Infrasense completed a subsurface utility mapping project at a large industrial park in Tyngsboro, MA using a combination of ground penetrating radar (GPR) and electromagnetic induction (EMI) locating methods. The GPR equipment included a 400MHz ground-coupled antenna mounted to a cart with an integrated distance encoder and GPS unit. This GPR antenna is capable of penetrating up to 8 feet below the surface. The EMI equipment included a Ditch Witch Subsite 750 TR unit. The EMI can be used to trace a signal induced onto conductive materials such as buried wire and conduit, steel, copper, and other metallic pipes, and tracer wires that are generally installed with new composite utility lines. The EMI receiver includes frequency bands to pick up passive ‘live’ electrical lines beneath the surface without a direct tie-in point. Utilities and service lines detected with the EMI tool were marked on the ground surface using paint and then surveyed using a sub-cm GPS with RTK real-time correction. The locations of site features including corners of buildings, catch basins, fire hydrants, and light poles were also surveyed using the RTK GPS system for accurate integration of the subsurface utility locations and client-provided base map. The final results were provided in a CADD-compatible format (.dwg).
