Understanding the new aquifer designation maps.
What are the new aquifer designations?
We help to protect groundwater by identifying different types of aquifer - underground layers of water-bearing permeable rock or drift deposits from which groundwater can be extracted.
From 1 April 2010 our Groundwater Protection Policy will be using aquifer designations that are consistent with the Water Framework Directive. These designations reflect the importance of aquifers in terms of groundwater as a resource (drinking water supply) but also their role in supporting surface water flows and wetland ecosystems.
The aquifer designation data is based on geological mapping provided by the British Geological Survey. It will be updated regularly to reflect their ongoing programme of improvements to these maps. We gratefully acknowledge this assistance.
The maps are split into two different type of aquifer designation:
- Superficial (Drift) - permeable unconsolidated (loose) deposits. For example, sands and gravels.
- Bedrock -solid permeable formations e.g. sandstone, chalk and limestone.
The maps display the following aquifer designations:
These are layers of rock or drift deposits that have high intergranular and/or fracture permeability - meaning they usually provide a high level of water storage. They may support water supply and/or river base flow on a strategic scale. In most cases, principal aquifers are aquifers previously designated as major aquifer.
These include a wide range of rock layers or drift deposits with an equally wide range of water permeability and storage. Secondary aquifers are subdivided into two types:
Secondary A - permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. These are generally aquifers formerly classified as minor aquifers;
Secondary B - predominantly lower permeability layers which may store and yield limited amounts of groundwater due to localised features such as fissures, thin permeable horizons and weathering. These are generally the water-bearing parts of the former non-aquifers.
Secondary Undifferentiated - has been assigned in cases where it has not been possible to attribute either category A or B to a rock type. In most cases, this means that the layer in question has previously been designated as both minor and non-aquifer in different locations due to the variable characteristics of the rock type.
These are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow.
Note: We are only able to display the principal and secondary aquifers as coloured areas on the maps. All uncoloured areas on the bedrock designation map will be unproductive strata. However, for uncoloured areas on the superficial (drift) designation map you will not be able to distinguish between areas of unproductive strata and areas where no drift is present. To do this you will need to consult the published geological survey maps.
Data and our policy
If the new aquifer designations result in a different Groundwater Protection Policy applying to a particular location, we will continue working to any agreements we have previously made, provided there is clear evidence of those agreements.
For the purposes of our Groundwater Protection Policy the following default position applies, unless there is site specific information to the contrary:
- if no superficial (drift) aquifers are shown, we will use the bedrock designation;
- in areas where the bedrock designation shows unproductive strata (the uncoloured areas) we will use the superficial (drift) designation;
- in all other areas, we will use the more sensitive of the two designations (e.g. if secondary drift overlies principal bedrock, we will adopt an overall designation of principal)
What about the previous groundwater vulnerability maps?
If you have been used to using our older groundwater vulnerability maps, aquifers previously designated as major and minor now become principal and secondary respectively.
Our groundwater vulnerability maps have not been completely withdrawn because the new maps do not provide information on surface soils. You will still need to refer to the groundwater vulnerability maps if you are assessing activities on undisturbed natural soils (e.g. agricultural land) and need the soil classes. In this case you should disregard the old geological classes and combine the soils information with the new aquifer designations. The older groundwater vulnerability maps are still available upon request from our National Customer Contact Centre (fee payable).
How do I request a copy of the aquifer designation dataset?
- The aquifer designation dataset is available on request from The British Geological Survey (fee payable). It is created as vector polygons and is available in a range of GIS formats, including ArcGIS (.shp), ArcInfo Coverages and MapInfo (.tab). More specialised formats may be available but may incur additional processing costs.
- Public sector organisations should be able to access the data from our DataShare service
- The aquifer designation dataset is based on, and limited to, an interpretation of the records in the possession of The British Geological Survey and Environment Agency at the time the data set was created.
- The aquifer designation dataset has been developed at 1:50 000 scale and should not be used at larger scales (e.g. 1:10 000).This equates to a 50m accuracy on the ground, so all spatial queries against the data should be done with a minimum 50m buffer.