Sump pump runs every minute -new home 3

[AndyWason]

I'm new here and and electrical engineer, so I'm hoping some of my geotechnical friends can help! My apologies if this is not the right discipline.

I bought a new end unit town house in Ridgeway, Ontario (4 units in the block). I noticed my sump pump would run any time it rains, fair enough. Now all the snow is melting and the developer has dug the basement hole for a second block of townhouses, about 25 feet behind us. It has filled with water, and the water level is about 2ft below grade. The soil is is a rocky shale and they had trouble digging that hole.

My sump pump runs about every minute. I checked my neighbours outlets, and theirs hardly seem to run at all.
I opened my sump to have a look (hey I'm an engineer, I can fix anything!) and I saw the pump sitting at the bottom of a garbage can sized abs sump. The feed from the weeping tiles comes in about halfway up, but there's no water coming in there. The water comes in from holes drilled in the circumference of the sump about 8" from the bottom. The pump is set to go on about 12 inches of water, and shut off about 9".

I disconnected the pump and watched the water rise. After about an hour, it was halfway up the sump. (about half way covering the main feed into the sump) It was rising slowly at this point, probably because it was back feeding into the main weeping tile feed.

It was rising really slowly at this point (I'm glad about that!) So I turned the pump back on, which emptied the sump pretty quickly, but had to wait for the back feed to the main feed to drain back.

Does this seem normal? Any obvious causes or fixes?
Thanks,
Andy

 

[PEinc]

Make sure that your pump discharge pipe has a check valve just above the pump. If not, pumped water may run back down the pipe, through the pump, and into the sump pit. Then, the pump will need to turn on again to pump the same water plus any other water that may have seeped in. This happened to me. My builder installed the pump without the check valve. The pump ran very often and quickly wore out.

http://www.PeirceEngineering.com

 

[oldestguy]

A few Questions. How old is your building? Are the discharge points for the sump pump visible? The question I have is related to possible undermining of the building. I would assume that it sits on that shale rock, which is good. Too frequently drain systems are perforated pipes backfilled with clear stone gravel. In some soil conditions these types of drains do not filter out any fine sand or silt and undermining can take place or the systems can plug up. If soil material is being brought along with the water, sometimes you can see a "delta' at the outlet of the discharge.

In your case the water coming in the sump probably comes along in that gravel backfill that also surrounds the sump crock.

Chances are the exterior drainage somehow finds its way easier to you than elsewhere. However, I recall seeing a long set of apartments in one building where water came in on one end and traveled the backfill to the basement all the way to the other end before coming in.

If you do see any indication of the water not being totally filtered of fines, keep an eye on things, since any plugging or undermining of floors, etc. may require replacing the system properly and the builder may have to be involved. For the time being any diverting of surface water from the building area that can be done should be considered. Remember the building basements were backfilled in a zone probably 10 or more feet from the wall. All infiltration there may tend to reach the building due to the probable sloping of the backfill layers aimed at the building. Downspouts should go well beyond that backfill, at a minimum of 10 feet.

When it comes to filtering the perimeter drains there are posts on these sites dealing with that. You may see my posts. Proper filtering is a subject that seldom gets taught in geotechnical classes, so don[t expect every civil engineer to know much about that subject.

 

[darthsoilsguy2]

if there is room, maybe you could raise your pump a little higher. maybe their pump might stay on instead if you're just a little lower than they are right now. residential developments have utility trenchs going all over the place. since many utility trenchs have a 6-inch porous bedding layer, it is very easy for standing water on 1 part of the site to equal basement flooding on another part. Another source can be all that snow piled up off the eaves against the foundation.

 

[AndyWason]

Good information! I think I remember the builder saying that the sumps were somehow tied together (probably through the weeping tile). This is so that if one owner is is away for a while (this is a bit of a vacation community)and their pump breaks down, the others will pick up the slack.
However, when I turned my pump off and let my sump fill half up, I didn't notice any of the other units pumps coming on, but it was hard to see.
All the town homes sump pump outlets are 'temporarily' drained through a piece of pipe to about 20 feet away from the units. I don't think I have a backflow valve on the unit, but it's definitely draining out where it should. The sump is filling up through the holes on it's circumference. i.e. from the gravel bed under the basement floor, not from the weeping tile inlet halfway up or the pump outlet. It hasn't rained and all the snow is gone from around the foundations. The ground slopes away from the house with no collection of water near the walls. Downspouts are at least 3ft away from the walls
When they start building the identical units behind me this spring, I'll keep a close eye on the construction to get an idea of what's going on.

If I raise the pump (or float) Is there any risk in letting the sump fill up to the point where the weeping tile inlet is half covered with water, i.e. the sump is feeding back into the weeping tile?

 

[oldestguy]

In my view you are between a rock and a hard place. Unless everyone makes more effort to keep surface and roof water from getting into the backfill to the buildings, you all will continue to be pumping water. Once water gets below the surface in backfill, it forgot the surface condition and follows the slope of those soil layers there. What are the chances of losing power to the whole area or your whole building? Does any one have a generator that can do the job then?

For my house, not quite sitting on rock, but with shallow water table, the former owner experienced his sump pump running a lot. When I bought, I recognized the fallacy of short (three foot) downspout discharges as well as some landscaping goofs. I then re-shaped (it did have slope before) and waterproofed the ground surface over that basement backfill, as well as extending all downspouts. After that work, the pump has only come on once in three years since, after a very heavy rainfall event that raised the ground water level in the development.

In your case, if the owners wish to go into such a ground surface treatment, it would take a geotech engineer who is experienced in the use of bentonite for waterproofing lagoons, etc. as well as a suitable contractor (but you can do it yourself with rental equipment, if there are capable people there).

 

[darthsoilsguy2]

there shouldn't be any risk in your last question specifically of having water above the weeps. The sump would not be feeding back into the weep. if the water pressure is greater outside the sump, it will raise the water until it equalizes or you evacuate it by pump.

The RISK has to do with water and existing conditions there are always risks of unintended consequences... including things you might not be telling us and maybe things you are unaware of. The easiest risk to understand would be that a higher groundwater elevation at the sump means a higher groundwater elevation everywhere.... you may have a spot far from the sump where the groundwater pressure is ready to break through.... higher water level means more risk of moisture vapor both coming from the sump bucket but the underslab stone... and whether the vapor will have unintended consequences

it might be easiest to think in a hypothetical.....
imagine you have a clay subgrade that doesn't let any water through and are building a house. you cut the sump pit and backfill it with stone and the sump. Everywhere else is on a higher shelf of clay. Then you spread out 4" of stone on that clay shelf to cast your slab for your floor. Maybe you put a vapor barrier down... Maybe you didn't.... maybe you did but ran out of materials or messed it up..... In this slab, you could pull the pump and watch the water rise, but then it looks like it stops coming up when it is 8-inches below the slab. that must be the point where it is stabilizing... right?... or is all the water just filling up that stone layer below your slab, which is effectively a large-area thin-depth sump... and now some serious moisture is being introduced to areas which may have enjoyed drained conditions..... Maybe there is no problem in an exposed basement slab with a dehumidifier, but there is a region with carpet, tiles with biodegradable adhesives, or a sill plate for an enclosed shear wall that isn't taking the moisture very well.... Maybe the extra moisture was all it took to make the house more appealing to a termite colony.....

Now you take the same house and tell me that the sump is 4 feet deep.... i would have no problem bringing the pump up to -12" below the slab. You may have a deeper sump than everybody else, which makes YOUR house the sump.

Your unit is the end unit so you are getting exposure from 3 sides while everybody else is getting hit by 2 sides.

If your end unit has a lower slab elevation than all the other units, there may be nothing you can do but pump and raise hell at HOA meetings about this being a building problem not a unit problem.

 

[cvg]

So I turned the pump back on, which emptied the sump pretty quickly, but had to wait for the back feed to the main feed to drain back.

I don't think I have a backflow valve on the unit...

while this whole conversation on ground water is interesting, it seems that the pump is missing a check valve which would theoretically solve the problem...

 

[oldestguy]

Mr. Darth:

Your comments are correct. I don't think that artesian conditions are present as you have described. Normally we expect water to seek the easiest way until things stabilize. I'd take the approach that the whole area is sufficiently porous that, were it not for the buildings and the soil there, this would be a lake at times. Yes, there may be restrictions at times and thus one part of the "house" basement may get flooded from below (I would not trust any slab, vapor barrier or clay layer to be waterproof) and still the water near the sump may not be as high as floor level. That's the risk of any perimeter drain or drainage layer under a floor. That's why I introduced the comments at the start about plugging. Since this is a "new" building, I relate to several "new" buildings with perimeter drain systems that plugged up because they were not designed with the principles of filtering involved. Unfortunately many builders, architects, and yes, engineers, think that open graded stone is great due to the big drainage "holes". Unfortunately those holes easily are plugged and then nothing works as planned.

Just keep observing what is going on and I hope no restrictions along the way will negate the drainage pathways toward the sump. Making it deeper is unlikely to solve a possible plugging somewhere well away from it.

Under a circumstance like you have, if a problem comes up in the next few years, document everything since contractors and architects can be sued for not "doing it right". I have been in court on the side of home owners in cases like this and that documentation came in handy then. Yes, we won.

In the new construction coming up nerdy carefully document the details of any drainage system they use, It may good or bad, but likely is what you have also.

 

[dicksewerrat]

Take lots of pictures of the new building site and all trenches.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[AndyWason]

Thanks for all the great feedback. A little more info...

Last November when I moved in, my next door neighbour (2nd in the block) had a leak in the water main in her front yard. This caused exactly the same symptoms as I'm getting now (my pump continuously cycled). I would assume therefore that that the soil is pretty porous.

In February my water main froze. The city came and dug up my front yard and the road to fix it. I thought maybe I had a leak this time, so I called the city yesterday and they came out, but they couldn't detect a leak. However...

We took a walk in my back yard and we found that the third unit in the block was exhibiting the same problem as me. They're out of town so we couldn't talk to them. The city guys felt that the problem was coming from 'Loch Ness' behind me. The cycling of my pump didn't start till the snow melted and filled the excavation with water. (see attachments)

I've got a call into the city to see if the developer can drain the pond to see if that stops the problem.(I'm thinking good luck with that!)

I'm wondering if I raise my float maybe some of the other units can 'share the burden' as I think only two units out of the four are cycling.

 

[AndyWason]

I've included the images here as attachments as my dropbox links may not be work.

http://files.engineering.com/getfil...-a8dfe88b450c&file=2015-03-20_14.07.03_sm.jpg

http://files.engineering.com/getfil...-a8dfe88b450c&file=2015-03-20_14.07.03_sm.jpg

http://files.engineering.com/getfil...-a8dfe88b450c&file=2015-03-20_14.07.03_sm.jpg

 

[oldestguy]

The risk you have in raising the float is that there may be enough resistance to free flow along the line from way back there the water table elevation may get above the floor surface elevation. Of course you might try it, but watch carefully. Obviously raising the float will raise the water elevation in you area, and somewhat elsewhere. Thus, you are right, let the neighbors bear some of the cost of pumping.

This brings me to a point that has not raised before. I'm assuming the shale rock there is reasonably impervious. You might check that by observing the drained bottom of the excavation next door. If you don't see any or at least much water coming up out of the rock, maybe consider a perimeter dam. This would be a dam fully surrounding the building, including all utility trenches. We have done this on some landfill sites to keep the leachate from seeping sideways out into neighboring lands. In this case it would be to keep water out. A crude definition of the dam would be a trench filled with clay, in simple terms. However, that dam would have to be designed as to exactly what goes in it and how done.

Of course all efforts also would be needed to keep surface water out, as with long downspout discharges and maybe the surface waterproofing I touched on above.

The advice of an experienced geotechnical engineer would be best needed to do this right.

It is not an unheard of "device" but it has to be done with knowing all possible info about the site.

What is bothersome about your comments is that your water supply pipe froze. Chances are the trench was filled with sand, not clay. The more water in the soil, the lesser the depth of freezing due to heat of fusion available in the clay as compared to sand. I'd think about changing that backfill or adding insulation as a barrier to that movement of cold temps. Perhaps you can bring in the builder on this (even if he followed some spec). What is the City standard depth of water pipes? Are they without much pipe freezing problems? I'd guess you may have to be at least 8 feet down in your climate.

 

[AndyWason]

Thanks oldestguy. The city guys who fixed my frozen waterline determined that it was about 22" below grade at the city end as it came 'over 'the main watermain rather than 'under' it. Not sure what that means. Also, they said that it wasn't insulated properly and they'd need to come back and fix it. Of course Fort Erie's budget for infrastructure repairs is probably shot for this year due to the very cold winter, so that's unlikely, even though I brought it to their attention a couple of times. I'll keep a faucet running on a dribble next winter just in case. Normal depth for fence posts etc. around here is 36", but the winters have been (like a lot of places) abnormally cold for the last couple of years.
I've ordered a high level water alarm , and once that's installed in my sump, I'll shut off my pump for a while and keep an eye on it. As it may take several hours to reach the (what I'll call) the high watermark, I'll rely on the alarm in case I forget to check it. I'm hoping it stabilizes at some point and the other units in the block start to cycle (I'll watch out for that). I'm retired, so I've got time, but not to watch paint dry!
Main water pipes seem to be pretty shallow, but I can check that out back in the new subdivision. What diameter/colour/material would they be? I see lots of green plastic piping around 18" diameter.
Andy