Electrical Imaging of Landfill Bedrock

Concerns were expressed about underlying bedrock conditions affecting settlement for a proposed expansion cell at a municipal waste landfill in the Southeastern United States. Drastic variability of weathering in this region leads to the formation of pinnacles of rock surrounded by a thick, highly plastic clay soil profile. THG was contracted to identify and delineate the location of bedrock pinnacles and deep soil profiles within the footprint of the proposed expansion cell.

THG designed an electrical resistivity imaging (EI) survey to image the 21-acre property. A series of parallel 2-D EI profiles were collected across the site, spaced 20-30 feet apart. Each profile was acquired using an electrode configuration that acquired high resolution data to a depth of approximately 60 feet along the length of the line (90 m-350 m).  A wide range of resistivity values were measured in the study area and were representative of a variable bedrock profile with shallow, pinnacle features and detached bedrock blocks throughout the site.  Depth to competent bedrock was determined as well as the placement of pinnacles and detached bedrock blocks.