Fact Sheet December 2012 Purified Recycled Water in the Lockyer Valley The water supply security of South East Queensland (SEQ) has recently been increased by the construction of the Western Corridor Recycled Water Scheme. The infrastructure of advanced wastewater treatment plants provides purified recycled water (PRW) to the SEQ Water Grid for indirect potable reuse of effluent from urban areas. With a maximum combined production capacity of 232 million litres of PRW a day, it is the third largest recycled water scheme in the world and the largest in the southern hemisphere. This additional water supply is critical during drought conditions but is underused in wet periods. The provision of recycled water in an environmentally Background sound and socially-equitable manner requires measured The Urban Water Security Research Alliance (the Alliance) understanding of the potential impacts on the region’s worked closely with the Queensland Water Commission, soils, groundwater system, environment (such as salinity the former Queensland Department of Environment and issues) and the economy. Therefore, a holistic framework Resource Management, WaterSecure (now Seqwater) and was required to inform an integrated water management the SEQ Water Grid Manager, as well as irrigators and the plan involving the use of PRW. This was achieved through farming community. a multi-tiered assessment incorporating environmental risk analysis, climate modelling, regulatory considerations and Together we explored the feasibility of providing agro-economics. approximately 20 million litres per year of PRW to supplement irrigation supplies in the Lockyer Valley, 80 km The environmental risks and benefits from the supply of PRW west of Brisbane. were the core subjects addressed by this research, using a combination of field research, water quality and quantity Alliance research explored whether the use of PRW can serve modelling , and unstructured stakeholder interviews. to provide a long term groundwater buffer against drought. A key hurdle to the uptake of PRW has been its high cost The Lockyer Valley is a major contributor to the vegetable compared to the traditional natural water resources, as well supply of SEQ. The region has both a high intensity of as concerns about environmental impacts. agricultural enterprise and a complex hydrogeology. It is supplied by more than 5,000 alluvial bores used by farmers to irrigate their crops. Maintaining high groundwater levels will increase our resilience against drought. According to the 2010 South East Queensland Water Strategy, 32,000 megalitres (ML) per year of recycled water will be available for rural production in the Lockyer Valley when not required to supplement Wivenhoe Dam. Fit-for- purpose recycled water could also be made available from Researchers obtained deep soil cores to assess the impact of local wastewater treatment plants. PRW on soil structure and health. Leading water research and knowledge in South East Queensland www.urbanwateralliance.org.au In this scheme, wastewater from Brisbane city is treated to The highest recorded groundwater level occurred in 1990, potable water standard (branded as PRW) with the intent with an estimated stored water volume of 106 ML. This to supplement Wivenhoe Dam, which has a capacity of could supply the highest irrigation demand of 22 ML, approximately 1,200 ML. Water from Wivenhoe reservoir required during 1993, for more than three years until the discharges into the Brisbane River and is tapped further characteristic low water levels, an estimated groundwater downstream for the drinking water treatment plant at Mt storage of 36 gigalitres (GL) recorded between 2006-2007, Crosby. Currently, PRW is used to augment Wivenhoe Dam would be reached (assuming negligible lateral flow out of only when the combined supply in SEQ drinking water dams the alluvium in that period). drops to 40%. However, simulations based on long–term, historic flow records (1880-2010) indicate that reservoir Research outcomes to date levels would have dropped below this trigger level only twice with existing and committed infrastructure projects. Initial Alliance research provided a clearer understanding of This current infrequency leaves significant volumes of groundwater aquifers and the potential risks of irrigation PRW available to supplement non-potable uses such as supplemented by PRW on soils and salinity in the Lockyer agriculture. Valley. The project then developed a conceptual framework of how PRW will interact with groundwater levels, soils, Additionally, preliminary results from climate modelling salinity and crop types. indicate that future groundwater levels are likely to drop significantly in the Lockyer Valley and drought conditions Modelling confirmed that current salt accumulations in would worsen, highlighting the need to secure water supply the deeper soil, produced as a result of irrigation with from alternative sources. low quality groundwater, will slowly move towards the groundwater table over the coming decades. Using low salinity PRW for irrigation instead of the low quality groundwater in some parts of the Lockyer Valley would actually reduce salinity issues and create long term environmental benefit. PRW could improve the environment in the Lockyer Valley due to its low salinity and its availability on demand. Analysis of PRW chemistry and tests with soils from the Lockyer Valley showed only a minor potential for soil Deep drainage map based on remote sensing landuse mapping. structural changes when irrigating with PRW. This is very similar to the risks already induced by rainfall or overhead The estimation of sustainable groundwater yield can be irrigation with fresh surface water. Such impacts are easily performed using numerical groundwater models, but relies managed by the landholders with current farming practices. on the information from a metering program quantifying abstraction rates by irrigators. Currently, only part of the Lockyer Valley is metered for groundwater use, leading to considerable uncertainty regarding the influence of agriculture on groundwater levels and conditions. Development and validation of customised hydrological models by the Alliance has enhanced our understanding of water use and demand across the catchment. PRW comes at a relatively high production cost (>$AUD 500 per ML) due to the extensive treatment required for indirect potable reuse. This cost can be compared to current irrigation water charges of a maximum of $AUD 30 per ML in the Lockyer Valley. For this reason, irrigators have Comparison of soil chloride profiles sampled in 1998 and 2010. indicated they will avoid using PRW while groundwater or The existing Lockyer Valley water resources were also tested an alternative surface water supply is available. for evidence of pharmaceuticals and other trace organic The primary benefit of maintaining high groundwater levels compounds to compare the quality of the existing water is the increased resilience against drought, which has been with the imported PRW. The screening showed influences confirmed for the SEQ region by this Alliance research. Based of wastewater in Lockyer Creek and the three major local on recorded groundwater levels in the central Lockyer Valley reservoirs, with traces of carbamazepine, acesulfame, between 1990 and 2007, the alluvial aquifer would be able metolachlor and caffeine. In this respect, the quality of to supply the highest irrigation demand for more than three PRW is significantly better than the existing water quality years. downstream of Gatton. Page 2 Researchers also assessed how groundwater levels have This research has demonstrated the application evolved over the past 100 years, which showed how low the of the methodology for evaluating environmental water levels fall in drought conditions. considerations in importing PRW or other local recycled Preliminary modelling of changing climate scenarios suggest water for irrigation in a complex system like the Lockyer these low levels may occur twice as frequently in a median Valley. The results will also allow the SEQ Water Grid climate change scenario if pumping rates remain similar. Manager to make an informed decision about whether It indicates that under these conditions, the Lockyer Valley to proceed with the supply of 20 GL of PRW to the system will require an input of water to sustain agricultural Lockyer Valley in future. practices as they are now. Alternatively, the region will require higher efficiency in irrigation practices. Future research opportunities Potential future crop uses with the benefit for PRW – PRW supplementation could be implemented The project team mapped the recent history of land use in in the Lockyer Valley without damaging the the Lockyer Valley. It would be necessary for planners to look environment if the irrigation areas are kept in more detail at potential future irrigated cropping areas broadly the same. and crop types if PRW was used to augment irrigation supplies. If this is confirmed by more detailed studies, then the increased demand for PRW or other local recycled water in the Lockyer Valley would need to be actively managed, using the groundwater system’s total storage of 300-360 ML as a climate buffer. Historic variations in groundwater storage during the last twenty years suggest a variation in storage volume of 70 ML just in the central Lockyer Valley. Results from proof-of-concept modelling indicate that an average 37 ML per year water import would be required Irrigation demand time series