1. Groundwater Pollution
Some sample exam questions

2. 1. You have just started investigations at a hazardous waste site and you discover a “drum nest”—a pile of old 200 liter drums and other debris. A quick check of the pile shows that it remains contaminated with organic chemicals. You cannot remove the drums and debris until you get further into your site cleanup, but you want to cover it for now to prevent rainfall from infiltrating the waste and spreading contaminants to soil and ground water. You may need to keep it covered for as long as a year or two. What type of liner material would you specify for covering the pile?

3. The cover is only needed for a short time.
Best would be a flexible membrane liner (some type of plastic).
It must be able to stay in sunlight (UV).
It must be strong and flexible to cover the drums.
It must be able to stand chemicals.
Using clay directly on the waste doesn’t work because it could soak up waste and would need further disposal.

4. 2. What is natural attenuation?
What happens in natural attenuation?
People say it is not a “do nothing” method. What do they mean?

5. Natural attenuation is where there is no human action to remediate the pollution. The pollution is naturally reduced.
Monitoring is used to make sure that the pollution is being reduced.

6. 3. An underground leak (at a 3 m depth) at a gas station resulted in the loss of several thousands of liters of gasoline into subsoil. The gasoline then contaminated the ground water that is 4 m below the surface.
Give 2 possible remediation techniques for the vadose zone and 2 techniques that could be used to clean up the ground water.
For both the vadose zone and the ground water say which one of the two methods you would use and also say why you would use them.

7. Vadose zone – dig up the soil and incinerate, or wash etc.
- use soil vapor extraction (SVE) to evaporate and remove the gasoline.
- use bioremediation, adding nutrients, water air etc to increase microorganisms.
If the volume is small use dig and treat, if the volume is big use SVE maybe with bioremediation.

8. Groundwater – pump and treat with air stripping.
- use in-situ bioremediation, adding nutrients, air etc to increase microorganisms.
In-situ bioremediation is cheaper but takes longer.

9. 4. Draw a picture of showing possible groundwater contamination with DNAPL.
What is DNAPL?
What methods would you use to remediate this contamination?

10. A diagram showing the migration of DNAPLs

11. The liquids with very low solubility are called non-aqueous phase liquids (or NAPLs)
Dense NAPL (DNAPL) is more dense than water. It will move down through the groundwater.

12. Remediation depends on the contaminant.
eg. - could use sorption barriers
- add methane, H2 or other electron donor to give reductive dechlorination.
- deep DNAPL pools need to be removed, maybe using heat or detergent to flush out the pollutant.

13. 5. Draw a picture of showing possible groundwater contamination with LNAPL.
What is LNAPL?
What methods would you use to remediate this contamination?

15. The liquids with very low solubility are called non-aqueous phase liquids (or NAPLs)
Light NAPL (LNAPL) is lighter than water. It will float on the groundwater.

16. Treat the vadose zone and the groundwater.
Remove the LNAPL from the surface of the groundwater, maybe by bioslurping.
Use sparging, bioremediation, SVE etc.

17. 6. Draw a picture showing possible groundwater contamination with metal.
What methods would you use to treat this contamination?

19. Possible treatments
- Dig and treat
- Solidification
- Enclosing in barriers
- Maybe precipitate with Na2S, or other compounds
- Use a permeable reactive barrier.

20. 7. Draw a diagram of the different electron acceptor zones of an oil spill.

21. Draw a diagram of the different electron acceptor zones of an oil spill.

22. 8. How can some metal oxides be used to remove organic contaminants from the soil or groundwater?

23. Organic contaminants can be naturally degraded by redox reactions
Organic contaminants can be naturally degraded by redox reactions. Mn and Fe-oxides can oxidize aromatic pollutants.

24. 9. What is the first and most important step of a typical soil and/or groundwater remediation project?

25. The first and most important step of a typical soil and/or groundwater remediation project is to find out the extent of contamination.
Site characterization determines the conditions at the site.

26. 10. The pollution can occur in groundwater in a plume
10. The pollution can occur in groundwater in a plume. Give three questions that could be asked about the contaminant plume.

27. The questions to ask about the contaminant plume are
Where is the contaminant plume?
What is in the plume?
How big is the plume?
How long has it been there?
Where is it going?
How fast will it go?

28. 11. What is a redox reaction?
What do we call the chemical which gains electrons?
What do we call the chemical which loses electrons?

29. A redox reaction is a half-reaction of oxidation and a half-reaction of reduction.  
Both half reactions involve the transfer of electrons between the chemicals in the system.
The chemical gaining electrons in the half-reaction of reduction is the oxidizing agent.
The chemical which loses electrons in the half-reaction of oxidation is the reducing agent.

30. 12. Describe the difference between attenuation of organic compounds and attenuation of metals.

31. The difference between attenuation of organic compounds and attenuation of metals is:
Naturally occurring biodegradation can completely convert some organic contaminants to harmless products.
Metals can only be transformed to forms that are less mobile or less toxic.

32. 13. Why aren’t “Pump and Treat” systems of groundwater remediation be used all the time?

33. “Pump and Treat” systems of groundwater remediation aren’t used all the time because they are not very successful in removing all contaminants.

34. 14. Describe two different in-situ remediation methods.
Include what contaminant each is used for, what are some advantages and disadvantages.

36. 15. Describe two different ex-situ remediation methods.
Include what contaminant each is used for, what are some advantages and disadvantages.

37. See handout

38. 16. How can some metal oxides be used to remove organic contaminants from the soil or groundwater?

39. Organic contaminants can be naturally degraded by redox reactions
Organic contaminants can be naturally degraded by redox reactions. Mn and Fe-oxides can oxidize aromatic pollutants.
Another example:

40. 17. How does sorption affect the movement of contaminants through the groundwater?

41. Sorption is the attraction of an aqueous chemical to the surface of a solid. It involves bonding between the contaminant and adsorption receptor sites on the solid.
Sorption slows the traveling of contaminants though the groundwater.
Adsorption is the attraction between the outer surface of a solid particle and a contaminant.
Absorption is the uptake of the contaminant into the physical structure of the solid.

42. 18. Draw a diagram showing how a reactive barrier works.
What are some pollutants which can be treated with a reactive barrier?

43. ABIOTIC AND BIOLOGICALLY MEDIATED ABIOTIC ATTENUATION METHODS
REACTIVE BARRIERS
example

44. 19. What is bioaugmentation?
Give an example

45. Bioaugmentation involves seeding aquifers with microorganisms.
For example, adding halorespiring microorganisms in anaerobic plumes that contain electron donors and chlorinated solvents.
The microorganisms should spread and grow and increase the natural attenuation capacity.