Water service from large mains 8

[mflam]

I'm replacing about a mile of unlined 6-inch cast iron pipe in a busy suburban street. The line has about 100 services. In the same street there is a newer 16-inch CLDI distribution main in parallel, with several cross connections. I can either remove and replace the old line and reconnect the customers to the new line or I can abandon the old line and connect the customers to the 16. Any advice? What are the disadvantages in serving customers from a large distribution main?

 

[stanier]

You need to just consider the diurnal pressure fluctuations in the large manin tos ee if this will impact on the residents supply. Is the main subject to surge? Is the supply reliable in the distrubution main? Is it super chlorinated or subject to chloramination that may kill off all the residents gold fish?

Much more detail is required before advice can be given.

 

[cvg]

If the 16 is a distribution line as you say (not a transmission line) then probably few disadvantages. Especially since the two mains are already cross connected, your large main is essentially serving these customers already. I can't see a good reason to reinstall the 6 inch line. It can't provide sufficient fire flow and twice the amount of maintenance for two lines. It will be much easier to connect each service to the 16 inch main and when all are connected, sever and abandon the 6 inch with very little interuption in service (or none.)

 

[dicksewerrat]

CVG said it all.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[bimr]

Also agree with cvg.

 

[pittsig]

I also agree with all that cvg wrote.

However, additional considerations would be based on the type of "busy suburban street" and the locations of the 6 and 16 w.r.t each other and to other utilities within the street, as well as who maintains the street (e.g., same city/entity as distribution system or city water and state road?).

Some additional questions you need to ask (not necessarily respond to in this forum) are:


What are potential conflicts with other underground utilities, storm drains, or other subsurface conditions (rock, etc.) with either option?

Instead of removing and replacing the old 6 can a parallel 6 (or 8) be installed allowing customers to remain in service until service line changeover (abandon the old 6 in place). R&R will create looooong, unacceptable service disruptions (installation, testing, service changeover). If a parallel main is not an option, read no further and change everything over to the 16.

How will traffic be affected during construction?
Is this a multi-lane road or a busy two lane street? Are the 6 and 16 within the same travel lane, or separated by one or more lanes? Can service changeovers be accomplished with minimal excavation at 6 and 16 with service line pushed/bored between them, or will each service be open cut between the two mains?

How will traffic be affected after construction?
Will the street be resurfaced soon? If not, is a long, essentially longitudinal patch (e.g. from installing parallel 6) preferable to 100+ transverse patches based on ride quality, politics, etc.? Compaction is often a problem on services and taps, and on mains to a somewhat lesser extent (depends on who's doing the work and who's looking over their shoulder...).

All that said, depending on the width of the street and who is footing the bill, it still will most likely be cheaper/better/preferrable to open cut all the service line changeovers and interconnection removals, take the 6 out of service, and overlay several lanes or the entire street than to install a parallel 6 and still have to change all the services over from the old 6 to the new 6 plus still perform extensive patching.

 

[Maury]

I agree with CVG about connecting services to the 16-inch line, but what about fire hydrants? Do they come off of the 6-inch or 16-inch line?

 

[stanier]

Same old story. If the supply is reliable and meets the code why not the 16"?

 

[LHA]

I've recently put a job on the street for bids. 20" main and an 6" capped dead-end were available. The water company preferred both the new dom. and fire hydrants come off the 20". They prefer the 20" so much so, that they are cutting and abandoning the 6" at their cost. This is very unusual, I suspect they want to get rid of a dead-end.

mflam:
This may be your case. I'd bet the 6" is only still there because of the existing connections AND it probably dead-ends eventually (maybe not showing up on the extents of you drawings). The 16" is probably the active loop, and you may be able to get more cooperation than normal - both in financial and plan review times - if you use the 16". The advantage is all to the Utility provider though,. I can't see how it could affect you either way. See if you can get them to remove the 6" if you agree to tap the 16".

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve