Despite holding a minority 39.9% interest in Marcopper Mining at the time of a 1996 tailings spill on Marinduque Island in the Philippines,
In March 1996, approximately 1.6 million cubic metres of tailing accidentally escaped through a failed drainage tunnel from an impoundment area and flowed into the Boac River system, which runs 26 km to the sea. Marcopper, the mine’s operator and a publicly traded Philippine corporation, immediately suspended operations and undertook engineering studies to stop the flow of tailings into the river system. The mine has never reopened.
Although Placer transferred its minority shareholding back to Marcopper a year later, the Vancouver-based major took full responsibility for the incident and voluntarily committed to rehabilitate the Boac River system to the state it was in before the incident occurred, and to fund compensation to affected communities.
For 30 years, Placer owned 39.9% of Marcopper Mining, which started mining the Mt. Tapian copper deposit on Marinduque Island in 1969. The mine used conventional crushing, grinding, flotation, filtering and thickening to produce a copper concentrate. The process used neither cyanide nor mercury.
The Philippine government, which had owned the majority interest in Marcopper, sold it to the private sector in 1994. Placer had a minority representation on Marcopper’s board of directors. In addition, Placer supplied two senior management staff and two to four consulting advisors to the Marcopper mine.
Mine tailings from the Mt. Tapian deposit were discharged into Calancan Bay between 1975 and 1988. It was estimated by the United Nations that no less that 84 million tonnes of mine tailings were dumped into the ocean.
During the development of the Tapian deposit, a 2,000-metre-long drainage tunnel was driven from the lower part of the open pit to the Boac River catchment so that accumulations of rain water could be drained from the pit. When Marcopper started developing the nearby San Antonio orebody, government authorities initially agreed that Marcopper could continue disposing the tailings into the bay. But by the time San Antonio entered production, in 1992, local opposition against the continued dumping of mine tailings into Calancan Bay had forced the government to ensure that the tailings be contained in the Tapian pit, pending development of an alternative long-term disposal system. A concrete plug, designed by Marcopper, was installed in the drainage tunnel to retain the tailings in the pit.
Flow ceases
The Tapian pit was used as a tailings dam for a period of four years before rock around the concrete plug fractured and gave way. Most of the tailings spill occurred in the first four days, after which the tunnel became blocked with solids. The flow of tailings gradually decreased on its own, and completely ceased by mid-June 1996.
Placer reported that the tailing discharge settled mainly in the upper reaches of the Makulapnit and Boac Rivers, covering about a dozen hectares of land used for agricultural purposes. The river was temporarily unusable for irrigation, for watering livestock and for washing clothes. In addition, vehicle access was cut off and fishing in the river was impaired.
Following the spill, the United Nations provided an independent assessment at the request of the Philippine government. A team of six specialists, who visited the site at the end of April 1996, found that the tailings had reached as far as the coastal area, with the deposition of between 1 and 2 metres of tailings occurring in the upper sections of the rivers, where the river valley is somewhat confined. Approximately 700 families were directly affected by the discharge. The initial effects of the spill were the loss of most river crossings and road connections, and the inundation of between 6 and 10 ha of cropland.
The UN team concluded that the physical process of sedimentation had severely degraded the aquatic life, productivity and beneficial use of the rivers for domestic and agricultural purposes. It was determined, however, that concentrations of trace metals in the mine tailings were not sufficiently high to represent an immediate toxicological threat and that there was no evidence of acute poisoning in the exposed population as a result of the tailings.
Stopping the flow
Placer immediately began installing a temporary plug to seal the tunnel. More than 230 holes were drilled from surface into the tunnel so that both concrete and bitumen could be pumped in to fill the tunnel void. By November 1996, the temporary plug was achieved at a cost of US$8.2 million.
In order to install a permanent plug, an access tunnel was started in September 1996 and driven parallel to the drainage tunnel, for a total length of 610 metres. It broke through into the drainage tunnel in March 1997, some 500 metres downstream of where the temporary plug was placed. A 20-metre-long permanent concrete plug, backed by a 40-metre-long earth filter, was designed and constructed by a team of international engineers for a total cost of US$6.1 million.
When the spill occurred, Placer and Marcopper responded by building new access roads to villages, developing new water supplies, relocating houses to higher ground (because of the added risk of flooding), assisting with food supplies, providing medical attention, and compensating people for lost income or crops damaged by the spill. The compensation payments have totalled more than US$1 million.
Several alternatives for cleaning up the rivers were considered, including the removal of tailings to dry land. Placer contends that this would have been a logistical nightmare and would have required long-term containment and monitoring to prevent oxidation of the sulphide minerals in the tailings, leading to acid drainage. Placer instead chose to rely on the natural action of the river to move the material downstream.
Rehabilitation plan
Placer initiated a staged rehabilitation project for the river system in 1996. A settling basin capable of holding 530,000 cubic metres was excavated in the delta of the river, followed by the construction of temporary embankments designed to inhibit the further spread of tailings out of the river channel on to adjacent agricultural areas during times of high river flow. The company has carried out two years of extensive studies on the impact of the tailing incident on the river, its environment and the socio-economic environment of the Boac River Valley.
Much of the river system was initially covered by tailings, but Placer reports that about 75% of the tailings have now been removed by natural or mechanical means. Studies indicate that the former river bed morphology and its associated marine life are re-establishing themselves in some parts of the river and shallow coastal areas.
However, Placer is concerned that the remaining 25% of tailings material in the river system is likely to cause contamination problems through the generation of acid run-off. The company contends that the best way to deal with this problem is to store the tailings under deep water in the sea through a managed submarine disposal program.
In July 1997, Placer applied to the Philippine Dept. of Environment and Natural Resources (DENR) for approval to complete the removal of some 500,000 cubic metres of mixed tailings and sediment from the river system by pumping the dredged material through a pipe to an area roughly 1,000 metres offshore from the mouth of the Boac River, in a water depth of 80 metres. The natural marine transport processes would further move the material offshore and into water depths of up to 700 metres.
The DENR announced in March 1998 that this dredging and submarine disposal program would require an environmental impact assessment (EIA) in order to determine its technical viability and social acceptability.
In March 1999, Placer completed an EIA study that compared the submarine tailings disposal method to 12 alternatives for the final rehabilitation of the Boac River system. In the meantime, Placer has suspended its river cleanup activity, while it awaits a decision from the DENR.
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