Through Sydney Water Corporation’s (SWC) ongoing systematic inspections of sewer lines across Sydney, a range of structural, service, exfiltration and infiltration problems have been identified in various locations within the sewerage system. In response, SWC initiated the Sewer Rehabilitation Program (SRP) 2005-06, with the objective of rehabilitating these sewer lines to their original condition and performance levels.
Sydney Water commissioned Kembla Watertech to undertake remediation works of many of these deteriorated pipes, a number of which are located in areas identified by Sydney Water as being environmentally sensitive. All worksites under the SRP contract have been divided into two categories, A and B. Category B sites are environmentally sensitive sites including National Parks, urban bushland, heritage conservation sites and SWC requires that site specific environment impact mitigation measures be developed for these sites.
Kembla prepared a Construction Environmental Management Plan (EMP) to ensure that all potential environmental impacts that could reasonably be expected to occur during the proposed works are minimised and fall within acceptable and agreed limits. As part of this proactive approach to environmental management one particular Category B site, at Truscott Place, Killara, was identified as presenting a very difficult situation.
Location and existing environmentArticle continues below…
The site works for this 225 mm diameter sewer were located within a gully of Garigal National Park, which follows Gordon Creek and is approximately 300 m from the nearest vehicular access point. An unsealed narrow path traverses the steep gully side before crossing the creek and roughly following the line of the sewer. It was considered that with heavy traffic, the path would become slippery and possibly unstable.
The EMP identified that:
* All manholes are located within 25 m of a natural waterway and within dense bushland that is relatively undisturbed. * Two manholes are located within the watercourse itself. * The odour of sewage at the site suggested that water quality was currently being impacted by the sewer line and confirmed the need for urgent rehabilitation. * Access is via a steep embankment leading off Truscott Place. * The clearing of vegetation along the limited access could increase the erosive potential of the site. * Due to the relatively undisturbed condition of the site, the presence of a waterway and the presence of sandstone outcrops, a search of the Aboriginal Heritage Sites register was undertaken and identified an open camp site and an axe grinding groove some 250 m from the site. * Access to the manholes would be restricted to foot access. * Access during wet weather would not be permitted.
The 225 mm diameter of this sewer makes it ideal for Kembla’s Ex lining method. This No-Dig technology involves a PVC pipe which is pulled into the sewer in a folded shape and then reshaped (‘formed’) into a circular pipe by the application of heat and pressure which moulds the liner to the host pipe surface. The solid wall structural Ex pipe is tight fitting to the existing sewer and is joint free for its entire length.
While it is possible to position the steam boiler unit some distance from a site and simply pump the steam through a small pipe, it is necessary to position the coil of Ex lining and the pulling winch at the manholes.
The critical focus for the project management team became how to transport this equipment and material to the site, given the potential impacts and associated safeguards identified by the EMP.
Because of environmental and safety concerns associated with access to this site, Kembla had a meeting with all stakeholders and proposed the use of a helicopter. Kembla had determined that it was possible to use a helicopter to pick up the basic materials and equipment from a nearby reserve and drop these directly at the appropriate sewer access chambers.
While at first seeming an ‘extreme’ solution, after careful planning and cooperation between SWC and Kembla personnel this option proved to be the ideal solution. It solved all the concerns raised in the EMP concerning safe access and environmental protection. However, it did raise new concerns and so Kembla issued a revised work method statement specifically addressing the use of the helicopter on this project.
Following SWC approval to proceed, a Works Certificate was obtained from the NSW National Parks and Wildlife Service and then a Landing Strip Permit from Ku-ring-gai Council. The landing permit set aside a specific area on a nearby oval.
Once all safety procedures were in place and the helicopter subcontractor had obtained the necessary approvals, the work was carried out with clockwork precision in late November. The helicopter picked up the materials and equipment in a series of lifts from the designated loading zone and lifted these into the dense bushland, where Kembla personnel were waiting to set it up.
The lining work was completed quickly and without any safety or environmental incident. The helicopter then returned to lift out the equipment and the National Park was left untouched.