IMPACT OF THE LIMIT SETTING PROCESS ON STORMWATER DISCHARGES

The paper discusses the implications of the National Policy Statement for Freshwater Management 2014 (NPS-FM) for managers of stormwater assets.

The NPS-FM requires Regional Councils to establish water quality limits for all water bodies in consultation with their community, the “limit setting process”. As part of this process, the community decides what level of water quality they think is acceptable in each water body, from pristine, some impact, or just above national bottom line.

The paper identifies the critical impact of the level of water quality selected through the limit setting process in determining the numerical limits for water quality. These limits will become the water quality standards against which discharges, including stormwater, will be assessed and hence will influence the ability to gain Resource Consents for stormwater discharges.

In this paper the numerical limits in the NPS-FM are compared to guidelines commonly used in consent applications to show whether they represent a step change in required compliance. The numerical limits from limit setting processes already completed around the country are also assessed to indicate the numerical limits which could apply at other locations.

The paper then discusses the impact of the narrative (i.e. word based) values in the NPS-FM and their impact upon the assessment of toxicity and nutrient effects and the numerical limits that could result from their implementation.

Stormwater quality data is reviewed from a range of locations in both urban areas and rural townships. This data is used to determine expected level of compliance with potential limits after reasonable mixing for typical areas.

The impact of available management or treatment regimes for stormwater discharges on the affected parameters and whether they will achieve compliance with the potential limits is then discussed.