Explanatory notes to accompany the Aquifer Vulnerability GIS for Aberdeenshire Council

O Dochartaigh, Brighid. 2002 Explanatory notes to accompany the Aquifer Vulnerability GIS for Aberdeenshire Council. Edinburgh, UK, British Geological Survey, 14pp. (CR/02/107N) (Unpublished)

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Abstract/Summary

These notes are designed to accompany the ArcView geographical information system (GIS) format aquifer vulnerability maps produced by the British Geological Survey (BGS) for Aberdeenshire Council. The GIS is based on digital geological information for both bedrock and superficial deposits. It covers the whole of the Aberdeenshire county area plus a 3 km ‘buffer zone’ around the county area to account for any differences in boundary area data and to allow for more meaningful interpretation at county boundaries. The purpose of the GIS is to show, in broad terms, the vulnerability of groundwater to contamination. Groundwater is contained within aquifers of various types. Abstractions from these aquifers provide water for potable supplies and various domestic, industrial and agricultural uses. Some highly permeable aquifers are very productive and of regional importance as sources for public water supply while less permeable formations are important locally. Groundwater also provides the baseflow to surface watercourses. Groundwater is typically of high quality and often requires little treatment before use. However, it is vulnerable to contamination from both diffuse and point source pollutants, from direct discharges into groundwater and indirect discharges into and onto land. Aquifer remediation is difficult, prolonged and expensive, and therefore, the prevention of pollution is important. The approach and classifications used in the production of this vulnerability GIS can also be used in the assessment of specific land use practices, proposed developments and land use changes over aquifers where these could have an impact on groundwater quality. More detailed site specific assessment of vulnerability will be required where it is considered that development may have an impact on groundwater quality. This GIS is a compromise between the representation of natural complexity and simplicity of interpretation at a scale of 1:50,000. This places limitations on the resolution and precision of map information. In this case, the variety of geological strata and potential pollutants that have to be covered is wide, and the classification used is, of necessity, generalised. Individual sites and circumstances will always require further and more detailed assessment to determine the specific impact on groundwater resources. The GIS only represents conditions at the surface of the solid and/or drift geology and, therefore, where these formations have been disturbed or removed, for example, during mineral extraction, the vulnerability class may have been changed. Hence, where there is evidence of disturbance, site specific data need to be used to determine the vulnerability of the groundwater. The methodology used for this GIS map has not included consideration of the soils. The overall permeability of each geological unit has been interpreted, enabling an estimation of the vulnerability of groundwater occurring under the Aberdeenshire area. The vulnerability classification does not follow the methodology devised for published groundwater vulnerability maps used by the Scottish Environment Protection Agency (SEPA). The latter methodology includes a system in which superficial geology and soil data are used to produce a series of detailed vulnerability classifications. The accompanying GIS system used in the current methodology, however, provides a broad-based view of both the vulnerability of groundwater and the location of the more permeable aquifers under the Aberdeenshire area. The data used for the compilation of the vulnerability GIS use part of the 1:50,000 DigMap solid and drift geology coverage. The ‘thick drift’ polygons found in the GIS were interpreted and drawn based on BGS borehole records. The GIS should not be used at scales larger than 1:50,000. There are three themes within the GIS: Solid Geology Permeability, Drift Geology Permeability and Aquifer Vulnerability, formed by combining solid and drift geology permeability.

Item Type:	Publication - Report
Programmes:	BGS Programmes > Groundwater Management
Funders/Sponsors:	British Geological Survey, Aberdeenshire Council
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
Additional Keywords:	GroundwaterBGS, Groundwater, Groundwater protection
Date made live:	07 Apr 2020 13:15 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/527416

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