STILL: Groundwater accounts for more than 30% of our total water consumption in Australia. In Victoria, more than 65 towns rely on groundwater as part of their water supply.

VOICE OVER: Victoria’s groundwater resource is monitored using approximately 2,500 bores located across the State. These bores are collectively known as the State Observation Bore Network.

JENNIFER FRASER: We get two types of information from the State Observation Bore Network. We take water level readings every quarter from every bore in the network, and from time to time we take quality samples from the water. So this information is available on our website, and it helps water managers and water users understand what’s happening with the groundwater resource in their area.

VOICE OVER: The Victorian Government has initially invested nearly $11 million to refurbish the State Observation Bore Network.

This includes installing new bores to ensure greater monitoring coverage, and decommissioning old bores that have failed. The Killarney bore is an example of a bore that has failed.

The bore at Killarney is located near Port Fairy, approximately 4 hours drive from Melbourne.

MATTHEW POTTER: The bore at Killarney is more than 40 years old. Its structure was deteriorating and it no longer provided accurate information relating to the groundwater system. The bore was leaking and needed to be decommissioned to prevent water loss and also to protect the surrounding environment.

ALAN WADE: The bore is not only not particularly useful for monitoring it’s also a liability, it actually leaks at the ground surface, has been doing for years.

A decision was made by DSE to decommission this bore. They hired PB to do that and our drilling subcontractor is Drilltech.

MATTHEW POTTER: A considerable  amount of planning went into this project. That included the preparation of a risk register outlining the risks and mitigating strategies that needed to be considered.

It can take up to 12 months to obtain the relevant approvals and permits necessary to undertake works of this nature.

Safety is critical for any drilling works. Our particular concern was for those on site and for passing traffic.

VOICE OVER: The site at Killarney was excavated for the decommissioning project. More than 300 tonnes of crushed rock were laid to create a stable pad for the drilling rig to decommission the bore.

To start the bore decommissioning a drill stem was lowered to the aquifer where the water flow originates.

The depth of the bore was 726 metres but it was blocked with sediment at 643 metres. Heavy drilling fluid was placed into the bore hole at 643 metres to balance the high natural water pressure, and temporarily stop the upward flow of water.

Cement grout containing between 2 and 5 percent bentonite was used to seal the inside of the bore.  At a depth of 500 metres a casing cutter was used to perforate holes in the bore casing. The cement grout then filled any gaps between the bore hole wall and the bore casing. This process was repeated again at 250 metres.

The cement grout stops any future water leakage by plugging all possible connections between the source of the water and the ground surface.
The cement grout seals and permanently decommissions the bore.

Displaced water was directed to the nearby wetland so water wastage was minimised. Excess drilling fluid was disposed safely off-site.

JENNIFER FRASER: The State is becoming increasingly reliant on groundwater, and there are a number of areas where authorities using water for town supply are looking to supplement their water resources, and drill for groundwater to provide for towns. Businesses are also looking for groundwater.

This means that there’s been drilling for groundwater in new areas. We need the State Observation Bore Network to also be located in those areas, and make sure that it can give us good information about the impact of extraction on that resource, so that we can ensure that any extraction of the resource is sustainable into the future.

JENNIFER FRASER, Director, Groundwater and Licensing Branch, Department of Sustainability and Environment

MATTHEW POTTER, Manager, Resource Monitoring and Reporting, Department of Sustainability and Environment

ALAN WADE, Principal Hydrogeologist, Parsons Brinckerhoff