
40
80
Tarr Creek
Eighth Ave
Contaminated Transect
MLA2
258
ML6
ML5
ML4
DO
NO3
256
shallow, BTEX
254
252
int
250
deep
shallow, BTEX
int
deep
248
0
5
10
0
5
mg/l
10
0
5
10
0
5
10
Fe(II)
258
SO4
256
shallow, BTEX
shallow, BTEX
254
int
deep
int
252
250
deep
248
0
40
80
0
40
80
mg/l
0
40
80
0
40
80
Tarr Creek
Eighth Ave
Contaminated Transect
Conclusions
• Groundwater chemistry at “pristine”
sites can vary temporally and
spatially at local scales
• Geochemical signatures can help to
delineate local flow paths
• Geochemical heterogeneity at a local
scale reflects a combination of
distinct flow paths and reactions
Implications for Assessing
Contaminated Sites
Interpreting changes induced by
contaminants and predicting potential
for natural attenuation or enhanced
remediation require adequate
characterization of background
geochemical heterogeneity