Iron ocher

Source: Board of examiners

The iron ocher

The iron ocher is the result of a chemical reaction or a biological process, both of which can occur individually or simultaneously:

  • Chemical reaction: When the soil contains iron, it migrates with the water to form the drain and into contact with the air of an iron hydroxide sludge;
  • Biological process: When the iron bacteria is present in the groundwater, it produces as a result of the oxidation of iron in contact with air, a gelatinous mass.

When the biological process is added to the chemical reaction, the oxidation effect is greatly increased.

In both cases, the result is the formation of slime on the walls of slotted drains. It is this deposit is called ocher.

How iron ocher does manifest?

The development of this material is more likely in a more aerated soil, such as sandy soil containing silt and less likely in a clay soil.


Chemical or biological reaction is also faster:

  • Where the soil is rather neutral (pH about 7);
  • When the drain is grooved;
  • When the drain openings are punched instead of being cut, which gives more grip deposits;
  • When the drain is surrounded by a filter membrane.

Under the action of iron ocher, even crushed gravel loses its filtering properties. Soils rich in iron and iron bacteria produce iron deposits indefinitely.