New guidance recognises the potential advantages of combining geotechnical and contaminated land investigations.
ISSUES OF quality, value and accountabilty in ground investigation are not new and nor is the industry's frustration at the perceived reluctance of client organisations to pay for high quality work.
Combining geotechnical and contaminated land investigations potentially offers many benefits, but industry has been divided on the technical incompatabilites. Recently the balance of opinion has swung in favour of combined investigations. New and impending guidance on site investigation addresses the issues.
The July 1999 version of the draft Code of Practice on Investigation of Potentially Contaminated Sites (the document formerly known as DD 175) notes that 'benefits can be gained from investigations that combine the needs of contamination and geotechnical objectives in some circumstances. However, the use of an integrated investigation should not result in compromising the objectives or requirements of either investigation.'
The Association of Geotechnical and Geoenvironmental Specialists (AGS) is developing a guidance document for combined geoenvironmental (ie contaminated land) and geotechnical investigations. This recognises that although the possible work activities for each type of investigation may appear similar, their objectives may be very different and so may the means of achieving them. Nevertheless there are potential advantages.
A joint meeting of the Environment Group and Engineering Group on 7 December at the Geological Society explored issues surrounding combined investigations. David Shilston (WS Atkins) co-convened the meeting with me and I also chaired the proceedings.
Mike Smith (Stanger Science and Environment), who is heavily involved in the AGS document, said that provided the different technical requirements to meet the investigation objectives were addressed, the combined investigation had a number of advantages, including: simplified project management, common use of equipment and procedures, use of exploratory holes for more than one purpose, and combined interpretation of field and analytical data to develop a conceptual site model.
Technical differences arise from practices such as the addition of water during drilling, as this would affect groundwater quality monitoring; cross-contamination within a borehole where contaminated fill is penetrated; cross-contamination between boreholes; and different sampling requirements for physical and chemical characterisation.
Nicola Legg and Liz Harrison (WS Atkins) presented three case studies of combined investigations ranging in size from the Millennium Dome down to one comprising a single exploratory hole. Contamination sampling techniques can be both time consuming and labour intensive and the large quantity of contamination samples required can restrict the amount of geotechnical sampling that can be carried out, they warned. They also made the point that storage requirements for contamination and geotechnical samples are different.
Adrian Marsh (STATS Consulting Group) explored the issues of quality, value and accountability in site investigation. He defined quality as being the provision of the correct answers to the right questions but acknowledged that 'value' is a perception (sometimes a proven fact) in the mind of the project promoter.
Marsh compared the virtuous circle and downward spiral in this perception depending on the experience any given project promoter had in his dealings with the site investigation industry.
The virtuous circle begins with a ground model of the whole site, including anomalies, that is calibrated against exploratory holes and describes engineering geological hazards and their potential effects on the development and relates parameters to the engineering geology of the site.
Several themes emerged during the discussion, including the need for a team approach to combined investigations, the importance of good engineering geological descriptions and full reporting of analytical methods in contaminated land reports, the differences in sample type, handling and storage and finally the different objectives and client base for the two types of investigation.
Paul Nathanail, director of the Land Quality Management division at Nottingham University