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First to Field Mass Mixing In-Situ Stabilization/Solidification Remediation in Uncharted Waters of Kendall Bay
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Background/Objectives.

Once home to the largest manufactured gas plant (MGP) in the southern hemisphere, the former MGP site was remediated and developed for medium density residential use almost two decades ago. With an area of the shoreline declared a "Remediation Site" by NSW EPA, Jemena subsequently prepared a Voluntary Management Proposal for remediation of sediments within the adjacent Kendall Bay impacted with hydrocarbons (polycyclic aromatic hydrocarbons, total recoverable hydrocarbons, and BTEX) by former MGP operations. The adjacent residential land use presented challenges for developing a remedial approach that addressed the impacted sediments while minimizing impacts to adjacent residents. For this reason, in-situ stabilization/solidification (ISS) of impacted sediments and subsequent capping was selected as the preferred remedial approach for the site, rather than traditional dredging. This method allows management of nuisance odor and minimization of truck traffic. This presentation provides an overview of the technical and design approach to move this project from a laboratory bench-scale treatability study to full-scale field application in an expedited manner, and presents invaluable lessons learned in overcoming many unexpected technical challenges.

Approach/Activities.

A multi-stage laboratory treatability study was performed to identify the optimum mix design evaluating a range of cementitious reagent dosages, grout modifiers, and enhancers to achieve the performance criteria for the remedy. Following the treatability study, a two-phase pilot study was designed and implemented to assess the constructability, construction approach, and field verification of the remedy effectiveness. Based on the comprehensive site-specific data collected during laboratory treatability and field pilot studies, Geosyntec developed a tiered validation plan using a multiple lines of evidence framework to allow pass/fail determination within 2 to 7 days from field mixing and received regulatory approval. In addition, Geosyntec performed the detailed design of the full-scale remediation. The additional design elements consisted of quantitatively establishing a soft sediment buffer zone to mitigate excess surface water ingress to the mixing zone, and associated means and methods to reduce mixing energy. The full-scale ISS remediation was commenced in early 2020. Geosyntec oversaw the ISS works, provided on-site support to address unexpected challenges encountered in the field in real-time by collectively developing technical solutions to fine tune the ISS implementation and validation process to meet project schedule. Full-scale ISS remediation was completed in November 2020.

Results/Lessons Learned.

It is understood this project is the first field implementation of ISS remediation of subaqueous sediments using mass mixing techniques. Geosyntec and Ventia team demonstrated that ISS can be successfully implemented in subaqueous sediments, breaking new ground in the use of innovative sediment remediation technology. The project was completed two months ahead of schedule and under budget in the midst of COVID-19 restrictions and lock-downs. Upon completion, the project received numerous awards from Australasian Land and Groundwater Association, Australian Institute of Project Management, and Edison Awards in 2021.

Publication Summary

  • Geosyntec Authors: Dogus Meric, Chris Robb, Phil Hutson
  • All Authors: Dogus Meric, Chris Robb, Phil Hutson (Geosyntec Consultants, Inc., IL, USA), Jayson Gaul, Allan Garland, Matthew Clutterham, Nathan Sparke (Ventia Utility Services Pty. Ltd., Sydney, NSW, Australia)
  • Title: 2023 Battelle Sediments Conference
  • Event or Publication: Event
  • Practice Areas: Sediment assessment and remediation, Contaminated site assessment and clean up
  • Citation: Battelle's International Conference on the Remediation and Management of Contaminated Sediments at the JW Marriott in Austin, Texas, on January 9 through 12, 2023
  • Date: January 9 through 12, 2023
  • Location: JW Marriott in Austin, Texas
  • Publication Type: Platform Presentation