RECENT ADVANCES IN GROUNDWATER FLOW MODELING FOR WELLHEAD PROTECTION IN MINNESOTA

As the lead agency for the Wellhead Protection Program in Minnesota, the Minnesota Department of Health has been engaged in groundwater flow modeling for the past 30-years. Recent developments include a shift from local-scale models based primarily on analytic element methods to regional-scale models built in MODFLOW NWT/USG/6, and a standardized approach to uncertainty analysis of well capture zones using Monte Carlo methods in PEST. The shift to regional-scale modeling has been driven by the water resources planning framework in Minnesota, which is based largely on watersheds, and the move to MODFLOW is to create a unified, standardized set of interlocking models that can be used both for wellhead protection area delineations and broader aquifer protection efforts. The shift to a Monte Carlo approach for capture zone uncertainty analysis is driven by a goal of standardizing uncertainty analysis within the MODFLOW and MODPATH framework, enabled by enhanced flexibility in code development and modification that automates the process and creates a standard set of outputs.