(1) All plastic casing shall be installed only in an oversized drill hole without driving. Wells cased with plastic shall have steel casing extending a minimum of 25 feet below the surface and 18 inches above the ground surface. Plastic casing to be used must be specifically designed for water well construction and bear NSF approval. Methods of installation shall be:

(a) installing a larger size steel casing on the outside of the plastic casing with a minimum of four feet of overlap (see Figure 6A at the end of this subchapter); or

(b) attaching directly to the plastic casing a threaded plastic to steel coupling (Figure 6B).

(2) Thermoplastic well casing shall conform with ASTM Specification F480-81, or its latest revision, as follows:

(a) minimum standards dimension ratio shall be 26 for inner casing in bedrock applications;

(b) minimum standards dimension ratio shall be 21 for unconsolidated formations greater than 125 feet;

(c) minimum pipe stiffness shall be 224 foot-pounds/in² [kiloneutron (meter meter)] when tested according to section 5.4.1 of ASTM Specification F480;

(d) all casing five inches (12.7 centimeters) and larger shall be tested for impact resistance and shall meet or exceed IC-1 impact classification according to section 6.5 and Table 6 of ASTM Specification F480; and

(e) carry the seal of the national sanitation foundation.

(3) All casing shall have additional thickness and weight if standard thickness is not capable of withstanding forces to which it is subject.

(4) The well casing must be clearly marked by the manufacturer showing: nominal size, type plastic material, standard dimension ratio (SDR), ASTM designation, and National Sanitation Foundation seal of certified approval.

(5) The use of plastic well casing in connection with a pitless adaptor is not acceptable.