Reducing wastewater overflows - Lessons learned in Hutt City

The Waiwhetu area of Hutt City is a residential area that is over 50 years old and sits on alluvial gravels that experience high fluctuating groundwater conditions in wet weather. The wastewater reticulation system is aged and until recently experienced significant infiltration that caused overflows of diluted wastewater to the Waiwhetu Stream. In 2004, the Council obtained resource consents that permitted wet weather overflows from two overflow structures to the Waiwhetu Stream for a period of 5 years.

Those consents required Council to implement an effective upgrading programme that would result in overflows being largely avoided in rainfall events up to a 5-year return period. In early 2010 Council was granted renewals to those consents for a period of 15 years as the programme had demonstrated a significant reduction in the frequency and duration of the overflows.