Iron ochre results from a chemical reaction or a biological process, and both of these causes may occur either individually or simultaneously:
Chemical reaction: When the soil contains iron, it migrates along with the water towards the drainage system. When it comes in contact with the atmosphere, it forms a sludge of iron hydroxide.
Biological process: When iron bacterium is present within the water table, this bacterium, following oxidation of the iron upon coming into contact with the atmosphere, produces a gel-like mass.
When the biological process adds up to the chemical reaction, the oxidation effect is considerably increased.
Both cases result in the formation of a viscous deposit on the corrugated wall of drain pipes. This deposit is what we call iron ochre.
What conditions give rise to iron ochre?
This substance is more likely to develop in a more aerated soil, such as the sandy soils containing silt, and will less likely develop in clay soils. The chemical or biological reaction is also quicker:
- where soil tends to be neutral (pH of approximately 7);
- when the wall of the drain is corrugated; • when the openings of the drain are punched instead of cut out, which creates
- attachment zones for the deposits;
- when the drain is wrapped in a filtering membrane.
Under the action of iron ochre, even crushed gravel loses its filtering properties. The soils rich in iron and in iron bacteria will produce ferrous deposits indefinitely.
What consequences has the presence of iron ochre?
Iron ochre causes several issues with buildings: •
- It causes ocher-colored slimy sludge deposits to accumulate in the rain water catch basin and in ditches.
- It creates reddish deposits on the concrete slab of basements. These deposits give a sulfur-like odour.
- It obstructs agricultural tile drains: since runoff water is no longer channelled at a distance from the foundations, it infiltrates the basement, at the junction between foundation walls and slab.
- It obstructs the backflow valves.
Can one eliminate iron ochre or prevent this bacterial growth?
Iron is naturally present in the soil. Thus, it is very difficult to eliminate altogether. Even if one would replace the soil surrounding a building, iron originating from the neighbouring soils would still migrate towards the drain of the property through natural water runoff. To prevent bacterial growth, one would need to eliminate from the soil two natural elements – water and air – which is impossible. It is therefore not feasible to prevent the chemical reaction giving rise to iron ochre.
How can we prevent iron ochre deposits, and how can we remedy it when present?
It is possible to prevent iron ochre deposits, either before or after the construction.
Before the construction, one must keep vigilant when tell-tale signs appear such as the presence of reddish waters, after a rainfall, in ditches or on the ground surface.
During the construction of a property, it is recommended to enquire, with the neighbours and the municipality, about any history of iron ochre formations in the area. A professional evaluation of the current conditions should also be made before proceeding with the construction.