Total dissolved solids (TDS)    if TDS is greater than 1000 milligrams per liter,

the electrical conductivity of the water is great enough to cause serious

electrolytic corrosion;

Carbon dioxide (CO )    corrosion is likely if the CO content of the water

2

2

exceeds 50 milligrams per liter; and

Chloride (Cl

), bromide (Br

), and fluoride (F

) content    if the Cl

, Br

, and F

concentrations together exceed 500 milligrams per liter, corrosion can be

expected.

Combinations of any of these corrosive conditions generally increase the corrosive effect.

Carbon steels were produced primarily to provide increased resistance to atmospheric

corrosion. Achieving this increased resistance requires that the material be subjected to

alternately wet and dry conditions. In most monitoring wells, water fluctuations are not

sufficient in either duration or occurrence to provide the conditions that minimize corrosion.

Therefore, the difference between the corrosion resistance of carbon and low carbon steels in

the unsaturated or in the saturated zone is negligible, and both materials may be expected to

corrode approximately equally.

Corrosion products include iron, manganese, and trace metal oxides as well as various

metal sulfides (Barcelona et al., 1983). Under oxidizing conditions, the principal products are

solid hydrous metal oxides; under reducing conditions, high concentrations of dissolved

metallic corrosion products can be expected (Barcelona et al., 1983). While the electroplating

process of galvanizing improves the corrosion resistance of either carbon or low carbon steel,

in many subsurface environments the improvement is only slight and short term. The

products of corrosion of galvanized steel include iron, manganese, zinc, and traces of

cadmium (Barcelona et al., 1983).

The presence of corrosion products represents a high potential for the alteration of

ground water sample chemical quality. The surfaces where corrosion occurs also present

potential sites for a variety of chemical reactions and adsorption. These surface interactions

can cause significant changes in dissolved metal or organic compounds in ground water

samples (Marsh and Lloyd, 1980). According to Barcelona et al. (1983), even purging the

well prior to sampling may not be sufficient to minimize this source of sample bias because

the effects of the disturbance of surface coatings or accumulated corrosion products in the

bottom of the well are difficult, if not impossible, to predict. On the basis of these

observations, the use of carbon steel, low carbon steel, and galvanized steel in monitoring

well construction is not recommended in most natural geochemical environments.

Several different types of stainless steel alloys are available. The most common alloys

used for well casing and screen are Type 304 and Type 316. Type 304 stainless steel is

November 1992

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