Aerial investigation simplifies site analysis
The aerial photograph shows a brownfield site in Newcastle-upon-Tyne. The colour-contoured overlay shows the rsults of magnetic profiling carried out by Zetica (of Geo_Services International (UK) Ltd) for the client, Taylor Woodrow Construction Ltd.
The red dominated colours clearly indicate the made/disturbed ground. The vertical red anomaly in the top left is a good example of the type of new information to be gained from such a survey. In this case the anomaly was subsequently identified to be a previously unknown trench that was filled with metal-contaminated ground. The sub-surface remnants of cooling towers, tunnels, culverts, bunkers/air raid shelters, building foundations, other ferrous objects and evidence of reclaimed land were also shown up by this one survey.
Individual non-invasive methods map a selected geophysical parameter of the sub-surface to a selected depth of penetration; and some can image the earth in three dimensions. Often a single method is sufficient to reveal the required information, but if not then the skilled interpretation of two or more integrated methods can yield powerful corroborating evidence of sub-surface features. Information gained from pits and boreholes is spatially ambiguous and comparatively anecdotal unless these are sited with the benefit of a non-invasive survey. This is important because the BSi code of Practise for the Investigation of Potentially Contaminated Sites asserts that a conceptual site model is reqiired; and the appropriate density of soil, gas and water sampling per site is defined as “enough to reduce unacceptable uncertainty in the conceptual model” using professional judgement.
“Traditional trial pit and borehole site investigations provide too little information on the real nature of environmental and engineering problems,” says GSI managing director Dr Asger Eriksen. “Complete site coverage means that our clients have a major advantage in risk assessment.”
Technical director Jon Gascoyne has designed a range of services to provide a dependable non-invasive package of rapid reconnaisance tools through to state-of-the-art detailed studies. “We have put together a package of tried and tested methods to accurately detect the source of problems in plan view, 2D or 3D. The results are very clearly presented to allow targets to be accurately followed up wth invasive methods and further geophysical work.”
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