Of the methods listed, which is the best method of obtaining soil samples during the drilling of a monitoring well?

• A. Grabs from borehole wall
• B. Push-probe sampling
• C. Shelby tube and/or split spoon sampler
• D. Core barrel sampling

Answer: (C)

The key idea is getting representative, minimally disturbed soil samples while the well is being drilled so you can accurately describe the soil layers and their properties for monitoring. A Shelby tube or thin-walled tube paired with a split-spoon sampler is best because each is designed to preserve useful information during drilling. The Shelby tube yields an undisturbed sample, which is crucial for evaluating in-situ properties like density, moisture content, plasticity, and stratification in cohesive soils. The split-spoon sampler provides a practical way to obtain samples for grain-size and index tests and to document the soil layers as drilling progresses. Together, they give reliable, well-preserved material that most accurately reflects the in-place conditions encountered, which is essential for interpreting aquifer tests and informing well design.

Grabs from the borehole wall tend to be highly disturbed and not representative of the larger formation. Push-probe sampling can be quicker but often compromises sample integrity and may not capture the full stratigraphy. Core barrel sampling is more suited to rigid, rock-like formations and can be impractical for typical unconsolidated soils encountered in many monitoring-well projects.