Private Utility Locating and Electromagnetic Induction (EMI) Scan - Seattle, WA

GPRS, LLC. of the Pacific Northwest was called out to provide a utility location scan and electromagnetic induction sweep prior to demolition of an existing warehouse in the industrial section of Seattle. GPRS first started the project by using ground penetrating radar to grid scan the entire area in question, with 5’ spacing. Many utilities were found on site, including storm sewer, sanitary sewer, underground power, communication lines, water/hydro lines, and gas lines. These utilities were marked in the field, and a Trimble GPS device was used to capture each utility digitally so that documentation could be produced of the findings. While on site, many different patches of concrete and asphalt provided visual evidence that indicated that there may have been existing or previously removed underground storage tanks (USTs) on site. It was then decided that an EMI scan would also be conducted to determine focus areas where buried debris or USTs may be located. The photo below shows the 400 MHz GPR cart, and the EMP Profiler EMI paddle that were both used on this project.

EMI works by sending a magnetic field into the ground as the operator walks through the project site in a typical grid pattern of 5’ spacing. This magnetic field interacts with areas of high conductivity (buried construction debris, rebar reinforced slab, underground storage tanks, etc) which then create a secondary magnetic field that is interpreted by the EMI device. A color scale map (which looks similar to a thermal map) is then generated which can be overlaid onto a Google Earth satellite image. The operator in the field can then take this information and pinpoint “Hotspots” where USTs or buried debris may be present.

The image above is the output that is generated using the EMI Profiler. Each yellow or “hot” color represents an area of high conductivity. GPRS then used traditional GPR scanning to locate a storage tank highlighted with the red arrow. The location of these previously unknown utilities and storage tank allowed the contractor to avoid a potentially dangerous and costly situation on this project. Areas with older buildings in downtown areas typically have utilities or buried tanks in various locations that may or may not be documented on city or private plans.

If you are in need of, or would like a free quote for any of our underground utility locating services (private or public), such as utility locating, underground storage tank locating, soil boring clearance, trench scanning, or EMI scanning in the Pacific Northwest, please contact:
Jesse Moorhouse at (206) 200-9293 or at jesse.moorhouse@gprsinc.com.