Access to wastewater reticulation

Household units with access to wastewater reticulation services  

Purpose of indicator

Reticulation and treatment of wastewater improves freshwater quality by removing nutrients and faecal bacteria better than individual septic tanks. Groundwater, streams and lakes can be contaminated with sewage from septic tanks directly entering into or seeping through shallow soils into these water bodies. Reticulation of wastewater, from lakeside communities in particular, reduces the risk of lake water contamination.

Current information and trend

Public wastewater reticulation of the urban settlement on the southern shore of Lake Rotorua has been in operation since 1971. Reticulation was implemented in response to public health risks due to the contamination of drinking water and surface water bodies from septic tanks.  In 1991 the council moved towards tertiary treatment of wastewater by spraying treated effluent into the Whakarewarewa forest.  Since 1991 Council has undertaken upgrades to the wastewater treatment plant, further reducing nutrients reaching the lake.

Lakeside settlements outside of this area have traditionally disposed of wastewater using individual septic tanks. These are not always effective, especially if they are not emptied and maintained regularly. Council, with support and funding from Ministry of Health and Ministry for the Environment, is implementing a number of lakeside settlement wastewater reticulation schemes. Figure 1 shows each stage including number of households to be provided access to reticulation and amount of estimated nutrients being diverted from direct input to lakes, streams and groundwater.

While public reticulation and land treatment of wastewater and effluent is effective, some nutrients are still present in treated wastewater and will enter streams and lakes of that catchment. This is estimated to be approximately 10% of the content of raw untreated wastewater.

Through the reticulation schemes an additional 1652 household units have access to wastewater reticulation in 2012, building on the base number of 27,000 households within the urban Lake Rotorua area on its southern shore. A further 703 are yet to be provided access, totalling an additional 2355 households by 2015.

A new wastewater treatment plant is proposed to service the southern Rotoiti and Rotoma lakeside communities.  The wastewater treatment plant will be a membrane bioreactor, capable of removing over 85% of nitrogen and 100% of the bacterial pathogens in the wastewater.  The treated wastewater will be disposed to land using rapid infiltration trenches allowing 100% removal of phosphorus through adsorption by the soil.  It is estimated the wastewater treatment plant will remove over 10 tonnes of nitrogen and 3.3 tonnes of phosphorus from the Rotoiti and Rotoma catchments per year.  

Figure 1. Wastewater reticulation works and cumulative tonnes of nutrients diverted from direct entry to lakes, streams and groundwater.
Source: Rotorua Lakes Council, 2011

In Summary

  • In 2012 almost 28,000 household units will have access to wastewater reticulation
  • By 2015 an additional 2355 households will have access to wastewater reticulation
  • By 2015 approximately 25.3 tonnes of nutrients (nitrogen and phosphorus) will be diverted from direct input to lakes, streams and groundwater
  • An additional treatment plant is to be constructed in 2013, in the Rotoma catchment.
Page reviewed: 20 Feb 2015 1:58pm