Applications of Hydrogeologic settings in Groundwater vulnerability mapping in LaGrange County, Indiana, USA Solomon A. Isiorho, PhD Dept. of Geosciences Indiana University - Purdue University Fort Wayne, IN

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

Problems More than 60% depend on Ground water (100% in the study area) 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 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 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 )) Increase in human population (~18% in 10 yrs (9% State wide 6.2 m )) Contaminated potable water supply Contaminated potable water supply Several methods for assessing…produce different maps Several methods for assessing…produce different maps

Study Area LaGrange Map of Indiana USA North America

LaGrange County, Indiana

Hydrogeologic Setting

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

Groundwater flow direction (from T. Fleming, 1996)

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

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

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

DRASTIC Criteria Data Source DRASTIC Criteria Data Source Depth to groundwaterWell logs USGS and IDNR Net recharge Water resource Reports Indiana 30 year Average Aquifer media Hydro-geologic report Soil media Soil Survey State Soils Geographic Database Topography Published Topographic maps USGS and IDNR Impact of vadose zone media Published Geologic reports K of an aquifer Published Hydrogeologic reports.

Vulnerability Map derived from DRASTIC (from Cooper, 1996)

Soil Map of LaGrange County

Vulnerability Map DRASTIC map SOIL map

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

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

LaGrange County showing Nitrate levels above 10ppm LaGrange County showing Nitrate levels above 10ppm Nitrate levels Nitrate levels

Comparing Nitrate levels with DRASTIC Vulnerability Map

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

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

Effects of abandoned wells and impact of other land use (After Petty, 1996)

Conclusions Hydrogeologic mapping is important in the determination of groundwater vulnerability in any given area. 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. 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. 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.