IMAGER

The aim of the Investigation & Monitoring of Aggregate Deposits Using Geo-Electrical Resistivity Imaging (IMAGER) project is to develop 3D electrical resistivity tomography (ERT) as a nationally applicable method for investigating economically and strategically important onshore sand and gravel deposits.

ERT is a very powerful geophysical ground imaging tool that can be used for both deposit characterisation and groundwater monitoring; IMAGER will develop ERT for both these purposes.

Project partners

IMAGER is a Mineral Industry Sustainable Technology Programme (MIST) funded project, carried out in partnership with the BGS, Minerals Industry Research Organisation (MIRO), Tarmac, Hanson, CEMEX, Lafarge and Aggregate Industries.

Deposit characterisation

3D ERT image of a complex sand and gravel deposit. Click to enlarge.

When used as a geological characterisation tool, 3D ERT can provide high-resolution volumetric images of the ground and is therefore particular suited to investigating complex deposits or deposits that are difficult to drill.

Although research has begun into the use of ERT for sand and gravel deposit evaluation it has still yet to be tested in many economically important geological settings in the UK. Moreover, there is still much work to be done to quantify the performance and resolution of ERT, and to quantify the economic and environmental benefits of integrating ERT into the deposit investigation process. The IMAGER project will address these knowledge gaps.

Deposit visualisation

3D visualisation of a resistivity image of a quarry. Progressive removal of the bedrock and overburden reveals the extent of the sand & gravel deposit. Click to view video.

As part of the project, ERT has been successfully used to image the subsurface architecture of sand & gravel deposits at a number of commercial quarries. Advanced 3D modelling and voxel visualisation permits the quarry operator to see the full spatial distribution of a deposit prior to drilling, and hence to estimate the potential tonnage. By setting appropriate resistivity iso-surfaces, the background overburden or bedrock can be removed from the tomographic image to further define the sand and gravel geometry (see animation).

Groundwater monitoring

Monitoring of dewatering in a sand aquifer using time-lapse ERT, red = unsaturated, blue = saturated, and the dashed line shows the water table. Click to view video.

Time-lapse ERT data can be used to monitor changes in both groundwater levels and quality. By using the state-of-the-art BGS-designed ALERT (Automated Time-Lapse ERT) monitoring system it will be possible to spatially image in real-time rapidly changing hydrogeological conditions caused by quarry dewatering. Although ERT monitoring is now being used in other sectors, e.g. contaminated land investigation, waste management & groundwater. It has yet to be applied by the minerals industry.

The IMAGER project will therefore demonstrate proof-of-concept for this technology in relation to sand and gravel workings. Our focus will initially be on deploying time-lapse ERT for high-risk sites, where particular care has to be given to groundwater management, e.g. at sites with significant environmental/ecological sensitivities, such as SSSI’s, or at sites in complex hydrogeological settings where dewatering could affect surrounding aquifers or eco-systems.

Contact

For further information contact Dr Jonathan Chambers IMAGER Project Leader