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