How fast can water move through the ground and aquifers?

• A. As fast as 20 feet per day
• B. As fast as 5 feet per day and as slow as a few inches or less per day
• C. As fast as 1 foot per day
• D. As fast as 100 feet per day

Answer: (B)

Groundwater flow velocity depends on how permeable the material is and how strong the hydraulic gradient is, so water moves at very different speeds underground. In materials with high permeability, like coarse sand, gravel, or fractured rock with good connectivity, water can travel relatively fast for groundwater—on the order of a few feet per day. In finer materials such as clay or tightly packed rock, or where the gradient is small, movement is much slower, down to a few inches per day or less. That wide range—fast up to about five feet per day and slow down to mere inches per day or less—best reflects the real variability of groundwater movement. Very large speeds, like 100 feet per day, aren’t typical for underground flow in most soils and rocks, and consistently slow speeds of one foot per day or faster than several feet per day don’t capture the full range either, making the described range the most accurate.