PRIVATE WATER SYSTEMS - Design - Mineral and Biological Composition

Mineral and Biological Composition

The effects of water on well materials may be either corrosion or incrustation.

Corrosive water is indicated by the presence of high concentrations of carbon dioxide, dissolved oxygen, total dissolved solids, and hydrogen sulfide (causes the odor of rotten eggs). The deterioration of only a small amount of the metal in the well screen can permit an excessive amount of sand to enter the well.

Other contributors to corrosion include high flow velocity and the use of more than one type of metal. The faster the flow rate through the screen, the faster the protective residue left by corrosion is swept away exposing fresh surfaces. Also, the use of two types of metal, steel casing and a brass screen, for example, should be avoided since corrosion is usually greatest at the points of contact between two different metals.

Ordinary steel and iron are not resistant to corrosion, but stainless steel, various copper based alloys (brass, bronze), and pvc pipe are corrosion resistant.

Incrusting (alkaline) water tends to deposit minerals on the surface of the screen and in the pores of the formation just outside of the screen. Deposits of calcium carbonate (lime scale) also occur in pipes carrying alkaline waters. To a lesser extent, deposits of iron and manganese minerals cause reddish-brown and black deposits respectively.

Ground waters having appreciable amounts of iron may contain iron bacteria. The presence of these bacteria is not a health problem, but they do produce accumulations of slimy material of jelly-like consistency that can cause major clogging of well screens.

Treating the well with a strong chloride solution will kill the organisms. Treating with strong hydrochloric acid will dissolve the minerals deposited on and around the screen, but may cause corrosion in non-resistant screens and casings.

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