Long-term In-Situ Groundwater Bioremediation

The Challenge

A smelter currently on care and maintenance identified persistent groundwater contamination exceeding water use licence limits for multiple parameters. Hexavalent chromium (Cr⁶⁺), nitrate (NO₃), and sulphate (SO₄) were detected above compliance thresholds across a dispersed borehole network covering both on-site and off-site locations. With the facility in care and maintenance, the client required a sustainable, repeatable remediation strategy that could be implemented periodically to maintain groundwater compliance – without permanent infrastructure.

Our Approach

iWater designed a cyclical in-situ bioremediation programme with bi-annual infiltration rounds, using adaptive borehole selection based on evolving monitoring data. The programme has now completed four rounds since 2022.

• Borehole selection in collaboration with client HSEC management, informed by latest monitoring chemistry and plume dynamics
• Downhole EC profiling at each borehole to identify fracture zones and optimal injection depths (8–25 m below ground level)
• EVO-based electron donor mixed with borehole water, injected at target depth, followed by 1 000 ℓ groundwater flush to drive migration through fractures

The Results

Previous infiltration rounds demonstrated Cr⁶⁺ reduction to below detection limits (BDL) within one month across all treated boreholes. The programme’s adaptive approach – targeting different boreholes each round based on monitoring data – has maintained groundwater compliance across the broader site.