Flushing/disinfecting large diameter pipe

[Glenhed]

I am working on a 36-inch diameter ductile iron pipe project. Has anyone out there had experience with flushing and disinfecting such pipe? AWWA 651 states that flushing such large pipe may not be practical, and that the installation crew should take great care to keep dirt and debris out of the pipe during construction, and that in the end it is up to the "owner" to ensure their pipeline is clean. Well, it is nearly impossible to keep foreign material out of the pipe, despite taking every precaution. Flushing will be necessary to get rid of any dirt. The recommended flow rate is 2.5 feet per second, or for a pipe this size, about 8,000 gpm. That’s a lot of water! How to disperse that much water? Any advice would be appreciated.

 

[rconner]

You may consider "swabbing" or swab cleaning (e.g. with foam pigs designed for that purpose), as I understand is sometimes done e.g. in sandy areas like Florida etc. [See e.g. ftp://onetgov.net/divisions/Utilities/pub/PlanReview/ManualOfStandardsAndSpecs/Manual_Approved2011/StandardsAndSpecs/4210%20Testing%20and%20Inspection%20for%20Acceptance%20of%20Water%20Systems.pdf ]. Of course, at least some sort of appropriate access/structure would have to be provided for this purpose.
While I do not have any direct experience pig/cleaning that size pipe, I understand the principles regarding pig cleaning are that with a suitably designed pig much lesser quantities of propelling water can effect very high flow velocities in a sheet of water around the pig (that in turn propel at least some amount of debris quite effectively in front of same). I did see a 12” line effectively cleaned many years ago, with water from a fire hose in this manner. You thus may wish to talk to the folks who make cleaning/swabbing pigs.

 

[bimr]

One alternative that has been used involves the use of flexible foam pigs that can be introduced and moved through the pipe with water pressure to remove most of the larger particles through a scouring action. However, the use of pigs must be anticipated during the design process so that valve types and insertion and removal points for the pig are included in the project.

Another alternative is the feed chlorine as a concentrated slug.

http://www.bcsunited.net/2009_Files/Specs/Water/331300.pdf

Ozone has been used as an alternative in some locations because the water that is wasted is easier to dispose of:

http://www.ncsafewater.org/Pics/Tra...ctionDistribution/AC08CD_Tues1100_Lapsley.pdf

What has the project's design engineer put into the specification?