On 16 January 2020, an engineering team at Siguiri mine was preparing to connect the new Tinkisso river water supply pipeline to the existing raw water pipeline at the Return Water Dam area, 1.7km from the Siguiri processing plant.

The team needed to drain the existing pipeline to complete the tie-in. Unfortunately, the tailings Return Water pipeline running alongside the existing raw water pipeline, was opened and drained for three hours.

The drained water, assumed to be raw river water, was directed to the nearby Diamon stream. The team was alerted to their mistake and immediate remedial action was taken.

Power outages during mid March at Siguiri mine’s Wartsila power plant resulted in the overflow of the mills and various process plant tanks.

This occurred while construction to upgrade the plant’s pollution dam was underway and temporary spillage control infrastructure was being used.

An estimated 25m³ of the water being held in the temporary containment system, seeped through the slightly porous laterite wall, pooling outside the fenced area and was discovered during a security patrol.

Samples recorded contaminants higher than the IFC effluent standards.

On 5 June 2020, a leak developed on a section of Cuiabá mine’s tailings pipeline, located between the plant and the TSF.

Most of the material spilled onto the unpaved TSF access road, but despite additional measures to contain the spill with geotextiles, an estimated 5m³ entered the Cuiabá Creek via a system of stormwater ditches and sedimentation sumps.

Samples of the impacted stream found manganese and turbidity outside of compliance limits.

On 20 June 2020, a buried pipeline conveying impacted storm water from Obuasi mine’s dormant Pompora TSF facility, for treatment at the Pompora Water Treatment plant, was reported to be leaking.

An estimated 200m³ of impacted stormwater was released to the clean stormwater bypass canal running alongside the TSF and discharging into the Kwabrafo stream.

Subsequent investigation found that the pipe was likely damaged by earth moving equipment passing next to it, but being buried, the damage remained undetected until rain was being routed off the TSF.

A leak on Mineração Serra Grande’s tailings pipeline was detected by mine staff during inspections at the end of June 2020.

On evaluating the extent of the spill, it was discovered that released slurry had reached the Vermelho River via a natural drainage path.

Water sample results taken in the river did not detect any appreciable changes in its water quality.

Community and local authority representatives enquired about the incident and responses were provided by mine staff.

Following a 40mm rainfall event in mid July, on the Saddle 3 area of Siguiri mine’s TSF, a large volume of stormwater runoff accumulated against Saddle 3’s paddock wall. The paddock system is designed to contain runoff from the outer slopes of the cycloned TSF wall.

Static pressure from the standing water caused a rathole to form at the base of the paddock wall, allowing the stored water to be released onto the TSF perimeter road. This overwhelmed a secondary containment bund located outside of the TSF perimeter road and the spill continued beyond the TSF outer fence, onto community-owned cashew farms.

Water samples showed some contaminants were above the IFC Effluent Discharge Standards.

After searching for the source of sporadically elevated levels of contaminants in a nearby stream, on 30 July 2020, the Obuasi mine’s environmental monitoring team discovered a vandalised HDPE pipeline discharging water into a drainage system.

On investigation it was found that a ~3m portion of the pipeline had been removed and stolen by unknown person(s).

The source of the water was identified as a bypass stream from the water treatment plant, which intermittently directs excess process water to the mine’s Pond 3 facility, for temporary storage.

At the Obuasi mine during mid November, the crew of an engineering contractor was tasked with installing a new 400mm isolation valve on the South TSF return water pipeline.

The task required draining residual water from a partly opened flange on the pipeline, to a predetermined containment zone. However, when the supervisor left his crew to fetch some additional tools, they further opened the flange to increase the flowrate of the water being drained.

This resulted in process water overrunning the intended containment zone, and spilling an estimated 25m³ into a storm drain that leads to a natural wetland area.

Samples at the point of the release recorded contaminants in excess of the EPA guidelines. Fortunately, upstream and downstream analyses did not show a determinable impact from the event.