Before conducting an infiltration test, how long should the groundwater level be stabilized?

• A. 12 hours
• B. 6 hours
• C. 24 hours
• D. 48 hours

Answer: (C)

Stabilizing the groundwater level before an infiltration test ensures the test reflects natural hydraulic conditions rather than disturbances from drilling or recent changes in water levels. After installation, the surrounding soil and wells respond to the disturbance, causing drawdown or fluctuations that can bias infiltration measurements. Giving time for the hydraulic head to re-equilibrate yields a steady-state condition, so the infiltration rate you measure is representative.

About a day is typically needed for this re-equilibration, which is why 24 hours is the best choice. Too short a period may still capture transient effects from installation; a period this long balances practicality with the need for steady conditions. Longer periods may not offer additional benefit and can introduce other variables.

So, waiting 24 hours allows the groundwater level to stabilize and provides more accurate infiltration results.