I) Iron Bacteria Sulphate-Reducing Bacteria

The growth of bacteria is a common problem in water wells. Although not a cause of health problems in humans, bacteria can be a nuisance to well production.

Iron Bacteria are often found in wells completed in aquifers which have a high iron content. Iron Bacteria oxidize dissolved (ferrous) iron, forcing it to come out of solution. The oxidized (ferric) iron is deposited on the well casing/screen. As Iron Bacteria multiply, they produce a stringy jelly-like slime. A combination of the iron deposit and bacteria build-up on casing perforations, screen slot openings and even in the, pore spaces of the water bearing formation, can severely reduce the yield of a well.

Sulphate-reducing bacteria can be a problem in wells completed in aquifers which have a high content of naturally occurring sulphate. Sulphatereducing Bacteria feed off of sulphate and produce Hydrogen Sulphide gas (H2S), which is characterized by a “rotten egg” odour. H2S gas corrodes iron and steel casing/screens and produces a scale called Ferric Sulphide (FeS2). As this scale deposit and the Sulphate-reducing bacteria accumulate, the slot openings on the casing/screen become plugged, and well yield is severely reduced.

When a water system has an excessive amount of Iron or Sulphate-reducing bacteria, shock chlorination treatment is recommended. This procedure is relatively inexpensive and easy to perform. It will not completely solve the problem, but through minimum yearly application etc., shock chlorination will reduce bacteria to a minimum and hold it in check.

II) Effective Control Against Iron and Sulphate-Reducing Bacteria—Shock Chlorination

  With the Shock Chlorination procedure, the entire system (from the water-bearing formation, through the wellbore and the distribution system) is exposed to water which has a concentration of chlorine strong enough to kill Iron and sulphate-reducing bacteria. To be effective, enough chlorine solution must be used to disinfect the entire cased section of the well and the adjacent water-bearing formation. Bacteria collect in the pore spaces of the formation as well as on the casing or screened surface of the well.

Highly chlorinated water can be prepared by dissolving the chemical Calcium Hypochlorite in water. This chemical is marketed today in granular and tablet form, and contains from 60-65 percent available chlorine. The granular form is recommended because it dissolves quickest. It may be purchased from your local water well driller or chemical supply distributors. Calcium Hypochlorite is a hazardous material and can cause burns. Take care and follow manufacturers safety precautions.

Calcium Hypochlorite is recommended rather than household bleaches and other commercial solutions containing weaker concentrations of Sodium Hypochlorite. The chlorine content in these solutions ranges from 3 to 15 percent, and due to the unstable nature of these compounds, the strength of the chlorine weakens so that at the time of use, they may not contain the labelled amount of available chlorine.

The table illustrates the quantities of Calcium Hypochlorite to be used based on the characteristics of an individual well.

Amount of Chlorine Required to Obtain a Chlorine Concentration
of 200 PPM in a 100 ft. Column of Water

III) Procedure

1)  Store enough water to meet household and farm water needs for a minimum of 12 hours.

2)  Before disinfecting the water system, remove or bypass any water conditioner or carbon filter in the system. Be sure that the hot water heater is turned off.

3)  Measure the column of water in the well. Calculate, from the table, the amount of water needed for chlorination (for example, a 245 ft. well, 8' diameter, with a non-pumping water level of 45 ft. has a column of water of 200 ft.; the amount of water needed would be 2 x 435 or 870 gallons of water).

4) Then, calculate the amount of chlorine that is required and mix it with the water previously measured (in the example, 870 gallons of water should be mixed with 2 x 22 oz. or 44 oz. of chlorine). Siphon the solution into the well. This may take a few minutes or several hours. The water well will only take fluid at the same rate as it will produce water i.e. 5 gpm. Be patient. When all the fluid is in the well make sure to replace the well cap and fasten securely.

5) Open each hydrant, faucet, etc. in the distribution system, (all appliances that use water such as dishwasher, washing machine, furnace humidifier) until the water at each outlet has a chlorine odour. This will thoroughly chlorinate the plumbing fixtures. Allow the hot water tank to fill completely.

6) Leave chlorine mixture in the entire distribution system for a minimum of 12 to 24 hours.

7) Chlorinated water should never be allowed to drain into the septic tank.

8) After the minimum 12 hours, (optimum time 24 hours), run the well off through an outside hydrant or tap “Slowly”. This may take anywhere between 2 to 24 hours. Be Patient. Run the water on an area where it will not kill the grass. Some discoloration of the water is normal. Continue to run the water until the chlorine odour is gone. If excessive amounts of coarse sand begin to appear call your drilling company for further information.

9) Backwash all filters and softeners and flush the hot water tank.

This procedure for Shock Chlorination will work for most wells with a bacteria problem. If the water still has a foul odour after chlorination, particularly in the case of sulphate-reducing bacteria, the entire procedure should be repeated as such odour is a sign that not enough chlorine was used.

Note that this procedure will not completely eliminate bacteria from the water system but will hold it in check. Shock chlorinating should be repeated yearly in order to control reoccurring bacteria and maintain a clean well and pumping system.

CAUTION: If a well is slow yielding or tends to pump any sediment, go about the shock chlorination procedure very cautiously. Slowly siphon the solution down the well and pump it out very slowly. Overpumping the well may worsen the sediment problem.

IV) Prevention of Iron Bacteria Contamination

Iron Bacteria are naturally present in surface waters and are also often found in the soil. If a well is improperly sealed there is potential for contamination of the producing aquifer. There is evidence that Iron Bacteria can travel from one well to another through water bearing formations. Old and unused wells should therefore be properly abandoned to prevent contamination.

Notice to readers: these procedures and products are dangerous. Improper use or sanitization of a well can cause serious illness or death. The Alberta Water Well Drilling Association hereby disclaims any liability or responsibility for any injury or damage resulting from the use of information contained herein.