The Use Of Ground Penetrating Radar To Evaluate The Location And Formation Of Sinkholes Associated With A Retention Pond

Abstract

Development and construction over karst often leads to unintended results. In this case study, a retention pond was built in a new subdivision to capture surface runoff and add appeal for potential homeowners. However, water never rose to the proposed level and has drained suddenly and frequently since construction in the year 2000. The failure of the retention pond to perform as designed is due to the presence of carbonate bedrock beneath the site. The bedrock, the Prairie du Chien dolomite, is highly weathered and prone to many relatively small sinkholes. Geophysical surveys were proposed to evaluate the subsurface conditions and to determine the extent of sinkholes below the pond shorelines in an attempt to propose engineering solutions to the problem. Four geophysical surveys were performed: ground penetrating radar (GPR), seismic reflection and refraction, electromagnetics (EM), and subbottom profiling. Although all methods provided subsurface information, the GPR surveys were most useful to site characterization. The GPR surveys show evidence of severely disturbed soil in the subsurface that is associated with sinkhole formation. These surveys help delineate the areas around the retention pond that may produce additional sinkholes and failure and will help to focus remediation efforts.