9.7 Investigative studies and research monitoring
Investigative studies and research monitoring can be used to increase understanding of a water supply system, identify and characterise potential hazards, fill gaps in knowledge, and inform targeted capital expenditure, system augmentation and operational improvements. By improving understanding of the factors affecting water quality characteristics, such monitoring allows suppliers to anticipate periods of poor water quality and respond to them more effectively.
Investigative studies and research monitoring can often also be used to provide further information for the risk assessment process and reduce uncertainty. Examples include:
baseline monitoring of characteristics or contaminants in potential new water sources, to identify water quality problems (Box 9.7);
source water monitoring, to understand the temporal and spatial variability of water quality characteristics;
event-based monitoring in source water and catchment areas, to determine the magnitude of impacts (duration and maximum concentrations);
developing early warning systems, to improve the management of poor water quality;
examining mixing effects within a water storage;
evaluating characteristics of an aquifer through pumping tests and analyses;
studying the movement of water within reservoirs, to determine short-circuiting effects;
examining backwash return water and its effect in increasing microorganism load;
examining the effects of natural events that affect drinking water quality, such as bushfires or floods (Box 9.8).
Baseline monitoring of new drinking water sources
Baseline monitoring of raw water quality should be carried out for all new water supplies being considered, as well as any poorly characterised existing systems.
Baseline monitoring informs the hazard identification and risk assessment process, and the development of effective ongoing monitoring regimes, by identifying major water quality problems and the key characteristics that should be routinely measured. This characterisation of the water supply also establishes a base for assessing long-term trends and changes in water quality over time, and provides information to compare and select source waters for future supply.
The extent of sampling and the timeframe required for a baseline assessment will depend on land use in the catchment, levels of pollution found, and variability or trends in water quality. A land-use survey of the catchment should be carried out to identify any important features likely to affect water quality. Where catchments and supplies are beyond the water supplier’s jurisdiction, exchange of information and collaborative assessment of the quality of source waters is strongly recommended.
The baseline water quality and potential levels of risk should be periodically assessed to identify any significant changes in water quality arising from changed land-use practices or the impacts of water abstraction (particularly from unconfined aquifer systems), as well as longer-term natural variability in water quality that may not have been evident from initial baseline monitoring.
Detailed advice on what characteristics to consider in a baseline monitoring program can be found in CRCWQT report 11 – A Guide to Hazard Identification & Risk Assessment for Drinking Water Supplies (2004).
Investigative studies on the effect of floods on water quality
Following many years of drought, a record dry year in 2006 yielded the lowest streamflows on record for Melbourne’s protected water supply catchments. The dry conditions continued until a storm in late June 2007. While not enough to break the drought, the resulting run-off produced very turbid inflows to Upper Yarra Reservoir and ultimately high turbidity into some of Melbourne’s unfiltered water supply.
As turbidity increased in the water supplied to customers, Melbourne Water carried out monitoring to determine whether:
the stormwater run-off from the forested catchments represented an increased risk of protozoan or bacterial pathogens in the raw water; and
the existing ultraviolet (UV) and chlorination processes could adequately inactivate bacterial pathogens at higher turbidities.
Inspection and monitoring of the streamflows in the Upper Yarra catchment in the days following the storm event indicated the potential for a major water quality incident in the days following. The turbidity of streamflows in the Yarra River and water transferred from the Thomson River (via a tunnel to the Yarra River) were in the range of 50 to 100 NTU two days after the storm.
A range of investigations and sampling were undertaken within and downstream of Upper Yarra Reservoir in response to the turbidity incident (Hellier and Stevens 2009). This included genotyping of Cryptosporidium isolates.
A beneficial outcome of the incident has been the increased knowledge of water quality risks associated with the catchments and improved disinfection validation information.
The experience with pathogen monitoring highlighted the importance of rigorous risk assessment, underpinned by previous catchment research, to support water supply management decisions (e.g. whether boil water advisories are warranted).
An important lesson was the value of event sampling of streamflows into reservoirs for future events to characterise the turbidity and microbial load – first bacterial indicators, then pathogens if warranted. This was not carried out in the 2007 incident and would have assisted in an earlier determination of pathogen risks (Hellier and Stevens 2009).
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