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Infiltration and Inflow Reduction

Infiltration and Inflow (I&I)

Council is planning to take a pro-active approach to the management of Infiltration and Inflow (I&I) within our wastewater network.

Inflow and infiltration refers to rain water and ground water that enters the sewer (wastewater) system. 

As part of our Asset Management Plans, Council is setting aside funds to undertake I&I studies, and subsequently target rectifying defects found to reduce the amount of unnecessary stormwater and groundwater the wastewater plants have to treat as well as reducing the amount of rain water and ground water entering the sewer system on private property to limit overflows.

What is Inflow?

Inflow is stormwater that enters directly into the sewer (wastewater) system. The cause is low gully traps, illegal downpipe connections to the sewer, cracked or damaged pipes.

What is Infiltration?

Infiltration is stormwater that seeps into the ground and enters the sewer system through pipes and connections.  The cause is connection defects, cracks and joints in the pipes.

Problems caused by inflow and infiltration..

During heavy rain, the sewer network starts to fill with stormwater as a result of inflow and infiltration. Excess water in the sewerage system can cause it to back up and overflow sewage into homes and the environment.

The first area to study is Otane - planned for Mid 2019, click the drop down link below for greater detail.

II explained

 The following Water NZ guide on Infiltration and Inflow is the best practice guide for controlling I&I :

Update - 08 July 2019

CCTV and Visual Inspections are progressing well on the project.

800m of sewer mains and approx 60 laterals have been examined.

Greater progress with the visual inspections have been made, approx 75% of homes have been inspected to date.

Update - 10 June 2019

CCTV and Visual Inspections are progressing well on this project.

CCTV of mains have been completed in Rochfort Street and Henderson Street, covering approx 550 metres.

121 Visual Inspections have been completed to date - noting gully traps, ponding areas, and other areas for potential ingress into the sewer network.

The Map below from our digital visual inspection tool, shows the progress to date on the visual inspections;

10 June 19 Visual Inspection Progress Map
Update - 20 May 2019

Following letters drops to all affected properties, Drain Care has begun the CCTV of the Otane Waste Water Network.

This work is vital in identifying the unnecessary inflow and infiltration into the wastewater network.

Paul and the Drain care team will be in the area over the next couple of months inspecting infrastructure and the lateral connections from houses to the mains network.

As part of these CCTV inspections CHBDC will also be undertaking visual inspections around houses for compliance of gully traps and down pipes around the same times that CCTV is being completed as part of the overall Otane Infiltration and Inflow Study.

Update - 08 May 2019

A project flyer was delivered to all Otane households in early May 2019.

Council has engaged CCTV Operator - Draincare to undertake the work to CCTV all mains and laterals to understand the additional flows as outlined below.

Works is expected to start Mon 20th May 2019.

Update - 05 April 2019

Infiltration and Inflow

The purpose of this program is to manage and reduce inflow and infiltration (I&I) into the wastewater network to assist with compliance with the resource consent, free up capacity in the pipe network and assist with the development of CHBDC’s capital works programmes.

Council is currently finalising the scope of works for the I&I study to be commissioned in Otane.

Shortly home owners will receive a letter outlining the proposed works.

The wastewater network operated by CHBDC for the provision of wastewater services to the residents of Otane consists of the following assets:
 7.0 km of gravity wastewater mains
 1.9 km of service laterals
 270 wastewater connections
 83 wastewater manholes
 1 wastewater treatment plant

Otane WW network


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