Using GPR and EM Technologies for Environmental Assessment Surveys

Geological, Geophysics, Environmental & Geotechical Engineering

Date posted: 11/28/15

Brian Jones reports that geophysical surveys can be the foundation of today environmental projects, from locating abandoned underground storage tanks (USTs) and utilities, to complex mapping of geology in remedial investigations, to finding landfill boundaries and other buried unknown problems. In the past few decades, a variety of non-destructive testing methods are gaining in popularity over expensive and time consuming drilling and digging for environmental projects. Among these, the method of pairing ground penetrating radar (GPR) with electromagnetic (EM) induction instruments is one that shows great promise in significantly reducing survey time and costs. In the past, most environmental scientists and geologists relied on destructive technologies, including drilling and excavating test pits. Depending on the site (and project budget), a survey may require drilling or digging one or two holes for a small site, or as many as 20- to 30-plus holes for large sites. On average, each borehole into the ground on an environmental site costs about $5,000 to $10,000, so costs for drilling or soil sampling can be very high. And not only are these methods slow and costly, they merely produce point measurements, rather than a continuous profile. In response to the expense and safety of destructive surveys and concern about the accuracy of relying on point measurements, companies have more recently come to rely on a variety of other non-destructive survey methods. Chief among these is GPR, which works by sending a tiny pulse of energy into a material via an antenna. An integrated computer records the strength and time required for the return of any reflected signals. Subsurface variations will create reflections that are picked up by the system and stored on digital media. These reflections are produced by a variety of materials, including geological structure differences and man-made objects like pipes and foundations.