Keeping waters apart - New separation distance guidelines for onsite wastewater systems and wells

The discharge of domestic wastewater to ground and the proximate abstraction of groundwater for domestic purposes can contaminate drinking water. Adequate separation distances between these two activities can reduce the likelihood of well-water contamination. However, none of the existing separation distances used by regional councils are designed to protect against the most infectious pathogens, viruses. The environmental robustness of these organisms means that they may still be viable, and therefore infectious, after travelling substantial distances through the ground. Moreover, present separation distances do not take account of how differing subsurface materials affect contaminant transport. To address these shortcomings, a two-year, Envirolink-funded project developed scientifically defensible separation distance guidelines, based on virus transport through various combinations of hydrogeological settings and using Monte Carlo techniques to take account of uncertainties in the input data. The Guidelines document, with a full technical discussion, is now complete and available on the Envirolink website (http://www.envirolink.govt.nz/Envirolink-reports/). This paper briefly describes the guidelines, outlining the approach taken to the modelling and its limitations, and explains the use of the Guidelines.