Groundwater Management in Mining: The Drainage and Reinjection System in Cobre Las Cruces, Spain

Juan C. Baquero1, Mª José de los Reyes1, Emilio Custodio2,3, Laura Scheiber2,3,4, and Enric Vázquez-Suñé3,4

1. Water Technology Department of Cobre Las Cruces, Gerena (Sevilla) 41860, Spain

2. Department of Civil and Environmental Engineering, Technical University of Catalonia (UPC), Barcelona 08034, Spain

3. Hydrogeology Group (UPC-CSIC), Barcelona 08034, Spain

4. Institute of Environmental Assessment and Water Research (CSIC), Barcelona 08034, Spain

Abstract: Cobre Las Cruces (CLC) is an open-pit copper mine located in SW Spain. The ore body is embedded in a low permeability Paleozoic basement covered by a Cenozoic sandstone formation known as the Niebla-Posadas aquifer. At the mine site, this aquifer is confined under a 120-150 m thickness marl formation. Under natural conditions, groundwater in the confined area at the CLC site shows a north to south natural quality degradation due to high As, NH4 and B contents. This groundwater is neither appropriate for human consumption nor for irrigation in the confined area and is almost no renewable based on 3H, 14C and 36Cl results. The mine pit intersects and discharges the Niebla-Posadas aquifer. In order to allow the mine drainage and preserve the groundwater resources in the surroundings, CLC has set up a complex Drainage and Re-injection System (DRS) consisting in a ring of 32 peripheral drainage wells, which is connected to a second ring of 28 re-injection wells. This system manages about 3.2 hm3/year. Prior to be injected, the drained water must be treated by reverse osmosis to remove metals and undesirable dissolved substances, with 91% water recovery.

Key words: aquifer management, mine drainage, re-injection, recharge water treatment, reverse osmosis