“Such failures can cause pollution of waterways and groundwater and mean that valuable nutrients are lost to farming systems,” council proactive monitoring manager Ross Wightman said.
The day at Putaruru, being run with Debbie Care of AgVice, would offer a lot of practical advice about how to avoid pond failures.
South Waikato pond failures and the design considerations to take into account when constructing new effluent storage will be discussed.
“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 South Waikato a pond failure occurred without warning in mid-2012. The pond was built in a friable rhyolite soil. Effluent tunnelled through the pond wall and caused a significant discharge 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.
“Volcanic rhyolite soil can be found throughout South Waikato and Taupo as a non-welded, gravelly and sandy pumice soil or as a dense welded rock. Rhyolite soils are common in Waikato through the Taupo volcanic zone that stretches from Mount 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 day runs from 10.15am to1.30pm at Jack and Elizabeth Scheres’ property on 169 Leslie Road, Putaruru, Fonterra, supply number 77783. Lunch provided.
