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Quality Assurance and Quality Control (QAQC), when explained in terms of a sample of water from a lake, river or stream, means that the analysis of the sample is carefully controlled to guarantee that the results are assured to be accurate within acceptable limits and recognized standards.
The first step is to adopt standard methods for each parameter to be tested, i.e., total phosphorus, Secchi disk measurements, nitrates, etc. Secondly, all workers in the laboratory must be carefully trained so that they understand the importance of each step in the analysis procedure. Thirdly, all steps must be properly logged and continuously reviewed to be sure no hitch occurs.
Laboratories who want to have national validation of their laboratory and its procedures will request blind test samples from the EPA, will run those samples through their testing procedure and send their reports to the EPA. Test results which fall within the limits established by the EPA confirm the integrity of the laboratory's procedure and results.
Securing a representative sample from a lake for a chemical water quality test is nearly insurmountable. The parts per billion of phosphorus in a lake, for example, varies considerably depending on where in the lake the sample is collected, the depth at which it is collected and the time of the year it is collected . The best time of the year to take a sample for phosphorus analysis is when the concentration of phosphorus is nearest to being uniform throughout the water column. This is shortly after the ice is gone, and after the wind and wave action has had a chance to mix the lake. A test for phosphorus at other times will require tests that are from different parts of the lake and at different depths. The parts per billion at the different depths should then be equated with the volume of water at that depth . Only by taking these precautions will it be possible to get an approximate representative sample of the entire lake.
Probably a more thorough study every five or ten years will give more accurate information than annual tests which have questionable validity. Testing a lake for the parts per billion of phosphorus in the lake every year, for example, is not as valuable as knowing how much phosphorus comes into the lake and to know where it is coming from. Only then can a wise management program to reduce phosphorus loading of the lake be adopted.
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