Time domain electromagnetics TDEM tool used for subsurface investigation.

Underground Storage Tank UST Investigation

One of the most useful applications of geophysical survey techniques is the location and identification of underground storage tanks (USTs).  USTs are often made of a material that is compositionally drastically different than the surrounding materials which make them especially simple to locate through geophysical methods like electromagnetics and Ground Penetrating Radar (GPR).  Even in scenarios where tanks are made of composite materials that may not be able to be detected with electromagnetics, their shape, size and often relatively shallow burial depth make them perfect targets for GPR.   Many projects our clients approach us, like contaminant mapping, utility surveys and site characterization, involve USTs and make locating them a priority.

THG recently worked on a project locating USTs during a site characterization project in Ohio.  THG was contracted to survey the site to determine if any USTs are present.  THG utilized time-domain electromagnetics (TDEM) and GPR to survey the site once thought to function as a gas station.  To perform the TDEM, THG deployed a Geonics EM-61.  TDEM imaging detects metal by utilizing a transmitter antenna that emits a pulsed electromagnetic signal and a receiver that measures the slow decay of energy from excited ferrous and non-ferrous sources (in milli-Volts). The EM-61 was integrated with GPS which eliminated the need for timely grid-style set up and collection methods.

Once the TDEM data were collected, it was processed and analyzed in the field to determine the location of anomalies.  One anomaly was identified on the site.  GPR was then deployed to image the anomaly to determine if it displayed any of the characteristic GPR signatures of a UST.  The GPR was able to confirm the presence of the UST and maps its extents and depth.  This effective UST survey was completed in less than one day making it much more time and cost effective than traditional invasive methods of locating USTs.


Time domain electromagnetics TDEM example data for an Underground Storage Tank investigation.