Publication record details

Title Baseline groundwater chemistry of aquifers in England and Wales: the Carboniferous Limestone aquifer of the Derbyshire Dome
Ref no OR/08/028
Author Abesser, Corinna; Smedley, Pauline.
Year of publication 2008
Abstract This report characterises the spatial and temporal variations in groundwater chemistry in the Carboniferous Limestone aquifer of the Derbyshire Dome. The report incorporates results from available archive groundwater-chemistry data, together with rainfall and host-aquifer mineralogical and geochemical data and the results from strategic sampling and analysis of new samples from 31 groundwater sources. The Derbyshire Dome is an anticlinal structure which consists of marine Carboniferous (Dinantian) Limestone flanked by shales and sandstones of the Millstone Grit (Namurian). The Limestone is extensively mineralised in some parts, in particular in the east of the study area. The mineralised areas display a distinct zonation in mineralogy with a west-east progression from calcite to barite to fluorite as the dominant gangue minerals. The Carboniferous Limestone forms a regionally significant aquifer for potable and industrial use. The hydrogeology of the area is dominated by natural karstic features but even more by the 'anthropogenic karst' which has developed as a result of the extensive historic mining activities. This has created a network of mine passages and drainage adits ('soughs'), some of which are now used for public water supply. The results from this study suggest that the natural baseline chemistry of the groundwater is largely controlled by differences in bedrock lithology and by the extensive mineralisation that occurs in the study area. The latter is responsible for the increased concentrations of trace elements including F, Ba, Ni, Pb, Zn, Mo and U in the groundwaters, although their mobility is also controlled by mineral solubility and/or redox conditions within the aquifer. The influence of bedrock lithology on the groundwater composition is obvious from the dominance of Ca-Mg-HCO3 waters, reflecting the prevalence of limestone. The influence of Millstone Grit can be inferred in many groundwaters (especially near the Dinantian/Namurian interface) from the occurrence of increased concentrations of Fe, Mn and Si which result from varying lithologies and redox conditions. The presence of thermal waters which contain varying proportions of long-residence-time groundwater, has also affected the regional groundwater baseline as these are enriched in a number of solutes, particularly Sr, SO4 and Cl. Anthropogenic influences on the groundwater chemistry appear to be minor compared with natural processes, although one of the solutes most significantly impacted is nitrate. Comparison with a previous survey in 1967/8 suggests that nitrate concentrations in the groundwater have increased two-fold during the last 40 years and locally exceed the NO3-N drinking-water limit of 11.3 mg L-1. Extensive mining activities have also impacted on the groundwater chemistry, firstly by lowering the base drainage level and promoting the upconing of thermal/deeper waters in parts of the aquifer, and secondly, by providing artificially high surface areas for enhanced bedrock weathering. The impact of mining on the baseline concentrations of solutes is difficult to quantify.
Publisher British Geological Survey
Place of publication Nottingham, UK
Series Open Reports
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