Geophysical Surveys and Investigations

Geological/Geotechnical

• Geophysical Sinkhole Investigations
• Top of Rock/Void Delineation
• Top of Clay Mapping
• Hydrogeologic Evaluations
• Excavation Conditions

Environmental

• Locating Tanks and Piping
• Buried Debris/Wastes Identification
• Delineation of Boundaries for Contaminated Soils
• Groundwater Contaminant Plume Mapping
• Landfill Boundaries Determination

Projects Completed

Geophysical Services, Hernando County Landfill Site Master Plan Task 3, Brooksville, Florida

ATI Companies conducted a subsurface geophysical investigation for Brown & Caldwell, Inc., at the proposed site of future expansion of the Hernando County Landfill. The purpose of the geophysical survey was two-fold: 1) to determine depth to limestone bedrock, and 2) to determine presence of karst features. To meet the task’s objectives, ATI Companies used seismic refraction to determine the depth to the limestone bedrock and ground penetrating radar to identify near-surface karst features. The date obtained were used to direct a geotechnical subsurface investigation that followed the geophysical study and the data from both investigations were then correlated to provide a comprehensive description of subsurface conditions. ATI presented the geophysical and geotechnical data in the form of a contour map showing the depth to bedrock along with a map showing locations of suspected karst features.

Geophysical Services, Leroy Selmon Crosstown Expressway Roadway Collapse, Tampa, Florida

ATI Companies conducted a geophysical investigation for both URS Corporation and Ardaman and Associates to help determine the cause for the collapse of a supporting foundation pier which occurred during construction of the elevated Leroy Selmon Crosstown Expressway. ATI also conducted an investigation around 45 additional foundation piers where suspected karst-related geological conditions were identified. ATI used multiple geophysical technologies including ground-penetrating radar, high resolution seismic reflection, seismic crosshole shear wave testing, and seismic downhole testing. Results from the investigation indicated the collapsed pier was in the center of a suspected paleo-collapse feature that occurred at a depth range of 80 to over 250 feet below land surface. ATI found an excellent correlation between the weak soils identified in the geotechnical Standard Penetration Test borings conducted and the seismically derived-shear wave velocities.

Geophysical Services, Proposed Reclaimed Water Reservoir, Tampa, Florida

ATI Companies conducted a geological characterization study at the proposed location for construction of a reservoir intended for use to store reclaimed water. The project objectives were to assist in characterizing the subsurface hydrogeologic conditions and to identify potential sinkhole features. Special emphasis was placed on the planned location for the reservoir berm. ATI’s services included ground-penetrating radar, electrical resistivity imaging, electromagnetics, data imaging, and preparing seismic cross-section profiles and maps of subsurface features. Correlation of the geophysical data obtained with geotechnical drilling data obtained for the site allowed for extrapolation of the drilling information and identification of several features that would have been otherwise missed without these data.

Geophysical Services, South Riding Point Site, Grand Bahama Island, Bahamas

ATI Companies performed a geophysical investigation at the future location of two large petroleum storage tanks for a bulk storage facility to characterize subsurface geological features. Results from a preliminary geotechnical study performed in the 1970s indicated the presence of a near-surface weak/weathered limestone unit underlain by a more competent limestone unit and the presence of larger diameter voids in the lower limestone unit.

ATI’s study was designed to identify and map the near-surface, weathered limestone and to identify and map any large-diameter voids in the lower limestone unit. ATI conducted the study using electromagnetics ( EMS) to evaluate conditions to an approximate depth range of 45 feet below land surface and used electrical resistivity imaging to evaluate conditions to 90 feet below land surface and only in areas where anomalous EM responses were observed.

Geophysical Services, Statia Terminal New Storage Tanks Site, St. Eustatius, Netherlands Antilles

ATI Companies conducted a subsurface geological characterization survey at the Statia Terminal located in St. Eustatius, Netherlands Antilles, within an area planned for new storage tanks. The location of the proposed tanks required a portion of the site be excavated. Geophysical tests were performed to determine whether the volcanic rock (crystalline andesitic tuff) was rippable or would need to be excavated using explosives. ATI used seismic refraction to determine compressional wave velocity of the rock and develop topographic profiles showing P-wave velocities and used seismic down-hole seismic shear wave testing at several locations to determine the shear-wave velocity with depth. The seismic surveys identified only one portion of the site where velocities near the non-rippable range were present and would have to be excavated with explosives. Subsequent geotechnical drilling results confirmed the geophysical results.

Geophysical Services, US Navy Base Property, Sabana Seca, Manati County, Puerto Rico

ATI Companies conducted a geophysical subsurface survey for CDM Corporation in rough terrain and heavy vegetation on US Navy property located in Manati County, Puerto Rico. The area had become a center for major US and European-based companies and the US Navy planned to return a portion of their property to the future development. The objective of the survey was to determine if hazardous materials or other military debris were present in the subsurface prior to transfer of the property. To meet the objective, ATI used state-of-the-art geophysical technologies that included electromagnetics and magnetometry, collected the data using a differentially corrected GPS system so only minimal site clearing had to be performed prior to the survey. ATI presented the data in geo-referenced ARC View format.