Interpretation and modelling : geology, to support the development of an Integrated Site Descriptive Model

Taking into account the experiences of sister organisations and best practice in other sectors such as oil and gas it is anticipated that the characterisation of the site will best be undertaken by the development and progressive updating of a single integrated Site Descriptive Model, i.e. a model describing the geometry, properties of the bedrock and water, and the associated interacting processes and mechanisms, which will be used to address the information requirements of all the end users (NDA 2010). Such an approach will ensure that • The understanding of the different aspects of the geosphere such as the geology, hydrogeology and hydrochemistry is developed in a consistent manner; and • The different end users base their design and assessments on the same understanding and evidence base. There are several elements to the preparation of a Site Descriptive Model, including: • Definition of the volume of ground that needs to be included in the model; • Subdivision of the model into geometric units so as to permit the description of spatial variability in a meaningful manner; and • Assignment of parameters (values and/or statistical distributions) to the defined geometric units. It is anticipated that, in a similar way to the approach adopted by SKB and Posiva, the integrated Site Descriptive Model will be divided into parts comprising clearly defined disciplines which may form either chapters or discipline-based models. The discipline-based models that are likely to be developed for UK sites comprise the following: • Geology; • Hydrogeology; • Hydrochemistry; • Geotechnical; • Transport properties; • Thermal properties; and • Biosphere. The Site Descriptive Model will provide the understanding of the characteristics of the site, sufficient to allow further qualitative and quantitative modelling to be undertaken as part of the development of the Environmental Safety Case