In this article, you will learn...
- how to diagnose irrigation well problems
- steps to rehabilitate the well
Irrigation wells are critical to the farming and ranching areas of our nation and around the world. The systems that are supplied by these wells require that they produce water at the rate for which they were designed. Many times, irrigation wells and other types of wells lose their original specific capacity. This can happen over a long period of time, or in some cases, very quickly, depending on the cause. For example, we recently experienced a 1,850 gpm irrigation well being reduced over time to 50 gpm. After rehabilitating the well, it was returned to the original output of 1,850 gpm.
Wells that consistently lose capacity can be put on a proactive rehab schedule. Fast or slow, loss of well yield can happen for several different reasons and sometimes a combination of problems. The more common causes include:
- A drop in the water table from over-pumping or drought conditions
- Problems with the well pump
- Scale buildup in the well
- Bio-fouling caused by organisms that can grow into large colonies
- Plugged screens due to native clay in the formation or bentonite drilling mud left over from the drilling of the well
- Plugging of the screen by fine sands and silt
The problem of the dropping water table is not easy to fix. In some cases, the well can be drilled deeper in order to get down to the water bearing zone. If the problem is the pump, there is an easy, although expensive, way to fix this by replacing the pump.
Keeping detailed records from the time the well is drilled and brought into production is very important in helping determine whether the loss of well yield is a problem with the pump or the well. It is a pump problem if the pump yield and AMP readings are lower than the original readings. If it is a problem with the well, the gallons per minute and well yield have both been reduced.
It is the last four well problems on that list on which this article will focus. These problems can usually be fixed by rehabilitation, mechanically and chemically treating it. There are many different products on the market than can help clean the well and hopefully return it to its original output. These products are effective and safer to use than products like muriatic acid or chlorine, which are more caustic and more dangerous to use. In the case of chlorine, it does not have the ability to penetrate the sheath on which bacteria fouling forms. The newer products can penetrate this sheath and prolong the time it takes for the scale or bio-fouling to return.
The next issue is trying to determine which of the problems listed above is causing the lower yield. If the specific capacity of the well has declined slowly over time, this is an indicator of mineral scale. Other indicators are:
- Hard scale on the pump or pump column when the pump is pulled
- Bubbling on the pump or pump column
- Corrosion nodules on the pump or pump column
- Fluctuation of water chemistries including pH, iron, hardness, sulfates and manganese
- Color of scale is an indicator of the type of mineral scale: iron is red/brown, manganese is black, sulfates are green/blue and calcium is white/light brown
If the well’s specific capacity declines quickly, this is a sign of bio-fouling. Other things to look for include:
- Slime forming on the pump or pump column
- Oily film on the water in the well or a musty odor
- Rotten egg smell
- Increasing iron concentrations
If none of the above conditions exist, clay/bentonite or sand plugging the screen may be the issue. Here are some questions to ask in order to determine if this is the problem: Are there native clays in the formation? Was the well drilled with bentonite drilling mud? Is there sand in the formation? Is there a history of any of these problems in the local area? There could also be a combination of these problems in the well. For example, some wells may have both mineral scale and bio-fouling.
When there is a clear or reasonable indication of the problem, it is time to choose the proper product for dealing with it. There are some great products available that can deal with each of these problems. There are mild acids for removing mineral scale or bio-fouling. If both problems exist in a well, there are products that can be used together in one treatment. However, make sure to check with the manufacturer to be sure they are safe to use together. There are a number of products that will break down clays, bentonites, sand and silt.
The next step concerns the correct application of the product you have chosen. Each product should be used according to the manufacturer’s specifications.
The first step in the treatment process is to check the pH of the water in the well. The pH should be checked throughout the treatment process, then the well should be mechanically brushed and any resulting debris should be removed.
After the product is added to the well, there are several recommended steps for successful rehabilitation:
- Plan treatment for 24 to 48 hours.
- Use agitation a couple of times during the treatment period, for example two hours in the morning and two hours in the afternoon.
- Use a good agitation tool such as a surge block (which is preferred) or a jetting tool.
- Maintain the pH level at 3 or below during the treatment. If the pH rises above 3, add more product.
- When treatment is complete, pump the waste into a pit or tank and treat with soda ash to neutralize the acid.
- Check the pH of the well to make sure it has returned to normal and all of the acid has been removed.
- After the pH has returned to normal, a shock treatment of chlorine is recommended.
- Dispose of the neutralized acid according to local, state and federal regulations.
With the proper use of well rehabilitation chemicals, irrigation wells can have their production rates greatly improved so they can do what they were designed to do.