Post on 23-Jan-2016
description
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• 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
InjectionInjectionWellWell
DitchDitch
5864
Ele
vati
on
(ft
)
0 6 12 18 24 30
Tim e (Days)
0 . 0
0 . 2
0 . 4
0 . 6
0 . 8
1 . 0
C/C
o BromideNitrate
mm58-4
0 6 12 18 24 30
Tim e (Days)
0 . 0
0 . 2
0 . 4
0 . 6
0 . 8
1 . 0
C/C
o
BromideNitrate
mm64-3
m m 20
m l8
m l9
m m 38
m m 7
Ditch
10 feet
m m 20
m l8
m l9
m m 38
m m 7
Ditch
10 feet
0 5 10
Fe
1000
1005
1010
1015
1020
1025
1030
1035
mm 7 & 20
0 5 10
Fe
1000
1005
1010
1015
1020
1025
1030
1035
ml 8 ml 9
0 5 10
Fe
1000
1005
1010
1015
1020
1025
1030
1035
mm 38
Ele
vati
on
(f t
)
(mg/l) (mg/l)(mg/l)
0 5 10
Fe
1000
1005
1010
1015
1020
1025
1030
1035
mm 7 & 20
0 5 10
Fe
1000
1005
1010
1015
1020
1025
1030
1035
ml 8 ml 9
0 5 10
Fe
1000
1005
1010
1015
1020
1025
1030
1035
mm 38
Ele
vati
on
(f t
)
(mg/l) (mg/l)(mg/l)
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
ml 8 ml 9
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
mm 7 & 20
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
mm 38
Ele
vati
on
(f t
)
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
ml 8 ml 9
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
mm 7 & 20
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
mm 38
Ele
vati
on
(f t
)
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
ml 8 ml 9
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
mm 7 & 20
0 2 4
Ca/Mg
1000
1005
1010
1015
1020
1025
1030
1035
mm 38
Ele
vati
on
(ft
)E
leva
tio
n (
ft)
Discharge zones in a glacial aquifer of Northern Wisconsin
Lower Site
Middle SiteElizabeth Keating
Reactions Simulated
Plag + 5 H+ Ca2+ + clay + 3[cations]+
Fe(OH)3 +3H+ Fe3+ + 3H2O
Dissolution
Acid/Base
Redox
CO32- + H+ HCO3
-
H2CO3 HCO3- + H+
Fe2+ Fe3+ + e- 1/2 O2 + 2H+ + 2e- H2O
Calibration Parameters
• Hydraulic conductivity zones
• Plagioclase dissolution rate constant
• Electron source rates for different electron acceptors
Middle SiteStreambed +Hillslope
Lower SiteStreambed +Hillslope
Upper Site
1
0
4
9
Ele
vati
on (
m)
Fractured dolomite in Door Co., Wisconsin
Fracture Mapping
Bissen Quarry
Maureen Muldoon
Elevation
(ft)
0 20 40 60 80SO4 (mg/l)
6 0
7 0
8 0
9 0
Ele
vati
on
(ft
)Multilevel 17, Bissen Quarry
May 1996
October 1996July 1996
0 100 200 300 400 500Time (days) starting May 5 1996
0
20
40
60
80
100
120
140C
lori
de
(mg
/l)
Multilevel 14-4, Bissen QuarryC
hlo
rid
e (
mg
/ l)
Fractured shale at Oak Ridge, Tennessee
vector mean=180
grid Ntrue N
vector mean=200
grid Ntrue N
45
vector mean=249
grid Ntrue N
vector mean=180
grid Ntrue N
Water table Shallow bedrocka)
b)
Ho
rizo
nta
l gra
die
nt
Ho
rizo
nta
l flo
w d
irec
tio
n
45
1 hydraulic gradient2 calculated flow direction3 bedding orientation4 horizontal reference line
January 3, 1995
1
23
A'A 2
4+48
-15-20
z
x
July 8, 1994
1
23
A'A1
4+52
z
x
- 2 0 - 1 3
January 1995 July 1995
cations anions cationsCa Ca Na+KNa+K
MgMg
ClHCO3+CO3 HCO3+CO3
SO4
anionsCl
SO4
SO4+
ClC
a+Mg
Na+K
HC
O3+
CO
3
SO4+
Cl
Ca+M
g
Na+K
HC
O3+
CO
3
Ca-Mg-SO4
Ca-HCO3
Ca-Na-HCO3
Na-Ca-HCO3
Na-Ca-HCO3-SO4
Na-HCO3
Pine Ridge sample mixing line
Ca-Mg-SO4
Hydrochemical Facies from Multilevel Samples
Spatial Distribution of Hydrochemical Facies
Approx. horizontal flow direction
1
23
x
45
z
+48-15-20
-18
+3
1 hydraulic gradient2 calculated flow direction 3 bedding orientation4 x-axis reference line5 range of inferred flow directions from hydrochem ical facies
BTEX plume in sandy aquifer, Fort McCoy
Maddy SchreiberPete Taglia
Tarr Cre
ek
Locations of Uncontaminated and Contaminated Transects
Uncontaminated Transect
0 5 10
248
250
252
254
256
258
260
0 5 10 0 5 10 0 5 10 0 5 10
D O
N O 3
m g / l
0 40 80
248
250
252
254
256
258
260Fe(II)
SO4
0 40 80 0 40 80 0 40 80 0 40 80
MLA3 MLA1 ML1 ML2 ML3
m g/l
shallow
int
deep
shallowint
deep
shallow
int
deep
shallow
int
deep
Nin
th A
ve
Eig
hth
Ave
Tar
r C
reek
Ele
vati
on
(m
)E
leva
tio
n (
m)
BTEX
benzene
toluene
1E-41E-30.01 0.1 1 10
248
250
252
254
256
258
1E-41E-30.01 0.1 1 10 1E-41E-30.01 0.1 1 10 1E-41E-30.01 0.1 1 10
MLA2 ML5 ML6 ML4
log concentration m g/l
Eig
hth
Ave
Tar
r C
reek
Contaminant Profiles
Ele
vati
on
(m
)
Contaminated Transect
0 5 10
248
250
252
254
256
258
0 5 10 0 5 10 0 5 10
0 40 80
248
250
252
254
256
258
0 40 80 0 40 80 0 40 80
MLA2 ML5 ML6 ML4
m g/l
m g/l
Fe(II)
SO4
DO
NO3
shallow, BTEX
int
deep
int
deep
shallow, BTEX
int
deep
shallow, BTEX
intdeep
Eig
hth
Ave
Tar
r C
reek
shallow, BTEX
Ele
vati
on
(m
)E
leva
tio
n (
m)
Contaminated Transect
0 5 10
248
250
252
254
256
258
0 5 10 0 5 10 0 5 10
0 40 80
248
250
252
254
256
258
0 40 80 0 40 80 0 40 80
MLA2 ML5 ML6 ML4
m g/l
m g/l
Fe(II)
SO4
DO
NO3
shallow, BTEX
int
deep
int
deep
shallow, BTEX
int
deep
shallow, BTEX
intdeep
Eig
hth
Ave
Tar
r C
reek
shallow, BTEX
Ele
vati
on
(m
)E
leva
tio
n (
m)
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