Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Sources of nutrient contamination in groundwater at Recycled Water Plants and implications for management (399)

Kate Dowsley 1 , William Rajendram 2 , Luke Hateley 2
  1. Jacobs, Melbourne, VIC, Australia
  2. Western Water, Sunbury, VIC, Australia

EPA licences for operation of recycled water plants (RWPs) often require that no change in groundwater quality occurs as a result of RWP operation. However, nutrient contamination of groundwater at RWPs is ubiquitous. The non-compliance with EPA licences leads RWP operators to explore methods of reducing groundwater contamination that often includes significant capital expenditure for limited, or uncertain, reductions in contamination. This study characterised nutrient contamination in groundwater at seven RWPs, aiming to find more appropriate and cost-effective approaches to managing and remediating groundwater contamination. It also explored the management tools available to the EPA to manage remaining contamination and reduce expenditure on remediation.

Conceptual modelling and analytical modelling was used to develop a detailed understanding of background groundwater quality, and likely contaminant transport pathways for nutrients. Data availability meant it was difficult to distinguish between two key nutrient sources: lagoon leakage, and on-site irrigation. Lagoons liners were mostly constructed to industry standards, which would impose a delay of several decades between lagoon leakage and groundwater contamination. Nevertheless, nutrient contamination had occurred. Conversely, irrigation occurs with little regulation and no constructed liner to prevent infiltration to the subsurface. The likelihood of irrigation being a significant source of nutrient is therefore high.

 A holistic conceptualisation of the sites and surrounding catchments put the risks from groundwater contamination into perspective, and suggested that as risks were low, significant investment in actions of unknown effectiveness (such as relining lagoons) was not warranted. Instead, a remediation program was designed that focused on a series of cost efficient measures. These included adoption of policy measures such as attenuation zones, different interpretations of licenced discharge points, and review of irrigation efficiency.

The results present a alternative approach to managing contamination issues at RWPs, which combines policy measures, an improved understanding of the water balance, and tweaks to irrigation practices. The approach shows how policy tools and engineering measures can be used in conjunction to help operators achieve their goal of keeping water prices low for their customers.