Encrustation of Water Bores due to Iron-Related Bacteria
Iron-related bacteria occur naturally in groundwater and are increasing rapidly
throughout the world.
The interaction of dissolved iron and iron-related bacteria forms a solid, resulting in an encrustation. With age, bores and wells can develop a build-up of encrustation that causes a decrease in the bore yield and water quality. While most groundwater contains a certain concentration of dissolved iron, iron-related bacteria do not affect all bores. When the bacteria infect a bore with iron in the groundwater, their interaction results in growths which may either be suspended in solution or cause encrustation on the bore casing, screens, pumping equipment and in extreme cases in the gravel pack around the bore. This is termed “biofouling”. The occurrence of biofouling in groundwater systems will result in:
- Decreased flow through the screen pump and pipelines causing increased pumping costs;
- Plugging of the voids in the gravel pack surrounding the bore, leading to a decreased yield;
- Increased resistance to heat flow across the submersible pump motor causing operating problems and potential burn-out;
- Possible metal corrosion – the bacteria are thought to secrete an acidic substance;
- Decreased water quality (taste, colour, odour) due to a biofilm build-up as well as undesirable staining, usually red or brown;
- Plugging of drip irrigation systems due to the small nozzle orifice.
There is some debate as to why certain bores suffer adversely from iron-related bacteria while others never become infected. The following list describes some ways in which bores may become infected:
- The bacteria may exist in the groundwater before the bore is drilled;
- Bacteria may travel through the aquifer, infecting previously uninfected bores;
- Bacteria may be introduced to the bore via contaminated water taken from swamps or creeks used during the drilling process;
- Bacteria may be introduced by floods inundating unsealed bores;
- Changes in the chemistry of groundwater may provide an environment in which bacteria can become established.
In extreme cases a mechanical clean may be necessary in the first instance to remove the encrustation to ensure the effectiveness of the Clearbore treatment. Once the rejuvenation is complete, the bore’s performance and water quality should be monitored. Regular Clearbore treatments should be carried out as determined by the monitoring process. As a guide we recommend using Clearbore every 12 months or so to keep the bore in a clean condition.
Confirming the presence of iron-related bacteria
One or more of the following symptoms indicates iron-related bacteria in a bore:
- Reduction in the capacity of the bore
- Deterioration of water quality – colour, odour, taste and staining
- Motor burn-out in the submersible pump
- Encrustation on the pump, column, bore casing, screens and reticulation system.
Once contamination by iron-related bacteria has been confirmed the following treatment is recommended:
- Determine the pH of the bore water and carry out a specific capacity test for comparison purposes after the Clearbore treatment.
- Carry out the Clearbore treatment as per the directions on the pail.
- After the Clearbore treatment, pump out the bore until the pH is within 0.5 units of the pH value before treatment, or use the testing liquid supplied in each Clearbore pail.
- Conduct a specific capacity test on the bore. If the treatment has been successful, the drawdown should be less than previously measured.