Flooding of inspection chambers - Flooding with groundwater

[rayb]

At the end of my drive I have an inspection chamber placed around 1988 and probably 1.5 meters deep. Made up of concrete sections. The chamber is sealed from the sewage system by screw cover. Was planning new manhole cover but found chamber half full water. Emptied but two weeks later half full again. Not sewage since screw cover not leaking. Water flowing into chamber through joins in concrete sections.

Can anyone advise - do I need to do anything or leave well alone?

[lutonlagerlout]

is this a foul ic or a rainwater ic?
i know in some parts of luton they have rainwater systems that go to big sump pits (sic) but if its clay these can flood
why do you need to change things?
a picture would be handy
regards LLL

[seanandruby]

Is there a channel, or just a pipe in and a pipe out with about 300 ml below inverts. Sounds like it could be a catch pit if the latter. If that is the case then it will have water in it. The idea is to catch silt etc; which sinks to the bottom and allows the water to flow clean. Are sections raised to form an intended gap? If so could be a soakaway.

[DNgroundworks]

I thought catch pit if it were a rainwater ic

[rayb]

Thanks for all the suggestions but it is a sewer inspection chamber and it used to be dry since I used it probably 15 years ago to free up a blockage. In Scotland all the inspection chambers for sewage have sealed access ports. The problem is that when I want to access the sewage system I have to bail out 18 inches water to access the system or get wet opening the access port. I was wondering if the chamber needed replacing (big job) or was there a way of sealing it to prevent ground water leaking in?

[Tony McC]

Have I got this right? You have an IC through which runs a sealed sewer pipe which can be accessed via a screwed plate cover, so, in effect, the sewerage never makes contact with the IC itself.

In such an installation, it's possible that groundwater is penetrating the IC, as it may have been constructed as a SW IC rather than a foul IC, which would/should have sealed joints to prevent egress of sewage out of the chamber in the case of surcharge within the system.

There's no cheap fix. There are chamber lining products that would effectively seal the IC internally but they are a specialist installation requiring deep pockets. Occasionally, you can persuade an insurance company to fork out, but in most cases, they claim it is a pre-existing condition for which they have no liability.

If you can bale out the chamber, it may be possible to seal the joints from within using mastic, pitch or similar. Failing that, it may simply be a matter of re-building the chamber.

[seanandruby]

You may have whats known as a bristol trap. I can't believe we still put them in, but we do. They are a pain in the arse. Installed lots of them and also have broken loads out so that the sewage just flows. They are an old idea to stop gases, ie methane, escaping and rats climbing up the run. It will probably need jetwashing, that should cure it short term. Avoid flushing grease down the waste pipe as this builds up and causes its own problems. You can seal the joints with stop gap, fondue or sika mixed with neat cement. You have to use small amounts and be be quick with the mix as it goes off in about 40 seconds. its an unforgiving job that can take forever and means you have to be inside the manhole, not good as it is will come under confined space regulations. If the gaps are'nt letting silt in and not a lot of water, i would be inclined to leave it once you've got it flowing ok.

[seanandruby]

Yes or no ???

[rayb]

No it's an inspection chamber to access the sewage supply. The sewage line runs underneath the concrete base of the inspection chamber and access to the sewage is via an oval shaped section that is held in place by two screws. Effectively it is a rodding point to access the drain. The problem is that it fills up with rain water quite rapidly through the walls of the inspection chamber and consequently needs draining before access can be gained to the drain for rodding.

I have since found out that from manufacturers websites that now they are built with a drain to allow the rain water to run away.

Problem is that to add a drain requires I think a major excavation around the chamber. I cannot think of a way of adding a drain without having to dig through the concrete floor and risk rupturing the sewage line

Any other suggestions gladly received?

[seanandruby]

Ok now we are getting somewhere. What you have is a sealed inline chamber. Threw me because you would'nt normally have one outside, ( would normally be a traditional type with channel, slippers, benching etc; ) they are normally used inside buildings to stop gases etc emitting through. It's not a problem for the manhole to be half full of water most, if not all will have some water inside them.I install mainly this type of drainage ( must post some photos soon ) you would only remove the water if you had a problem with the line and therefore had to gain access.Then you would pump the water out. Don't worry about it until next time you have a blockage, then you can access it. As it is outside i would leave the plate raised up slightly so any water going in will drain away next time.

[rayb]

In Scotland I think all the access chambers are built this way whether indoors or outside. The other problem is that the access plate has a rubber seal around the edge so even if I do not tighten the screws the water cannot drain away because of the downward pressure of the water. With all the rain recently I have left the trap off but am a bit worried that if I get a blockage downstream then the chamber will fill up with sewage.

However I think I will take your advise and simply let it fill up unless I need access. Many thanks

[seanandruby]

Yes it will have a gasket between plate and chamber. I use a couple of metal shims to lift it slightly, it don't need to be much, just a few mil. I had 60 manholes like that on my last contract, lots of pumping and over pumping. They had to be airtight for the air test, so had to empty them for cleaning, then benching, then drill steps and final cctv, was forever pumping :laugh:

[rab1]

trust me sean knows about drains, if he tells you not to worry. dont