Deciding on a Chlorination Plan for your next Water Line Project.
Chlorination is one of the last
steps in any
pipeline project or repair. Planning for this phase at the beginning of any project is one of the
things you can do to assure this part of finishing any job comes off without
Project specifications should call out the approved process for chlorination that will be used at the end of the job. It may be as simple as the stating that the current ANSI/AWWA C-651 standard shall to be followed or it could involve a detailed process description that the owner/specifier provides. Typically when a chlorination procedure is called out by the owner it is for special field conditions that need to be met.
Let’s assume your project specifications call out requirements to follow C-651 with no real guidance on chlorination method or type of chemical to be used. The specification calls for high volume flushing with dechlorination of all water discharges, including super chlorinated water, to the ANSI/AWWA C-655 Field Dechlorination standard.
The need for high volume flushing and dechlorination will determine what chlorination method you choose for this project. Why the requirement of high volume flushing? Most projects have always had flushing, however in the latest C-651 standard the flushing rate has been increased from 2.5 feet per second to 3 feet per second. This increase is needed to insure all debris from line installation is cleared from the pipeline. The cleaner the line the easier it is to chlorinate and dechlorinate, which helps the owner insure a good clean line at the time it is turned over for service.
You have four methods for field chlorination to choose from, so if you are given the option to choose which chlorination method you use, along with the requirement for high volume flushing and dechlorination of all discharges, be aware that some methods will not comply with all conditions outlined in the standard.
· The Tablet/Granular method of loading the line with calcium hypochlorite during construction is out of the question unless you are able to discharge your water into a sanitary sewer or transport the water to a treatment plant. This is a very time consuming and costly option. While chlorination with this process is less expensive than other methods the cost of chemical required for dechlorination can make this one of the most expensive methods.
· The spray method is for large diameter piping so unless your project is large diameter this is not the method to be used.
· The slug method is feasible with any pipe line size however, the problem is with the slow movement of the water and the need to bring the chlorine slug back to proper residual levels during the movement of the water. Once your slug drops below the proper CRL you need to relocate your equipment, tap back into the piping system to inject chemical to bring the CRL back up to the proper level, and then restart the water movement. This method historically has been used for the large diameter piping systems. With the spray method now available this method will be used less often for very large diameter piping systems.
· The continuous feed method will eventually become the method of choice by all contractors, unless you are doing a large diameter pipe line project. This method allows you to build the system and pressure test the with potable water, which in most cases will not have a significant CRL after it is loaded into a new line that has not been cleaned prior to the filling. This means that if you have a leak during pressure testing you will not be discharging highly chlorinated water into the environment. You would have this problem if you loaded the pipeline with Tablet/Granular chlorination chemical by during construction, which would result in pressure testing with super chlorinated water. Once again, high volume flushing will be easy with continuous method because of the low CRL (if any at all), so dechlorination of this discharge at the high volume flow will be doable with just about any dechlorination equipment able to handle neutralization of potable water. After you have flushed the system of debris then chlorination can take place using the H2O Neutralizer which offers the ability to control chemical flow and maintain chlorine residual at necessary levels. This means using less chlorine to do the job because of a cleaned pipeline, compared to having to over chlorinate to compensate for the dirt still in the line. A lower CRL means you will need to use less dechlorination chemical to neutralize your discharge, which adds up to a lower cost for your chlorination/dechlorination procedure.
If you are going to use the continuous feed method of chlorination the following should be in your chlorination/dechlorination plan;
No matter what method you chose to use, all water entering the new system must be through a temporary by-pass line. The temporary by-pass needs to be tapped into the new system within the first ten feet, the reason being that chlorine will not travel back to the isolation valve if the entry point is farther down the line. Now your water source can be any distance from your entry, all you will have to do is string out hoses to connect to the source.
What does this really mean? Many in the industry have been allowing the isolation valve to be opened to fill the new system, which is like playing RUSSIAN ROULETTE with all the bullets loaded. At some point you will have a backflow of super chlorinated water into the existing system, which can cause major damage.
I recommend that you have a test port at the same location as your chlorination device, as this allows you the best control over your CRL.
If your pipeline has many elevation changes and your pressure is not the best you might have to relocate your chlorination set-up farther down the line when you can no longer push the water. This will only be a problem with systems that have a low pressure.
When it comes to using the continuous method the H2O Neutralizer offers the widest range of performance for dealing with a variety of project conditions. The H2O Neutralizer will work with a full vacuum down to 9 GPM and will only lose all vacuum at just under ONE GPM of flow.
As an example we had a contractor down in the Austin TX area that chlorinated a 24” DIP water line 8,400 feet long with two elevation raises of 85 feet each with a river crossing in between. They chlorinated the complete project by locating the device at the beginning of the project without having to relocate the device.
CHLORINATING THE SYSTEM
When completing projects with the continuous method we recommend that you divide your systems water volume into 1/3’s with the first third of the chlorination at a higher level then what is required by specifications. The second third at a high level but lower than the first third of water, with the last third of water at a level just above the specification requirement. This may need to vary depending on the layout of the piping system. If your system is like a tree with a main line and lateral lines going out from the main line, your chlorination result will be different compared to if you have a transmission line that has a straight run. Remember to pre-plan your testing points during construction, as the standard calls out for samples to be collected every 1,200 feet, plus at the end of the line and each branch greater than one pipe length.
Your discharge point will vary depending on your project. If you have straight transmission line your discharge point is simple, at the end of the line. However, if your system has many lateral lines going off the main line your plan needs to be carefully laid out.
If you have a straight pipe line it’s simple to set up your dechlorination device at the end of the line on a blow-off or fire hydrant. Remember, this needs to be at the end of the line. If your fire hydrant isn’t the end of the line you should install a temporary blow-off at the end.
If your project has multiple branch lines with a main line, it’s easier if you isolate the main line from the branches, flush and dechlorinate the main line first, close the discharge point at the end of the main line, then open each branch one at a time to flush and dechlorinate each separately. When flushing the branch lines start at the beginning of your project and work to the end. You must also relocate your dechlorination device to the head of each segment you flush each time you start a new segment.
You can determine when you are finished by testing your discharge water’s CRL. When it registers the same CRL as your source water you are finished flushing that section.
Chlorination and dechlorination of any project are the final steps in passing the new system for service and turning it over to the owner. Any delays at this time can cause a loss in profits and delay you from moving on to the next project.
So, how can you complete the final requirements of the project with as little cost as possible and in the shortest amount of time? With the H2O Neutralizer.
The H2O Neutralizer is the only device you can use to chlorinate and dechlorinate water systems, and used on 1 inch service lines and larger. The H2O Neutralizer preforms with a full vacuum at flows as low as 9 GPM and can maintain vacuum throughout its entire flow range. Full vacuum gives you a draw rate of up to one gallon of solution per minute entering the venturi, which is controlled with the feed solution control valve.
Compare your options before you choose your method and finalize your chlorination/dechlorination plan, as the H2O Neutralizer is the only device that will provide the range of performance needed to meet the wide range of conditions outlined in the updated standards and found in field applications.