Vern. Lecture 5

Question 1

What are DNAPL and LNAPLs?

Answer 1

• Dense non-aqueous phase liquids: moves into saturated zone, sinks through water, can in some cases move with water
• Light non-aqueous phase liquids: less dense than water, floats on top of water table, moves along any gradient

Question 2

Give examples of DNAPL

Answer 2

Extra heavy crude oil

Coal tar

Creosote

Polychlorinated biphenyl (PCBs)

Mercury

Question 3

Give examples of LNAPLs

Answer 3

Fuel and other light hydrocarbons

Question 4

Describe LNAPL transport

Answer 4

Question 5

Describe DNAPL transport

Answer 5

Question 6

Describe the process of pump and treat (ex-situ remediation)?

Answer 6

Question 7

Describe soil vapour extraction (SVE) (in-situ remediation)

Answer 7

Question 8

How does bioventing work?

Answer 8

Injection of air into the soil or groundwater stimulates oxic respiration by bacteria. The bacteria degrade (oxidise) organic pollutants into CO2 byproducts.

Question 9

Why does bioventing appear a simpler system than SVE?

Answer 9

Unlike SVE the byproduct is harmless CO2 so byproducts do not need to be collected.

Question 10

How does ISCO (in situ chemical oxidation) work?

Answer 10

Powerful chemical oxidisers such as permanganate, Fenton’s Reagent, persulfate, ozone and hydrogen peroxide are injected into the soil.

These abiotically oxidise the organic pollutants into harmless CO2

Question 11

Describe the process of aerobic digestion during biodegradation

Answer 11

Question 12

Describe the process of anaerobic digestion during biodegradation

Answer 12

Question 13

Where does anaerobic and aerobic digestion take place in a landfill site?

Answer 13

Question 14

What reactions produce carbon dioxide?

Answer 14

Question 15

What reactions produce carbon dioxide and methane?

Answer 15

Question 16

What does TEA stand for and name three examples

Answer 16

TEA - terminal electron acceptors

NO₃-, Fe³⁺, SO₄^2-

Question 17

What is leachate?

Answer 17

Liquid containing decay products and non-decayed mobile components from landfill

Question 18

Fresh Kills in New York is one of the largest refuse heaps in history. It produced 3 million litres of leachate a day and 700nanomoles per kg per day of methane. Why did it produce so much methane and leachate?

Answer 18

High moisture content = fast biological reactions = fast leachate and methane productions

Question 19

What four layers comprise a landfill liner?

Answer 19

Natural ground

Impacted ground

Imported material (clay)

Imported synthetic (geotexile fabric/plastic e.g. polypropylene)

Gravel and drain pipe also needed in case of leakage

Question 20

Why is clay used in landfill liners?

Answer 20

V. low permeability (<10^-9m/s)

Likes to bind metals

Swelling clays good (e.g. smectite)

Smectite has good cation exchange which absobs toxins