Willowton Oil Spill Summary.
An unfortunate accident occurred on Tuesday 13th of August 2019 at the Willowton Group Facility in Pietermaritzburg, KwaZulu-Natal, South Africa. Above ground storage tanks containing vegetable oil, sunflower oil, and diluted caustic soda collapsed or were damaged, spilling approximately 110 tonnes of contaminant into the Baynespruit River, a tributary of the uMsunduzi and uMngeni Rivers. Of these 110 tonnes, approximately 70 tonnes were recovered by emergency spill response crews, with the rest running into and contaminating the system.
GroundTruth were contracted to complete a baseline aquatic impact assessment as part of the short-term remedial actions. This assessment was conducted through sampling and analysis of both biological and physico-chemical parameters, as well as aerial surveys. The assessments were conducted along Baynespruit, Msundusi, and uMgeni Rivers, as well as on major tributaries that represented potential refugia from the spill impacts.
After the spill, GroundTruth found that there was extensive fish die-off, as well as low benthic diatom and South African Scoring System (SASS) version 5 scores, all evidence of severe impacts of the spill on instream biota. There were also elevated Escherichia coli, chemical oxygen demand, and phosphate levels across the catchment, showing mixed pollution impacts.
Overall, the assessment clearly indicated that the spill had severely degraded the downstream river ecosystem. However, monitoring at sites unimpacted by the spill also showed significantly degraded ecosystems, suggesting that the system was already stressed by other pollution sources independent of the spill.
Rehabilitation of the fish community
Following the assessments of the spill impacts, GroundTruth, with support from freshwater researchers from the University of KwaZulu-Natal (UKZN) Department of School of Life Sciences, were appointed to undertaken rehabilitation interventions. The primary rehabilitation action was to re-introduce native fish.
Rehabilitation efforts focused on the KwaZulu-Natal Yellowfish (Labeobarbus natalensis), as the spill had a severe impact on the population abundance and structure of this endemic species. Yellowfish were translocated from within the uMsunduzi River Catchment, with real-time water quality monitoring, chemical water quality analyses, and aquatic biomonitoring maintained to track the recovery of the fish and broader ecosystem. A total of 138 fish were translocated. Of these, 87 fish were tagged with passive integrated transponder (PIT) tags.
Ongoing assessment of this system shows that the integrity of the Baynespruit and uMsunduzi Rivers, including regions both unimpacted and impacted by the spill, remains seriously impaired. Degraded water quality demonstrates ongoing inputs and negative impacts emanating from the urban-industrial area of Pietermaritzburg, unrelated to the spill event. The degraded state of the Baynespruit and uMsunduzi Rivers continues to hinder the recovery of fish communities following the spill.
Based on ongoing monitoring, GroundTruth developed several remediation actions, including urgently addressing the multitude of other sources of pollution in the catchment (primarily overhauling sewage reticulation and treatment infrastructure) and the establishment of a Baynespruit Conservancy to enable continued engagement with the broader community and stakeholders who are either dependent on, or affected by, the goods and services emanating from this catchment.