Geophysical Monitoring Through a Tidal Cycle at Crescent Beach State Park, Maine

This paper presents results of an experiment in which data from a combination of geophysical methods (resistivity, induced polarization, electromagnetic profiling, and magnetic profiling) were used to identify shallow geologic and hydrogeologic structure, and to enhance understanding of groundwater flow in a dynamic beach environment. Based on this study, well sorted beach sand is underlain by laterally variable glacial till, which overlies bedrock. An extensive patch of glacial till was mapped toward the ocean side of the beach. Bedrock has lithologic variability, as evidenced by a non-uniform magnetic response. In particular, a northeast-southwest trending magnetic body, believed to be a basalt dyke, was detected by its magnetic signature. During the transgressive phase of the tidal cycle, saline groundwater flow appeared to be quite rapid, extending ahead of the surfical water by at least 4m, as evidenced by the electromagnetic response. During the regressive phase, a slug of saline water remained up b...