Moving Loop Electromagnetics survey to support monitoring of derelict tailings dam
SERVICE
Environmental, Geotechnical and Minesite Infrastructure
METHOD
Electromagnetics
LOCATION
Central NSW
BRIEF
A client was assessing water seepage around the tailings dam of a derelict mine in central New South Wales. Seepage control is a critical management task because seepage, if not managed, can result in dam failure. Dam failure consequently may result in environmental, human health and economic impacts in the surrounding area. Methods for controlling seepage through embankments, abutments, and foundations rely on understanding the seepage pathways. Therefore, determining the seepage pathways is crucial to assess remediation measures and ensure dam integrity.
Visual inspection of the leaching pathways provides only part of the picture and Fender was engaged to image the subsurface seepage pathways around the dam and embankments.
CLIENT REQUIREMENT
Fender was contracted in 2017 to conduct a comprehensive time domain electromagnetic survey to map the underground seepage around the mines tailing pit. The aim of the project was to reveal conductivity anomalies that correlated with fluid seepage in depths of up to 50 metres adjacent to the open pit mine and the tailings dam. The data would provide vertical two-dimensional images of the subsurface that would identify areas of risk and inform the optimal placement of ground water monitoring bores.
INNOVATIONS AND APPROACH
Fender provided a high-resolution time domain electromagnetic survey to assist with seepage detection on the site. As expected, highly conductive zones readily resolved against the surrounding low conductivity rock and compacted soils, indicating possible seepage paths from the tailings pit. This seepage mapping provided an opportunity for the client to design cost and time effective remediation works.
The EM profiles were spatially arranged for further evaluation of conductive features that correlated with seepage paths. This offered a highly accurate risk map of seepage paths and the direction of flow within the affected areas of the tailing pit.
The results were presented on Google Earth allowing the client and other stakeholders easy access to understand the spatial distribution of seepage pathways.
LESSONS LEARNT
Integration of survey data with surface expressions of seepage was a critical aspect of the project as it provided a more reliable interpretation of the data.
OUTCOME
The electromagnetic profiles provided subsurface images that correlated well with seepage observed at the surface. This allowed accurate placing of groundwater monitors to assess subsurface fluid flow and ensure the long-term safety of the mine site. The survey data also provided a baseline dataset to guide future remediation strategies if required.
