Urban Manchester : hydrogeological pathway project

This report summarises the results of a collaborative study jointly funded by the North-west Region of the Environment Agency (the Agency) and the British Geological Survey (BGS). BGS was commissioned to carry out a geological and hydrogeological characterisation of the superficial deposits of the Central Manchester and Salford district as a contribution to a regional groundwater study of the Manchester and Cheshire aquifer being undertaken by the Agency. The overall objective of the study was to use a three-dimensional (3D) model of the superficial deposits to examine potential groundwater-surface water interactions. By integrating the modern 1:10,000 geological map with sub-surface (site investigation) information, the relationships within the quaternary deposits have been characterised and potential hydrogeological pathways between the surface water bodies and the deeper sandstone aquifer were identified. The work has shown that the Permo-Triassic aquifer is largely protected by glacial clay and silt deposits. However, the distribution and thickness of these deposits varies greatly across the area and hydraulic windows have been identified in the lowland areas where recharge may occur. Extensive sandy outwash sheet deposits, which are locally in contact with the underlying Permo- Triassic aquifer, offer the potential for lateral migration of groundwater in perched aquifers. Large areas and thicknesses of man-made material have been described and modelled and these could form potential sources of pollution, especially where they are in direct contact with the major aquifer or perched aquifers. The work involved four main tasks: • Determining the geometry, composition and spatial distribution of the principal superficial (drift) deposits; • Identifying potential pathways for groundwater movement through the drift; • Constructing a suite of land-use maps to help assess the locations of potentially contaminative activities; • Constructing a domain-based aquifer vulnerability model. Outputs of the study include: An attributed model of the superficial geology that can be interrogated at any x,y,z location An indication of potential flowpaths along bespoke sections through the 3D model and in plan view along the major superficial aquifers A novel hydrogeological domains map, based on established domain principals, but derived by computation from the 3D model A detailed dataset on past contaminative land use and the distribution, thickness and variation of the main areas of artificial ground All data delivered digitally (CD-ROM) and as a printed report with maps