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

isiorho@ipfw.eduisiorho@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.