What is the drawdown of a well that yields 129 gpm with a specific yield of 45 gpm/ft?

• A. 13.7 ft
• B. 2.87 ft
• C. 129 ft
• D. 45 ft

Answer: (C)

The drawdown is found from the relationship s = Q / Sy, where Q is the pumped discharge and Sy is the specific yield (discharge per foot of drawdown). With Q = 129 gpm and Sy = 45 gpm/ft, the calculation is 129 ÷ 45 ≈ 2.87 ft. So the water level would fall about 2.87 feet. The 129 ft or 45 ft options don’t fit because they don’t reflect the division by the specific yield needed to get a length.