A general contractor in the Milwaukee needed to identify the location of a known underground tunnel constructed in the 1880’s for use by nuns and clergy before performing storm sewer upgrades; they contacted GPRS to use Ground Penetrating Radar (GPR). Marcus Thie, Project Manager for the Wisconsin market was able to locate the underground tunnel, which connected several churches over multiple city blocks, with a GSSI 400 MHz antenna and RD8100 radio detection wand. GPRS was able to mark out the location, extents and approximate depths of the tunnel in various locations throughout the span of the project clearly for the client. Since the data is displayed in real time, the areas were marked easily, and the team could move forward with their process without worry of damaging a Milwaukee historic landmark. GPR is also used to determine the presence of underground utility lines and underground storage tanks in plants, factories, and other occupied spaces because it does not emit harmful radiation, produces virtually no noise or interference, and will not disturb business operations. It can also be used to determine the presence of obstructions in concrete prior to saw cutting or drilling.