Summary

Hydrogeochemical studies of the Folkestone Beds and Hythe Beds aquifers of the Lower Greensand formation of Surrey and Hampshire indicate that both aquifers are very depleted in readily soluble mineral species. The lack of such minerals, particularly the carbonates, removes a potential buffer control upon acidic recharge water and ensures that the unconfined groundwaters in both aquifers exhibit pH values generally less than 7.0 and have low concentrations of total dissolved solids. At the onset of confined conditions the dissolved oxygen is rapidly removed and the redox potential Eh decreases as the aquifer conditions become strongly reducing. Saline water is present at depth in the confined zones. Apart from iron and manganese all heavy metal concentrations are low, most samples exhibiting values around the detection limit of 0.01 mg/litre. Tritium and stable isotope analyses indicate that confined borehole sources are abstracting a gradually increasing component of post-1953 recharge water. All sources contain tritium concentrations in excess of 5 tritium units and some have concentrations exceeding 15 tritium units.

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