Why are gasoline and volatile solvents objectionable when present in a sewer?

Gasoline and volatile solvents are objectionable in a sewer primarily because they produce an explosion hazard. The presence of these substances can lead to the accumulation of flammable vapors, which can ignite and lead to explosive incidents. In confined spaces like sewers, where ventilation is often limited, the risk of explosion increases significantly if these volatile compounds are present.

Additionally, these substances can create other hazards, including toxic fumes that pose a risk to workers and the environment. Their flammable nature is a critical safety concern in any wastewater management scenario, as safety regulations strictly prohibit their introduction into sewer systems due to the potential for severe consequences.

In contrast, the other options do not accurately represent the risks or characteristics associated with gasoline and volatile solvents in sewer systems. These substances do not create a pleasant smell, assist in treatment processes, or enhance sewer flow; instead, they disrupt the intended function of a sewer system and compromise safety.