GSHP Screening Tool

GSHP Screening Tool

Click on map to assess potential for open-loop (>100kWth) systems

Navigating the map

To pan: left-click on the map and drag.
To zoom: Drag the vertical slider on the left of the map, use the mouse wheel, hold down the Shift key and drag a rectangle, or use the 'Go to location' to enter a known location e.g. a place, postcode.

Initial screening layer

The application opens displaying the initial screening layer. The initial screening layer highlights all areas (light blue) where there is potential for the operation of open-loop GSHP systems (>100kWth). In these areas, a productive aquifer (> 1 L/s) is present within 300 m below the topographic surface.

Query initial screening layer

Click anywhere on the initial screening layer to show details of GSHP data layers at that point. The information presented is described in more detail below. A number of the results provide a 'Map' button which opens a sub map containing the data layer. A blue circle is displayed on the sub map showing the location queried on the initial screening layer. The sub map can also be queried by clicking anywhere on the map.

Bedrock aquifer layer

The bedrock aquifer layer shows where an aquifer is present at the surface (“at outcrop”) and/or “concealed at depth” (i.e., the aquifer lies under less permeable rocks). Each category includes a yield range which refers to the maximum yield that can be obtained from a single borehole. Concealed aquifers were mapped for the main geological formations that form important aquifers at depth and can provide yields of at least 1 L/s.

Depth to source layer

This layer estimates the depth (below the ground) to the water source. This is typically the depth to the water table or to the top of the water bearing strata (=aquifer) where it is covered by superficial deposits or by less permeable bedrock (i.e., concealed aquifer). The layer is included here to give an indication of the minimum depth of drilling that is required for borehole installation. It refers to the uppermost aquifer where more than one is present.

Protected areas layer

The layer outlines where protected areas, including Source Protection Zones (SPZ), Sites of Special Scientific Interest (SSSIs) and/or National Parks are present. In these areas additional protection is required to safeguard drinking water supplies, wildlife and habitats or special landscape qualities through restricting activities that may affect any of these features. These are included here to show where restrictions on water abstraction/reinjectionmay apply. For further details see:, and

Existing licensed abstractions layer

This field shows what abstraction volumes have been licensed by the Environment Agency within a radius of 600m around the search location. The values refer to the total daily abstraction allowance per site/licence and can represent the combined yield from multiple boreholes. Where two or more values are found, these may refer to different aquifers and depths. The information is included here to show what daily yields can be achieved in the area of interest. It is not indicative of the licence that can be agreed with the Environment Agency as this will depend on the availability of water in the area. Details on this can be found at the Environment Agency’s website at .

Groundwater chemistry layer

Groundwater chemistry data are provided for all groundwater sampling points within 600m radius of the search location. Where two or more values are found, these may refer to different aquifers, depths or times of sampling. These data are included here to give an indication of the groundwater chemistry that can be expected around the area of interest. Please note that these data are only available for about 2% of the mapped area.

A set of empirical indices is provided that estimate (1) the tendency of the water (at in-situ temperature) to form/dissolve calcium carbonate scale (Langelier Saturation Index, Ryznar Stability Index) and (2) the corrosiveness of the groundwater towards steel (Larson-Skold Corrosive Index) (Table 1). It is also shown if iron concentrations in the groundwater are beneath or above the threshold value of 500µg/L . Concentrations equal to or greater than this threshold value may cause problems for open loop GSHPs due to precipitation and clogging of the pump or wells.

Langelier (LSI)

Ryznar (RSI)

Larson-Skold (LSCI)

LSI > 0.4

RSI < 6

Calcium carbonate precipitation
= scaling likely

LSCI < 0.8

No corrosion

0.4 > LSI > -0.4

6 < RSI < 7

No dissolution/
no precipitation

0.8 < LSCI < 1.2

Some corrosion

LSI < -0.4

RSI > 7

Calcium carbonate dissolution, =scaling unlikely

LSCI > 1.2

Corrosion likely

Table 1: Interpretation of scaling/corrosion indices

Note: Some experts prefer LSI > 1.5 (up to 2.5) as the break point for scale formation and LSI < -1.5 as indication of aggressive water. Likewise, some experts consider only waters at RSI <4.5 as definitely scale forming and waters at RSI > 8.5 as clearly aggressive.

Limitations of the tool

  • The tool is not updated. It is based on, and limited to, the data that were available from various databases at the time this data set was created between August 2011 and April 2012.
  • The tool has been developed at the 1:250, 000 scale and must not be used at larger scales. It does not provide definite answers at the site scale and all spatial searches against the data should be done with a minimum 250m buffer.
  • This tool is intended to be viewed onscreen only. Some of the data supporting this screening tool is restricted due to national security.
  • The tool only considers the main hydrogeological units as providing aquifers at depth, namely the Chalk, Corallian, Great Oolite, Inferior Oolite, Lower Greensand, Magnesian Limestone and Sherwood Sandstone. Other formations can also provide concealed aquifers locally, but these have not been included here.
  • Superficial deposits can also provide productive aquifers. These have not been considered in this tool.
  • Estimates of bedrock aquifer productivity are based on best-case scenarios, i.e. the maximum possible yield from a single borehole.
  • The tool does not consider the reduction in aquifer productivity near the outcrop boundaries due to decreasing thickness of the aquifer, i.e., aquifer thinning. As a result, there is a higher degree of uncertainty regarding the predicted aquifer potential near these boundaries which needs to be considered when using the tool. This is particularly important at boundaries between the base of a productive unit (aquifer) and the top of a less productive unit (no suitable aquifer).
  • The tool does not consider the suitability of the subsurface to accept water, i.e. the suitability for re-injecting water. Such information needs to be obtained from site-specific investigations or field tests. There are also alternative methods for discharging the water that do not rely on the subsurface properties, e.g. discharge via the sewer system or to surface water courses. Permission from the Environment Agency (EA) and/or the relevant water company will be required for the proposed discharges.
  • Sustainability of the open loop GSHP system is not considered by this tool and this is not within the remit of the EA or BGS. This may be an issue in areas where a large number of schemes have been installed within a certain area and where thermal interference between these systems can occur. Similarly, incorrect design can reduce the sustainably of a scheme significantly and some systems had to be abandoned due to this. You should discuss this with your installer, as changes to environmental permission may not be allowed.
  • Being in a favourable area does not guarantee you will obtain the environmental permissions you require for an open-loop scheme, as the tool does not consider local variations, water availability or discharge of water from the scheme. The EA will always require developers to obtain more detailed, site-specific information, for example by applying for Groundwater Investigation Consent.
  • The existing abstraction data can represent the combined licensed yield from multiple boreholes. For example, where two or more abstraction values are displayed for a search location, these may refer to the same licence (in which case they have the same value). Conversely, they could be boreholes that abstract from different aquifers and/or depths.
  • There are a number of risk factors that may affect the suitability of a site for GSHP installation which are also not considered in this tool. These include:
                - the location of mine workings and shafts
                - areas where geohazards may occurs (voids or collapse/stability issues)
                - evaporites
                - locations of known or suspected contamination
                - ambient groundwater temperatures
                - underground infrastructure restrictions.
  • The groundwater quality and existing abstraction licence data layers both incorporate information on superficial deposits (overlying the bedrock) which are not otherwise considered by this tool. Values returned by these layers do not necessarily relate to the main source identified in the bedrock aquifer potential / depth to source layers.

For further information see:

Technical Guide - A screening tool for open-loop ground source heat pump schemes (England and Wales):

Non-technical Guide - A screening tool for open-loop ground source heat pump schemes (England and Wales):

GSHP data layers