Explain how to estimate groundwater velocity using Darcy's law and identify the data required.

• A. v = -K i / n; requires hydraulic conductivity K, hydraulic gradient i, and porosity n (or effective porosity).
• B. v = K i n; requires K, i, and porosity n.
• C. v = -K / (i n); requires K, i, and n.
• D. v = K i / (n^2); requires K, i, and n^2.

Answer: (A)