Saving a mine
Kipoi’s ponds have been designed in such a way that 90% of the catchment of process water either get utilised or ends up in the process water pond (PWP for short). PWP is the main pond that has a high risk of discharging into the environment. Discharging is a major event that has caused mines to shut down.
To prevent the PWP from overflow, water is pumped to the nearby much larger tailings facility (TSF3). During a 100 year rain event (defined as 240 mm of rainfall in 3 days) a pump needs to be able to pump 250 m3/hr to ensure the level does not increase of the PWP. This large inflow is from the catchment area of all the other process ponds, the catchment from the massive heaps and the nearby hydromining. It also important to note that there was no flow meter on this, or way of remotely monitoring this pump other ensuring the modelled pond level matched the actual pond level.
WIRE (MMS's proprietary software tool) keeps track of two levels, namely the calculated level and the last available physical measurement. Everytime a level reading is taken, the calculated level is rebased. The calculations involved in estimating a level take can become complex and take into account flows with flow meters, or flows that have been given estimates, calibrated rainfall and catchment areas, pond evaporation ,drainage and any forced evaporation that may be taking place. Given the amount of unmeasured variance, the calculated level get’s less accurate the further one forecasts into the future. Closely monitoring the accuracy of the calculated level allows you to see discrepancies or unknown flows within the system and train ones model further.
During the 2017 rainy season a pump was placed with a supposed capacity to pump 250 m3/hr to the nearby TSF3. In 2017’s rainy season it was identified that the pump could only effectively pump 100 m3/hr this caused a near spillage, before the pump was replaced by one that could actually pump 250 m3/hr. One of the reasons that let the issue become so critical in 2017 is that the level sensor on the process water pond was very badly calibrated and often overestimated the level, causing the mine to get irritated with false alarms when they could physically see the pond was not overflowing. One of the actions made for 2018’s rainy season was to rely more heavily on the daily pond level surveys that get done by the mine, instead of relying on a potentially faulty sensor.
So now in 2018 it was know that closely monitoring the PWP was crucial to managing the water balance risk of the mine. As is expected bad things can happen at the worst possible time, as during December 2018 the DRC was going through an election which had been delayed for two years. Many expats were offsite and mine was on a skeleton staff. Nevertheless a mine can’t stop the copper needs to be produced. During this time the mine had been instructed to run the pump from PWP to TSF3 at a minimum of 140 m3/hr continuously for the next two months .
The mine listened to the instruction but instead of running it at 140 m3/hr they just ran at full capacity. Which we have estimated to be not 250 m3/hr but closer to 200 m3/hr. One of the problems with running a pump at its maximum capacity is that it is much more likely trip. Which this pump of course did a lot. Thus it was effectively pumping at much less than 100 m3/hr, this caused the pond level continue to rise. All this was while there were no significant rainfall events, just the standard 12-20 mm per day as expected during that time of year. To make things worse the surveyors where taking advantage of the lack management presents by simply not updating the surveys. Our personnel onsite was taking leave a few hours from the mine, but thankfully he kept pestering the surveyors to give him the PWP level. As soon he arrived back onsite on the 29 of december he looked at the Wire water balance and went straight to the PWP to see if the calculated level at 99.7% matched reality and it did. The mine personnel were notified, the fixed the pump issue by just running it at 80% capacity, which was estimated to be running at least the minimum of 140 m3/hr required. On the 30th the mine had partial shutdown so that the staff could go vote, this actually now played in the mines favour because no water from tank leach was added that. For a short period of time on the 1st the mine was advised to temporarily stop hydromining to stop hydroming till the PWP level dropped to an acceptable amount, given the risk of the pump tripping again.
After that the mine kept running and the level began dropping to acceptable levels. Now the big question is how did an uncontrolled discharge get so close to happening. As always issues occur when multiple causes stack up, elections, surveyors and faulty pumps and faulty sensors. There will always be multiple issues on a site, and as the