What is the primary purpose of sealing above the filter pack in a monitor well?

• A. To prevent vertical movement of fluids
• B. To anchor the casing
• C. To reduce surface infiltration
• D. To improve sample collection

Answer: (A)

Sealing above the filter pack creates a hydraulic barrier in the annulus that stops fluids from moving vertically between formation layers and from the surface into the well. This vertical isolation keeps the water entering the screen representative of the specific aquifer around the screen, preventing cross-contamination from other zones. While the seal can also reduce surface infiltration, its primary role is to maintain this vertical isolation to preserve sample integrity. Anchoring the casing is accomplished by other parts of the installation, and sealing above the filter pack does not directly improve sample collection.