Up to 250,000 cubic metres of sand generated from tunnel boring on the Sydney Metro West project could be used to nourish Cronulla's eroded beaches.
Sutherland Shire Council is considering an offer from a Transport for NSW project team, with a decision on whether to embark on a detailed investigation of the proposal needed by July 1.
A council report said the Metro project would involve tunnelling through Sydney sandstone using tunnel boring machines, which would generate about 900,000 cubic metres of virgin sand.
"Sydney Metro West had advised that the extracted sand can be screened to generate a fine to medium grained sand fraction of less than five millimetre diameter, known as 'minus 5 mm', and a coarse sand to gravel fraction of greater than five millimetre diameter, known as 'plus 5 mm'," the report said.
"Each fraction would comprise approximately 450,000 cubic metres of material.
"The minus 5 mm material has been identified as suitable for beach nourishment.
"The plus 5 mm material is only considered suitable for depositing offshore, and may form a temporary offshore reef.
"The offshore depositing of the coarse sand is not being considered by council as there is low confidence in any associated social and environmental benefits."
The report said, based on preliminary investigations, Sydney Metro West had already identified beaches in several council areas, including Bate Bay, as the most feasible sites for the placement of sand for the purpose of beach nourishment.
"Sand would be screened at White Bay in Sydney Harbour and barged to the placement sites," the report said.
"Sand will be generated from TBM (tunnel boring machine) operations commencing December 2022."
The report said beach nourishment had been undertaken successfully at Cronulla, using marine sand dredged from the Port Hacking.
It is expected a large proportion, if not most, of the 60,000 cubic metres to be dredged from Port Hacking in 2021/22 in a project announced earlier this year will again be used to nourish Bate Bay beaches.
The report said the offer of further sand from tunnel boring - "potentially up to 250,000 cubic metres metres of minus five millimetre material" - was "considered to be a very cost-effective option given it would essentially be at no cost".
The report said the initial feasibility of beach nourishment was being assessed as part of the Bate Bay Coastal Management Program.
"Sydney Metro West wishes to enter into an agreement with Council in order to confirm Council's role as a proponent for the detailed feasibility assessment, design and approval of beach nourishment," the report said.
The offer will be considered by the Infrastructure Committee on Monday night, June 7, before it goes to the full council later in the month.