HGI’s G.O. Cart System

Successful geophysical mapping depends entirely on physical property contrasts within the subsurface. No physical property contrast means no detectable parameter. Geophysical surveys are most commonly performed using a single survey method which generally provides information about a unique physical property such as conductivity, radioactivity, or magnetic susceptibility. The complexity of environmental site characterization frequently demands information about multiple physical properties that when combined may be used to enhance remediation efforts. Recent technological advances in mobile computing and geophysical instrumentation have greatly improved the ability to provide simultaneous multi-method surveying.  Faster data acquisition rates, GPS navigation, and portable pocket size computers are the leading factors  driving this development.

We have successfully integrated this mapping technology on a towed geophysical trailer.  The platform is almost entirely non-metallic making it suitable for acquisition of high quality magnetic, radiometric, and electromagnetic data.  Geophysical instruments are coupled with a GPS navigation system and controlled by a Pocket PC (PDA).  The Geophysical Operations CART or “G.O.CART” is towed by an all terrain vehicle (ATV) which is operated by a single person. These technologies provide a multi-parameter geophysical surveying capability for identification and characterization of TRU-contaminated radiological and hazardous materials.

Our G.O.CART system is most effective for site clearance and characterization that may include:

  • Pre-remediation surveying for background baseline measurements
  • Pre-remediation characterization of waste and soil variability
  • Potential magnetic mapping of areas affected by burning
  • High precision location of trenches, caissons and drums for excavation
  • Post –remediation surveying for regulatory compliance and documentation

The Platform: The G.O.CART platform is almost entirely non-metallic, constructed of high-density fiberglass which provides the maximum rigidity for the lowest weight.  Large diameter composite plastic wheels were selected for their superior all terrain handling and are mounted individually. The wheel mounting structure eliminates the need for a through-axle and increases the ground clearance to nearly 3-feet.  The area between the wheels can also be used to mount ground coupling sensors such as ground penetrating radar. The CART can be adjusted to hold a variety of geophysical instruments and has a retractable telescoping boom that can extend up to 30-feet.  This separation distance is important for towing by an ATV which typically adds unwanted interference due to its large metallic mass. 

GPS Navigation: G.O.CART includes a GPS guidance and tracking system that eliminates the time consuming effort of pre-survey manual grid layout. Station accuracy is greatly improved since geophysical data points are localized to real-world coordinates during the acquisition phase. Random walk site clearance surveys can be accomplished as easily as predefined grid surveying.  The real-time GPS location is presented to the operator via a “heads-up” data display (Pocket PC) which is mounted on the ATV.  In this manner, the operator can monitor the position relative to predefined survey boundaries and even control the rate of travel, an important aspect for certain surveying methods.

 

G.O. Cart equiped wtih Electromagnetic and magnetic Sensors using GPS Heads-up Navigation towed with an ATV

 

 

G.O.Cart Can Carry a Variety of Sensors:

  • Magnetics:  Magnetic and gradiometric surveys provide the ability to define soils that have been disturbed (e.g. through trenching), and provide direct detection of ferrous pipes and caissons containing fissile materials. Characterization of disturbed soils is routine in archaeological-type investigations – a common application for the GSM-19 Overhauser unit. The new GSMP-40 Potassium unit has even higher sensitivity and will enhance characterization of subtle soil disturbances by an order of magnitude (i.e. identification of soils disturbed through trenching).  Another application for magnetics / gradiometrics is geologic mapping; a procedure that may be effective for constraining depth of burial (through basement mapping) and location of geologic structures that may represent potential fluid migration pathways for contaminants. Magnetics / gradiometrics  provide an effective means of directly detecting ferrous targets that serve as containers for contaminants.  Ferrous targets may also include utilities, wells, drums, rebar, re-mesh, caissons, and tanks.

 

Contour map showing detected subsurface infrastructure

  • Very Low Frequency Electromagnetics (VLF): VLF surveys work on the principle of detection of electromagnetic responses due primarily to steeply dipping mineralized or conductive structures (e.g. faults) or massive metallic objects. VLF can provide a “fast-pass” technology for direct detection of containers and geologic structures that may represent potential fluid migration pathways. Within the Hanford area, VLF should have a substantial depth of investigation (compared to shorter focus EM methods).
  •  Multi-frequency Electromagnetics (EM): The Geophex GEM-2 frequency domain electromagnetic system provides the ability to discriminate subsurface features with depths of burial up to 30 feet. It can be used for mapping contrasts in soil conductivities that may result from varying soil moisture or migration of contaminant plumes.  Electromagnetic surveying is particularly suited to detection of buried objects and infrastructure that may include foundations, trenches, utilities, drums, wells, and caissons. This instrumentation represents a significant enhancement to VLF both in terms of its range of frequencies and also in terms of the interpretation methods available for frequency domain EM. These include comparison of In-phase and Quadrature responses for characterization and discrimination of specific types of metallic / ferromagnetic containers, and conductivity mapping of variations in soil.

Contour map showing detected landfil plume

  • Radiometrics: (Rad): Radiometrics is the primary method used in detecting surface contamination due to radio-nuclides as well as naturally occurring radioactive minerals. Typical site investigations use hand-held instruments with small sensor volumes. Hand-held surveys also typically provide data at discrete point locations. The G.O.CART allows large volume sensor capacity which offers increased sensitivity, continuous coverage, and greater depth of investigation for optimal site characterization. Continuous profiling can provide a detailed contour map of radionuclide site contamination. Pre-defined windows can be set to detect gamma ray emissions at unique spectral windows corresponding to Co, Cs, and Eu – the typical gamma by-products of man-made transuranic wastes.

 

Contour map of radiometric data