casing is a rigid, strong unplasticized polymer formulation that has good heat resistance and

impact strength.

Two ABS material types are used for well casings: 1) a higher strength, high rigidity,

moderate impact resistance ABS, and 2) a lower strength and rigidity, high impact strength

ABS. These two materials are identified as cell class 434 and 533, respectively, by ASTM

standard specification F 480 (American Society for Testing and Materials, 1981). High

temperature resistance and the ability of ABS to better retain other properties at high

temperatures are advantages in wells where grouting with cement results in high temperature

caused by the cement's heat of hydration.

Aller et al. (1989) describe some of the research that has been performed regarding

degradation of thermoplastic materials and the adsorption/desorption of contaminants

onto/from various thermoplastic materials. The potential sources of chemical interference

from thermoplastic well casing materials, either from desorption or chemical degradation, are

1) the basic monomers from which the casing is made (e.g., vinyl chloride monomer), and 2)

a variety of additives that may be used in the manufacture of the casing, including:

plasticizers, stabilizers (e.g., PVC heat stabilizing compounds such as dimethyl tin and dibutyl

tin), fillers, pigments, and lubricants. The significance and impact of these sources of

chemical interference is not currently known, and may vary based on site specific conditions.

With respect to chemical interference effects, Aller et al. (1989) explain that another potential

area of concern is the possibility that some chemicals could be sorbed by PVC well casing

materials. Studies regarding sorption of chemical species onto PVC are inconclusive with

respect to both the significance of contaminant sorption by PVC and the ability of well

purging to correct any sample interferences.

The following advantages and disadvantages of PVC materials are highlighted in Aller

et al.'s (1989) discussion and by Nielsen and Schalla (1991).

Advantages of PVC well casing and screen materials:

Completely resistant to galvanic and electrochemical corrosion;

Lightweight for ease of installation;

High abrasion resistance;

Requires low maintenance;

Flexible and workable for ease of cutting and joining;

High strength and low weight per unit length;

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