Heating, Cooling and HVAC

Synonym of: Goethite, Hematite, Limonite
Definition:
Iron exists in two forms Soluble Ferrous Iron and Insoluble Ferric Iron. Iron exists in the Ferrous form within the country’s mine workings. Upon exposure to the surface the Ferrous Iron oxidises to become Ferric Iron, a hydrolysis reaction which causes the precipitation of ferric hydroxide, these particles fall from the solution and join together to form a thick substance that coats the river bed. It is this substance that causes effected watercourses to appear a red / orange colour.
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Localities for Iron Ochre
Locations affected by Iron ochre
Mineral Reference Lookup for Iron Ochre

When it comes to removing the Iron Ochre from the settlement lagoons, the Authority use a floating pump arrangement to extract the ochre, this is passed into a centrifuge which spins the mixture and extracts the water. Once this has taken place the Iron Ochre sludge, which is a thickened form of the ochre, remains and is stored awaiting delivery to landfill.
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How iron ochre is formed
When exposed to water and oxygen, iron in the soil oxidizes, forming an iron hydroxide mud that progressively clogs the drain. This deposit is first seen on the inside face of French drains and may partially or completely block it.

There are two kinds of ochre deposits, i.e. those of bacterial origin and those resulting from a chemical reaction. These deposits are rust-coloured. Ochre deposits usually occur in two types of soil, i.e. aerated soils such as sands and in soils located in permanently saturated low-lying areas. The organic matter dissolves in the water contained in the soil, creating an anaerobic environment that allows the ochre to dissolve in drainage water. On contact with the air, the ochre deposits or precipitates.

The problem of ochre formation is found in different forms throughout the world. Some studies have shown that the minimum iron concentrations required to form ochre is between .15 and .22 ppm. To get an iron ochre reaction, three factors must be present, i.e. soil type, pH and temperature; these factors will determine whether the ochre will be permanent or temporary. Québec soil types which are rich in iron and red fibrous ochre deposits will produce iron deposits indefinitely, unlike the types of soils found in other area which can in some cases be temporary.

Currently in Québec, the cases we have seen tend to be of the permanent type. This is a serious problem. Corrective action options in these cases are more costly, and often only short-term. They include the addition of highly porous materials or materials with a pH that will neutralize that of iron, including wood chips and hay, installing cleanouts or, more radically, waterproofing the foundation and even raising the property to take it out of the affected area. Other solutions have been put forward in various documents.

Soil conditions that contribute to the formation of iron ochre
Several studies have been conducted in the U.S. to determine whether there is indeed a relationship between types of soil and ochre forming in drains. The types of soils that seem to have the greatest potential for forming ochre are fine sands, silty sands, organic soils and soils containing minerals. Another factor is location, for instance in a potential flood zone, such as at the bottom of a hill or in an area where the water table varies. We believe that the variation in water levels can increase the risk of ochre formation.

Without digging but simply by observing the surrounding area, including ditches and river shores, it is often possible to see whether the soil is a candidate for forming iron ochre. Sometimes ochre deposits can be seen floating on the surface of stagnating ditchwater. A laboratory analysis confirming the presence of Fe2+ in the soil indicates the potential for an iron ochre reaction.

Measures to minimize the formation of iron ochre in drains
Various approaches are currently under study to minimize the risk of or help reduce the formation of iron ochre in drains around residential and commercial buildings. These methods are only temporary and their long-term effectiveness has not yet been assessed. Since each situation is unique, it is important to talk to an expert to determine the scope of the problem.

Only three permanent solutions exist to prevent the ochre from reaching the drain and infiltrating the building:

1. Installing a waterproof lining around the foundation;

2. Raising the property out of the affected area;

3. Filling the basement with granular materials (i.e. sealing off the basement).

Solution of recurring problem is to clean the drain lines with high speed jet pump as and when required.

Conclusion
Because there are cases where the source of the ochre is such that the problem will always recur, the simplest methods, as seen above, are often only temporary and palliative.

Resources:

http://www.coal.gov.uk/resources/environment/whatisochre.cfm?jHighlights=arrangement

http://www.pioneerbasement.com/forum/showthread.php?t=743

http://www.concretewatersolutions.com/photos/showgallery.php?cat=511&password=&page=