Las Tortolas Tailings Storage Facility

Since 2010, RGC has been provided technical services to Anglo American Sur S.A. (“AAS” or “Anglo”), a subsidiary of Anglo American Plc, which owns and operates the Las Tortolas Mill and Tailings Facility approximately 35 km northwest of Santiago. The site has been operated since July 1992 to process the copper and molybdenum ore produced by the Los Bronces Mine and to store the tailings produced from the milling process. One of RGC’s key projects for Anglo is the development a plan to mitigate groundwater impacts in the Ex-Bosque, a Land Application Area (LAA) developed southeast of the mill and planted with eucalyptus trees.

The Ex-Bosque LAA was irrigated from 1994 to 2006 using water from the reclaim tailings pond to manage the size of the reclaim pond at that time. While some of this water was used by eucalyptuses for evapotranspiration, a significant portion percolated through the root zone and reached the water-table, resulting in the development of a seepage plume. This practice was stopped in late 2006 following the detection of elevated sulphate concentrations in groundwater in monitoring wells immediately downstream of Anglo’s property.

In 2012, RGC developed a numerical groundwater model to complete a preliminary assessment of potential mitigation options and identify areas requiring additional site characterization. The 2012 model suggested that the sulphate plume in the eastern Ex-Bosque sector could be controlled by pumping the three existing BN wells while an additional fence of extraction wells would be required to control the sulphate plume in the western Ex-Bosque sector. Subsequently, routine operation of the BN wells commenced in 2012 and additional drilling was undertaken in 2013 and 2014 to improve the delineation of the sulphate plume and install additional pumping wells as part of the Phase II drilling program.

In 2015, RGC completed a full update of the 2012 Ex-Bosque groundwater model to evaluate alternative mitigation scenarios and identify a recommended option that, according to modelling predictions, is expected to meet the stated mitigation objectives. RGC subsequently provided technical support for a comprehensive drilling program from January 2018 to November 2019, which involved the installation of 20 monitoring wells and 11 pumping wells. This drilling program provided significant improvements to our understanding of the Ex-Bosque site conditions through detailed logging of soil and bedrock, hydraulic testing, and water quality sampling. In 2021, RGC updated and re-calibrated the groundwater model for the Ex-Bosque to evaluate alternative mitigation scenarios and identify a recommended option that, according to modelling predictions, is expected to meet the stated mitigation objectives.

• Data review
• Multiple hydrogeological field programs (including drilling, hydraulic testing, and groundwater monitoring) to characterize the hydrogeology of the Ex-Bosque aquifer and that of other sectors within the mill site
• Numerical modelling of groundwater flow & solute transport

Anglo American Cobre

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