JEMENA’S INNOVATIVE REMEDIATION METHOD AT KENDALL BAY, SYDNEY

JEMENA WITH ITS PROJECT PARTNER VENTIA, ADDRESSED THE CHALLENGES ASSOCIATED WITH WORKING IN A MARINE ENVIRONMENT, THROUGH THE IMPLEMENTATION OF AN INNOVATIVE REMEDIATION SOLUTION.

With a long history of industrial activity, portions of the Parramatta River have succumbed to sediment contamination. To remediate the sensitive marine environment while limiting the impact to nearby residential developments during the clean-up, Jemena used innovative remediation designs and solutions.

Located just 10km west of Sydney’s CBD and on the south of the Parramatta River, Kendall Bay is nestled between the Breakfast Point residential development and Cabarita Ferry Wharf. For over 100 years, it was also home to the largest gasworks in the Southern Hemisphere, the former Mortlake Gasworks operated by The Australian Gas Light Company (AGL). After the decommissioning of the gasworks, the land was remediated in the early 2000s and re-developed, forming part of the large residential development, now known as Breakfast Point.

Jemena inherited AGL’s obligations and responsibility for the Kendall Bay sediment contamination following corporate transactions in 2006 and 2007 and shortly after, undertook a detailed assessment to determine the level of sediment contamination. The detailed assessment undertaken across Kendall Bay determined the nature and extent of contamination in sediment resulting from the historical operation of the gasworks. The assessment identified two areas within Kendall Bay that required remediation, referred to as the Northern and Southern Remediation Areas. These areas correspond to areas of activity related to the former gasworks, including the former coal wharf that extended into Kendall Bay.

The Sediment Remediation Project required an innovative remedial design to remediate the contaminated sediment and satisfy the large number of stakeholders (both government regulators and the local community). Gasworks remediation is known to be very odorous, so the project design needed to limit impacts to the residential community as far as practical. Following a remediation options assessment and a two-year field based technology refinement program by project partner Ventia, in-situ stabilisation (ISS) was selected as the main remediation method.

Former Mortlake Gasworks (1937).

(Source: Royal Australian Historical Society, Set 72157640448188933, ID 30079569931, Original title Mortlake-Gas Works – Parramatta River – 1937)

ISS is commonly used on land-based projects but only a few small-scale examples have been completed in a marine environment. Despite this, the options assessment suggested that ISS would generate less odour, less disposal to landfill and less impact on the surrounding environment compared to traditional dredging. In the marine setting, ISS involved mixing marine cement with the sediment underwater to form a stabilised raft-like structure to permanently contain the contaminated sediments.

A trial within Kendall Bay was successfully undertaken in September 2018, with lessons learnt and results provided to the Environment Protection Authority (EPA)-accredited site auditor. That gave Jemena confidence that the technology could be scaled. Jemena received Department of Planning, Infrastructure and Environment (DPI&E) approval for Jemena’s State Significant Development (SSD) application for the fullscale remediation works in May 2019.

The marine environment included mangroves, which provide important habitat for the local ecosystem, so a number of environmental controls were installed prior to commencing the works to protect the marine environment, including silt curtains and sheet piles. A custom-designed floating cement batch plant was fabricated to supply cement to the bespoke designed excavator barge, which in turn undertook the stabilisation of the sediment in place below the riverbed (refer to image below).

ISS Mixing in Northern Remediation Area. Breakfast Point Residential Development in background.

(Source: Jemena)

The excavator was fitted with real-time kinematic (RTK) positioning and telemetry, which allowed the project team to track the successful completion of the works as it progressed.

Jemena’s Project Manager, Phil Hutson, said the Kendall Bay clean-up presented a number of unique challenges.

“Together with our project partner Ventia, we had to address the challenges associated with working in a marine environment. This meant contending with tides and changing weather conditions while operating equipment on floating barges all within close proximity to the local community. The innovative remediation method proved to be the correct option, as it enabled the remedial objectives to be achieved while limiting impacts on the local community”.

Understood to be the first time in the world a full scale marine application of ISS has been implemented, the project was successfully completed in October 2020: two months ahead of schedule, under budget, during a worldwide pandemic and with great feedback received from the adjacent community.

Project Director, Oliver King, said “We’re delighted this popular area of waterway can now be returned to the community and we thank the community for their support throughout the project.”

Jemena is working with the EPA and DPI&E to finalise the project. Project snapshot:

• 80,000 hours worked, all Loss Time Injury (LTI) free

• Two months ahead of schedule

• Understood to be World-first fullscale remediation of its kind

• Total capital investment - $50 million

• Refined strategy to protect existing mangroves

• Eliminated 450 round trip truck movements through treatment in-situ

• Full scale remediation works completed between Sept 2019 to Oct 2020

• Total size of Remediation Areas 11,800m2

Author: Phil Hutson, a Senior Project Manager, has delivered environmental site assessment and remediation projects for a wide range of clients at sites across Australia. This has included assessments and largescale remediation works for the oil/gas industry, government agencies and the waste industry. Phil is the Jemena Project Manager for the Kendall Bay Sediment Remediation Project on the Parramatta River at Mortlake, NSW.