Answer to Question 1
Most pesticides do not dissolve when they mix with water. Instead, they go into suspension, which means that the particles will separate from the water if they are allowed to sit for awhile.
Answer to Question 2
Hydrological vulnerability refers to the degree of likelihood that pesticides and other chemicals in the soil will be able to pass into the groundwater. The depth of the soil is a factor because the deeper the soil, the farther the pesticides have to travel, and the less likely they are to enter the groundwater. The other main geological factor is the texture of the soil. Coarse, sandy soils allow water to pass through easily, while clay soils provide a better barricade.