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Applications of Hydrogeologic Applications of Hydrogeologic settings in Groundwater settings in Groundwater vulnerability mapping vulnerability mapping
in LaGrange County, Indiana,in LaGrange County, Indiana,USAUSA
Solomon A. Isiorho, PhDSolomon A. Isiorho, PhDDept. of GeosciencesDept. of Geosciences
Indiana University - Purdue University Indiana University - Purdue University Fort Wayne, IN 46805Fort Wayne, IN 46805
[email protected]@ipfw.edu
Outline of PresentationOutline of Presentation
ProblemsProblems
Study areaStudy area
Hydrogeologic SettingHydrogeologic Setting
Methods/DiscussionsMethods/Discussions
ConclusionsConclusions
ProblemsProblems More than 60% depend on Ground water (100% in the study More than 60% depend on Ground water (100% in the study
area)area)
Three-dimensional detail geologic mapping…..to support Three-dimensional detail geologic mapping…..to support informed decisions on land use, water resources development informed decisions on land use, water resources development and protection, etc, is lacking and protection, etc, is lacking
USEPA (1992)…maps did not correlate well with water quality USEPA (1992)…maps did not correlate well with water quality analysis performed in the national Survey for Pesticides in analysis performed in the national Survey for Pesticides in Drinking WaterDrinking Water
Increase in human population Increase in human population (~18% in 10 yrs (9% State wide (~18% in 10 yrs (9% State wide 6.2 m6.2 m))))
Contaminated potable water supplyContaminated potable water supply
Several methods for assessing…produce different mapsSeveral methods for assessing…produce different maps
Study AreaStudy Area
LaGrange
Map of IndianaUSAUSA
North AmericaNorth America
LaGrange County, IndianaLaGrange County, Indiana
Hydrogeologic SettingHydrogeologic Setting
Unconsolidated Aquifer Unconsolidated Aquifer Groundwater flow directionGroundwater flow direction
(after Clendon & Beaty, 1987)
Groundwater flow directionGroundwater flow direction
(from T. Fleming, 1996)
MethodsMethods
Examination of existing vulnerability mapExamination of existing vulnerability mapDRASTICDRASTIC
Collection of nitrate level dataCollection of nitrate level data
Compare nitrate levels distribution with Compare nitrate levels distribution with DRASTIC groundwater vulnerability mapDRASTIC groundwater vulnerability map
DRASTICDRASTIC
DDepth to ground water, epth to ground water,
RRecharge rate, echarge rate,
AAquifer media, quifer media,
SSoil media, oil media,
TTopography, opography,
IImpact of the vadose zone and mpact of the vadose zone and
CConductivity of the aquifer (DRASTIC). onductivity of the aquifer (DRASTIC).
Assumptions in DRASTIC Assumptions in DRASTIC The developers of DRASTIC noted thatThe developers of DRASTIC noted that
1. Method does not replace site specific investigation1. Method does not replace site specific investigation
2. A measure of 2. A measure of relativerelative groundwater vulnerability…… groundwater vulnerability…… one of many criteria used in decision making one of many criteria used in decision making
3. Erroneous or inaccurate data entered may affect reliability of the results3. Erroneous or inaccurate data entered may affect reliability of the results
4 Major Assumptions4 Major Assumptions
Uniform conditions within the subsurface environmentUniform conditions within the subsurface environment
Contamination reaches groundwater by precipitationContamination reaches groundwater by precipitation
Contaminant has the mobility of waterContaminant has the mobility of water
Area of the study is greater than 100 acresArea of the study is greater than 100 acres
DRASTICDRASTIC CCriteria Data Sourceriteria Data Source
Depth to groundwaterDepth to groundwater Well logs Well logs USGS and IDNRUSGS and IDNR
Net recharge Net recharge Water resource ReportsWater resource Reports Indiana 30 year Indiana 30 year AverageAverage
Aquifer media Aquifer media Hydro-geologic reportHydro-geologic report
Soil media Soil media Soil Survey Soil Survey State Soils Geographic DatabaseState Soils Geographic Database
Topography Topography Published Topographic mapsPublished Topographic maps USGS and USGS and
IDNRIDNR
Impact of vadose zone media Impact of vadose zone media Published Geologic reportsPublished Geologic reports
K of an aquifer K of an aquifer Published Hydrogeologic reports. Published Hydrogeologic reports.
Vulnerability Map derived from DRASTICVulnerability Map derived from DRASTIC(from Cooper, 1996)(from Cooper, 1996)
Soil Map of LaGrange CountySoil Map of LaGrange County
Vulnerability MapVulnerability MapDRASTIC map SOIL map DRASTIC map SOIL map
Collection of Nitrate level DataCollection of Nitrate level Data Survey questionnaires 400Survey questionnaires 400
800 water bottles….507 nitrate data points…Health County 800 water bottles….507 nitrate data points…Health County personnel.personnel.
Total of 1010 data points Total of 1010 data points (503 from existing points)(503 from existing points)
Thirty one percent (311) high nitrate levelsThirty one percent (311) high nitrate levels
But only 15% (150) are above 10ppmBut only 15% (150) are above 10ppm
90% wells with high nitrate <15 m90% wells with high nitrate <15 m
Regression analysis…animal waste/depth significant with respect to Regression analysis…animal waste/depth significant with respect to nitrate level (F=-5.26, p<0.008)nitrate level (F=-5.26, p<0.008)
Nitrate Level Distribution MapNitrate Level Distribution Map(Red>10 ppm; Green =2-10ppm,Blue <2ppm; Black=0)(Red>10 ppm; Green =2-10ppm,Blue <2ppm; Black=0)
LaGrange County LaGrange County
showing Nitrate levels showing Nitrate levels
above 10ppmabove 10ppm
Nitrate levelsNitrate levels
Comparing Nitrate levels with DRASTIC Vulnerability MapComparing Nitrate levels with DRASTIC Vulnerability Map
Why no perfect match between DRASTIC and Why no perfect match between DRASTIC and Nitrate level maps?Nitrate level maps?
Hydrogeologic Setting/LanduseHydrogeologic Setting/Landuse(from Summit Risk Inc)(from Summit Risk Inc)
Good correlation between nitrate detect and pesticides…Good correlation between nitrate detect and pesticides…implication for other contaminantsimplication for other contaminants
(from ???)(from ???)
Effects of abandoned wellsEffects of abandoned wells and impact of other land useand impact of other land use
(After Petty, 1996)
ConclusionsConclusions
Hydrogeologic mapping is important in the determination Hydrogeologic mapping is important in the determination of groundwater vulnerability in any given area. of groundwater vulnerability in any given area.
Different methods yield slightly different groundwater Different methods yield slightly different groundwater vulnerability maps and would change with time. vulnerability maps and would change with time.
Vulnerability maps produced for any area should be Vulnerability maps produced for any area should be regarded as a working document. Future land use, regarded as a working document. Future land use, including well construction and abandonment, would including well construction and abandonment, would have great impact on such vulnerability maps.have great impact on such vulnerability maps.