Background

A water treatment project was carried out by a civil engineering company on behalf of the Water Corporation, Western Australia. The company based in Perth supply services to the construction industry, as well as the mining industry.

  • Their goal by involving PR Water’s water treatment solutions was to treat high pH concrete cutting wash water and dredge silt from behind the spillway of the reservoir at Big Brook Dam in Pemberton.

Objective

The reservoir at Big Brook Dam was constantly losing water as it was seeping through the porous material either side of the dam’s spillway and ultimately began to affect the watercourse that fed into a private fish farm as well as Pemberton’s main water supply.

To prevent an overflow of water from the dam during a storm event the project required the civil engineering company to cut down the existing spillway to allow the water to flow over it as opposed to around it.

  • The spillway was cut using a diamond wire saw which requires water to lubricate and wash away excess concrete fines. When the water mixes with the concrete fines there is potential for the pH of the water to reach 12.5 pH thus increasing the pH level with similar properties to bleach.
  • As part of the works the civil engineering company also had to refurbish the scour pipe at the base of the spillway which required divers to dredge in behind the spillway to expose the pipework.
    This dredged material had a high volume of suspended solids that could also have a detrimental effect on the watercourse in that flora and fauna would not have access to oxygenated water due to the suspended solids blocking vital UV rays and resulting in low oxygen levels.

Solution

The aim of the project was to re-condition this material to allow the reservoir to again become watertight. The project required the dam water level to be drawn down to allow for the porous material to be removed.

  • PR Water supplied their Siltbuster HB60 units along with their chemical dosing system to treat the high pH concrete washings and the dredged silty material. To do this they first utilised a pH correction system that dosed a strong acid proportionally to pH to bring the levels down from 12.5pH to 7pH which was the background pH level for the water in the dam.
  • The fine material from the concrete cuttings also was able to settle out in the HB60 to allow clear neutral pH water to be discharged safely back into the watercourse. They then altered the system to treat the dredged material from behind the spillway using two stages of chemical treatment. The chemicals used were a coagulant and a flocculant to help agglomerate the fines and encourage settlement in the HB60 unit.
  • All this treatment (pH, NTU and Flow) was recorded using our remote access monitoring system to allow for any problems to be identified and resolved quickly with the treatment.

The result was clean, clear pH neutral water to be discharged to the watercourse and the waste sludge to be collected in the HB60 hoppers for disposal later.

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