SURFICIAL GEOLOGIC MAPS AS A BASIS FOR AQUIFER DELINEATION IN MAINE

Sand and gravel deposits of glacial origin are significant groundwater resources in Maine. Nearly 200 community water supplies and numerous non-community supplies in Maine are served by sand and gravel deposits. Water bottlers and agricultural irrigators also rely heavily on this resource. Unconsolidated aquifers of this nature are more vulnerable to contamination by surface activities which, therefore, are strictly regulated. Furthermore, the distribution of sand and gravel aquifers is significant to the determination of aquatic base flows in watersheds. Surficial geologic maps provide the starting point for aquifer delineation. The surficial maps show the distribution of Pleistocene units of glacial origin that drape the solid bedrock. Coarse-grained deposits suitable as aquifers include glacial-marine deposits (deltas, submarine outwash fans) and meltwater deposits (eskers, outwash fans, kames). These coarse-grained deposits are further investigated to establish whether or not they meet the definition of a significant aquifer – one that can provide 10 gallons per minute or more to a well. Subsurface information in the form of test borings and geophysical seismic surveys provide information about depth to bedrock, depth to water table, and other characteristics of the deposit which further define the extent of the aquifer. Aquifer maps based on surficial mapping are used to facilitate decisions regarding practices and uses that impact the groundwater resource.