The double-cased monitoring well is designed to prevent migration of contamination between aquifers.

• A. It is designed to prevent migration of contamination between aquifers
• B. It increases pumping rate
• C. It reduces the need for a filter pack
• D. It eliminates the need for a seal

Answer: (A)

Isolation of aquifers within the borehole is the key idea. A double-cased monitoring well uses two concentric casings with a cemented annulus between them to create a sealed barrier that stops vertical movement of groundwater and any contaminants along the wellbore. This keeps each aquifer hydraulically separate, so samples come from the intended layer and contaminants don’t migrate between aquifers through the well itself. This isolation is essential for accurate monitoring of plume behavior and aquifer conditions.

It isn’t about increasing pumping rate, since monitoring wells aren’t designed for production. The need for a filter pack relates to preventing entry of fines and protecting the screen, but it doesn’t achieve the vertical isolation that a double-cased design provides. And sealing is still essential; the annular seal is what makes the isolation possible, so the idea that a double-casing eliminates the need for a seal isn’t correct.