A good sampling point will be at the ___ side-to-side, and at the proper ___ of the flow stream.

• A. Endpoint - Depth
• B. Center - Depth
• C. Midpoint - Height
• D. Midpoint - Depth

Answer: (D)

To get a representative wastewater sample, pick a point that reflects the typical flow in the cross-section and depth of the stream. Sampling at the midpoint across the width avoids wall effects, eddies near the sides, and any stratification that can bias results. Sampling at the proper depth means choosing a position within the vertical flow, not right at the surface or bottom, so the sample represents the bulk of the flow.

That’s why the best choice is the midpoint across the cross-section and at depth in the flow. Sampling at edges or near the surface or bottom can skew results due to special conditions there, and using height instead of depth refers to a different measurement convention.