Sewer main rehabilitation in Lake Macquarie

Jun 22, 2007

Kembla Watertech recently undertook the rehabilitation of a sewer main in environmentally sensitive Lake Macquarie.

A 300 mm concrete sewer main along the foreshore of Lake Macquarie was found to be badly corroded. Several manholes in this 1,800 m section were located in the Lake itself and were only accessible by boat. Any sewage spill into the recreational waters of the Lake was environmentally unacceptable and so it was not surprising that the client called on Trenchless Technology as a solution to this problem.
Established in 1892 as the Hunter District Water and Sewerage Board, Hunter Water Corporation (HWC), as it is now known, is a statutory state-owned corporation providing water and wastewater services to almost half a million people from five local government areas – Newcastle, Lake Macquarie, Maitland, Cessnock and Port Stephens.
HWC’s vision is ‘Caring for our Community and the Environment’ and in line with this vision, HWC has embraced Trenchless Technology as the most cost effective and least disruptive answer to the rehabilitation of their ageing underground assets.
Lake Macquarie
Lake Macquarie is located just south of Newcastle, approximately 100 km north of Sydney. The immense size of the lake is a surprise to many when they first visit the region. With a surface area of 109 sq km it is the largest coastal saltwater lake in Australia and is four times the size of Sydney Harbour. Pristine waters and beaches make it a haven for all kinds of fauna as well as all forms of water sports.
The sewer main was buried below the water level of the lake and followed the curved foreshore with changes of direction at every access chamber. There was a steep grade from the foreshore up to nearest road access and vehicular access was possible at only a few points along the sewer. There were no alternative mains available for sewer diversion and waterfront properties were located along the sewer alignment. Of course, there was zero tolerance to sewer spills.
The total project involved 1800 m of lining but the rehabilitation strategy is best illustrated by concentrating on the 400 m length of sewer shown in the plan to the right.
Project execution
Cleaning
This 300 mm concrete pipe was in an advanced state of deterioration with severe gas attack and continual infiltration. Over ten tonnes of silt and debris were removed from this section of the sewer as part of the cleaning process. In the past, if a homeowner happened to have an access chamber inside their property then a number of separate visits by different crews and equipment where necessary to complete the rehabilitation of the pipeline. This was disruptive and inconvenient for all parties. Kembla utilised its specially developed multi-purpose pipeline rehabilitation units to deliver a number of different tasks and so minimise the number of return visits to a particular site.
Diversion of the existing sewer flow
Based on available flow data it was established that a 100 mm diesel portable sewage pump could handle the expected flow in the sewer for the duration of the installation. Getting this pump near to the access chamber where the sewer plug had been installed represented a special problem and this was solved by the use of a barge. In order to ensure no leakage, and due to the rough terrain, it was decided to purchase 100 mm ID polyethylene pipes to use as the delivery line. Four metre lengths were connected together to form a 600 m delivery line that was laid out across and around the foreshore. Prior to any lining work being undertaken, a full scale test of the bypass set up was carried out to confirm it could handle the flow without any leakage. An Environmental Spill Response Trailer was established and maintained on site to provide an immediate response to any environmental incident.
Lining installation around the foreshore
As can be seen from the plan, this section of sewer follows the foreshore and almost comes a full circle back onto itself. Vehicular access was only possible to one access chamber in this entire 400 m length. The CIPP lining method involves a flexible fibrous tube of any size and length which is impregnated with a suitable resin system. The resin impregnated tube is inverted into the existing conduit while still in a ‘soft’ state by the use of a hydrostatic head or pressure and is finally cured to a hardened state while held in intimate contact with the conduit - hence the generic classification of CIPP (cured in place pipe). CIPP systems have been an integral part of the Trenchless Technology industry for over 25 years and the process is well known to authorities around the world. A long continuous length with changes of direction at each access chamber was the ideal situation for an experienced crew to show off the advantages of a CIPP system and so this 400 m length was lined in a single installation.
The works program for the 400 m installation can be summarised as follows:
  • Day 1: Mix resin and impregnate 400 m of lining in the factory at Newcastle. Set up bypass pump and polyethylene delivery pipes around the site a total length of 600 m).
  • Day 2: Plug the flow and operate the bypass set up.
    Flush clean the pipe in preparation for lining.
    Install and cure the lining.
    Reinstate the house connections using robotic equipment.
  • Day 3: Pack up the bypass set up and post lining CCTV survey.
Lining of Branch Sewers
This sewer main also had several relatively short 150 mm diameter branch lines connected to it, servicing houses which • were elevated and some distance from the 300 mm main. While CIPP was a lining option for these branches, Kembla also offers a fold and formed PVC system called the Ex method. This method is also a joint free structural lining similar to CIPP but it is quicker to install and less costly than CIPP in 150 mm – 225 mm diameter sizes. An Ex lining can be completely installed in half a day and so the use of this system for lining these branch lines provided HWC and the customer with the most cost effective and least disruptive solution.
Conclusion
All rehabilitation work was completely No Dig, and each lining installation was completed within 24 hours with minimal disruption to the community and the environment. There was not one environmental incident during the entire lining program. The linings were designed to provide a minimum of 50 years life and the smooth joint free nature of the lining not only eliminates potential leaks but also provides increased hydraulic flow characteristics to the rehabilitated sewer.
Utilities, small and large alike, are now more than ever under the spotlight to operate in an efficient, safe and environmentally conscious manner. The forces of competition, increased customer focus, quality assurance and productivity improvements all influence the commercial manner in which these authorities are managed. The long term contract between Hunter Water Corporation and Kembla Watertech is proving to be a key element of the Corporation’s mission statement: ‘Continuous improvement in being commercially successful while delivering value-for-money water, wastewater and associated services in an environmentally responsible way.’
This article was first published in Trenchless Australasia magazine.

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