By: Jeremy Summerville, Western PA &WV area manager
In most areas it is illegal to use heavy equipment within 18 or 24 inches of a marked buried utility. This tolerance zone is applied not from the center of the line, but from the outside diameter. If someone were to dig outside those marks and hit your line, fines may be assessed to the locate company or organization. The big question is, can these mis-marks be avoided? The answer, in most cases, is yes.
Newer locate receivers give the user a number of double checks as to the accuracy of the locate. Listed below are a few of those:
- Do the null arrows and highest peak reading put you in the same place? If the signal is nice and round, with minimal bleed-off, then these 2 reading should be in the same place.
- Is the compass reading on the receiver straight up and down? This is typically a good indicator that you are directly in-line with a utility.
- Are you getting a consistent depth reading? If 1 and 2 check out, but the depth is off, you may have stacked utilities in the same trench.
- 1, 2, and 3 will indicate if you are directly over a utility line, but do not indicate if it is the correct line. There are 2 additional ways to verify you are over the correct line.
- Follow the signal to a visual indicator (valve, hydrant, curb box, electrical panel).
- Use the milliamp (mA) reading on the receiver. The mA reading will almost always be greater on the line you are connected to and much lower on the line the signal is bleeding off into. This is the most versatile tool to identify a line when bleed-off is present. However, not all receivers have this function.
If the above indicators are not correct, there is most likely interference from another line. Try reducing the frequency and/or power output to minimize bleed-off. Typically, 512Hz works best in congested areas. Try the tests again with the lower frequency. If the tests still do not pass, this is where the art side of locating comes in. I will discuss some additional options in a future post.