Private Utility Locates
Design Survey Locates & Private Locates in Washington State (Everett, Renton, Seattle, & Tacoma) and Oregon (Eugene & Portland)
The Utility Notification Center (811) is responsible for marking all publicly owned utilities but will not typically mark depths, privately owned utilities, or design survey requests (sent to 811). CNI Locates has the ability to designate the location of public and private utilities with the latest underground utility locating technology. To receive a comprehensive/complete locate, a private utility locating firm must be utilized to ensure that all buried utilities are located. This service allows contractors, engineers, property management companies, and anyone else to develop or update as-built drawings. Clients use these files for preplanning, to avoid utilities, or to document the history of their site on various CAD and GIS systems.
An active signal is a signal that has been artificially generated by an external source. Active electromagnetic methods can allow different services such as but not limited to telephone and electric to be individually identified. Active methods involve the use of a transmitter. The transmitter can either be used for direct connection or for induction. Direct connection involves the application of an active signal to a conductor using a clip or clamp. Induction involves a signal being radiated from the internal antenna of the transmitter which is induced to any conductors in the vicinity and re-radiated. Generally, 8, 33, 65, or 83KHz frequencies are used. It is often possible to determine the depth of the service in these modes.
A passive signal is a signal that occurs ‘naturally’ on a buried conductor. Passive electromagnetic methods will provide an indication only that services are present underground. Passive methods use the electro-magnetic fields already present around the underground utility to locate them. Two modes are generally used:
Surveying in the traced services
As the survey progresses the positions of the detected services are marked unobtrusively onto the ground surface. Our clients receive field markings in the form of paint, pin flags, stakes, or any other method they request. The coordinates of these points can be surveyed using a total station allowing quick and accurate transfer into AutoCAD.
Ground Penetrating Radar (GPR)
Electromagnetic techniques are unable to detect non-metallic buried services including plastic water and gas pipes and clay drainage pipes. To overcome this potentially hazardous situation, we can often combine the use of Radiodetection with Ground Penetrating Radar (GPR). GPR is able to detect nonmetallic as well as metallic pipes. It will also give an indication of the location and depth of buried services but will not identify them.
GPR works by emitting a short pulse of energy into the ground. Echoes are returned from the different interfaces between different materials in the ground. As the antennae emit a “cone” shaped pulse of energy an offset target showing a perpendicular face to the radar wave will be “seen” before the antenna passes over it. Resultant characteristic diffraction pattern is thus built up in the shape of a hyperbola. A classic target generating such a diffraction is a pipeline when the antenna is traveling across the line of the pipe. However, it should be pointed out that if the interface between the target and its surroundings does not result in a marked change in velocity then only a weak hyperbola will be seen, if at all.