What characteristic must an unperforated well casing have when a flowing well is encountered?

For an unperforated well casing encountered in a flowing well scenario, it is crucial that the casing is sealed into the confining stratum. This sealing is essential to prevent the water from the aquifer or groundwater source from escaping uncontrollably to the surface through the annular space between the casing and surrounding soil or rock. By sealing the casing into a confining layer, it ensures that the pressure from the flowing well is contained, minimizing the risk of contamination and maintaining the well's structural integrity.

The other characteristics mentioned, such as being made of aluminum, being flexible, or needing to be perforated, do not apply in this situation. Aluminum is not a requirement for well casing material, and flexibility is not beneficial in this context as a rigid structure is typically preferred for stability. Additionally, if the well casing is unperforated, perforations would not contribute to managing the flow; rather, the unperforated design is specifically intended for use in situations where the flow must be controlled when the casing is properly sealed into the confining stratum.