Water quality & sampling

Things to know about sampling

The appropriate technology and sampling strategy also depends in water on the planned investigation objective and the local conditions. We have compiled the most important points:

Mixing/sampling points

Water in the liquid state mixes very easily, resulting in good homogeneity. Nevertheless, significant spatial differences also exist in water for some parameters, for example due to stratification, currents or discharges. To obtain meaningful samples, you must take these structures into account.

On the one hand, this may involve increased effort if, for example, you want to obtain the sample from a great depth or in the middle of a large body of water. Also consider the temporal component, as these spatial distributions are subject to temporal changes: for example, due to seasonal changes, tidal influences, or anthropogenic influences such as the opening of weirs or temporary discharges.

On the other hand, this means that these spatial distributions must not be influenced during sampling, if possible. In particular, the insertion of measuring and sampling equipment, but also already the access to the sampling point can lead to mixing. If the same material is used in different places, carryover can occur if the material is not thoroughly cleaned in between.

The right material

To obtain meaningful samples, it is important that the parameter under consideration is not affected by the sampling equipment. For chemical tests, this means that every piece of sampling equipment that comes into contact with water must be inert to the substance under investigation. Attention should also be paid to the material of internal components such as hoses or pump membranes.

Furthermore, for some parameters you should make sure that the water is not subject to temperature fluctuations. In this case, you should avoid pumps or valves that heat up strongly. In addition, you should prevent temperature changes during transport as far as possible, for example by using insulated transport containers.

For sediment load or microbiology studies, it is critical to have no bottlenecks or turbulence in the sampling line where material is retained. For example, valve culverts, or hose bends often create restrictions in material transport.

Sampling in water doesn`t always mean to extract the sample from the open water body. Sometimes also water samples from the sediment or samples including the deposed sediment for further examination are necessary. In this case adapted sampling technologies allow for a disturbed or mainly undisturbed sampling. Thus aso layers in the sediment can be considered.

For sampling groundwater bodies there is the particular specificity that these are usually closed towards the atmosphere and not accessible from the outside. Through wells this access is possible. However, thereby also a contact to the atmosphere is established, which can affect the actual parameters. Flushing the monitoring well with fresh inflowing groundwater allows for realistic samples, but may also lead to significant influences on the hydrological regime.

Therefore sampling plans for groundwater monitoring wells have to be adjusted to the aquifer. Groundwater wells are particularly prone to intermixing, since the water is easily mixed within the well by inserted technology.

It is also important to note that the removal of water from a well can cause influx from other depths of the aquifer as the backfilled space around the well casing may allow for a preferential flow path. When working with groundwater monitoring wells, it requires special carefulness since the entry of foreign substances may affect an aquifer decisively.

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