Kaipara District Council staff are asking Mangawhai house owners and residents on the wastewater system to flush water through their drains, toilets and showers and prevent gases from backing up into their homes.

Recent monitoring at pumpstations has detected elevated levels of hydrogen sulphide in the pipes coming from houses and the wastewater network. Hydrogen sulphide is the key odour contaminant from wastewater systems – in low concentrations it has the distinctive smell of rotten eggs.

While elevated levels of the gas in the wastewater system is not unusual, it has triggered Council staff to ask residents, and in particular bach owners, to run water through their systems and make sure their p-traps are working as they should.

“If you have been away for a while and smell odour, we ask that you open up windows and doors when you arrive, and do a quick run of all your taps, showers, baths, flush the toilets, anything with a drain that connects to the system,” says Anin Nama, Acting General Manager for Infrastructure Services.

“Same applies if you have a bathroom or laundry that hasn’t been used for a while. We’re asking people to talk to their neighbours so everyone gets the message. Running water (just for a short time) ensures your p-trap is full of water and performing its function as an airtight seal, blocking any gases from backing up into your house.”

The p-trap is the u-bend part of the pipe found under sinks, showers, baths and laundry tubs. A p-trap is designed to always hold a small amount of water in the bend of the pipe, creating an seal or plug which prevents foul odours and gas from entering homes. Toilets have an s-bend which act in a similar way. Each time water is run, toilets are flushed, showers flow, the p-trap is filled with new water.

Showers tend to have a p-trap that hold less water making them more prone to evaporation if they haven’t been used in some time. A leaking pipe can also cause a p-trap to empty. A build-up of debris in the p-traps can break the airtight seal, allowing gas from the system to filter through.

Mr Nama believes the elevated levels are due in part to some house connections not being used often, causing wastewater to stagnate in some pipes and release hydrogen sulphide as it breaks down. Breathing high levels of hydrogen sulphide in confined spaces can be fatal.

“We’re keen that people know how important a functioning p-trap is so they can take their own preventative measures,” says Mr Nama, “we’re keeping a close eye on the hydrogen sulphide levels and are taking necessary actions to reduce the gas to an acceptable level.”

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