Where would you expect to find a large LNAPL spill in a well?

• A. Floating on the water table surface
• B. Seeping into the aquifer
• C. Accumulating at the well bottom
• D. Escaping through the casing vent

Answer: (A)

Light non-aqueous phase liquids are less dense than water and immiscible with it, so they don’t sink when they enter groundwater. Instead, they rise and form a separate liquid layer at the surface of the saturated zone—the water table. In a well, that means a large LNAPL spill will collect as a distinct layer floating on top of the water column at the water-table level inside the borehole. It sits above the water in the well rather than sinking to the bottom or seeping deeper into the aquifer. The casing vent is just an outlet to the atmosphere and doesn’t indicate where the liquid will accumulate inside the well.