AS results from the water quality monitoring program for the inner harbour deepening project were released, a marine biologist warned surface dumping of dredged silt at North Fremantle was creating a two-million tonne “time bomb” on local beaches.
Marine biologist Jean-Paul Orsini was “horrified” to learn last week about the Fremantle Port Authority (FPA) pumping silt over a seawall to create 27ha of land in a new Rous Head basin.
“With 2.1 million cubic metres (of silt) set to be spilled out, that’s about two million tonnes of water that is going to be displaced and will flow to the sea,” he said.
“Councils with coasts from Port to North Cottesloe beaches may have a duty of care to put signs up warning people of toxins in their sand and water.”
However, a spokesman for the FPA said the dredged sand was being pumped into an area that was fully enclosed by a seawall lined by geofabric.
“It is normal practice for the discharge pipe to be positioned above the water line so the sand settles in a uniform way,” he said.
Environmental Protection Authority (EPA) chairman Paul Vogel said the FPA had monitoring criteria and if a parameter was above the trigger level, the FPA was required to implement contingency management measures and notify the office of the EPA.
The FPA released the first results from the monitoring program for January 7 on Friday.
The results related to physical water quality parameters, which include temperature, salinity, pH, turbidity, LOI, secchi depth, total suspended solids and dissolved oxygen.
Of the eight parameters tested at four locations, one parameter exceeded the applicable guideline at one location, although the other water quality measures were within the guidelines. The secchi depth trigger level of 1.6 metres was not met at Preston Point Beach.
A representative for the FPA said secchi depth was a measure of visibility within the water column, and reductions were to be expected when a plume was present.
Fremantle MLA Adele Carles said she was seriously concerned about the dredging, especially with children swimming in the waters.
“Within one week the plumes have moved twice as far up the river as the EPA had predicted as a worst-case scenario,” she said.
Ms Carles said the public would be the last to know if the pollution levels exceed the conditions laid down by the EPA.