Crowded locate problem

[testtech]

I locate utilities primarily in conjunction with testing to locate leaks in underground water lines. I need the length and location of the water line. Without this information, I cannot pinpoint the leak.

I had a job yesterday where we lost the water line (6" steel) in a tangle of utilities including gas, electric, telephone. I tried various frequencies as well as direct connection/ ground and induction. Every method I tried ended up placing signals on everything. I use an RD 4000, but low frequency did not work well so I could not use the CD feature. I don't believe CD would provide much help, since we are placing a signal on the main water line where the main building ground is terminated.


Does any one have any tips on cutting through the clutter?

[yahoo]

pressure washer and a vacuum that sucks up mud is my suggestion......no matter if you disconnect every ground in the entire area from every utility..you would still get a signal on every utility........my opinion

[Metroman]

This might sound silly but did some idiot ground out to your line at the building.Ive seen this alot on regular homes.If not you might want to ask the other locators to unbond the main ground in there peds (tv and tel only)nearest to your area.I have done this with great results(I was locating all utilities so no problem for access to grounds).Try to stick with a low frequency, less bleed off.Just keep trying different things every locate can be very different.Hope this helps.

[GWJ_CAS]

Call a GPR guy...

[testtech]

I am a GPR guy. I have a Sir3000 with all the bells and whistles. Great for concrete, but in MD, I have had very little success using 400 and lower frequency antennas for subsurface. Every time I drag it out, it is a waste of time. It has been a major disappointment.

[GWJ_CAS]

I am a GPR guy. I have a Sir3000 with all the bells and whistles. Great for concrete, but in MD, I have had very little success using 400 and lower frequency antennas for subsurface. Every time I drag it out, it is a waste of time. It has been a major disappointment.

Sorry to hear of your troubles. We are major GPR guys (since the early 90's), and we have had fair success in Maryland. Here's some of the kind of radar we do: http://www.mps3d.com/v2/3d.asp (http://www.mps3d.com/v2/3d.asp)
and more:
http://www.mps3d.com/v2/ait.asp

Also, NRCS has some great GPR soil suitability maps that may help you.

http://soils.usda.gov/survey/geography/maps/GPR/index.html

Here is Maryland's map:
ftp://ftp-fc.sc.egov.usda.gov/NGDC/ssatlas/gpr/md_de_e.pdf

[nxs]

I locate utilities primarily in conjunction with testing to locate leaks in underground water lines. I need the length and location of the water line. Without this information, I cannot pinpoint the leak.

I had a job yesterday where we lost the water line (6" steel) in a tangle of utilities including gas, electric, telephone. I tried various frequencies as well as direct connection/ ground and induction. Every method I tried ended up placing signals on everything. I use an RD 4000, but low frequency did not work well so I could not use the CD feature. I don't believe CD would provide much help, since we are placing a signal on the main water line where the main building ground is terminated.


Does any one have any tips on cutting through the clutter?

As already pointed out the problems with common bonding will present issues keeping your signal isolated to your target line, and you will need to keep this in mind when connecting to your pipe. The RD does have current measurement; have you had any success using current measurement? As long as you are not bonded to other utilities at hookup, it could help you navigate through your tangled mess. But you should use a direct connection (good mA), lowest frequency (that will work), low power and dual peak mode on the receiver to guarantee accuracy. It does sound like a good location to try GPR .

[testtech]

GWJ: That looks like fascinating equipment. However, will it perform well in soils where the conventional radar system does not? How has your success be in locating underground water leaks? I noticed you indicated that as one of your services.



NXS: For some reason, low frequency did not locate well so I could not use the CD feature. Since many utilities were directly connected through the building ground, I do not think the CD feather would work well. This is not a case of signal being induced on adjacent structures.

We did find the leak. We could find no evidence of a leak on the main service. All services to the units in the building were overhead. However, one unit had a dentist office. Next to the dentist chair is a pedestal with water run in the floor slab. That was the leak source. The water traveled about 100 feet under the building to reach the concrete slab perimeter, where it emerged, just a few feet away from the building water service line.

[GWJ_CAS]

GWJ: That looks like fascinating equipment. However, will it perform well in soils where the conventional radar system does not? How has your success be in locating underground water leaks? I noticed you indicated that as one of your services.


We have had better than average success in soils where traditional 2D GPR fails, that is not to say always though. We sometimes have complete failure on the radar side, but that is when our EM array and EM61 systems come into play and help us piece the pozzle together.

As for water leaks, on our main page, www.mps3d.com (http://www.mps3d.com), we have an image of a system in Pinellas County, FL that clearly shows leak plumes from the main, in vivid 3D color. The caveat is this, the leak needs to occur in otherwise dry soils OR, the leaking fluid must be significantly dissimilar to the groundwater i.e., oil vs. water.