Integrated Geophysical Characterization Of The Winthrop Landfill Southern Flow Path, Winthrop, Maine

Abstract

The U.S. Geological Survey (USGS), in cooperation with United Technologies Corporation,<br>used an integrated suite of borehole, surface, and water-borne geophysical methods near the site of the<br>former Winthrop Landfill, Winthrop, Maine, to investigate the hydrogeology controlling the transport of<br>leachate from the landfill to nearby Annabessacook Lake. During the fall of 2000 and summer of 2001,<br>the USGS conducted borehole electromagnetic (EM) induction and gamma logging, and inductive<br>terrain-conductivity, two-dimensional (2D) resistivity, continuous seismic reflection, and magnetic<br>surveys.<br>The objectives of this integrated geophysical study were to provide constraints on the location<br>and extent of the southern flow path(s) of contamination from the landfill to the lake; identify shoreline<br>seep geophysical signatures; identify potentially hidden seeps in the lake; and determine depth to<br>bedrock below Annabessacook Lake in the study area.<br>Interpretation of surface 2D resistivity, magnetic, and inductive terrain-conductivity data and<br>borehole EM logs delineates an electrically conductive anomaly consistent with a leachate plume<br>moving from the current landfill boundary southward through the overburden to the shores of<br>Annabessacook Lake. Surface and borehole geophysical data collected south and southeast of the<br>landfill indicate the presence of discrete, shallow conductive anomalies at the southeastern edge of the<br>landfill and near the lakeshore. The conductive anomalies appear at increasing depths closer to the lake.<br>Magnetic anomalies offshore confirm the presence of iron-rich landfill leachate discharging into the lake<br>south of the landfill. High-resolution swept-frequency seismic data used to map sediment and grain size<br>distribution in the lake sub-bottom along the shoreline identified sediment-infilled bedrock lows that<br>may act as conduits for contaminant migration.