A solar farm was expanding onto a hill where a limestone rock outcrop was observed. This raised concerns about shallow rock that could impede installation of the driven rods that support the solar panels. In soil, the rods need to reach a specified depth to prevent wind from lifting the panels. If the rock is shallow, a different kind of support can be anchored into it. Knowing ahead of time how many of each type of support will be needed saves construction time and money.

Seismic refraction surveys are very effective for recording top-of-rock profiles and rock rippability (ease of excavation). But on a large site, with a potentially irregular rock surface such as limestone, many profiles would normally be required to fully characterize rock depths. Fortunately, a fast and efficient electromagnetic (EM) mapping method is also sensitive to rock depth in the right geologic setting when properly applied. RETTEW completed several highly accurate seismic profiles spaced across the site. The EM data were then compared to and calibrated with the seismic profiles to produce a detailed and comprehensive bedrock depth map for solar panel support planning.

RETTEW’s ability to conduct coincident seismic profiling and EM mapping was critical to allaying concerns of shallow rock impeding installation, leading to a successful outcome on this solar farm.