GPS Location Of Underground Utilities

[ed downey]

Has anyone used GPS location of underground utilities? I was thinking this could be very useful on a campus type setting where the utilities do not locate.
Is there a system or piece of equipment that anyone has used?
What is the accuracy of this type of system?

Any help would be greatly appreciated.

-Ed

[stanley]

Hi Ed, I'm assuming that you mean to gather coordinates of an underground electric cable/conduit etc. during installation for future location reference.

If so, you would need very expensive GPS equipment that would give a resolution to a few centimeters. This type of equipment is licensed by the Fed. Gvt. and hard to get.

I have about six years experience using GPS navigation. (I'm a sailor.) and even with the newest commercially aviallable GPS w/DPGPS and WAAS enabled the best resolution I have seen is six feet. Which works just fine to find an inlet in the fog but would be disasterous trying to find a 12.7KV cable.

Stan

[dereckbc]

Accuracy is the problem. Close enough to get you in the ball-park, but not close enough for a locate. Unfortunately our government will not allow GPS manufactures to release units with 3-foot accuracy. Military has them, but not consumer grade equipment.

[don_resqcapt19]

You can buy and install a local transmitter and receiver that provides a correction factor. I have no idea how much this equipment would cost but the high end equipment used by some surveying companies can get you within centimeter over a 40 kilometer radius from the local transmitter.
Don

[ed downey]

Thanks for your responses.
-Ed

[tom baker]

In washington state the locating tolerance is +/- 2 feet by state rules. Anything with in 2 feet has to be hand dug.

A GPS:
1. is not accurate enough
2. is slow to pick up the signal
3. Doesn't always get the signal- I have locations in the woods where it just won't work.

The locators we use send a signal onto the underground wires and a reciver picks it up, its accurate to inches and gives depth. For a plastic water line, a 12 AWG tracer wire is buried with the water line.
A inductive locator of the type we use, "metro-tech" is about $2500 new.