Flushing of Water Main 5

[valdeng]

A client has a 10" dia. city water main feeding a 100000 s.f. building domestic water and fire protection system. Downstream from the 10" dia. is a 2" dia. feed to a 13000 s.f. building. Tenants in the 13000 s.f. building complain of solids / rust etc. in the water. Is there a recommendation / protocol for flushing the 10" dia. main to eliminate solids etc. from 2" dia. feed?

 

[CESSNA1]

VALDENG: It sounds like this needs more investigation. If there is stuff in the 2" lne, why does nothing show up in the 10" line? Have you analyzed the water to find out exactly what is in it? If this water is used for human consumption there are standards for that, does it meet these standards? You may want to remove sections of the 10" and 2" line for examination. Ordinary flushing may or may not not solve the problem.

Regards
Dave

 

[semo]

As Cessna said, there might need to be more investigation.

How long is the 10-inch and 2-inch pipeline (ie. what is the volume of water in it?) What is the water use of the two users. That will tell you how long the water sets in the line.

Is there any disinfection residual at the 13000 sf building?

How old are the lines and what are they made of?

Is the water aggressive? Check in the 2-inch line and prior to the 10-inch line.

Flushing might help; but, it might not.

When flushing you will want to reach scour velocity to pick up any sediment in the main or it will just carry through later. This means you will probably have to flush the 10-inch and then the 2-inch. Flushing through the 2-inch alone probably won't reach a scour velocity in the 10-inch.

 

[dicksewerrat]

Talk to the City water Dept. about this. they may have amainline flushing progam and can move this line to the top of the list. Otherwise they may flush the 10" line for a fee. either way they have to do the work.

 

[HB2U]

It sounds as if the problem may be within your clients portion of the system. The local water purveyor may not be responsible for the part of the system that's causing the trouble.

As was recommended above, flush the larger diameter pipe first at as high a flow as possible to be sure that scouring velocities are reached within the main. then proceed to the two inch main, working towards the end point of the system.

You amy also want to check to be sure that the fire system in your clients building is seperated from the potable water system with an appropriate backflow preventer. it could be that the building is experiencing periods of decreased pressure which mingled some of the stagnant water from the fire system with the potable water.

Good Luck.

HB

 

[valdeng]

More Info:
10" dia is 720' long connected to 12" dia. municipal water main, serving an unoccupied 100000 s.f. retail building. The 10" dia. is sized for sprinklers. The 2" dia. is 320' long from the end of the 10" dia., also serving 13000 s.f. retail.
The site also contains a 55000s.f. occupied retail building served by an 8" dia. connected to the same 12" dia. muncipal water main. The lines are 40+ years old and are assumed to be cement lined ductile iron.
Future development of the site may consist of 4-6 18000+_s.f. box retails with partial demolition of the 100000 s.f. building. Our current thought is to extend the 8" dia to the 10" dia. to create a loop allowing some flow through as well as allowing connections for future development, feeding 13000 s.f. building from new loop and flush out all existing piping. Isolation valves in the new loop would also allow repair or replacement of existing piping while maintaining service to other buildings. Thanks to all for your responses.

 

[dicksewerrat]

Making the loop is the best idea for you. It will allow fire water to come from both directions. May lower insurance cost. As you said, the loop will give some constant movement of all the water.

 

[KRSServices]

Hmmm,

From what I have read so far, it appears as though there may issues on both side of the service line. CML D.I. can deteriorate over time, but more importantly, if the prpoerty owner has never flushed lines onsite, and the municipality has equally not exercised the hydrants, a buildup of material in the main can accumulate over time, particularly if the source was has a high turbidity and the treatment process does not always or cannot remove all particles. That may be one source of the material your mentioned.

Regarding the loop, maybe I missed something but if the existing 8" is connected to the 10" in a looped effect, the problem is now only being made worse.

Since the land use is retail and the 10" was sized to accomodate sprinklers, I assume that the 8" was sized for that purpose as well. Both lines are sourced by the 12" municipal main. I don't even have to run a hydraulic model to know that the water is going to flow in the path of least resistance, however since we are only referring to ADD or MDD flows, the velocities in those pipes are likely not going to change very much from what is is today....the square footage of the buildings are pretty much the same. The loop is not going to cause a flow through because the water demand is exclusive for the site itself, unless the municipal main runs through the site, at which case this discussion would be moot. Since the 10" and 8" are already sized for sprinklers, looping them may help only in the case of improving flow to the building. Since the fire flow is provided by the municipal line, I would wager a guess that the flow improvement in this case would be marginal - maybe 10 or 20 gal/min...maybe more, depending on the system.

The bottom line is that since improvements to the site will occur, flushing hydrants should be installed and a program be adopted for annual or semi-annual flushing of the lines should occur, hopefully in conjunction with the municipal program.





KRS Services

http://www.krs-services.com

 

[semo]

Unless I am visualizing the system wrong. I don't think looping will help with the problem. You still have a large line with low velocity. Only now you have additional large line for more detention time.

Assuming the 12-inch municipal main does not have these problems, you might isolate the sprinkler supply from the potable supply by extending the 2-inch potable service to the 12-inch municipal main. This would reduce the residence time of the water.