Sampling of groundwater Flashcards
What is generally the difference in water quality between surface water and groundwater?
Groundwater is generally cleaner than surface water and lacks oxygen. Surface water is exposed to changes is temperature, organic matter and other factors.
How does the porosity of a soil/rock effect the velocity of the groundwater?
Bigger particles – bigger pores –> higher flow
Small particles – small pores –> low flow
Sampling of ground water should take place where there’s high velocity since you otherwise don’t get enough groundwater.
In which direction is the main groundwater transport? Horizontal or vertical?
Horizontal
Mention three methods to install groundwater pipes
Drilling – using a screw to make the hole.
Hollow stem auge - drilling and casing the hole simultaneously, thereby eliminating hole caving problems and contamination of soil samples
Direct push – just pushing a tube into the ground. The tube needs to be strong enough to withstand the push.
What is important to consider when installing the groundwater pipe filter?
The risk of hole collapsing, cross contamination, soil sampling and controlling, exploration depth, filter installation, speed/costs.
Having the filter at the correct depth: If there are volatile contaminants they will float on top of the water table so the filter needs to be covering that area. If there are heavy contaminants they will be in the bottom of the groundwater and then the filter needs to be covering that area. If there are dense soil layers the pipe should go past them and into a softer soil in which the filter should be placed.
Which pipe material is recommended when monitoring metals such as copper and zinc?
HDPE or PTFE (teflon). No pipes which contain metals.
List three technics (pumps or other devices) to sample groundwater. What are the main advantages and disadvantages?
Peristaltic pump has the advantage of being able to change tube after every sample – there will be no cross contamination (the pump itself is up at ground level). No exposure to oxygen. The main disadvantage is that you can only sample down to ca 7 meters depth since it depends on gravity. It’s not suitable for volatile substances.
Pressure pump is installed under groundwater table, which makes it possible to sample volatile substances. Problem with cross contamination when you want to sample from multiple holes and with poor drainage or water with high turbidity. Advantage of being able to pump as deep down as you want. Has a good capacity.
The bailer has the advantage of being very simple to use. Disposable so no cross contamination. Could come with a valve that allows sampling at different levels. The disadvantage is that the samples will come into contact with oxygen which can lead to changed speciation of redox elements. Risk of losing volatile compounds.
Explain the common procedure for groundwater sampling
Before sampling you measure groundwater level and sometimes the level of the contamination layer on the water table. Then you also do circulation pumping, it is necessary to get representative samples: pump 3-5 times the water volume of the tube, note how the inflow to the well is, pump with small capacity to avoid mobilization of fine material, do not empty groundwater pipe.
Then sampling can begin: use plastic gloves, label bottles, clean the equipment. Use pumps only with low flow, filter the sample in situ, fill bottles carefully, keep the bottles cold.
What are the common on site analysis that can be done when sampling groundwater?
Measuring pH, conductivity, temperature and redox potential
Why should you always filter groundwater? Contradictory to surface water that can vary
Because groundwater has no contact with oxygen and therefore you should see which particles are dissolved and with are in the particulate phase to see which particles that could be taken up by humans or plants. Speciation can change if the samples come into contact with oxygen which could give false results.
