CESSWI Erosion & Sediment Control Principles 4 — Questions and Answers
Question 1: What is the primary reason that compacted construction site soils typically generate more runoff than undisturbed soils?
- Compaction increases soil organic matter content
- Compaction reduces macropore space, decreasing infiltration capacity (Correct answer)
- Compacted soils have higher erodibility K factors
- Compaction increases surface roughness and slows overland flow
Correct answer: Compaction reduces macropore space, decreasing infiltration capacity
Soil compaction collapses macropores and reduces infiltration capacity, causing more precipitation to become overland flow rather than infiltrating.
Question 2: A stabilized construction entrance is primarily designed to accomplish which of the following?
- Prevent stormwater runoff from entering the construction site
- Remove mud and debris from vehicle tires before they exit onto public roads (Correct answer)
- Provide a stable surface for heavy equipment during wet conditions
- Divert runoff from site access roads into sediment traps
Correct answer: Remove mud and debris from vehicle tires before they exit onto public roads
Stabilized construction entrances use coarse aggregate to dislodge mud and debris from vehicle tires, preventing tracking of sediment onto adjacent public roadways.
Question 3: Which of the following best describes the concept of 'phased grading' as an erosion control strategy?
- Grading the entire site before installing any BMPs to maximize efficiency
- Limiting the area of disturbance at any given time to reduce exposed soil (Correct answer)
- Using multiple grading passes to achieve a smooth, compacted surface
- Grading in phases based on equipment availability and crew scheduling
Correct answer: Limiting the area of disturbance at any given time to reduce exposed soil
Phased grading minimizes the area of disturbed soil exposed at any one time, directly reducing the source of erosion on a construction site.
Question 4: An inspector notices that a fiber roll (wattle) installed on a slope has separated from the soil surface, leaving a gap underneath. What is the most likely consequence?
- Increased infiltration beneath the wattle improves soil moisture
- Runoff will flow under the wattle, bypassing the sediment control barrier (Correct answer)
- The gap increases the structural integrity of the fiber roll
- Sediment will accumulate in the gap, eventually sealing it naturally
Correct answer: Runoff will flow under the wattle, bypassing the sediment control barrier
A gap between the fiber roll and the soil surface allows runoff to bypass the barrier entirely, negating its sediment control function.
Question 5: Under what condition is a sediment basin REQUIRED rather than a sediment trap for construction site stormwater management?
- When the disturbed area contains slopes steeper than 5%
- When the contributing drainage area exceeds 10 acres (Correct answer)
- When the site is located within 500 feet of a water body
- When the project duration exceeds 6 months
Correct answer: When the contributing drainage area exceeds 10 acres
Common standards require a sediment basin when the contributing drainage area exceeds 10 acres because sediment traps lack sufficient storage and retention capacity for larger watersheds.
Question 6: Which SWPPP element is specifically designed to track the installation, maintenance, and removal of each BMP on a construction site over time?
- Grading plan
- BMP inspection log (Correct answer)
- Drainage area map
- Pollution prevention team roster
Correct answer: BMP inspection log
A BMP inspection log provides a chronological record of each control measure's installation date, condition during inspections, maintenance performed, and eventual removal.
Question 7: How does vegetative cover reduce erosion compared to bare soil?
- Vegetation increases runoff velocity, moving sediment away from the site faster
- Vegetation intercepts rainfall, reduces surface sealing, and anchors soil with roots (Correct answer)
- Vegetation increases soil compaction, limiting infiltration and runoff
- Vegetation shades the soil, reducing evaporation but not erosion
Correct answer: Vegetation intercepts rainfall, reduces surface sealing, and anchors soil with roots
Vegetation reduces erosion through multiple mechanisms: canopy interception dissipates raindrop energy, roots bind soil particles, and leaf litter maintains infiltration rates.
CESSWI Erosion & Sediment Control Principles 4
What is the primary reason that compacted construction site soils typically generate more runoff than undisturbed soils?