Casing, Grouting, and Sealing
Core concepts
Casing keeps the hole open and isolates aquifers; grout seals the annular space to prevent contamination and cross-connection between aquifers. Know casing materials (steel, PVC, stainless), wall thickness/schedule, and joint types (threaded, welded, solvent-cemented). Understand centralizers, which keep casing centered so grout forms a continuous sheath, and the difference between neat cement grout, bentonite grout, and cement-bentonite mixes. Know the purpose of the grout: hydraulic seal, structural support, and protection from surface water. Understand the required grout depth (from surface to the seal depth required by regulation) and the use of a tremie pipe to place grout from the bottom up.
Traps
A classic trap is placing grout from the top down - it must be placed from the bottom up through a tremie to avoid voids and dilution. Another is confusing bentonite (a clay seal, good but can shrink) with cement grout (stronger, more durable). Questions may ask whether centralizers are required - they are best practice and often required to ensure a continuous sheath. Watch for confusion between the casing shoe and the grout shoe, and between annular seal and well cap.
Worked example / rule of thumb
Grout volume ≈ annular volume × 1.1–1.5 to account for washouts and lost returns. Annular volume = π/4 × (hole diameter² − casing OD²) × length. Always tremie from the bottom up and verify returns at the surface.