Site Clearance

Site Clearance is typically used for brownfield sites and by definition, a brownfield site is “a former industrial or commercial site where future use is affected by possible environmental contamination.” These sites usually contain hidden subsurface infrastructure associated with previous usage.  HGI employs a number of geophysical methods to locate and map buried infrastructure and objects for site clearance, often in advance of an excavation or an exploratory drill program.  These include magnetic, electromagnetic (EM), and ground penetrating radar (GPR).  The same tools are frequently applied to explore and map archaeological sites.

Buried Metal EM Reconnaissance Survey:

A common occurrence on industrial sites is to loose track of monitoring well locations, especially after periods of intense construction.  Below is a site where an EM survey was completed to locate a “lost” steel cased monitoring well.

EM survey completed to locate a “lost” steel cased monitoring well.

Remedial Site Clearance EM Reconnaissance Survey:

The industrial lot pictured below is the location of a turn of the century former oil refinery.  Recently the land was purchased and slated for development pending clean up of the pre-existing infrastructure and known environmental issues.  An EM 61 survey was completed as an initial step prior to re-leveling the site.  The contractor noted rumors of a buried vehicle as well as potential train tracks.

EM 61 survey of an industrial lot.

Complex Infrastructure Mapping:

HGI has developed an extensive base of relevant project experience in performing studies that include GPR, EM/MAG surveys and resistivity investigations at the Hanford Site.

Waste site areas outside of the tank  farms are rapidly characterized with  the use of a  patented Geophysical Operations Cart (G.O.CartTM) which includes an ATV and a fiberglass towed  trailer and attached instruments for simultaneous measurements of  electromagnetic (EM) induction and  magnetic gradiometry.

Electromagnetic measurements make use of the induction of  an  electromagnetic field into the subsurface and the resulting  secondary EM field.  Good electrical conductors are the preferred conduits for the induced eddy current flow which, in turn, results in an anomalous secondary EM field.  As a result, discrete conductive objects like magnetic pipelines, underground storage tanks, and buried debris are readily detectable and mapped enabling site clearance to occur .

GPR surveys were conducted using a Noggin 250 Smart Cart system (Sensors and Software, Mississauga, ON), which included a GPR system (transmitting and receiving antennae, battery, and energy source) and digital output display, both housed on a fiberglass cart.  The Smart Cart was outfitted with a Leica 1200 RTK GPS unit (Leica Geosystems AG, Heerbrugg, Switzerland) for geo-referencing of data and a heads-up display/GPS light bar (Ag Leader Technology, Ames, IA) to allow real-time navigation while traversing the area for site clearance activities.