Previous studies of the hydrogeology of the Lower Greensand of the London Basin have suggested that recharge from the north and south is insufficient to balance current abstractions. Studies of the Lower Greensand have demonstrated the existence of a number of depositional troughs / tidal channels, the significance of which have been largely overlooked by previous hydrogeologists. Sedimentological studies show that these troughs consist of well sorted uncemented almost pure quartz coarse sands and act as conduits enabling rapid recharge of the London Basin from outcrops to the north and west. This study uses noble gas and uranium groundwater geochemistry to determine groundwater migration and mixing in the Lower Greensand. The noble gases were determined by mass spectrometry and the radioelements by alpha and gamma spectrometry and scintillation counting. Uranium disequilibrium and noble gas data have been used to confirm the existence of a zone of ancient (up to 50,000 years old) saline water in the central and deep basin. This data has also confirmed that recharge must occur from the Chalk and that this water is of considerable age ( -115, 000 years). The uranium data shows these waters are mixing in the south with very rapidly recharged water and in the north with recent recharge water. The volumes of these recharge waters are insufficient to support current abstractions and therefore saline water is being drawn from the deep aquifer to account for this short fall. This water in tum draws into the deep aquifer water recharged at the western outcrops, through the tidal channels. It is predicted that this western outcrop groundwater will have an age of -8000 years and in time will be detected, mixing with the deep saline water. There is some evidence from the dissolved radioelements to suggest that another trough may allow recharge from the south.