Tentafrågor Flashcards
Explain the difference between hazard and risk. Describe, using an example, the basic prerequisites for a risk to occur at a contaminated site.
A hazard is a contaminant or a substance that has a potential to cause an effect on the environment or for human health.
A risk is the combination of the probability and the severity of the effect of the hazard.
For something to be considered a risk there needs to be a source, a pathway, and a receptor. For example, say that there is industry that releases a contaminant such as As to the ground. The industry could then be considered a source or a hazard. The As can then travel down into the ground and after a while, reach the groundwater. The water is then considered a pathway since it transports the As. The groundwater is then used to water crops on farmland. The plants could then be considered a target or a receptor. If animals eat the vegetation the plants are considered a pathway and the animals are then the receptor.
Explain how pH affects the mobility of a) cationic elements and b) anionic elements in the soil environment.
a)The cations has positive charge. At a higher pH ther will be a stronger negative charge which results in a higher CEC (cation exchange capacatiy). The mobility for the cations at high pH will therefor be lower. At low pH the mobility increases since ther will be more H+ precent which can “take the place” of other cationic elements in the soil, making them be more mobile
cations: high pH=low mobility, Low pH=high mobility
b)The anions has a negative charge. At low pH there will be more positive charge which results in a higher AEC (anion exchange capasaty). The anionic elements will therefore be keept in the soil, the mobility is decreased. At higher pH ther will be more OH- that cationic elements can bind to, mor aionic elements can therefore “be free” which increases the mobility.
anions: high pH=high mobility, low pH= low mobility
Explain the principle of the Swedish method for inventories of contaminated sites (MIFO). List the five criteria that are used to classify risks.
The purpose with MIFO is to investigate and do a risk classification for contaminated sites. The classification is based on the following criterias:
Hazard assessment
- See what contaminants are present, how hazardous the contaminant is considered to be.
Contamination level
- The level of the contaminants and in what media they occur as well as their current condition.
- How much it deviates from reference values
- Total amount of each contaminent, total volum of contaminated material
Migration potential
- How the contaminants are spread and how fast
Sensitivity value
- How large the potential is for human exposure (now and future) and if there are more sensitive groups
Protective value
- How large the potential exposure is for the environment (now and future). How important is it to protect the area
Using the following species sensitivity distribution curve determine (values in mg/L) and explain the meaning of the following: a) NOEC b) LOEC c) EC50
a)NOEC is the value for no observed effect concentration. It is the concentration where no effect can be regestrerd for the species in the experiment. (or if the standard deviation reach zero). In the curve NOEC is 3 mg/L
b)LOEC is the value lowest observed effect concentration. This is the lowest concentration that the species are exposed to thet has an effect on the species. In the curve LOEC is 5 mg/L
c)EC50 is the value for effective concentration where 50% of the species in the experient has shown to be affected by the concentration. In the curve EC50 is 10 mg/L since tht is where 0.5 (50%) of the total amount of species has shown some effect
Which group of soil contaminants can be treated using biological soil remediation methods? Why?
Biological soil remediation works for organic compounds. The microorganisms used in biological remediation can use the organic compound as a source of energy and metabolize the chemicals to produce carbon dioxide or methane
Explain what CEC is and why it is important for the contaminant transport in soil
CEC is cation exchange capacity. It represent how many cations a soil can hold. It is important sicnc many contaminants are cations (they have a positive charge). If the soil then can hold many cations, it can hold many contaminants, they are more likely to stay in the soil instead of being transported away.
Explain the difference between the batch leaching test and the sequential extraction test. What information do you get from these tests and how it can be used in the risk assessment of a contaminated site?
A sequent extraction if done by adding different extractants in increasing aggressiveness to see what fraction is leached out. The risk of the element leaching out decreases for each step since more aggressive extractants needs to be used for the element to leach out. Depending on what extractants you use you can also find out if what for the contaminants are in, what type of mineral ex.
A batch leaching test is done by adding material and water with variating L/S ratios. The flask is then mixed and then filtrated to see which contaminants and what concentrations there is in the leachate. You get the results in mg elements leached per kg of dry matter. You can use the result to see what elements you could expect to leach out from the soil and if it therfor should be considerd as hazardous, non hazardous or inert (if waste)
What would be the most suitable in situ soil remediation technique for a site that: a) Contains copper as a main contaminant, the soil is gravelly sand. b) Contains organic degradable compounds (e.g. pentachloroethane), the soil is predominantly silty. Motivate your choice
a)for metals in a gravelly sand a possible method could be phytoremediation. With this method you plant vegetation that could take up and immobilize the metals in the soil. It is a non intrusive method that work good in situ. The Cu is also a nutrient for the plants, if it is in the right form (it needs to bio bioavailable for the plants to take up). The method does however take long time, and thereby long monitoring.
b)For organic degradable componds biological remediation is a good method. You can use the microorganisms to degrade the compounds and thereby reduce their toxicity. This method is also quite easy and the contaminants get degraded (destroyed). It can however be hard to controle and require monitouring. It is also hard to predict the effectiveness and the concentratin of the contaminents may not be reduced as much as required.
What are increment delimitation error and increment extraction error? What can you do to minimize those errors while sampling the soil?
Increment delimitation error is if the shape of the sample isn’t correct for getting a reperentasive sample of the whole pile. It has to do whit geometry shaped. You want to take the sample with the same dimensions as the whole pile. Ex. Pile samlple a sphere inside the pile (3-D). Elióngated pile a cut out parallel to the pile (1-1D).
The extraction error has to do with how the sample is taken. If not the right equipment is used or if it is not used correctly .
What happens to the surface charge of organic soil matter when pH changes from 3 to 9? (1P) How will this change affect the sorption of a) cationic elements and b) anionic elements in the soil environment?
When the pH increases to 9 there will be higher CEC (cationic exchange capacity). The negative charge on the surface of the organic material increases (becomes more negative)
a)More cations can be in the soil which reduces the mobility of cations.
b)For anions the mobilite increases instead since there is a larger negative charge (överskott av neg. laddning)
Explain how hydraulic gradient influences the contaminant transport in soil. What happens to the contaminant spreading when the hydraulic gradient is equal to 0?
The hydraulic gradient depends on difference in pressure head between two points and the distance between the points. It affects the flowrate of the water in the soil. A higher hydraulic gradient resultst in a higher flow rate and thereby a faster spread of the contaminent.
Is the hydraulic gradient would be zero ther would be no movement of the water. This would cause the contaminent to stay in the soil since ther is no flow rate/force that is moving it in any direction.
Explain the difference between generic guideline values and site specific guideline values for contaminated land. Indicate some of the major advantages and drawbacks of their application in risk evaluations.
Guideline values are based on the lowest value of the risk to human health, spreading and soil environment. The GV makes it easier for non-experts to make decisions and could reduce costs of risk assessment. They are quite easy to understand and give some guidance. They can however be used wrong to simplify, just because something exceed the limit doesn’t meen it is a need of remediation. They also don’t take all risks int consideration and ingnroe additive effects
Site specific guideline values has been adapted to a specific location. It may have been adjusted depending on the concentration variation in depth or only taking some of the pathways into consideration. It can however be hard to get acceptance for the values and there is no standard for how to decide these values.
In what cases should you use the diffusion leaching test when characterizing soil?
You use this leaching method when you want to se what is leached from the surface area. You get the results in mg/m^2
A site is contaminated with tetrachloroethene (C2Cl4). What is the most suitable soil remediation technique to destroy this compound in situ? Describe the basic principle of the compound degradation to ethene.
You could use reductive dichlorination where H substitute Cl in a stepwise exchange until ethene is formed (which is non-toxic). For the method to work there needs to be a high DOC (dissolved organic carbon), a low redox and a presence of microorganisms.
What criteria should be met to achieve a representative sub-sampling from a large sample? Illustrate your answer with an example in the field of soil remediation.
Use a good method to split the sample. This could be by taking a riffler splitter or by coning and quartering. If you take a sample directly from a big pile you want to make sure you take the propper shape (use the righet sampling dimension)
