RETTEW worked to determine the depth of a suspected clay layer beneath our client’s site so a suitable remediation plan could be designed. The clay was overlain by a series of sand and gravel layers, which created a good physical contrast between the layers and the underlying target. So, RETTEW conducted an electrical resistivity imaging (ERI) survey to map the electrical contrast between the resistive sand and gravel layers and the deeper, more conductive clay.

The four cross sections, laid out in a tic-tac-toe pattern across one area of the site, depict the relatively thin, shallow sand and gravel layers overlying the deeper, thicker clay layer. A short hachure line marks the assumed approximate boundary between these two electrically distinct features. Minimum clay layer thicknesses were estimated from each of the cross sections.

Data from the cross sections were then used to create a contour map showing the depth to the top of the clay layer across the site. Knowing the “topography” of the buried clay layer enabled our client to design a suitable remediation plan for the site. The cost of the ERI survey was offset by reducing the number of borings our client would have installed to “ping” the top of the clay layer intrusively.