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What will new international standards mean for the Conceptual Site Model?

The Conceptual Site Model (CSM) is the heart of all contaminated land assessments. What it is and how it should be approached is well established in a wide range of published standards and guidance (BS5930; BS10175 and CLR11).


However, the new International Standard ISO CD 21365 Soil quality – Conceptual site models for potentially contaminated sites is about to be published.  It is dedicated to the CSM alone.  Initially my questions are – ‘is it needed?’ and ‘What value will it add?’

My experience of producing contaminated land reports and providing advice to developers or site owners is that contamination is one of a number of concerns to our clients. The technical information needs to be presented in such a way as to inform the client clearly. It is a given that it follows the relevant technical guidance. So, there is science in the report but more importantly there is an art – the art of communicating risk.

Published guidance is usually documentation of a process, this is really important to the quality of a report. Today, data collection can be achieved efficiently by search engines and database providers, the modern consultant is now focussed less with this process and more with the engagement of interpretative skills and communication of outcomes. 

The new standard gives an opportunity for reflection on what makes a really good Conceptual Site Model and I would suggest three principles for the Conceptual Site Model:

1. Communication of Risk:  CLR 11 provides a choice on how a CSM is communicated; in words or in a picture.  I would advocate a picture.  A picture is more consistent between practitioners.  Some authors can’t stop themselves when it comes to writing and often risk losing their reader or even introducing inconsistencies or errors to the CSM.  A picture is easily sketched using any of the most common software, it conveys the source-pathway-receptor linkages clearly and - no Art GCSE is required.

2. Context : The reason for the report being commissioned is a key driver for the relevance of the CSM.  Operational industrial sites are different from legacy derelict sites.  The client has requested work that will assist in their aspirations for the site, the CSM should be relevant to this.

3. Accuracy: There is no excuse given the tools available today for not compiling the factual information so that the basis of the CSM is robust.

So what will the new standard add?  The answer is not too much with respect to data collection.  However, it will improve the emphasis on the CSM and help to increase its value to site owners, developers and purchasers.  Is it needed? Yes – the discipline of collecting data is less intensive and the future is to invest the time saved by consultants in the interpretation and communication of risk.  So previous guidance needs updating. 

The Phase 1 Risk Assessment Report isn’t valued in megabytes, it is the first understanding of ground risk and communication of risk to the site owner, prospective purchaser or regulator.  A good CSM will ensure that subsequent site decisions are the right ones, avoiding blind alleys, wasted time and money.

Andy Moore is technical director for ground risk and remediation at WSP UK.