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On May the 2nd, I had the chance to meet with Stephane Odriozola who is a chemist technician working at the laboratory of water and environment protection in the State of Geneva. A part of his job is to measure, in continuous, physical and chemical parameters in Geneva’s watercourses.

He has a few probes on the field, so I went with him on one of his field trips to check the integrity of the probes and retrieve the data they measured. The site he chose to show me is at the “pont du centenaire” in the Aire watercourse, between Onex and Plan-les-Ouates. He chose this site because he had two probes near each other there, one that was directly in the Aire and the other one that was installed at the exit of clear water coming from the industrial area of Plan-les-Ouates.

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The probe itself

The main purposes of these measurements is to detect pollution in water and find its source, like a specific point source who may be polluting its clear water. And that is typically illustrated by the situation in which the two probes we went to see. The one measuring the exit of the water of the industrial area of Plan-les-Ouates focusing on what is coming from a more precise area.

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Clear water coming from the industrial area of Plan-les-Ouates

So we went in the watercourse to check the first one which was immersed under a bit more than 1 meter of water. And there was already a problem, the probe was stuck in a lot of roots, fortunately Stephane, with the help of a colleague, managed to free the probe. After that he told me that sometimes it is also difficult to get to the probes because of strong water currents. So this showed me even more that in such projects, an important part of designing the field probe, is to evaluate risk and problems that might happen and then try to avoid them.

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The Probe was stuck in roots underwater

With these probes, one must go physically to the field probes and the data must be retrieved on site. Stephane showed me the process of retrieving the data collected by the probe. It is done in two steps. First, we connect a device to the probe with a cable to retrieve the data in the device and then, the device is connected to a computer to get the data. This illustrated that retrieving data by hand is not the easiest nor fastest way. I for myself will try to avoid the need to retrieve data in this way, it should be a lot more convenient if the data are directly sent to a server. Even if my probe will not be completely immersed (that is the design for now) the collection of the data by hand will only be used as a “backdoor” if the sending trough the network fails.

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The device used to collect the data

Now for the technical part, Stephane explained to me that he can choose at which frequency the measurements are performed – and a good timing is every 10 min. There are 3 parameters that he measures: conductivity, pH and temperature of the water. He told me that turbidity is not that interesting and there are always problems (it gets dirty and measurements are wrong, etc…). It is with a correlation of the 3 measured parameters that he can determine if there is pollution in the water. At first I thought of measuring only the temperature and turbidity, but with these considerations I may look to add a pH and conductivity sensor to my probe.

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The sensors, they are modular (the 3 at the top are empty slots)

One of the last things we did together was calibrate the pH sensor. He had brought 2 solutions, one neutral (at pH 7) and the other at pH 10. This calibration was performed with the help of the device connected to the probe, so if I want to add a pH sensor calibration must be taken into consideration in the design.

In conclusion, this visit was very interesting. The most important fact that captured my attention here was that there are a lot of constraints imposed by the environment that must be taken into account and dealt with. Even things such as if the probe is not secured properly the probe could be stolen… So these constraints beside the technical measuring devices is not to be neglected and is pretty important in my opinion for such installations to work properly.

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