A city notes that after a heavy rain event (more than 3 centimeters of rainfall), an increase in runoff containing motor oil, hydrocarbons, and nitrates was discharged to the local river. What proposed action would best mitigate the level of runoff after a rain event?

Grow more vegetation.

Explanation:

Grow more vegetation between the rainfall region and the local river is the best method to reduce the level of runoff after a rainfall because the vegetation absorb most of the runoff water and also slower down the flow of water. The soil of vegetative cover is porous which has high capacity to absorb water so if there is a large vegetation in the way of runoff water so all the water or most of the water and pollutants is absorbed by the soil and no contamination of local river water occurs.