The Waiwhetu Stream in Lower Hutt has been subjected to industrial contamination over the last two decades and is prone to flooding during heavy rainfall. Greater Wellington Regional Council decided to take action to enhance the stream environment and reduce the flooding risk.

Brian Perry Civil was chosen as contractor on the project. The work involved:

• Excavating approximately 12,000 cu.m of contaminated sediment from the stream bed within working cells formed by sheetpiled coffer dams. 
• Widening and deepening the stream, including erosion protection works. Where neighbouring buildings inhibit widening parallel CFA secant walls were installed.
• Services into and across the stream were upgraded through rationalisation, realignment and duplication.
• Ecological enhancements to the area through planting native vegetation, wildlife features and wetlands.

The major challenges to the team on this project were: safely removing about 4,500 truck movements of contaminated sediment and sludge; working around a large number of live services and bridge structures; and working within very strict resource consent conditions.

Works Complete August 2010

The project was successfully completed in August 2010, with the following highlights:

• The project was completed on time, which is a remarkable achievement given the amount of heavy rainfall that occurred.
• Outstanding environmental control and protection was achieved. This was no mean feat as the project required moving over 4,000 truck loads of contaminated sediment and sludge.
• The project won the 2010 NZ Contractors’ Federation Hirepool Construction national award for projects of value between $5-20 million. The award recognises outstanding project management and construction methodologies, and also the protection of the environment throughout the work.
• This national award is also a great acknowledgement for all the hard work and planning that the guys on the ground put into the job through some very trying weather and ground conditions.
• A number of important Key Performance Indicators were met, including: 
            - Actual TRIFR (Total Recordable Injury Frequency Rate) of 14 vs target rate of 26

            - Zero adverse environmental impacts from our machinery and operations
            - No permanent construction defects, particularly on the BPC-designed secant piled walls with precast
               facing panels in the U channel.