IGS Miscellaneous Map: Near-surface Aquifer Sensitivity in Indiana

Status Start Date End Date Locations
completed Oct 1, 2015 Dec 31, 2016 All Counties
Director: Sally Letsinger
Other Researchers: Matthew Johnson, Kevin Russell, Deborah DeChurch
Funding: Indiana University - Indiana Geological & Water Survey
Issue: As the transport of most potential groundwater contaminants from the surface to the water table occur in the aqueous phase, recharge represents a significant control on aquifer sensitivity to contamination. In support of that idea, multiple studies have hypothesized that the key to understanding aquifer sensitivity relies on a reliable estimation of recharge.
Objective: Develop a conceptual model of the physical factors and processes that control groundwater recharge in Indiana, and devise an objective measure of recharge over the landscape. Develop a statewide assessment of aquifer sensitivity to near-surface contamination based on the relationship of recharge to migration of contaminants through the unsaturated zone.
Approach: The proportion of baseflow to runoff in stream hydrographs (n=189), determined using a local-minimums approach with a recession slope test, was used as the measure of recharge in this study. A multiple regression model was developed to spatially distribute recharge point values to continuous estimates. Partial correlation coefficients were used to identify and rank the most statistically influential (p=0.001) independent variables in the study domain, as follows: the elevation of the near-surface water table, the proportion of sand in the subsurface (as determined by lithologic logs of water-well records), and the thickness of near-surface clay. Other factors that appear to explain the spatial distribution of recharge include: the cumulative upstream area occupied by water bodies (streams, lakes, ponds), the density of wetland areas, and the cumulative upstream area occupied by forest.
Products: A map in the IGS miscellaneous map series showing the relative risk of near-surface aquifers to surface contamination in Indiana.
Benefits: A statewide aquifer sensitivity map can be used by decision makers to understand where contaminants can most easily migrate to the water table, thereby contributing to wise stewardship of our water resources.

Map of Indiana showing near-surface aquifer sensitivity