Official Information Request - 7 December 2018

Sent: Friday, 21 December 2018 1:27 p.m.

Subject: TRIM: Official Information request - Mamaku water supply

I refer to your online Official Information request of 7 December 2018 for the following information regarding the Mamaku water supply:

• A breakdown of the costs re the million dollar water treatment upgrades in Mamaku eg cost of purchase of UV treatment and installation breakdown etc.
• Cost of new pump and reasons for need to replace previous pump and life expectancy of the pumps.
• Costs and breakdown of the other filtration methods installed.
• The reasons for replacing the pump and the new water monitoring system installed.
• Information regarding the use and management of the original bore.
• Information regarding the use and management of the second deeper bore.

Background

In a community water supply, three aspects of a water source are most important: adequate quality, adequate quantity (including for peak consumption and forecast growth), and resilience to ensure continuity of supply in the event of problems from natural causes, or equipment breakdown.

The Mamaku water supply operates in a similar manner to most of the other Rotorua Lakes Council supplies, in that water is taken from the source, treated and pumped to storage reservoirs before being piped to the distribution network. In all other Rotorua Lakes Council supplies, water is available at the ground surface (springs, Lake Rotorua) and there are nearby hills to put reservoirs on which provides gravity pressure throughout the distribution network. As Mamaku is located on an elevated flat plateau, water must be pumped to the surface from drilled bores, and also pumped from the storage tanks through the network to provide pressure and flow for the community, including fire fighting.

When the original supply was built in 1987, there was one bore with a pump approximately 90 metres deep, one reservoir of 220,000 litres capacity, a chlorination treatment system and a set of pumps for the network, including enough capacity to provide fire fighting flow for hydrants.

Over time, Council added a standby generator to maintain network flow during power cuts and another reservoir of 110,000 litres.

Around 2006, it became apparent that the aquifer (underground water body) that is the source for the original bore, was diminishing in capacity and was unable to supply enough water for the peak summer demand. After several years of investigations, a new bore and pump was installed into a deeper aquifer (approximately 270 metres deep) in 2011. This aquifer has a very good capacity and stable quality.

Around 2015, in response to changes to the Health Act regarding public water supply compliance requirements, Council undertook a year-long intensive sampling programme of the source water to test for the presence of bacteria. This programme found that the shallow bore was subject to occasional bacterial contamination and therefore it required additional treatment in order for the water supply to fully meet the Drinking Water Standards for New Zealand. Cartridge filtration and ultraviolet light was chosen as the most appropriate treatment methods and this was installed in late 2018 and is now operational.

These treatment systems are required to have comprehensive automatic 24/7 monitoring systems to ensure and record that they are operating correctly at all times, and to send out alarms if there is a problem.

Replacement of Infrastructure, including pumps

The new treatment processes impose additional energy requirements and operating pressures and so the standby generator was replaced with a larger unit and the bore pump was replaced with one capable of providing a higher pressure to the treatment system.

The existing network pumps within the pump/treatment building were also at the end of their economic lives and so were replaced in conjunction with the treatment upgrade. The expected life of this type of water pump is 30 years.

Use and Management

The bore pumps are operated one at a time, as often and as long as is required to keep the reservoirs full or near full all of the time. The reservoirs hold approximately one day's water needs.

The management plan for the bores is to use them alternately, but to favour the use of the shallow bore as this costs less in energy costs to raise the water from a shallower depth. In peak demand times when the shallow bore cannot keep up, the deep bore can be run to "top up" the reservoirs.

If there is a problem with one of the bores or bore pumps, the other one can be used until the failed one is fixed.

The network pumps (including fire pump) operate automatically 24/7 maintaining the correct pressure in the network to supply treated water to consumers.

Cost of Mamaku water treatment and pump station upgrades

(Information based on the tendered construction contract price plus actual expenditure for the generator supply and design/supervision costs.)

As per the Act, we are obliged to advise that you may contact the Ombudsman at the address below if you have any concerns with the response provided by Council, by writing to:

The Office of the Ombudsman

PO Box 10 152

WELLINGTON 6143

Alternatively, you may email info@ombudsman.parliament.nz or use the online complaints form available at www.ombudsman.parliament.nz/make-a-complaint.

Regards