Depth to the water bearing zone(s) to be monitored and anticipated well depth;

Geologic environment;

Geochemistry of soil, unconsolidated material, and rock over the entire interval

in which the well is to be cased;

Geochemistry of the ground water at the site, as determined through an initial

analysis of samples from both background wells and downgradient wells and

including:

natural ground water geochemistry,

nature of suspected or known contaminants, and

concentration of suspected or known contaminants; and

Design life of the monitoring well.

The most frequently evaluated characteristics that directly influence the performance of

casing and screen materials in ground water monitoring applications are strength and

chemical resistance/interference. These characteristics are discussed in more detail below.

Strength Related Characteristics

Well casing and screen materials should maintain their structural integrity and

durability in the environment in which they are used over their operating life. Monitoring

well casings and screens should be able to withstand the physical forces acting upon them

during and following their installation, and during their use, including forces due to

suspension in the borehole, grouting, development, purging, pumping, sampling, and forces

exerted on them by the surrounding geologic materials. When casing strength is evaluated,

three separate yet related parameters should be evaluated:

Tensile strength;

Compressive strength; and

Collapse strength.

The tensile strength of a material is defined as the greatest longitudinal stress the

material can bear without pulling the material apart. Tensile strength of the installed casing

varies with composition, manufacturing technique, joint type, and casing dimensions. For

monitoring wells, the selected casing and screen materials should have a tensile strength

November 1992

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