Karst is a type of landscape that is formed by the dissolution of soluble rocks, including limestone. Common geological characteristics of karst regions that influence human use of its land and water resources include ground subsidence, sinkhole collapse, groundwater contamination, and unpredictable water supply.  Mapping these subsurface features can provide crucial information for potential sinkhole formation, contamination conduits, stormwater infiltration plans, and rock removal projects. 

            Recently Delta Geophysics Inc. has completed several geophysical investigations for various Karst related issues.  Geo-electrical geophysical techniques have been widely used to study Karst formations, but these techniques can be affected by cultural noise in urban areas.  This investigation addresses the use of the Multi-channel Analysis of Surface waves (MASW) technique to study areas of limestone dissolution in urban areas covered with asphalt and concrete and shows to be a good tool in areas with suspected dissolution. Here at Delta we have accomplished several successful investigations in known karst formations with the MASW technique.  Below is a description of a project completed by Delta Geophysics using MASW in a karst terrain.

            For this project Delta characterized the regolith and the underlying limestone bedrock.  The project area was a 15-acre Site consisting of a mixture of blacktop pavement and natural or landscaped terrain. The project was initiated after numerous test borings and wells failed to adequately define migration pathways. The objective was to map fractures and bedrock/soil irregularities that were potential conduits for migrating contaminants. Depth to bedrock was very variant throughout the site.  Drilling depth to bedrock ranged from 5-70 feet below ground surface.  Delta was asked to provide more detailed information around the site to map the variations of the bedrock.  Over 12,000 linear feet of MASW survey was conducted on this site in one week.  Data from the site was processed by sophisticated processing software and mapping programs for detailed interpretation.  Drilling operations could only provide snapshots of the depth to bedrock.  Using MASW Delta was able to map large areas in a short amount of time from the surface with no intrusive testing.  The survey results were mapped and presented to our client after several days of processing.  Results of the survey matched closely with drilling operations.  Below is several cross-sections with labeled features from the project.