How to Effectively Treat Water Wells with Chlorine
Matt Ryan, chemist with Cotey Chemical Corp. for the past three years, runs a lab that researches water samples from all over the world. His clients are drillers and water well professionals that run into roadblocks, often when a well suddenly drops in capacity. He says that predicting what could be plugging a well starts with knowing the chemistry of the water. He determines many water characteristics including mineral content, alkalinity, hardness, pH and bacteria. He also collects samples of scale from the field, and works with company product enhancement and product development.
Ryan earned a bachelor’s degree in chemistry from Texas Tech University, then taught high school and college chemistry for 31 years before joining Cotey Chemical three years ago. He still teaches part time at a private school in Lubbock, Texas, where he is based. He says that it is important for water treatment professionals to understand that there are a lot of different variables to consider and that every water well is different.
At the 2016 South Atlantic Jubilee in Myrtle Beach, Ryan led a session titled “Chlorine: Use and Misuse.” Afterward, National Driller interviewed him on common chlorine misconceptions, factors that impact its effectiveness, and the pros and cons of its most popular forms.
- What significance does a clear understanding of chlorine hold for the water well drilling and servicing community?
- Chlorine is probably one of the most widely used chemicals in a water well. Sometimes it’s a requirement to disinfect a water well. The industry standard for disinfection is some sort of chlorine compound. One of the first misconceptions that a lot of people have is when you say chlorine you’re really talking about different compounds that contain chlorine. The actual element chlorine is just Cl2, and it’s not a compound, it’s an element. What a lot of people call chlorine are your compounds, your hyperchlorites, sodium hypochlorites, calcium hypochlorites and there’s a sodium dichloroisocyanurate, which are all just compounds that contain chlorine. When you put it into the water, a series of chemical reactions start to take place. Based on different conditions, those chemical reactions will change and produce different compounds.
The targeted compound you’re trying to form for disinfection is hypochlorous acid, which is HOCl. That’s the best molecule at killing bacteria. Unfortunately, when you put something like sodium hypochlorite or calcium hypochlorite in a water well, you don’t get 100 percent of that molecule. You get several different molecules and there’s a shift that takes place back and forth between those molecules based on different variables such as pH, temperature, other chemicals in the water, the hardness and alkalinity of water. There are just a lot of variables that can change which chemical is being produced.
We think it’s important that people understand that when you’re dealing with chlorine it’s a very reactive substance and it’s very volatile; it changes into other things easily. If you can kind of monitor those things, especially the pH and the water chemistry, you’re going to be more successful in using chlorine. It can also be very dangerous because it is such a reactive substance. It can do harm to an individual and to the environment if misused. So it’s really important to have some understanding so you don’t hurt yourself or damage your equipment or harm the environment.
- During the session you highlighted three different kinds of bleach. How do they differ with respect to well treatment? What are the pros and cons of each?
- Probably the most familiar to anybody that does laundry is sodium hypochlorite. That’s what most people call bleach. You can buy it in the grocery store. It’s a liquid solution. It has a relatively low available chlorine content because there is a lot of water in it. It’s about 5 to 10 percent available chlorine. It’s very effective at clearing free-swimming bacteria. Its pros are that it’s relatively inexpensive compared to other forms of chlorine, it’s widely available, it’s easy to use because it’s already in liquid form and you don’t have to dissolve it. One of the major cons though is it has a very short shelf life. It’s constantly decomposing, offgassing, forming other molecules. It typically is only good for about six months on the shelf. So by the time it’s manufactured and transported somewhere and somebody buys it and then they start to use it, it doesn’t take long for six months to pass. It decreases its effectiveness over time. In about six months, you’re down to something that’s probably about half as effective as what it started at and it just decreases from there. It’s also fairly caustic, it’s high pH and it is fairly pH sensitive, so when you start to use it, it’s going to have a pH around 11 or 12, which is pretty high up on the pH scale. It can be corrosive and damaging to equipment. It’s a good product, but you just kind of have to be careful with it and know what you have.
The second form, which is probably most widely used in the water well industry and even swimming pools, is calcium hypochlorite. It has higher available chlorine. It’s about 65 or 70 percent available chlorine. It’s in a solid, either granular or pelleted form typically. Its pros are it’s effective at killing free-swimming bacteria, it’s relatively inexpensive, it’s widely available. It has a little better shelf life than bleach, but it’s only about a year. It does offgas some. There are some storage issues with it. If you’ve ever been around it, you really smell the chlorine smell and you have to be careful what you store it next to. It’s pH sensitive like bleach, it’s ineffective on biofilms — it won’t break down slime — it doesn’t dissolve any kind of scale in the well. It is a fairly corrosive chemical, just like bleach. You have to be careful with it. It can damage your equipment, it can harm the environment and it can hurt the individual if you spill it. It does produce chlorine gas and other chlorine compounds, which can be gases that can damage a person’s lungs and cause illness and even death if you’re exposed to too much of it. One last thing is it has a tendency, when you put it in the well — especially in the pelleted form — not to dissolve very well since it is solid. We’ve heard of circumstances where people have dropped these pellets in the well and they sink to the bottom and they don’t dissolve. Then after a while the well’s clogged up and what’s clogging the well is the actual chlorine, the calcium hypochlorite. It’s a product that’s best used when you dissolve it above ground and then pour that solution into the well.
The third form is a sodium dichloroisocyanurate and it’s about 55 to 60 percent chlorine. It’s also a solid. It comes in a pelleted or granular form. It has a much better shelf life than the other forms of chlorine. It’s about a three-year shelf life. It doesn’t offgas as much as the calcium hypochlorite. It’s pH neutral when you mix it. When you put it in water you’ll get a pH of about seven, so it’s not nearly as caustic from the get-go. It’s been used a lot for water disinfecting in third-world countries because at the right concentration it is safe to drink, which is also the case with the bleach and the calcium hypochlorite. If you have a low enough concentration, you can drink it. Most municipal water treatment facilities use some form of chlorine to treat their water. This has probably been used a little more in that realm than the other two, but it is starting to be used some in the water well business. Its cons are it’s ineffective on biofilms, it’s pH sensitive, doesn’t dissolve scale and it’s not quite as widely available.
- What is biofilm, what challenges does it pose and how effective is chlorine at penetrating it?
- Biofilm is something the bacteria make to protect itself. When bacteria colonize, they form, as people call it, slime polysaccharide coating. It’s something that helps to encapsulate and protect the bacteria. When the bacteria are dormant they form it. Sometimes when they colonize they form it. Not all bacteria form this biofilm or slime. They’re kind of categorized into slime formers and non-slime formers. Not all bacteria make it, but the ones that do make the bacteria more difficult to remove and to treat because the slime is sticky, mucus-like material and it’s designed to protect the bacteria from things like chlorine, things that would damage or kill the bacteria.
The chlorine, whether it’s the recommended 200 ppm or even up to 1,000 ppm, does not penetrate that biofilm. Chlorine, the molecule itself, HOCl, has a very similar shape and size to the water molecule. That is why it is effective at penetrating the cell wall of free-swimming bacteria. Slime is different than the cell wall of the bacteria. Slime does not allow water to penetrate it, so it does not allow the hypochlorous acid molecule to penetrate it either. To penetrate that and to break it down, you need something like an organic acid that actually decomposes the slime. Chlorine doesn’t penetrate it and doesn’t decompose it.
What will happen sometimes if you have a well that has bacteria in it, you’ll treat it with chlorine and that removes all the free-swimming bacteria, so if you do a test it’ll show that the bacteria is at a low concentration, which is good. But then, a few days later or a few weeks later when you do another test, the bacteria is back again at a high concentration because the bacteria that was trapped in the slime has reproduced and recolonized the well. So if you don’t remove the slime and all the bacteria, you tend to have a recurring problem.
- How significant are the differences between pH levels? How is it important to take those differences seriously when treating wells?
- The first thing to keep in mind is that pH is a logarithmic scale, meaning it’s based on exponents. When you move from one unit to another, it’s a 10 time increase or decrease in hydrogen ions. Hydrogen ions are, in pure water, there at a relatively low concentration. So it doesn’t take a lot. You add a few drops of lemon juice to a glass of water, that’s going to change the pH. If you have water starting around seven, if you add a few drops of lemon juice it’s going to drop it down to six pretty quick. Add a little bit of acid to the water, it’ll drop the pH. Add a little bit of base to the water, it’ll raise the pH. So pH changes relatively easy in that range near neutral, but as you get lower and lower or higher and higher on the scale, it starts to be more and more significant. As you go from, let’s say pH seven down to pH three, that’s a 10,000 times difference in hydrogen ions, which makes that solution considerably more acidic than water. It’s relatively easy to change the pH when it’s near neutral, but then it becomes more difficult, as the pH gets lower or higher, to increase or decrease the level of hydrogen ions. It’s all based on concentration of hydrogen ions.
- What factors affect chlorine’s ability to effectively kill bacteria in water?
- pH is one of them because at the mid-range pH, somewhere between three and seven, that’s when you typically have the highest concentration of hypochlorous acid. That’s when your chlorine is most effective at killing bacteria. Temperature is a factor, but when dealing with water wells we don’t see a huge temperature fluctuation. If we’re dealing with water, usually we’re dealing with temperatures that are fairly stable and in a fairly stable range. In the lab if you start dealing with lower or higher temperatures, that affects the equilibrium and the amount of hypochlorous acid also. The background water chemistry is a key factor; what’s in the water you’re treating? Whether there’s a lot of magnesium or manganese or iron, if those ions are present that’s going to affect the equilibrium and shift those molecules that are being produced by the chlorine. If you have a typical situation where it’s relatively low calcium, relatively low iron and low ions, then it’s not as big a deal. Every water well is different and there are some situations where you have very high calcium content or very high iron content, and that is going to also impact how effective your chlorine is. When you put chlorine in that kind of water, those ions are going to consume the chlorine and it’s going to be less effective. If you’re aware of that to begin with, you may have to add more than you might predict to get that concentration you’re looking for, around 200 ppm. If the water’s unusually hard or unusually high in iron content, that’s a good thing to know. A well contractor, if he works in a particular region, is going to be familiar with the water in that area and kind of know what’s typical.
- You mentioned that it isn’t uncommon for drilling contractors to use an overload of chlorine to shock the system. Is that OK or not, and why?
- Shocking is basically adding way more chlorine than you really need. The 200 ppm is really sort of the target, but if you add 1,000 ppm or 5,000 ppm you know you’ve put enough to make sure you’ve wiped out all the free-swimming bacteria. The problem is you still haven’t dealt with any of the slime. Even at a high concentration — 1,000 or 2,000 or 5,000 ppm — that still will not penetrate any of the biofilm. So shocking it is not going to really do you any good. You’re kind of wasting your chemical and then you end up with something in the end that is somewhat dangerous. You have this high-chlorine wastewater, and what do you do with it? You should never poor it into a stream or lake or anything like that because it’s going to be very damaging to the aquatic life. … Chlorine, because it is so reactive, doesn’t take long to decompose. It’s essentially biodegradable given a reasonable amount of time, but what do you do with it in the meantime? So by shocking you have this solution that has a high chlorine content and it’s going to be producing some chlorine gas as well, so it’s just not a good idea to use way more than enough. … If you can calculate the amount you need to reach that goal, that’s the best practice.
- Are there any other common mistakes or misconceptions you see with chlorine and water well treatment?
- One of the most common things is to overuse it and use chlorine as a cure-all. They say, “My water well is clogged. It’s not producing as much water as it used to. Let’s add chlorine to it and see if that will fix it.” Sometimes it does provide a temporary fix or a small increase, but it’s definitely not a cure-all. You need to look at other chemicals, other chemistries, to unplug the water well. There are all kinds of mechanical techniques also to help unplug a well, from brushes to surge blocks to compressed air. Some of those things are very effective at unplugging a well and then if you use chemistry in addition to those, that tends to be where you have the most success. With the mechanical methods you can remove the stuff on the surface and some of the stuff that’s in the cracks and the screens and whatnot, but to actually penetrate into the formation a bit and unclog the other side of the screen and some of the clogging that’s in the gravel pack, your chemistry tends to do a better job there.
If nothing else, what do you hope attendees take away from your session on chlorine, bacteria and water wells?
- As a lifelong educator, I’m most concerned with people having enough knowledge to be able to do their job efficiently and safely. Treating water wells is like treating patients if you’re a doctor. It’s not an exact science. There are so many variables and you’re trying to do the best you can to bring the water well back to where it’s healthy again, just like you would with a patient. When someone gets sick, they want something to make them healthy again. That’s what we’re trying to do is get the water well back to where it’s healthy. Often it takes some experimentation. … I think that’s a good idea in the water well business, that you come in and you give it your best shot, but then sometimes you need to come back and take a second look at it. Maybe there’s another approach that could bring the well back. I think sometimes we want things to be quick and fix the problem the first time, but it doesn’t always work out that way. Mainly, I just want people to expand their knowledge and understanding of some of the chemistry that’s taking place in the well, some of the chemistry that’s involved with the chlorine so they can safely and effectively do their job.
- For drillers who run into questions and roadblocks during the water well treatment process, where can they go for help? How important is it for them to seek guidance when they’re unsure?
- They can, of course, go online. There are companies there that have excellent websites. There are many websites that I use to help diagnose different kinds of situations that come into our lab. Cotey Chemical has a good website that has diagnostic tool on it for different kinds of situations that come up in a water well. We’ve also produced an app to help the contractors calculate the amount of chemical you might use to treat a certain situation in the water well. Of course we also take phone calls if a contractor is curious about a certain situation, not understanding a particular chemical or whatever. They are welcome to call Cotey Chemical and we’ll try to answer their question and point them in the right direction. Otherwise, a lot of times we’ll say, “Send us a sample of this and we’ll take a look at it and see if we can’t come up with a solution.”