BROMINE GEOCHEMISTRY OF BRITISH GROUNDWATERS

The concentrations of Br in potable groundwaters in the United Kingdom range from 60 to 340 mu g l(-1). The occurrence of Br is described in terms of the Br/Cl weight ratio which enables small changes in bromid e concentrations to be assessed in terms of salinity. Median values of Br/Cl in groundwaters range from 2.60 to 5.15 x 10(-3) compared with a sea water ratio of 3.47 x 10(-3). In recent shallow groundwaters the Br/Cl ratio is rather variable in response to a range of natural and anthropogenic inputs (marine and industrial aerosols, industrial and a gricultural chemicals including road salt). Some slight enrichment in Br/Cl also occurs naturally during infiltration as a result of biogeoc hemical processes. Evolution of Br/Cl along groundwater flow lines ref lects the sources of increasing salinity; either the influence of mari ne sedimentary formations or evaporites. The groundwaters in the Trias sic sandstones of the English Midlands show significant Br depletion d ue to the evaporite source, in contrast to groundwaters in Cumbria. Br /Cl ratios in the Sherwood Sandstone of the East Midlands mainly refle ct the natural input sources and can be used to help understand the pa laeohydrology.