Water Main Construction / Testing Difficulties 2

[mathmday]

I currently have a Client that is installing water main extension(s) to rehabilitate an existing system and is encountering difficulties that I believe are beyond his control. Any advise on means or meathods that he can utilize to mitigate this problem would be greatly appreciated, and ideas of other potential causes of the problem.

Existing System - 4in dia cast iron, leaded joints every 20', unclorinated, wells provide source water, approximately 40% loss of produced water due to leakage.

Improvements - 8in dia C900 PVC, cast iron fittings, flushing / chlorination / pressure and bacteriological testing being performed in accordance with the appropriate AWWA standards.

Problem - Currently he has installed approximately 6,750 LF of pipe. Through the course of construction this season he has had 27 failed Bac-T tests due to coliform hits. This equates to a failed test for every 250 LF of pipe installed.

Hypothesis - Due to the abnormal amount of tests indicating the presence of coliform without a significant and measurable amount of chlorine being utilized in the disinfection process, as indicated by the residual, we hypothesize that either: pressure transients induced by the specified flushing procedures or other systemic causes are providing a pathway through existing pipe deficiencies, or biofilm containing coliform is being stripped from the existing pipe walls into suspension thus causing difficulties passing our bacteriological tests.

 

[bimr]

These bacteriological testing tests are very sensitive and must be done by a qualified person and trained person.

I would recommend that you have a qualified person and trained person oversee the testing process.

 

[mathmday]

Bimr, to clarify the samples are being taken by the Project Engineers field inspector and to the best of my knowledge he is taking the appropriate precautions and following the appropriate proceedures. Assumeing that this is true do you have any insight / opinion on my proposed hypothesis? Thanks for taking your time to discuss!

 

[kwdwaterengineer]

mathmday,

without being there, it is difficult to find a solution to the problem and I may have more questions than answers?

* For each test, what is being tested? Is it only the blow off, or is it both the blow off and the injection tap that was used to inject the chlorine mixture into the new main? I normally test both as a check. In an unchlorinated system, I would do a third likely from a nearby house from where the water is fed to fill the main. This will establish that the water used to flush will pass a bac-t test.
* What method is being used to determine if the test passes or not? Absence/presence testing will need to be confirmed if it is e-coli or not. WAS THIS ACTUALLY DONE? Membrane filtration needs to have the "green sheen" to confirm the presence of e-coli, but one can determine how prevelent the growth on the membrane. WAS THIS ACTUALLY DONE? When trouble shooting such a problem, there is a big differnce between one growth and too numerous to count growths. Any growth may or may not be e-coli, it often takes an additional 24 hours. (don't quote me on this one, I do not have an up to day "Standard Methods" book at hand)
* What is the turbidity of the samples taken?
* What is the total chlorine on the samples taken?
* What are the sampling ports? Are they clean? Have the samples been taken through a fire hose? (I have had a main fail because of this)
* What was the disinfection method used? Was it slugged or did it sit for 24 hours?
* What was the initial concentration of Cl2 in the main when the test started? The standard is now 25 ppm, but historically it was 50 ppm and not dropping to less than 25 ppm after 24 hrs. And the concentraion during the flushing. (I would not bother this test unless I was having problems)
* When the main was flushed, what was the velocity? Was it greater than 2.5 fps, as required in AWWA C651?
* When the samples were taken from the main, how long before the lab ran the samples, either through the membrane or prepped for absense/presense? How were they handled in this time? In a cooler with ice or left on their own in the cab of a truck? Do you have a chain of custody form for each sample?
* When the sample was taken, was the entire area sprayed down with alcohol to prevent contamination from another source?
* What has been the attitude of the inspector that took the samples? Is it a person that does the minimum or one trying to find a solution to the problem too?

After all these questions I have posed, I would be be pointing to the existing water system and that the water being used to flush is already contaminated, this may be able to be confirmed with an additional sample taken from where the source water is comming from. (I have been told of this problem like yours with an unchlorinated system) If the owner/engineer does not want to do the additional testing, I would demand to see the chain of custodies for each failed sample, and then start talking about a change order for delay if they cannot be produced imediately. If the main cannot be flushed at 2.5 fps because of restrictions in the system, or excessive velocities in the existing system to get the proper flushing, I would be complaining that the contractor was being set up for failure.

Sorry I do not have a direct answer for you, but to solve problems like this, it requires looking at all of the inputs that my have caused the failure. (or being reported as failure)

Jefferson

 

[mathmday]

kwdwaterengineer, once I get a chance to sit down this weekend I will get your questions answered and give a synopsis that is more encompassing! Thank you for your time and I have to say this is a great tool for us engineers to be able to utilize. As I am a manager within my company I am going to impliment this website as one of our standard websites to reference for information.

 

[bimr]

Really not following your concept. You say that the disinfection process is following the AWWA procedures, but then state that you think no significant amount of chlorine has been used. The AWWA test calls out for 50 mg/l residual.

Attached is the procedure for your review. What part of it is not being followed.

 

[FlaCivEng]

Jefferson certainly makes many valid points which illustrates the fact that the disnfection process and bacteriological sampling needs to be correctly done in order to be successful. But looking at the big picture for a moment for sake of this discussion, let's assume that the pipe has been properly installed, pressure tested, disinfected, and sampled by the qualified personnel. If that's the case, then I would certainly, test the water being used for flushing the pipe after disinfection for the coliforms. I don't see the pressure transients during flushing being a factor here, especially if the main passed a recent pressure test. If you you are not certain about whether the pipe has been properly disinfected, flushed, and sampled, then by all means, certainly use Jefferson's post as a troubleshooting guide. Good luck.

 

[mathmday]

Bimr, when the Contractor clorinates the line he has an "inital" residual of 50mg/l. After 24 hours he staill has a 50mg/l residual. In essence none of the disinfectent is being utilized. Cheers to you Bimr :O) I do want to clarify something about my knowledge base; I am more of a structural geek and contract geek. So if you all bear with me I will hopefully be able to return the favor in those areas on this website.

 

[kwdwaterengineer]

bimr,

I am refrenceing AWWA C651 2005 revision. The initial dosage 25 ppm and the residual shall not be less than 10 ppm at the end of the 24 contact period. I have written into my past specification for 50 ppm. I found a 1986 C651 and for the continous feed method, it also lists the inital dose shall not be less than 25 ppm and at the end of the 24 hour period the residual shall not be less than 10 ppm These are the actual C651 standardard published by AWWA, not what someone transcribed into a spec. book and the specs keep getting reused for too many years without review. I have been guilty of that crime as well. I can scan the 2005 version of C651 if you like, but AWWA frowns on that practice.

I put into my specs the 50 ppm minimum with the 25 ppm minimum after 24 hours. It seems to be what has normaly been done, and if a little is good, more is better. Its my stamp on the specs and plans. I want success when the disinfection is done, and no retests.

mathmday, I wish we could p.m., I would give you my contact information so we could talk out through and find a solution. I have done water main testing since my teens and have taken a intrest in your delemma.

Jefferson

 

[kwdwaterengineer]

What the heck, here is a scanned section of C651.

 

[bimr]

You may be having false positives because of the water quality. High total dissolved solids (TDS) may interfere and result in false positives.

false positive total coliform samples are not unusual. See #18 in this link:

http://www.elibrary.dep.state.pa.us/dsweb/Get/Rendition-764663/index.htm

In light of the number of positive samples, you should have the samples tested to determine what microorganism or whatever is causing the samples to test positive. The state

 

[mathmday]

Jefferson,

Your expertise and intrest in this delema / debacle is appreciated! Now that I am getting familiar with this forum I have read the rules and understand that it would be taboo to exchange information through this website. I do believe that I could still contact you outside of this website with your permission?

Cheers and have a great weekend!

 

[mathmday]

Jefferson,

Finally have had time to research and get your questions answered and proceedures clarified...

1.) What (location) is being tested - Only the blow off, unless as required by the specifications an additional sample port every 1000 LF. I agree with sampling from a nearby house and the injection tap; I will have the Contractor request to do so in the future.

2.) Lab Test Methods - Although this may not mean anything to me at this time the test reports state that the testing method is, "SM 9223B". The report lists E-coli and Total Coloform being tested for Absence / Presence and amount in cfu / 100 ml.

3.) Turbidity - The Contractor has not utilized a turbidity meter when taking the samples but has been advised by others that he should utilize this when flushing the main as his Superintendent has verbaly stated to me that there is noticeable sediment being purged during flushing operations. Additionally, he also stated to me that he could see particles floating in the last sample taken for this Construction season.

4.) Total Chlorine Of Samples - The samples contain no detectable chlorine as they are required to flush prior to sampling such that the water left in the extension to be sampled is the same or less than the existing system which has no residual.

5.) Sampling Ports - All but one port has been a temporary 2 IN blow-off, and once an existing hydrant was utilized due to the section only being a tie-in to existing. (This was a debacle) As to the cleanlyness I would say that they are utilizing new materials and taking greater care then they would in disinfecting installed ports on other Projects due to the difficulty they have encountered on this Project.

6.) Disinfection - They have been Clorinating the main with an inital concentration of 50 ppm and after 24 hrs prior to clearing the main with this existing system water the residual concentration is 50 ppm. When they clear the chlorine from the line they have no measureable concentration.

7.) Inital Flushing - Flushing has been problematic at times from what I have heard. The Contractor does not believe that they are getting 2.5 fps. I need to dive a bit deeper on this one to verify.

8.) Test Sample Handling and Timeframe - Samples are being placed in a insulated lock box delivered to the lab and tested on a rush order; typically all within 3 hours. There is a chain of custody number on each test report but no formall paperwork that the Contractor is filling out. Spraying of the area, as most of these tests are not taking place in the trench I believe that they are disinfecting only the blow-off port or in the case of the hydrant any external surface immediate to the port.

9.) Inspector Attitude - Lot's of attitude but in no way is there any effort to find ways to mitigate / identify the real problem, and likewise find a solution. The general attitude is it is the Contractor's fault.

I am so used to being able to identify problems such as, "There was groundwater under your foundation that caused the underlying clay to swell and subsequently cause your structural failure" in this case we are talking about little bacteria that are natuarally occuring and can be anywhere! Your help on pinpointing the cause whether it be the Contractor's methods, the Existing system water, or Sytemic issues is GREATLY APPRECIATED :O)

 

[kwdwaterengineer]

mathmday,

There seem to be some potential "red flags" from what are able to give. Can't go back in time and add another test port. The prepackaged sample bottles used for the absence/presence testing that we use are extreamly sensitve to user contamination and false positives. Filling a second bottle and having the lab run a turbidity test on it is a clue that may lead one to believe that it could be a false positve if it is higher than 1 NTU. The disifection seems to be "by the book", but having difficulty getting water to properly flush may be the problem.

If you want to reach me, (I am not a consultant) I am not too hard to find. If you use a search engine for "kennebec water district" and then go to contacts, I can be found and contacted.

Jefferson

 

[dicksewerrat]

Can the entire system be shut down so you can put a camera inside the pipe? We had a water main we couldn't get the coliform to pass. When we opened up the pipe ,found a shirt from one of the laborers in the pipe. The only other thing is you aren't getting a good flush of the pipe. The water should be running clean before you test. And wth new construction that should not be that hard to do.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com