Frequently Asked Questions

Yes. Council has stopped the practice of recycling Clean In Place (CIP) waste back into the treatment process at the Milton Water Treatment Plant (WTP) to address concerns raised by the regulator, Taumata Arowai.

Taumata Arowai (New Zealand drinking water regulator) served a Compliance Order on Council on Friday 24 November for the Milton drinking water supply, following a review of Milton’s drinking water safety plan (DWSP).

The Compliance Order identified several non-compliant issues including insufficient monitoring and record keeping and the practice of recycling the supply’s waste stream back into the treatment process without appropriate controls.

The compliance order is issued under section 120 of the Water Services Act 2021 and details the reason for the order, requirements of the order, directions or conditions relating to the order and requires actions to be taken by certain timeframes.

In summary, the compliance order requires the Council to:

• Install appropriate monitoring infrastructure.
• Keep and maintain accurate records of monitoring data.
• Amend and implement the supply’s DWSP.
• Identify all necessary infrastructure upgrades, including for recycling waste streams.

Actions have been identified in conjunction with Taumata Arowai and a plan is in place that is being implemented.

These actions include:

• Ceased the practice of recycling waste stream including CIP waste at the treatment plant to address concerns that it could compromise Milton’s drinking water.
• Install specialised monitoring equipment to monitor the recycled waste. This has been ordered and expected to arrive for installation in January 2024.
• Install, commission, and operate a second chlorine analyser at a different location in the plant. This has been ordered and expected to arrive for installation in January 2024.
• Develop and implement systems to keep and maintain accurate records in accordance with the Water Services Act 2021. This work is ongoing.
• Ensure staff are trained and competent in the operation of the Milton drinking water supply to the reasonable satisfaction of Taumata Arowai. This work is ongoing.

No, taste issues can be seasonal and result from overall changes in the source water.

No, traces of the CIP chemicals in the water supply have been well below the required levels.

Yes, the backwash water from the filtration process must be monitored for turbidity and instantaneous flow (in place). But there were shortcomings that will be addressed, in particular the monitoring of turbidity. Taumata Arowai have indicated that current monitoring does not demonstrate full compliance.

A turbidity meter to monitor the backwash recycle water has been ordered and will be commissioned at the WTP after its arrival in January 2024.

CIP is commonly referred to as a Clean in Place backwash. It involves using acid and alkali chemicals, most commonly citric and sulphuric acid along with sodium hypochlorite and caustic soda to clean some equipment used within the treatment process.

Typically, these backwashes are carried out every few days however may need to occur more frequently depending on a range of factors including the age of the membrane units, the build-up of foulants, performance, and the quality of incoming water. In between these cleaning cycles additional backwashes using water only can occur several times a day. Return of these backwashes to the plant is considered to be appropriate.

Yes, the CIP backwash was designed to be recycled into the water supply and is our only plant that was doing it.

The practice of recycling CIP waste back into the treatment process has ceased as of 10am 30 November 2023 at the Milton Water Treatment Plant. The waste is being stored in an onsite tank for transport and disposal.

To manage the process going forward it is proposed to install an additional 25cuM3 tank and divert the CIP backwash waste stream directly into the tanks from where it will be transported off site for disposal most likely at either Milton or Balclutha wastewater treatment plants.

Yes, the plant was originally designed to recycle the CIP backwash.

The recycled back wash was part of an approved and acceptable standard when the plant was designed and built in the 2007.

During low flow periods in the Tokomairiro River, the Milton water treatment plant also relied on the recycled flow to provide a buffer.

The first deadline is in January regarding installation of monitoring equipment for the backflow water and an additional chlorine analyser.

Treatment plants use chemicals to remove actual or potential contaminants and ensure water is safe to drink. The treatment processes are designed to provide water with much lower concentrations of these chemical elements as per the drinking water standards.

Under the Water Services Act 2021 Taumata Arowai has been tasked to review one treatment plant’s drinking water safety plan for each supplier in New Zealand, before moving to the next treatment plant.

Milton was chosen for audit review because of its previous issues with water including colour and supply.

Taumata Arowai conducted a site visit and talked to Council staff, reviewed sample, and SCADA data all of which helped form the list of recommended improvements. An action plan was developed by Council staff and submitted to Taumata Arowai. This is regularly updated and reported on.