The Lower Greensand Formation, a major aquifer in the Thames Basin, is best developed to the south of the London anticline in the Weald Basin, where it occupies a greater outcrop area.
North of the London Basin the Lower Greensand Formation tends to be more arenaceous and rests unconformably on Jurassic limestones.
The Lower Greensand Formation is comprised of two aquifer units these being the Hythe Formation consisting of fine-grained sands and sandstones and the Folkestone Formation, a poorly consolidated, cross-bedded sand.
These two aquifer units are separated by the Sandgate Formation which comprises poorly sorted sands and silts. While piezometric data and groundwater dating show the two aquifer units to be hydraulically independent the Sandgate Formation is not laterally persistent and may allow vertical leakage.
The Hythe Formation exhibits both fracture flow in cemented sandstones and intergranular flow through poorly consolidated sands.
The Folkestone Formation, in contrast, is the only aquifer within the Thames Basin regarded as generally homogenous containing intergranular flow only. Where intergranular flow dominates, transmissivity values are accordingly reduced.
High storage, within the Folkestone Formation in particular, provides diffuse baseflow to rivers and a characteristic steady groundwater head with minimal seasonality.
Beyond the outcrop the Lower Greensand becomes confined by the Gault Formation and the individual aquifer units behave more as one. The groundwater resource potential is however more limited in the confined Lower Greensand aquifer as the formation thickness and permeability are reduced.
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Contact Stephanie Bricker for further information