CESSWI Sediment Control BMPs 3 — Questions and Answers
Question 1: A construction site inspector finds silt fence buried under 18 inches of sediment. What is the CORRECT action?
- Replace the fence with a higher fence
- Remove accumulated sediment and restore fence height (Correct answer)
- Add a second row of silt fence downslope
- Flag the area and allow natural consolidation
Correct answer: Remove accumulated sediment and restore fence height
When sediment accumulates to one-third to one-half the fence height, it must be removed to restore the fence's storage capacity and structural integrity.
Question 2: What is the purpose of the J-hook or 'J-turn' method when installing silt fence at the ends of a run?
- To anchor the fabric to adjacent vegetation
- To prevent runoff from flowing around the ends of the fence (Correct answer)
- To allow controlled overflow at a designated point
- To create a sediment sump at the terminus
Correct answer: To prevent runoff from flowing around the ends of the fence
Turning the ends of a silt fence upslope in a J-hook formation prevents concentrated flow from bypassing the barrier at the fence endpoints.
Question 3: According to general CESSWI standards, what minimum freeboard should remain above accumulated sediment in a sediment basin before cleanout is required?
- 6 inches
- 12 inches
- 18 inches
- The basin should be cleaned when 50% of design storage is lost (Correct answer)
Correct answer: The basin should be cleaned when 50% of design storage is lost
Most design standards require cleanout when sediment has reduced the basin's design storage volume by 50%, ensuring adequate capacity remains for future storm events.
Question 4: Which BMP is BEST suited to slow concentrated flow in a vegetated swale on a construction site?
- Silt fence installed across the swale
- Fiber rolls or compost socks placed perpendicular to flow (Correct answer)
- Riprap channel lining over the entire swale
- Plastic sheeting staked to swale bottom
Correct answer: Fiber rolls or compost socks placed perpendicular to flow
Fiber rolls or compost socks placed as check dams in vegetated swales slow flow velocity and trap sediment without completely blocking the swale.
Question 5: What is the recommended maximum ponding depth behind a silt fence before the fabric is considered overstressed?
- 6 inches
- 12 inches (Correct answer)
- 18 inches
- 24 inches
Correct answer: 12 inches
Most silt fence installations are designed for a maximum ponding depth of 12 inches (1 foot); greater depths can cause fabric or post failure from hydrostatic pressure.
Question 6: Why should sediment control BMPs be installed BEFORE grading activities begin on a construction site?
- To comply with building permit requirements only
- To intercept sediment before it can leave the site during the first rain event (Correct answer)
- To protect equipment from site erosion damage
- To establish vegetation prior to earthwork
Correct answer: To intercept sediment before it can leave the site during the first rain event
Installing sediment controls before grading ensures that any runoff from the first storm event after disturbance is captured before sediment leaves the site.
Question 7: A wattled straw roll is placed on a slope. Which orientation relative to the slope contours is CORRECT?
- Parallel to the slope direction to channel water
- Perpendicular to the slope, along the contour (Correct answer)
- At a 45-degree angle to maximize coverage
- Orientation does not affect performance
Correct answer: Perpendicular to the slope, along the contour
Straw wattles must be installed perpendicular to the slope (along the contour) to intercept sheet flow across the slope and allow sediment to settle behind the roll.
CESSWI Sediment Control BMPs 3
A construction site inspector finds silt fence buried under 18 inches of sediment.
What is the CORRECT action?