Is There Any Benefit for Enhanced Stormwater Treatment from Non-Forecourt Discharges?

In 1998, the Oil Industry Environment Working Group (OIEWG) finalised a set of “Environmental Guidelines for Water Discharges from Petroleum Industry Sites in New Zealand” (the Guidelines). These guidelines have been used as a means of compliance with permitted activity rules in some regional plans, but this is less common with newer plans. The OIEWG has initiated a review of the guidelines and determined a number of areas requiring further evaluation. Research has been conducted in these areas to assist with a revision of the Guidelines. Non-forecourt discharges are the focus of this paper.

Since January 2016, Pattle Delamore Partners (PDP) on behalf of Z Energy Limited (Z) have been monitoring the quality of stormwater discharges derived from active service station non-forecourt areas. Non-forecourt areas are defined as the service stations impermeable surface areas where refueling is not carried out, or where the stormwater discharge is not treated via an oil-water separator (or similar) device (i.e. where there is a low risk of any spill). Typically, these non-forecourt areas would be treated using catch pits only. However, recently in Christchurch (and some other centres), Z have also been required to include Stormfilters (in addition to catch pits) to treat non-forecourt stormwater discharges.

To understand what stormwater treatment performance is being achieved by the catch pits and Stormfilters, water quality monitoring has been conducted using irrigation systems. The purpose of using the irrigation systems is to allow stormwater quality assessments to be conducted using flow rates which are equivalent to the peak flow rates that the Stormfilters can treat. Furthermore, first flush or peak contaminant concentrations are also able to be obtained using irrigation systems, which is typically difficult to achieve when monitoring true rainfall events.

This paper outlines: the monitoring methodology; a summary of the water quality results obtained; and answers if there are benefits for requiring enhanced stormwater treatment for service station non-forecourt stormwater discharges?