Coliform bacteria in well water

We had a water test done on the well water of a vacation home we are considering buying. The test was positive for coliform bacteria and negative for E.coli. We have been told that the presence of coliform bacteria is common in vaction homes that are not used often and can be eliminated by shocking the well. How does the lack of use casue the bacteria to be present? Also, if the water was negative for E.coli, can we assume this means that the source of contamination was not from the septic system?

Thanks for all replies.

 

You need to ask those that told you sitting causes coliform bacteria problems to prove their theory, which they can't. No the absence of E-coli doesn't say the coliform isn't from septic any more than having E-coli present says it is. It comes from a number of sources and the US standard is no coliform present in a 100 ml of the water. many folks may suggest shocking the well, and if you/they do, restest after 3-7 days after the smell of chlorine is gone if you want to know if there is a recurring problem. Otherwise you get a negative test result, go to closing and find out a few weeks later you or someone else aren't feeling good or the dog won't drink the water and you restest to find it present again. At least that happens here quite frequently. Personally I'd go with treatment equipment like UV and any pretreatment needed.

Gary
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Doug Aleshire, Super Moderator 2

 

First of all don't go panic stricken, confusing E.coli with common coli. Many wells, (especially the 3-4 foot wide ones with a concrete or wooden lid ) are found to have coliform. As Gary said, it can come from a number of sources. Coliform is bacteria present in all animals and vegetation. It can enter a well through slugs, woodlice, spiders, roots, leaves etc. E. coli, or Eschicheria coliform is the really dangerous one and comes from the intestines of warmblooded mammals.
(for an excellent explanation of this go to the site of Maine Government Water Treatment)

I frequently shock wells to get rid of coliform ( see thread below -"shocking the well" ) I do 2-3 a week on average and usually get rid of the coli. first time. There ARE exceptions however and I have had to do some wells 3-4 times to get rid of it. After the shock I always advise owners of these wells to pour in a gallon of domestic bleach every month directly into the well. By the time this gets to the house it has dissipated, but hopefully killed any coli.

I would recommend hiring a good well guy or company to do it first time, follow them around and ASK lots of questions with the object of doing it yourself next time.

 

nomind, I gotta disagree some. Shocking isn't always bad but IMO it is overdone from a water quality and a few other points of view. Shocking a well can cause water quality problems that without testing for THMs (trihalomethanes) or specific DPBs (disinfection by products) you won't know exist; or were created. It can also cause pump problems and water treatment equipment problems that should be by-passed first and then sanitized independently and properly. Shocking can also cause migration of dirty chlorinated water to neighbors' wells which if that happens upsets them more than a bit... Shocking can also cause other problems in the well, like bacteria caused slime production and encrustation formation which can lead to reduction in recovery rate and submersible pump problems. Chlorine alone can not penetrate the slime or encrustations and using more chlorine raises the pH of the water and pH above about 7.2 results in chlorine being less effective. It also becomes less effective in the future due to the slime and encrustations. I've shocked many wells over the years and done followup coliform testing on many of them. I used to do an average of 18 bacteria tests per day and about 4-6 out of 10 would show positive for coliform and after shocking those, 6 to 8 out of the 10 would still show positive for coliform within 2 weeks to 12 months after shocking. In some cases shocking was repeated with the same result but shockiing wasnt done 3-4 times.

So I decided that shocking wasn't a viable solution and started to propose water treatment and cautioning that shocking was at best a temporary 'fix' as the PA DEP starting saying. Within the past year or two a web search had shown a number of states that have done studies concurring with me; and the PA DEP. So my advice is to shock knowing of the potential problems it can cause and not to rely on one or two negative test results soon after shocking.

Gary
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Doug Aleshire, Super Moderator 2

 

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Gary - thanks, you've pointed out a relatively new and very complex issue.

I'm going to look for and review lots of research on THM and similar before I attempt to answer; Just a few points I must clarify though:-
1. Any water treatment equipment is by-passed before I shock.
2. ph is measured and I don't do it unless below 6.8
3. All chlorine is thouroughly flushed from the system before anyone uses it

You may well be correct that it's only a temporary solution - I just need to be convinced by researched facts and figures.

 

Then you're doing it right. Try
http://www.groundwatersystems.com IMO that's the best source for all you ever wanted to know about well problems and solutions. You may already know about it... I'll be back to you tomorrow on the other message.

Gary
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Doug Aleshire, Super Moderator 2