The Cape Cod National Seashore comprises part of Provincetown, Massachusetts, which lies at the northern tip of Cape Cod. The hydrologic regime in this area consists of unconsolidated sand-and-gravel deposits that constitute a highly permeable aquifer within which is a freshwater lens floating on denser sea water. A network of wells was installed into this aquifer to monitor a leachate plume emanating from the Provincetown landfill. Wells were located along orthogonal transects perpendicular to and parallel to the general groundwater flow path from the landfill to the seashore approximately 1,000 m to the southeast. Temperature, epithermal neutron, natural gamma. and electronmagnetic induction logs were obtained in five wells to depths ranging from 23 to 37 m. These logs identify the primary contamination and show that its movement is controlled by and confined within a dominant hydrostratigraphic unit about 2 to 5 m thick that exhibits low porosity, large representative grain size, and high relative permeability. A relation is also found between the temperaturegradient logs and water quality, with the gradient traces serving as effective delineators of the contaminant plume in wells nearest the landfill. Contamination is not detectable in the well nearest the seashore and farthest from the landfill, and the induction log from this well clearly identifies the freshwater/seawater transition zone at a depth of about 18 m. The geophysical logs provide fundamental information concerning the spatial distribution of aquifer properties near the landfill and lend valuable insight into how these properties influence the migration of the leachate plume to the sea.