Development of a Regional Groundwater Flow Model for Source Water Protection Area Delineation, Great Miami Buried Valley Aquifer, Southwest Ohio

The Great Miami Buried Valley Aquifer (GMBVA) is a designated sole source aquifer that supplies water to 300,000 residents and thousands of businesses in Butler and Hamilton Counties, Ohio.  Total pumping withdrawals from the aquifer exceed 100 million gallons per day (Mgpd) during peak demand, and are projected to exceed 120 Mgpd in the next ten years.  Despite over 50 years of pumping, groundwater levels in the GMBVA have remained nearly static. The aquifer remains productive due to its high hydraulic conductivity, large saturated thickness, and its capacity for recharge from both precipitation and surface water infiltration.  Unfortunately, these characteristics also make the aquifer vulnerable to contamination. 

To protect the aquifer resource, several municipalities and private companies have formed a groundwater consortium (Consortium).  Eight major well fields are operated by the Consortium members.  One of the Consortium’s strategies for protecting the GMBVA has been to develop Source Water Protection Areas (SWPA) for its pumping well fields in accordance with the Safe Drinking Water Act.  This has been accomplished using three-dimensional numerical modeling and particle tracking. 

The Consortium recently teamed with URS Corporation to develop a basin-scale model of the aquifer to improve their SWPA delineations.  The model was developed in MODFLOW using hydrogeologic data from boring logs, monitoring wells, stream gages, low-head dams, and a riverbed conductance study.  The model was calibrated to baseflow conditions measured in September 2007.  Projected pumping rates anticipated over the next ten years were applied in the predictive model, and reverse particle tracking techniques were used to delineate one, five, and ten year SWPAs for the well fields.  The results were used to update previously-defined SWPA zones, thus enabling the Consortium to focus aquifer protection efforts in the most sensitive areas of the watershed.