Permanent Dewatering

[bmoc]

A local contractor contacted me about setting up a permanent dewatering system for a church site. Currently ground water seeps through cracks in a low area of the parking lot. Can anyone help with a permanent dewatering system to lower the watertable?

 

[Focht3]

Where is the church located?

 

[bmoc]

Church is located in Midland, Michigan.

 

[Focht3]

Hmmm,

You have several issues - at least one is outside my experience (freezing ground.) And you definitely need the services of a local geotechnical engineer who is well versed in dewatering system design and construction. My comments will be somewhat general - but apply to site dewatering in general.

In order to effect the lowering of the groundwater, you will probably have to either lower the water level significantly in "a few" areas, or put drain laterals through the pavement. While the "few" drains may be more attractive for many reasons, these are seldom effective because the well's radius of influence is too small. This approach may work if the affected area is fairly small.

Keep in mind that the design of laterals isn't dependent on how far down the water table is drawn down at the lateral - the key is the drawdown between laterals. The phreatic (top of water) surface isn't level if water is flowing; while this is pretty obvious, it is often overlooked by the "casual" designer of dewatering systems. Dewatering system design is pretty involved - not for the inexperienced.

If you want a good starting place to learn more, find a copy of Harry R. Cedergren's book on pavement dewatering - it is titled, "Drainage of Highway and Airfield Pavements" and was published by Wiley - Interscience. It has lots of useful information.

 

[dicksewerrat]

First you have to find the static water level. You will have to put in a couple of holes to measure this. Put one uphill from where the water is coming out. Then you will have to install one or more drain lines to lower the water table. you may want to hire a company that dries up basements by installing tiles and a sump pump. does the water have aplace to go by gravity?

 

[TJWATKINSPG]

A quick synposis of topography would be in order.

I suspect that you are dealing with glacial till? if this is so then perm should not be to much of an issue. The soil type may dictate some of your systems parameters.

I prefer Gravity or Passive systems to those that require sumps/ and or mechanical equip to maintain. Review site for a low place for the water to go.

The truth will set you free. Best of luck. Geodude

 

[Focht3]

Since water is flowing, it isn't really "static." A better term would be "steady state" although that isn't completely accurate, either. In my experience, these kinds of shallow seepage problems often show significant changes in short time periods - even if the outflow volumes don't seem to vary much. You will need three - or more - piezometers to get the full picture on the flow of groundwater at your site. Water finds the path of least resistance; you may be surprised by the groundwater's gradient.

For a geologist, [blue]TJWATKINSPG[/blue] gave you pretty good advice - try to use a gravity system if at all possible. (Just teasing, [blue]TJWATKINSPG[/blue]!) But even gravity systems have to be maintained...

Do you have any geotechnical borings from the design of the church? They could be useful in evaluating the problem.

And look for grassy areas upgradient from the parking lot - they may be the source of your flow. You can do some dye testing to see if you have correctly identified "the source."

 

[jheidt2543]

Another thing to consider with a permanent dewatering system is, depending on the volume of water, the astronmical operating costs. Before you install any type of pumping system have a dewatering contractor or engineer provide an estimate of the operating costs. By that I mean, the daily electrical costs, labor to check on and operate the system and maintenance costs for spare parts etc. Even the small duplex systems installed in homes, don't run forever without maintenance.

Once you look at the annual operating costs and add them to the installation price, I think you will find that you could pay for a pretty extensive foundation waterproofing job. All I'm saying is to be sure to look at all your options before you start spending the money.

 

[BigH]

If it is glacial till, then I suspect it is a clayey till. You may not get a 'ell of a lot of water flow unless there are other features permitting it.
Depending on the topography and the "size" of the low area, why can't you just raise the parking lot in the low end of the site? Of course, you will need to know the "highest" groundwater level. Groundwater levels flucutate seasonally so this, too, needs to be kept in mind.
Focht3 is correct about the spacing of any laterals. I had a client who wanted furrow drains installed under his highway at 20m spacings to keep capillary water out of the pavement. More than likely, they needed to be at 1m spacings to satisfy his target concern - then why bother. But . . . - 20m they were!

 

[MRM]

Hi bmoc,
Another avenue to check before proceeding to a more costly fix is your surface drainage situation. The Bay City/Midland/Saginaw area is, in general, a relatively low area consisting of a lot of lucustrine clays and other fine soils. I think that you could possibly have surface water collecting near the structure and making its way down the side of your foundation, and finally into the church's basement in the form of seeps. I've seen other situations where relatively impermeable soils combined with poor surface drainage result in a situation that you're describing. My folk’s house had the same problem until we installed some rain gutters. Be aware that gutters may cause some maintenance problems in Michigan since ice/snow is heavy and collects on roofs. This can possibly damage the system. Also, look into changing the grades near the church so that rain runs away from the building too. Of course, also consider the good advice of the others and check to see if it is, in fact, a groundwater problem which may require another fix as described in the other posts.