CLAYTON BAY - Work to remove the regulator at Clayton Bay will start in October, about a year after it was breached.
Department for Environment and Natural Resources (DENR) spokesperson Stephen Cox told The Times the first phase will be to excavate sand from the site by starting at the point where the regulator was breached in September last year, then work backwards towards Hindmarsh Island.
Mr Cox said the sand will be disposed of on private land on Hindmarsh Island.
"An agreement has been reached with a local landholder who has appropriate approvals in place, capacity and willingness to receive the material," he said.
As for the threat of acid-sulfate soils emerging, Mr Cox said the excavation works will seek to remove only 'clean fill' sand material that was imported during construction.
"A number of soil cores and chemical tests have been taken from the regulator over recent months. These tests have provided information about any changes to the chemical nature of the material and have helped to ascertain whether any treatment is required.
"As a precautionary measure, a section of the disposal site will be lined with lime and any material showing the characteristics of acid sulfate soils will be laid over this layer. During the removal and disposal project, regular soil testing will be undertaken to define the rate of lime dosing (treatment) needed. The treatment/dosing rate will be in line with EPA requirements and consistent with all approvals."
During the second phase, a cutter-suction style dredge or a more traditional excavator mounted on a barge will be used, depending on contractor equipment availability, the conditions at the site and experiences from the first phase.
"The site will most likely be operated from Hindmarsh Island. At this point, the actual 'over water' operational logisitics are under development and will be heavily influenced by the equipment used and the advice from the civil works contractor," Mr Cox said.
"It is not anticipated that any mixed material will be removed from the water; only 'clean fill' sand is targeted and, unlike phase one, only the material above the pre-construction bathymetry (the Goolwa Channel bed's original profile) is targeted for removal.
"The removed 'clean fill' sand material will be disposed of on private land on Hindmarsh Island in close vicinity to the regulator, under similar treatment conditions to those described above."
A DENR newsletter said if a third phase of removal is required, it will involve moving the sediment displaced by the temporary flow regulator (mud waves) into the void created during the first phase of removal.
Regular monitoring will be carried out to ensure there are no environmental or water quality issues, and excavation will stop immediately if any risks are detected.
The temporary flow regulator at Clayton Bay will be removed by June 2012, as agreed by the Australian Government.
DENR and the Department for Water are holding a public information session on Tuesday, September 20 to discuss timeframes and methods for the regulator.
It will be held at the Clayton Bay Community Hall and starts at 7.30pm.
To register your attendance and for further information contact Gemma Cunningham on 0427 018 783 or email gemma.cunningham@sa.gov.au
In April this year, an extension was sought by the Department of Environment and Natural Resources chief executive Allan Holmes to extend the date by which the regulator could be removed from May 6 this year, to June 30, 2012.
On April 14 The Times reported Mr Holmes said this was because "the original date was made at a time when future water availability could not be predicted, and the processes required to complete removal of the structures were not well understood."
The Clayton and Currency Creek regulators were completed in August and September 2009 respectively to combat the threat of acid sulfate soils because of low water levels in Lake Alexandrina and the Goolwa Channel.
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