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Sampling – “It affects everyone”
By Ian Couling
When you buy groceries, go out for tea, gamble at the races, buy fuel or milk – you are relying on correct and representative sampling to make sure the product is what it says it is. Sampling ensures correct volumes and weights, sufficient profit and reduced loss for a manufacturer, fair performance from a thoroughbred athlete, four legged or two.
Collect representative samples
Now, whether dealing with water or any other material, incorrect sampling can be minor (value for money) to life-threatening (contaminated product) or costing millions. Incorrectly collected samples are far too easy to obtain. Whether sampling manually or using automatic equipment, uncertainties in test results may arise. One common problem is incorrect preservation and/or leaving the sample too long resulting in deterioration, loss of volatile compounds, settling of decomposition of organic material, etc. Or, more simply, the sample is contaminated.
Remember the ultimate objective is to always collect representative samples. Therefore all staff involved with sampling should be working from the same manual, “singing from the same song-sheet”, “networking” so as to work as a team.
Differing sampling techniques can have a significant impact on sample quality and thus analytical results. Remember that the “analytical results are only as good as the sample as received”.
Now it is all very well for a laboratory to put that statement on their report but it is a bit of a cop-out - the laboratory should take some form of responsibility to at least ensure that the sample has a fair chance of being representative. The laboratory may issue sampling instructions (that are clear and in no way confusing) enabling non-technical persons to submit suitable samples.
When the samples need to be analysed the laboratory’s own quality assurance procedures need to be followed. Most analytical laboratories have external third-party auditors – such as IANZ or SGS that are “watching over their shoulders” for the activities within the laboratory – that does not always extend to the samples collection.
When preparing to perform a sampling exercise, advice should be given at the planning stage. However, generally the client goes to the laboratory just before the sampling is about to start, to get bottles, or rings to tell the laboratory that the samples are on their way! For this reason it is standard practise for a laboratory to state that the results are “as received” having had limited control over the actual sample collection process.
To assist all in the sampling realm, Opus Environmental Training Centre offers courses in Water Sampling and Environmental Sampling, involving theory and practical training to expand on skills most candidates already have. NZQA unit standards are offered; namely
- Unit Standard 17878: Undertake sampling and testing procedures for wastewater treatment, and
- Unit Standard 17890: Undertake sampling and testing procedures for water treatment.
The purpose of this training is not to question laboratory activities but to highlight the inadequacies with sampling and sample collection in the water quality and environmental industry before the samples actually get to the laboratory.
Although there are standards for sampling (namely AS/NZS/ISO 5667:1998) few outside the laboratory or professional samplers’ field have knowledge of them.
General principles of sampling
AS/NZS/ISO 5667 is a good starting point. These standards provide general principles of sampling for the purposes of process control, quality characterization, identification of sources of pollution and the monitoring of background levels.
In the “real world” the reasons for taking water and wastewater samples are many and often varied, but will include;
- Quality and trends of a Water Resource.
- Pollution source and impact (Resource Consent Compliance)
- Operational performance of a treatment plant and Effluent quality
- Trade waste dischargers to wastewater reticulation systems
Before thinking of taking a sample, be aware of what you need to know or have to know (regulations, etc) and what the overall purpose of the sampling is; for example;
- Water treatment plant efficiency
- entering the treatment plant;
- leaving the treatment plant; - Water quality
- in the distribution system - potable water or process water;
- as a result of a customer's feedback/complaints. - Monitoring of the corrosive potential of potable water in supply plumbing.
- Quality of water treatment by-products.
Environmental sampling is generally designed to establish the current status of an environment and thus enable control in maintaining or improving that status. The environments could be running water such as stream or river, still water such as a lake or other impoundment (natural or man-made), or the sea. Generally these are waters receive pollution in one form or another – stormwater, wastewater, leachate, etc.
It is the job of the environmental scientific community to protect these sites. To protect, however, you need planning. To plan you need knowledge, and knowledge comes from samples.
Ian Couling is a well known industry figure throughout the country, with 25 years experience in laboratory management, operations of and training personnel from wastewater treatment, water treatment, and swimming pools.
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