Devon South management catchment: baseline length of rivers and estuaries polluted by abandoned metal mines
Published 12 March 2025
Applies to England
© Crown copyright 2025
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This is one of 20 reports, one for each polluted management catchment, on the water quality monitoring undertaken by the Environment Agency to determine the baseline length of rivers and estuaries considered polluted by any of the Environment Act target substances from abandoned metal mines in 2022.
A length of river or estuary is considered polluted where the concentration of one or more of the 6 target substances (arsenic, cadmium, copper, lead, nickel and zinc) exceeds the relevant Environmental Quality Standard (EQS). EQS concentrations are based on ecotoxicology data and set by government at a level that should prevent harmful environmental impacts. When the concentration of a substance in a water sample is higher than the EQS, adverse impacts on the aquatic ecosystem can be expected. The relevant EQS for each target substance are set out in The Water Framework Directive (Standards and Classification) Directions (England and Wales) 2015.
The purpose of calculating this baseline was to enable measurement of the statutory abandoned metal mines target set out in Part 4 of the Environmental Targets (Water) (England) Regulations 2023. This regulation requires that the combined length of English rivers and estuaries polluted by the target substances from abandoned metal mines is, by 31 December 2038, at least 50% lower than the baseline.
In the Devon South management catchment, the baseline length of polluted rivers for the abandoned metal mines water target is 21km. We will aim to identify the key sources of metal pollution in this management catchment by carrying out detailed monitoring investigations.
You can find further background and context on the Environment Act abandoned metal mines water target in the national baseline report which should be read together with this report.
The Devon South management catchment
The Devon South management catchment covers an area of approximately 1,514km2 and includes areas of Dartmoor National Park and the South Devon National Landscape. Please go to Devon South Management Catchment on the Catchment Data Explorer for an interactive map showing the 4 operational catchments that make up the management catchment. The boundary of the Devon South management catchment and all 4 operational catchments are highlighted in Figure 1.
Metal mining in the Devon South management catchment
Metal mining in South Devon dates to pre-Roman times. During medieval times, tin mining was of importance to the local economy. Lead and barium mines opened during the 19th century, including Wheal Exmouth and Bridford Barytes mine, and, during this time, mining was at its peak, with some silver and zinc also being extracted. However, many mines closed in South Devon at the end of the 19th century, and mining declined. Bridford mine continued to produce barium until the mid-1950s when it also stopped operating.
Figure 1 shows the locations of mineral veins, known mine water discharges, closed mine waste facilities known to be causing serious environmental harm, and areas of abandoned mine wastes (mining spoil) in the Devon South management catchment.
This information has been gathered from various sources including:
- BGS Geological mapping - GeoIndex - British Geological Survey
- Prioritisation of abandoned non-coal mine impacts on the environment
- Inventory of closed mining waste facilities causing serious environmental impacts
- Defra-funded ‘Source apportionment of pollution from non-coal mines’ research project by Newcastle University and Hull University (unpublished)
- Environment Agency water quality data archive
As we can see in Figure 1, historical mining activities in the Devon South management catchment is almost entirely limited to the Teign operational catchment, with very small pockets of mining elsewhere.
Figure 1. Map showing the abandoned metal mines, mineral veins and baseline river monitoring sites in the Devon South management catchment
© Environment Agency
The tables below list the catchments (surface water bodies) that are polluted by target substances from abandoned metal mines in the Devon South management catchment. These tables highlight where there are known point sources (mine adits or mine drainage levels) and diffuse sources (mine wastes or spoil heaps) within the catchment. The Environment Agency is continuing to investigate point and diffuse sources within the Devon South management catchment by undertaking a series of catchment characterisation studies. These studies will help us identify which sources of metals need to be tackled to achieve the long-term statutory target.
Teign operational catchment: sources of metal pollution
Table 1 summarises which type of pollution sources from abandoned metal mines have been identified within the catchments (surface water bodies) in the Teign operational catchment.
Table 1. Summary of metal pollution sources in the Teign operational catchment
| Catchment (Surface water body) | Point sources of pollution | Diffuse sources of pollution |
|---|---|---|
| Teign (Lower) | Yes | Yes |
| Beadon Brook | Yes | Yes |
Baseline monitoring
The objective of the baseline monitoring was to establish the upstream and downstream extent of surface waters polluted by the target substances from abandoned metal mines. We selected the baseline monitoring sites by first completing a desk study to review previous water quality data, maps and reports. We then made initial site visits to collect samples and to assess the suitability of the site for continued sampling. Generally, at least twelve water quality samples were then collected from each monitoring site.
Within the Devon South management catchment, water quality monitoring was undertaken in one of the 4 operational catchments (Teign). This catchment is highlighted in Figure 1. We did not carry out monitoring in operational catchments where there is either no historical metal mining within the catchment or a combination of current and historical monitoring data shows that waterbodies within these catchments are not polluted by abandoned metal mines.
In total, 8 monitoring sites were selected across the Devon South management catchment to determine the baseline length of rivers polluted by target substances from abandoned metal mines. The locations of these monitoring sites are shown in Figure 1.
Water quality data collected between 1 January 2022 and 31 March 2024 have been used to determine and validate the baseline length of rivers and estuaries considered polluted in 2022. The length of rivers polluted by abandoned metal mines fluctuates in response to natural variation in rainfall and river flows. However, this length will not materially change unless remediation measures like mine water treatment schemes or diffuse interventions are installed to decrease inputs of metals. Therefore, data collected after 31 December 2022 are considered to be representative of rivers, provided no new remediation measures had been constructed since 2022. No new remediation measures have been constructed in the Devon South management catchment since 2022.
Water quality monitoring results
In the Devon South management catchment, the target substances measured were cadmium, copper, lead, nickel and zinc. We did not undertake testing for arsenic in this management catchment since historical monitoring data and knowledge of the local geology across the catchment indicated that no rivers are polluted by arsenic in this management catchment.
The baseline water quality data for all monitoring sites are available on the Environment Agency’s public water quality archive.
For a river water quality sample to be considered polluted, concentrations of one or more of the target substances must exceed the relevant EQS set by government when assessed as an “annual average”. The EQS are set out in The Water Framework Directive (Standards and Classification) Directions (England and Wales) 2015.
The EQS are derived using ecotoxicology data and set at a level that should prevent harmful environmental impacts. When the concentration of a substance in a water sample is higher than the EQS, adverse impacts on the aquatic ecosystem can occur, and the sample is considered to be polluted.
To understand the severity of pollution, we calculated a numeric “pollution level” by dividing the measured concentration of the target substances by the EQS. If the pollution level is greater than 1, the monitoring site is considered polluted by that target substance. Therefore, the higher the numeric pollution level, the greater the likelihood of harm to aquatic life.
Baseline polluted river length: Devon South management catchment
Our detailed monitoring across a range of flow conditions between January 2022 and March 2024 shows that in the Devon South management catchment, the baseline length of polluted rivers for the abandoned metal mines target is 21km.
Figure 2 shows the rivers in the Devon South management catchment that are polluted by target substances from abandoned metal mines.
Figure 2. The baseline length of rivers polluted by target substances from abandoned metal mines in the Devon South management catchment is 21km
© Environment Agency
Table 2 shows the river length (in km) that are polluted by each of the target substances within the Devon South management catchment. In general, the most polluted rivers are impacted by more than one target substance.
Table 2. River length (in km) polluted by each of the target substances within the Devon South management catchment.
| Target substance | Polluted river length (km) | Pollution level: less than 3 times | Pollution level: 3 to 5 times | Pollution level: greater than 5 times |
|---|---|---|---|---|
| Cadmium (Cd) | 21 | 17 | 0 | 4 |
| Lead (Pb) | 2 | 0 | 0 | 2 |
| Nickel (Ni) | 1 | 0 | 1 | 0 |
| Zinc (Zn) | 14 | 10 | 0 | 4 |
| Copper (Cu) | 1 | 0 | 0 | 1 |
Rivers polluted by abandoned metal mines: Devon South management catchment
Teign operational catchment: baseline polluted rivers
The lower River Teign is polluted by both zinc and cadmium. Three tributaries are heavily polluted by zinc, cadmium and lead: Rookery Brook (which is polluted by the Bridford mine), Beadon Brook, and the stream running through Wheal Exmouth mine.
Figure 3. The baseline length of rivers polluted by target substances from abandoned metal mines in the Devon South operational catchment is 21km
© Environment Agency
It should be noted that due to close proximity of some of the sampling points to each other, some of the sampling point markers on this map (blue squares) may overlap.