Explanatory notes to accompany the Groundwater Vulnerability Index GIS for Stirling Council

O Dochartaigh, B.E.. 2002 Explanatory notes to accompany the Groundwater Vulnerability Index GIS for Stirling Council. Edinburgh, UK, British Geological Survey, 15pp. (CR/02/161N) (Unpublished)

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These notes are designed to accompany the ArcView geographical information system (GIS) format groundwater vulnerability index maps produced by the British Geological Survey (BGS) for Stirling Council. The maps are based on digital geological information for both bedrock and superficial deposits: they do not take account of soil cover. They cover the whole of the Stirling Council area plus a 2 km ‘buffer zone’ around the area to account for peripheral data and allow for more meaningful interpretation at Council boundaries. The purpose of the GIS maps is to show, in broad terms, the vulnerability of groundwater to pollution. 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 still of local importance. 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 the groundwater vulnerability index 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 and printed maps are a compromise between the representation of natural complexity and the simplicity of interpretation at a scale of 1:50,000. This places limitations on the resolution and precision of map information. In this case, there is a wide variety of geological strata and potential pollutants, 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 map coverages in the GIS only represent geological conditions (bedrock or superficial) at their upper surface. 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 has not included consideration of the soils. The overall permeability of each geological unit has been interpreted, enabling an assessment of the vulnerability of groundwater occurring under the Stirling 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 current methodology, however, provides a broad-based view of both the vulnerability of groundwater and the location of the more permeable aquifers under the Stirling 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 and associated maps 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, Stirling 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 12:53 +0 (UTC)

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