Tutor profile: Reese M.
Subject: Environmental Engineering
Define and explain the difference between LNAPL and DNAPL.
LNAPL stands for Light non-aqueous phase liquid, such as gasoline. It is less dense than water therefore it tends to float at the top of an aquifer. DNAPL stands for Dense non-aqueous phase liquid, such as dry cleaner solvents. It is more dense than water and therefore it tends to "sink" in the aquifer. It would be found at highest concentrations typically at a confining layer (such as clay) where the plume will spread out. The difference between these two types of contaminants is important with determining where you will find the highest concentrations and where to screen your monitoring well accordingly.
What are invasive species? What problems arise with invasive species?
Invasive species are defined as species existing in a space that they do not naturally occur. Often they are brought to a new location by human beings, sometimes by natural means (such as on rafts through oceans). Since the species existing in the ecosystem did not evolve with the invasive species, they often lack the means to defend or push out the invasive species. An easy example of this would be domestic cats which kill birds or zebra mussels which incapacitate native mussels. Ecosystems evolve to have species in set niches coexisting in food webs and overall invasive species disrupt that naturally evolved ecosystem or community.
What is the difference between correlation and causation. Give an example.
Correlation is when two variables have a statistical relationship but it may not necessarily be connected or dependent. Correlation does not imply causation so in statistics it is important to understand and examine the two. Causation is when two variables are related where one directly affects the other. An example to compare the two would be that ice cream sales increase as sunglass sales increase. These two are not actually related, they just appear to be since they both trend the same. However, ice cream sales and outside temperature are correlated- the hotter it gets the more likely you are to go buy ice cream. Sunglass sales and ice cream appear related since they both trend in similar ways, but the reality is they both are related to weather rather than to eachother at all.
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