Europe's largest waste stream sits around abandoned sulphide pits, bauxite tailings and legacy heaps that have not been surveyed since the operator left. A new EU regulation says every Member State now has to catalogue them. The decision between leaving a site to recover, rehabilitating it, and reprocessing it for critical raw materials is being taken, in most places, without a current picture of the ground.
Mining and quarrying produced 22.7% of the roughly 2.2 billion tonnes of waste generated in the EU in 2022, making extractive waste the single largest waste stream in the Union. Most of it sits in heaps and tailings ponds around sites that stopped operating decades ago, and in many cases a century ago. The pilot the Lab is running covers one European mining province, the Iberian Pyrite Belt in southern Portugal and Spain: in the Spanish part alone, nearly a hundred sulphide mines have left around 4,800 ha of affected land, about 60% of it waste dumps, and iron and cadmium exceeded regulatory limits in 98% of effluents sampled in the rainy season (Pérez Ostalé, 2014).
Three things have shifted in the last two years that make these sites a current problem rather than a historical one.
Article 27 of the Critical Raw Materials Act (Regulation (EU) 2024/1252) now requires every Member State to build a database of closed and abandoned extractive waste facilities, holding location, area and waste volume, operator information and the quantities and concentrations of raw materials relevant to recovery. Finland is assigning the task to its geological survey from 1 November 2026. Portugal's National Exploration Programme 2025 to 2030 names the valorisation of legacy mining waste under Article 27 as a goal. The MIN4EU mining-waste database, maintained through the European Geological Data Infrastructure, already lists such sites in more than twenty European countries.
The regulation says what to catalogue; it does not say how to find out what the sites currently look like. For most facilities on these lists, the last field survey was the one commissioned at closure, often more than thirty years ago. A geological survey being handed a national mandate from a standing start has to decide, with limited field capacity, which of hundreds of facilities deserve a site visit first.
Every closed extractive waste facility now faces a choice between three pathways, and the choice is a social one before it is a technical one.
The three pathways are not just the responsibility of the geological survey or the ministry. They land on specific villages. In the Iberian Pyrite Belt, Minas de São Domingos and Lousal are heritage landscapes that have become tourism assets; Minas de Riotinto and Nerva sit on the Río Tinto itself, a global reference for naturally acid water, with an operating mine (Atalaya Mining) inside a historic district; Aznalcóllar, site of the 1998 tailings dam failure, received regional approval to reopen in 2025 with production planned from 2028, and the planned discharge to the Guadalquivir estuary is actively contested.
Residents of each of these villages live with the site next door. They are rarely consulted systematically about which pathway should win.
The last two years have changed what an independent party can read about a legacy site without buying a satellite tasking. Copernicus Sentinel-2 Level-2A covers Europe at 10 m resolution every five days, free and open; the European Ground Motion Service publishes subsidence and uplift from Sentinel-1 interferometry for every EU and EEA site; the Copernicus DEM GLO-30 is good enough to estimate heap volume as a proxy for the Article 27 field; ESA WorldCover 2021 classifies the land each hectare of a footprint replaced; the JRC Global Surface Water record shows whether a pit lake pre-dates the latest decade; the GHSL population grid says who lives within one and five kilometres. Hyperspectral imagery (PRISMA, EnMAP, and the planned CHIME mission in 2028) can calibrate the Sentinel-2 iron and clay signals against reference material: Pereira et al. (2025) report pixel-wise R² of 0.81 to 0.85 between PRISMA and Sentinel-2 iron ratios in the Cartagena-La Unión mining district.
The evidence base is a public good. Keeping it on a geological survey's internal GIS is a reasonable first move for an authority that owns a national mandate, but it does not help a municipality beside a heap, a resident with a question about dust, or a reprocessor shortlisting sites in a region before committing field capacity. A single, open method that each of these actors can see does make that help possible.
Four features are necessary for a tool that supports the three-pathway decision at pilot scale and transfers across the European mining-waste register. Each is observable from existing open data.
A baseline that does not drift. A tool whose indicators change silently from one quarter to the next is worse than no tool. Every reading needs a published method version, imagery date and threshold value, so a residents' group reading last year's heap area can tell whether the number has moved because the heap moved, or because the method moved. The pilot runs one method, documented in full, with every threshold in a configuration file rather than in the UI code.
A ten-year context, not a single-moment snapshot. The three pathways diverge over decades. Any screening tool that shows only the latest snapshot is deciding for the user that recent conditions are enough, which is not true at legacy sites. Ten-year Sentinel-2 composites from 2017 onwards are now routine. A natural-recovery clock derived from the vegetation trend over valid years converts the time series into a sentence a non-technical reader can actually use.
A classifier whose decisions can be read. The pixel classifier that decides which hectare is bare, which is vegetated, which carries an iron oxide signal, and which shows the colour of acid drainage, has to be auditable. A geological survey that submits a report to a competent authority has to be able to defend each number. Transparent decision trees calibrated against hyperspectral and field reference data satisfy this; black-box neural classifiers do not.
The people and the landscape alongside the pixels. The population within one and five kilometres, the Natura 2000 overlap, the distance to the nearest watercourse and the land cover around the site are the context in which any pathway choice lands. Reporting the satellite indicators without those is a map, not a decision aid.
A tool with these four features is reachable, now, from a laptop in a browser. The Lab's Strata tool is one implementation of that argument, built from open Copernicus data and running the method above as an open method with twenty-six unit tests. It is not the only possible one. The point of this piece is that the data has caught up with the regulation, and no Member State has to build an Article 27 database from a standing start without a current picture of the ground.
Satellite indicators describe surface change. They do not describe what the dust feels like in late summer, or what reopening a mine means for a town that has worked out, over thirty years, how to live without one. The communities beside legacy mine waste have views the regulation does not, by itself, create a channel for.
Three Iberian communities (Mina de São Domingos, Minas de Riotinto + Nerva, Aznalcóllar) are the subject of the Lab's social-needs research through 2027, in parallel with the satellite work. Residents will be interviewed about what they already know about the site next door, what they want to happen, what they distrust about outside evidence, and how they would prefer the three pathways to be presented. The tool will carry anonymised themes, pathway preferences and quotations beside the satellite indicators on the same site card, which is the condition on which a residents' group can use the same evidence base as the geological survey and the reprocessing company.
That is the point of catalogue work under Article 27 at the European scale: not the catalogue itself, but the shared language the catalogue makes possible.
If this reads close to a decision you are weighing, we would like to hear about it. A short note is enough to start.
The Lab is an independent research team, not an advocacy organisation. We do not campaign, endorse products, or accept commissions where a finding is expected in advance. Where a partner's own theory of change is what needs testing, that is a legitimate engagement, and the Lab tests it honestly.