Certified Storm Water Operator Practice Exam

Fine sediment particles are difficult to capture with standard control techniques. Which two particle types are mentioned?

1. Sand and Gravel

2. Clay and Silt

3. Silt and Clay

4. Rock and Debris

The correct answer is: Silt and Clay

Fine sediment particles, due to their small size and low density, present significant challenges when it comes to capture using standard stormwater control techniques. The two types of particles that are typically mentioned in this context are silt and clay. Clay particles are extremely small, often less than 0.002 mm in diameter, making them highly mobile in water and difficult to filter out using conventional methods. Their minute size allows them to remain suspended in water longer than larger particles, leading to issues such as water quality deterioration and increased maintenance for stormwater systems. Silt, slightly larger than clay but still fine enough to cause the same issues, also has trouble being captured efficiently. Silt particles range from 0.002 mm to 0.05 mm in diameter and can similarly evade standard filtration systems, compounding problems related to turbidity and sedimentation in water bodies. The other choices include sand and gravel, which are larger, coarser materials that are typically much easier to manage and capture through conventional sediment control techniques. Rock and debris also refer to larger, often more solid materials that are less likely to be continuously suspended in stormwater compared to the fine particles observed with silt and clay. Hence, silt and clay are highlighted as the challenging