Modernization of Groundwater Protection Area (Zone II) Delineations: A Case Study

The Zone II of an aquifer is defined as the area of the aquifer that contributes water to a well under the most severe pumping and recharge conditions. The Massachusetts Division of Water Supply (DWS) definition of the most severe conditions is a groundwater-supply well pumping at its designed safe yield for 180 days in the absence of recharge from precipitation. Since the mid-1980s, the Massachusetts Department of Environmental Protection (DEP) has identified or approved wellhead protection areas (WHPAs) for public groundwater resources, one of which is Zone II. The delineation of Zone II and other WHPAs included conceptual desktop studies, meaning that the boundaries were drawn using topography, historic geologic mapping, and simplified analytical calculations. Conceptual Zone II delineations often resulted in little or no consideration to the position of the water table relative to the stratigraphy of the basin in question. In this study, we incorporate a more rigorous and integrated field and numerical modeling approach to Zone II delineation. This modernization decreases uncertainty and provides a more defensible hydrologic interpretation of an aquifer’s response to stress. We use data and software in the public domain to supplement the integrated approach, including the Massachusetts’ Sustainable Yield Estimator (SYE), which calculates daily upstream and downstream flows of a watershed using a referenced, gauged basin. The results illustrate the importance of more rigorously evaluating the saturated thickness of aquifer materials during Zone II delineation. The framework offered by this case study presents a model to develop cost-effective and technically defensible modernization of existing conceptual Zone IIs.