early planning stage the British Geological Survey (BGS) and the Environment Agency (EA) have collaborated to develop a screening tool that gives planners and developers an initial indication of the depth, productivity and quality of potential aquifers that exist in a given area. What are the initial questions? Successful planning requires a consideration of ..... Bedrock aquifer potential layer Depth to source layer Protected areas layer Hydrogeology Regulations Economics Locations of bedrock aquifers Estimated productivity (water yields) Depth to the water (drilling/installation costs) Location of protected areas
The tool has been created for England and Wales at the 1:250,000 scale It is accessed, free, on the web at http://mapapps2.bgs.ac.uk/gshpnational/home.html At its top level the tool displays the viability for open loop GSHP as Where favourable means Aquifers are present with yields per borehole of at least 1 L s-1 with a maximum depth from the topographic surface of 300 m. These conditions are considered favourable for installations with a capacity ≥ 100 kWth More detailed information is available by clicking on the favourable layers
tool is built from 5 layers Bedrock aquifer potential layer – shows where aquifers are present at outcrop or concealed at depth that can provide a borehole yield of 1 L s-1. The possibility of variable yields from some carbonate rocks is highlighted. Depth to source layer – Minimum drilling depth required to access the source Protected areas layers – Distribution of protection zones in England and Wales Groundwater quality layer – where available, data on scaling, corrosion and encrustation Existing licensed abstractions layers - abstraction volumes that have been licensed by the Environment Agency in a given area for all available aquifers
classified as, o no suitable aquifer (including all aquifers with productivity <1 L/s) o moderate aquifer (1- 6 L/s) o good aquifer (> 6 L/s). Concealed aquifers at depth (within 300 m) are considered from, Chalk Lower Greensand Corallian Great Oolite Inferior Oolite Sherwood Sandstone Magnesian Limestone But no yield estimate is given, multiple aquifers may occur at some localities Superficial deposits are not considered Bedrock aquifer potential layer
are three situations to consider A. Where the aquifer is unconfined it is the depth to the water table B. If superficial deposits are present it is the depth to the bedrock aquifer or the depth to the water table within the bedrock aquifer C. If the aquifer is concealed, it is the depth to the top of the aquifer
the following Source Protection Zones (SPZ) Environment Agency zones (1-3) aggregated into a single category National Parks in England and Wales Data from Natural England (NE) and by the Countryside Council for Wales (CCW) under an Open Government Licence Sites of Special Scientific Interest (SSSIs) Data from Natural England (NE) and by the Countryside Council for Wales (CCW) under an Open Government Licence A protected area doesn’t mean a GSHP is not possible; extra permissions and regulations may apply!
are presented The Langelier Saturation Index (LSI) and Ryznar Stability Index (RSI) are empirically derived indices that indicate the tendency of the water to form/dissolve calcium carbonate scale Langelier (LSI) Ryznar (RSI) LSI > 0.4 RSI < 6 → Ca-Carbonate precipitation, scaling likely 0.4 > LSI > -0.4 6 < RSI < 7 → No dissolution or precipitation LSI < -0.4 RSI > 7 → Ca-Carbonate dissolution The corrosiveness of the groundwater is given by the Larson-Skold Corrosive Index (LSCI) LRSI < 0.8 → No corrosion 0.8 < LRSI < 1.2 → Some corrosion possible LRSI > 1.2 → Corrosion likely The potential for encrustation associated with high iron (Fe) concentration (≥ 500 μg Fe L-1) The tool returns data from a radius of 600 m from the selected point (limited to a max of 10 values). Note: only 2% of the area is covered by these data
layer gives the abstraction volumes that have been licensed by the Environment Agency within a radius of 600 m from the selected point (max 10 values) as of 12 August 2011. (Note: that less than the licensed volume may actually be being abstracted.) This data is useful because It gives an indication of the actual volumes that can be abstracted It gives an indication of where large abstractions are already licensed that may impact on new licenses being granted It shows where there is an increased risk of interference between abstractions, potentially risking early thermal breakthrough
The tool is developed for open-loop, non-domestic schemes with > 100 kWth capacity. The tool has been developed at the 1:250,000 scale and does not provide definitive answers at the site scale. At depth, only the major concealed aquifers have been considered. Locally, other aquifers or superficial deposits may provide a viable resource. Near outcrop boundaries, aquifer productivity may be less (aquifer thinning). Sustainability of a scheme is not considered. Detailed planning of a large open loop GSHP would require further on- site investigation and interaction with the Environment Agency
be accessed free from the BGS website www.bgs.ac.uk > Our research > Energy > Geothermal Energy > Open-loop GSHP screening tools Or directly at http://mapapps2.bgs.ac.uk/gshpnational/home.html Non technical and technical guides are available on the website Feedback and suggestions for further dissemination would be welcome Thank-you for your attention Jon Busby – British Geological Survey – Keyworth – Nottingham – UK Tel: +44 (0)115 9363440; e-mail [email protected]
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