Geochemical Heterogeneity of Groundwater in Uncontaminated and Contaminated Aquifers

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Geochemical Heterogeneity of Groundwater in
Uncontaminated and Contaminated Aquifers

• Jean M. Bahr
• University of Wisconsin - Madison

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Hydrogeologists expect spatial variations in
concentrations at contaminated sites
A Aquifer Water Levels and TCE Plumes, 1983
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But background concentrations often determined
by a single upgradient well
Background well
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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

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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

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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
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Discharge zone in Wisconsins Central Sands
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Lucy Chambers Meigs
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Multilevel Construction and Installation
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Miniature Multilevel Installation
Completed Miniature Multilevels
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Field sampling and analysis
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Colorimetric kits for DO, Fe, NO3 and others
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Ditch
Injection Well
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64
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Elevation (ft)
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(No Transcript)
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(mg/l)
(mg/l)
(mg/l)
Elevation (ft)
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(mg/l)
(mg/l)
(mg/l)
Elevation (ft)
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Elevation (ft)
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Elevation (ft)
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Elevation (ft)
Elevation (ft)
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Discharge zones in a glacial aquifer of Northern
Wisconsin
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(No Transcript)
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Elizabeth Keating
Middle Site
Lower Site
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(No Transcript)
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Reactions Simulated
Dissolution
Plag 5 H ? Ca2 clay 3cations
Fe(OH)3 3H ? Fe3 3H2O
Acid/Base
CO32- H ? HCO3-
H2CO3 ? HCO3- H
Redox
Fe2 ? Fe3 e-
1/2 O2 2H 2e- ? H2O
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Calibration Parameters

• Hydraulic conductivity zones
• Plagioclase dissolution rate constant
• Electron source rates for different electron
  acceptors

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Middle Site Streambed Hillslope
Upper Site
Lower Site Streambed Hillslope
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1
0
9
4
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Elevation (m)
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Fractured dolomite in Door Co., Wisconsin
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(No Transcript)
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Bissen Quarry
Maureen Muldoon
Fracture Mapping
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(No Transcript)
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Elevation (ft)
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(No Transcript)
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Chloride (mg/l)
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Fractured shale at Oak Ridge, Tennessee
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(No Transcript)
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(No Transcript)
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Hydrochemical Facies from Multilevel Samples
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Spatial Distribution of Hydrochemical Facies
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(No Transcript)
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Approx. horizontal flow direction
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(No Transcript)
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BTEX plume in sandy aquifer, Fort McCoy
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Maddy Schreiber
Pete Taglia
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Locations of Uncontaminated and Contaminated
Transects
Tarr Creek
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Uncontaminated Transect
Elevation (m)
Elevation (m)
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Contaminant Profiles
Elevation (m)
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Contaminated Transect
Elevation (m)
Elevation (m)
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Contaminated Transect
Elevation (m)
Elevation (m)
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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

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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