Drainage 2

[KParkes]

We have a problem that we have a storm water attenuation pipe (1.5m dia) that fills with Methane everytime the barometric pressure falls, we'd like to seal the joints of the pipeline to prevent the ingress of gas.

Any suggestions??

Regards, K. Parkes

 

[RDK]

I would look more at venting the methane from the ground because it can cause other problems. Sealing the pipe would work for a while but eventually you would have to do some maintenance on the sealing. Since we all know that maintenance is not always up to standard, you will eventually get some methane inflows again.

Can you give us more information, type of pipe, depth of bury, length of pipe and length of the methane plume causing the inflows?

What are the end conditions of the pipe? Can the methane be safely vented from the pipes?

Does the pipe go through an old landfill or swamp? What is the source of the gas?




Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[RWF7437]

I'd suggest you answer Rick Kitson's last question first since it is the most important one ! Methane is "natural gas" and must come from decaying organic matter. It is also explosive!

Find that source and eliminate it and your other questions become academic.

Good luck,

Russ

 

[cvg]

rather than venting, I would use posative pressure to force the methane out

 

[RWF7437]

How do you know the Methane is coming in to the pipe from outside ? It could be generated inside the pipe from decaying organic matter, couldn't it? If so venting may be a lot more expensive than eliminating the organic matter.

To repeat, be sure you know what the problem is before developing a solution.

Good luck,

Russ

 

[daqingwa]

Have you verified a methane problem by testing, and not just based on a bad smell. Methane is odourless but often accompanied by hydrogen sulphide (bad egg smell)

Treating the smelly part would be simpler if there was no major methane problem.

I assume below that you have detected methane.

The best solution is, as Rick noted, to vent the surrounding ground. Drill boreholes and fit a wind powered extractor on top of each borehole. (Think factory roof)

This could be expensive and aesthetically undesirable. Alternately use a caulking compound on the joints, google search for (tunnel caulking "asbestos free&quot I can vouch for PC4 AF.

Methane is explosive at between 5.3% and 14%. Gas monitors normally display %LEL (5.3% methane is considered as 100% LEL)

Legislation in your country will probably apply if man entry takes place at levels over 5% LEL (0.25%)

Take any man entry into this pipe very seriously, "confined space" good practice including ventilation and gas monitoring, no hot works / sparks / smoking, electrical equipment selection etc are essential. Read relevant codes of practise e.g. BS6164, 5345 et al if youre in UK or possibly Bureau of Mines in your country.

If the gas level is over 5.3% any spark will kill every man in the pipe, take care.

 

[KRSServices]

What are you folks recommending here? RWF hit the nail on the head here!

Firstly, determine the source of the methane. The relationship of the falling barometric pressure and filling of the pipe may be coincidental. You firstly have to determine the type of gas, the level of the gas and the source of the gas. These tests should be performed by someone whom is competant and experienced in this field. This individual(s) will then be able to provide sound advice as to the recommendations specific to your site.

While the advice posted on this thread may be well intended, without a site reconnaissance and allowing an expert to observe the issues and properly evaluate all the factors, any remedial propositions on this site are purely academic guesses at best. If this gas is indeed methane, it is dangerous lethal.

You would be wise to contract an expert first and then proceed accordingly! Provision of any other advice at this stage is not only foolish but reprehesible and certainly unprofessional. This thread is not about a nut, pipe type, thrust block, how to calculate a curve, or soils. It is about a potentially lethal gas and how to seal a pipe from this gas. Very dangerous work for the inexperienced and certainly not addressed b a casual thread posting.

In my opinion, RWF's advice should be well heeded.

KRS Services

http://www.krs-services.com

 

[KRSServices]

P.S.

Sorry for all the typo's...I was upset and consequently thought faster than I typed.

Cheerio!

KRS Services

http://www.krs-services.com

 

[KParkes]

Thankyou, for all your comments, regarding this thread. Sorry for the delay, normal busy workload commitments took over!

In answer to some of the questions.

Details: Surface water only, Concrete 1.5m dia pipe at 3-5m deep, 4 manholes and 70m length. Laid within dewatered sandstone bedrock

Source: Methane is mine gas from a closed coal mine colliery

Specification: A confined spaces entry has confirmed the surface water pipeline has been satisfactorily built to Sewers for Adoption 5th edition (UK specification).

Upon the discovery of the gas, the manhole covers have been permanently removed to allow for the gas to be diluted and it is now safe, however this in not a fulltime solution.

A proposed pumping station is to be built opposite the site to ‘suck’ the rock dry, however this will not stop the immediate ingress of gas into the pipeline.

The pipeline runs through the centre of a new housing development. Venting the system permanently is not an option. The new adopted owners will not allow for it, their specification will not allow venting stacks near to the new housing.

I appreciate KRS views and our company has the experience and understanding of the risks, my thread was originally brief as I was looking for suitable materials and didn’t really want to discuss sources etc.


Regards, Kevin

 

[tonks]

It might not be just the joints that allow the methane to enter the pipe. I've come across some porous concrete pipes in the past. A suitable method of sealing the joints and the barrel of the pipe needs to eliminate/minimise the need for man entry. A suitable method might be a cured in place lining, whereby a sock is inserted into the sewer by an inversion process under water pressure. When this flexible lining is in place, it is cured by circulating hot water. Of course you will need to check that the whole process is intrinsically safe!

With you post refering to Sewers for Adoption, I assume you are working in the UK? If so, the Sewer Rehabilitation Manual by the Water Research Council might be a good source of reference.

Tonks

 

[johnd43]

Confined spaces are the subject of a very interesting thread in the water and distribution forum. Everybody reading these notes should be aware of that discussion, and the fact that it was started by consideration of the circumstances that led to a fatality. Don't underestimate confined spaces.

Kevin, in this context, you should remember Abbeystead! I would very much recommend that you look through the records of that disaster - many bits of what your description are ringing bells!

Regards,

John