CESSWI - Certified Erosion, Sediment, and Storm Water Inspector Sediment Control BMPs Questions and Answers — Questions and Answers
Question 1: An inspector observes a rock check dam in a channel with a 4% grade. The crest of the downstream dam is at the same elevation as the toe of the upstream dam. Sediment has accumulated to approximately half the height of the downstream dam. What is the most appropriate action for the inspector to recommend?
- Add another check dam between the existing ones to improve efficiency.
- Remove the accumulated sediment from the upstream side of the dam. (Correct answer)
- Reconstruct the dam to be 12 inches lower in the center than at the edges.
- No action is needed as the check dam is functioning as designed.
Correct answer: Remove the accumulated sediment from the upstream side of the dam.
Regular maintenance is crucial for the effectiveness of check dams. Sediment should be removed when it accumulates to one-half of the dam's height to restore ponding capacity and prevent sediment from being washed downstream in subsequent storm events.
Question 2: A CESSWI is inspecting a large construction site (over 10 acres) with significant grading. Which of the following sediment control BMPs is most appropriate for managing sediment-laden runoff at the primary discharge point for a large drainage area?
- A series of silt fences installed along the site perimeter.
- Inlet protection devices on all nearby storm drains.
- A sediment basin designed to detain runoff and allow sediment to settle. (Correct answer)
- Fiber rolls placed along the contours of the disturbed slopes.
Correct answer: A sediment basin designed to detain runoff and allow sediment to settle.
Sediment basins are specifically designed to handle runoff from large drainage areas (typically 5 to 100 acres) by creating a temporary pond that allows sediment to settle out before the water is discharged from the site. Silt fences, inlet protection, and fiber rolls are typically used for smaller drainage areas or as secondary controls.
Question 3: During a site inspection, you notice a silt fence has been installed in a swale where concentrated flow is expected. The fabric is bulging and there is evidence of undercutting. What is the fundamental issue with this installation?
- The support posts are spaced too far apart.
- The fabric was not properly trenched into the ground.
- Silt fences are not intended for use in areas of concentrated flow. (Correct answer)
- The accumulated sediment has not been removed in a timely manner.
Correct answer: Silt fences are not intended for use in areas of concentrated flow.
Silt fences are designed to intercept and detain sheet flow, not concentrated flow. When placed in ditches, swales, or other areas of concentrated flow, they are likely to fail due to the high velocity and volume of water, leading to undercutting and collapse. Check dams or other channel-specific BMPs should be used in these areas.
Question 4: Which of the following is a critical maintenance requirement for all storm drain inlet protection devices?
- Replacing the filter fabric after every measurable rainfall.
- Ensuring the device is removed as soon as the contributing drainage area is stabilized. (Correct answer)
- Re-grading the area around the inlet to create a permanent sediment trap.
- Anchoring the device with concrete blocks to prevent movement.
Correct answer: Ensuring the device is removed as soon as the contributing drainage area is stabilized.
Inlet protection is a temporary BMP. It is crucial to remove the device once the surrounding area is permanently stabilized to prevent it from becoming a long-term source of concentrated flow or a blockage in the storm drain system.
Question 5: A site superintendent plans to use straw bales as the primary perimeter sediment control measure. As a CESSWI, what advice should you provide?
- Ensure the bales are tightly bound and staked securely to be effective.
- Recommend using straw bales only for concentrated flow channels.
- Advise against using straw bales due to their high failure rate and suggest alternatives like silt fence or fiber rolls. (Correct answer)
- Suggest wrapping the straw bales in geotextile fabric to improve their filtering capacity.
Correct answer: Advise against using straw bales due to their high failure rate and suggest alternatives like silt fence or fiber rolls.
Straw bale barriers have a high failure rate. They are prone to rotting, being displaced by runoff, and allowing water to flow around or underneath them. Professional guidance often recommends avoiding their use in favor of more reliable and effective BMPs such as silt fences, compost filter socks, or fiber rolls.
Question 6: According to the NPDES Construction General Permit (CGP), when must sediment be removed from a sediment basin?
- When the basin is completely full.
- At the completion of the construction project.
- When sediment has accumulated to one-third of the basin's design capacity.
- When sediment storage capacity has been reduced by 50% (i.e., it is half full). (Correct answer)
Correct answer: When sediment storage capacity has been reduced by 50% (i.e., it is half full).
Standard maintenance protocols for sediment basins and traps require that accumulated sediment be removed once it has reached 50% (or one-half) of the design volume. This ensures the basin has adequate capacity to function properly during the next storm event.
CESSWI - Certified Erosion, Sediment, and Storm Water Inspector Sediment Control BMPs Questions and Answers
An inspector observes a rock check dam in a channel with a 4% grade.
The crest of the downstream dam is at the same elevation as the toe of the upstream dam.
Sediment has accumulated to approximately half the height of the downstream dam.
What is the most appropriate action for the inspector to recommend?