Event-based stormwater quality measurement: sampling methodologies for urban catchments

Event-based stormwater quality measurement: sampling methodologies for urban catchments

Stormwater is one of the last major untapped water resources that can be utilised for urban water supply in major Australian cities. In Brisbane alone, the volume of annual stormwater runoff is estimated to be 1.45 times the volume of potable mains water imported from external catchments. To date, end-uses of treated stormwater are mostly for public open space irrigation, but potable substitution in urban developments as well as augmentation of drinking water reservoirs are of increasing interest. The critical issue of stormwater reuse is similar to other recycled water sources, which requires appropriate understanding of the associated health and environmental risks as outlined in the current Australian Guidelines for Water Recycling (Phase 2) – Stormwater Harvesting and Reuse and related reports. The intrinsic hazards associated with raw stormwater use include human and zoonotic pathogens and trace organic contaminants (ie, pesticides, pharmaceuticals and personal care products, heavy metals, petroleum derivatives, etc) from point (eg, sewer leakage) and diffuse (eg, car, pesticide application) sources. Whilst there is an abundance of scientific data available for total suspended solids, nutrients and to a lesser extent, heavy metals in stormwater, much less scientific information is available for the occurrence and detection of organic contaminants and pathogens (as opposed to indicator microorganisms).
In this study, we will measure the event mean concentration (EMC) for individual stormwater contaminants in up to three contrasting urban catchments in SEQ (Fitzgibbon, Brisbane CBD and Southbank) over a wide range of runoff events (n >20). This will be compared with data from similar studies in other Australian cities (from the Cities as Water Supply Catchments program). Our main focus will be on pathogen detection and quantification (including virus and protozoan), individual trace organic contaminants, and bioanalytical tools as sum parameters for mixture of organic contaminants with a common mode of toxic action. The use of bioassay will provide a screening test for a range of human-health related and environmental endpoints that in turn will guide the focus of (more expensive) confirmatory chemical analyses.
The key challenges in stormwater quality sampling are (1) the high number of samples from the entire storm event which directly translates into high analysis costs; and (2) the volume of sample required to obtain positive results for specific microbial pathogens enumeration (eg, 100L for Cryptosporidium). To resolve these challenges, we have developed a flow-weighted sampling protocol that captures the hydrograph and concentration changes during a storm event and composites them into one sample for subsequent EMC analysis. With the EMC outcomes, a risk assessment can be performed according to the specific end-uses of stormwater, and subsequent fit-for-purpose treatments can be devised to achieve the regulated water quality standard (eg, a defined pathogen log-reduction; acceptable chemical concentration, etc). This study will be one of a few to characterise individual microbial pathogens and chemical contaminants in stormwater, and should facilitate the planning of large-scale stormwater harvesting and potable water substitution projects in Australia.

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