Disadvantages of stainless steel well casing and screen materials:
May corrode under some geochemical and microbiological conditions;
May sorb cations and anions;
May contribute metal ions (iron, chromium, nickel, manganese) to ground 
water samples;
High weight per unit length; and
Type 304 and Type 316 stainless steel are unsuitable for use when monitoring
for inorganic constituents.
Thermoplastic Materials
Thermoplastics are human made materials that are composed of different formulations
of large organic molecules. These formulations soften by heating and harden upon cooling,
and therefore, can be easily molded or extruded into a wide variety of useful shapes including
well casings, screens, fittings and accessories. The most common types of thermoplastic well
casings and screens are polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS).
PVC plastics are produced by combining PVC resin with various types of stabilizers,
lubricants, pigments, fillers, plasticizers and processing aids. The amounts of these additives
can be varied to produce different PVC plastics with properties tailored to specific
PVC materials are classified according to ASTM standard specification D 1785, which
covers rigid PVC compounds (ASTM, 1986). This standard categorizes rigid PVC by
numbered cells designating value ranges for certain pertinent properties and characteristics,
including: impact strength, tensile strength, rigidity (modulus of elasticity), temperature
resistance (deflection temperature), and chemical resistance. ASTM standard specification
F 480 covers thermoplastic water well casing pipe and couplings made in standard dimension
ratios. This standard specifies that PVC well casing can be made from only a limited number
of cell classification materials, predominantly PVC 12454 B, but also including PVC 12454 C
and PVC 14333 C and D (American Society for Testing and Materials, 1981).
ABS plastics are produced from three different monomers: 1) acrylonitrile, 2)
butadiene, and 3) styrene. The ratio of the components and the way that they are combined
can be varied to produce plastics with a wide range of properties. Acrylonitrile contributes
rigidity, impact strength, hardness, chemical resistance, and heat resistance; butadiene
contributes impact strength; styrene contributes rigidity, gloss, and ease of manufacturing
(National Water Well Association and Plastic Pipe Institute, 1981). The ABS used for well
November 1992
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