Research and analysis

Perspectives on protection of deep groundwater

Published 29 October 2020

1. Chief Scientist’s Group research summary

Most of the groundwater that supports rivers and abstractions in England derive from aquifers lying no more than 400 m below the surface. However, deeper groundwater, including springs that have their sources at depth, may also have value as a resource (for example, the hot springs at Bath) and potentially could be abstracted for other purposes. It is important to develop a better understanding of these waters and the volumes available so that they can be protected, where necessary, from activities that take place at depth such as the exploitation of onshore oil and gas.

This project looked at deep subsurface activities and whether we need constraints in order to protect deep groundwaters. These constraints would depend on the value of the groundwater and the risks posed by the activities.

1.1 What did this project involve?

Deep source groundwater often contains significant levels of minerals and may be partly saline or ‘brackish’. The project sought to define criteria for ‘usable brackish groundwater’, taking account of the potential uses and any economic considerations.

The possible impact of the abstraction of deep water on shallow aquifer systems was assessed.

A catalogue of known deep-sourced springs was prepared and the possible existence of other deep-sourced springs was considered, including whether groundwater might rise from depth to near surface aquifers, without appearing as springs. The hydrogeological settings of deep springs, and the Bath spring system in particular, were reviewed to help illustrate how best to assess their provenance.

The use of geothermal schemes and their impact on groundwater temperature in deep aquifers was reviewed.

A review of how other European countries delineate deep groundwater bodies for the Water Framework Directive helped to develop a method for delineating the source waters of deep-sourced springs.

1.2 What were the findings?

Groundwater with more than 600 mg per litre of total dissolved solids was taken to be brackish. This includes 16.5% of groundwater samples in the Environment Agency’s records for 2017. Most of this groundwater would be suitable as is for livestock watering and the irrigation of crops. It would also be suitable for drinking after blending or treatment.

The exploitation of deep groundwater (deeper than 400 m) may lead to impacts on near surface groundwater. For example, there could be increased flushing of salinity from deeper aquifers, the introduction of oxidising groundwater to previously anaerobic environments, and the loss of any deeper fresh groundwater that may exist. If available in sufficient and sustainable amounts, deep and/or brackish groundwater could be used to compensate for increased demand for fresh water.

Springs originating from depth may also combine with shallower groundwater and so protection of the system as a whole needs to be considered. For example, the water flowing from Bath springs includes a component of modern leakage into the spring flow system.

Identification and mapping of the three-dimensional catchment of a deep spring is a vital part of any risk assessment. From a consideration of English and European examples for protecting deep springs, a tiered methodology for characterising and delineating deep spring protection zones was recommended.

1.3 What are the next steps?

Future study could be focused on quantifying the amount of available brackish water that is not already accounted for in existing catchment water balances. An assessment of hydrochemical data, with further sampling where necessary, would help to understand the vertical distribution of brackish water.

A more comprehensive literature review of European approaches to spring protection would be valuable, particularly for countries with karst aquifer systems that support deep spa, mineral and thermal spring waters. A method for delineating spring protection zones would also be useful.

1.4 Publishing details

This summary relates to information from project SC180015 reported in detail in the following output(s):

Report:

SC180015

Title:

Perspectives on protection of deep groundwater

October 2020

Project manager:

Ian Davey, Research, Analysis and Evaluation

Research contractor:

Stephen Buss,
Environmental Consulting Ltd,
32 Port Hill Road,
Shrewsbury
SY3 8SA

This project was funded by the Environment Agency’s Research, Analysis and Evaluation 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