Situated in the scenic Shire of Byron Bay, the Brunswick Area Sewerage
Augmentation Scheme is an upgrading program that Diona has been working
on since July.
At present the sewerage treatment plants (or STP's) in Mullumbimby and Brunswick Heads, or Mullum' and Bruns' as the locals call them, are operating at full capacity. Because of this a moratorium has been placed on development. This is evidenced by the lack of available housing in the area, which is something Tricia in the office had to overcome when securing accommodation for the twenty-something workers on the project.
The new scheme consists of two pumping stations, one in each town, and a new STP half way between them. The plan is to divert sewerage from the existing STP's to a new STP by pumping it via rising mains from the new pump stations. Diona is responsible for building the pump stations and rising mains, while the new STP is being constructed by another civil contractor, Fulton Hogan. The rising mains are a range of sizes, but are generally 375mm DICL and 450mm PVC. In total there is approximately 6km of pipelines. These pipelines traverse a range of terrains, but are predominantly located in bush and pasture. In typical Diona style, the diff erent areas of site were given place-names, some of which like: 'The Rain-forest', 'The Swamp', and 'The Jungle' give you an idea of what we were working in.
In general the area is only a few meters above sea-level, in close proximity to the Brunswick River. The water table is high, even above ground in some places, and the soil structure is poor. In the worst areas the ground could only be described a 'quick-sand', hardly fi t to support a person, let alone the pipeline. To overcome this, we drew down the water-table using pumps, and replaced the ground beneath the pipe with imported rock. Thankfully we had a great run with the weather, getting thirteen weeks, from the middle of July without any signifi cant rain. This enabled us to get the majority of the pipelines in, and the surface restored, in time for the seasonal rains in November. At present our grass seed has germinated, and is starting to take-hold, and hopefully before long, the construction corridor will be back to the condition we found it in.
Because the Brunswick River meanders (bends) a lot between Mullum' and Bruns', rather than extend the length of the pipelines, the design called for river crossings. In total the pipelines cross the Brunswick River three times. To achieve this we used directional drilling. There were three additional drills, two crossing ox-bow lagoons (Billabongs), and one under the Pacific Motorway. Pipeline Drillers P/L brought their CMS 200 rig to site. With 200,00lbs (90tonne) of pull back capacity, this 35t machine had no problem getting the crossings up to 200m installed.
The pumping station sites also presented a range of challenges. Access at the sites is quite restricted; and using large plant capable of excavating over 6m deep to install the 3m diameter pump wells; space was at a premium. A large emergency storage tank was constructed at one of the sites. The tank consisted of a twin 2400mm diameter concrete pipeline on the side of a residential street. Installation of the tank progressed well, using a slide rail shoring system; which supported the full width of the 6.5m wide trench and enough under-strut clearance for the pipes.
All going well, the project will be wound up before Christmas; handing over the infrastructure to Byron Shire Council until the new STP construction is complete next winter. Then we will have to come back for fi nal commissioning and to change over the sewerage system.