1. Geochemical Heterogeneity of Groundwater in Uncontaminated and Contaminated Aquifers Jean M. Bahr University of Wisconsin - Madison

2. Hydrogeologists expect spatial variations in concentrations at contaminated sites “A” Aquifer Water Levels and TCE Plumes, 1983

3. But “background” concentrations often determined by a single upgradient well Background well

4. 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

5. 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

6. 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

7. Discharge zone in Wisconsin’s Central Sands

8. Lucy Chambers Meigs

9. Multilevel Construction and Installation

10. Miniature Multilevel InstallationCompleted Miniature Multilevels

11. Field sampling and analysis

12. Colorimetric kits for DO, Fe, NO 3 and others

13. InjectionWell Ditch

14. 58 64 Elevation (ft)

17. (mg/l)

18. Elevation (ft) (mg/l)

19. Elevation (ft)

22. Discharge zones in a glacial aquifer of Northern Wisconsin

24. Lower Site Middle Site Elizabeth Keating

27. Reactions Simulated Plag + 5 H +  Ca 2+ + clay + 3[cations] + Fe(OH) 3 +3H +  Fe 3+ + 3H 2 O Dissolution Acid/Base Redox CO 3 2- + H +  HCO 3 - H 2 CO 3  HCO 3 - + H + Fe 2+  Fe 3+ + e - 1/2 O 2 + 2H + + 2e -  H 2 O

28. Calibration Parameters Hydraulic conductivity zones Plagioclase dissolution rate constant Electron source rates for different electron acceptors

29. Middle Site Streambed + Hillslope Lower Site Streambed + Hillslope Upper Site

30. 1 0 4 9

31. Elevation (m)

32. Fractured dolomite in Door Co., Wisconsin

34. Fracture Mapping Bissen Quarry Maureen Muldoon

36. Elevation (ft)

38. Chloride (mg/l)

39. Fractured shale at Oak Ridge, Tennessee

40. vector mean=180 grid N true N vector mean=200 grid N true N 45 vector mean=249 grid N true N vector mean=180 grid N true N Water tableShallow bedrock a) b) Horizontal gradient Horizontal flow direction 45

42. Hydrochemical Facies from Multilevel Samples

43. Spatial Distribution of Hydrochemical Facies

45. Approx. horizontal flow direction

47. BTEX plume in sandy aquifer, Fort McCoy

48. Maddy Schreiber Pete Taglia

49. Tarr Creek Locations of Uncontaminated and Contaminated Transects

50. Uncontaminated Transect Elevation (m)

51. Contaminant Profiles Elevation (m)

52. Contaminated Transect Elevation (m)

53. Contaminated Transect Elevation (m)

54. 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

55. 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