Stormwater Tank Damage

Newstead QLD

As a part of a major development project in Brisbane in 2008, the site developer proposed a stormwater harvesting system with underground storage, to irrigate the proposed parkland.  Subsequently, Rocla Water Quality proposed that the underground tank should consist of large [1,800 mm diameter] Plastream Composite pipes due to the aggressive nature of the groundwater and the need to ensure a long design life of the tanks.  The installation was later constructed under engineering and geotechnical review;  in late 2009, the underground tanks were successfully hydrostatically tested.

In December 2009 saline water from the nearby Brisbane River was noted in the tanks;  later in 2010 additional cracking and deformation of the tanks was observed.  Subsequently, and because of further deformation / movement, the stormwater tanks were filled with an inert filler in April 2012, and the stormwater harvesting system decommissioned.

During the ensuing litigation against the contractor and engineer, Rocla Water Quality was joined to the proceedings, with allegations being made that:

  1. The Plastream pipes were not fit for purpose, and not strong enough.
  2. The joints between the Plastream pipes had been faultily made.

Consequently, and because of SCE’s extensive experience with underground plastic structures and knowledge of geosynthetics, SCE were engaged to advise on the most probable cause of the damage and leakage to the tanks, as well as conducting an extensive review of the site construction processes and adopted methodology for installation of the tanks.  Subsequently, and because the resulting SCE report and review determined that:

  • the actual installation was not in accordance with requirements of the Rocla Water Quality technical manual and associated Australian Standards;
  • the engineering design of the excavation and adopted methodology for tank installation placed excessive & unbalanced loads on the Plastream composite pipes;

SCE concluded that the cause of the tank deformations and leakage was faulty construction practices, allied with incorrect engineering and geotechnical advice.

Subsequently, and shortly after the detailed SCE report was submitted, the litigation against Rocla Water Quality ceased.