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Isotope Investigations in Wellhead Protection Areas

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  1. Isotope Investigations in Wellhead Protection Areas Jim Walsh MDH

  2. Isotopes Can Tell Us • How old is it? • Where did it come from?

  3. Precipitation and Groundwater from Direct Infiltration Plot on Meteoric Water Line Krabenhoft, 1990

  4. Mass-balance approach to mixing

  5. Steps in Wellhead Protection Wells In Need of Protection

  6. Develop Conceptual Model

  7. Develop and Calibrate Flow Model

  8. Delineate Wellhead Protection Area

  9. Delineate DWSMA

  10. Assess Vulnerability Low High

  11. Inventory and Manage Contaminant Sources Low High

  12. Isotope Techniques Apply To: • Conceptual model development • Model calibration/validation • Vulnerability assessments

  13. It’s A Protected Aquifer, So I Don’t Need To Worry About Surface Water. Right ?

  14. Elevation (Ft. Above Sea Level) Tritium = 18-39 TU Clay-Rich Till Sand and Gravel

  15. ~70% lake water ~10 – 20% lake water

  16. High

  17. The Case of The Likely Lake • Shallow Buried Drift Aquifer • CFC Recharge Age of 15-25 years

  18. Do I Need To Worry About That River 200 Feet Away ?

  19. 15-60% River Water At Wells Located Within 250’ 100’ 250’ 1,200’ Delta18O (per mil) Date

  20. Low High

  21. Little Geologic Cover • Nitrate and Pesticide Contamination OPDC CSLF CJDN

  22. Delta18O (per mil) Date

  23. How About Those Mine Pits? Dewatered Taconite Pits Keewatin, 1996

  24. Keewatin Isotope Results, February, 1996

  25. Keewatin Isotope Results, February, 1996

  26. Keewatin, 2001

  27. Keewatin Trends

  28. Keewatin Wellhead Protection Area With Mesabi Chief Pit Dewatered

  29. Proposed Wellhead Protection Area With Pits Filled

  30. A Tale of Two Wells

  31. Till

  32. Differing Isotope Signatures • Also Differing: • Tritium Results • Water Chemistry (Chloride)

  33. Well Construction Problems ?

  34. TC Positive • Tritium = 11.6 TU Well Casing Uncased Borehole

  35. Well Casing • TC Negative • Tritium = 6.3 TU Uncased Borehole

  36. Isotopes Are Your Friends For: • Conceptual model development • Model calibration/validation • Vulnerability assessments • Well construction investigations

  37. Thick Unsaturated Zones Peat Till Minnesota River