UTILIZING SURFICIAL GEOLOGIC MAPS FOR AQUIFER DELINEATION IN MAINE

Glacially derived sand and gravel deposits are significant groundwater resources in Maine. Approximately 200 community water supplies and numerous non-community supplies in Maine utilize these aquifers, as does the water bottling industry, commercial farming, and recreational-based activities. The distribution of sand and gravel aquifers is critical to the determination of aquatic base flows in watersheds. Surficial geologic maps can provide an initial base for aquifer delineation because surficial maps show the areal distribution of glacial units that drape the underlying bedrock. Coarse-grained deposits suitable as aquifers include glacial-marine deposits (deltas, submarine outwash fans, stratified end moraines) and meltwater deposits (eskers, outwash fans, glacial-lacustrine deltas). The coarse-grained deposits can be further investigated by subsurface data such as test borings and geophysical seismic surveys to provide information about depth to bedrock, depth to water table, saturated thickness, and other characteristics of the deposit. These data define the aquifer's extent and establish whether or not it meets the definition of a significant aquifer as designated by the Maine State Legislature – one capable of yielding ten gallons per minute or more to a properly constructed well. Aquifer maps based on surficial geologic mapping may facilitate decisions regarding practices and uses that impact the groundwater resource.