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Water Table Question - Basement

Water Table Question - Basement

(OP)
I got back my soils report for residential lot that I am looking to build a house on. During borings, the neighbor told me that there is a high water table in this area and for me to be carful if I am considering building a basement. Did 2 borings and the Recorded Water Levels, W.D./A.D. came back as dry/dry for the first boring and 11.5/9.0 for the second boring. Talking with the PE who stamped the report he said "Dont worry about building a full basement, should not be a problem". Just looking to get other people opinions. Much appreciated.

RE: Water Table Question - Basement

A few thoughts to ponder...

What's your neighbor's profession?
How long has he been there?
Could the neighbor have an agenda? - sometimes happens...

What time of the year were the borings taken?
What kind of soils are you dealing with?
Could thge neighbor be taking flooding due to an impermeable soil as a high water table causing flooding?

I would do a little more research here if I were you.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

RE: Water Table Question - Basement

I would be just as concerned about your engineer. a water depth of 11.9 feet is fairly shallow and if it rises in a wet year it might impact your basement. building the basement is easy, keeping the water out long term might be more challenging.

your neighbor apparently has experienced water in the basement, I would take care to properly design and construct the basement to avoid similar problems.

RE: Water Table Question - Basement

(OP)
Thanks MSquared 48. To answer your questionos.
Neighor is a commerical property assessor.
Been there 20+ years.
May have an agenda. Dont know him well.

Borings were taken in December 2012.
Soils are clay.
Not sure what the neihbor is considering. He doesnt have a basement. Said 15 years ago he built an extension. Trenched some footings one day and the next day he had to pump water out of the trench. He said water table was that high.

Thanks cvg.
Would it make sense to do an english basement and go down only 5ft instead of 10ft?

RE: Water Table Question - Basement

Clays are very impermeable. Local surface flooding is still possible here even with a low watertable. You might even have a perched watertable above the clay.

As for the 5 foot basement, check with your local codes. 7 feet is usually the minimum head
height in the US, but it varies. You could still go with only a 4 foot burial and a full height basement if your local codes would allow the higher ridgeline to the roof.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

RE: Water Table Question - Basement

With a basement in clay soil, I would certainly build the basement with a drain tile system (or even interior and exterior) when you build, since is so so much cheaper than trying to correct or adjust for the differences between the supposed and real world. I know of large builders that automatically build every home with both interior and exterior drain tile because it is cheaper than a problem.

Clay poses a bit of a construction problem because the excavation limits could be wider than anticipated or planned. The backfill will hold water since is will have a high voids percentage and clay will keep the water in and around the foundation walls/footings. Any excessive excavation beyond what is needed for construction could also collect water and require special treatment for roof runoff (excessively long downspout extensions). Any utility excavation could also be a pipeline to conduct water back into the excavated around the completed foundation.

You are basing a lot of design information on two borings and there could be a possibility of a local perched water table that can be a real source of problems if it is intercepted.

Just a couple of thoughts based on years of fighting with water penetration -

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

RE: Water Table Question - Basement

Because the borings were taken in December, the water levels (of 11.5/9.0) probably do not represent the highest anticipated level for the year. So you should anticipate groundwater above this level and should design/construct accordingly. The idea of drain tile (assuming you daylight the pipe correctly) and/or raising the foundation are a good start.

RE: Water Table Question - Basement

(OP)
Thanks for the responses. I need to determine if I am going to go ahead and purchase this lot and build on it. At the end of the day I have 2 borings and know the soil is mostly clay. I would build a basement that is similar to a split level home (4 feet above grade and 5 feet below). Also, I would do the double drain tile construction on the inside and outside. I realize that it is hard to say if I will have issues with a basement flooding issues. But given the above information, I need to decide if I am comfortable with going forward knowing what I know and having to be ok with what I do not know. Any advice is greatly appreciated.

RE: Water Table Question - Basement

if you have engineering controls for the water table position you'd be fine. If you need a sump that'd be a problem when power's out. If you can daylight, make sure it doesn't get plugged over time.

I have no doubt you can engineer a basement that'll work.

f-d

¡papá gordo ain’t no madre flaca!

RE: Water Table Question - Basement

Your soils is clay with water and your not concerned with swelling or shrinking? Humm..... Well Mira-drain on the outside of buried basement and ring drain to precast sump away from house is what I think a good "general" problem solver for basement flooding. Nearly, 90% of all buried potable water concrete tanks we build have that kind of system.

RE: Water Table Question - Basement

There might be better information than two borings and a neighbor. There must be some local contractors that do excavations as well as maybe a city engineer. Do some asking around. Usually there are contractors that will gladly offer there experiences as well as maybe hoping to get a job. Sometimes basement problems are mainly related to bad surface water removal, not ground water. Look at the lay of the ground. Many times it is obvious from that as to potential ground water.

What was experienced when the utilities were dug in the area? Ask some questions of more than real estate persons.

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