Title: The Natural (Baseline) Quality Of Groundwaters In England And Wales - The Culm Aquifers, SW England;
Author: Environment Agency
Author: British Geological Survey
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_630, Representation ID: 208, Object ID: 1963
Abstract:
This document forms one of the regional studies being carried out on representative aquifers or parts of aquifers in England and Wales to provide an improved understanding of the natural baseline quality of groundwaters. It serves as a reference document against which current water quality and future trends (improvements and deteriorations) may be assessed. Section I provides a brief summary .of the water quality situation and in section II, further information is given concerning the controls on water quality necessary for an informed interpretation of the hydrogeochemical data. Groundwater in the Culm is slightly acidic but is buffered by traces of carbonate minerals, very few acid (less than pH 5.5) waters (with consequent high Al) are to be found, although enrichment of some metals may occur in relation to reducing conditions. The groundwaters show an extremely wide range of major element compositions reflecting differences in depth, residence time and bedrock lithology. The baseline chemistry of many elements, notably Cl, is influenced by atmospheric inputs, especially in coastal areas, but the influence of reactions with the bedrock may be recognised by the increasing alkalinity and in the concentrations of several major ions relative to chloride. There is little contrast between groundwaters in the three geological sub-units of the Culm (Lower Carboniferous; Crackington; and Bude Formations). Reactions with pyrite in the shale members of the Culm give rise to increases in sulphate. The median concentrations for minor and trace elements provide a gqod summary of their natural abundance and these mainly reflect the extent of reactions with the bedrock, although in some cases (e.g. F) the atmospheric contribution remains important. The most significant feature of groundwaters in the Culm is the tendency for high concentrations of dissolved Fe and Mn which are produced mainly as a result of sulphide mineral oxidation and the resultant reducing conditions in the shallow aquifer. The slightly acidic overall conditions probably help to maintain the high dissolved concentrations which may then give rise to metal precipitates on re-aeration.
Publisher: Environment Agency
Subject Keywords: Groundwater; Baseline surveys; Hydrology; Freshwater ecology
Geographic Keywords: Cornwall
Extent: 44
Permalink: http://www.environmentdata.org/archive/ealit:4532
Total file downloads: 281
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