Soil and groundwater at an active dry cleaning facility located in Tallahassee, Florida have been impacted with dry cleaning solvents, primarily tetrachloroethylene (PCE). The facility is undergoing remediation under the Florida Department of Environmental Protection (FDEP) Dry Cleaning Solvent Cleanup Program.
As a part of the site assessment and remedial activities, soil borings, groundwater monitoring wells, and vapor extraction wells were completed near and in the vicinity of the building. In July 2010, two vapor extraction wells were installed about 15 feet from a building at an angle of 50 degrees to the horizontal using rotosonic drilling technique. The angled wells went underneath the building and were estimated to be 18 feet below the wall of the building. In June 2011, a crack approximately inch wide on the wall of the building was reported. Several other small cracks were observed on the building. The owner of the building expressed concerns that the July 2010 rotosonic drilling was the cause of the cracks and wanted assurance that subsequent drillings would not exacerbate the problem.Geotechnical forensic investigation was performed to evaluate the potential cause(s) of cracking in the building and whether future drilling would impact the building and the foundation structure system. Site reconnaissance surveys were performed to identify potential movements of the building and occurrence of other distresses. Site topography, site drainage and weather patterns for the locality were evaluated. Site-specific field investigations, including Standard Penetration Test (SPT) soil borings and real-time vibration monitoring during SPT borings were performed. In addition, crack monitoring devices were installed on the cracked sections of the wall to monitor the propagation of the cracks over time. Geotechnical laboratory analyses, including index properties and compressibility (consolidation and swell) tests, were performed on undisturbed Shelby-tube and select split-spoon samples obtained during field investigations. The results of the investigations indicated that the presence of highly expansive soils (fat clays) in the subsurface soils, differential settlement or heave and effects of poor drainage and root penetration were the likely cause(s) for the development of cracks in the building.The results from the forensic investigation including geotechnical site investigations, real-time vibration monitoring, and crack monitoring are discussed. Based on these results, potential causes for the development of cracks in the wall of the building and recommended repair measures are discussed.