Which system does not require annual sampling of the effluent?

• A. Aerobic trench
• B. Filter bed
• C. Mound system
• D. Holding tank

Answer: (B)

Effluent sampling is mainly used to verify that wastewater is being treated adequately before it leaves the system. A filter bed is a soil-based, passive treatment stage—the bed and the surrounding soil do most of the polishing as the effluent percolates down. There isn’t a distinct, accessible effluent stream from the bed to sample on a regular basis, so annual effluent sampling isn’t typically required for that component. Instead, the monitoring focuses on how the soil absorbs and treats the wastewater and on general system performance. The other systems involve either active treatment components or storage where regulators commonly require ongoing checks of effluent quality or system integrity, which is why they generally carry annual sampling requirements.