APA owns and operates the Amadeus Gas Pipeline (AGP), a bi-directional gas transmission pipeline extending from the Amadeus Basin in the south of the Northern Territory to Darwin, in the north. It transports natural gas to Darwin, Alice Springs and regional centres, principally to fuel power generation. The Channel Island Bridge Pipeline Replacement Project is proposed to replace a short section of smaller diameter pipeline on the existing Channel Island Bridge with a pipeline to be installed under Darwin Harbour using Horizontal Directional Drilling (HDD). The project is proposed to ensure the pipeline can be monitored on an ongoing basis to ensure its integrity can be maintained.

Project Background

Channel Island Power Station is the primary power generation facility for Darwin and its surrounding areas. The power station fuel gas comes through the existing Amadeus Gas Pipeline. In the area around Channel Island, the pipeline generally follows the Channel Island Road and is attached to the side of the existing Channel Island Bridge. The section of pipeline attached to the bridge is narrower than the rest of the pipeline and does not allow in-pipe inspections tools (called PIGs) to be used to monitor the ongoing integrity of the pipeline. The pipeline section is, therefore, being replaced with a section of pipe the same diameter of the existing pipeline to allow for the use of in-pipe inspection tools. To minimise potential environmental impacts, the pipeline will be installed under Darwin Harbour using Horizontial Directional Drilling.

APA has submitted a Notice of Intent to the Northern Territory Environment Protection Authority (NT EPA) regarding the project. On 10 April 2020, the NT EPA issued a Statement of Reasons Decision stating that the project required no additional environmental assessment to proceed.

The project was referred to the Commonwealth Department of Agriculture, Water and the Environment in accordance with the Environment Protection and Biodiversity Conservation Act. The project was determined to be not a controlled action on 2 July 2020 (EPBC Ref: 2020/8672TBA).

APA has developed, and will implement, a Construction Environmental Management Plan (CEMP) and a standalone Acid Sulphate Soil Management Plan to manage potential environmental impacts associated with the project. Works on the project are expected to be completed in Q3 2021.

What is Horizontal Directional Drilling (HDD)?

Horizontal Directional Drilling (HDD) is generally used for the crossing of major watercourses where standard open-cut methods are less desirable. HDD may also be used for areas of sensitive environmental value, road or railway crossings, where required.

The installation of a pipeline by HDD involves drilling a pilot hole beneath the surface, from an entry point on one side of the crossing to an exit point on the other side of the crossing. The hole is then enlarged by reaming to allow for a welded pipe string to be pulled back through the drill hole from the exit point side to the entry point side without damaging the coating.

Pipe sections are then welded together to form a pipeline string. Once the pipe string is installed and tied into the main section of the pipeline, the entry and exit points are remediated.

Drilling is conducted by a specific HDD rig, operated by a specialist contractor. The size of the HDD rig and its associated footprint depends upon the size of the pipe, the nature of the subsurface geology and the length of the drill.

Drilling mud (typically bentonite) is used to hydraulically drive the drilling head, as a coolant, to wash in-situ material (cuttings) from the drilled hole and to seal and line the hole to facilitate insertion of the pipe. Cuttings are screened at the HDD rig to remove drilling mud, which is recycled. Screened cuttings are diverted to skip bins prior to disposal in landfill. Treatment of cuttings would only be required for acidic soils. If encountered, acidic cuttings would be treated with lime to neutralise and then disposed of in landfill. 

The alignment of the HDD and circulation of drilling muds are monitored throughout the HDD operation for indications of an inadvertent drilling mud release.

The location of the entry and exit points of the HDD have been designed to be collocated, where feasible, with the existing Channel Island Road to minimise disturbance to mangrove unities fringing Darwin Harbour.

Further Information

We have developed a factsheet with more information about the Channel Island Bridge Pipeline Replacement Program.

If you wish to find out more information or provide feedback about the project, please contact us by:

Phone: 1800 290 598
Email: [email protected]