Kendall Bay is located 10 km west of Sydney’s Central Business District. In this area, a gasworks facility operated between 1886 and the 1980s. As a result, the shore was contaminated with harmful organic compounds in the sediments. These sediments were black and oily and had a strong tar, hydrocarbon, or naphthalene odour that is characteristic of gasworks contamination. Levels of polycyclic aromatic hydrocarbons (PAHs) and petroleum hydrocarbons (TRHs) were greatly in excess of sediment quality guidelines. This highly contaminated sediment was present to a maximum depth of more than 4 m in the north- west area of the bay, where the coal and coke wharves were located and to a maximum depth of almost 8 m in parts of the south end of the bay, where a former stream had cut into the sandstone bedrock.
The New South Wales Environment Protection Authority (NSW-EPA) issued a declaration of remediation for significantly contaminated area adjacent to the former gasworks facility. It was determined that remediation was required where the sediments contained total PAH concentrations on average of more than 25 mg/kg and maximum above 60 mg/kg (normalised to 1 % total organic carbon) and TRH concentrations on average of more than 4000 mg/kg and maximum above 5500 mg/kg.
Site Investigation showed that these thresholds were exceeded at various points: Accessible foreshore areas and the western end of the mangrove area had total PAH concentrations greater than 1 mg/kg; The rest of the mangrove area had total PAH concentrations greater than 120 mg/kg; and wading areas had total PAH concentrations greater than 60 mg/kg. The challenges associated with remediating the riverbed contaminants are complex and required an innovative solution not used before in Australia. The remediation method approved by the Site Auditor and NSW-EPA included in-situ stabilisation, an activated-carbon geocomposite and capping layer. To address any potential low-level dissolved phase impacts that could leach out of the ISS layer, Tektoseal Active AC – HUESKER’s geocomposite with activated carbon was installed above an in-situ stabilisation layer. Protective measures were installed prior to commencing the works to preserve the marine environment, including silt curtains and sheet piles. To prepare the waterbed for the capping, larger debris and other materials that could damage the geosynthetic mat- tress were removed. After the close and heedful work with designers and relevant authorities, the selected active geocomposite for this project was Tektoseal Active AC 3400. It consists of 3400 g/m² of activated carbon, which was tailored, following the specific requirements of the site. This way, optimal absorption of contaminants is ensured for several decades. Tektoseal Active AC 3400 was attached to the shoreline and unrolled of a barge while assisted by divers. The contractor also used a frame to sink the geocomposite and ensure controlled ballasting with cobble and sand. This thin cobble and sand layer was installed above Tektoseal Active AC to provide mechanical protection to the geocomposite and provide a surface for benthic recolonisation. The full-scale remediation works was successfully completed between Sept 2019 and October 2020.
With many industrial factories located on waterbodies surroundings, subaqueous sediment capping is a great solution to reduce the impact on local community by treating underwater contaminants in place.
Capping remediation are faster to implement and quickly reduces exposure and related risks, e.g. compared with dredging.
Tektoseal range can be used to contain and remediate a wide variety of dissolved-phase contaminants type, including NAPLs and PFAS.
Capping remediation with Tektoseal allows a clean solution and environmentally friendly alternative, reducing disruptions to the environment.
Project: Kendall Bay Sediment Remediation
Location: Sydney – Australia
Client: Jemena Limited
Design: Geosyntec Consultants Global Inc. and JK Geotechnics
Main Contractor: Ventia Utility Services Pty Ltd Tektoseal
Installation: Polaris Marine Pty Ltd Construction
Period: July – August 2020
Product: Tektoseal Active AC 3400