In this post, we will review one of the sample questions from AP Environmental Science. Let’s get straight to it! One of the practice questions is shown below:
“In a well-designed sanitary landfill, methane”
The choices for that question are:
- can be trapped and used for energy.
- is controlled by plastic liners.
- escapes and adds to air pollution.
- leaks into groundwater.
- is not a problem because it is used in decomposition.
The correct answer to this question is choice 1, where methane can be trapped and used for energy. Why is this the best answer out of all the choices? For this question, word-choice is key into getting the right answer here. The question states in a “well-designed” landfill meaning a landfill that does its job correctly. The purpose of a sanitary landfill is to allow for a location where waste can be properly disposed of and managed and where pollutants to the environment can be controlled. In the case of this question, the pollutant of concern that needs to be controlled is methane.
Evaluating each answer choice reveals how some don’t make sense. Plastic liners control the liquid leachate emissions, not gases like methane. Release of methane into the atmosphere adds to green-house gas emissions, so a well-designed landfill should not allow the escape of methane into the atmosphere. Methane is a gas, so it cannot leak into groundwater. And methane is a byproduct of decomposition of waste in a landfill under anaerobic conditions, therefore it is not used during decomposition. Since, methane is a gas and has intrinsic energy properties, it is typically controlled by gas collection systems where it is sucked out of the landfill and used to generate electricity.
Image Source: http://article.sapub.org/10.5923.j.chemistry.20120201.05.html