The parameters for identifying areas of environmental risk may include:
- land slope
- soil type
- erosion potential
- building density and property size
- groundwater levels
- groundwater recharge zones and/or groundwater protection zones
- proximity to waterways, including fresh water and the coastal environment
- sensitivity of the local environment
- flood hazard
- existing buffer zones or rules in regional plans relating to on-site systems.
The criteria for identifying hotspot areas may include:
- locations with a history of problems with on-site wastewater disposal, identified through sanitary surveys or pollution hotline complaints or monitoring
- areas identified in plans or strategies as locations for intensification of land use, long-term growth or development, where sewage reticulation may not parallel development
- communities with a high proportion of on-site systems that use shallow groundwater for drinking-water
- areas of highly seasonal occupation (relevant especially in attractive tourism spots) and not adequately designed on-site systems to cope with shock loads.
Councils could consider undertaking a broad-scale risk assessment utilising GIS assessment and spatial modelling that considers the range of factors listed above. The development of a risk model would require the selection of parameters appropriate to the specific region (eg, slope, soil types, section size), determination of hazard classes (eg, 10 per cent slope = low hazard), and the application of weightings to each parameter (eg, section size may be weighted as it is more critical to system performance than soil category). In addition, hotspot areas next to the areas of environmental risk need to be considered.
Stakeholder consultation could then be undertaken within these shortlisted areas to allow the council to make an informed decision on where the proposed standard would be appropriate.