Iron is one of the most common elements making up the earth’s crust, so it’s easy to understand why iron occurs
in groundwater. Water is known as the “universal solvent”, meaning it dissolves anything it comes into contact with. So as water percolates through layers of soil and other geologic formations, it dissolves the various minerals contained, most commonly iron and manganese.
How is it regulated?
Iron is regulated by the EPA as a secondary contaminant at a level of 0.3 mg/L. A Secondary standard is a non-enforceable guideline for contaminants that do not cause health concerns but may cause aesthetic problems in water such as taste, odor and/or staining.
Testing for Iron?
There are a variety of onsite testing methods available using colorimetric method by using either drop kit or colorimeter. Laboratories analyzing drinking water samples can utilize various methods including EPA method 200.8 which utilize an Inductively Coupled Plasma (ICP) or the Standards Method 31138 which uses Graphite Furnace
Water Treatment Options
There are numerous way to treat for iron and it is dependent on which form of iron is present. Polyphosphates are used for low levels of iron, and will react with dissolved iron by trapping it in a complex molecule that is soluble in water. As a result the iron is not available to react with oxygen and precipitate. Polyphosphates can be fed into the water system with controlled injection equipment, such as chemical feed pumps.
Polyphosphate treatment is a relatively cheap way to treat water for low levels of iron and manganese. Depending on the type of polyphosphate used, water with 1 to 3 ppm of iron can be adequately treated. Ion exchange can be used to remove iron, depending on the manufacture softener can remove up to 10 ppm of iron while others can only handle up to 1ppm. If you are treating hardness in addition to iron and other nuisance contaminants such manganese, hydrogen sulfide and nitrates you should check with manufacturer for recommendations.
Chlorination and Filtration is usually recommended when levels are above 10 ppm. A chlorine solution is injected with a chemical feed pump ahead of a sand filter. Soluble iron will begin to precipitate almost immediately after contact with the chlorine solution. However, adequate contact time is needed, for the precipitate to form particles large enough to be filtered.