Question

What occurs when used engine oil is poured into the pit in the ground?

The oil seeps through the soil until it leaks into, and mixes with, the groundwater.


The oil seeps through the soil but stops before it reaches the groundwater due to the difference in densities.


The oil remains sealed in the small disposal pit and does not affect the groundwater.


The oil creates a membrane barrier between the water table and the groundwater.

Answer 1

Correct answer: The oil seeps through the soil until it reaches and contaminates the groundwater.

Brief explanation:
- Used engine oil percolates through soil pores. When it reaches the water table it does not form a perfect seal — most petroleum oils are lighter than water and form a floating separate phase (LNAPL) on top of groundwater while soluble toxic components dissolve into the water and spread.
- It will not “stop” above the water table because of density (lighter-than-water oils will float on the water once they get there), it will not stay perfectly sealed in a small pit, and it does not create a reliable membrane barrier.
- Used oil contains persistent toxic compounds (PAHs, heavy metals) that can contaminate drinking water and soil and are difficult and expensive to remediate.

Do not dispose of used oil in the ground — take it to a recycling or hazardous-waste facility.