Water Table Under Foundation, Settling & Sump Drainage

[beerski1]

We have been living in our home for over 28 years. Backyard drainage has always been an issue during significant rain events with some minor flooding. We have a storm drain on the border of our property and we receive our surrounding neighbor's run-off. Our sump runs every 30 seconds during heavy rain events. I have set the sump float near the top of the sump pit to keep it from running so often. Considering we are having the rainiest year on record here in New Jersey...our sump now never fully drains. The water table is high in this area. So...we have been living with this. We have had a sump overflow once when the power went out. We have a drainage expert coming in to run a french drain to catch water coming in from the surrounding neighbor's properties...but...I understand this most likely now a water table issue.
Current Issue of Concern:
1) The walls in our house have been very stable for over 28 years with no cracking and few nail pops...but this last winter we are seeing cracking in in corners of a number of doorways on the first and second floors. They radiate sideways from the corner of the frames.

2) The vertical crack in our back foundation wall (which has been there for a long time) is more obvious and pronounced at the top. May a 1/16" wide.

3) We have never had - and still do not have - water coming through the foundation walls into our finished basement.

4) We never see water outside right up against our foundation.

5) The 3 concrete supports (we have a total of 12) for our 20x15 deck closest to the house have been sinking slowly for years. Over the last 3 or 4 years, we have heard loud bangs from the deck in cold weather. I have adding adjustable jack posts to support the deck closest to the house. The deck is also attached to the house...which overhangs the foundation in the back by around 2 foot.

Questions:
1) I suspect that the added drainage system in the backyard will help...but this won't solve a water table problem, correct?

2) I have been leaving the sump pit full recently thinking that I don't really want to be pumping water out if it is taking out soil from under my foundation with it. (The water in the sump is mildly cloudy.) Is this good or bad to do? Will the foundation footing be compromised by stagnant water around it?

3) Could the weight of deck pulling down on the house cause such cracking? (I have not witnessed any particular stress issue where the deck is attached to the house.)

3) Do you think that we are seeing significant foundation damage after 28 years?

Sorry for the long post. I am hoping to provide enough info to qualify my questions. Frankly, Question #2 is my most pressing concern right now.
Thanks,
Beerski

 

[GeoEnvGuy]

1. The more water diverted the better, Rear lot swales in sloping developments with shallow bedrock usually are at the groundwater table. A French drain dug deep can lower this level assuming you can get grade to the outlet without lift station.

2. The foundation soils have probably already settled as much as they are going to. If you have clay below the foundation you can possibly get some rebound upwards by raising the groundwater table. If it more on sand no real impact on rebound or settlement after 28 years.

Cloudy water can mean you are losing material below your basement or in your weeping tile.

3. Your deck is probably going through frost heave or temperature changes expanding and contracting the materials.

4. Slow damage is most likely to occur in clay deposits altered by the building footprint.

The first stage of site investigation is desktop and it informs the engineer of the anticipated subsurface conditions. By precluding the site investigation the design engineer cannot accept any responsibility for providing a safe and economical design.

 

[oldestguy]

Agree generally with the above. I bring up the situation with the "French drain". These usually work fine if planned well, but they can go bad. For one thing the backfill to the drains commonly (and for no dumb reason other than habit) is clear stone with big voids. A problem when lot of water is collected is that soil fines will come along. That can undermine foundations. More importantly however, it can plug the drains. One method for holding back the fines is to surround the gravel with a filter fabric. Fabric on the pipe alone may clog over the slots. Years ago (many years) the US Corps of Engineers tested various materials for filtering and also carrying water. The best and simplest filter is fine aggregate for concrete (not the coarse material), simply concrete sand.. Using a pipe with small slots or fabric, the sand backfill is easily placed and will work forever. Sometimes you can dump the collected water on site, but I'd plan to run it wherever the sump dumps. Don't depend on a sub-drain to work as a draw down drain. These drains should be placed to cut-off the flow coming toward the area to be protected. In other words create a moat around the area to be drained, but use that sand filled trench and pipe to do the job. Your description of cracks, etc don't sound serious to me especially after that many years. If your building inspector insists on gravel as the drain backfill, surround that with the filter fabric (all the way around it). It ain't easy!

Edit: I got to thinking about the situation and you might do some checking. The wall cracking at doors sounds like differential settlement somewhere. You can check floor elevations with a simple level. Take a section of garden hose and get fittings for each end to attach about a 3 ft. length of clear plastic hose. Fill with water. Check that air is gone by holding the two ends side by side. Should be same elev. With two yard sticks go around and compare height of water above the floor. A contour map then can be drawn to show elevation differences against one place in each room or whole floor..

I'd also check as best as you can to see if you are bringing along any silt with your sump pump operations. Get a sample of that cloudy water and see if something settles out. Is your collection system properly filtered? That old habit of using coarse gravel backfill to collection drain pipe might be your situation and that can be a problem in the long run, especially when pumping a lot of water. It might explain the deck thing. I'd keep a high water level in the sump to slow down the the rate of flow(erosion).

If you really want to solve the water erosion issue, a different method for ground water removal than now might do the job. The "Moat" thing might be considered around the whole house. That would require deep wells for at least temporarily lowering the water table so you can do the job in the dry.

 

[beerski1]

GeoEnvGuy and Oldestguy,
Thanks a lot for the quick and detailed responses. I really appreciate it!!! A couple of notes:
1) I've attached a PDF with pics showing our flood issue, sump setup (also fed by perimeter drain that is always dry) and cracking (that's really the worst crack in a door on the second floor farthest from the sump; everyting else very slight). I swear the damn house is breathing as the cracks and door creaking we get very subtly changes over time.) The water in the sump is not usually that high, but over the last few months - due to incredible rain in NJ - it has been at that level. I set the pump float high to keep it from running so much. I didn't read a specific response to my question about leaving this much water in place in the sump and around the footings for long periods of time. Assuming levels simply rise and fall overtime does this average high level actually undermine the foundation? Does it degrade the concrete footings and such?

2) Regarding a "filter" surrounding the sump basin...is that something that can be retrofitted? If so, how would that be done?

3)Regarding the drawn down drain system...in the flooding photo...we are going to run a 4in "french drain" (bottom perforated pipe in a 12in wide 2% graded trench on a bed of stone, wrapped in fine stone and filter paper, outside the stone.) That will run from the top center of photo where most of the water comes onto our property down to the lower right (out of the picture) where the storm drain grate is. We are going to tap right into the city's underground drainage pipe (with their blessing.) We may need to run a second drain from lower left as well. I will work this out with our drainage contractors. I don't see how a new drain around out foundation footing would work as there is no place to move the water other than with an external sump pump to the city drain pipe (which is where of sump and downspout water is already going). Is that often done? Trying to drain the water table anywhere is going to be a losing proposition,I guess.

4)Regarding the level testing within the house...those are some great ideas. My suspicion is that we are getting something of a fulcrum effect as the crack in the foundation is at the mid-width point of the house. The left sump-side with deck is sinking a bit apparently. Maybe some front to back settling, but I think it may be a very slight twisting in the structure causing those kind of horizontal cracks. The cracks only appear in doors perpendicular to the long side of the foundation.

5) Finally, what type of local professional would I employ to investigate my problems more fully? Is it a civil engineer, a structural engineer...or ???? I had a building contractor take a look and he didn't have a real clue about the structural issues. Of course, my drainage contractor handles just drainage issues. Is there a way (GPR??) for this engineer to do a non-invasive sub-surface analysis by my foundation to get a sense of what is going on? Is it the water table...or...some kind of void collecting water drain from the flood in our back yard? Sorry for the naive questions.

Thanks again!
Beerski

 

[oldestguy]

OG here again. Management here doesn't like us "helping home owners", but you are an engineer on this job, so I'll stay.. I'll try to cover every question, but may miss something. First comment, other than water all around in back, etc. I don't see what your problem is other than the sump running a lot. The cracks shown don't seem important. Temperature and moisture changes sometimes are to blame. Anyhow I've seen a lot worse and even no problem then. Floor elevation survey would tell more as to conditions. Outside views of the house may help also. What would help a lot would be "side views" and "section cut views" possibly even sketches with elevation scale reasonably close to a scale, if possible. For instance showing the basement, sump, outside drains, etc. especially in relation to elevations.. In particular what is the elevation of the top of sump with respect to the perimeter drains that apparently would feed to the sump. It's difficult to see how there would be water at the sump and none at the usual drains in cases like this. Where is the water coming from that the sump drains?.

1. Undermining of foundation usually is the result of flow of water, not just saturation. Thus if the sump pump keeps the water level low, there is a hydraulic gradient that is steeper than if the sump stays near full. The steeper the hydraulic gradient,the faster the flow and erosion. I don't see where water at or near the foundation soil means much either way for your case unless this is a recent thing and all the soil is a high plasticity clay.

2. Wrapping the sump with filter fabric would hold back silt movement THERE ONLY. Would not do much out at footlings well away from the sump. I'd not consider that filter as doing much for you.

3. I'd not start that proposed yard drain system just yet until this situation is well understood (by me any how). Normally we don't do any installation of a subsoil filtered drain system to collect any surface water. That's usually done by surface drainage, ditches. While a shallow filtered drain system will collect water from the surface, it should not be depended upon permanently. The reason is no one maintains these and silt and clay on the surface gradually seals off the entry into those buried drains.

4. From what you show so far I do not see a problem with house support. If there is a serious problem you will see numbers of large width cracks, doors that don't close, stuff on a table runs off, etc.

5. We might be able to help a lot without a specialist, but only if we have ALL, THAT IS ALL the info. Many times what may seem unimportant is left out. My specialty is a branch of civil engineering formerly called soil engineer but these days they make it more fancy with Geotechnical Engineer. Preferably he/she should be a licensed professional engineer (a P.E.). These kind of problems usually are not covered in college courses. So preferably the engineer should be well experienced and with a similar case or two to point to. I'd not hire a recent graduate. Hourly rates may run somewhat over $100/ hr. While not something I'd recommend right now is using a company that has at least one test boring crew (with a rig) and obviously a well equipped laboratory. The one that has the flashy posting in the Yellow pages would not be the one I'd hire. Perhaps a word of mouth from architects in your area would help, especially when it comes to them having job foundation problems. How did their advice help?
I'm usually around here at age 90 and would sure be interested to see how this goes. You might not have a problem.

 

[oldestguy]

OG back. I tried to see if there would be some way for you to find a well experienced geotech engineer by doing a search on line. Also I tried to find some publication or article on line. Unfortunately not much is written on this problem, except for some on highway drainage. University professors also an unlikely source. They don't teach drainage much in soil mechanics courses. A rare article on this common problem in the journals of ASCE Geotechnical section may show up but rarely. Beware of contractors willing to "solve your problem". Many are out there and you have to carefully check their reputations and success with their customers first. I have found one needs a conventional contract with plans and specifications to get the job you need. It is best to have an experienced engineer involved if there would be work needed.

This link might help a little.

https://www.codot.gov/programs/envi...esignmanual_chapter18_groundwater_and_see.pdf

In looking at your photo of the sump it seems this sump is well below the perimeter drain system. Why? Do you need the water table lowered that much? It might be possible to raise up that sump pump and pump less water. Normally a sump pit is just below a basement floor and the perimeter drains enter it from the side, not from well above. For me an explanation is needed. It might come down to getting that llocal well experienced geotech and maybe a test boring, who knows. However don't hire any contractor yet. Sit back and hopefully come up with a plan, if any, that is well planned first.

 

[GeoEnvGuy]

Hello again, i See OG has provided a detailed response just wanted to provide feedback regarding the drainage system and which professional would have knowledge.

3. On a residential scale I have only once seen a drainage pipe installed and this was approved by the cities drainage engineer, as the drainage plan from the 80's had no outlet until the mid 90's. This issue was incorporated on Lot Drainage Plans, other places may call these grading or elevation plans. When a subdivision is laid out by developers the drainage pattern has to be submitted for approval for each lot and used to justify storm sewers sizes in the subdivision. To alter this drainage pattern can put you in a position of making a problem for someone downhill.

This type of approval was first required late 90's in my area, I am not familiar with how things work in your jurisdiction but they may not have this in the submission for newer developments or at the time of your subdivision development.

5. I see your problem as more of a lot drainage problem from the photos with large pooling areas, your property is not supposed to act as a stormwater retention pond. Landscaping/clearing the existing swales and making your lot have positive grade in accordance with local requirements for lot plans will probably alleviate alot of your issues and make your lawn not as spongy. You can contact the developers in your area and ask who fills out the permits on new subdivision grading/drainage/elevation plans and sizes the storm sewers or ditches. On the other side you can ask for the cities drainage engineer to come out and show you how your lot is supposed to be graded to the storm sewers or ditches, which are the cities responsibility, without causing problems downhill.

To address the foundation condition, I have not heard of geophysics to do this. Foundation repair, weeping tile and basement waterproofing contractors are who you would need to contact.

 

[oldestguy]

In regard to re-grading the lot, it normally does not require any permits in locals I have been in (USA). Just don't cause a problem elsewhere. Once we get more site info, maybe we can help. So far let's wait here and hold any recommendations for work to do.

 

[beerski1]

Thank you both for the detailed responses. OG, thanks for the PDF link. Regarding the sump depth...that is the way the builder did it. You will note I have a pedestal sump and it is set to its maximum trigger height. The level in the picture is where the water level typically stops these days and just before the sump kicks in. If I run the pump for a loooonnnng time it will eventually drain, but never fully. Again, I don't want to be moving that much soil if it is undercutting the foundation.

GeoEnvGuy, thanks for the details regarding townships, developers and grading. I have not been happy with the fact that we are collecting upstream runoff from all of our neighbors in the back of our property on all sides. The fact that this is happening so severely now is a big problem. When I brought the topic up with the township engineer he said that back in 1989 when the house was built such cross property drainage to the common storm drain was allowed. Stupid me. Our neighbors on the left side regraded their backyard about 2 years ago and that is when things started to Go to Hell. The neighbor behind them now has a lake in this yard that drains into ours. He has done nothing a alleviate the problem. I am not sure if I have any legal recourse for a complaint with the neighbors or the township. Apparently, the township dropped the ball with the original builder not ensuring that adequate drainage and grading was done on the property. The township says - "Oh, that was 28 years ago... a lot settling has occurred." Regardless, it is not my water doing the flooding. The neighborhood is built on clay and shale so I can't imagine that drainage and perk issues could not have been anticipated. We have standing water now...which is a new phenomenon. The township has offered no $$$ubstantive assistance. They have approved our request to allow us to tap into the storm drain system that runs front to back on right side of the property. Frankly, I would like to see the township fix the problem. (Yeah, like that is going to happen.) Where would I find the applicable site drainage code and site approvals that were in effect at the time (1989)? This would be in township archives accessible to the public?

Thanks again. I am taking everything you all have provided into account and will work up a POA. I will be looking for a local geotech pro to lend an opinion and a solution.

 

[GeoEnvGuy]

You're neighbours graded there lots and changed the drainage pattern is what I understand from your response. Did the city approve the change in drainage with a permit?

If yes then blame city.
If no blame neighbour.
If there is no permit to apply for this yell at city and neighbour.

A rear lot swale is a 6 inch depression at the back that must maintain positive grade between neighbours until the end of the line which has a catch basin.

The easy fix is to get the swale back, the more expensive fix is to put a rear catch basin and connect to city sewer.

The city of Sudbury has nice pictures in the back which show the concept nicely in there lot grading policy. Most municipalities have this in writing. They also show a 2 metre wide swale aka easement for new developments. It doesn't need to be this wide and there is no easement back in the day.

https://www.google.com/url?sa=t&sou...FjABegQIBhAB&usg=AOvVaw0qiVocT2_oJXMF79kvWY-O

The first stage of site investigation is desktop and it informs the engineer of the anticipated subsurface conditions. By precluding the site investigation the design engineer cannot accept any responsibility for providing a safe and economical design.

 

[GeoEnvGuy]

Hi again I just wanted to further comment on rear lot catch basins and drainage options. These are typically on easements as the city now owns that catch basin which is part of the storm sewer system. If you install a catch basin, is it your catch basin to maintain and operate as you see fit, or are you gifting it to the city. Also if your installing it are you just connecting a catch basin for surface water or are you connecting a French drain to lower the groundwater table and capture surface water? From the city perspective they didn't cause a problem and they don't want a catch basin or infrastructure to maintain and replace. Also if your property settled so did your neighbours and the pattern should still be the same.

I think your best solution would be to figure out what the old subdivision drainage pattern was or should have been and reinstating it by talking with your neighbours. Which probably means getting a narrow ditch/depression to go one way or the other at the back of your properties. This might mean making a steep/thin and deeper depression at the back for neighbours which graded there lots higher and split the drainage to change the pattern and caused pooling. If they don't want a swale than a culvert can be put in to connect the pool to where it used to go. A swale might not be as visually appealing and might require a weed wacker to mow if it's really steep and deep, but it's cheaper than installing a small diameter pipe as a culvert, that will clog and freeze. You can try and French drain the inlet and outlet of culverts to pretty it up and reduce clogging and freezing issues but you may need a bigger size pipe. Both those options are considerably better than a random catch basin at the back that will also clog with debris or freeze but be harder to clear.

If your neighbours did change the pattern and are not receptive to changing the pattern back. Than they caused your new ponding problem than they can fix it. If they don't want to than this might take more time and may require a lot of process either through the city or legal. It may be more advantages to partially block and pool water uphill with a gentle perimeter berm to direct water coming from your neighbours property onto yours. There combined runoff is considerably more than yours and contribute more to your pooling problem. As the drainage pattern has changed you can either install a catch basin, French drain, culvert, or use your downhill side lot swale. The side lot swale or culvert can be made to bring the water from the back to the front and onto the street if there is overall grade. Going with a side lot swale can mean you will need to excavate a thin and deeper depression to make grade. That material can be used to berm the uphill side to direct neighbours runoff. You may pool a lesser amount of water inside a perimeter berm but it will help convey your neighbours runoff and stop it from contributing to your pooling and reduce the groundwater infiltration by moving more water away.

The first stage of site investigation is desktop and it informs the engineer of the anticipated subsurface conditions. By precluding the site investigation the design engineer cannot accept any responsibility for providing a safe and economical design.

 

[oldestguy]

One comment on the above long post. Never use the term "French drain" if you want a filtered drain system since the old system with large aggregate readily plugs. I'd use the term "sub-drain".

On this question, I suspect none. Where would I find the applicable site drainage code and site approvals that were in effect at the time (1989)? This would be in township archives accessible to the public?

Your best procedure now probably is not using this post method, since we do not know all the facts. That WELL EXPERIENCED geotech engineer in your area would be the way to go now.