Urban storm water is considered to be one of the last unexploited water resources in Victoria but can carry a range of contaminants that could impact on reuse opportunities. In recognition of this, this project used innovative new tools to measure organic micro-contaminants in storm water in order to assess potential risk to receiving waters and in irrigation schemes.
In Melbourne, the amount of stormwater runoff from urban catchments is approximately 540 GL per annum, or almost twice annual potable water use. This highlights the potential of stormwater to meet much of Melbourne’s water demand provided it is managed correctly. There are guidelines in Victoria for the amount of litter, suspended solids, total nitrogen and phosphorus in storm water, but none for other chemical pollutants in storm water that might impact water reuse in the urban environment and threaten the end user of harvested water (i.e. parks and gardens).
Best practice approaches to urban storm water management are rapidly evolving. The key principles for urban storm water management include integrating storm water treatment into the urban landscape and reducing potable water demand by using storm water as a resource through capture and reuse for non-potable purposes. This will require protecting water quality while minimising development/utilisation costs.
A myriad of trace substances may exist in storm water. Some contaminants are known to be present in Victorian storm water (the “known”), some contaminants are known to be present in storm water elsewhere in the world and/or otherwise suspected of being in Victorian storm water (“known unknowns”) with other chemical micro-pollutants present but as yet unidentified (the “unknown unknowns”). In that context, the broad aim of this project was to advocate appropriate techniques to screen Victorian storm water for micropollutants. The specific aims of SWF Project 8OS-8100 were to:
- Use a range of standard water quality techniques to assess nutrient and metals concentrations in storm water across Melbourne.
- Use a range of high quality chemical analytical screens to assess herbicide concentrations in storm water across Melbourne.
- Use a GC-MS-database method to screen for more than 900 semi-volatile organic compounds (through collaboration with researchers at the University of Kitakyushu, Japan)
- Use a rapid bacterial toxicity test and an algal toxicity test to assess the potential impact of storm water on primary producers.
- Produce a set of draft sampling and testing guidelines for collected storm water samples for micro-contaminants industry consultation.
Project Outcome: By January 2014, CAPIM, and SWF, and other water authorities, will have access to information with which to assess the potential impact of micro-contaminants (including nutrients, metals, herbicides and a wide range of other semi-volatile chemicals) on storm water quality and re-use options.
The project team identified 8 sites receiving storm water from areas with different urban land-use. Sites included run off from a shopping mall/residential area, urban residential areas, areas with limited industrial activities, industrial areas and a rural urban location. Grab water samples were collected in October 2012 and February 2013 from these sites, and tested for the “known knowns” (nutrients (nitrogen and phosphorus), metals), and “known unknowns” (herbicides), the “unknown unknowns” (through multi-residue testing), and their toxicity to microorganisms and algae assessed.
Unsurprisingly there were nutrients in the storm water samples, although rarely at levels that might affect irrigation systems. Of the 16 metals and metalloids screened, copper and zinc were observed in every sample, but never at concentrations that might threaten urban environments.
Of the 29 herbicides screened in waters, 15 were observed on one or more occasions, although rarely at levels that might be of ecological concern or might threaten terrestrial ecosystems. Almost 100 semi-volatile organic chemicals were observed in the samples using a GC-MS-database testing method.
All samples were moderately to strongly toxic towards the photobacterium used, and while there is some variability in the data, it seems that that most of the toxic compounds were highly water soluble chemicals. All samples caused toxicity to microalgae in terms of their growth and/or photosynthetic activity equivalent to or greater than that induced by 0.1 mg/L atrazine.
A review of best-practice methods for the collection and analysis of storm water was undertaken and using the information obtained, draft guidelines for the monitoring of storm water were prepared for review by SWF and EPA Victoria prior to further review and use by industry
To provide greater confidence that the storm waters are ‘fit for purpose’ and likely to have minimal impact on the aquatic or terrestrial environments when used to supplement urban water supplies, further hypothesis-based investigative studies should be undertaken across a larger range of harvesting systems more times across the year and over longer time periods (multiple years) to see how representative this project’s data is of Melbourne’s storm water quality geographically and to assess the impact of drier years on water quality and toxicity.