The towns involved are Cobargo, Wolumla, Candelo and Kalaru. Over the four villages there is a total of approximately 22,900 metres of reticulation to be installed including 610 collection wells. In addition to the new low pressure sewerage project, BVSP are also upgrading five existing sewerage treatment plants including a $A2.2 million upgrade of the Tura Beach Sewerage plant and the Tathra Reclaimed Water Storage Lagoon. These state of the art projects are being incorporated into the area to improve health, environmental issues and modernise the areas waste management systems.

The low pressure system is relatively new to Australia but over the last few years has been successfully installed throughout numerous small towns situated around Australia including some towns on the outskirts of Sydney. The system works by collecting the sewerage from individual dwellings into pots located on each property which reduces the effluent size down to a thin slurry via grinder pumps fitted in each pot. The sewerage is then transported through a network of small low pressurised pipelines until it reaches a sewerage treatment plant. Once the sewerage has been treated it can be used for irrigation in areas such as ovals, racecourses or golf courses.

Advantages for installing the low pressure sewerage system include:

• Being a pressurised system, any type of terrain can support it. • When installed in areas that have numerous changes in terrain, a more cost effective construction can be achieved compared to that of a gravity system. • Pipe depths are minimal and can be easily repaired if required. • Minimal environmental impact during construction. • As a grinder pump reduces the effluent to a thin slurry, blockages should not occur.

After completing similar projects for Sydney Water, Sydney based company Infrastructure Constructions (IC) was handed the job of installing the reticulation pipe work and all the boundary kits throughout Cobargo, situated 41 km north of Bega, which is the largest of the four towns.

The pipe work is to be installed using both open trenching and Horizontal Directional Drilling. In September 2005 construction started at Cobargo on the street mains and property installations. The work included the installation of approximately 9,000 metres of reticulation pipe work and 240 pots/boundary kits. The reticulation pipe is contructed from polyethylene and ranges from 40 mm through to 140 mm. The main pipe was joined using electro fusion collars with the bulk of the pipe being supplied in lengths of 50 metres to 200 metres.

As the project location was 6 hours drive south of Sydney, all personnel and equipment had to be self sufficient, including maintenance and breakdown issues. As delivery time to transport additional items would be expensive and could cause unwanted downtime, it was decided to include other equipment in the initial move that may not be normally required. BVSP had acquired a yard in Corbargo where all the materials and equipment could be stored. All IC personnel were set up with local accommodation. In addition to IC personnel local labour was also used. These included labourers, plumbers and excavator operators. IC supplied three excavators, several support vehicles, a dump truck and to complete all the bores one of IC’s JT17020’s was transported down to site along with a mixing system and a vacuum truck.

The route of the designated pipelines varied considerably off the boundary line. This ranged from 500 mm to 5,000 mm. By using the HDD machine minimal disturbance was created to the footpaths and even more so when in close proximity to the road. The blocking of driveways was a non-event except when open trenching was involved. Using HDD also meant minimal restoration to the area was required and the construction site easy on the eyes for the locals, as there were minimal spoil piles. Several utilities were encountered including a major Telstra network, Optus Fibre, Nextgen Network and water pipes.

The ground conditions comprised mostly decomposed granite which at first glance did not cause too many problems. The excavators found the going quite easy but as the project got underway it was discovered that the JT1720 was finding the going a little tougher. The standard drill head was having trouble penetrating the ground even though a bill was fitted with tungsten carbide pieces. A Talon bit had been added to the equipment in Sydney just in case some hard ground formations were encountered, so this replaced the existing bill. A much better penetrating rate was noted with a pilot hole of 110 mm being produced. All bores were to travel at a depth allowing them to enter a pit dug outside each property prior to boring. This might mean the intersection of up to ten pits over a single bore. This pit was for the connection of the property line to the main reticulation line and had a minimum cover of 600 mm. Due to the size of the pilot hole, the installation of the 40 mm, 50 mm, 63 mm, 75 mm and 90 mm PE pipe could all be installed without requiring a back reamer.

For the installation of the 110 mm PE pipe a small 130 reamer was manufactured in the workshop back in Sydney and for the 125 mm and 140 mm a standard 180 mm reamer was used. Another factor that was discovered after the completion of several bore holes was the increased wear being produced by the decomposed granite. This would cause the rebuild of all ground engaging equipment after only a relatively short time, and also minimised the life of the current drill rods which would now require replacement before too long.

With the village of Cobargo completed, the next town to begin construction is Wolumla which is located 20 km south of Bega. This will take place early February 2006 with the JT1720 HDD. Wolumla is a much smaller town with only 151 properties and approximately 4,763 metres of reticulation to be completed.

The BVSP is a long term project which IC is totally committed to. IC have added specialised personnel and equipment to their inventory to increase their mobility and capabilities into successfully completing many more similar project in the future.