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OBJECTIVE

SPATIAL AND TEMPORAL NITRATE CONCENTRATION VARIABILITY WITHIN THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER ON SMALL SCALE AT SELECTED ARKANSAS, USA SITES.

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OBJECTIVE

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  1. SPATIAL AND TEMPORAL NITRATE CONCENTRATION VARIABILITY WITHIN THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER ON SMALL SCALE AT SELECTED ARKANSAS, USA SITES Ken Steele1, Ralph Davis1 Tim Kresse2 and Steve Boss1 1Department of Geosciences, University of Arkansas, Fayetteville 2Water Division, Arkansas Dep.t of Environmental Quality, Little Rock

  2. OBJECTIVE To ascertain spatial and temporal variability of aqueous nitrate concentrations within the alluvial aquifer at 3 sites in Arkansas.

  3. WoodruffCounty Pulaski County Monroe County ARKANSAS

  4. Shallow Monitoring wells ~ 30 feet deep Deep Wells ~ 100 feet Cypress Site – Pulaski County

  5. Cypress Site – Pulaski County

  6. Pulaski County

  7. Shallow Monitoring wells ~ 30 feet deep Deep Wells ~ 100 feet Robe Site - Monroe County

  8. Robe Site – Monroe County

  9. Monroe County

  10. Augusta Site – Woodruff County

  11. Augusta Site - Woodruff County

  12. Site Descriptions

  13. Site Descriptions

  14. POSSIBLE SCENARIOS • Recharge flushes nitrate from fertilizer • Septic effluent added during recharge • Denitrification • Oxidation changes related to recharge

  15. SCENARIO PROBLEMS • Lack of nitrate concentration relationship with: • Season (?) • Depth to water (?) • Potential flow paths do not predict nitrate contamination • “Constant” concentrations of chloride and sulfate argue against redox or septic tank effluent influence

  16. Pulaski County

  17. MonroeCounty

  18. Pulaski County

  19. Pulaski County

  20. MonroeCounty

  21. Monroe County

  22. CONCULSION “Preliminary”

  23. Conclusions It is hypothesized that the following factors may be responsible for spatial and temporal variation of nitrate concentrations: • Seasonal nitrate input, • Different lag times for nitrate transport to the wells, and • Alternating directions of ground water flow.

  24. CONCLUSION CONCLUSION • Nitrate contamination of the alluvial aquifer may be missed if sufficient spatial and temporal samples are not collected. • Optimum isoconcentration intervals for mapping require this type of data.

  25. Site Crops Soil Relief Well Depths Cypress Soybean Keo & Rilla –well drained Perry - clayey 1.1’ Shallow - 30’ Deep 80 -100’ Monroe Soybean +Rice Foley & Dundee- poorly drained 0.69’ Shallow - 30’ Deep 100-110’ Augusta Dubbs –permeable Amagon-more clay “flat” Shallow - 30’ Site Descriptions Soybean

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