Question:
The Environmental Management Plan states "Where PASS is identified and oxidation is likely to occur, material will be managed as ASS and treated accordingly (e.g. with

agricultural lime) prior to disposal to prevent the generation of acidic leachate. Traditionally where PASS is identified Chip Tray testing has been completed to corrobrate ANC and if this has not been completed, lime treatment is usually prescribed to mitigate the risk of PASS. Is the contractor required to include a nominal cost for undertaking lime injection/ treatment works?

Also the sediment has not been chacterised for disposal to landfill in accordance with NEPM HILs, PFAS NEPM, WRR Act, ERA60 or acid sulfate soil guidelines (i.e. Dear et al, 2024). Has Kelsey Creek Waste Facility said they will accept the material, despite it not being characterised as not regulated waste and are they willing to accept potential acid sulfate soils?

Answered on 15/Sep/2026 10:28 AM:


Any characterisation of the sediment at the boat ramp now is subject to change. Hence, the characterisation of the marine sediment will be undertaken following the dewatering period, and the sediment has been contained. These characterisation results will determine treatment and reuse options or disposal to Kelsey Creek Waste Facility as a last resort. However, tenderers are requested to price disposal (loading and transport only) to Kelsey Creek Waste Facility as a provisional item in the event this is required. Kelsey Creek Waste Facility are aware of the potential for the marine sediment to be disposed of at the facility, pending suitable characterisation results.

If treatment of the marine sediment is required prior to reuse or disposal, the Contractor may be asked to perform this and will be subject to a variation. However this can't be known until final characteristion of the dredged marine sediment is undertaken.

Tenderers are reminded that loading and transport of the marine sediment to Kelsey Creek Waste Facility is a provisional item.

Question:
Good morning,

Please can you confirm the SG of the material to be dredged?

What were the assumptions that were made regarding the height that the dewatering tubes can be pumped up to? Was the SG of the material taken into consideration? What is the factor of safety?

Is there additional available space at the dewatering area that can be used (either in the car park or the park itself) should a larger number or different lengths of dewatering tubes be required?

Does council have any specific requirement to utilise dewatering tubes with a 9m circumference? Is council open to tubes with a larger circumference?

Can the design of the dewatering area be adjusted to improve operational efficiency or provide cost savings?

What is the approved discharge point for the filtrate leaving the dewatering tubes?

Is there a limit on the duration of time between filling the tubes and emptying them? Is there a deadline for the return of the dewatering area following completion of the project?

Many thanks

Answered on 28/Sep/2026 01:41 PM:


1. The SG of the material is unknown, however the following assumptions have been made:

a. The target SG for the dredged material based on the marine silt characterisation the samples noting a combination of clayey silt material is 1900kg/m3.

b. The final in-situ consolidated volume target is 451m3

2. This will be determined on the type of tube adopted by the contractor and the method of pumping the slurry to be used, manufacturers recommendations, etc. It is expected that multiple fill-and-dewater passes will be required and therefore 3 tubes have been recommended to enable change over during dredging process. The height the tubes will be based on the type of tube adopted and the specific manufacturers recommendations to determine the safe maximum fill height (approx. 20% of the circumference)

3. Council is open to utilising additional space if required in the parkland area. Any additional space required to achieve your dewatering methodology will need to be outlined in the Tender response for approval. Remediation and make good arrangements would expand to the additional area requested. Use of the carpark for the dewatering tubes won’t be permitted, full availability/operation of the carpark must be maintained during the works.

4. Council has no specific requirement to utilise dewatering tubes with a 9m circumference. Council is open to tubes with a larger circumference. Tenders are to outline their proposed dewatering tubes and space requirement in the Tender response.

A particular type of tube or manufacturer has not been specified to provide flexibility to the contractor based on the contractor’s dredging methodology to be adopted and the availability of preferred tubes (or other dewatering systems), etc.

5. Yes, the design of the dewatering area can be adjusted to improve operation efficiently or provide cost savings. Please outline the benefits and cost savings etc., in your Tender submission.

6. The discharge point for the filtrate is the nearest point in the adjacent bay through the mangroves, utilising/adjusting the existing slope where possible (building up the tube benched area) to discharge the filtrate evenly without causing concentrated flows.

7. There is no limit on the duration of time between filling the tubes and emptying them. The timeframe would depend on the type of bag selected and weather conditions, or if a centrifuge system was proposed. Practical completion for Separable Portion 1 has been listed as TBC, as the dewatering period is unknown and Tenderers are welcome to nominate a reasonable time period for negotiation. However, we estimate a couple months for the dewatering period, and a subsequent couple weeks for dewatering pad remediation/restoration.