Variation in performance of media based stormwater treatement systems

INTRODUCTION Stormwater treatment systems (STSs) are being integrated across our urban landscapes in New Zealand and around the world with the intent of contaminant removal. Consistent downstream water quality and ecological health improvements are expected to follow STS installation; however, this is often not the case due to variability in treatment performance. A major source of variability in treatment performance comes from variation in contaminant load, which is a function of local climate and storm attributes as well as activities and changes in a catchment (Jefferson et al., 2017). Another source is variation in treatment systems themselves, which can be as wide ranging as the temporal differences in maintenance, age, and installation quality between units, and as detailed as the range of contaminants removed at a given location compared to another. Quantification of the variability witnessed in treatment performance and the determination of its sources can not only help designers to build and select more optimal treatment systems for a given location, but can also help planners set realistic expectations to improvements in water quality from investment. Zinc is a priority metal of concern in Christchurch’s urban waterways as identified by Christchurch City Council, and non-point source runoff from roofs contributes a substantial amount of the total load (Margetts and Marshall, 2018). While zinc occurs naturally in the aquatic environment, overexposure through bioaccumulation can lead to adverse health effects in humans and is toxic to aquatic organisms from microorganisms to vertebrates (Harding, 2005, Seto et al., 2013). Recent research suggests crushed mussel shells have a capability of removing dissolved zinc from stormwater runoff (Bremner et al., 2020). This ongoing study seeks to identify and quantify the impact of the most influential variables affecting the removal of dissolved zinc within two proprietary, at-source STSs: the Storminator™ developed at the University of Canterbury (UC), and the StormFilter™ sold by Stormwater 360