CESSWI Erosion & Sediment Control Principles 2 — Questions and Answers
Question 1: Which factor in the RUSLE equation accounts for the ability of soil to resist detachment and transport by rainfall?
- K factor (soil erodibility) (Correct answer)
- R factor (rainfall erosivity)
- LS factor (slope length and steepness)
- C factor (cover management)
Correct answer: K factor (soil erodibility)
The K factor in RUSLE represents soil erodibility, reflecting the soil's susceptibility to detachment and transport by rainfall and runoff.
Question 2: A contractor installs a silt fence parallel to the slope contours on a 15% grade. What is the primary concern with this installation?
- Silt fence is not recommended for slopes exceeding 10% (Correct answer)
- Parallel installation diverts flow around the fence ends
- The fabric permeability is too high for steep slopes
- Posts must be installed uphill of the fabric on steeper grades
Correct answer: Silt fence is not recommended for slopes exceeding 10%
Silt fences are generally not recommended on slopes steeper than 10% because concentrated flow can overwhelm the barrier and cause failure.
Question 3: During a post-storm inspection, an inspector finds that a sediment basin outlet riser pipe is submerged and the basin is overtopping the embankment. What is the most likely cause?
- Clogged perforations in the riser pipe
- Inadequate principal spillway capacity for the storm event (Correct answer)
- Excessive vegetation on the embankment
- Anti-seep collars impeding flow through the barrel
Correct answer: Inadequate principal spillway capacity for the storm event
Overtopping an embankment during a storm typically indicates the principal spillway was undersized and cannot convey the runoff generated by that event.
Question 4: Which erosion mechanism involves the removal of a thin, relatively uniform layer of soil from the land surface by raindrop splash and sheet flow?
- Rill erosion
- Gully erosion
- Sheet erosion (Correct answer)
- Streambank erosion
Correct answer: Sheet erosion
Sheet erosion removes a thin, fairly uniform layer of soil across a broad area through the combined action of raindrop impact and shallow overland flow.
Question 5: A SWPPP requires a sediment trap to be sized for a drainage area of 2 acres. Using a volumetric standard of 1,800 cubic feet per acre, what minimum storage volume is required?
- 900 cubic feet
- 1,800 cubic feet
- 3,600 cubic feet (Correct answer)
- 7,200 cubic feet
Correct answer: 3,600 cubic feet
Multiplying the 2-acre drainage area by 1,800 cubic feet per acre yields a required storage volume of 3,600 cubic feet.
Question 6: Which of the following best describes the purpose of an anti-seep collar on a sediment basin outlet barrel?
- To prevent erosion around the pipe inlet
- To lengthen the seepage path and reduce piping failure risk (Correct answer)
- To anchor the barrel against buoyancy forces
- To regulate flow velocity through the outlet structure
Correct answer: To lengthen the seepage path and reduce piping failure risk
Anti-seep collars extend the seepage path along the outside of the barrel through the embankment, reducing hydraulic gradient and the risk of internal erosion (piping).
Question 7: A construction site experiences a severe rain event that causes sediment to discharge into an adjacent stream. Under NPDES permit conditions, what is the operator's immediate obligation?
- Submit a Notice of Termination for the permit
- Document the event and notify the permitting authority within the required timeframe (Correct answer)
- Remove all BMPs and start fresh with a revised SWPPP
- Transfer permit responsibility to the general contractor
Correct answer: Document the event and notify the permitting authority within the required timeframe
NPDES permits typically require operators to document unauthorized discharges and report them to the permitting authority within a specified timeframe (often 24–72 hours).
CESSWI Erosion & Sediment Control Principles 2
Which factor in the RUSLE equation accounts for the ability of soil to resist detachment and transport by rainfall?