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

USEPA);

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

cement);

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