Insight User Guide: Hydrogeology

Superficial aquifer - England and Wales

Provides details of aquifer status of groundwater held within superficial geology. The data is based on 1:50,000 scale geology.

The aquifer maps display the following aquifer designations:

Aquifer designation	Description
Principal	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.
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.
Unproductive strata	These are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow.

Data source: British Geological Survey, the Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Superficial aquifer - Scotland

Provides details of aquifer status of groundwater held within superficial geology. The data is based on 1:625,000 scale geology.

Aquifers fall into one of two categories:

Aquifers where intergranular flow is significant
Concealed aquifers, aquifers of limited potential, regions without significant groundwater.

Data source: British Geological Survey and Scottish Environment Protection Agency
Data update schedule: Quarterly

Bedrock aquifer - England and Wales

Provides details of aquifer status of groundwater held within bedrock geology. The data is based on 1:50,000 scale geology.

The aquifer maps display the following aquifer designations:

Aquifer designation	Description
Principal	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.
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.
Unproductive strata	These are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow.

Data source: British Geological Survey, Environment Agency and Natural Resources Wales
Data update schedule: Quarterly

Bedrock aquifer - Scotland

Provides details of aquifer status of groundwater held within bedrock geology. The data is based on 1:625,000 scale geology.

The aquifer maps display the following aquifer designations:

Aquifer designation	Description
Highly productive aquifer	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.
Moderately productive aquifer	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.
Low productive aquifer	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.
Rocks with essentially no groundwater	These are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow,

Aquifers are also classified according to the flow mechanism present as follows:

Flow is virtually all through fractures and other discontinuities
Significant intergranular flow.

Data source: British Geological Survey and Scottish Environment Protection Agency
Data update schedule: Quarterly

Groundwater vulnerability

An assessment of the vulnerability of groundwater to a pollutant discharged at ground level based on the hydrological, geological, hydrogeological and soil properties within a 1km grid square. Groundwater vulnerability is described as High, Medium or Low. Bedrock and superficial aquifers have separate classifications within this dataset.

Classification	Description
High	Areas able to easily transmit pollution to groundwater. They are likely to be characterised by high leaching soils and the absence of low permeability superficial deposits.
Medium	Intermediate between high and low vulnerability.
Low	Areas that provide the greatest protection from pollution. They are likely to be characterised by low leaching soils and/or the presence of superficial deposits characterised by a low permeability.

Data source: British Geological Survey, the Environment Agency and Natural Resources Wales
Data update schedule: Annually

Groundwater vulnerability - soluble rock risk

This dataset identifies areas where solution features that enable rapid movement of a pollutant may be present within a 1km grid square.

Data source: British Geological Survey, Environment Agency and Natural Resources Wales
Data update schedule: Annually

Groundwater vulnerability - local information

This dataset identifies areas where additional local information affecting vulnerability is held by the Environment Agency. Further information can be obtained by contacting the Environment Agency local area groundwater team through the Environment Agency National Customer Call Centre on 0370 850 6506 or by email on enquiries@environment-agency.gov.uk.

Data source: British Geological Survey, Environment Agency and Natural Resources Wales
Data update schedule: Annually