Performance of New Stormwater System at Fonterra Tirau

Fonterra has undertaken a program to significantly improve storm water management on a number of manufacturing sites in response to aging infrastructure, poor environmental performance, and rising expectations from stakeholders. A nationwide risk-based management approach has been recently developed to align stormwater projects, whereas in the past the approach varied between sites.

Tirau is one of the first large scale capital upgrades to be implemented, with construction and commissioning taking place in early and mid-2017. This provides an opportunity to review performance and adjust design criteria for current and future projects. The new system is separated from clean cooling water and comprises a 350 m3 first flush and spill containment tank with online monitoring and divert. Contaminated water is sent to wastewater treatment with the remainder discharged to a swale which discharges to the Oraka stream after further monitoring. No non-compliant discharges have been reported since commissioning, despite high rainfall and influent flows from some drainage areas with contamination. This compares with five stormwater non-compliances reported in the previous season.

This paper analyses monitoring data including suspended solids, total nitrogen, phosphorus, COD, conductivity, pH, and turbidity of the new system. The volume and composition of diverted stormwater streams is also considered. Options for optimising the current system are given, as well as improvements to the approach to future projects on other sites.