CPESC Sediment Control Best Practices 3 — Questions and Answers
Question 1: What is the key advantage of a fiber roll (wattle) over a silt fence for sediment control on a slope?
- Fiber rolls can handle concentrated flow better than silt fences
- Fiber rolls are more effective at filtering fine clay particles
- Fiber rolls can be installed on steeper slopes and conform to irregular terrain (Correct answer)
- Fiber rolls require no maintenance after installation
Correct answer: Fiber rolls can be installed on steeper slopes and conform to irregular terrain
Fiber rolls are flexible and conform to ground contours, making them suitable for installation on steeper slopes and uneven terrain where silt fences cannot be trenched properly.
Question 2: In the context of CPESC, what does 'perimeter control' refer to?
- Fencing around the entire construction site for security
- BMPs installed along the downslope and side boundaries to intercept runoff before it leaves the site (Correct answer)
- Stormwater inlets placed at the perimeter of paved areas
- Vegetation buffers planted outside the property line
Correct answer: BMPs installed along the downslope and side boundaries to intercept runoff before it leaves the site
Perimeter controls are sediment-trapping BMPs positioned at the site boundary to capture runoff and sediment before they discharge off-site.
Question 3: Which sizing parameter is MOST important when designing a sediment basin for stormwater quality treatment?
- Basin depth only
- Surface area (footprint) relative to the drainage area (Correct answer)
- Embankment height and freeboard
- Outlet pipe diameter
Correct answer: Surface area (footprint) relative to the drainage area
Surface area governs the hydraulic residence time and settling opportunity; adequate surface area per unit of drainage area is the primary design criterion for sediment removal.
Question 4: A contractor wants to install a floating silt curtain. This BMP is MOST appropriate for:
- Steep slopes adjacent to wetlands
- Open water bodies such as lakes, ponds, or slow-moving streams (Correct answer)
- Road ditches with intermittent flow
- Graded areas with sheet flow runoff
Correct answer: Open water bodies such as lakes, ponds, or slow-moving streams
Floating silt curtains (turbidity curtains) are designed for use in open water to contain turbid plumes during in-water construction activities.
Question 5: What is the primary function of outlet protection (riprap apron) at the end of a culvert or pipe outlet?
- Filter sediment from stormwater before discharge
- Prevent concentrated flow from eroding the receiving channel or land surface (Correct answer)
- Reduce peak discharge rates from the drainage area
- Increase infiltration of stormwater into the soil
Correct answer: Prevent concentrated flow from eroding the receiving channel or land surface
Outlet protection dissipates the energy of concentrated flow emerging from pipes to prevent scour and erosion at the discharge point.
Question 6: Under NPDES Construction General Permit requirements, stabilization of disturbed areas must typically begin within how many days of final grading?
- 3 days
- 7 days
- 14 days (Correct answer)
- 30 days
Correct answer: 14 days
The EPA Construction General Permit generally requires that stabilization be initiated within 14 days of the last land-disturbing activity in that portion of the site.
Question 7: Which sediment control practice is best suited for protecting a storm drain inlet on a paved roadway during construction?
- Silt fence installed 5 feet upstream of the inlet
- Gravel bag or filter sock placed around the inlet grate (Correct answer)
- Sediment basin located adjacent to the roadway
- Fiber wattles staked across the pavement surface
Correct answer: Gravel bag or filter sock placed around the inlet grate
Gravel bags or filter socks placed around storm drain inlets on paved surfaces allow water to pass while trapping sediment without impeding traffic.
CPESC Sediment Control Best Practices 3
What is the key advantage of a fiber roll (wattle) over a silt fence for sediment control on a slope?