GEOPHYSICAL
ENGINEERING

Underground Storage Tanks

Left : 3D rendered image of the GPR survey results presented in CAD. The tanks are visualized along with a service running over their top.

Underground Storage Tanks are prevalent on sites throughout the UK including petrol filling stations (PFS), council depots, fire and ambulance stations, military bases and industrial sites.

Many of these are sites have been identified for development and so locating them is key before design and construction can commence. Additionally, USTs can cause contamination across the site, so knowing their location is fundamental for health, safety and environmental concerns.

The Answer – A Combined Geophysical Survey

The most suitable technique for detecting tanks in many applications is Ground Penetrating Radar (GPR). It works in a wide range of congested environments and will detect tanks made from both metallic and non-metallic materials, as well as provide depth information to top of the tank.

Above : Example GPR radargram (section view). In the centre two broad crested anomalies can be seen showing the location of two fuel tanks.

Above : Timeslice (plan view) showing 3 adjacent tanks. Above Right : Interpretation of GPR data in CAD showing the 3 tanks (A-C) at 0.5m depth.

Other techniques that can be used are Magnetic Survey and Ground Conductivity depending on the site conditions and the materials from which the tank has been made. These techniques are lower resolution, but more cost effective, enabling large areas to be surveyed and then targeted with GPR for improved accuracy and depth information.

Above : Ground Conductivity data in Plan and section view showing 3 possible tanks showing the amplitude of response.

All three techniques carried out on-site on the same day, with most sites taking no more than a day to survey. Immediate initial results may be presented on-site, with more detailed post-processed results available shortly afterwards to suit your timescale.