Swab and Chlorinate Newly Installed Water-Mains

Hi,

Thank you very much for your answer been a great help, the only problem I have is the client is insisting on a contact period of 24hrs, but I'm hoping to get around that by proving that it doesn't require such a lengthy contact period, any idea where I might put my hand on any relative literature as I have to prepare method statements to satisfy the client before he will allow me to proceed.

That sounds like allot of pipe you have on your hands, do you mind me asking how you regulate the flow of the swab and monitor it current position in such long lines??

24 hours at 50 mg/L is the standard used by AWWA and US EPA for disinfecting new or repaired lines. There is some leeway for repairing and you can view the literature here for alternatives. Manual M20 and Standard 651 are used in most jurisdictions in N. America. The AWWA also has an on line service but if you are not a member you will be charged $20.00 for the information. Hope the info helps and it may explain why the client is insisting on the 24 hours as mandated by rules.

AWWA staff are good contacts and will likely answer your questions.

"Just an Engineer" has what I think is the best idea (GA btw). I know the AWWA standards we use here in the US may not apply there in Ireland, but the AWWA standard C650 allows for a shorter contact time of 3 hours, provided the chlorinated slug of water is dosed to 100 mg/L initially and never drops below 50 mg/L.

This may be a wild idea, but I wonder if some kind of pig exists that could be moved through the empty line, spraying a fairly high concentration of sodium hypochlorite in the inner pipe surface; then followed by rinsing with the quality of water the line is intended to carry.

If only there was

Not sure where you are located, but first thing you need to do is refer to the governmental requirements. If not, you could be held responsible for any negative repercussions.

Yes, the last thing you need to be held responsible for is forcing the waterline users to perform the 'Aztec Two-Step' or the Toilet Trot', or some other ghastly dance that results from ingesting contaminated water.

I remember a contractor friend relating a story regarding a several-mile-long water supply line that his company installed and then tried for several months to obtain a passing bacteria test on the water in the line. They had dropped hypochlorite tablets into the line periodically as they were installing it and believed that they secured the open pipe end at the conclusion of each day's work. However, some varmint was able to get into the line and evidently died there, as they finally discovered its remains at one end of the line when they ran a pig through to remove what they suspected was in there. They were quite relieved as they had anguished over this issue for months and were beginning to look both stupid and incompetent to the owner of the system.

One never knows what surprises lurk for the unsuspecting.

Using Steam is an idea.

In addition using septic tank cleaner fluids poured directly into smelly manholes or in non-potable water might keep some of that sewer gas from changing the atmosphere.ds

Thanks for the feedback. Some questions have been asked so I'll give some overview responses.

We control pig location by knowing how much water we have passed into the line (delivery end flowmeter) with a simple calculation on diameter it's easy to know that 1000l = ?? m of pipe. We confirm this by having the next scour "cracked". When the pig arrives, the flow from the scour is temporarily interrupted.

Our expectations for new pipelines is also 24 hours exposure at the very high concentration. You might be able to increase the length of chlorinated water behind the first pig in my suggestion to say 960m and have it moving at constant speed of 40m/hr, giving 24 hours exposure time as it passes.

I would strongly recommend DO NOT use compressed air!!! This is a dangerous practice even for short lengths but what happens if something fails while you have it charged at 50m head with air? That's one heck of a blowout for a 9 km long pipeline!

In reality, the cost of the water and chemical to fill the line once and do it properly should be negligible relative to the construction and operation costs.

You also have another problem on the horizon. How do you dispose of that highly dosed "sterilizing" water? It cannot be dumped into a watercourse and the local sewer authority might not be too happy to accept it.

Good luck.

By the way, what diameter pipe are we talking about? Most of our longer ones range from 225mm to 750mm.

Thanks for all the feed back guys,

To answer a few questions. the pipe line is a 355mm/250mm diameter H.D.P.E pipe line with approx 2KM of 250 and the remainder 355, I also have a number of smaller diameter pipeline's 180 & 125.

I understand the risk's associated with compressed air and would agree that it is bad practice, but my frustration Lie's with the fact that the pipeline is for a local government authority here in Ireland, and they are the only people who can supply the water volumes we require but yet they insist they cannot supply it, as it says in our contract in the fine print that we should not presume water is available from them, yet they are the only people in the island of Ireland who can supply it, quite frustrating, I think they expect me to import it from the UK....It's no wonder our country is in the shape it is.

To dispose of the "sterilizing" water I plan to neutralize it using a chemical agent prior to disposal which is an acceptable practice here in Ireland, I'd be glad to hear any other methods used further a filed than Ireland, as we are generally a couple of years behind in technological advance, which is why I am subscribed to this forum I enjoy learning engineering techniques from further a filed.

Have you ever used a pig to swab lines made up of two different diameters without having to split the line at the taper location? As the majority of my pipe lines are in main/busy roads I have constructed a temporary pre-cast concrete chamber at the taper locations as I couldn't get a supplier here who could confidently assure me that the pig would pass through the taper, so I just couldn't take the chance given the locations.

Again thanks for all your help guys

Tricky

Thanks for the reply.

I am not aware of any swabs that would be suitable for the diameter change that you indicated and it seems now is a good time for you to have discussions with the water authority.

Your temporary concrete pits to enable swab recovery and insertion of alternate diameter swabs have significant importance. The water authority will need the same features for when they are swabbing the lines (in a few years time). These pits may become a variation to contract in your favour.

You may also want to talk of the difference between sterilization and cleaning.

It seems "by the letter of the contract" that you could use your non potable water, dosed with appropriate chemicals to sterilise the line, but then the water authority would need to flush the line with potable water using swabs and high flow and lots of waste to clean the pipes.

Given your diameter changes and the need to dismantle spools and remove swabs, it seems logical to sterilise in portions, allowing the dosed liquid to remain in each portion for "at least 24 hours" (Meaning that each second day your crew can do the necesary work to move the dosed water into the next section.) But you need confirmation from the water authority of what they will use for "follow on" water in the sterilised pipes. It's no good following with air or non-potable water or anything other than the intended potable supply as the line then will require sterilising again before introduction to use.

I am certain that talking together there is a best alternative solution for all involved.

Tricky, the 24 hour period is required for inactivation of microbes. It is a tried and true method for sterilization of water mains. I wouldn't start messing around with alternatives especially if the Owner is requiring it.

You've been feed some great advice in here so far. I suggest that you follow it, especially following the AWWA, USEPA, and NSF standards to the letter.

What does the Engineer of Record require for sterilization? I'd ask him/her first.

What diameter, please?

Hmmmm, if the powers that be in Ireland can't supply you water yet require you to disinfect the mains with chlorinated water, then WTF???? Than their thinking is ass-backwards through and through IMO!

Have you even considered drill a temporary water well to supply the raw water for your disinfection of the mains and appurtenances?

If only using 355mm (14") over the 9 km length, then you'd need at least 257,000 gallons......and if you pumped the well at a delivery rate of 50 gpm, then it would take 3.6 days to fill the mains, give or take, and not counting leaks.

Look at it this way.....free water except for the drilling and electrical costs!