Report on geophysical logging and core description from five new Thames Water boreholes in the Chalk Group along the River Kennet, Marlborough, Wiltshire

This report provides a summary of borehole geophysical logging operations from five new Thames Water boreholes in the Chalk Group along the River Kennet between East Kennet and Marlborough, Wiltshire (Figure 1). Borehole drilling (carried out by Soil Engineering Ltd) and geophysical logging (undertaken by BGS) took place during May and June, 2021. One of the boreholes (Marlborough STW) was cored and reached a maximum depth of 100.45 m. The other boreholes ranged from 40-47 m deep (Table 1). The boreholes were drilled for research purposes to investigate the impact of Chalk stratigraphy on groundwater behaviour beneath this western part of the River Kennet, which is subject to highly variable flow. The coring and geophysical logging were an integral part of the borehole installation, guiding the drilling toward a target depth just beneath the Melbourn Rock. The main purpose of this report is to provide Thames Water with a summary of work undertaken, some results and interpretative observations and an index of associated files and documents.