Lafayette still needs to build acid mine drainage system

Lafayette still needs to build acid mine drainage system

The Rapu Rapu mine has to ensure that an effective control against polluting acid mine drainage (AMD) is in place before government can lift its suspension to ensure that it will not bring adverse effects on human, aquatic life, and the environment.

Mines and Geosciences Bureau (MGB) Director Horacio C. Ramos told a press briefing that an AMD program is one of two conditions that Rapu Rapu operator Lafayette Philippines Inc. (LPI) has yet to comply with before government can issue it a permanent lifting order.

“Within 30 to 60 days, they will be hiring expatriates to review that (AMD program). As of now it’s working well, but we’re requiring other experts to come it and check it,” said Ramos.

The other condition is the certification from a third party expert on the integrity of the design of its tailings dam.

Carmelita Pacis, LPI pollution control officer, said that while sulfide (unlike oxide) which will be mined out in Rapu Rapu (to produce copper and zinc) may be reactive to air and water and thus threatens acid mine generation, LPI is using “encapsulation” to prevent acid mine generation.

A waste material of nine parts may be dug for every one part of ore in Rapu Rapu, and such waste may be potentially acid forming (PAF), normally whiteshaded compared to other materials. Encapsulation prevents a PAF waste dump from exposure to water and air since an impermeable clay core underneath and on top of this waste dump locks the dump inside.

LPI has built a sedimentation pond where PAF material is sunk down on the waterbed of the pond so that the PAF will not be exposed to water and cause AMD. The pond is treated using anoxic limestone drain which allows for neutralization of the acidic liquid to a normal ph 7.

The sedimentation pond leads to a polishing pond (for further AMD corrective measures) and to a wetland where any dissolved metal is filtered with the presence of a bioremediation plant specie “typha augusto folia” which absorbs dissolved metal (copper, zinc, iron, trace metals).

An untreated acid mine can seriously degrade habitat and water quality, killing fishes and can be toxic to vegetation when recharging shallow groundwater. It may have adverse effects on agricultural (irrigation and livestock) and industrial resources (corrosion of manmade structures like pump, dams, and bridges).

It can lead to reduction of bio-diversity (insects, macroinvertebrates) while increased carbon dioxide tension and chemical reactions contribute to toxicity and water turbidity.

It makes water unfit for use in locomotive and power plant boilers, and definitely unfit for drinking and household use and cause reddish brown spots on fabrics in laundries and textile factories.

Manuel Agcaoili, LPI affiliate Rapu Rapu Minerals Processing general manager, said that for its events pond (expanded from 600 to 800 cubic meter capacity) which contains spillage from its processing plant, trigger alarms have been installed upon reaching 25 to 30 percent water level.

This automatically pumps out pond content at 25 percent level using four pumps (two submersible and two diesel pumps, rather than just one).

The tailings dam has a 14 meter freeboard and has a spillway allowing for disposal excessive rainfall water which will go to the sedimentation pond.

At mine closure, LPI will remove any PAF materials along open pit walls, provide diversionary drainage to keep surface runoff away from the pit slope, shotcrete the exposed walls to 100 millimeter thickness to preven rainfall infiltration, provide weep hopes to relieve seepage pressure, and pump pit water to tailings storage facilities to be neutralized by alkaline pond water.

To avoid erosion in the mine site, LPI has used topsoil-covered slope that encouraged growth of shrubs supplemented with stoplogs and vetiver, sediment traps (gabions), silt fences, cocomatting, shotcreting, sheeting, slope engineering and lined drainage.

The US Department of Environmental Protection earlier observed adverse effect of AMD on the environment.

“Severely degraded conditions are characterized by dominance of certain taxonomic representatives of pollution-tolerant organisms, such as earthworms (Tubificidae), midge larvae (Chironomidae), alderfly larvae (Sialis), fishfly larvae (Nigronia), cranefly larvae (Tipula), caddisfly larvae (Ptilostomis), and non-benthic insects,” it said.

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