Research and analysis

Geochemical techniques to define deep thermal spring protection zones - summary

Published 17 December 2021

1. Chief Scientist’s Group report summary

This project reviewed the range of geochemical methods that can be used to understand thermal spring systems in the UK. This information will help the Environment Agency protect thermal springs from subsurface activities in the future.

1.1 Background

There are 5 thermal spring systems (defined as having temperatures > 150C) in the UK; Bath (The King’s Bath, Cross Bath, The Hetling Spring), Bristol (Hotwells), Matlock (East Bank Rising, New Bath Hotel), Buxton (St Anne’s Well) in England and Taff’s Well in Wales, with temperatures ranging from 20.5 to 47oC. These thermal springs occur where groundwater rises relatively quickly from deep within the Earth’s crust, where it is warmer, and emerges with increased temperatures. Thermal springs are important natural resources, providing water for spas, drinking water and supporting local ecosystems. Groundwater in the springs can be recharged by rain falling many miles from where the spring emerges, with long pathways through the rock.

Geochemical data from the springs can be used to determine where and how long ago the groundwater was recharged, and the pathway that the groundwater takes through the rock. This information can help us understand the systems and identify if they may be vulnerable to over-exploitation, pollution or hydrological change from human activities in the subsurface.

1.2 Aims and approach

The project reviewed the types of information about the thermal spring systems that different types of geochemical data such as major ions, trace metals, stable isotopes and markers created by humans, can provide. It also reviewed the assumptions and uncertainties associated with the different methods. It summarised the data that was collected for each of the 5 UK thermal spring systems and identified gaps in this data where knowledge of the thermal springs could be improved.

1.3 Findings

A wide range of geochemical data has been used to understand the origin, age and flow pathways of deep thermal spring systems in the UK since the 1970s, including:

• major ion (for example, bicarbonate and calcium) and trace metal (for example, strontium, lithium)concentrations, to understand water-rock interactions, maximum water temperatures and depths ofcirculation
• water stable isotopes (18-oxygen and 2-hydrogen) to understand groundwater sources and rechargeconditions
• radiocarbon (14-carbon), noble gas isotope activities (4-helium, 39-argon, 81-krypton) and markerscreated by humans (CFC, SF6, tritium, nitrate) to estimate the age of the water

These geochemical data have greatly improved understanding of the hydrogeology of the thermal spring systems. While there are large uncertainties and assumptions for individual methods, these can be reduced when different types of data are combined and used with an understanding of the 3D geology in order to constrain the possible origin and geological pathways. Nevertheless, even for the Bath thermal springs, the most well-studied thermal spring system, there is still a considerable range of age estimates of the groundwater (from 1,000 to 12,000 years) and uncertainty about the size/location of the recharge zone. Other thermal spring systems, such as Hotwells in Bristol, lack important geochemical data that could help to refine our understanding of hydrogeological processes.

1.4 Conclusions

Geochemical data from the thermal springs in the UK has provided a wealth of information about their sources and pathways, but there are still uncertainties about the systems that make protecting the springs challenging. The report highlights that further geochemical investigations, monitoring and integrating geochemical and geological information could be considered in order to improve our understanding of sources and pathways of the springs and their vulnerability.

1.5 Publication details

This summary relates to information from the following project:

• Report: SC210017
• Title: Geochemical techniques to define deep thermal spring protection zones

Author: Helena Pryer, University of Bristol

Internship supervisors: Sian Loveless and Natalie Kieboom, Chief Scientist’s Group

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency