Determination of the possible requirement for remediation of manganese impacted groundwater at an industrial facility in Nelspruit

[摘要] English: A formerly operational manufacturing company, Delta E.M.D (Pty) Ltd (Delta) was, until recently, located in Mbombela (Nelspruit), Mpumalanga and produced electrolytic manganese dioxide (MnO2:EMD), an inorganic compound used for dry-cell batteries including alkaline and zinc-carbon batteries. The operational site has been subject to various site investigations between 2010 and 2015 which ultimately informed a site-wide rehabilitation and closure plan. The site has since been demolished as part of a site rehabilitation activity undertaken during 2015 and 2016.During the course of 2014 to 2015, the author developed a site investigation strategy that utilised multiple site investigation technologies to characterise the geological, hydrogeological and contaminated groundwater situation at the site. This allowed for a site specific remediation strategy to be developed.The site is located within an industrial area of Mbombela (Nelspruit), Mpumalanga within the Mbombela Local Municipality. To the immediate north of the site, a wide single-carriageway road is present which overlooks undeveloped bush land leading towards the Crocodile River located 200 m beyond. The local area is underlain by medium to very coarse grained granite which has been intruded by numerous basic dykes and sills. The granite is fractured and highly weathered in the upper 15 m. North-South trending geological structures are present which represent preferential pathways for groundwater flow and the migration of contaminants.The site characterisation work undertaken involved several phases of investigation including both non-intrusive and intrusive site investigation and sampling techniques. Specifically, the investigation involved: desktop research; geophysical surveying; borehole drilling and geotechnical drilling; monitoring well construction; soil and groundwater sampling; chemical analysis, and aquifer testing. The work undertaken resulted in identification of several sources of groundwater contamination and ultimately the development of an in-situ groundwater treatment strategy.Three hot spots of groundwater contamination were identified on site; the majority of the contamination was considered to be present within a phreatic shallow aquifer represented by a weathered horizon. The groundwater flow direction is in a northerly direction towards the Crocodile River, with a constant source of recharge being supplied by a man-made canal located along the western boundary of the site. Groundwater flow and contaminant migration towards the Crocodile River, was shown to be structurally controlled by the presence of faults and dykes.A source-pathway-receptor (S-P-R) assessment was undertaken which confirmed an active S-P-R model scenario would result in elevated concentrations of manganese and sulphate and low pH groundwater reaching the Crocodile River, which could negatively impact surface water quality.The information obtained and conceptual model that was developed was used to design the layout of a targeted on-site groundwater remediation system utilising the injection of lime to neutralise low pH water on site and allow for the precipitation of manganese from solution.The study, explores, how multiple site investigation technologies can be utilised to develop targeted and site-specific remediation strategies for contaminated groundwater within a fractured rock environment.

[发布机构] University of the Free State