Magnetometer, Gradiometer, and electro-magnetic or RF utility locators are generally best employed for tracing the route of a utility line when a physical connection to the line can be made at one end, or in a manhole or trial pit. The methods will not work with plain plastic pipe such as older gas transmission lines. If the plastic pipe has been installed with marker magnets at the couplers, wire markers, or conductive tape laid in the excavation, then these tools might be considered.

　　In the authors experience, the most efficient survey program for a location where no accurate utility information is available is to use EM for an initial search, then use GPR to refine the data in areas where EM indicated conductivity anomalies.

　　A magnetic plastic gas pipe has been developed under the auspices of the Gas Research Institute, and is currently being evaluated under field conditions. If the durability of the material lives up to expectations, and the cost becomes competitive with current gas line products, location of the new lines will be greatly simplified, and current utility location tools will become much more useful.

　　Choose one phrase from the List of phrases to complete each Key point below.

　　The information in the completed sentences should be an accurate summary of the points made by the writer.

　　NB. There are more phrases than sentences, so you will not need to use them all. You may use each phrase once only.

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