PROBLEMS WITH IRON IN BORE WATER
When there are high levels of iron in water, you will see this from the black and red stains left by the minerals. These stains accumulate and build up deposits in pipes and the areas around it. You often see paving, concrete, garden walls etc stained with this mineral which has not been treated. Often untreated iron can cause significant damages to the surrounding areas over time. Replacing these damaged areas can be an expensive and short term solution which will result in the same damages from the iron over time. The iron in the water can lead to environmental damage of the surrounding areas to nature, trees and wildlife. The iron damage in the area can affect the integrity of assets, including; playground equipment, benches, structures, poles, buildings and more. Iron may also stain clothes washed in iron-rich water and plumbing fixtures such as basins and toilet bowls. These rust stains resist cleaning with soaps, detergents and bleach.
HOW DOES IT GET IN THE WATER?
Iron typically comes from the rocks and soils around the water source. As water moves through the rocks and into the aquafer, it dissolves the iron that is naturally found in the environment.
Iron is the metal that is most abundant on Earth and is therefore very common in soils and groundwater. Dissolved iron occurs naturally in groundwater in concentrations of up to around 50 mg/L. Iron salts become increasingly soluble as groundwater becomes more acidic. In oxygen deprived and acidic groundwater (with a pH below 5), iron concentrations of between 1 and 20 mg/L are common (usually as stable carbonates). Iron is normally found dissolved in groundwater in the reduced ferrous form (Fe2+) and oxidises to relatively insoluble ferric form (Fe3+) when the pH of groundwater (alkalinity) is raised and it is exposed to oxygen in the air.
When acidic iron-rich groundwater is extracted and mixes with air, carbon dioxide and hydrogen sulfide (rotten egg gas) is frequently released, the pH rises and the iron is deposited as ferric hydroxide (rust) on any flat surface as water evaporates. Over time this oxide coating builds up causing discolouration particularly to light-coloured surfaces.
Iron may also be naturally present in groundwater as slimy, sometimes foul smelling bacteria filaments (such as Acidithiobacillus ferrooxidans). These bacteria are harmless, unlikely to settle out, and discolour the water brown, often with an oily sheen.
Iron deposits and iron bacteria may cause encrustations and blockage problems in irrigation systems, especially those that rely on small orifices for pressure control or delivery via water drippers. Iron scale may also affect heat transfer in hot water systems.
Iron staining is unsightly, but shouldn’t cause serious harm to plants, animals or humans or structural damage. With high concentrations of iron (more than 20 mg/L) some plants with iron staining may experience a reduction in photosynthesis and vigour.
AREAS WHERE IRON STAINING IS LIKELY?
Acidic iron-rich groundwater is often found in the water-table close to present or past wetlands where organic carbon and sulfides are prevalent; the water table is shallow and contains little or no dissolved oxygen. Prior to drilling a well, it is wise to check with neighbours to see if they have experienced iron problems with their bore water. Old or damaged galvanised steel pipe-work may add to iron staining problems as acidic waters attack pipe walls.