From the magazine, HDD

Orica groundwater remediation project

The project involved drilling vertical wells on vacant land adjacent to the operating site and a series of wells along Foreshore Road as a second defence against the plume reaching the open water. These bores were then linked using surface and underground pipes to a decontamination plant on the Orica site.

UEA was engaged to carry out two bores as part of the project to link the wells to the plant. Bore one was to install 150 m of 400 mm diameter polyethylene carrier pipe and four 110 mm PVDF carrier pipes under a railway line. Bore two was to bore 520 m from Foreshore Road to Orica’s Southlands site and install one 250 mm poly carrier pipe and four 63 mm electrical conduits.

Specific problems involving the first bore included crossing a railway line, crossing a series of 330, 132, 33 and 11 kVA Energy Australia HV cables, high pressure gas lines, unique ground conditions, contaminated soil and stringent site regulations when operating within the confines of the plant.

Bore two site specific problems included negotiation and location of Energy Australia HV cables, two high pressure gas mains, a jet fuel line running to Sydney Airport, a Sydney Water “SWOOS” (large diameter above ground trunk sewer), interference from buried railway tracks under Botany Road, Botany Golf Course where no excavation of services could be carried out, a lack of access along easement to be followed, the depth of the bore and changing scope.

Prior to and following the award of this project, UEA spent some months working with project engineer Kellogg Brown & Root and Orica to develop safe work method statements and procedures to carry out the construction and minimise associated risks. However, as the projects unfolded there were many construction issues that changed as a result of the deadlines imposed by the EPA and the numerous authorities and land owners involved.

The purpose of the first bore was to install a connecting pipeline from the wells on the Southlands site to the decontamination plant on the Orica site. This involved Horizontal Directional Drilling (HDD) under the main container terminal rail line, a transmission HV easement approximately 20 m wide and under two high pressure gas mains.

The geotech report identified sand and silty sand ground conditions, so a vacuum system was used to pothole each of the high voltage cables and gas mains prior to drilling. Energy Australia also insisted that the HV run was further protected by ramming sheet piles to 4 m below the invert of the cables on the approach side of the bore to act as a barrier. Rail Infrastructure also insisted that the rail line be surveyed prior to the project starting and after each drilling or reaming pass.

Once the rail gave the go ahead, the pilot bore was completed in a day, however on the back-ream problems were encountered with the ground conditions. The reamer and rods became bogged and on further investigation it was found that the site had a peat lens at 6 m deep and due to the increased depth required to bore under the rail line and the power easement, the bore had intersected it. The reamer and drilling fluids used for sand were not suitable for the peat conditions so wash-over pipes were used to free up the tail string and drill string before the rods and reamer could be freed.

Once the reamer was freed and the ground conditions reassessed, a different reamer and drilling fluids were used to overcome the expanding nature of the peat and the 400 mm PE sleeve was pulled in. Four 110 mm PVDF carrier pipes and one 63 mm PE pipe were pulled into the 400 mm sleeve.

This second bore was to link the wells located along Foreshore Road back to the Southlands site for connection back into the main pipeline. It consisted of 520 m of a 250 mm sleeve – which would carry a 160 mm PVDF carrier pipe – and four 63 mm electrical conduits.

The bore was broken into two separate sections. One was from Southlands to Botany Road while the other was from Foreshore Road to the eastern side of Botany Road. As with the previous bore there were many major services to be located and dealt with, as well as private land owners and a council owned golf course.

Other than maintaining distance and direction underneath Sydney Water’s “SWOOS”, the bore from Southlands to Botany Road was straight forward and the pilot hole was bored and pulled back within two days.

However the bore from Foreshore to Botany Road was much more complicated. There was a group of HV cables located under a bank within the council owned golf course and the council would not allow UEA to pothole the cables for depth verification. They did allow UEA access to the course at night to install sheet piles on the approach site of the cables. The same was done to a high pressure gas main adjacent to Foreshore Road. Even with the sheet pile in place one of the asset owners required that drilling be done at 15 m deep to ensure a clear distance from the service, which posed a problem during the pilot bore as signal was lost under Botany Road due to interference from old tram tracks in the road and a heavily reinforced concrete surface designed to withstand the volume of truck movements each day.

To overcome these difficulties, a wire-line steering system was purchased from Digitrak. The system had been hired once before to undertake a large river crossing and UEA was confident that it would be the only way to steer the bore to the projected exit target.

The system proved invaluable and the final pilot bore was achieved in three days. The pipe string was then attached and pulled back the following day. As with the previous bore the 160 mm PVDF carrier pipe was then pulled through the sleeve which by this time had been jointed where the two bores met – making it 520 m in total. To achieve the installation, the drill rods were fed down inside the pipe to pull the PVDF from Southlands to Foreshore Road, taking care not to fracture the pipe which was quite rigid, unlike the polyethylene (PE) which was used for the sleeve.

In the end, despite the almost impossible task of getting access to private property, railways, golf courses, not to mention the timeframe placed on the project by the EPA, the deadline to have contaminated water being processed by the treatment plant was reached, signalling the end of another successful project for UEA.

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