Title: The Natural (Baseline) Quality Of Groundwaters In England And Wales - The Chalk Of Berkshire And The Chilterns
Author: W IM Edmunds
Author: L J Brewerton
Author: Environment Agency
Author: British Geological Survey
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_972, Representation ID: 289, Object ID: 2259
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. This account describes chemical data from 65 boreholes in the Chalk aquifer of Berkshire and the Chilterns. Data, from 169 samples from 32 sites on the unconfined Chalk and 101 samples from 33 sites on the confined Chalk are utilised. Data are compiled from Environment Agency (EA) and British Geological Survey (BGS) data files. It is estimated that of the Berkshire and Chilterns Chalk sources, some 80% of the groundwaters in the unconfined aquifer considered in this study, have significant contributions from agricultural sources. Apart from this, the natural geochemical signature predominates. Rainfall chemistry forms a major contribution for several ions (eg Cl, F; Mg) of the initial groundwater composition. However, the characteristic chemistry of chalk groundwaters is mainly established by water-rock reactions taking place in the top few metres of the unsaturated zone. Despite its purity, the small amount of other elements substituting in the calcites forming the Chalk have a disproportionate effect on controlling the water chemistry. The main water quality characteristics are controlled by the various reactions with the carbonate matrix, redox and ion-exchange reactions and mixing with slightly saline water at depth. The progressive reaction of the chalk sediment leads to release of a number of trace elements (notably Sr, F, Mn and Fe). Strontium in particular can be used as an indicator of the groundwater evolution and residence time. The report also contains detailed information on the occurrence and distribution of a number of other significant trace elements.
Publisher: Environment Agency
Subject Keywords: Groundwater; Water quality; Baseline surveys; Hydrology; Nitrates; Chalk streams; Agricultural pollution; Freshwater ecology
Geographic Keywords: Berkshire
Extent: 49
Permalink: http://www.environmentdata.org/archive/ealit:4552
Total file downloads: 317
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