Which sampling method is commonly used to obtain soil samples during monitoring-well drilling?

• A. Shelby tube and/or split spoon sampler
• B. Grab samples from surface soil
• C. Soil coring with a rock drill
• D. Pore water extraction only

Answer: (A)

When drilling a monitoring well, the goal is to get soil samples that truly represent the subsurface conditions at depth. Using a Shelby tube or a split-spoon sampler does exactly that by capturing a relatively undisturbed slice or core of soil as the borehole is advanced. The Shelby tube is a thin-walled tube pushed into the soil, preserving natural structure and moisture for accurate analysis of properties like moisture, density, and plasticity in cohesive soils. The split-spoon sampler, a thicker-walled device that can be driven or pushed into place, yields a solid sample that’s particularly useful for coarse-grained layers and provides material for grain-size analysis and stratigraphic interpretation.

Grab samples from surface soil don’t reflect the subsurface conditions where the well screens and groundwater flow occur, so they’re not suitable for characterizing the intervals of interest. Soil coring with a rock drill is more typical in hard rock or unconsolidated rock situations and isn’t the standard approach for general monitoring-well soil sampling. Pore water extraction focuses on the liquid phase and lacks the solid matrix needed to evaluate many soil properties and the stratigraphy of the borehole.