Pyramid Geophysical Services conducted a geophysical investigation across a project site that contained buried waste and exhibited the potential to contain buried infrastructure such as former foundations. Our client wanted to delineate the lateral extent and depths of any buried waste and locate any former foundations that may prove problematic for construction purposes. Multiple electromagnetic instruments, in conjunction with ground penetrating radar (GPR), were used to investigate the project area. Specifically, Pyramid utilized a Geonics EM61-MK2 metal detection instrument, a Geonics EM31-MK2 conductivity meter, and a GSSI UtilityScan DF GPR unit with a dual frequency 300/800 MHz antenna. A variety of waste, metallic debris, and concrete debris was expected to be present across the site.
The electromagnetic surveys clearly identified widespread areas of minor to significant buried metallic waste, as well as a well-defined former foundation. The combination of both a metal detection survey and a conductivity survey allowed Pyramid to more comprehensively evaluate the lateral extent and types of buried waste and infrastructure across the site. A map of metallic anomalies detected by the EM61-MK2 survey is presented below.
The EM31 ground conductivity survey helped to further constrain the boundaries of the former foundation, as well as assisting in identifying the most significant areas of buried metallic waste. These conductivity results also provided an understanding of possible zones containing non-metallic buried waste that would not have been identified with the metal detection survey alone. Follow-up GPR was performed across all anomalies and the suspected former foundation to provide more specific information regarding the depth, shape and size of each feature.
Pyramid ultimately classified the various features identified by the geophysical surveys into four categories: Minor to moderate metallic debris (Category 1), Moderate to significant metallic debris or clusters of smaller metallic debris (Category 2), Possible buried metallic drum or structure (Category 3), Foundation of former building (Category 4).
This projects helps to show the effectiveness of electromagnetic geophysics as well as the importance of combining multiple geophysical methods to more accurately understand the subsurface at a particular project site. Pyramid also uses this same approach to delineate former landfill sites where the location and limits of buried waste is uncertain or unknown.
