Establishing an urban geo-observatory to support sustainable development of shallow subsurface heat recovery and storage

Abstract

Low-enthalpy ground source heating and cooling is recognised as one strategy that can contribute towards reducing reliance on traditional, increasingly insecure, CO 2-intense thermal power generation, as well as helping to address fuel poverty. Development of this technology is applicable in urban areas where high housing density often coincides with the presence of shallow aquifers. In urban areas groundwater temperatures can be elevated due to the subsurface Urban Heat Island effect. Uptake and development of this technology is often limited by initial investment costs, however, baseline temperature monitoring and characterisation of urban aquifers, conducted in partnership with local authorities, can provide a greater degree of certainty around resource and sustainability that can facilitate better planning, regulation and management of subsurface heat. We present a novel high-density, city-scale groundwater temperature observatory and introduce a 3D geological model aimed at addressing the needs of developers, planners, regulators and policy makers. The Cardiff Geo-Observatory measures temperature in a Quaternary aged sand and gravel aquifer in 61 boreholes and at a pilot shallow open-loop ground source heating system. We show that repurposing existing infrastructure can provide a cost effective method of developing monitoring networks, and make recommendations on establishing similar geo-observatories. Anthropogenic factors, including land cover, heat loss from buildings, basements and subsurface infrastructure, can result in the warming of shallow groundwater in urban areas, known as the subsurface Urban Heat Island effect (sUHI) (

Borehole temperature log from the Glasgow Geothermal Energy Research Field Site: a record of past changes to ground surface temperature caused by urban development

“…Finally, as part of our analysis we have established the manner in which surface warming in the Glasgow area has been partitioned between global warming and UHI development. Our efforts thus increase to three the inventory of British cities for which this has been determined, following Cardiff (Patton et al 2015(Patton et al , 2019 and Newcastle upon Tyne (Westaway and Younger 2016). Similar effects have also been recognized in other cities, such as Zürich, Switzerland (Bayer et al 2016).…”

Hydro-geomechanical characterisation of a coastal urban aquifer using multiscalar time and frequency domain groundwater-level responses

“…To this end, TSA has been applied to derive spatially distributed hydraulic properties (e.g. BE, aquifer compressibility and storativity) across the aquifer using a high-resolution, 23-year-longtime-series dataset from a preexisting groundwater monitoring network (Mitchell 1996), now incorporated in a geothermal energy observatory in Cardiff, UK (Patton et al 2019), comprising 234 boreholes. Data from 116 of these have been considered here, based on the availability of continuous data for the maximum number of boreholes monitoring the glaciofluvial sand and gravel aquifer and the made ground.…”

Measurement and monitoring

“…Abesser et al ( 2020) also present the findings from research investigating temperature changes in the ground but from quite a different perspective to that of the paper by Patton et al (2020). This study focusses on temperature changes and estimation of thermal conductivity in very near surface ground, which is of relevance to soil science and agronomy applications but also in principle to those at depth relating to ground source heating-cooling systems.…”

“…There are eight papers within the set: six were published in the first issue of this year's QJEGH volume and the final two in this issue. These are summarised briefly in the following paragraphs given in an order starting with two papers (by Patton et al, 2020 andAbesser et al, 2020) that both concern the measurement of ground temperature and in the second thermal conductivity as well. Abesser et al focus on the use of fibre optic sensors and the next paper (by Puzrin et al, 2020) continues this theme, but this time for ground monitoring to determine displacements with a view to assessing geohazard risks.…”

“…The paper by Patton et al (2020) covers the development of an urban 'geo-observatory' set up to assess groundwater temperature changes from subsurface heat recovery and storage systems. This new system operated in Cardiff, Wales, monitors groundwater temperatures within the shallow Quaternary sand and gravel aquifer that lies beneath the city.…”