Queensland’s Mt Crosby Water Treatment Plant treats 60% of the water servicing the greater Brisbane region. The plant processes water from the adjacent Brisbane River. Mt Crosby Water Treatment plant consists of; Mt Crosby West Bank WTP and Mt Crosby East Bank WTP. The East Bank WTP is the largest treatment plant owned and operated by Seqwater.
The plant has 20 sand filters. Seqwater required 12 filter inlet gates to be replaced as they had reached the end of their useful life. These were the original inlet gates installed from 1945 and were leaking significantly. The specific requirement for this project was that the new penstocks had to be supplied without any leakage.
Seqwater will use the new penstocks as a positive isolation for their upcoming filter upgrade project for which a completely dry filter cell is required. The new inlet penstocks were installed within existing filter boxes, and affixed to existing concrete walls. All equipment supplied was purpose built, suitable for the specified operating conditions and constructed for a minimum design life of 25 years.
Installation of the new filter inlet penstocks required the settled water channel to be isolated and drained, a process that results in a 60% reduction in plant capacity which was considered a high risk activity with the threat of not being able to meet the water demand. Construction was therefore planned for the replacement for all 12 inlet penstocks at the same time. Several installation crews were required, working simultaneously, 24hr /day.
All penstocks were installed within Seqwater’s potable water infrastructure. The work site and all equipment in contact with potable water, was to be kept clean and disinfected at all times. Numerous mitigations were in place to avoid contamination of WTP assets and/or treated water during the delivery of this project. All construction and cleaning materials used were not to impact on water quality, required an AS/NZ 4020 certification and was subjected to an audited system of quality control.
The penstocks are downwards closing AWMA WLF-SS-R wedge penstocks manufactured from grade 316 stainless steel. All penstocks were free from visible leaks, delivering a 100% drip tight seal. All welds were pickled and passivated to ASTM A380. All penstocks have a 780mm square opening, rising spindles and are fitted with electric (open/close) actuators.
The penstocks underwent Factory Acceptance Testing, including hydrostatic and seal performance testing, with a certificate of compliance provided for each gate. Further testing and inspection processes ensured full compliance in regards to sustained penstock quality during sustained operation.