Interpretation of pumping tests in the Sherwood Sandstone Group, Sellafield, Cumbria, UK

In 1995 as part of the process to assess the suitability of a site near Sel lafield, Cumbria, for a deep geological repository for solid intermediate l evel and some solid low level radioactive waste, United Kingdom Nirex Limit ed (Nirex) commissioned a series of long duration pumping tests in the vari ous stratigraphic horizons at the site. Two of the pumping tests were condu cted in vertically adjacent sections of the lower Sherwood Sandstone Group (SSG) whilst pressures were monitored at discrete intervals in surrounding monitoring boreholes. Response were observed in over twenty monitoring zone s at various levels around the pumped sections during both tests. In order to arrive at an understanding of the hydraulic system in the SSG, a systematic methodology was adopted to analyse the data sets from the pump ing tests. Preliminary analysis of the data from each responding zone used the standard 2D radial flow analytical approach. This indicated that, whils t responses conformed broadly to this model, there were important deviation s. Three different analytical modifications were adopted to assess the sign ificance of these deviations; a partial penetration model, a bounded aquife r model and a generated radial flow model. The use of the different models allowed a conceptual model of flow processes occuring in the SSG to be deve loped.