A rural homeowner moves into an old house with an old septic tank. (Septic tanks are used to treat household sewage.) After a few weeks, she notices smelly water

pooling in her yard near the septic tank. She decides to wait to see if the problem will go away. What two types of pollution are demonstrated in this real world example

Toxic

Sediment

Nutrient

Bacterial

a) Toxic (gases)

d) Bacterial

Explanation:

Septic tanks are underground structures usually built with concrete or plastic in which wastewater is treated. These tanks are generally used in rural areas and are located near bathrooms and laundry rooms.

If a septic tank is working correctly, it should produce any unpleasing smell. However, when an individual perceives a certain strong bad smell it could be due to the presence of gases (low levels of hydrogen sulfide and high levels of carbon dioxide, and methane) and anaerobic microorganisms such as sulfur bacteria which also produce methane and, therefore, strong smell.

It all depends of what kind of bad smell is the person perceiving. For example, the smell of "rotten egg" is usually due to microbial pollution and gases. Although these gases are not toxic in low levels, they could become highly toxic. It is extremely important to pay attention to smell and give the appropriate mainteinance.