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Fluid flow in the Chalk of England

Summary The Chalk aquifer of England can be thought of as a multi-porosity medium. The matrix is a fine-grained limestone which generally has high porosity but small pore throats, so that its permeability is typically only 0.1 to 10 millidarcys (10−4 to 10−2 m day−1). A fairly uniform fracture system imparts a secondary permeability, which appears to be about 100 to 1000 mD (0.1 to 1 m day−1). Where the Chalk forms a major aquifer, most of the transmissivity results from the enlargement of fractures, by solution, to form a few highly permeable zones. Over much of the outcrop, weathering leads to the development of shallow permeable layers to form an additional component. Each of these permeability systems influences some aspect of subsurface water movement, with implications for resources, quality and construction.