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Water-related environmental studies for a coal mine project in Chilean Patagonia

SRK Chile has recently participated in defining the water base line required by the EIA to obtain an environmental permit for the Riesco Island coal project, and in other water-related works. Riesco Island is located 60 kilometers northwest of Punta Arenas in Region XII of Magallanes. The project involves a pit with an in-pit waste dump, external waste dumps, a stockpile at the port and supporting infrastructure. West of this project, the same company has started feasibility studies on another coal deposit. Because the local community has been very sensitive to the potential environmental impacts on Riesco Island, the studies have been carried out to a high technical standard.

The area has continuous rainfall, with average monthly values of 30mm and mean annual precipitation of 447mm/year. Studying the storm water management, conservation of the river water quality and protection of the peat and the watershed zones posed a great challenge.

Land forms in the project area are heavily influenced by the erosive action of old glaciers, generating deposits of moraine-type glaciofluvial materials, glaciolacustrine, drumlins, etc. The underlying bedrock comprises a folded sequence of Tertiary marine and sedimentary deposits that include sandstone intermixed with mudstones and siltstones (Loreto Formation). The several coal layers of economic interest are found in this formation.

The hydrogeological setting is dominated by two areas. The upper glaciofluvial layer is mostly an aquitard composed of heterogeneous material of predominantly low permeability. The lower layer is the Loreto Formation where the groundwater flows through zones associated with open joint systems or layers of high porosity within the sedimentary rocks.

SRK used its experience in fieldwork, including geophysical prospecting, piezometers drilling and installation, Lugeon testing and water quality sampling to understand hydrogeological systems and assess environmental impacts from future mining activities. Chemical and geophysical studies provided key information to interpret the hydrogeologic dynamics, as did the impact assessment study on the surrounding small lagoons and peat lakes. High tritium content, indicating younger waters in rock formation than in the glaciofluvial cover, helped to explain the recharge mechanism and provided valuable information for use in the future modelling of the pit dewatering.

Beatriz Labarca:

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