The hydrogeology of the Enfield-Haringey artificial recharge scheme, north London

Abstract

Abstract The Enfield-Haringey artificial recharge scheme comprises 23 abstraction/recharge boreholes located between Enfield and Haringey in north London. It is a strategic groundwater development aimed at increasing drought yields to meet the 'target level of service' defined by OFWAT for availability of water resources. The hydrogeology of the scheme, revealed by the drilling and testing of 15 new production boreholes is described and its strategic use summarized. The hydrochemistry of the groundwater in the Chalk and Basal Sands aquifer is briefly considered and the likely effects of re-saturation after recharge on the quality of the pumped groundwater is commented on. This and previous studies have led to a better understanding of the aquifer system and the hydraulic relationship between the Basal Sands and the underlying Chalk. Intensive exploitation in the past led to some dewatering but reduction in abstraction since the 1950s has allowed water levels to recover, a process that is continuing. In most of the Enfield-Haringey area the aquifer is still only partially saturated, hence the potential for artificial recharge. The Chalk aquifer has been found to be typically anisotropic and heterogeneous with the upper 30–40 m being productive. Acidization was found to produce significant increases in well yields. Chalk groundwaters are mainly of a calcium bicarbonate type while those of the overlying Basal Sands are dominated by sulphate. Both groundwaters become progressively richer in sodium at the expense of calcium from north to south, in the direction of groundwater flow and towards more deeply confining conditions.