Kokopu School Wastewater Upgrade

In April 2021, project managers Avail Pacific asked WaterFlow to inspect the school's drainage as part of a 10-year maintenance plan. WaterFlow's Ken Hoyle, who led the project, walked the site with the caretaker, checked every downpipe, gully and vent, and mapped everything we could find.

What we found was a system that had grown up one addition at a time:

• A septic tank hidden under a deck between a toilet block and the pool changing rooms. Poor venting meant a persistent bad smell right where children walk past every day.

• A second old septic tank that appeared to sit under the court area.

• Old earthenware pipes letting in groundwater and tree roots, with the risk of wastewater leaking into the ground.

• A collapsed culvert under the driveway, and stormwater cesspits that were no longer working.

• A drain nobody could trace. As our report put it, we had no idea what it was connected to.

We started with a full site assessment, beginning with the ground itself. Bore hole testing showed Class 5 soil (sandy clay, light clay and silty clay), which drains moderately to slowly. That ruled out a simple soakage solution and shaped every decision that followed.

The school also has no town water. Everything comes from rain collected off the roofs, so protecting the land and groundwater around the school mattered even more.

Working alongside the school's engineers, LDE, we designed:

• An EconoTreat twin secondary treatment system with pumped discharge, sized for 250 staff and students and a design flow of 7,500 litres a day.

• A 2,500 m² disposal field of pressure-compensating dripline (PCDI), laid on the surface and split into four zones by an indexing valve. Each zone gets a rest between doses, so the slow-draining clay can absorb treated water evenly.

• Telemetry monitoring, so the system can be checked remotely and issues flagged before anyone on site notices a thing.

The design was approved under a building consent from Whangārei District Council in July 2024.

The treatment system had to fit into a strip of about 17 by 7 metres at the front of the school, beside Kokopu Road. The rest of the site was already being reshaped for new car parks, stormwater drains and three 25,000-litre rainwater tanks as part of a wider redevelopment.

Timing was just as tight. The work had to happen while the school was empty, so the team planned a start on 16 December 2024, three days after the school closed for summer.

At an on-site planning meeting with civil contractors United Civil, the WaterFlow team agreed a few key moves:

• Measure first, install second. Before any tank went in, the team would trace all the pipework from the eastern toilet block to confirm exact pipe levels. Getting this right could also let the tanks sit higher, with less digging.

• Around 120 metres of new drainage, including a 70-metre run across the driveway.

• Keep the site clear. Spoil would go by dumper to the civil contractor's yard across the road, with installation materials stored there too, so the school grounds stayed tidy.

The system was commissioned on 15 January 2025, about a month after work began. Kokopu School now has a modern secondary treatment system built for its full roll of staff and students.

• The smell is gone. The new system sits neatly out of the way near the road, with no odour at all. The old septic tank under the deck has been decommissoned.

• Cleaner water, protected land. Wastewater is now treated to a secondary standard, then dosed across four zones of a 2,500 m² dripline field in turn. That protects the soil and groundwater around a school that relies on rainwater.

• Zero lost school days. All the work happened over the summer holidays, and the system was running before Term 1.

• Looked after for the long term. WaterFlow services the system every six months under a contract running to January 2028. Telemetry monitoring lets problems be picked up early, and the tanks carry a 15-year warranty.