Sampling of groundwater

Question 1

What is genetally the difference in water quality between surface water and groundwater?

Answer 1

• Groundwater does not contain as much oxygen as surface water
• Groundwater could be acidic
• Groundwater is clearer (cleaner)

Question 2

How does the porosity of a soil/rock effect the velocity of the groundwater?

Answer 2

• Silt, not so much speed, smaller pores

- In eskers, there is higher speed.

Question 3

In which direction is the main groundwater transport? Horizontal or vertical?

Answer 3

Horizontal

Question 4

Mention three methods to install groundwater pipes

Answer 4

• Drilling
• Casing drilling with flushing medium (water or compressed air)
• Hollow stem auge. Leave the screw in the hole
• Direct push

Question 5

What is important to consider when installing the groundwater pipe filter?

Answer 5

It is important to consider where and what type of pollutant you have

• Contaminants that are more volatile than water
• Contaminants that are heavier than water
• In presence of dense soil layers

Question 6

Which material is recommended when monitoring metals such as copper and zinc?

Answer 6

• Plastic, HDPE, PTFE, PVC

- Plastic, since metal tubes can contaminate. You don’t know of the copper/zinc is from the water or the pipe

Question 7

List three techniques to sample groundwater. What are the main advantages and disadvantages?

Answer 7

Peristaltic pump: Water is exposed to suction. Only usable up to approx. 7 meters. They can reach 10 meters, but you get problems at 8 meters. Not suitable for volatile substances
Pressure pump: The pump is installed under the groundwater table. Suitable for volatile compounds. Good capacity. Advantage for circulation pumping. Problems with poor drainage or when water has a high turbidity. Risk of cross contamination
Bailer: Simple to use. Disposable sampler. No risk for cross contamination.. Available with a valve, which allows sampling at different levels. Bad for circulation of groundwater. Risk of losing volatile compounds. Oxidation. Fe2+  Fe3+
Check valve system: Tube with check valve. Good for volatile substances. Problems when there is only a small water column in the groundwater pipe
In-situ sampler, ex. BAT system: Completely enclosed sampling. Requires installation of special sampling tip. Difficulties when large volumes of water required. Problems with filling the container without applying vacuum. Small risk of contamination

Question 8

Explain the common procedure for groundwater sampling

Answer 8

• Measure groundwater level
• Clean pump the groundwater pipe, ca 3-5 times the water volume in the pipe
• Groundwater that is already in the tube is exposed to oxygen and therefore not representative
• Start the sampling and filter the water in situ
• Fill the sample bottles all the way to the top and close the cap tightly

Question 9

What are the common on site analysis that can be done when sampling groundwater?

Answer 9

• pH
• Conductivity
• Temperature
• Red-ox
• Oxygen level

Question 10

Why should you always filter groundwater? Contradictory to surface water that can vary

Answer 10

• Groundwater = anoxic
• When water comes up and in contact with oxygen  all particles will get filtered away = try to keep it out of contact with oxygen.
• Also, there could be intrusions of sand, clay etc. that will affect the results with extreme values.
• Surface water is almost always in contact with oxygen…