1. Isotope Investigations in Wellhead Protection Areas Jim Walsh MDH

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

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

5. Mass-balance approach to mixing

6. Wells In Need of Protection Steps in Wellhead Protection

7. Develop Conceptual Model

8. Develop and Calibrate Flow Model

9. Delineate Wellhead Protection Area

10. Delineate DWSMA

11. Assess Vulnerability Low High

12. Low High Inventory and Manage Contaminant Sources

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

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

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

17. ~10 – 20% lake water ~70% lake water

19. High

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

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

26. Delta 18 O (per mil) Date 100’ 250’ 1,200’ 15-60% River Water At Wells Located Within 250’

29. Low High

30. OPDC CJDN CSLF Little Geologic Cover Nitrate and Pesticide Contamination

32. Delta 18 O (per mil) Date

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

34. Keewatin Isotope Results, February, 1996

37. Keewatin, 2001

38. Keewatin Trends

39. Keewatin Wellhead Protection Area With Mesabi Chief Pit Dewatered

40. Proposed Wellhead Protection Area With Pits Filled

41. A Tale of Two Wells

42. Till

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

44. Well Construction Problems ?

45. Well Casing Uncased Borehole TC Positive Tritium = 11.6 TU

47. Well Casing Uncased Borehole TC Negative Tritium = 6.3 TU

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

50. Till Peat Thick Unsaturated Zones Minnesota River

51. Thick Unsaturated Zones 1.1 Tritium Units

52. Thick Unsaturated Zones

54. g

55. Krabenhoft, 1990

56. USGS

59. Age of Water Useful Tracers Years or lessYears or less Years to a century A century to 30,000 years Artificial Tracers, CFC, Tritium-Helium, Tritium Tritium, CFC, Tritium- Helium, Chemistry Carbon-14 and Chemistry

61. Tritium in Precipitation Ottawa, Canada (IAEA)

62. Groundwater Age Classification Recent Water = 3H > 10 TURecent Water = 3H > 10 TU –water entered the ground since late 1950’s Mixed Water = 3H between 1 and 10 TUMixed Water = 3H between 1 and 10 TU – probably a mixture of recent and vintage Vintage Water = 3H < 1 TU Vintage Water = 3H < 1 TU – water entered the ground before 1953 Source = ECA Jr., 1995

63. Confining Unit

64. .. Simple Capture Zone Conjunctive Delineation Surface Watershed