Readily available;
Lower cost than PTFE or metallic casing materials;
High open area screens available; and
Potentially best "compromise choice" when monitoring for low concentrations
of both organic and inorganic constituents (Parker et al., 1990; Hewitt, 1992).
Disadvantages of PVC well casing and screen materials:
May degrade in high concentrations of certain organic solvents, especially low
molecular weight ketones, amines, aldehydes, and chlorinated alkenes and
alkanes (Barcelona et al., 1983 and the Science Advisory Board of the
May fail if subjected to high differential pressures (i.e., during surging); weaker
and less rigid than metallic casing materials;
May fail if subjected to high temperatures (i.e., during grouting with neat
Long term exposures of some formulations of thermoplastics to the ultraviolet
rays of direct sunlight (above ground portions of casings) and/or to low
temperatures may cause brittleness and gradual loss of impact strength that may
be significant; and
Unsuitable for driven wells.
The National Sanitation Foundation (NSF) has set specifications for certain chemical
constituents in PVC formulations. The purpose of these specifications as outlined in NSF
Standard 14 (National Sanitation Foundation, 1988) is to control the amount of chemical
additives in both PVC well casing and pipe used for potable water supply. Most of the
maximum contaminant levels correspond to those set by the Safe Drinking Water Act for
chemical constituents covered by the national Interim Primary Drinking Water Standards.
Only PVC products that carry either the "NSF wc" (well casing) or "NSF pw" (potable water)
designation have met the specifications set forth in Standard 14. Other non NSF listed
products may contain chemical additives not addressed by the specifications, or may contain
concentrations of the listed chemicals that are higher than permitted by the specifications. In
all cases, the material used should have been demonstrated to be compatible with the specific
applications. For example, even though neither lead nor cadmium have been permitted as a
compounding ingredient in United States manufactured NSF listed PVC well casing since
November 1992
6 34






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