A suite of reflection seismology investigations of the shallow subsurface was conducted at Hill Air Force Base, Ogden, Utah, at a groundwater contamination site with very large subsurface mechanical heterogeneity. The investigations were designed to expand and improve understanding of the subsurface environment developed from well data and previous seismic investigations. The goal of the investigations was to image the sides and bottom of a paleochannel eroded in a clay layer below the surface. The paleochannel is filled with a mix of sands, clays, and gravels of different compaction and water saturation. The paleochannel acts as a contaminant trap for dense nonaqueous-phase liquids (DNAPLs). Therefore, a detailed map of its geometry, lateral boundaries, and depth is crucial to remediation efforts. The results of processing a 3D reflection data set over the channel showed that it is possible to image and delineate the geometry and depth of a very shallow structure. Seismic results agreed well with the available well data in the deepest part of the buried paleochannel. The map of the channel derived from seismic data replaces the need for many wells.