Natural water treatment for DWS compliance and water quality improvement - Groundwater source engineering investigations for two NZ aquifiers

Many New Zealand water suppliers are facing significant financial burdens to achieve compliance with NZ Drinking Water Standards (DWS). This paper presents studies that URS New Zealand Ltd has undertaken for Central Otago District Council in Alexandra and the NZ Defence Force in Woodbourne, to seek alternatives to high cost treatment plants.

The studies demonstrate the use of groundwater science to investigate the causes of water quality issues, and how the treatment properties of the ground can potentially be optimised by understanding and capitalising on these natural systems.

UV filtration offers a cost effective means to achieve 3 log credits under the DWS, which is sufficient to meet the protozoal compliance requirements for some water sources. These credits are only applicable, however, if turbidity remains below the prescribed limits. Higher turbidity can mean filtration plant is required, with significant cost implications. The source and transport of suspended particles were investigated at both study sites, and conclusions drawn on how the water supplies could be engineered to achieve low turbidity sources.

Hardness is a significant source of dissatisfaction for the Alexandra town water supply. The cause of hardness was investigation, and groundwater source engineering options put forward for development of a low hardness supply.