1 The first city-wide map of shallow groundwater 2 temperatures in the UK to support the development of 3 ground source heat systems 4 Gareth Farr1, Ashley M. Patton1, David P. Boon1, David R. James2, Bernard Williams2 & David 5 I. Schofield1. 6 1British Geological Survey, Columbus House, Tongwynlais, Cardiff, CF15 7NE, UK 7 2Cardiff Harbour Authority, Queen Alexandra House, Cargo Road, Cardiff Bay, CF10 4LY, UK 8 *Corresponding author (e-mail:
[email protected]) 9 10 Keywords: ground source heating, open loop, urban heat island, low enthalpy, Cardiff, Wales. 11 12 Abstract: Low enthalpy ground source heating systems can help to reduce our dependency on fossil 13 fuels, in turn reducing greenhouse gas emissions and increasing energy security. In order to de-risk and 14 support the sustainable development, regulation and management of ground source heating systems in 15 urban areas, detailed baseline mapping of groundwater temperatures is required. Groundwater 16 temperatures were measured in 168 monitoring boreholes primarily within a Quaternary sand and gravel 17 aquifer in the city of Cardiff, UK. The data has been used to create the first city-wide map of shallow 18 groundwater temperatures in the UK. This map can be used both to support development of ground 19 source heating but also to act as a detailed baseline from which to measure change. Shallow groundwater 20 temperatures under the city were found to be 2°C warmer than the UK average groundwater temperature 21 and this additional heat is attributed to the Urban Heat Island. The Zone of Seasonal Fluctuation varies 22 from 7.1 and 15.5 mbgl within the shallow Quaternary aquifer, averaging 9.5 mbgl.