Sally Letsinger
Geological Research at the IGS

Relating groundwater recharge to near-surface aquifer sensitivity in Indiana

Status Start Date End Date Locations
completed May 23, 2012 Jun 30, 2015 All Counties
Director: Sally Letsinger
Other Researchers:
Funding: Indiana Department of Environmental Management (IDEM)
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: Using estimated groundwater recharge rates, as well as additional relevant data, a derivative aquifer sensitivity layer will be developed showing the relative risk of groundwater contamination owing to geologic materials and distribution in Indiana. A GIS data layer and metadata documentation for unconsolidated aquifer sensitivity for Indiana will be the final product for this portion of the project.
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.
Publications:

Spatially distributed regional recharge-rate estimation to guide an aquifer-sensitivity assessment for mid-continental glacial environments, USA
Letsinger, S.L., 2014, Spatially distributed regional recharge-rate estimation to guide an aquifer-sensitivity assessment for mid-continental glacial environments, USA [Abs.], Geological Society of America Abstracts with Programs Vol. 46, No. 6.

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