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Groundwater Vulnerability Mapping in LaGrange County, Indiana

This presentation highlights the application of hydrogeologic settings in groundwater vulnerability mapping in LaGrange County, Indiana, USA. It addresses issues like contaminated water supply and the correlation between nitrate levels and vulnerability maps using the DRASTIC method. The study emphasizes the importance of accurate hydrogeologic mapping in decision-making regarding land use and water resource protection.

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Groundwater Vulnerability Mapping in LaGrange County, Indiana

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  1. Applications of Hydrogeologic settings in Groundwater vulnerability mapping in LaGrange County, Indiana,USA Solomon A. Isiorho, PhDDept. of GeosciencesIndiana University - Purdue University Fort Wayne, IN 46805isiorho@ipfw.edu

  2. Outline of Presentation • Problems • Study area • Hydrogeologic Setting • Methods/Discussions • Conclusions

  3. Problems • More than 60% depend on Ground water (100% in the study area) • Three-dimensional detail geologic mapping…..to support informed decisions on land use, water resources development and protection, etc, is lacking • USEPA (1992)…maps did not correlate well with water quality analysis performed in the national Survey for Pesticides in Drinking Water • Increase in human population (~18% in 10 yrs (9% State wide 6.2 m)) • Contaminated potable water supply • Several methods for assessing…produce different maps

  4. Study Area North America LaGrange USA Map of Indiana

  5. LaGrange County, Indiana

  6. Hydrogeologic Setting

  7. Unconsolidated Aquifer Groundwater flow direction (after Clendon & Beaty, 1987)

  8. Groundwater flow direction (from T. Fleming, 1996)

  9. Methods • Examination of existing vulnerability map • DRASTIC • Collection of nitrate level data • Compare nitrate levels distribution with DRASTIC groundwater vulnerability map

  10. DRASTIC Depth to ground water, Recharge rate, Aquifer media, Soil media, Topography, Impact of the vadose zone and Conductivity of the aquifer (DRASTIC).

  11. Assumptions in DRASTIC The developers of DRASTIC noted that 1. Method does not replace site specific investigation 2. A measure of relative groundwater vulnerability…… one of many criteria used in decision making 3. Erroneous or inaccurate data entered may affect reliability of the results 4 Major Assumptions Uniform conditions within the subsurface environment Contamination reaches groundwater by precipitation Contaminant has the mobility of water Area of the study is greater than 100 acres

  12. DRASTICCriteria Data Source Depth to groundwater Well logs USGS and IDNR Net recharge Water resource ReportsIndiana 30 year Average Aquifer media Hydro-geologic report Soil media Soil Survey State Soils Geographic Database Topography Published Topographic mapsUSGS and IDNR Impact of vadose zone media Published Geologic reports K of an aquifer Published Hydrogeologic reports.

  13. Vulnerability Map derived from DRASTIC(from Cooper, 1996)

  14. Soil Map of LaGrange County

  15. Vulnerability MapDRASTIC map SOIL map

  16. Collection of Nitrate level Data • Survey questionnaires 400 • 800 water bottles….507 nitrate data points…Health County personnel. • Total of 1010 data points (503 from existing points) • Thirty one percent (311) high nitrate levels • But only 15% (150) are above 10ppm • 90% wells with high nitrate <15 m • Regression analysis…animal waste/depth significant with respect to nitrate level (F=-5.26, p<0.008)

  17. Nitrate Level Distribution Map(Red>10 ppm; Green =2-10ppm,Blue <2ppm; Black=0)

  18. LaGrange County showing Nitrate levels above 10ppm • Nitrate levels

  19. Comparing Nitrate levels with DRASTIC Vulnerability Map

  20. Why no perfect match between DRASTIC and Nitrate level maps?Hydrogeologic Setting/Landuse(from Summit Risk Inc)

  21. Good correlation between nitrate detect and pesticides…implication for other contaminants • (from ???)

  22. Effects of abandoned wellsand impact of other land use (After Petty, 1996)

  23. Conclusions • Hydrogeologic mapping is important in the determination of groundwater vulnerability in any given area. • Different methods yield slightly different groundwater vulnerability maps and would change with time. • Vulnerability maps produced for any area should be regarded as a working document. Future land use, including well construction and abandonment, would have great impact on such vulnerability maps.

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