For the last nine years, Severn Trent Services has managed a contract for mine water treatment across the Coal Authority estate, including 73 mine water treatment schemes in England, Scotland and Wales. These schemes take the form of three types: passive, pumped-passive and active.
At most sites, mine water is pumped to a treatment facility which employs oxygenation, filtration and sedimentation to raise the quality of the water in compliance with discharge consents.
“Mine water from legacy coal mines is treated at many of these sites utilising settlement lagoons and reed beds,” explains Oren Environmental’s data and reporting manager Paul Robinson. “The effective management of these resources is heavily dependent on reliable data, including water level measurements, and we have been using OTT instruments to support this since 2016.
“In addition to the older ecoLog 500s and the newer ecoLog 1000s, we also utilise five ecoLog 800s to collect and monitor conductivity measurements. Conductivity data can be used to assess the quality of water by identifying minerals that are present in the water.”
Where the ecoLogs are deployed in surface water weirs, the level measurements are translated into flow, which further informs the management of the treatment process.
Force Crag Mine in the Lake District is a good example of an extremely remote former mine with challenging environmental conditions. Cellular coverage is very limited on-site, so OTT built a local network which transmits water level data via radio to two loggers located in a higher position. Data from these loggers are then transmitted regularly to Oren’s FTP Server.
Mining commenced at Force Crag in 1835, and it became the last working metal mine (zinc, lead and barytes) in the Lake District, prior to its final closure in 1991. Metal pollution (zinc, cadmium and lead) from the mine polluted the Coledale Beck, a tributary of the River Derwent and Bassenthwaite Lake Special Area of Conservation.
The Coal Authority, working in partnership with the Environment Agency, Newcastle University and the National Trust, devised an innovative passive mine water treatment scheme to reduce the levels of metal pollution entering the river. The scheme, which officially opened in 2015, diverts water from the Level 1 adit and routes it through a buried transfer pipe to two vertical flow ponds for treatment.
The ponds were built using the existing bunding of the former mining tailings lagoon, lined with a geomembrane, and filled with a compost treatment mix. Water is fed into the ponds, where it flows down through the compost and passes into a wetland, planted with soft rushes.
“Each site presents its own challenges,” Robinson concludes. “Many are in remote areas and in different environments, so we do our best to ensure we maximise the equipment to hand such as the OTT ecoLogs.” Looking forward, he says: “Remote telemetry is particularly advantageous, because it provides access to more frequent data than manual dips due to the schedule of visits that we work to.”