Spectrum geophysics

Services: Utility Location/Borehole Investigation/Excavation Pre-Screen

Spectrum’s integration of geophysics and utility locating provide our clients with options that other utility locating firms can’t match. The use of standard utility-locating methods integrated with the geophysical methods of GPR and TDEM provides our clients with unsurpassed information from the subsurface.

The following methods are used to conduct utility surveys and borehole investigations:



• Passive and Active EM utility locating

  Passive and active EM utility-locating methods are used in an effort to identify the surface trace of detectable underground utilities and abandoned piping. These utilities include but are not limited to electric, water, telephone, natural gas, storm drain, sanitary sewer, fuel piping, and compressed air as well as abandoned piping.

  Passive locating is possible when electrically conductive conduits are energized by ambient radio frequencies (RF) that are often produced by 50/60 cycle electrical, radio, audio, television, and communication transmissions. A receiver tuned to these frequencies can be used to locate the re-radiated signal emitted by the conductor (i.e., conduit).

  Active locating is initiated by directing an EM signal at a known frequency (8 and 33 kHz, for example) on a conduit with a surface expression. A receiver, tuned to these frequencies, is then used to locate the signal maxima (or surface trace) of the applied signal.

  Small transmitters can be attached to a rod or probe and inserted into storm drains and sewers. The location of the transmitter is then identified using a paired receiver and the utilities’ lateral location is marked on the ground surface.

  A hand-held metal detector is also used in areas where reinforced concrete is not present. Each proposed boring or excavation location is investigated using a shallow focus terrain conductivity meter to identify possible buried and abandoned metal conduits as well as piping which may have no surface expression or which may be less than 20 feet in length. This instrumentation can also be used to identify metal connections along transite or PVC piping as well as identifying lost vault lids, cleanouts, underground storage tank fill ports, and storm grates.

  
  

• Ground Penetrating Radar (GPR)
  

  We employ GPR methods in areas where non-metallic/non-electrically conductive utilities are expected (e.g. transite, PVC, and/or vitrified clay pipe) and over accessible areas where proposed excavations and borings are proposed. Spectrum Geophysics uses the Sensors and Software Noggin Smart Cart or a MALA ground penetrating radar unit in an effort to identify possible buried utilities. A high frequency radio signal is transmitted into the ground via the antenna. As radio waves propagate into the ground, these signals are reflected off structures with differing electrical properties. These reflected signals are then captured by the receiver and are presented as vertical profiles on the GPR unit. These data are reviewed to identify possible subsurface interferences.
• Time Domain Electromagnetics (TDEM)
  
  
  

  EM-61 – High Sensitivity Metal Detection
  EM-61 methods are highly recommended in open areas of high profile sites such as chemical plants, refineries, and tank farms or at demolished facility locations where no surface expression of the former buildings or utilities exist and utility location using standard methods is very limited.

  EM-61 data is collected and a contour map of the data is produced onsite. This map is reviewed for linear trends indicating the presence of metallic or metal bearing conduits. EM-61 data can also be used to identify reinforced foundations, pilings, or underground storage tanks associated with former structures.