Groundwater recharge in the Lower Greensand of the London Basin—results of tritium and carbon-14 determinations

Abstract

Summary Groundwater derived from the Lower Greensand of the London Basin has been ‘dated’ by the use of tritium and carbon-14 techniques. The data indicate that replenishment from the northern outcrop is feasible but that movement from the southern outcrop is extremely slow and possibly restricted.

Hydrogeochemical indications of regional flow in the Lower Greensand aquifer of the London Basin

“…The first published account of radiocarbon dating applied to groundwater in the UK was focused on the LGS of the London Basin (Mather et al 1973). Results were reported from eight sites along a transect from the Woburn Sands outcrop in the north to the Farnham area in the south (approximately the line A-B in Fig.…”

“…Further LGS environmental isotope data ( 14 C and stable isotopes) were obtained in the 1990s by the British Geological Survey. These covered approximately the same geographical range as Mather et al (1973), but with a higher number of sites. The results confirmed Pleistocene recharge ages for deep groundwaters, and that they were depleted in stable isotopes (Darling et al 1997).…”

“…Younger age sites can vary a little either way; some of this variation over two decades may be 'real' (for example at Netley Mill which abstracts water of recent age from the only wholly unconfined site considered here), but the main benefit of AMS measurement (beyond ease of sampling) would seem to be at low 14 C activities, though this is where radiocarbon dating becomes more uncertain because of the exponential nature of the decay curve. Nevertheless, it is clear that apparent groundwater age in the Slough area has continued to lie at or near the limit of 14 C groundwater dating (~30 ka) over the past 40 years of observation, from Mather et al (1973) onwards, and by implication over the whole century of abstraction from the LGS.…”

“…The very steep age gradient from the southern outcrop to the Aldershot area led Mather et al (1973) to conclude that any southerly recharge to Slough must be negligible, and that the only feasible source was the NW outcrop around the Woburn area (Fig. 1).…”

Regional groundwater flow in sedimentary basins in the U.K.

“…Artesian conditions exist in the Lower Greensand where waters of Pleistocene age are developed for supply near Slough (Mather et al 1973), and there is isotopic evidence for Pleistocene water in the Lower Greensand of Kent (Evans et al 1979). The potential in the Middle Jurassic limestones of the Cotswold Hills is generally greater than 150 m ASL and attains maxima of over 200 m, generally 50 m greater than similar values for the Chalk.…”