The accumulation of nuisance organisms such as fungi, algae, molds and various bacteria is a real problem in some areas. Generally speaking, this problem is best solved by preventive treatments rather than waiting until the well is plugged. Usually these organisms can be controlled if every well is sterilized with some accepted method when the well is first completed and then treated periodically. Of prime importance is to construct the well to eliminate any surface contamination. If growths of nuisance organisms are present they can be cleaned up with suitable chemicals and then kept under control with periodic treatments.

All water wells, even if used for cropland irrigation, stock or industrial purposes, should be periodically sterilized. The common test for water pollution is for the presence of coliform bacteria which originates in the intestinal tracts of warmblooded animals. Certainly, the presence of any coliform content in well water shows that other pathogens may also be present which could transmit dysentery, infectious hepatitis, burcellosis or salmonellosis to humans, or scours to swine and livestock. In fact, although caution is seldom exercised in supplying stock water, polluted water will produce a higher than average mortality rate in most animals, being particularly noticeable in slow weight gains and abortions in swine and cattle.

The standard method of treating water supplies for bacterial pollution is by chlorination. Chlorination is adding chlorine to water, essentially utilizing one of three forms of chlorine: chlorine gas, sodium hypochlorite (liquid bleach) or calcium hypochlorite.

Chlorine gas, when added to water, efficiently produces hypochlorous acid, the most effective disinfectant form of chlorine. However, chlorine gas is difficult to handle and is dangerous to humans and animals alike.

Sodium hypochlorite is a liquid product usually obtainable in 5-12 % available chlorine. The problem with sodium hypochlorite is that it has a very short "shelf life". This grocery store bleach product is made with 5.5% available chlorine and 94.5 % water. But, because it is relatively unstable, the bleach could quickly break down into mostly water if not used in a few months. For years it has been customary for drillers and household occupants to "disinfect" their water wells using household bleach. This method is almost totally ineffective because of the low level of chlorine concentration in the bleach and the small amount of bleach commonly used. As a typical example, let's take a 400-foot deep, 12- inch well with 300 feet of water. This well contains about 1765 gallons of water. In order to reach a chlorine concentration of + or - 200 ppm, 7 gallons of bleach is required. Unfortunately, treating this well with the "supermarket method" would probably consist of dumping one jug of laundry bleach down the hole rather than the 7 gallons actually needed to do the minimum job.

Calcium hypochlorite is a granular product usually available in 60-70% available chlorine. It is easier to handle and store than chlorine gas and is relatively stable in that it retains 90% of its chlorine content for 12 months after manufacturing. Cotey Chemical recommends using calcium hypochlorite found in Cotey's WEL-CHLOR to disinfect and sanitize new and old water wells and systems, remove nitrates, iron, sulfites (not sulfates), and manganese, and control algae, fungi and bacteria (including slimeforming, iron and sulfate-reducing bacteria).

When WEL-CHLOR is added to water the available chlorine produces hypochlorous acid (HOCl), a potent, fast-acting disinfectant. In fact hypochlorous acid is the workhorse in any chlorine application for sanitizing purposes. The amount of WEL-CHLOR required to create sufficient quantities of HOCl depends on:

  • Bacterial numbers: If there are large numbers of aerobic or anaerobic bacteria in the water, a high chlorine dosage is required to ensure that all disease-causing organisms have been destroyed;
  • pH: Hypochlorous Acid (HOCl) is the most effective form of chlorine for killing bacteria. It is most readily and safely developed in water whose pH is between 6.0 and 7.0. Above 7.5 most of the chlorine dissociates to the hypochlorite ion, which is up to 250 times less effective a disinfectant than HOCl. Below a pH of 5.0 Chlorine gas (Cl) begins to form. Chlorine gas, a poor biocide, is a powerful irritant that can inflict damage to the eyes, nose, throat and lungs or may cause death by asphyxiation.
  • Temperature: Affects disinfection speed (high temperature = fast disinfection);
  • Turbidity: Chlorine is a surface-active agent. Any suspended particles (turbidity) will interfere with its disinfection ability. Therefore, enough WEL-CHLOR must be used to deal with these interfering elements and have enough left over to destroy all microorganisms in the well. It would be best to remove as many suspended particles as possible by pumping or developing the well for a period of time first and then add WEL-CHLOR.

For best results, premix a solution of water, WELCHLOR and Cotey's CHLORINE ENHANCER in a tank. CHLORINE ENHANCER is formulated to lower pH in a controlled fashion - unlike HCl (muriatic acid). Use CHLORINE ENHANCER to lower the pH of water in the tank to about 6.0. Add WEL-CHLOR and allow it to dissolve. The WELCHLOR will raise pH into the appropriate range for maximum HOCl production. Then introduce the solution into the well. Make sure to flood the well with at least three times the volume of water in the well.

Do not use muriatic (hydrochloric) acid to lower the pH of the water for chlorination, as this may produce dangerous gas.

Bacteria are usually present in the well, gravel pack and formation. However, chlorine is often just poured into the top of the well and circulated with the pump. The chlorine cannot kill bacteria that it doesn't come into contact with. The procedure must ensure that the chlorine solution reaches into the formation and is evenly distributed throughout the system. Cotey recommends using a surge block, a jetting tool, or one of the Cotey WELL CLEANING BRUSHES (the bristles on Cotey's BRUSHES are so tightly placed that they act, not only as a scrubber on the inside of the well, but as a surge block giving the service provider a "plunger" effect that is not available with most handmade brushes) to do the job.

Chlorine is a great product to use for disinfecting water wells, an important step in well rehabilitation. However, Chlorine is not a complete rehabilitation chemical. It is very effective at oxidizing and killing free-swimming bacteria. But chlorine is ineffective if the bacterium in the well are encapsulated in slime, because it doesn't penetrate the slime barrier very efficiently.

Many water wells commonly contain bacterial slimes that plug water-bearing formations close to the well, gravel packs, and well screen and/or casing perforations. Such slimes are produced by iron and sulfate-reducing bacteria. The problem in these wells is not simply to kill the bacteria in the well but to remove the slime that is harboring the bacteria.

Likewise, we know that 70-80 % of all wells in the United States have a buildup of mineral deposits. Mineral deposits not only block water flow, but also allow bacteria to attach to an otherwise clean surface. As mentioned previously, Cotey Chemical has several products designed to penetrate and dissolve mineral deposits and biological slime. Therefore, we recommend that all deposits, whether mineral or biological, are broken down using Cotey's products and pumped to waste prior to chlorinating.