No need to excavate
February 1st 2005

With increased pressure on property developers to reclaim former industrial land, developments in the use of geophysics are proving to be a vital and cost effective tool for identifying buried hazards without the need to excavate, says Nick Russill, director of TerraDat UK

Cardiff-based company TerraDat has pioneered the use of these specialist noninvasive techniques on sites around the country.At one such site, a former gasworks,TerraDat were contracted by Bristol-based Westmark Developments to identify buried structures that could have an economic and environmental impact on redevelopment.

TerraDat undertook a range of geophysical surveys which nondestructively measured the physical properties of the subsurface, such as magnetism, density and electrical conductivity.Geophysical surveys enable rapid mapping of all accessible areas of a site (up to two hectares per day) as the instruments are hand carried and generally do not contact with the ground.This reduces the need for more expensive trial pitting or drilling and there is less risk of missing buried hazards.

The results are integrated with site plans and historical information to provide landowners or developers with information that can be used for subsequent ground truthing or ameliorative works.

The gasworks site occupied around 3000 sq. metres and all surface structures had been removed to ground level. In addition, partial remediation of the site had been carried out by a previous owner, with various new materials imported to the site.

Table 1 summarises the techniques used on site, together with the targets.

Surveys using each technique were carried out on a regular grid using real-time kinematic GPS to provide accurate positions.The data from each instrument were downloaded to a portable field computer and processed using dedicated mapping software.This allows for rapid quality control of the data and same-day positioning of targets.

Examples of results of the main techniques are shown on the accompanying figures.

The geophysical survey gave the client a better understanding of the structures that lay beneath their site, beyond the findings of a desk study of old plans.The risks of missing buried hazards that could affect the value of the land or have a detrimental effect on the local environment were also significantly reduced.

TerraDat specialises in site investigation using non-invasive techniques. Its services are called upon for a wide range of applications including land remediation,mineral and water exploration.The Cardiffbased company has expanded rapidly over the last 10 years and undertakes contracts throughout the world.With the support of a grant from the WDA’s Environmental Goods and Services Programme,TerraDat was able to expand with new premises,more staff and additional specialist equipment.