Coastal Aquifer Energy in Plymouth, UK

Matthew Bailey , David Birks, Rod Smith, Jon Selman, Orri Faulkes, Eve Langman, Harper Nicholas, Billy Andrews

Plymouth, UK, is a city underlain by a coastal karstic aquifer system, impacted by saline intrusion. The aquifer is being investigated as a source of ambient water for a city-wide heat network. Findings of aquifer-energy pumping tests are reported, highlighting the arising opportunities and challenges. The concept presented here deviates from typical aquifer energy systems, in that thermally spent waters are discharged directly to sea rather than reinjected into the aquifer, thereby negating the risks associated with reinjection wells and heat balance. However, at our study site in Plymouth, high sediment load persisted during pumping, likely sourced from either paleo-karst infill within the limestone, or buried tidal channels. We also present new structural data, which provides insights into the nature of the Plymouth Aquifer with respect to porosity architecture and fracture networks. Data are indicative of NNE-SSW trending structures which align with mapped faults and, porosity which is dominated by these fractures and cave systems within the limestone. Matrix porosity is low (mean: 5.2%), a result of diagenetic recrystallisation and post-diagenetic calcite precipitation in microfractures, indicating a low risk of irreversible salinisation. Development of the project at Plymouth could offer a blueprint for coastal aquifer energy systems elsewhere.