Pipe flushing

[dawatcher]

Hi there,

we have a typical groundwater system with a well supplying to storage tank providing water to the building. to avoid cost of digging another well to comply with groundwater rule, the owner wants to tie into city's water system for backup. since the two water supplies employ different treatment methods, it is advised that they not be mixed or to keep the mixing at a minimum. i tried to see if someone else in our state has dealt with such a problem and i found out that we are the first ones to encounter such an issue (because everyone else that have a groundwater well as primary source have another well as a backup and do not tie into an existing system). anybody have any ideas as to how to proceed?

thanks in advance!

 

[RWF7437]

First, your situation is NOT unique. Public water supply systems are responsible for water quality, i.e. safety, from the source to the customer's tap. For that reason, few, if any, will allow the interconnection between their system and another source system of unknown quality.

Because this is a responsibility placed upon all nearly all water suppliers by the Federal Clean Drinking Water Act it is NOT unique to your State.

If you wish to continue to use your well for some uses, irrigation for example, you can but you will likely be required to completely and permanently disconnect it from any public system. This may result in higher water costs for your building but the public water supplier is required by Federal Law to protect the public health.

How to proceed ?

Examone the costs and consequences of three alternatives:
1. Continue as you are on a completely private system
2. Disconnect the private well system and go completely to the public system
3. Operate two independent systems for different uses.

good luck

 

[dawatcher]

Firstly, thanks for your response.

Well, I guess I should have mentioned that I do not think the system is unique in any way. I merely meant that no one has encountered it here in my state that I know of.

The owner wants to use private system (well) for ALL purposes including potable water supply and use public system just for backup (in case the well goes offline for some reason).

So when the well goes offline, we would like to kick in the public system's water in to our system. This is where our problem arises when trying to find ways to avoid rapid mixing of these two different sources since the private system water is in the system (to avoid any kind of problems such as odor, taste, color, reduced chlorine residuals, etc.)

Some kind of mixing is inevitable, but we want to keep it at a minimum and flush the water out of the pipe system. I just wanted to see if anybody had to do this and get any ideas.

Thanks in advance!

 

[bimr]

Many public water supply systems will require you to put in some type of a break tank system to ensure no interconnection. Tyically you would have the public supply entering an atmospheric tank with an air gap between the public water and the water surface. You would then have to repump to pressurize.

Talk to an engineer at the water supply agency. They should be able to provide you with their requirements.

If you water supply is potable, there should not be any great concerns about mixing the two different waters. Mixing two potable supplies is not going to have a synergistic effect where the mixed water is not potable.

 

[redbridge]

I agree with bimr that you may need a break tank or a backfrow preventer. There is no problem with mixing the water as long as they are disenfected the same.

 

[RWF7437]

"There is no problem with mixing the water as long as they are disenfected the same."

If disinfection was the only responsibility of a public water supplier, this would be a true statement. Protection of the public health requires a lot more of both water suppliers and the agencies who regulate water systems. All of the contaminants listed by the USEPA and by State Health Department ( at least in Oregon for the last 47 years, in my experience ) must be controlled to acceptable, legally enforceable levels. Any public water supplier who accepts responsibility for a water source it does not control is risking public health and probable lawsuits. Any State agency charged with overseeing public water systems can be similarly at risk.

 

[bimr]

That is why you need to talk to an engineer at the water supply agency. The water supply agency will provide you with their requirements before they will sell the water to you.

 

[redbridge]

I must of misunderstood, I thought the tank was privatly owned.

 

[bimr]

After reading your post again, another potential water quality issue comes to mind.

If just one of the water supplies happens to be using chloramination for disinfection, there will probably be an issue with mixing the waters. Other than that issue, there probably will be nothing signficant to worry about insofar as mixing of the two supplies.

 

[stephenw22]

Your public water company should be able to provide the specs for, or install a backflow preventer in their system where it enters your building.

For flushing the system when it switches sources, a small PLC or relay panel could easily do it for you. Just use a 3-way solenoid valve to switch water supplies and another one to flush the system to the sewer. Using a timer block on a relay would regulate the amount of water you use to flush the system.