Although the Department of Environment and Natural Resources (DENR) insists that the issue of flooding is still being contested, the more urgent concern are the sacks of mine tailings piled on the banks of the Boac River which, if left unattended, might seep into the waterway during heavy rains.
Last Monday, experts of the US Geological Survey (USGS), accompanied by local officials, surveyed the mine sites and the rivers affected by the 1996 spill, and saw how the sacks of mine tailings are tattered, thus putting local communities at risk again.
The USGS is a "third party" which will study the effects of the tailings spill and come up with independent recommendations for the final rehabilitation of the Boac River and other affected areas.
The Marinduque provincial government was the one which endorsed tapping the services of the USGS.
Mike Cabalda, chief of the Mining Environment and Safety Division of the DENR’s Mines and Geosciences Bureau (MGB), admitted that if the mine tailings seep back into the Boac River, the riverbed might rise, possibly causing flooding during the rainy season.
Boac residents themselves fear that the unattended mine tailings might endanger their health and livelihood.
"The tailings in the river appear to be no longer reactive. But the fresh tailings, when exposed, may react and produce acid drainage," Cabalda said.
Despite this, the DENR and Marcopper have yet to agree on what to do on this urgent concern.
Cabalda said Marcopper has suggested hauling the mine tailings recovered from the riverbed of the Boac River back to the Tapian pit.
"But the DENR has been rejecting its proposal due to unresolved technical matters," he said.
Marcopper’s program to remove mine tailings from the Boac and Makalupnit rivers is still being revised up to now to meet the MGB’s technical considerations.
Marcopper’s proposal was first submitted to the MGB in December 2001, but the company, according to the DENR, has yet to satisfactorily comply with the technical requirements.
Cabalda said the proposal should address concerns about the Tapian pit, including the renovation of the 310-Tunnel, the setting up of a more permanent drainage structure such as a spillway, and the installation of a water treatment facility.
But Marcopper, he said, failed to incorporate these in its proposal since the company, for instance, does not recognize the need to construct a spillway.
Although it might be better to replace the steel pipes in the 310-Tunnel with plastic ones, Cabalda said Marcopper should make sure they have the correct dimensions.
"For one, the plug at the 310-Tunnel is not in A-1 condition," he said. "And if they would repair the 310, they should ensure that what they put in there should be of the right dimensions in consideration of the volume of water that could possibly come out of it."
The "bagging" of the mine tailings that spilled into the Boac River was part of Marcopper’s cleanup. It began in the summer of 2000.
Cabalda estimates the volume of recovered mine tailings stacked along the banks of the Boac River to be about 67,000 cubic meters.
A total of 800,000 cubic meters of mixed tailings spilled out of the Tapian pit on March 24, 1996 when the rock around the plug of the drainage tunnel broke.
According to Marcopper engineer Ralph Ante, an earthquake that occurred a week before the incident could have caused the tunnel’s plug to break.
The tunnel had been used to drain water from the Tapian pit since Marcopper started mining in Marinduque in 1969.
When it stopped mining in the area in 1991, the pit’s inlet portal was sealed and a three-meter thick concrete plug was built in a section from the outlet portal.
The tunnel’s first plug was completed on Oct. 18, 1996, and the final plug, later certified to last a thousand years, in August the following year.
Immediately after the disaster, the DENR ordered Marcopper, co-owned by Canadian firm Placer Dome Inc., to suspend its mining operations. It subsequently issued a closure order and cancelled the company’s environment compliance certificate.