Well Chlorination & Submersible Motors

This issue of Franklin Aid discusses chlorination of water wells only in the context of possible adverse effects to submersible motors if caution is not exercised. This issue is not meant to serve as an all-inclusive procedure for chlorinating wells. This would be impossible since specific requirements and regulations vary by state and locality. For additional information on correct chlorination procedures, please contact your local health department or your State Department of Natural Resources.

Chlorination of new and existing water wells is a common practice in our water systems industry. Chlorination disinfects water supplies and kills bacteria, which may be present in the well or was introduced into the well during normal drilling and casing operations. Ideally a water well should be chlorinated without a submersible water system installed, but this is not always practical.

When chlorine solutions are introduced into a water well, hypochlorus acid (HClO) and hypochorite ions (ClO-) are formed. These two oxidizing agents perform the disinfecting process. Unfortunately, these two agents are very corrosive and can cause corrosion damage to submersible motors, pumps, metal piping and metal casings if these components are left in contact with the chlorine solution for very long.

The amount of chlorine solution required to disinfect water wells is normally quite small, ranging from one to six parts per million. As an example, if a 5.25% chlorine solution, as described below, were used at a rate at one part per million, one gallon of solution would treat about 50,000 gallons of water. Also, the actual time of exposure required is normally very short. Once the chlorine solution is fully circulated throughout the water well, it completes its disinfecting job in a matter of minutes.

Local health department requirements and guidelines should always be followed, and consideration should be given as to how much chlorine solution is really required to disinfect the well.

The following lists the types of chlorine solutions normally used in disinfecting water wells and the suggested maximum exposure time for each:

1) Sodium Hypochlorite (NaClO): Normally sold as a water and chlorine solution and commonly used for laundry bleaches. Sodium hypochlorites are typically available in two strengths, “domestic” and “commercial”.

  • a) Domestic: This is common, ordinary household bleach and is available in stores under names like “Clorox”, “Purex”, and others. It typically consists of a 5.25% chlorine solution. Exposure time for submersible motors to these agents should be limited to 2 – 3 days.
  • b) Commercial: These bleaches are generally available from chemical wholesalers and/or some hardware stores and consist of 10% to 19% chlorine solutions (15% is very common). Since the concentration levels are higher than household bleaches, smaller amounts can be used to accom- plish the same task. Exposure time for submers- ible motors to these agents should be limited to 1 – 2 days.

2) Calcium Hypochorite (Ca(ClO)2): This form of chlorine is normally sold as powders or tablets and is available from chemical wholesalers or dairy supply houses under names such as: “H.T.H.”, “Perchloron”, among others.

They consist of 30% to 75% active chlorine by weight with 65% mixtures being common. If these types of chlorine are merely dumped into the well, they will probably come in contact with a submersible motor before they dissolve. If they adhere to the motor or merely collect in the bottom of the well they are likely to cause corrosion damage as they dissolve. Powder or tablet forms of chlorine should always be dissolved at approximately 1 part product to 10 parts water before being introduced into the well. Exposure times for submersible motors to these agents should be limited to 1 – 2 days.

In some cases, hydrochloric acid (HCl) is added with chlorine solutions to lower the overall pH level and speed the disinfecting process.

This practice is unnecessary and is not recommend because the hydrochloric acid makes for a much more corrosive mixture.

In all cases, the exposure time is much more important than the type or amount of chlorine mixture used. These solutions should never be left in contact with submersible motors any longer than required and certainly not more than a few days. Extended contact could start corrosion of the stainless steel outer materials, especially in the welded seams. Once this corrosion starts, it can continue even after the chlorine has been pumped off and can contribute to early motor failures.

If these guidelines are followed, chlorinating a well should have no adverse affects on your submersible motor.