Well controls?

I think that benefits of shock chlorination 2-4 times per year outweigh the negatives of chlorine treatment. I would agree that a chlorinator should be approached with caution and some water chemistry analysis.

Have you ever seen well cam picks of a well that has not be chlorinated? It is amazing. We have some great footage of a city well screen that is unrecognizable. After some chlorine and Nuwell acid we could see through the screen to the artificial gravel pack. The Nuwell was used first and the chlorine was used last as a disinfectant after our equipment contaminated the well.

On irrigation wells we are able to do a nice job of chlorination. For an average 12†x 120’ well we will use 5 pounds of chlorine pellets. We then rawhide the well. This does a great job of stirring up the water, dissolving the pellets, and moving water in and out of the formation. This can be accomplished because of the volume of water in the column pipe of the turbine pump. Finally, we are able to pump all of the chemical and bacteria out of the well at very high flow rates. It is true that in a five inch water well the effectiveness of such chlorination is not as easy to achieve. It is difficult to move enough water in and out of the formation to really get a good treatment. I guess I am agreeing that shock treatment is often done in a lazy fashion and could be more effective in many cases.

I would also like to note that rust bacteria in a well has a bit of a snowball effect. When rust begins to form on well screens it plugs off part of the screen reducing the flow area in the well. Consider Q=VA where Q is flow, V is velocity, and A is flow area. If the flow remains constant and the flow area decrease, then the velocity must increase. Rust bacteria in fact thrive and grow in high velocity area. This is the snowball effect and one of the reason I feel it is important to control the rust bacteria.

On more addition to my lengthy soliloquy. There is a danger in a bacteria rebound. This is something I am familiar with, however I need some refreshment on the subject. I believe that if the chorine kills the only the bacteria on the surface it provides a greater surface area for growth and a larger energy source for bacteria. This can actually cause a greater concentration of bacteria in the well and more problems. What I don’t remember is if a longer residence time is required or if a second application of chlorine days later is needed. Some help on this issue would be good.

Yes I've seen pictures and pulled encrusted pumps. And I know that bacteria thrive were the velocity is greatest; well screening. They also produce slime and then encrust, shutting down recovery water flow because chlorine can not penetrate the encrustation. And more chlorine only raises the pH which reduces the disinfection properties of chlorine. Then the bacteria thrive under and in the encrustations and the reason to shock the well is back in a week or so. Thereby shocking residential wells usually, over time, makes the situation worse. And if there is any galvanized pipe being used, chlorine attacks it and causes it to rust more. Which adds more iron to the water for the softener to remove but it isn't set up to do that so the resin loads up and you end up with rust stains in the house, on'n on. So I caution those talking about doing it for the slightest reason. But I'm like a whisper in a hurricane when everyone else is suggesting it...

Gary
Quality Water Associates

For most wells bi-annual shock chlorination and chlorination after introducing contaminates when serving would be sufficient.

For severe encrustation, Johnson Nu-Well acid is the way to go. Johnson also has some other products that might be more specifically suited to a well; however, Nu-Well in general gets most of what ails a well. A treatment with Nu-Well, a bit of air development, bailing, and pumping will clean up most modern screens. Wells with bi-annual chlorine treatment shouldn’t ever get to this point though.

Has the original question been answered?

I think the OP's questions were answered or he'd be asking more.

The owner of Design Water, IIRC, he used to be with Johnson.

shack, with that shocking, is there any potential to cause the creation of THMs or have you tested for them after shocking?

Gary
Quality Water Associates

Are THM's a risk with single shock chlorination? If the treated water is pumped out of the well, is there a part of the treatment that stays in the well?

Good question, and IMO someone supporting frequent shocking of wells might want to know if the "cure" is causing another problem that can be a serious health risk before making the suggestion or doing the shocking; especially for customers. And I don't bring that up because I'm easily scared by the thought of liabilities; I'm not, but I know a bit about THM creation although I've never been able to find anyone looking to see if there is a subsequent problem, they just suggest and support shocking.

So another question... how much water must be removed from the well, in what time frame, before any THM contaminated water may have migrated away from the well to return to the well over time?

Also, is migration possible while allowing the well to sit, in some cases for 24 hours plus, before the well is pumped off? And how can we tell if it's possible and has occurred or not and then going to return x to XX weeks later? Or has it maybe migrated to the neighbors' wells; especially in high recovery wells?

Gary
Quality Water Associates

My gut feeling is that pretty much all the treated water gets pumped out right away. The biggest problem in treatment is getting the chlorine water out into the formation to kill the bacteria where it originates. The reason that we have to go back and chlorinate is because we can't get out there far enough and the bacteria migrate back in. This tells me that the chlorine and the byproducts don't get far. Also, the amount of chlorine used less the amount that gets pumped on the ground is a drop in the bucket compared to the amount of water in most aquifers.

You make an excellent point. I am going to have to do some more research into THM"s and think harder about what we are doing. I was completely dumbfounded by your dissention on chlorine until the THM argument.

I am not ready to abandon shock treatment, yet. The diet coke I drink several times a week can give me cancer too!! Where do we want to place our risk??

Actually, when you surge a well, you have no idea of where or how far the water goes back into the formation. OR what percentage goes where or in what direction. So there's no way to know if all the chlorinated water THMs are out of the formation after pumping.

And the bacteria aren't entering through the well to contaminate the formation, they are in the ground and groundwater and just happened to have been in the area where the well was drilled. So there's no way to know how far into the formation the chlorine needs to go to kill 'all' the bacteria but.. I can tell you, you're saying as I do that shocking doesn't work well in screened wells in most cases. Which means there's no hope for it to work at all in rock bores.

The MCL (maximum contaminate level) of THMs is 80 ppBillion. That is a very small amount.

Gary
Quality Water Associates

I guess I don't agree with well surging. It is very difficult to get good treatment outside of the screen, so I feel that most of what you would put into a well is going to stay there. The exception in this case of course would be injection with intention to force foreign material into the aquifer, but for shock chlorination chemicals just don't get that far into the formation.

On the THM's, well that I need to do a bit more research on and learn what is going on there. If there is a better substance than chlorine to disinfect, keep rust bacteria in line, and clean up a well I would like to know.

Isn't your "rawhiding" that you mention, surging?

As to migration, are you saying the water doesn't move past the well at all; especially in a screened well in a sand and gravel aquifer? And how would we know it didn't?

Gary
Quality Water Associates

Yes raw hiding is surging. There is definite groundwater flow or migration. When people talk about an "underground river" it really is an underground river, but things move pretty slow. Without surging, well treatment is not very ineffective. With well surging I think that effectiveness improves. I don't feel that the chlorine is in the aquifer long enough for it to be moved past the well. I also don't think that it is pushed out into the aquifer enough for it to remain their after pumping. Ten feet of 5" well screen probably only has 15 gallons of water in it. This volume is easily pumped out on the last step of the treatment process.

Also, if the chemical is moved into the aquifer, there is a significant volume there and I would expect the small amount of chemical to be diluted by the time it reaches another extraction point.

If I am wrong or have a flaw in my theory, please inform me. I am trying to be open to new ideas here.

I used to use Nu-Well tablets in Michigan years ago. We used them on 4" wells with Stainless steel 3" screens since they couldn't be pulled. It would work well as long as the screen wasn't plugged so bad that the acid couldn't get through it. The way I did them was to put the required amount of acid tablets in the well, then continuously add water. The water would dissolve the tablets and push it through the screen's slots to dissolve the sulphur and iron. They worked well and the water and acid did of coarse run into the vein. The crust around a screen can get pretty large in diameter, and this is why the acid must be forced out into the vein around it. I agree with Shack, it wouldn't have to go very far before it gets totally diluted.

Gary, from I have learned, water moves in an aquifer of sand and gravel about 3 feet per day. That's pretty slow, but then where has it got to go anyhow?

bob...

THMs from Ground Water

Here is a brief quote from a University of Maine site. The essence of it is that there is minimal risk of THMs from chlorinating ground water. I added the bold emphasis.

http://www.umaine.edu/waterquality/publications/7115.htm
When chlorinating water supplies, you need to be careful that trihalomethanes (THMs) don't form in the process. These chemicals form when free chlorine reacts with natural organic substances.

Methylene chloride, bromodichloromethane and chloroform are examples of THMs. These chemicals are considered carcinogens. Several studies have shown that they may increase your risk of getting pancreatic, bladder or rectal cancers (Ijsselmuiden et al., 1992; Morris et al., 1992).

However, remember that
1. there is very little organic material in groundwater;
2. the potential for human exposure to THMs from drinking water varies with the season, contact time, water temperature, pH and disinfection method; and
3. the health risks from drinking contaminated, untreated water are higher than the risk of cancer from THMs.

If you shock-chlorinate and purge your well system, the chance of having any THMs is very low. On the other hand, if you take water from a lake or pond and super chlorinate the water, there is more organic material in the water and the potential for THM formation is higher.

I agree with you Bob NH. That makes sense. I had wondered about the amount of organic material in ground water. Excellent article from the extension service, this article pretty much sums up our discussions here.


What about tannins (sp) or water from coal? Will these types of formations have more organic mater? Any thoughts?

The problem with the article is that it doesn't address the many residential wells with surface water intrusion, or those that are not very deep with short/shallow casing in rock bore wells with recovery water running in just a handful of feet below the end of the casing, etc..

IOWs, IMO it's a blanket statement to support shocking wells, and until I see the data they used to arrive at the no organics conclusion... I wonder if they ever did any tests, I don't see any references in the article.

BTW, I've never seen a Chlorox bottle that didn't say something on the label like Caution, not for use in water treatment.

Gary
Quality Water Associates

Gary Slusser said:

BTW, I've never seen a Chlorox bottle that didn't say something on the label like Caution, not for use in water treatment.

Gary
Quality Water Associates

Click to expand...

Remember, though, we aren’t treating water. We are treating the well casing, the screen, the drop pipe, and the formation material not the water when we are shocking a well.

Remember, though, we aren’t treating water. We are treating the well casing, the screen, the drop pipe, and the formation material not the water when we are shocking a well.

Click to expand...

Shocking a well has nothing to do with water treatment...? I don't believe that nor do I know or know of anyone in any state DEP that would agree with that. And I'll add the US EPA.

Bob(speedbump), groundwater moves in any direction any distance it can at whatever speed it can, IMO there is no constant. It moves (in)to gaining streams, creeks, rivers, lakes, swamps etc.. Gaining streams are fed by groundwater. It moves away from losing streams, they feed the groundwater, they are the water table.

From http://www.groundwatersystems.com/rehabinv.html
Chlorine alternatives for biofouling removal

The use of chlorination in wells is becoming more restrictive in parts of North America and Europe (not entirely a bad thing). Both because of this, and because shock chlorination is seldom the most effective treatment, several other treatments are being used for biofouling control. NOTE: The operation of other well chemicals are described in detail in Borch et al. (1993) and Smith (1995).

And then see this, if you really want to understand well rehab.
http://www.agr.gc.ca/pfra/water/swwidev_e.htm

Gary
Quality Water Associates

Gary, I remember that from years ago at a meeting the Well drillers association had with a Geologist I believe. It was his belief (since no one has been in an aquifer that is made in sand and gravel) that ground water moves through the sand/gravel at about 3' per day. I am not talking about any kind of surface water to include lakes, streams, rivers etc. Strictly the aquifer. I agree it will go any way it wants to but I would think that direction is the same from day to day.

I'm no expert, I'm just repeating what I heard years ago.

bob...

There is a definite flow for ground water. It can be seen in well swl. It is the reason for springs. Aquifers often contribute or take away from streams and lakes. Some aquifers move rapidly and some slowly (relative to other ground water). As we all know water will seek a state of lowest energy and this is the reason for the movement. I would also agree that the water typically moves the same direction from day to day, but may change with the seasons.

Here is a better though to ponder: Does ground water move in the same fashion as the tide? If so, then aquifer flow may not be the same from day to day.

You could answer that Shack by the fact that here in coastal Florida, we have salt water intrusion from drought conditions and over pumping along the coast.

Near as I can tell, the only thing that keeps the water fresh under Florida is enough rain to keep the salt water out.

What were we talking about in the first place???

bob...