Poster Presentation Australasian Groundwater Conference 2017

Combining Quantitative Microbial Risk Assessment and groundwater modelling to investigate the risks of treated wastewater discharges to shellfish and bathers. (#63)

Brian G Barnett 1 , Dan Deere 2 , Steve McAleer 3
  1. Jacobs, Melbourne, Victoria, Australia
  2. Water Futures, Sydney, New South Wales, Australia
  3. Hunter Water Corporation, Newcastle, New South Wales, Australia

The Tanilba Bay Wastewater Treatment Plant discharges secondary treated and UV disinfected effluent via infiltration to shallow groundwater that flows to a nearby estuary of high value to the community for recreation and as an active oyster harvesting area.

MODFLOW groundwater modelling with analytical solute transport modelling and a Quantitative Microbial Risk Assessment (QMRA) were used to determine whether discharge to infiltration ponds is a safe disposal method in a highly sensitive receiving environment.

The MODFLOW numerical model determined particle residence times and pathways, which was coupled with a solute transport model to determine virus concentrations with distance using initial pathogens concentrations and biphasic decay.

Results were assessed using QMRA and compared to acceptable risk targets from the NHMRC Guidelines for Managing Risks in Recreational Water and using risk assessment models from drafts of the Australian Guidelines for Water Recycling and Australian Drinking Water Guidelines (in preparation). For the most exposed and at-risk cohort, children, the guidelines specify 0.6 viruses/L for less than 1% additional risk of gastrointestinal illness per person per event of recreational water activity.

For shellfish there is no agreed acceptable risk target, however the additional risk of gastrointestinal illness was quantified and compared to both a 1% additional risk of illness per person per meal criteria, as well as the 1 micro disability adjusted life year (mDALY) target as set out in the drinking water and recycled water guidelines (i.e.<1).

Conservative estimates of pathogen concentrations at the estuary boundary were 0.08 virus/L, more than seven-fold below the guidelines for primary recreation. With dilution in the estuary, final pathogen concentrations at the oyster leases was 0.0008 virus/L, representing a 0.14% increased risk of illness or an additional 0.7 mDALY.

Since the assessment was conservative it was therefore determined that acceptable risk benchmarks had not been reasonably foreseeable exceeded.

  • We are offering awards for Career and Early Career presentations and posters. Please indicate length of time since highest degree completed.: 0 to 5 Years or currently studying