SOURCE, TYPE AND EXTENT OF INORGANIC CONTAMINATION WITHIN THE BIRMINGHAM URBAN AQUIFER SYSTEM, UK

A survey of the inorganic quality of the groundwater of the Birmingham Triassic sandstone aquifer was carried out by sampling seventy 80-150 m deep industrial abstraction boreholes, 11 shallow monitoring piezometers, two submerged tunnels and two flooded industrial basements, and a set of trial pits. Borehole logging and historical data were also obtained. Given that the city of Birmingham is as long established as most industrial conurbations in the world, the degree of groundwater inorganic contamination as indicated by abstraction well samples is not excessive. Out of the 28 determinands measured, only NO3- and Ba2+ consistently approach and exceed their European Community Maximum Admissible Concentrations standards for drinking water and the barium is being supplied by the aquifer rather than having an anthropogenic source. However, a few abstraction boreholes have highly contaminated groundwaters, with for example milligram per litre levels of heavy metals. In addition, there is a correlation between land use and chemistry, with the highest salinity, sulphate, chloride, sodium, boron, and total heavy metal concentrations being associated with metal-working sites. High concentrations of heavy metals (and NH4+ are unexpected in the near-neutral pH Triassic sandstone groundwaters given the high sorption capacity of the sandstone: it is concluded that one reason for the occasionally high concentrations observed is the presence of very locialized high concentration recharge. Data from shallow piezometers confirm the considerable degree of heterogeneity in groundwater quality on a small scale - the pollution is mainly from point sources. Sampling from piezometers, tunnels, and basements demonstrates that the groundwater concentrations at shallow depths are often much higher than the pumped water analyses suggest. However, nitrate groundwaters appear to vary much less with depth than other species, reflecting a longer history of supply and a wider range of sources. Geophysical logging and sampling of well columns, and other observations indicate that the intermittent pumping of abstraction wells results in the pumped water quality being biased towards the shallower, high concentrations groundwaters rather than being a uniform mixture from all screened depths. Historical data show various trends, and these can be related to local hydrogeology, land use, and abstraction history. Comparisons of organic and inorganic pollution show that distributions are very different, reflecting differences in physical transport processes, chemical interactions, and histories of chemical usage.