The project is essential to securing Sydney’s existing supply of natural gas, as well as planning for the long-term needs of the growing population.

As a result of the Alinta/AGL transaction in 2006, Alinta became responsible for the delivery of the $100 million, 30 km, 500 mm diameter natural gas main and facilities between Liverpool and Marrickville.

SPL Project Manager Peter Sheridan said that despite the many challenges the project team had to deal with in installing a large diameter pipeline through suburban Sydney, the project was successfully delivered in November 2007, in line with the budget and the three year schedule.

The existing 550 mm primary main was constructed in the late 1970s. It transports gas from the interstate trunk mains in Western Sydney and follows a route through major roads and suburbs to finish at Port Botany. Branching from the primary main system is the northern steel primary main which supplies the Sydney North region.

An independent detailed risk assessment was carried out for Alinta on the existing primary main. The risk assessment identified a number of potential hazards that could result in a loss of supply.

The existing primary operation relies on a combination of protective measures to ensure its integrity, continuity of gas supply and safety. Additionally, environmental factors surrounding the primary main have varied since its construction. Rapid urbanisation, increasing easement encroachment, ageing of pipe coating and potential external interference all contribute to the threats to the long-term security and integrity of the system.

The risk assessment concluded that “the risk of loss of supply associated with the single primary main is considered unacceptable.” If the primary main was damaged and a section of the main had to be taken out of service, Alinta customers could be subjected to a large scale disruption of their gas supply that could take several months to resolve and depending on the season could affect up to 400,000 customers.

The integration of the new primary main loop (the SPL) reduces the risk of both gas supply and safety problems to an acceptable ‘low risk’ level. Also, the SPL allows Alinta to overcome the constraints on the existing main for maintenance, repair and inspection. SPL thus provides significantly increased ‘security of supply’ for gas customers in Sydney. In addition SPL also provides capacity for potential increase in gas demand in the southwestern suburbs of Sydney.

Route selection

The SPL Project passes through the Liverpool, Bankstown, Canterbury and Marrickville local government areas.

The route of the primary gas main was chosen after extensive technical investigations and consultation with key stakeholders.

John Portelli, Construction Manager, who was instrumental in the route selection, said “The principles behind the route selection were to minimise the impact on major public infrastructure, environmentally sensitive areas, residents and businesses along the route; to minimise disruption to the general public and services including power, water, sewerage and telecommunications; and, to ensure safe and efficient construction and operation of the primary gas main.”

An Environmental Assessment identified certain areas of bushland as having particularly high sensitivity along the alignment between Lt Cantello Reserve and Deepwater Park on either side of the Georges River (Hammondville/Milperra).

Both these parks feature bushland listed as endangered ecological communities under both State and Commonwealth Legislation. The construction zone was re-designed and kept narrow to prevent disturbance to the adjacent bushland areas to minimise environmental impacts and the horizontal directional drilling (HDD) was moved to a new location.

Contracting strategy

One of the keys to successful delivery of the project was the selection of contractor partners. Alinta project managed the complete SPL project from concept through to commissioning and was assisted by the following main contractors:

- GHD – detail design and engineering - Codmah – western section, 14 km open cut pipeline construction and installation of two automatic line break valves (ALBVs). - Diona – eastern section, 14 km open cut pipeline construction and installation of two ALBVs. - Coe Drilling – four river crossings using horizontal directional drilling. - Thomas and Coffey – offsite mechanical fabrication and construction of the primary regulatory station (PRS) and trunk receiving station (TRS).

Community consultation

Given the potential impact of the development of the SPL on the public, Alinta engaged with local communities on a range of levels. One of Alinta’s primary aims was to minimise impact on major public infrastructure as well as residents and businesses along the route by effective route selection.

Working closely with the four local councils allowed the project team to plan a construction methodology that included streets, parks, reserves and native bushland. Assessments identified that there would be short-term impacts associated with construction including access restrictions, amenity disturbances and traffic diversions. With this in mind, an Environment Management Plan was developed for the project, which provided a framework and procedure to minimise potential environmental impacts such as noise, vibration and dust.

The project community relations team introduced a range of public awareness programs, including public displays at local councils, community meetings, a project specific web site, and directed lines of communication within the company to mitigate the effects of construction on the public.

Environmental

Work done in the planning phase of the project allowed the identification of many items of environmental and heritage conservation significance. However, given the challenges of finding a suitable route through the urban environment for a gas main of this length it is impossible to avoid all sensitive environments and heritage items.

Where sensitive features were encountered along the alignment the potential impacts to these features needed to be minimised through minor alignment changes and the adoption of less disruptive construction methods and techniques.

Working around existing services

This project presented unusual challenges when compared to the usual large diameter transmission pipeline construction which takes place in often remote locations across Australia.

A typical pipeline will cross another service every 10 km. In the case of the SPL project the main crosses paths with hundreds of major and minor services every kilometre and so extensive fabrication and pipe bending is required. All excavation areas on this project are considered as confined spaces due to the depth. Benching of excavations is often not practical so most bell holes required shoring boxes or sheet piling to be installed. Close attention to services searching and extensive pre-planning of activities was essential to maintain acceptable production rates.

While a good day on a cross country pipeline is 3 to 7 km, a good day on the SPL was 200 metres between four work fronts.

The majority of the construction of the SPL gas main was typical open trenching methods that involve excavating a trench, laying a section of the pipe and backfilling the trench with suitable material. Due to the nature of the areas under construction, a considerable challenge was the disposal of the quantity of spoil that would normally be considered clean fill.

There were also four HDD water crossings and twelve significant cased bores under sensitive areas and major road crossings.

Ground conditions

95 per cent of the Sydney Primary Loop Project construction was open cut (trenching) and the construction crews encountered the full range of underground conditions from heavy rock, running sand, contaminated soils and high water tables.

Innovative use of equipment was devised by the construction partners to counter these conditions. Specialist equipment was required to break through the rock areas including rock saws, rock breakers, vibration monitoring equipment, noise monitoring devices and water spray to manage dust. A Vermeer trencher was used in suitable areas and good production was achieved.

Summary

Given the enormity of the task and the plethora of obstacles, the on-schedule and on-budget completion and handover of the SPL was no small feat. This can be attributed to the detailed planning and implementation that incorporated consideration of the project requirements of safety, technical, engineering, environmental, construction, community and stakeholders.

“The success of the project is due to all those personnel involved who contributed their best for the project,” said Mr Sheridan.