The hydrological and environmental rehabilitation of the abandoned mining areas of Alentejo was carried out in 4 phases and covered 3 areas of this mining complex.
Phase 1A took place between 2006 and 2007 and consisted of the following main activities:
- Construction of the floodway outlet channel of the Industrial Waters Dam (IWD);
- Construction of perimeter clean water drainage ditches to the north (L1) and east (L2).
Phase 1B took place between 2007 and 2008 and consisted of the following main activities:
- Removal of pyrite deposits and grey waste and packing into the former pit;
- Transport to a landfill site of industrial waste and scrap scattered across the area;
- Waterproofing of the base of the entire disposal area that will receive the materials during the different phases, and capping of the top of the deposits resulting from the operations of phase 1B;
- Construction of a subsurface drainage system in the disposal area that will receive the products of the excavations in the following phases;
- Construction of prop walls and LX1, LX2 and Lx3 leachate effluent collection trenches around the perimeter of the existing grey waste dump;
- Construction of LX4 leached water return trench, downstream of the dam located close to the cementation cells;
- Recovery of mining infrastructure with heritage or archaeological value, such as the cementation cells, the levee located upstream, and Roman slag.
In 2008, Stabilization of the Transtagana Chimney was performed, thus preventing the complete destruction of this symbol of mining activity.
Phase 2 took place between 2010 and 2011 and consisted of the following main activities:
- Construction of a pilot downstream of the IWD;
- Construction of evaporation-concentration basins south of the Algares pit and an aeration channel joining the concentration-evaporation basins with the pilot wetland;
- Construction of clean water and domestic water supply pipes to the pilot wetland;
- Completion of the leachate collection trench, started during the previous phase, in order to channel the abstracted flows to the dam located upstream of the cementation cells;
- Construction of a leachate collection trench for the purpose of collecting the leachate flow through the dam foundation and facilitating drainage to the pilot wetland;
- Protection of galleries and shafts identified as being of archaeological/mining and environmental interest;
- Lining and improvement of protection of the basin created in the S. João mining area.
The final stage, Phase 3, took place between 2014 and 2015 and consisted of the following main activities:
- Earthmoving, cleaning and removal of surface residues;
- Removal of deposits scattered around the Algares mining area, including complete drainage of the deposits located upstream of the cementation cells dam, in the bunkers and the left bank of the BAF;
- Cleaning and re-profiling of the slopes surrounding the winch;
- Packing into the Algares pit of materials from the full drainage of the BAF reservoir;
- Drainage of the river bed downstream of the Água Forte dam;
- Packing of material from the S4 grey waste dump;
- Partial waterproofing, through a multi-layer system and replanting of the central spoil heap;
- Construction of an internal surface drainage system;
- Biophysical and landscape rehabilitation;
- Creating of visitation routes;
- Drainage of the gallery and earthmoving and packing;
- Execution of gallery reinforcements;
- Slope stabilization;
- Execution of drainage system and drainage of the gallery bottom;
- Rehabilitation of metal structures, namely the Vipasca Winch;
- Execution of other works, namely the creation of stairs and an access lift to the surface and civil works.
The investment made in the period 2005-2008 was co-financed by the Alentejo Regional Operational Programme under the Third Community Support Framework