Field Repair & Testing: Important Issues Related to the Newly Updated AWWA C-651 Disinfecting Water Mains Standard Affecting Contractors & Utilities .
By Robert J.
Gordhamer - President of Measurement Technologies
AWWA sub-committee chair for the C-651 Disinfecting Water Mains Standard Committee.
With the newly issued C-651 Disinfecting Water Mains standard out over a month now and having encountered misinterpretations of it in my conversations with customers, we continue our discussion of what the changes in the new update mean to everyone working in the field.
This newsletter offers my interpretation of the standard and in no why reflects the opinion of other committee members, the Disinfection of Facilities committee, AWWA or ANSI.
Our fourth newsletter will cover Cutting/Repair of existing pipe and Verification;
Cutting Into or Repairing Pipe
Making your final connection to the existing water main remains the same in the revised standard, however the next section ‘Disinfection Procedures When Cutting Into or Repairing Mains’ has been expanded to better clarify disinfection procedures and explore three repair situations.
The old standard only covered the basics; what to do to the trench, swabbing fittings, flushing and slug chlorination if needed; no detail, just general statements. You were pretty much on your own to develop a plan. The newly revised standard has been greatly expanded based on input from AWWA Research Studies and field experience of those working on the front lines.
The Disinfection Procedure section goes into detail on which method should be used to match the field condition of the repair or cut-in being done. The disinfection procedure can be as simple as swabbing the repair fittings being used with chlorine solution, because water pressure was never turned off, to complete chlorination of the entire segment.
There are general conditions that apply for all degrees of planned, unplanned, emergency repair or cut-in work.
1. Minimize the work area and notify all affected customers.
2. Expose work area and prevent contaminants from entering the work area.
3. Dewater trench and maintain trench stability.
4. Disinfect all work tools and materials to be used in the work, including existing pipe.
The method of disinfection is determined by the severity of the repair required to complete the water main repair or cut-in. Ideally maintaining pressure throughout the entire process is desired. However in many cases you will have to shut down the water pressure once you have exposed the break. In the most severe cases when you have a blow-out condition in which the pressure is turned off before the damaged area is exposed more extensive chlorination will be required. Here’s a brief explanation of the three cases;
Controlled Repair Without Depressurization: This method requires maintaining positive pipe pressure throughout the entire repair. The trench is controlled using basic procedures for trench management which are to be followed under all repair/cut-in conditions. The repaired section should then be flushed to three turns of water, with no Bac-T testing required.
Controlled Repair With Depressurization: This method is used when the repair area has been exposed before the pressure is shut down. Follow all basic procedures and insure that all exposed pipe and repair material have been swabbed with a 1% chlorine solution. High volume flush for three turns of water, flushing until water runs clear and has the same chlorine residual as the existing system. If the interior of the existing pipe has been exposed additional inspection and cleaning will be required. Checking for Bac-T’s may be needed in this situation.
Uncontrolled Pipe Break: With an uncontrolled break the likelihood of contamination prior to repair is most likely a given. In situations where contamination within the existing system is known to have taken place decontaminate with specific chlorine doses as outlined in section 220.127.116.11 of the standard. Chlorine levels required depend on the decontamination method used; however, if the section cannot be isolated and you have a potential of customers being exposed to higher chlorine levels, then and alternate method should be used as explained in the above referenced section of the standard. This type of repair requires careful review of all procedures before taking repair steps.
All repairs on systems need proper pre-planning to insure that when the time comes your crews will be prepared to react correctly.
The major change is the addition of alternate times allowed between tests. In the old standard the wait time was 24 hours before your 2nd test could be taken. In the newly revised standard you have two options, taking two sample with a wait time of 16 hours between the tests with no water movement for the wait time then two samples a minimum of 15 minutes between tests with the water running. If for no other reason get a copy the new standard and review this section yourself to make sure it is clearly understood.
So how does this newly revised standard effect your daily operations?
Weather you do main line construction or repair work your needs are the same;
· Equipment that will chlorinate and dechlorinate with line connections ¾” and larger is needed.
· Field conditions vary so your equipment should perform under full conditions at low flows as well as high flows.
· For main line construction or repair the requirements are for high volume flushing with dechlorination.
· Repair work may require the need to chlorinate through a ¾” service line or a fire hydrant, so your equipment should be able to handle any field condition.
· Your equipment should NOT require outside power sources as you never know where your work will be bring you.
· Chlorine test equipment should give you readings to 0.01 mg/L and high range for super chlorinating.
Understanding proper testing and construction techniques is critical in assuring good construction practices. Purchase your own copy of the newly revised ANSI/AWWA C-651 Disinfecting Water Mains standard is your best answer for understanding the specifics of what it requires and answering all your concerns.
When looking into equipment to chlorinate and dechlorinate your projects, remember that not all projects have the same field conditions, so when comparing equipment make sure the equipment you consider will perform both duties, deliver the right performance at flows ranging from very low to extremely high flow rates and still do the job. Such as the H2O Neutralizer which offers the best range of flow of all devices available today. Check us out for yourself and confirm what we say true.
Coming up Next
Keep an eye out for our next newsletter in which we will explore how using the continuous feed method with the H2O Neutralizer can make field chlorination & dechlorination easier, plus we will share several stories about projects where the H2O Neutralizer helped get the job done faster with fewer complications.