Education day on avoiding pond failure

How to avoid effluent ponds leaking or even collapsing is the topic of an education day being run by Waikato Regional Council, along with Debbie Care of AgVice.

‘‘Such failures can cause pollution of waterways and groundwater, and mean that valuable nutrients are lost to farming systems,’’ council’s proactive monitoring manager Ross Wightman said.

‘‘Our education day at Putaruru will offer a lot of practical advice about how to avoid pond failures.’’

South Waikato pond failures will be discussed, as will the design considerations to take into account when constructing new effluent storage.

‘‘There are often no warning signs when an effluent pond fails but the risk of failure can be minimised if the pond has been constructed and maintained correctly,’’ Wightman said.

In the South Waikato, a pond failure occurred without warning in mid-2012. The pond was constructed in a friable rhyolite soil.

Effluent ‘’’tunnelled’’ through the pond wall and caused a significant discharge of effluent into water and contaminated a nearby water supply.

This pond failure highlights how farmers need to take special care when constructing holding facilities on rhyolite, Wightman said.

‘‘ Volcanic rhyolite soil can be found throughout the South Waikato and Taupo as a non-welded, gravelly and sandy pumice soil, or as a dense welded rock. Rhyolite soils are common in the Waikato through the Taupo volcanic zone that stretches from Mt Ruapehu to White Island,’’ he said.

‘‘ The risk of pond failure can be minimised during the design and construction phase by ensuring that the pond is constructed of an appropriate material, that it is lined correctly, and that the location is structurally stable.

‘‘Also, when constructing a new effluent pond or assessing an existing one, it is very important to undertake a thorough site investigation to assess the soil profile and slope stability.’’

The effluent education field day will run from 10.15am to 1.30pm on April 30 at Jack and Elizabeth Scheres’ property on 169 Leslie Rd, Putaruru, Fonterra supply number 77783. Tea, coffee and lunch provided.

For further information and to register for the education day call Katrina Daysh on 0800 800 401.

Not good: This is an example of what happens when ponds fail in areas with pumice soils. Here effluent has breached the pond wall and flowed overland to a stream near Tirau.