Point-source impact methodology - A new way to look at discharges

Quantifying the impact of point-source discharges on water quality is crucial for regulatory authorities who undertake the management of freshwaters. By knowing the point-source contribution of contaminants to rivers, the diffuse component can be calculated and appropriate resource management decisions can be made. In order to quantify the impact of point-source discharges on the environment a new methodology, the Point-source impact method, (PIM) has been developed. The aim of this methodology is to provide an instream, effectsbased classification of a discharge across all water quality parameters.

The PIM is a statistically driven classification tool that builds on work carried out by Horizons Regional Council. The PIM method provides an improvement on other methods for analysing point-source impact. The method does this by enabling both the permit holder and the regulatory authority to understand the impact of each discharge on the immediate downstream environment and determine the direct and cumulative impacts of diffuse contamination and other point-sources upstream of the discharge. The method is particularly useful in situations where a discharge may not demonstrate catchment-wide impacts but is causing a localised water quality problem. Additionally analysis using this method can aid the permit holder in prioritising upgrades required to the discharge treatment process to improve effluent quality.