ALBERT

Description: Asturias, NW Spain, has a long coal and metal mining tradition including mining for mercury, which was intermittently exploited from Roman times up to 1974. In the valley of the Morgao Stream, there is a spoil heap from the Los Rueldos mercury mine immediately uphill from another one from the Morgao coal washery, both situated less than 3 km away from the town of Mieres (30,000 inhabitants). At the Los Rueldos site, arsenic is abundant in the form of As-rich pyrite. Total arsenic concentrations in representative samples from the spoil heap range from 4746 to 62 196 mg kg-1. Readily leachable Pb and Zn are respectively present at average concentrations of 3680 and 45 mg kg-1. Leachate from this spoil heap drains on to the El Batan coal spoil heap, together with acid drainage from old underground workings of the Los Rueldos Mine, which has very low pH (2.5), with up to 2900 mg 1-1 SO4, and between 5.3 and 8.3 mg 1-1 As. The total flow of polluted water from the Los Rueldos site that flows into the Morgao Stream is estimated to average 3200 m3 year-1 (corresponding to only 1% of the total flow from the Morgao drainage basin). Analysis of the Morgao Stream downstream of both spoil heaps clearly shows the results of the dilution effects, with the As content being lowered by more than 95%.