Certified Storm Water Operator Practice Exam

What particles may never settle out of a sediment basin?

1. Sand and gravel

2. Clay and silt

3. Gravel and rocks

4. Soil and debris

The correct answer is: Clay and silt

In a sediment basin, particles that are very small and lightweight, such as clay and silt, have a tendency to remain suspended in the water for extended periods. Their minuscule size and low density prevent them from settling quickly to the bottom, allowing them to be transported by even minor currents in the water. This characteristic means that these finer particles can accumulate over time in the water column rather than settling out like larger particles such as sand, gravel, or rocks, which are heavier and will settle out more readily due to their size and weight. Understanding the behavior of these sediment types is crucial in stormwater management practices, as fine particles can have significant environmental impacts, including pollution and habitat degradation. Efforts to manage sediment in stormwater runoff often focus on controlling the transport of clay and silt, highlighting their importance in sedimentation processes.