Detecting source of water damage - from water main? 2

[civilman72]

I observed a site yesterday where observable ground movement has started to cause displacement and overturning in deck post footings and adjacent retaining walls. This building complex was built almost 30 years ago, and this recent movement has only occurred in the last two-three weeks. It appears this movement is being caused by an increase in hydrostatic pressure, seemingly due to a significant increase in below-surface water flow. It has been very cold (-20F to 10F) here, so it is highly unlikely that this is a natural spring popping up, or a natural rise in the groundwater level.

My first reaction was a water line leak, but the HOA representative said the Water District came out and tested the water for chlorine and found none. So they conclued it was "not their problem." I vaguely recall a conversation years ago with an individual who stated that a lack of detectable chlorine levels in water does NOT preclude this water coming from a treated water pipe. Anyone know more about this?

An issue similar to this one popped up about five years ago at a single-family house and the water district (another one) tested the water for chlorine, found none and said it wasn't their problem. After months of finger-pointing, it turned out a leaky water main was the culprit, so needless to say I'm hesitant to trust this most recent investigation by the water district.

Discussion and thoughts would be appreciated.

 

[MiketheEngineer]

All semi-government offices lie. Go with your gut. Get it indpendently tested.

 

[GoldDredger]

I always enjoy a good mystery, especially engineering related. Out of curiosity, what indications of water are you seeing? Do you know if the retaining walls were constructed with a drain system behind them?

As far as the cold, is that unusually cold for your area or is it annual? The freeze/thaw would be my guess as the culprit, but if it is normal it wouldn't explain the recent problem.

I wouldn't take the water district's word for it either.

 

[civilman72]

Indications of water: Lots of freezing water at the base of the retaining walls, more than the HOA rep has ever seen. The property manager installed some heat tape on the ground at the base of the wall last week and it is now producing a detectable flow of water around the tape. Property manager said the water melted and "went away" during a few warmer (above-freezing) days we had recently. This is right next to a river, so I'm expecting very porous (river-rock) soils, which may explain why the water dissipated during warmer weather.

It does not appear that retaining walls have drains (only 4'-5' in height). Cold freezing weather is the norm here - usually don't see these issues arise until spring runoff (April-June), assuming they are caused by groundwater/springs.

If I got it tested, any ideas what should be tested? I think I need something else besides chlorine. Maybe I recommend the owner go directly to a pipe leak detection company (I've heard good and bad about both the results and costs)?

Because it could be a leak from their water service line (not a main), one idea was to turn the water off to the building and see if the leak at the base of the wall stops.

 

[cvg]

turn off all valves and then observe the water meter. if it is still spinning, your service leaks. lack of chlorine residual in your water sample is not a valid test, once it leaks into the ground the residual chlorine will react with organics in the soil and quickly dissipate. you might test for Trihalomethanes (THMS)

 

[GeoPaveTraffic]

When we are testing for treated water, we test for Flouride. Chlorine tends to disipate to very low levels very quickly. There are some areas of the country that have low levels of naturally occuring Flouride, so you need to check that you are not in one of those areas.

I agree with some of the other posts, not sure that I buy that it is a leaking water line causing the problem, could be, just not convinced yet.

Good luck.

Mike Lambert

 

[cr1973]

There are a variety of leak detection methods you could use to check the water main, and water service, for leaks. A leak of this magnitude would be pretty easy to locate.

 

[civilman72]

That's the direction we are going right now... possibly testing the water and also hiring a leak detection company.

I think we need to verify it's not from a water leak before we start designing for something more substantial.

Thank you for all comments. I will keep you posted.

 

[chicopee]

Water companies use ultrasonic detectors to listen for water leaks from underground water mains before digging. Do the same.

 

[dicksewerrat]

If there is a hydrant nearby, put a short pipe on the hydrant nut (top) and place your ear on the other end of the pipe. Should hear a hissing noise if a leak anywhere near.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[civilman72]

Update: water leaks were not detected during today's inspection so we are now convinced we are dealing with groundwater. We are now going to dig some test pits, uphill of the problematic area, to try to locate the source and determine if capturing and re-directing the groundwater is feasible.

 

[rconner]

Thanks for the update (I know folks on this list really appreciate follow-uo on these inquiries). Richard, many years ago I helped a Contractor who was having trouble passing the required hydrostatic test on a new 48" diameter pipeline installation (and who couldn't find the leak in the buried piping). When I got to the site it was indicated a quite high hydrostatic pressure was required (in excess of 250 psi, that I knew was beyond the normal seat test requirements for some large valves), so I asked what were the boundaries of the test section (i.e. were they testing against any valves etc.?) The answer was yes, and they then were able to rather quickly expose for me at least some of a large, buried in-line butterfly valve.
I took what could maybe best be described as a quite large steel "breaker bar" (socket holder/handle) I got from the Contractor and put one end of the bar against the exposed valve case while at the same time pressing the smooth convex end of the handle against my earway. When I did so, I could clearly hear leakage, and so could others there with the same sort of miracle tool (that they could hear unseen leakage with as well). Without recollection of all details/protocols used then, I know man-entry in the downstream side of the valve sure 'nuff found a stream of leakage going by the closed valve seat. The rubber valve seat was adjusted for tighter seal, and the Contractor then passed his test at the required high pressure level. I guess the principles by which I was able to hear this leak are similar to your "pipe" suggestion, that took me down this memory lane.

 

[dicksewerrat]

the leak inspectors in Mpls used old telephone ear peices to do the same. These were the old box phones that hung on the wall and you cranked them to get an operator. They just installed a nail to the back of the speaker in it. they were still using them when I was there in the 80's. Old science is sometimes better.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[GoldDredger]

Sounds to me that the retaining wall doesn't have any drainage immediately behind it, allowing hydrostatic pressure to build beyond the capacity of the wall.

I wonder if constructing a 4" slit trench about 4-5 feet deep with a trencher, then installing a 4-inch perf pipe and back filling with a gravel might work. Perhaps 3-feet behind the wall along it's length, and find somewhere to daylight the perf pipe either through the wall or around the side.

 

[civilman72]

GD - We've thought about installing a drain directly behind the wall, but it would require a large excavator. We need a heavy piece of equipment to dig through the frost. But getting access for this piece of equipment to the wall will require the removal of about 40-50 mature lodgepole pines and the removal of stairs and a carport. In order to avoid this, we are planning on digging test holes about 50' uphill of the walls. Assuming we locate the water source, we will install a curtain drain and daylight the discharge pipe via gravity-flow.

If we do not locate the water source in this area, we will probably be forced to get down behind the walls (where we know we will find the water source). The HOA will have to decide if the removal costs (and removal of irreplaceable trees) will be worth the costs. They are also discussing the possibility of not spending this money now and see how much worse the situation gets - certainly not something the design team is recommending, but pretty typical for HOAs.

 

[GoldDredger]

Civilman72,
What I was thinking of is a trencher, like a 'Ditch Witch'. They come in a variety of sizes from those that you ride on to hand pushed models (have seen rentals for them at Home Depot as well). There is a boom that is lowered with revolving blade like a chainsaw with bits for digging out narrow width trenches, usually for conduit or small piping, maybe 4-5 feet depth max, perhaps 4-inches wide.

That could probably be navigated between the pines to the wall. Then could dig a narrow trench, stuff a 4" perf pipe w/sock at the bottom, and backfill with 3/4 inch minus gravel. Daylight the pipe somewhere out the wall or around the side. (Not sure if the wall has any tie-backs, which would interfere with the trench idea.)

Since you mentioned mature trees in the area, I wonder if roots might not also be a factor, pushing on the wall. Could excavate behind a damaged portion of wall and see if there are any roots. Those ditch witch machines don't do well with roots I don't think.

You can upload pictures to this website I believe. Be good to see what the wall/site conditions look like. Might give others ideas on how to fix.

 

[civilman72]

GD - I will see if I can snap some photos next time I'm out there and try to download.

I know what you mean by a trencher, but (according to the contractor) they do not work in 4'-5' of frost.

 

[cvg]

if using the correct type of machine and teeth, they can trench through bedrock

try searching for Vermeer or rocksaw

http://rocksaw.com/

http://www.trencherq.com/Rock-Trencher.php

 

[civilman72]

cvg - that's some impressive equipment. But the size of these trenchers are not much different than a large excavator and will present the same access issues as mentioned previously.

 

[GoldDredger]

First rule of a site visit is take pictures!

What part of the world is this in? I wonder if groundwater subjected to a regular freeze/thaw cycle against the back face of the retaining wall over time hasn't adversely affected the integrity.

Any reason you can't wait until the spring thaw to make repairs or even make more observations? Seems that would be a better time if the ground is frozen.