Advantages of Three-Dimensional Wellhead Protection Area Delineation

Geographic Information Systems (GIS) was combined with a 3-Dimensional (3-D) computer ground water model to delineate a Wellhead Protection Area (WHPA) for the City of Owosso located in Shiawassee County, Michigan.  GIS was utilized to develop a layered conceptual model from data obtained during field investigations (drilling, aquifer test, etc.) and data (regional geologic data, mapping data, drinking water well locations, etc.) available on the internet from the State of Michigan - Center for Geographic Information and the United States Geological Survey websites.  The conceptual model layers were imported into a 3-D computer ground water modeling program to enable 3-D ground water flow simulation and particle tracking.  Ground water flow was simulated using the finite-difference ground water flow model, MODFLOW.  Particle tracking to estimate the time of travel was accomplished using the particle tracking post-processing package, MODPATH.  The result of the 3-D delineation approach and modeling demonstrate the following advantages over empirical or 2-D delineation approaches:
1)      The approach more accurately defines recharge areas, which are not necessarily the same as WHPA’s.
2)      Geologic heterogeneities and hydraulic boundaries can be more accurately represented.
3)      Well interferences and performance can be evaluated.
4)      The 10-year time of travel, defined by the Michigan Department of Environmental Quality (MDEQ) to represent the WHPA, can be more accurately estimated as some hydrogeologic settings (i.e. ground water coming from the other side of a river) cause the empirical and 2-D approaches to be wrong.
5)      Fate and transport of existing ground water contamination can be more accurately simulated.

The results show that by combining GIS with a 3-D computer ground water model, WHPA's can be more accurately delineated.