Paper No. 9-3
Presentation Time: 2:10 PM
CASE STUDIES OF SAFETY AUDITS OF MINING DAMS WITH NON-COOPERATING DAM OWNERS
On January 25, 2019, the failure of a tailings dam at the Córrego do Feijão mine near Brumadinho, Brazil, resulted in 270 deaths, although the consultants hired by the mining company had certified the stability of the dam only four months previously. This and related events have led some communities to believe that mining companies, their consultants, and regulatory agencies cannot be relied upon to assure the safety of downstream residents. As a result, some communities have requested their own consultants to evaluate the safety of mining dams. Typically, dam owners are under no obligation to provide records to community consultants or to allow them on the property. The objective of this abstract is to describe three case studies in which the author has been a participant in community-requested mining dam safety audits with non-cooperating dam owners. The safety audits reviewed tailings dams at the Mirador mine above Tundayme, Zamora Chinchipe, Ecuador (requested by Comunidad Amazónica de Acción Social Cordillera del Cóndor Mirador), the Morro do Ouro mine above Santa Rita, Minas Gerais, Brazil (requested by Associação de Pequenos Produtores de Santa Rita), and the Riotinto mine above Sotiel Coronada, Andalusia, Spain (requested by Ecologistas en Acción). From a highway only a few meters from the tailings dams at the Mirador mine, it was clear that the Quimi dam was being constructed using the upstream method with an outer embankment slope of 1V:1H (regarded as the minimum slope for prevention of failure by internal erosion), in violation of the permits that required centerline construction and an outer embankment slope of 1V:2H. From a dirt road close to the tailings dams at the Morro do Ouro mine, it could be seen that the tailings beach was almost non-existent at the Eustáquio dam. Moreover, erosion channels on the outer embankment of the Santo Antônio dam indicated that occasional overtopping had occurred. At the Riotinto mine, the dam owner allowed the community consultant onto the property, but not access to records. From the dam crest, it was clear that the water table directly behind the Aguzadera dam was only 2.9 meters below the surface and that uncontrolled seepage was occurring through the downstream embankment at the same elevation, indicating that both the dam and tailings were nearly completely saturated with water.