Wellhead Protection Area Delineation for a Small Community in a Buried Valley Setting Near Waynesville, Ohio

Dakin Estates, a small community located approximately 1.5 miles south of Waynesville, Ohio, obtains its drinking water from the Little Miami River (LMR) buried valley aquifer. The aquifer is composed of permeable sands and gravels overlain by a laterally continuous, clay-rich confining unit. While present water demand is easily satisfied by the aquifer, its inherent potential for contamination poses a serious threat to the community. Recognizing the detrimental effects of water pollution, the owner of Dakin Estates has elected to implement a Wellhead Protection (WHP) Program. The WHP program is designed to protect the drinking water of communities dependent upon groundwater. Hydrogeologic data was obtained from maps, well logs, previous and similar studies, outcrops, pump tests, and monitoring of groundwater and surface water levels. These data were used to formulate a conceptual model that was tested with a numerical flow model using the United States Geological Survey's (USGS) MODFLOW, a modular, finite-difference, groundwater flow model. Because LMR exerts a strong influence on groundwater levels in the vicinity of Dakin Estates, model calibration was based on fluctuation of groundwater levels corresponding to change in river stage. Water chemistry analyses were performed using the USGS PHREEQC aqueous geochemical mixing model. The geochemical results provide an independent assessment of the validity of the conceptual and numerical models. MODPATH, an advective transport particle-tracking model, was used to delineate the area contributing water to the pumping well for a specified time period. The results of this study indicate the Wellhead Protection Area (WHPA) extends upgradient, roughly paralleling the strike of the valley, without encountering significant flow boundaries. Results of the geochemical analyses suggest significant interaction between groundwater and surface waters is occurring, likely upstream from the WHPA. The water obtained by Dakin Estates is a mixture of underflow from upstream, infiltration of surface water, and aerial recharge. Predictive simulations indicate the aquifer is capable of yielding projected increase of future demand.