MINNESOTA GEOLOGICAL SURVEY INFORMATION CIRCULAR 36 RADIUM IN THE MT. SIMON-HINCKLEY AQUIFER, EAST-CENTRAL AND SOUTHEASTERN MINNESOTA UNIVERSITY OF MINNESOTA Minnesota Geological Survey Priscilla C. Grew I Director INFORMATION CIRCULAR 36 RADIUM IN THE MT. SIMON-HINCKLEY AQUIFER, EAST-CENTRAL AND SOUTHEASTERN MINNESOTA By Richard S. Lively, Roy Jameson, E.C. Alexander, Jr., and G.B. Morey This project was supported by the Minnesota Department of Natural Resources, Division of Waters University of Minnesota St. Paul, 1992 ISSN 0544-3105 The University of Minnesota is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation. CONTENTS Page Introduction .................................................................................................................................... 1 Geologic setting............................................................................................................................... 1 Hydrologic setting .......................................................................................................................... 8 Methodology .................................................................................................................................. 8 Results ............................................................................................................................................ 9 Radium distribution ...................................................................................................................... 34 Discussion ..................................................................................................................................... 35 Conclusions ................................................................................................................................... 36 References cited ............................................................................................................................ 38 Appendix-Sampling and analytic procedures ............................................................................... 57 ILLUSTRATIONS Figure 1. Map showing sample locations .......................................................................................... 2 2. Basement tectonic and structure map ................................................................................. 4 3. Paleozoic tectonic and structure map .................................................................................. 5 4. West-east Paleozoic basin cross section .............................................................................. 6 5. North-south Paleozoic basin cross section .......................................................................... 7 6. Graphic column based on core from St. Paul ...................................................................... 16 7. Graphic column based on core from northern Waseca county .............................................. 17 8. Enrichment diagram of selected trace elements in the Mt. Simon Sandstone....................... 19 9. Enrichment diagram of selected trace elements in the Jordan Sandstone ............................ 19 10. Piper diagram summarizing cation and anion chemistry for the Mt. Simon-Hinckley water samples ................................................................................ 33 11. Piper diagram summarizing cation and anion chemistry for the Jordan water samples ....... 33 12. Map showing distribution of calcium in the Mt. Simon-Hinckley well water..................... 40 13. Map showing distribution of magnesium in the Mt. Simon-Hinckley well water................ 41 14. Map showing distribution of bicarbonate in the Mt. Simon-Hinckley well water............... 42 15. Map showing distribution of sulfate in the Mt. Simon-Hinckley well water...................... 43 16. Map showing distribution of chloride in the Mt. Simon-Hinckley well water ................... 44 17. Map showing distribution of uranium in the Mt. Simon-Hinckley well water .................... 45 18. Map showing distribution of 234U/238U activity ratios in the Mt. Simon-Hinckley well water ..................................................................................................................... 46 19. Map showing distribution of radiocarbon age groups within the Mt. Simon-Hinckley well water ..................................................................................................................... 47 20. Map showing distribution of total radium in the Mt. Simon-Hinckley well water ............. 48 21. Map showing distribution of 226Ra in the Mt. Simon-Hinckley well water ........................ 49 22. Map showing distribution of 228Ra in the Mt. Simon-Hinckley well water ........................ 50 23. Map showing distribution of total radium in the Jordan well water .................................. 51 24. Histograms showing the frequency distribution of 228Ra and 226Ra in the Mt. Simon-Hinckley well water ........................................................................................... 52 25. Scatter plot of the 228Ra activity versus the 226Ra activity and a histogram showing the frequency distribution of the 228Ra/226Ra activity ratio in the Mt. Simon-Hinckley water ................................................................................... 52 26. Map showing distribution of the 228Ra/226Ra activity ratios subdivided into ratios <2.0 and >2.0 ................................................................................................. 53 27. Scatter plots showing the relationship of 228Ra and 226Ra to bicarbonate concentrations ............................................................................................. 54 28. Scatter plots showing the relationship of 228Ra and 226Ra to sulfate concentrations........... 54 iii 29. Scatter plots showing the relationship of 228Ra and 226Ra to chloride concentrations ........ 55 30. Scatter plots showing the relationship of 228Ra and 226Ra to iron concentrations ............... 55 TABLES Table 1. Analyses of Mt. Simon Sandstone core from the ATES BC-l well in St. Paul.. ..................... 10 2. Analyses of Mt. Simon Sandstone core from the Vermillion 66-9 well ................................ 11 3. Analyses of Mt. Simon Sandstone from the Northern Natural Gas test well 14 (NNG-337) ......................................................................................................... 12 4. Analyses of Mt. Simon Sandstone from Minnegasco Well W-4 ........................................... 13 5. Analysis of Mt. Simon Sandstone from Pan Ocean SQ-8 ..................................................... 14 6. Analyses of Jordan Sandstone rock samples ...................................................................... 15 7. Analyses of water from the Mt. Simon-Hinckley aquifer .................................................. 20 8. Analyses of water from the Jordan aquifer ....................................................................... 29 9. Trace-element analyses of water from selected Mt. Simon-Hinckley wells ........................ 30 IV INTRODUCTION Studies conducted in the 1960s showed that radium was a fairly common constituent in ground water throughout much of the Midwest. Concentrations of 226Ra ranging from 1 to 80 pCi/L (picoCuries per liter) were found in northern illinois, Iowa, and eastern Wisconsin (Rowland and others, 1977). The high radium values were associated with water from deep sandstone aquifers of Cambro-Ordovician age, but not with aquifers above or below. Additional studies and reports of radium in the Cambro­ Ordovician aquifers by Gilkeson and Cowart (1982, 1987), Hahn (1984), and Weaver and Bahr (1991) further delineated distribution patterns and have suggested sources for the observed concentrations. Radium is a naturally occurring radioactive element, formed by radioactive decay of uranium and thorium. The most abundant radium isotope, 226Ra, has a half-life of 1600 years and is part of the 238U decay series. Two other isotopes, 228Ra (half-life = 5.76 years) and 224Ra (half-life = 3.7 days), are part of the 232Th decay series. In 1976, the U.S. Environmental Protection Agency published regulations that established contaminant levels for radioactivity and radioactive nuclides in public water systems. The maximum contaminant level (MCL) for gross alpha activity was not to exceed 15 pCi/L and the combined 226Ra and 228Ra activity in the water was not to exceed 5 pCi/L (Federal Register, 1976). The U.S. Environmental Protection Agency is reviewing the contaminant levels for radioactive nuclides in drinking water. Testing of public water supplies by the Minnesota Department of Health showed that many communities in the southern half of Minnesota were not in compliance with the drinking water standards for radium. Sampling of some municipal wells indicated that high radium levels were chiefly associated with water from the Mt. Simon-Hinckley aquifer, a sandstone aquifer of Late Cambrian/Middle Proterozoic age. A few wells in the Jordan Sandstone of Late Cambrian age also showed elevated radium levels. Because these data were obtained from municipal wells in communities with known radium problems, it was difficult to detect a pattern or to isolate specific radium-producing horizons within the aquifer(s).