Neutral Barrier Technology

Controlling Fluid Flow with Neutral Barrier Technology (NBT)

Research by Earth Systems and ANSTO has led to the development of a new technique for building sub-surface hydrologic barriers referred to as Neutral Barrier Technology or NBT. NBT aims to control fluid flow in a wide variety of permeable rock or unconsolidated sediments.

NBT enables the formation of containment structures or barriers to impede the migration of water flows (polluted or otherwise) into the wider environment. The technique involves selectively sealing microscopic inter-pore channels that permit the passage of water through soil, sand, and porous rock.

Applications envisaged for the mining industry include:

• Plugging leaks in tailings dams or other water impoundments
• Restricting inflow of water into mine workings
• Groundwater intercept barriers
• Guides to reactive barriers
• Construction or enhancement of water or gas exclusion covers for sulphidic mine wastes in waste rock piles.

Unlike existing technologies, Neutral Barriers can be installed in sub-surface settings with no earthworks and negligible disruption. Some major advantages of the NBT compared to existing containment technologies are likely to be:

• The relatively low cost of barrier formation
• The potential for constructing barriers at far greater depths without any excavation
• The self-seeking characteristic of barrier formation means that detailed definition of the permeable zone or leak is not required

One of the key applications of this technology will be to minimise and control acid drainage. Tests have shown that the permeability of Neutral Barriers can be further reduced by interaction with acidic drainage solutions, and that barrier integrity is maintained.

Potential Applications

Potential applications of this new technique are numerous, and all carry the possibility of environmental benefit. From problems such as sealing leaks in dams and minimising the impact of groundwater and surface water on building foundations, to issues such as containing groundwater pollution plumes, controlling coal-bed gas emissions and fighting underground coal seam fires, NBT appears to have a range of potential applications.

There are predicted to be numerous NBT applications in the field of waste containment. Such wastes could be solid or liquid, nuclear, industrial, mining or municipal in origin. For example, solid and liquid wastes in municipal, industrial and hazardous landfills could be isolated from groundwater or surface water interaction with pore-filling barriers that can be retrospectively and essentially non-invasively installed at most sites. This approach has particular application to old landfill sites, which were not fitted with state-of-the-art lining techniques, which are in common use today.

NBT offers the potential to control fluid flow in aquifers. Appropriately located barriers could prevent local interaction between surface and groundwater, or isolate two different types of groundwater (eg. fresh and saline). NBT offers the possibility of manipulating groundwater levels to assist agricultural practices or minimise pollution in near surface settings caused by an altered water table (eg. acid sulphate soils). Other contaminated sites containing wastes or polluted water could also benefit from this approach. Minimising the formation of contaminated leachate by reducing rainwater infiltration, or preventing the release of pollution into aquifers by sealing off migration pathways could be achieved by sub-surface Neutral Barrier formation. If you are interested in further information on NBT, contact Earth Systems at water@earthsystems.com.au.