- 18th November 2020
- Posted by: Miranda Pont
- Category: Projects
Location: River West Allen, Northumberland
Metal mining in the UK peaked in the 18th and 19th centuries with more than 2000 active mines at one time. When mining activity ceased, many of these metal mines were abandoned and have left an environmental legacy: metal mines still pollute approximately 1500 km of rivers in England and contribute to about 50% of the cadmium, lead and zinc in surface waters.(1)
The Water and Abandoned Metal Mines Programme (WAMM) is a partnership between the Environment Agency, the Coal Authority and the Department for the Environment, Food and Rural Affairs (Defra). The Programme aims to support the Government’s 25 Year Environment Plan and River Basin Management Plans by implementing measures to address severe chronic river pollution and deliver a cleaner water environment for people and wildlife. WAMM Programme 2019
Monitoring by the Environment Agency in the north-east of England shows that historic mining wastes containing zinc, lead and cadmium makes a contribution towards pollution along 100km of the Rivers Nent, West Allen and South Tyne.
We initially carried out a geomorphological assessment of the River West Allen to identify potential sources of fine sediments, and to develop appropriate mitigation options for reducing the input of contaminated sediment into the river system. Read more about this project on our webpage.
The Carrshield Tailings Dam in Northumberland stores about 48,000m3 of metal contaminated mine wastes behind a drystone wall constructed in the 1800s. Up to three tonnes of zinc, cadmium and lead is eroded each year from these wastes, which contributes to pollution of 40km in the adjacent River West Allen and into the Tyne estuary. Ultimately these metals accumulate in the Tyne estuary sediments which has potential implications for dredging activities necessary to maintain deep water berths.(1)
Discover more about the Carrshield Tailings Dam and the WAAM programme in these videos produced by The Coal Authority:
During the 19th century Garrigill Burn was partially culverted and covered with mine waste. Over the intervening years the culvert has partly collapsed, allowing an estimated 3 tonnes of zinc, lead and cadmium to enter the watercourse and pollute around 10km of river. Around 60,000 tonnes of wastes remain on site, containing an estimated 1,400 tonnes of metals.(1)
Several intervention solutions were constructed between 2018 and 2019 to address the metals pollution and were funded by Defra and the North East Local Enterprise Partnership’s (NE LEP) Local Growth Fund. We worked on the scoping and design of two of these interventions: West Allen check weir and Garrigill Burn culvert.
West Allen check weir and fish passage is located immediately downstream of the Carrshield tailings dam. The objective of the check weir is to capture metal contaminated sediment already in the West Allen river, in conjunction with interventions at the Carrshield Tailings Dam to limit future inputs.
We designed a permanent structure across the River West Allen downstream of the Carrshield Tailings Dam to encourage deposition and capture of metal-rich sediments under typical flow conditions. The design consisted of large rocks spanning and damming the river creating the 1m high check weir.
Upstream of the weir, stone slabs were laid to the bed of the river to aid future dredging of contaminated sediments. Due to the gradient of the existing river, a number of pre-barrages and rock pools were also constructed so that fish passage can be maintained. We worked closely with the contractor and a local stone supplier to provide cut finished stone that would ensure both the long-term stability of the structure in the watercourse, whilst maintaining an aesthetically appropriate finish.
Garrigill Burn culvert. After considering 13 options for this Scheduled Monument site, we recommended installing a solid piped connection between the upper and lower culvert, re-profiling the spoil heap and installing a new revetment at the downstream end to mitigate future slippage and run-off. A detailed 3D survey of the existing culverts, the gap between them and their respective alignment was used to determine exact pipe lengths and angles. Once installed, approximately 6000m3 of spoil slopes were benched and re-profiled over the newly installed culvert.
Patches of a notable Calaminarian plant, Thrift, were temporarily translocated to an adjacent field during these works, and on completion they were placed back on the mine site under the supervision of a specialist ecologist – along with local wildflower species to help minimise erosion.
West Allen check weir is projected to capture approximately 1 tonne of zinc, cadmium and lead each year, and thereby limit the movement of particulate metal contamination down the River West Allen and into the Tyne estuary, whilst maintaining fish passage and movement.
Garrigill Burn new section of culvert, reprofiling of the spoil heap and installation of a new revetment at the downstream end will mitigate future slippages and run-off during high rainfall events. These combined interventions will significantly reduce the metal contaminants entering the watercourse each year.
Want to know more?
Email Tony Moran for more information about our work on these WAMM projects.
JBA Bentley have recently won a place on the next four-year Design and Build framework with The Coal Authority. It will be delivered from our collocated Leeds office and continues the successful relationship formed in 2013 to deliver the EA WEM Framework. JBA Bentley has been appointed to Lot 1 alongside Kier and will mini tender contracts for delivery over the next 4 years.
The work involves constructing new and refurbishing existing mining treatment schemes, as well as improving the environment where it has been adversely impacted by mining legacy. The Coal Authority anticipate circa £50m worth of construction works will be delivered by this framework and we hope that our prior experience puts us in pole position to deliver a substantial proportion of these projects.
JBA-Bentley is a joint venture between JN Bentley and Jeremy Benn Associates (JBA), established in 2013. The partnership brings together the specialist skills and expertise of the two firms: JN Bentley as a civil engineering contractor, and us (JBA Consulting) as a water and environmental consultant and designer.
(1)‘WAMM Programme 2019: Improving water quality in the metal polluted River Nent, West Allen and South Tyne’. Published 11 November 2019 in Water Projects online: https://waterprojectsonline.com/custom_case_study/wamm-water-abandoned-metal-mines-programme/