CSM CSM Erosion & Sediment Control 2 — Questions and Answers
Question 1: What is the maximum recommended drainage area for a standard silt fence installation?
- 0.25 acres per 100 feet of fence (Correct answer)
- 5 acres per 100 feet of fence
- 10 acres per 100 feet of fence
- No maximum area limit exists
Correct answer: 0.25 acres per 100 feet of fence
Industry guidance limits silt fence drainage area to approximately 0.25 acres per 100 linear feet to prevent overtopping and structural failure during storm events.
Question 2: What is the primary use of fiber rolls (wattles) in erosion and sediment control?
- To intercept slope runoff and capture sediment along the contour of a disturbed slope (Correct answer)
- To permanently stabilize stream bank soils
- To filter pollutants from stormwater in detention ponds
- To reinforce the base of retaining walls
Correct answer: To intercept slope runoff and capture sediment along the contour of a disturbed slope
Fiber rolls are placed along contours on disturbed slopes to slow runoff velocity, spread flow, and trap sediment moving downslope.
Question 3: What is turbidity and why is it a key indicator in stormwater management?
- Cloudiness of water caused by suspended particles; high turbidity indicates sediment pollution and can harm aquatic life (Correct answer)
- The temperature differential between surface and deep water layers
- The chemical oxygen demand of discharged stormwater
- The pH level of runoff from construction sites
Correct answer: Cloudiness of water caused by suspended particles; high turbidity indicates sediment pollution and can harm aquatic life
Turbidity measures water cloudiness from suspended sediment and other particles; elevated turbidity in receiving waters harms aquatic ecosystems and is often regulated under NPDES permits.
Question 4: What is the fundamental difference between erosion and sedimentation?
- Erosion is the detachment and transport of soil particles; sedimentation is the deposition of those transported particles (Correct answer)
- Erosion occurs in streams; sedimentation occurs only on land
- Erosion involves chemical weathering; sedimentation involves physical processes only
- Erosion is a natural process; sedimentation is always caused by human activity
Correct answer: Erosion is the detachment and transport of soil particles; sedimentation is the deposition of those transported particles
Erosion detaches soil particles from the ground surface through water or wind energy, while sedimentation is the settling and deposition of those transported particles at a new location.
Question 5: According to general NPDES Construction General Permit requirements, how often must sediment controls be inspected?
- At least every 7 days and within 24 hours after a storm event of 0.5 inches or more (Correct answer)
- Once per month regardless of weather conditions
- Only when a regulatory agency requests an inspection
- Weekly during the dry season; daily during the wet season
Correct answer: At least every 7 days and within 24 hours after a storm event of 0.5 inches or more
Most Construction General Permits require inspections at least every 7 calendar days and within 24 hours after qualifying storm events to ensure controls are functioning properly.
Question 6: How does soil compaction on a construction site affect erosion potential?
- Compaction reduces infiltration, increasing surface runoff volume and velocity, which can increase erosion on unprotected areas (Correct answer)
- Compaction binds soil particles together, permanently eliminating erosion risk
- Compaction has no significant effect on stormwater runoff patterns
- Compaction increases infiltration, reducing the amount of surface runoff
Correct answer: Compaction reduces infiltration, increasing surface runoff volume and velocity, which can increase erosion on unprotected areas
Compacted soils have reduced porosity and infiltration capacity, so more rainfall becomes surface runoff with greater erosive potential on unprotected areas downslope.
CSM CSM Erosion & Sediment Control 2
What is the maximum recommended drainage area for a standard silt fence installation?